SH-AWD
Encyclopedia
Super Handling-All Wheel Drive or SH-AWD is a full-time, fully automatic all-wheel drive traction and handling system designed and engineered by Honda Motor Company. The system was announced in April 2004, and first introduced in the North American market in the second generation 2005 model year Acura RL
, and in Japan as the fourth generation Honda Legend
. The company describes SH-AWD as a system "... that provides cornering performance that responds faithfully to driver input, and outstanding vehicle stability. A world's first, the SH-AWD system combines front-rear torque distribution control with independently regulated torque distribution to the left and right rear wheels to freely distribute the optimum amount of torque to all four wheels in accordance with driving conditions."
As first implemented in the Acura RL, SH-AWD allows torque to be continuously distributed between front and rear wheels from 70% front/30% rear to 30% front/70% rear, with up to 100% of the rear power being distributed to the outer left or right wheel to assist in cornering and dramatically reducing understeer. For example, in straight line full throttle acceleration, the RL is capable of distributing 40% of torque to the rear wheels and 60% to the front wheels. In a hard turn, of percentage of power distributed to the rear wheels, up to 100% of the rear wheel power can be distributed to the single, outer rear wheel. This action will push the rear around the corner, and helping with steering, reducing understeer and keeping the car balanced and controlled. The effect can be likened to steering in a row boat where applying more power to one oar can turn the boat.
The SH-AWD all-wheel drive system was lauded by Popular Science as one of the best automotive innovations of 2004, and as part of an already tech filled vehicle helped to earn the 2005 "Tech car of the year" from CNET.com
. All wheel drive systems for passenger cars, although common place today, have existed in the luxury car segment for quite some time. Audi's
all wheel drive system quattro was introduced in 1980 on the Audi Quattro
. Audi's parent company Volkswagen Group
has been developing four-wheel drive
systems almost since its inception during the Second World War.
Type SH. Honda introduced the Variable Torque Management 4WD (VTM-4) automatic all wheel drive system in late 2000 on the 2001 model year Acura MDX
sport utility vehicle (SUV) and later on the 2002 Honda Pilot
SUV.
The ATTS equipped front-wheel drive
Honda Prelude was labeled Type SH - for "Super Handling". The ATTS was able to distribute torque across the front drive wheels in order to reduce understeer in cornering, and provide more neutral handling for the front-wheel driven car. The ATTS garnered high praise for the 5th and last generation of the Honda Prelude, and earned the Type SH Prelude the best handling car under $30,000 award from Car and Driver
magazine. However, the real usefulness of this high technology differential, which came at a more than $2000 premium, was debatable in a car that was already well-known for its handling prowess. The ATTS was only available in the highest trim level, manual transmission form, or about 5% of the Preludes offered for sale.
The VTM-4 system claimed to be different from other all wheel drive systems in that it "anticipated" wheel slippage, rather than waiting for the vehicle to sense wheel slippage, after the vehicle may already be in trouble. The VTM-4 system
consisted of a pair of computer controlled wet clutches in the rear axle that worked in concert with the front wheels regardless of road conditions. On start-up, the VTM-4 system would send torque (power) from the front wheels to the rear wheels to supplement the normal front wheel drive mode. With all four wheels being powered on start-up, regardless of conditions, more tire adhesion is provided from four driving wheels rather than two front driving wheels. In the dry, this served to reduce front wheel drive torque steer, and provide more front tire adhesion for cornering. In the wet, snow or mud, power to the rear wheels moves the vehicle from rest with a minimum of wheelspin because all four tires are working together to move the car, rather than just two front tires. If conditions are really slippery and wheel spin is unavoidable, VTM-4 instantly reacts by adding rear-wheel torque in proportion to both the slippage and the rate of increase of slippage. VTM-4 was also designed with a special lock mode to help extract the vehicle from a stuck condition, such as a snow bank. This lock mode automatically engaged power to all four wheels at low speeds. As speeds increased, the power to the rear wheel would decrease, and by 18 mph, the system would revert to front wheel drive.
SH-AWD combined both the automatic all wheel drive VTM-4 system capability with the "super handling" torque shifting ability of ATTS on the rear axles.
In the North American market, Honda introduced the original SH-AWD system introduced in late 2004 with the second generation 2005 Acura RL. Two other SH-AWD variants were introduced in late 2006 in the then all new 2007 Acura RDX
and the new second generation 2007 Acura MDX
Sport Utility Vehicles SUV. In late 2008, an improved version of the Acura RL SH-AWD was introduced in the significantly revised Mid-Model Change (MMC) of the 2009 Acura RL. This improved version provided earlier SH-AWD intervention (first gear vs second) and more precise use of the rear differential electromagnetic clutch system to provide an improved limited-slip differential function.
Yet another version of SH-AWD was introduced in late 2008 with the fourth generation 2009 Acura TL
. The Acura TL implementation of SH-AWD is actually mechanically more similar to the SH-AWD layout in the Acura MDX and RDX in that the rear differential is over driven at a constant 1.7% faster than the front wheels, unlike the Acura RL, which, since its introduction in 2004, added an acceleration device which can over drive the rear wheels up to 5.7% faster than the front wheels.
As of 2010 the Acura RL remains the only SH-AWD configuration with the variable speed rear differential acceleration device. The newly introduced 2010 Acura ZDX
four-door sports coupe maintains a mechanically similar fixed 1.7% over driven rear differential configuration to the other Acura SH-AWD equipped vehicles
Acura announced in late 2008 that the 2010 Acura TL SH-AWD will be implemented with a six-speed manual transmission. Previous implementations of SH-AWD have all been with five-speed automatic transmissions.
On July 20, 2009, Acura announced the Acura ZDX four-door sports coupe, equipped with a new six-speed automatic transmission and SH-AWD. This would be the first time a six-speed automatic transmission would be mated to SH-AWD, as well as being the first six-speed automatic transmission introduced in either the Acura or Honda line up.
One week later, Acura announced a similar six-speed automatic transmission and SH-AWD with the 2010 Mid Model Change (MMC) refresh for the second generation Acura MDX
.
In December 2010, the 2011 Acura RL was announced with a second Mid Model Change, featuring, among other things, a six-speed automatic tranmission.
