Self Study Program 257 – Electric vacuum pump for brake servo unit

Self Study Program 257 – Electric vacuum pump for brake servo unit Design and Function PDF free online

Cars fitted with a petrol engine in combination with an automatic gearbox which comply with the EU 4 Standard have an electric vacuum pump. This is used for assisting the brake servo unit. In this engine-gearbox combination, the throttle valve is opened particularly wide when the engine is started from cold, as well as when it is idling with a drive position engaged and the brakes applied. This is intended to reduce the pressure drop in intake manifold.

The reasons for this greater opening of the throttle valve is the heating-up phase of the catalytic converter after a cold engine start, as required by the EU 4 emission standard, and compensating for the greater torque friction (resistance in torque converter) which exists under the conditions mentioned above.

Depending on the particular car model, two different versions of the electric vacuum pump are fitted:

1. open-loop controlled vacuum pump
2. closed-loop controlled vacuum pump

Pressure drop when throttle valve opened

If the throttle valve is slightly opened, a high vacuum exists in the intake manifold and thus also a high vacuum at the vacuum connection for the brake servo unit.

If the throttle valve is opened wide and the engine is running at a low speed, only a very
slight vacuum exists at the connection for the brake servo unit of the intake manifold.

CONTENTS

  • Introduction
    • Function of the brake servo unit
    • Design and function of the electric vacuum pump
    • Design and function of the vane pump
  • Open-loop controlled vacuum pump
    • Open-loop control version
    • Installation position
    • Operating conditions
    • Function diagram
  • Closed-loop controlled vacuum pump
    • Closed-loop control version
    • Function of pressure sensor
    • Installation position
    • Operating conditions
    • Function diagram
  • Hysteresis
  • Self-diagnosis
  • Test your knowledge

The Self-Study Programme describes the design and function of new developments! The contents are not updated. Please always refer to the relevant service literature for up-to-date inspection, adjustment and repair instructions.

Language: English
Format: PDF
Pages: 20

Self Study Program 257 – Electric vacuum pump for brake servo unit Design and Function PDF free online

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