Bragg-Kliesrath brake

A vacuum servo is a component used on motor vehicles in their braking system, to provide assistance to the driver by decreasing the braking effort. In the US it is commonly called a brake booster.

Albert Dewandre (Liege, Belgium), an engineer and business owner, was the inventor of servo-brake or brake booster system “Dewandre” in 1927. It is a brake boosting system that uses the depression caused by the suction in the intake manifold of an internal combustion engine to reduce the pressure on the brake pedal. The advantage of the Dewandre system is twofold: a softer push on the brake pedal, but also a notably shorter braking distance. His invention was manufactured and sold through the Robert Bosch company.

This article mainly refers to the mechanical device in the context of a brake power booster or vehicular braking-system assist. The term "vacuum servo" is actually a generic term for any device which uses a vacuum to amplify/boost the mechanical effort of a device by use of a vacuum in an assisting chamber, either attached to the input or output, or placed between the input and output. In a Vacuum brake servo, the unit is placed between the brake pedal and the hydraulic master cylinder, using stored vacuum to amplify the drivers pedal efforts, giving a greater braking force.

The term "vacuum Servo" can sometimes be mis-translated in vehicle engineering terms, to "vacuum operated valve" whereby a device is controlled either switched or proportionally by the use of a Vacuum. This device can be readily seen in modern off-road vehicles to engage 4WD and differential locks, and in older vehicles fitted with vacuum controlled servo motor cruise control.

A brake booster is used on virtually all vehicles which use hydraulic brakes for their primary braking circuit. Vacuum servos are not used on vehicles which use cables, rods (or other mechanical linkages), or pressurized air systems for their primary brake circuits.

A Vacuum Servo also known as a power booster or power brake unit uses a vacuum to multiply the drivers pedal effort and apply that effort to the master cylinder.

The vacuum can be generated in two distinct methods, dependent on the type of internal combustion engine, or other motive force (as in electric vehicles). In naturally-aspirated petrol engines, the manifold vacuum is used, whereas in turbo charged, diesel engines, and electric/hybrid vehicles a separate vacuum pump is used (or in certain high altitude places, naturally-aspirated vehicles are not capable of producing enough vacuum for the booster. The vacuum pump can be driven mechanically (from the engine) or by means of an electric motor. The vacuum is transferred to the servo along non-collapsible vacuum lines, and is stored in the servo by using a non-return valve.

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Wikipedia