On November 30, 2011, as part of the publicity surrounding the 2011 Tokyo Auto Show, Honda announced a new implementation of SH-AWD as part of its "Earth Dreams Technology". The new hybrid electric SH-AWD would be based on an all new 3.5 L V-6 and three electric motors
and lithium-ion battery technology. The V-6 would be mated to a 30 kW
electric motor which could operate independently of the V-6, unlike earlier mild hybrid
Honda IMA
configurations. In addition, each rear wheel would have a 20 kW electric motor that would operate independently, varying torque as conditions demand. On a turn, the electric motor would apply torque to the outside rear wheel, while the inside rear wheel motor would drag, amplifying the SH-AWD effect. At the same time, the dragging motor would act as a generator
, feeding power to the outside wheel motor. If the lithium ion pack became depleted, the V-6 would power the front electric motor as generator to feed electricity to rear wheels while also charging the battery. A prototype of this system was shown in a test mule using an 8th generation North American version of the Honda Accord
.
, either a turbo-charged in-line four cylinder Honda K-Series
engine in the case of the RDX, or naturally aspirated V-6
versions of the Honda J-Series
engine. The engines are mated to a front wheel drive transaxle
. There is no center differential. The transaxle is bolted to torque transfer unit that spins a center drive shaft that powers the rear differential unit. The rear differential is a T-shaped device. Power coming from the engine is transferred via a central hypoid gear that delivers power to each rear axle. Power to the each axle is modulated by identical planetary gear
sets and electromagnetic clutch packs which can vary incoming power side to side.
As described earlier, SH-AWD can vary torque side to side through the rear wheels. This ability to drive one of the rear wheels with more power (remember the row boat analogy) is accomplished through overdriving the rear wheels with respect to the front wheels. The Acura RL is designed with a third planetary gear set and clutch pack that are packaged into a so called "Acceleration Device", which is bolted in front of the rear differential unit. The Acceleration Device allows torque to be passed to the rear wheels at a near one to one ratio, but in cornering situations, the Acceleration Device variably increases the torque passed to the rear up to 5%, depending on the cornering situation.
As of early 2010, SH-AWD has been implemented by Acura in two functionally similar, but mechanically different configurations, with and without Acceleration Device. The more complex SH-AWD version uses the Acceleration Device and can be found in:
2005–2008 Acura RL
Sedan
2009–2010 Mid-Model Change Acura RL Sedan
2011–2012 Mid-Model Change Acura RL Sedan
The less complex version of SH-AWD omits the Acceleration Device and can be found in:
2007-TBD Acura RDX
CUV
2007-TBD Acura MDX
SUV
2009-TBD Acura TL
SH-AWD Sedan
2010-TBD Acura ZDX
SH-AWD Four-Door Sports Coupe
The Acceleration Device allows the rear wheels to be variably overdriven with respect to the speed of the front wheels up to 5.7%. The Acceleration Device in the Acura RL is positioned in front of the rear differential. During normal steady state driving, the Acceleration Device input shaft (from the engine) and output shaft (to the rear differential) spin at almost equal speeds. In a cornering situation, the output shaft spins up to 5.7% faster than the input shaft, effectively speeding up the rear wheels. The electromagnetic clutch packs, based on sensor inputs, will vary the torque sent to the rear differential from side to side providing constant and dynamic balancing of the car handling characteristics.
The SH-AWD configuration with no acceleration device overdrives the rear wheels at a constant 1.7% with respect to the speed of the front wheels.
The Acceleration Device was first introduced in the flagship Acura RL sedan, and continues in the MMC versions of the Acura RL sedan. This more complex configuration appears to be unique among the SH-AWD equipped Acuras. This more complex RL configuration could be considered an exclusive flagship vehicle feature, and not specified for vehicles with lower price points. On the other hand, the later SH-AWD configuration without the Acceleration Device could just be a simpler and less sophisticated version due to vehicle dynamics and price points, or it could represent a more refined, less complex and inherently more reliable, new standard for the SH-AWD configuration. The rationale for the two distinct configurations has not been publicized by Acura.
SH-AWD in the Acura RDX
and Acura MDX
use a default power split of 90% to the front and 10% to the rear. Like the unit in the RL, both can power the rear wheels with various amounts engine torque. The power split under straight-line, high-speed acceleration varies from vehicle to vehicle. In addition, in cornering situations, dependent on the specific vehicle balance and dynamics, the rearward power transfer ratios in the RDX and MDX differ greatly from the RL and TL sedans.
For example, in comparing the RL to the MDX, in hard cornering, the most power transferred to the rear wheels for the RL is 70%, whereas the MDX is only 50%. In straight line efficient cruising, different model years of the RL can transfer from 70 to 80% to the front wheels, while the MDX can transfer as much as 90% to the front wheels.
3 or 4 channel (model dependent) Anti-lock Braking System (ABS)
4 channel Vehicle Stability Assist (VSA)
Electronic Brake Force Distribution (EBD)
Throttle control system
Yaw Angle Sensor
Speed sensor
Steering Angle sensor
Lateral G-Force sensor
These systems and sensors all work together to enhance vehicle handling, and safety.
The second generation Acura RL
sedan, introduced in late 2004 as a 2005 model, was the first production implementation of SH-AWD. It is the most mechanically complex, and probably the heaviest implementation of SH-AWD. The RL is powered by either a 3.5L 290 hp VTEC
variable valve timing and lift V-6 (2005–2008) or a 3.7L 300 hp VTEC V-6 (2009–2010) transverse mounted in the manner of a typical Honda front wheel drive car. In fact, the RL uses a highly modified version of the Honda Global Midsize platform, versions of which exist for the Honda Accord, Acura TSX and Acura TL. However, the front transaxle is directly coupled to a torque transfer unit. Within the torque transfer unit is a short horizontal shaft and a hypoid gear set which turn the propeller shaft ninety degrees and moves it to the vehicle center line. An RL unique, two piece lightweight carbon fiber reinforced drive shaft carries power to the rear differential unit. Torque vectoring takes place in the rear differential which contains three planetary gear and clutch sets. Torque from the driveshaft passes through the differential's first clutch/planetary gearset, which as a unit is called the Acceleration Device. Two identical clutch/planetary gearsets power each rear wheel. The rear wheels are always overdriven with respect to the speed of the front wheels. The Acceleration Device can variably overdrive the rear wheel speed up to 5.7%.
