Additional force is provided by reduced pressure from the intake manifold. The brake booster is connected by a hose to the exhaust manifold. When braking, the difference in pressure between the outside air pressure and the reduced pressure in the exhaust manifold shifts the large elastic diaphragm and puts additional pressure on the piston in the brake master cylinder. If the engine is not running, then the amplifier cannot develop any (additional) braking force. If the engine suddenly stalls, then there is still a small reserve for a certain amount of braking; but then you have to rely only on the strength of the legs.
The five-cylinder engine has an additional vacuum pump (3), which increases the vacuum in the hose from the intake pipe (1). So, it became possible that there is always enough force in the hose from the pump to the brake booster to support the brakes. To prevent the low pressure from disappearing, a check valve is installed in front of the branch to the pump (2).
Depending on the loading state of the car, the brake force regulator (1) applies more or less pressure to the rear axle wheel cylinders. How loaded the rear axle is - this information enters the regulator through the connection to the rear axle, which consists of a small spring (2). The illustration on the left shows the brake force regulator for front-wheel drive vehicles, the image on the right shows the regulator for a four-wheel drive vehicle.
Vacuum pump
To improve brake force maintenance, the engine versions are equipped with an additional vacuum pump driven by the camshaft. Thanks to him, the reduced pressure in the hoses to the brake booster increases.
The following engines have such a pump:
All cars with 5-cylinder engines. The pump is installed on the left side of the cylinder head.
All cars with 6-cylinder engines. Here it is located behind the right cylinder head (then the vacuum pump is installed only in vehicles with automatic transmission).
From 3/92 on vehicles with 6-cylinder engines and automatic transmission, a jet pump is installed. The mechanical pump has ceased to exist.
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