![]() ![]() These fixed switching points are selected according to parameters of the vehicle braking system and the intended duty of the vehicle. In this arrangement on-switching occurs at −101 kPa*0.65=−65.6 kPa, and off-switching occurs at −101 kPa*0.80=−80.8 kPa. On and off switching values are selected, for example at 65% and 80% of this maximum available vacuum (MAV), as indicated by the vacuum sensor or switch. One switching strategy relies on percentages of absolute vacuum, which is typically −101 kPa (assuming atmospheric pressure at sea level to be 101 kPa). ![]() The control system includes a degree of hysteresis to avoid continual pump activation/deactivation, and has fixed on and off values. A switch provides simple on/off control, whereas a sensor provides an electric signal which is an analogue of the depression available in the booster both arrangements permit the pump to be switched on and off according to booster demand. Furthermore electric vacuum pumps can be switched on and off according to demand, and this can avoid the unnecessary energy consumption of an idling mechanically driven pump switching on demand also gives a potentially longer service life for the pump.Ī conventional electric vacuum pump for a vehicle brake booster incorporates a vacuum switch or sensor in the vacuum line to the brake booster, or in the brake booster chamber. More recently electric vacuum pumps have become preferred because they are independent of the vehicle engine and thus allow more flexibility in engine design and engine compartment utilization (packaging). The source of vacuum is typically a vacuum pump driven mechanically by the vehicle engine and/or engine inlet manifold depression. Suitable control means ensure assistance is proportional to the applied brake pedal load. By opening one side of the diaphragm to atmosphere, a net force can be applied by the diaphragm to a piston of a hydraulic brake circuit. In such a booster, vacuum exhausts a brake booster chamber which is divided by a diaphragm. Many different kinds of servo-assistance have been proposed, but vacuum assistance via a vacuum brake booster is most common. Motor vehicles are typically provided with servo-assistance of the braking system, so as to proportionately reduce the load applied to the brake pedal for a given braking effect. Aspects of the invention relate to a method and to a vehicle. ![]() The present invention relates to vacuum pumps for vehicle brake boosters, and particularly to electric vacuum pumps. ![]()
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