2005–2008 RL SH-AWD operating parameters include:
The 2005 and 2006 system normally sends 70% of power to the front wheels and 30% to the rear under normal conditions but these ratios can reverse according to dynamic driving conditions. The 2007–2008 brochures specification sections indicate that this ratio changed to 80%-20%, and vice versa. The system can work because the clutches can slip under circumstances where the vehicle is turning, thus allowing the rear and front wheels to turn at different rates around a curve. As noted above, the SH-AWD can take 100% of the power shunted through the rear differentials and variably direct power to each wheel, up to 100% of that power to the outside rear wheel. Adding power to the outside rear wheel on a turn has a steering effect on the vehicle which can greatly improve vehicle handling dynamics through the reduction of oversteer and more balanced handling. In limited situations, the vehicle may exhibit power oversteer, characteristic of more sporty rear-wheel-drive vehicles.
While the rear differential also acts like a limited slip differential in spirited driving, SH-AWD is deeply integrated into the Honda Vehicle Stability Assist (VSA) system and various onboard sensors which helps to keep the car under control in a variety of situations.
The 2009 RL was updated to have more aggressive intervention of SH-AWD to give the car more rear wheel drive like handling characteristics. 2009 RL SH-AWD operating parameters include:
Acura RDX
The Acura RDX was introduced in mid 2006 as a 2007 model year car. The first generation Acura RDX is a small crossover utility vehicle, and features a simpler implementation of SH-AWD than that found in the RL. The RDX does not have the Acceleration Device found in the Acura RL; instead the rear wheels are constantly overdriven at 1.7% higher speed than the front wheels. The RDX is distinguished by a unique 2.3L turbo charged 240 hp in line four cylinder VTEC engine mounted in what is purported to be a unique version of the Honda Global Small Light Truck Platform, a version different than the platform used for the Honda CR-V and the Honda Element. The engine is also transversely mounted.
SH-AWD operating parameters include:
Acura MDX
The second generation Acura MDX, introduced in late 2006 as a 2007 model, uses a simpler implementation of SH-AWD than that found in the RL, the main difference is that unlike the RL 70 front 30 rear distribution, the MDX offers the opposite having a 30 front 70 rear distribution. The MDX configuration is similar to that in the RDX in that there is no Acceleration Device as found in the RL. The rear wheels are constantly overdriven at 1.7% faster speed than the front wheels. The MDX is powered by a 3.7L 300 hp VTEC V-6 engine tranversely mounted in a version of the Honda Global Large Light Truck Platform, versions of which are used for the Honda Pilot, Honda Ridgeline, Honda Odyssey, and the 2010 Acura ZDX. As can be seen below, the vehicle dynamics of the Acura MDX require different operating parameters.
SH-AWD operating parameters include:
Acura TL
The fourth generation Acura TL, introduced in late 2008 as a 2009 model has two major trim levels, a front wheel drive version, and an upmarket SH-AWD version. Similar in layout to
the Acura RL, the Acura SH-AWD TL features a 3.7L 305 hp VTEC V-6, transversely mounted front engine in the Global Midsize Platform. The 2009 model uses a five speed automatic transmission, but Acura has also promised a new six-speed manual transmission for the 2010 model year. It remains to be seen if the 2010 model will also feature the newly announced six-speed automatic transmission featured in the prototype Acura ZDX
announced at the April 2009 New York Auto Show. Unlike the Acura RL, the SH-AWD TL does not have the Acceleration Device.
SH-AWD operating parameters include:
Acura ZDX
The first generation Acura ZDX was announced on April 8, 2009 at the New York Auto Show as a 2010 model, slated for introduction in late Fall 2009 as an all new prototype concept car, billed as a luxury four door sports coupe. The Acura ZDX went on sale December 15, 2010. The car is powered by an all-aluminum 3.7L 300 hp, 270 lbs-ft torque VTEC V-6, mated to an all-new 6-speed automatic transmission with Sequential SportShift and Super Handling All-Wheel Drive. The V-6 appears to be mechanically similar to the Acura MDX V-6. The Acura ZDX SH-AWD implementation description appears to be very similar to the Acura MDX SH-AWD implementation.
Acura RL
The Acura RL is the flagship car for North American luxury brand Acura — marketed in Japan as the Honda Legend and manufactured in Saitama, Japan...
, and in Japan as the fourth generation Honda Legend
Honda Legend
The Honda Legend is a mid-size luxury car made by the Japanese automaker Honda. It was the result of Project XX, a joint agreement started in November 1981 with the Austin Rover Group of Great Britain and was mechanically related to the Rover 800 series....
. The company describes SH-AWD as a system "... that provides cornering performance that responds faithfully to driver input, and outstanding vehicle stability. A world's first, the SH-AWD system combines front-rear torque distribution control with independently regulated torque distribution to the left and right rear wheels to freely distribute the optimum amount of torque to all four wheels in accordance with driving conditions."
As first implemented in the Acura RL, SH-AWD allows torque to be continuously distributed between front and rear wheels from 70% front/30% rear to 30% front/70% rear, with up to 100% of the rear power being distributed to the outer left or right wheel to assist in cornering and dramatically reducing understeer. For example, in straight line full throttle acceleration, the RL is capable of distributing 40% of torque to the rear wheels and 60% to the front wheels. In a hard turn, of percentage of power distributed to the rear wheels, up to 100% of the rear wheel power can be distributed to the single, outer rear wheel. This action will push the rear around the corner, and helping with steering, reducing understeer and keeping the car balanced and controlled. The effect can be likened to steering in a row boat where applying more power to one oar can turn the boat.
The SH-AWD all-wheel drive system was lauded by Popular Science as one of the best automotive innovations of 2004, and as part of an already tech filled vehicle helped to earn the 2005 "Tech car of the year" from CNET.com
CNET.com
CNET is a tech media website that publishes news articles, blogs, and podcasts on technology and consumer electronics. Originally founded in 1994 by Halsey Minor and Shelby Bonnie, it was the flagship brand of CNET Networks and became a brand of CBS Interactive through CNET Networks' acquisition...
