MIVEC is the brand name of a variable valve timing

Variable valve timing

In internal combustion engines, variable valve timing , also known as Variable valve actuation , is a generalized term used to describe any mechanism or method that can alter the shape or timing of a valve lift event within an internal combustion engine...

 (VVT) engine

Internal combustion engine

The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

 technology developed by Mitsubishi Motors

Mitsubishi Motors

is 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...

. MIVEC, as with other similar systems, varies the timing of the intake and exhaust camshafts which increases the power and torque output over a broad engine speed range while also being able to help spool a turbocharger more quickly.

MIVEC was first introduced in 1992 in their 4G92 powerplant, a 1,597 cc naturally aspirated DOHC 16 valve straight-4

Straight-4

The inline-four engine or straight-four engine is an internal combustion engine with all four cylinders mounted in a straight line, or plane along the crankcase. The single bank of cylinders may be oriented in either a vertical or an inclined plane with all the pistons driving a common crankshaft....

. At the time, the first generation of the system was named Mitsubishi Innovative Valve timing and lift Electronic Control. The first cars to use this were the Mitsubishi Mirage

Mitsubishi Mirage

Mitsubishi launched the Mirage as a three-door front wheel drive hatchback in 1978, as a response to the first fuel crisis some years before. It had a distinctive design with large windows and Mitsubishi's Super Shift transmission . A five-door joined the range in 1979...

 hatchback

Hatchback

A Hatchback is a car body style incorporating a shared passenger and cargo volume, with rearmost accessibility via a rear third or fifth door, typically a top-hinged liftgate—and features such as fold-down rear seats to enable flexibility within the shared passenger/cargo volume. As a two-box...

 and the Mitsubishi Lancer

Mitsubishi Lancer

The Mitsubishi Lancer is a family car built by Mitsubishi Motors. It has been known as the Colt Lancer, Dodge/Plymouth Colt, Chrysler Valiant Lancer, Chrysler Lancer, Eagle Summit, Hindustan Lancer, Soueast Lioncel, Mitsubishi Carisma, and Mitsubishi Mirage in various countries at different times,...

 sedan. While the conventional 4G92 engine provided 145 PS at 7000 rpm, the MIVEC-equipped engine could achieve 175 PS at 7500 rpm. Similar improvements were seen when the technology was applied to the 1994 Mitsubishi FTO

Mitsubishi FTO

The Mitsubishi FTO, is a front engined, front-wheel drive coupe produced by Mitsubishi Motors between 1994 and 2000. It was originally planned to be exclusively for the Japanese domestic market, although its popularity as a grey market import to the United Kingdom, Ireland, and New Zealand led to...

, whose top-spec GPX variant had a 6A12 1997 cc DOHC 24 valve V6 with peak power of 200 PS at 7500 rpm. The GR model, whose otherwise identical powerplant was not MIVEC-equipped, produced 170 PS at 7000 rpm by comparison.

Although initially designed to enhance performance, the system has subsequently been developed to improve economy

Fuel economy in automobiles

Fuel usage in automobiles refers to the fuel efficiency relationship between distance traveled by an automobile and the amount of fuel consumed....

 and emissions, and has been introduced across Mitsubishi's range of vehicles, from the i

Mitsubishi i

The is a kei car from Japanese automaker Mitsubishi Motors, first released in January 2006, twenty eight months after its debut at the 2003 Frankfurt Motor Show...

 kei car

Kei car

Kei cars, K-cars, or , are a Japanese category of small vehicles, including passenger cars, vans, and pickup trucks. They are designed to comply with Japanese government tax and insurance regulations, and in most rural areas are exempted from the requirement to certify that adequate parking is...

 to the high-performance Lancer Evolution sedan.

Newest developments have led to MIVEC system being evolved into a continuous variable valve timing

Continuous variable valve timing

Continuous variable valve timing offers a unique ability to have independent control of the intake and exhaust valves in an internal combustion engine. For any engine load criteria, the timing of intake and exhaust can be independently programmed...

 and also being the first VVT system to be used into a passenger car diesel engine

Diesel engine

A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...

