
3–413
Motorola Sensor Device Data
For More Information On This Product,
Go to: www.freescale.com
#
!!
! "
!
Prepared by: Marc Osajda
Automotive Sensors Marketing
Sensor Products Division
Motorola Semiconductors S.A.
Toulouse France
BRAKING SYSTEMS
Different types of braking principles can be found in vehicles
depending on whether the brake system is only activated by
muscular energy or power assisted (partially or completely).
Muscular activated brakes are mostly found on motorcycles
and very light vehicles. The driver’s effort on the hand lever
or pedal is directly transmitted via a hydraulic link to the brake
pads.
Power assisted brakes are found on most passenger cars
and some light vehicle trucks. In this case, the driver’s effort
is amplified by a brake booster
to increase the force applied
to the brake pedal.
BRAKE BOOSTER OPERATION PRINCIPLE
The vacuum brake booster is a system using the differential
between atmospheric pressure and a lower pressure source
(vacuum) to assist the braking operation. The brake booster
is located between the brake pedal and the master cylinder.
Figure 1 shows a simplified schematic of a vacuum brake
booster.
When no brake pressure is applied on the push rod (brake
pedal side), the air intake valve is closed and the vacuum
valve open. Thus, both the vacuum and working chambers
are at the same pressure, typically around –70 kPa (70 kPa
below atmospheric pressure). Vacuum is generated by either
the engine intake manifold or by an auxiliary vacuum pump.
Figure 1. Brake Booster Simplified Schematic
CONNECTION TO VACUUMPUMP
OR ENGINE INTAKE MANIFOLD
PUSH ROD FROM
THE BRAKE PEDAL
AIR INTAKE VALVE
WORKING CHAMBER
VACUUMCHAMBER
VACUUMVALVE
PISTION
RUBBER MEMBRANE
PUSH ROD TO
MASTER CYLINDER
SEMICONDUCTOR APPLICATION NOTE
REV 1
F
Freescale Semiconductor, Inc.
n
.