. All wheel drive systems for passenger cars, although common place today, have existed in the luxury car segment for quite some time. Audi's
Audi
Audi AG is a German automobile manufacturer, from supermini to crossover SUVs in various body styles and price ranges that are marketed under the Audi brand , positioned as the premium brand within the Volkswagen Group....
all wheel drive system quattro was introduced in 1980 on the Audi Quattro
Audi Quattro
The Audi Quattro is a road and rally car, produced by the German automobile manufacturer Audi, now part of the Volkswagen Group. It was first shown at the 1980 Geneva Motor Show on 3 March.The word quattro is derived from the Italian word for "four"...
. Audi's parent company Volkswagen Group
Volkswagen Group
Volkswagen Group is a German multinational automobile manufacturing group. , Volkswagen was ranked as the world’s third largest motor vehicle manufacturer and Europe's largest....
has been developing four-wheel drive
Four-wheel drive
Four-wheel drive, 4WD, or 4×4 is a four-wheeled vehicle with a drivetrain that allows all four wheels to receive torque from the engine simultaneously...
systems almost since its inception during the Second World War.
Development
On a very gross level, the SH-AWD system is combination of the Honda VTM-4 automatic all wheel drive system and the ATTS variable torque distribution system. Honda introduced the Active Torque Transfer System (ATTS) technology in the 1997 Honda PreludeHonda Prelude
The Honda Prelude was a sports coupe produced by Japanese automaker Honda from 1978 until 2001. It replaced the Honda S800, a front-engined, front wheel drive sports car...
Type SH. Honda introduced the Variable Torque Management 4WD (VTM-4) automatic all wheel drive system in late 2000 on the 2001 model year Acura MDX
Acura MDX
The Acura MDX, or Honda MDX as known in Japan and Australia , is a mid-size luxury crossover SUV produced by the Japanese automaker Acura since the 2001 model year. The MDX was the first crossover SUV to have third-row seating. It is related to the Honda Pilot. The alphanumeric moniker stands for...
sport utility vehicle (SUV) and later on the 2002 Honda Pilot
Honda Pilot
The Honda Pilot is a mid-size crossover SUV. The Honda Pilot is built in Lincoln, Alabama, and was also produced in Alliston, Ontario, Canada up until April 2007. The first generation Pilot was released in the summer of 2002 as a 2003 model, and in 2006 it received new front and rear fascias, a...
SUV.
The ATTS equipped front-wheel drive
Front-wheel drive
Front-wheel drive is a form of engine/transmission layout used in motor vehicles, where the engine drives the front wheels only. Most modern front-wheel drive vehicles feature a transverse engine, rather than the conventional longitudinal engine arrangement generally found in rear-wheel drive and...
Honda Prelude was labeled Type SH - for "Super Handling". The ATTS was able to distribute torque across the front drive wheels in order to reduce understeer in cornering, and provide more neutral handling for the front-wheel driven car. The ATTS garnered high praise for the 5th and last generation of the Honda Prelude, and earned the Type SH Prelude the best handling car under $30,000 award from Car and Driver
Car and Driver
Car and Driver is an American automotive enthusiast magazine. Its total circulation is 1.31 million. It is owned by Hearst Magazines, who purchased prior owner Hachette Filipacchi Media U.S. in 2011...
magazine. However, the real usefulness of this high technology differential, which came at a more than $2000 premium, was debatable in a car that was already well-known for its handling prowess. The ATTS was only available in the highest trim level, manual transmission form, or about 5% of the Preludes offered for sale.
The VTM-4 system claimed to be different from other all wheel drive systems in that it "anticipated" wheel slippage, rather than waiting for the vehicle to sense wheel slippage, after the vehicle may already be in trouble. The VTM-4 system
consisted of a pair of computer controlled wet clutches in the rear axle that worked in concert with the front wheels regardless of road conditions. On start-up, the VTM-4 system would send torque (power) from the front wheels to the rear wheels to supplement the normal front wheel drive mode. With all four wheels being powered on start-up, regardless of conditions, more tire adhesion is provided from four driving wheels rather than two front driving wheels. In the dry, this served to reduce front wheel drive torque steer, and provide more front tire adhesion for cornering. In the wet, snow or mud, power to the rear wheels moves the vehicle from rest with a minimum of wheelspin because all four tires are working together to move the car, rather than just two front tires. If conditions are really slippery and wheel spin is unavoidable, VTM-4 instantly reacts by adding rear-wheel torque in proportion to both the slippage and the rate of increase of slippage. VTM-4 was also designed with a special lock mode to help extract the vehicle from a stuck condition, such as a snow bank. This lock mode automatically engaged power to all four wheels at low speeds. As speeds increased, the power to the rear wheel would decrease, and by 18 mph, the system would revert to front wheel drive.
SH-AWD combined both the automatic all wheel drive VTM-4 system capability with the "super handling" torque shifting ability of ATTS on the rear axles.
In the North American market, Honda introduced the original SH-AWD system introduced in late 2004 with the second generation 2005 Acura RL. Two other SH-AWD variants were introduced in late 2006 in the then all new 2007 Acura RDX
Acura RDX
The Acura RDX is Acura’s first compact crossover SUV. Originally previewed as the Acura RD-X concept car, the production RDX had its debut at the 2006 New York Auto Show and went on sale on August 11, 2006....
and the new second generation 2007 Acura MDX
Acura MDX
The Acura MDX, or Honda MDX as known in Japan and Australia , is a mid-size luxury crossover SUV produced by the Japanese automaker Acura since the 2001 model year. The MDX was the first crossover SUV to have third-row seating. It is related to the Honda Pilot. The alphanumeric moniker stands for...
Sport Utility Vehicles SUV. In late 2008, an improved version of the Acura RL SH-AWD was introduced in the significantly revised Mid-Model Change (MMC) of the 2009 Acura RL. This improved version provided earlier SH-AWD intervention (first gear vs second) and more precise use of the rear differential electromagnetic clutch system to provide an improved limited-slip differential function.