.

Operation

Some types of variable valve control systems optimize power and torque by varying valve opening times and/or duration. Some of these valve control systems optimize performance at low and mid-range engine speeds. Others focus on enhancing only high-rpm power. MIVEC system provides both of these benefits by controlling valve timing and lift. The basic operation of the MIVEC system is altering the cam profiles and thus tailoring engine performance in response to driver input.

In essence, MIVEC serves the same function as "swapping cams", something that car racers might do when modifying older-design engines to produce more power. However, such swaps come with a compromise - generally yielding either greater low-end torque or more high-end horsepower, but not both. MIVEC achieves both goals. With MIVEC, the "cam swap" occurs automatically at a fixed engine speed

Revolutions per minute

Revolutions per minute is a measure of the frequency of a rotation. It annotates the number of full rotations completed in one minute around a fixed axis...

. The cam switch operation is transparent to the driver, who is simply rewarded with a smooth flow of power.

Two distinct cam profiles are used to provide two engine modes: a low-speed mode, consisting of low-lift cam profiles; and a high-speed mode. The low-lift cams and rocker arms - which drive separate intake valves - are positioned on either side of a centrally located high-lift cam. Each of the intake valves is operated by a low-lift cam and rocker arm, while placing a T-lever between them allows the valves to follow the action of the high-lift cam.

At low speeds, The T-lever's wing section floats freely, enabling the low-lift cams to operate the valves. The intake rocker arms contain internal pistons, which are retained by springs in a lowered position while the engine speed is below the MIVEC switchover point, to avoid contacting the high-lift T-shaped levers. At high speeds, hydraulic pressure elevates the hydraulic pistons, causing the T-lever to push against the rocker arm, which in turn makes the high-lift cam operate the valves.

In summary, MIVEC switches to the higher cam profile as engine speed increases, and drops back to the lower cam profile as engine speed decreases. The reduced valve overlap in low-speed mode provides stable idling, while accelerated timing of the intake valve's closing reduces backflow to improve volumetric efficiency, which helps increase engine output as well as reduce lift friction. High-speed mode takes advantage of the pulsating intake effect created by the mode's high lift and retarded timing of intake valve closure. The resulting reduced pumping loss of the larger valve overlap yields higher power output and a reduction in friction. The low- and high-speed modes overlap for a brief period, boosting torque.

From the 4B1 engine family onward, MIVEC has evolved into a continuous variable valve timing

Continuous variable valve timing

Continuous variable valve timing offers a unique ability to have independent control of the intake and exhaust valves in an internal combustion engine. For any engine load criteria, the timing of intake and exhaust can be independently programmed...

 (CVVT) system (dual VVT on intake and exhaust valves). Many older implementations only vary the valve timing (the amount of time per engine revolution that the intake port is open) and not the lift. Timing is continuously independently controlled to provide four optimized engine-operating modes:

• Under most conditions, to ensure highest fuel efficiency, valve overlap is increased to reduce pumping losses. The exhaust valve opening timing is retarded for higher expansion ratio, enhancing fuel economy.
• When maximum power is demanded (high engine speed and load), intake valve closing timing is retarded to synchronize the intake air pulsations for larger air volume.
• Under low-speed, high load, MIVEC ensures optimal torque delivery with the intake valve closing timing advanced to ensure sufficient air volume. At the same time, the exhaust valve opening timing is retarded to provide a higher expansion ratio and improved efficiency.
• At idle, valve overlap is eliminated to stabilize combustion.

Mitsubishi's 4N1

Mitsubishi 4N1 engine

The Mitsubishi 4N1 engine is a family of all-alloy four-cylinder diesel engines developed by Mitsubishi Motors, produced at the company's powertrain facility in Kyoto, Japan for use in Mitsubishi's small to mid-sized global passenger cars....

engine family is the world's first to feature a variable valve timing

Variable valve timing

In internal combustion engines, variable valve timing , also known as Variable valve actuation , is a generalized term used to describe any mechanism or method that can alter the shape or timing of a valve lift event within an internal combustion engine...

 system applied to passenger car diesel engines.

