Friction disk shock absorber
Encyclopedia
Friction disk shock absorbers or André Hartford dampers were an early form of shock absorber
or damper
used for car suspension
. They were commonly used in the 1930s but were considered obsolete post-war
.
within a stack of disks, clamped tightly together with a spring and clamp bolt.
disk between the two faces of the steel arms. As for the development of the clutch
and brake shoe
s, the development of these friction materials was in its infancy. Treated leather had been used for clutches and although it offered good friction behaviour, it was prone to stiction
when first moving off and also failed when overheated. Asbestos
-based friction materials were sometimes used for racing, in an attempt to keep dampers working correctly even when overheating.
The damping force of a friction shock absorber is adjusted with the central pivot and clamping bolt. A star-shaped spring applies a force to the stack of disks. The damping force is roughly proportional to this force and the clamping nut is provided with a pointer arm to indicate the approximate setting.
André Hartford dampers were made in four sizes, according to vehicle weight and intended use. These were a combination of two disk diameters: 3¼" & 4½" and as either single or multiplate designs. Single dampers had two friction surfaces: a single arm on one side was nested between two arms connected to the other. Multiplate dampers had two and three arms on each side.
Dampers were mounted to the chassis and axle through Silentbloc bushes at each end. Silentbloc bushes were another development of the early 1930s, a vulcanised rubber bush bonded into a steel tube. These provided the stiff location that accurate suspension required, but reduced vibration and road noise, compared to earlier cars. Many cars used a different design for front and rear, where the rear arms were rigidly bolted to the chassis, rather than with a swivelling bush.
s. Early Bugattis had used Bugatti's own pattern of multi-plate damper, similar to the André Hartford.
The de Ram damper used a metallic multi-plate disk stack, with alternate disks splined to either an inside or outside cylindrical carrier, much as for multi-plate clutches of the time. Owing to the weight of the casing, de Ram dampers were always mounted to the chassis, with a single arm to the axle.
cars from 1928. The earlier Mercedes
had used Hartford pattern.
A form using a cylindrical roller bearing with a resilient race was patented in 1930.
between stationary plates. For larger bumps the damping may even be reduced. This is particularly a problem for fast driving, when repeated high forces may cause the friction plates to heat up and lose their efficiency.
Motor racing in the 1930s was often an amateur affair, where sports car
s would be driven to racetracks such as Brooklands
, adjusted in the paddock to their racing trim and then raced. It was normal to re-adjust the damping between "road" and "race" settings.
The need for adjustable damping was so great that it was even useful to provide a means of adjusting this whilst driving. This was a feature only used on luxury cars, often larger cars that might need to set their suspension for varying numbers of passengers. Stiffness could be increased between "town" and a stiffer setting for the faster open road. These dampers were best known under the Telecontrol brand name. A hydraulic control, with an inflatable rubber bag in the disk pack, could be used to increase the clamping force and thus their damping stiffness.
One of the major reasons for the decline of frictional dampers post-war, in favour of hydraulic lever arm
s, was the hydraulic damper's better change of rate with suspension amplitude. Hydraulic dampers had a resistance that inherently increased with velocity of suspension movement, a far more useful behaviour. This useful inherent behaviour meant that manual adjustment was far less necessary, certainly not whilst driving.
Shock absorber
A shock absorber is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy. It is a type of dashpot.-Nomenclature:...
or damper
Damper
A damper is a device that deadens, restrains, or depresses.Damper may refer to:* Dashpot, a type of hydraulic or mechanical damper,* Shock absorber , a mechanical device designed to dissipate kinetic energy...
used for car suspension
Suspension (vehicle)
Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...
. They were commonly used in the 1930s but were considered obsolete post-war
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
.
Construction
The dampers rely, as their name suggests, on the frictionFriction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
within a stack of disks, clamped tightly together with a spring and clamp bolt.
André Hartford pattern
The friction disk material was usually a woodenHardwood
Hardwood is wood from angiosperm trees . It may also be used for those trees themselves: these are usually broad-leaved; in temperate and boreal latitudes they are mostly deciduous, but in tropics and subtropics mostly evergreen.Hardwood contrasts with softwood...
disk between the two faces of the steel arms. As for the development of the clutch
Clutch
A clutch is a mechanical device which provides for the transmission of power from one component to another...
and brake shoe
Brake shoe
A brake shoe is the part of a braking system which carries the brake lining in the drum brakes used on automobiles, or the brake block in train brakes and bicycle brakes.-Automobile drum brake:...
s, the development of these friction materials was in its infancy. Treated leather had been used for clutches and although it offered good friction behaviour, it was prone to stiction
Stiction
Stiction is the static friction that needs to be overcome to enable relative motion of stationary objects in contact. The term is a portmanteau of the term "static friction", perhaps also influenced by the verb "stick"....
when first moving off and also failed when overheated. Asbestos
Asbestos
Asbestos is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties. They all have in common their eponymous, asbestiform habit: long, thin fibrous crystals...
-based friction materials were sometimes used for racing, in an attempt to keep dampers working correctly even when overheating.
The damping force of a friction shock absorber is adjusted with the central pivot and clamping bolt. A star-shaped spring applies a force to the stack of disks. The damping force is roughly proportional to this force and the clamping nut is provided with a pointer arm to indicate the approximate setting.