Yet another version of SH-AWD was introduced in late 2008 with the fourth generation 2009 Acura TL
Acura TL
The TL "Touring Luxury" debuted as 1996 model, first with the 1996 2.5 TL available with the 2.5 L 176 hp SOHC 20-valve 5-cylinder engine from the Vigor. The 3.2 TL used the 3.2 L 200 hp SOHC 24v V6 from the second generation Acura Legend. The 2.5 TL was positioned as the...
. The Acura TL implementation of SH-AWD is actually mechanically more similar to the SH-AWD layout in the Acura MDX and RDX in that the rear differential is over driven at a constant 1.7% faster than the front wheels, unlike the Acura RL, which, since its introduction in 2004, added an acceleration device which can over drive the rear wheels up to 5.7% faster than the front wheels.
As of 2010 the Acura RL remains the only SH-AWD configuration with the variable speed rear differential acceleration device. The newly introduced 2010 Acura ZDX
Acura ZDX
The Acura ZDX is a mid-size luxury crossover developed by Honda for its upmarket brand Acura. The car was originally scheduled to be called the Acura MSX. The ZDX debuted at the 2009 New York International Auto Show on April 8, 2009...
four-door sports coupe maintains a mechanically similar fixed 1.7% over driven rear differential configuration to the other Acura SH-AWD equipped vehicles
Acura announced in late 2008 that the 2010 Acura TL SH-AWD will be implemented with a six-speed manual transmission. Previous implementations of SH-AWD have all been with five-speed automatic transmissions.
On July 20, 2009, Acura announced the Acura ZDX four-door sports coupe, equipped with a new six-speed automatic transmission and SH-AWD. This would be the first time a six-speed automatic transmission would be mated to SH-AWD, as well as being the first six-speed automatic transmission introduced in either the Acura or Honda line up.
One week later, Acura announced a similar six-speed automatic transmission and SH-AWD with the 2010 Mid Model Change (MMC) refresh for the second generation Acura MDX
Acura MDX
The Acura MDX, or Honda MDX as known in Japan and Australia , is a mid-size luxury crossover SUV produced by the Japanese automaker Acura since the 2001 model year. The MDX was the first crossover SUV to have third-row seating. It is related to the Honda Pilot. The alphanumeric moniker stands for...
.
In December 2010, the 2011 Acura RL was announced with a second Mid Model Change, featuring, among other things, a six-speed automatic tranmission.
On November 30, 2011, as part of the publicity surrounding the 2011 Tokyo Auto Show, Honda announced a new implementation of SH-AWD as part of its "Earth Dreams Technology". The new hybrid electric SH-AWD would be based on an all new 3.5 L V-6 and three electric motors
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
and lithium-ion battery technology. The V-6 would be mated to a 30 kW
Kw
kw or KW may refer to:* Kuwait, ISO 3166-1 country code** .kw, the country code top level domain for Kuwait* Kilowatt* Self-ionization of water Kw* Cornish language's ISO 639 code* Kitchener–Waterloo, Ontario, Canada...
electric motor which could operate independently of the V-6, unlike earlier mild hybrid
Mild Hybrid
Mild hybrids are essentially conventional fossil-fuel vehicles equipped with a large electric machine allowing the engine to be turned off whenever the car is coasting, braking, or stopped, yet restart quickly...
Honda IMA
IMA
- Institutions :* Indianapolis Museum of Art, an art museum in Indianapolis, Indiana* Indian Medical Association* Indian Military Academy, Dehradun...
configurations. In addition, each rear wheel would have a 20 kW electric motor that would operate independently, varying torque as conditions demand. On a turn, the electric motor would apply torque to the outside rear wheel, while the inside rear wheel motor would drag, amplifying the SH-AWD effect. At the same time, the dragging motor would act as a generator
Generator
Generator may refer to:* Electrical generator* Engine-generator, an electrical generator, but with its own engine.* Generator , any of several closely related usages in mathematics.Computing:...
, feeding power to the outside wheel motor. If the lithium ion pack became depleted, the V-6 would power the front electric motor as generator to feed electricity to rear wheels while also charging the battery. A prototype of this system was shown in a test mule using an 8th generation North American version of the Honda Accord
Honda Accord
The Honda Accord is a series of compact, mid-size and full-size automobiles manufactured by Honda since 1976, and sold in a majority of automotive markets throughout the world....
.
Function
Current SH-AWD configurations are all mated to a transverse engineTransverse engine
A transverse engine is an engine mounted in a vehicle so that the engine's crankshaft axis is perpendicular to the long axis of the vehicle. Many modern front wheel drive vehicles use this engine mounting configuration...
, either a turbo-charged in-line four cylinder Honda K-Series
Honda K engine
The Honda K series engine is a four-cylinder four-stroke engine introduced in 2001. The K series engines are equipped with DOHC valvetrains and use roller rockers to reduce friction. The engines use a coil-on-plug, distributorless ignition system with a coil for each spark plug...
engine in the case of the RDX, or naturally aspirated V-6
V6 engine
A V6 engine is a V engine with six cylinders mounted on the crankcase in two banks of three cylinders, usually set at either a right angle or an acute angle to each other, with all six pistons driving a common crankshaft...
versions of the Honda J-Series
Honda J engine
The J-series was Honda's second V6 engine family, introduced in 1996. It is a 60° V6 – Honda's existing C-series was a 90° engine. The J-series was designed for transverse mounting. It has a shorter bore spacing , shorter connecting rods, and a special smaller crankshaft than the C-series for...
engine. The engines are mated to a front wheel drive transaxle
Transaxle
In the automotive field, a transaxle is a major mechanical component that combines the functionality of the transmission, the differential, and associated components of the driven axle into one integrated assembly....
. There is no center differential. The transaxle is bolted to torque transfer unit that spins a center drive shaft that powers the rear differential unit. The rear differential is a T-shaped device. Power coming from the engine is transferred via a central hypoid gear that delivers power to each rear axle. Power to the each axle is modulated by identical planetary gear
Epicyclic gearing
Epicyclic gearing or planetary gearing is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear. Typically, the planet gears are mounted on a movable arm or carrier which itself may rotate relative to the sun gear...
sets and electromagnetic clutch packs which can vary incoming power side to side.