MIVEC-MD

In the early years of developing its MIVEC technology, Mitsubishi also introduced a variant dubbed MIVEC-MD (Modulated Displacement), a form of variable displacement

Variable displacement

Variable displacement is an automobile engine technology that allows the engine displacement to change, usually by deactivating cylinders, for improved fuel economy. The technology is primarily used in large, multi-cylinder engines...

. Under a light throttle load, the intake and exhaust valves in two of the cylinders would remain closed, and the reduced pumping losses gave a claimed 10–20 percent improvement in fuel economy. Modulated Displacement was dropped around 1996.

Current implementations

Engine code	Capacity	Configuration	Year
3A91 Mitsubishi 3A9 engine The Mitsubishi 3A9 engine is a range of all-alloy three cylinder engines from Mitsubishi Motors that were jointly developed with 4A9 engine family...	1124 cc	Straight-3 Straight-3 A straight-three engine, also known as inline-three engine, or a triple, is a reciprocating piston internal combustion engine with three cylinders arranged in a straight line or plane, side by side....	(2003–present)
3B20	659 cc	Straight-3	(2005–present)
4A90	1332 cc	Straight-4 Straight-4 The inline-four engine or straight-four engine is an internal combustion engine with all four cylinders mounted in a straight line, or plane along the crankcase. The single bank of cylinders may be oriented in either a vertical or an inclined plane with all the pistons driving a common crankshaft....	(2003–present)
4A91	1499 cc	Straight-4	(2003–present)
4B10	1798 cc	Straight-4	(2007–present)
4B11	1998 cc	Straight-4	(2007–present)
4B12	2359 cc	Straight-4	(2005–present)
4G15 Mitsubishi Orion engine The Mitsubishi Orion or 4G1 engine is series of straight-4 internal combustion engines introduced by Mitsubishi Motors in the 1970s, along with the Astron, Sirius, and Saturn. It was introduced in the Colt and Colt-derived models in 1978...	1468 cc	Straight-4	(2003–present)
4G69 Mitsubishi Sirius engine The Mitsubishi Sirius or 4G6/4D6 engine is the name of one of Mitsubishi Motors' four series of inline 4 automobile engines, along with Astron, Orion, and Saturn. The 4G6 are gasoline engines, the 4D6 diesels.-4G61:...	2378 cc	Straight-4	(2003–present)
4N13 Mitsubishi 4N1 engine The Mitsubishi 4N1 engine is a family of all-alloy four-cylinder diesel engines developed by Mitsubishi Motors, produced at the company's powertrain facility in Kyoto, Japan for use in Mitsubishi's small to mid-sized global passenger cars....	1798 cc	Straight-4	(2010–present)
6B31 Mitsubishi 6B3 engine The Mitsubishi 6B3 engine is a range of all-alloy V6 engines developed by Mitsubishi Motors. Currently, only one engine has been developed, a 3.0 litre V6 first introduced in the North American version of the second generation Mitsubishi Outlander which debuted in October 2006.All engines developed...	2998 cc	V6	(2006–present)
6G75	3828 cc	V6	(2005–present)

Past implementations

Engine code	Capacity	Configuration	Year
4G19 Mitsubishi Orion engine The Mitsubishi Orion or 4G1 engine is series of straight-4 internal combustion engines introduced by Mitsubishi Motors in the 1970s, along with the Astron, Sirius, and Saturn. It was introduced in the Colt and Colt-derived models in 1978...	1343 cc	Straight-4	(2002–06)
4G92	1597 cc	Straight-4	(1992–99)
4G63T Mitsubishi Sirius engine The Mitsubishi Sirius or 4G6/4D6 engine is the name of one of Mitsubishi Motors' four series of inline 4 automobile engines, along with Astron, Orion, and Saturn. The 4G6 are gasoline engines, the 4D6 diesels.-4G61:...	1997 cc	Straight-4	(2005–07)
6A12	1998 cc	V6	(1993–2000)
6G72	2972 cc	V6	(1995–97)
6G74	3497 cc	V6	(1997–2000)