André Hartford dampers were made in four sizes, according to vehicle weight and intended use. These were a combination of two disk diameters: 3¼" & 4½" and as either single or multiplate designs. Single dampers had two friction surfaces: a single arm on one side was nested between two arms connected to the other. Multiplate dampers had two and three arms on each side.
Dampers were mounted to the chassis and axle through Silentbloc bushes at each end. Silentbloc bushes were another development of the early 1930s, a vulcanised rubber bush bonded into a steel tube. These provided the stiff location that accurate suspension required, but reduced vibration and road noise, compared to earlier cars. Many cars used a different design for front and rear, where the rear arms were rigidly bolted to the chassis, rather than with a swivelling bush.
de Ram pattern
The invention of Georges de Ram, these were a more sophisticated and complex pattern, intended to provide a more consistent damping at high speeds. They were only used on high-end vehicles, notably BugattiBugatti
Automobiles E. Bugatti was a French car manufacturer founded in 1909 in Molsheim, Alsace, as a manufacturer of high-performance automobiles by Italian-born Ettore Bugatti....
s. Early Bugattis had used Bugatti's own pattern of multi-plate damper, similar to the André Hartford.
The de Ram damper used a metallic multi-plate disk stack, with alternate disks splined to either an inside or outside cylindrical carrier, much as for multi-plate clutches of the time. Owing to the weight of the casing, de Ram dampers were always mounted to the chassis, with a single arm to the axle.
Cylindrical friction elements
A similar pattern, with a cylindrical friction element, was used on Mercedes-BenzMercedes-Benz
Mercedes-Benz is a German manufacturer of automobiles, buses, coaches, and trucks. Mercedes-Benz is a division of its parent company, Daimler AG...
cars from 1928. The earlier Mercedes
Mercedes (car)
Mercedes was a brand of the Daimler-Motoren-Gesellschaft . DMG which began to develop in 1900, after the death of its co-founder, Gottlieb Daimler...
had used Hartford pattern.
A form using a cylindrical roller bearing with a resilient race was patented in 1930.
Adjustable damping
The damping rate for frictional dampers has less than ideal behaviour for car suspension. An ideal suspension would offer more damping to greater suspension forces, with less damping at low speeds for a smoother ride. Frictional dampers though had a mostly constant rate. This was even greater when stationary, owing to stictionStiction
Stiction is the static friction that needs to be overcome to enable relative motion of stationary objects in contact. The term is a portmanteau of the term "static friction", perhaps also influenced by the verb "stick"....
between stationary plates. For larger bumps the damping may even be reduced. This is particularly a problem for fast driving, when repeated high forces may cause the friction plates to heat up and lose their efficiency.
Motor racing in the 1930s was often an amateur affair, where sports car
Sports car
A sports car is a small, usually two seat, two door automobile designed for high speed driving and maneuverability....
s would be driven to racetracks such as Brooklands
Brooklands
Brooklands was a motor racing circuit and aerodrome built near Weybridge in Surrey, England. It opened in 1907, and was the world's first purpose-built motorsport venue, as well as one of Britain's first airfields...
, adjusted in the paddock to their racing trim and then raced. It was normal to re-adjust the damping between "road" and "race" settings.
The need for adjustable damping was so great that it was even useful to provide a means of adjusting this whilst driving. This was a feature only used on luxury cars, often larger cars that might need to set their suspension for varying numbers of passengers. Stiffness could be increased between "town" and a stiffer setting for the faster open road. These dampers were best known under the Telecontrol brand name. A hydraulic control, with an inflatable rubber bag in the disk pack, could be used to increase the clamping force and thus their damping stiffness.
One of the major reasons for the decline of frictional dampers post-war, in favour of hydraulic lever arm
Lever arm shock absorber
Lever arm shock absorbers were the first form of hydraulic shock absorber or damper used for car suspension. They appeared in the 1930s and were most commonly used in the 1950s and 1960s, but were replaced by telescopic shock absorbers in the 1970s...
s, was the hydraulic damper's better change of rate with suspension amplitude. Hydraulic dampers had a resistance that inherently increased with velocity of suspension movement, a far more useful behaviour. This useful inherent behaviour meant that manual adjustment was far less necessary, certainly not whilst driving.
Manufacturers
André Hartford held patents on this design but the manufacturing technology required was simple, and so many other makers also produced them.- André Hartford, probably the best-known brand pre-war.
-
- F. Repusseau & Cie made the Hartford pattern under license in Paris.Like many other motor racing drivers of this period, François Repusseau financed his hobby of racing by a business interest as a parts manufacturer.
-
- Bentley & Draper Ltd
- Telecontrol, noted for their adjustable dampers
- de Ram, a more complicated damper used on later BugattiBugattiAutomobiles E. Bugatti was a French car manufacturer founded in 1909 in Molsheim, Alsace, as a manufacturer of high-performance automobiles by Italian-born Ettore Bugatti....
s. An attempt to solve the problems that would later be addressed by hydraulic dampers.
Modern components and spare parts are still manufactured for restoration projects.
- Bentley & Draper Ltd
-
- F. Repusseau & Cie made the Hartford pattern under license in Paris.Like many other motor racing drivers of this period, François Repusseau financed his hobby of racing by a business interest as a parts manufacturer.
-