As described earlier, SH-AWD can vary torque side to side through the rear wheels. This ability to drive one of the rear wheels with more power (remember the row boat analogy) is accomplished through overdriving the rear wheels with respect to the front wheels. The Acura RL is designed with a third planetary gear set and clutch pack that are packaged into a so called "Acceleration Device", which is bolted in front of the rear differential unit. The Acceleration Device allows torque to be passed to the rear wheels at a near one to one ratio, but in cornering situations, the Acceleration Device variably increases the torque passed to the rear up to 5%, depending on the cornering situation.
As of early 2010, SH-AWD has been implemented by Acura in two functionally similar, but mechanically different configurations, with and without Acceleration Device. The more complex SH-AWD version uses the Acceleration Device and can be found in:
2005–2008 Acura RL
Acura RL
The Acura RL is the flagship car for North American luxury brand Acura — marketed in Japan as the Honda Legend and manufactured in Saitama, Japan...
Sedan
2009–2010 Mid-Model Change Acura RL Sedan
2011–2012 Mid-Model Change Acura RL Sedan
The less complex version of SH-AWD omits the Acceleration Device and can be found in:
2007-TBD Acura RDX
Acura RDX
The Acura RDX is Acura’s first compact crossover SUV. Originally previewed as the Acura RD-X concept car, the production RDX had its debut at the 2006 New York Auto Show and went on sale on August 11, 2006....
CUV
2007-TBD Acura MDX
Acura MDX
The Acura MDX, or Honda MDX as known in Japan and Australia , is a mid-size luxury crossover SUV produced by the Japanese automaker Acura since the 2001 model year. The MDX was the first crossover SUV to have third-row seating. It is related to the Honda Pilot. The alphanumeric moniker stands for...
SUV
2009-TBD Acura TL
Acura TL
The TL "Touring Luxury" debuted as 1996 model, first with the 1996 2.5 TL available with the 2.5 L 176 hp SOHC 20-valve 5-cylinder engine from the Vigor. The 3.2 TL used the 3.2 L 200 hp SOHC 24v V6 from the second generation Acura Legend. The 2.5 TL was positioned as the...
SH-AWD Sedan
2010-TBD Acura ZDX
Acura ZDX
The Acura ZDX is a mid-size luxury crossover developed by Honda for its upmarket brand Acura. The car was originally scheduled to be called the Acura MSX. The ZDX debuted at the 2009 New York International Auto Show on April 8, 2009...
SH-AWD Four-Door Sports Coupe
The Acceleration Device allows the rear wheels to be variably overdriven with respect to the speed of the front wheels up to 5.7%. The Acceleration Device in the Acura RL is positioned in front of the rear differential. During normal steady state driving, the Acceleration Device input shaft (from the engine) and output shaft (to the rear differential) spin at almost equal speeds. In a cornering situation, the output shaft spins up to 5.7% faster than the input shaft, effectively speeding up the rear wheels. The electromagnetic clutch packs, based on sensor inputs, will vary the torque sent to the rear differential from side to side providing constant and dynamic balancing of the car handling characteristics.
The SH-AWD configuration with no acceleration device overdrives the rear wheels at a constant 1.7% with respect to the speed of the front wheels.
The Acceleration Device was first introduced in the flagship Acura RL sedan, and continues in the MMC versions of the Acura RL sedan. This more complex configuration appears to be unique among the SH-AWD equipped Acuras. This more complex RL configuration could be considered an exclusive flagship vehicle feature, and not specified for vehicles with lower price points. On the other hand, the later SH-AWD configuration without the Acceleration Device could just be a simpler and less sophisticated version due to vehicle dynamics and price points, or it could represent a more refined, less complex and inherently more reliable, new standard for the SH-AWD configuration. The rationale for the two distinct configurations has not been publicized by Acura.
SH-AWD in the Acura RDX
Acura RDX
The Acura RDX is Acura’s first compact crossover SUV. Originally previewed as the Acura RD-X concept car, the production RDX had its debut at the 2006 New York Auto Show and went on sale on August 11, 2006....
and Acura MDX
Acura MDX
The Acura MDX, or Honda MDX as known in Japan and Australia , is a mid-size luxury crossover SUV produced by the Japanese automaker Acura since the 2001 model year. The MDX was the first crossover SUV to have third-row seating. It is related to the Honda Pilot. The alphanumeric moniker stands for...
use a default power split of 90% to the front and 10% to the rear. Like the unit in the RL, both can power the rear wheels with various amounts engine torque. The power split under straight-line, high-speed acceleration varies from vehicle to vehicle. In addition, in cornering situations, dependent on the specific vehicle balance and dynamics, the rearward power transfer ratios in the RDX and MDX differ greatly from the RL and TL sedans.
For example, in comparing the RL to the MDX, in hard cornering, the most power transferred to the rear wheels for the RL is 70%, whereas the MDX is only 50%. In straight line efficient cruising, different model years of the RL can transfer from 70 to 80% to the front wheels, while the MDX can transfer as much as 90% to the front wheels.
Systems integration
SH-AWD technology is deeply integrated with other systems and sensors implemented in Acura vehicles including:3 or 4 channel (model dependent) Anti-lock Braking System (ABS)
4 channel Vehicle Stability Assist (VSA)
Electronic Brake Force Distribution (EBD)
Throttle control system
Yaw Angle Sensor
Speed sensor
Steering Angle sensor
Lateral G-Force sensor
These systems and sensors all work together to enhance vehicle handling, and safety.
Implementation
Acura RLAcura RL
The Acura RL is the flagship car for North American luxury brand Acura — marketed in Japan as the Honda Legend and manufactured in Saitama, Japan...
The second generation Acura RL
Acura RL
The Acura RL is the flagship car for North American luxury brand Acura — marketed in Japan as the Honda Legend and manufactured in Saitama, Japan...
sedan, introduced in late 2004 as a 2005 model, was the first production implementation of SH-AWD. It is the most mechanically complex, and probably the heaviest implementation of SH-AWD. The RL is powered by either a 3.5L 290 hp VTEC
VTEC
VTEC is a valvetrain system developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine. The VTEC system uses two camshaft profiles and electronically selects between the profiles. It was invented by Honda R&D engineer Ikuo Kajitani, and was the first system...
variable valve timing and lift V-6 (2005–2008) or a 3.7L 300 hp VTEC V-6 (2009–2010) transverse mounted in the manner of a typical Honda front wheel drive car. In fact, the RL uses a highly modified version of the Honda Global Midsize platform, versions of which exist for the Honda Accord, Acura TSX and Acura TL. However, the front transaxle is directly coupled to a torque transfer unit. Within the torque transfer unit is a short horizontal shaft and a hypoid gear set which turn the propeller shaft ninety degrees and moves it to the vehicle center line. An RL unique, two piece lightweight carbon fiber reinforced drive shaft carries power to the rear differential unit. Torque vectoring takes place in the rear differential which contains three planetary gear and clutch sets. Torque from the driveshaft passes through the differential's first clutch/planetary gearset, which as a unit is called the Acceleration Device. Two identical clutch/planetary gearsets power each rear wheel. The rear wheels are always overdriven with respect to the speed of the front wheels. The Acceleration Device can variably overdrive the rear wheel speed up to 5.7%.
2005–2008 RL SH-AWD operating parameters include:
- During straight-line cruising and moderate cornering below about half throttle, up to 70 percent of the torque is delivered to the front wheels
- In full-throttle straight line acceleration, up to 40 percent of the power is sent to the rear axle
- In hard cornering, up to 70 percent of available torque goes to the rear wheels for enhanced chassis balance
- Up to 100 percent of this torque can be applied to the outside rear wheel if the situation dictates
- SH-AWD is active in second through fifth forward gears
The 2005 and 2006 system normally sends 70% of power to the front wheels and 30% to the rear under normal conditions but these ratios can reverse according to dynamic driving conditions. The 2007–2008 brochures specification sections indicate that this ratio changed to 80%-20%, and vice versa. The system can work because the clutches can slip under circumstances where the vehicle is turning, thus allowing the rear and front wheels to turn at different rates around a curve. As noted above, the SH-AWD can take 100% of the power shunted through the rear differentials and variably direct power to each wheel, up to 100% of that power to the outside rear wheel. Adding power to the outside rear wheel on a turn has a steering effect on the vehicle which can greatly improve vehicle handling dynamics through the reduction of oversteer and more balanced handling. In limited situations, the vehicle may exhibit power oversteer, characteristic of more sporty rear-wheel-drive vehicles.
While the rear differential also acts like a limited slip differential in spirited driving, SH-AWD is deeply integrated into the Honda Vehicle Stability Assist (VSA) system and various onboard sensors which helps to keep the car under control in a variety of situations.
The 2009 RL was updated to have more aggressive intervention of SH-AWD to give the car more rear wheel drive like handling characteristics. 2009 RL SH-AWD operating parameters include:
- During straight-line cruising and moderate cornering below half throttle, up to 70-percent of engine torque is delivered to the front wheels.
- In full-throttle straight line acceleration, up to 40-percent of the power is sent to the rear axle.
- In hard cornering, up to 70-percent of available torque goes to the rear wheels for enhanced chassis balance. Up to 100-percent of this torque can be applied to the outside rear wheel that can also be overdriven up to 5.7-percent by a built-in acceleration device.
- SH-AWD is active in all five forward gears
Acura RDX
Acura RDX
The Acura RDX is Acura’s first compact crossover SUV. Originally previewed as the Acura RD-X concept car, the production RDX had its debut at the 2006 New York Auto Show and went on sale on August 11, 2006....
The Acura RDX was introduced in mid 2006 as a 2007 model year car. The first generation Acura RDX is a small crossover utility vehicle, and features a simpler implementation of SH-AWD than that found in the RL. The RDX does not have the Acceleration Device found in the Acura RL; instead the rear wheels are constantly overdriven at 1.7% higher speed than the front wheels. The RDX is distinguished by a unique 2.3L turbo charged 240 hp in line four cylinder VTEC engine mounted in what is purported to be a unique version of the Honda Global Small Light Truck Platform, a version different than the platform used for the Honda CR-V and the Honda Element. The engine is also transversely mounted.
SH-AWD operating parameters include:
- Up to 90-percent of available driveline torque can be transferred to the front wheels during high-speed driving
- During straight line full-throttle acceleration, up to 45-percent of available torque can be transferred to the rear wheels
- In hard cornering during acceleration, up to 70-percent of available torque can be directed to the rear wheels for enhanced vehicle dynamics
- Up to 100-percent of the torque sent to the rear axle can be applied to either rear wheel as the conditions dictate
Acura MDX
Acura MDX
The Acura MDX, or Honda MDX as known in Japan and Australia , is a mid-size luxury crossover SUV produced by the Japanese automaker Acura since the 2001 model year. The MDX was the first crossover SUV to have third-row seating. It is related to the Honda Pilot. The alphanumeric moniker stands for...
The second generation Acura MDX, introduced in late 2006 as a 2007 model, uses a simpler implementation of SH-AWD than that found in the RL, the main difference is that unlike the RL 70 front 30 rear distribution, the MDX offers the opposite having a 30 front 70 rear distribution. The MDX configuration is similar to that in the RDX in that there is no Acceleration Device as found in the RL. The rear wheels are constantly overdriven at 1.7% faster speed than the front wheels. The MDX is powered by a 3.7L 300 hp VTEC V-6 engine tranversely mounted in a version of the Honda Global Large Light Truck Platform, versions of which are used for the Honda Pilot, Honda Ridgeline, Honda Odyssey, and the 2010 Acura ZDX. As can be seen below, the vehicle dynamics of the Acura MDX require different operating parameters.
SH-AWD operating parameters include:
- Direct Yaw Control promotes precise line trace in all conditions
- Full-time "active and intelligent" all-wheel drive requires no driver interaction
- SH-AWD direct control electromagnetic clutches provide ultra-quick response
- Grade logic control allows worry-free starting on steep grades with up to 70-percent of available torque being sent to the rear wheels
- Up to 70-percent of available torque can be directed to the rear wheels during hill climb acceleration for maximum traction
- Up to 50-percent of available torque can be transferred to the front wheels during cruising to help maximize fuel efficiency
- In hard cornering, up to 50-percent of available torque can be directed to the rear axle for enhanced chassis balance and increased cornering capability
- Up to 100-percent of the torque sent to the rear axle can be applied to either rear wheel as the traction conditions dictate
- 37-percent increase in rear torque capacity as compared to the previous MDX VTM-4 system
- 7-percent reduction in weight compared to the previous VTM-4 system
Acura TL
Acura TL
The TL "Touring Luxury" debuted as 1996 model, first with the 1996 2.5 TL available with the 2.5 L 176 hp SOHC 20-valve 5-cylinder engine from the Vigor. The 3.2 TL used the 3.2 L 200 hp SOHC 24v V6 from the second generation Acura Legend. The 2.5 TL was positioned as the...
The fourth generation Acura TL, introduced in late 2008 as a 2009 model has two major trim levels, a front wheel drive version, and an upmarket SH-AWD version. Similar in layout to
the Acura RL, the Acura SH-AWD TL features a 3.7L 305 hp VTEC V-6, transversely mounted front engine in the Global Midsize Platform. The 2009 model uses a five speed automatic transmission, but Acura has also promised a new six-speed manual transmission for the 2010 model year. It remains to be seen if the 2010 model will also feature the newly announced six-speed automatic transmission featured in the prototype Acura ZDX
Acura ZDX
The Acura ZDX is a mid-size luxury crossover developed by Honda for its upmarket brand Acura. The car was originally scheduled to be called the Acura MSX. The ZDX debuted at the 2009 New York International Auto Show on April 8, 2009...
announced at the April 2009 New York Auto Show. Unlike the Acura RL, the SH-AWD TL does not have the Acceleration Device.
SH-AWD operating parameters include:
- Up to 90-percent of available torque can be transferred to the front wheels during normal cruising.
- In hard cornering and under acceleration, up to 70-percent of available torque can be directed to the rear wheels to enhance vehicle dynamics.
- Up to 100-percent of the torque sent to the rear axle can be applied to either rear wheel, depending on conditions.
Acura ZDX
Acura ZDX
The Acura ZDX is a mid-size luxury crossover developed by Honda for its upmarket brand Acura. The car was originally scheduled to be called the Acura MSX. The ZDX debuted at the 2009 New York International Auto Show on April 8, 2009...
The first generation Acura ZDX was announced on April 8, 2009 at the New York Auto Show as a 2010 model, slated for introduction in late Fall 2009 as an all new prototype concept car, billed as a luxury four door sports coupe. The Acura ZDX went on sale December 15, 2010. The car is powered by an all-aluminum 3.7L 300 hp, 270 lbs-ft torque VTEC V-6, mated to an all-new 6-speed automatic transmission with Sequential SportShift and Super Handling All-Wheel Drive. The V-6 appears to be mechanically similar to the Acura MDX V-6. The Acura ZDX SH-AWD implementation description appears to be very similar to the Acura MDX SH-AWD implementation.
See also
- 4Matic4MATIC4Matic is the name of an AWD four-wheel drive system developed and used by Mercedes-Benz. It is designed to increase traction in slippery conditions....
- a four-wheel drive system from Mercedes-BenzMercedes-BenzMercedes-Benz is a German manufacturer of automobiles, buses, coaches, and trucks. Mercedes-Benz is a division of its parent company, Daimler AG... - Saab XWDSaab XWDXWD, an acronym for Cross-Wheel Drive, is an advanced all-wheel drive system designed by Haldex in partnership with Saab. Also known as Haldex Generation 4, it is an intelligent permanent all-wheel drive system that can pre-emptively and continuously change torque distribution before wheel slip...
- a four-wheel drive system from SaabSaab AutomobileSaab Automobile AB, better known as Saab , is a Swedish car manufacturer owned by Dutch automobile manufacturer Swedish Automobile NV, formerly Spyker Cars NV. It is the exclusive automobile Royal Warrant holder as appointed by the King of Sweden... - 4motion4motion4motion is a registered trademark of Volkswagen AG, used exclusively on Volkswagen-branded automobiles which utilise four-wheel drive systems. Volkswagen has previously used the term "Syncro" for its 4WD models....
- a four-wheel drive system from VolkswagenVolkswagenVolkswagen is a German automobile manufacturer and is the original and biggest-selling marque of the Volkswagen Group, which now also owns the Audi, Bentley, Bugatti, Lamborghini, SEAT, and Škoda marques and the truck manufacturer Scania.Volkswagen means "people's car" in German, where it is... - All-TracAll-TracAll-Trac was a proprietary full time symmetric all wheel drive system used on a variety of Toyota badged models from 1988 to 2000. It was considered a revolutionary advance for all-wheel drive automobiles into the mainstream consumer market and its electronic/vacuum controlled locking center...
- a four-wheel drive system from Toyota - ATTESAATTESAATTESA is a four-wheel drive system used in some automobiles produced by the Japanese automaker Nissan, including some models under its luxury marque Infiniti.-ATTESA:...
- a four-wheel drive system from Nissan - Quattro (four wheel drive system) - a four-wheel drive system from AudiAudiAudi AG is a German automobile manufacturer, from supermini to crossover SUVs in various body styles and price ranges that are marketed under the Audi brand , positioned as the premium brand within the Volkswagen Group....
- S-AWC - a torque vectoring all wheel drive system from Mitsubishi MotorsMitsubishi Motorsis a multinational automaker headquartered in Minato, Tokyo. In 2009 it was the fifth-largest Japan-based automaker and the 17th-largest in the world measured by production...
- Ricardo Cross-Axle Torque-Vectoring AudiAudiAudi AG is a German automobile manufacturer, from supermini to crossover SUVs in various body styles and price ranges that are marketed under the Audi brand , positioned as the premium brand within the Volkswagen Group....
- ZF Vector Drive for BMWBMWBayerische Motoren Werke AG is a German automobile, motorcycle and engine manufacturing company founded in 1916. It also owns and produces the Mini marque, and is the parent company of Rolls-Royce Motor Cars. BMW produces motorcycles under BMW Motorrad and Husqvarna brands...
External links
- http://www.acura.com/index.aspx?initPath=RDX_Learn_FeaturesOptions_Performance_SHAWD_SHAWDOverview