Combined Yaw Rate Sensor And Lateral Acceleration Sensor - Ford Transit 2002 Owner's Manual

The HCU comprises the ABS/ESP module, the valve block (with low-pressure accumulators)
and the ABS pump.
The valve block combines all of the brake pressure control valves in one unit. Depending on
the system, either simple changeover valves or proportioning valves (e.g. on EBD
(electronic brake force distribution) systems) are installed. The low-pressure accumulators
store the brake fluid that is returned from the wheel brakes during the pressure reduction
phase until it is drawn back into the system by the ABS pump.
The ABS pump is designed as a dual piston pump. This means that two separate pump
elements assure an increase in brake pressure during control interventions. A direct current
motor drives the pump pistons via an eccentric shaft.
The ABS/ESP module monitors the input signals of all sensors and actuates the electro-
magnetic brake pressure valves and the ABS pump as required. For reasons of safety, the
module is of the redundant type, whereby processing of the signals is carried out via two
separate processors that also monitor each other.

Combined yaw rate sensor and lateral acceleration sensor

The heart of the combined yaw rate sensor and lateral acceleration sensor is a small,
double-sided tuning fork made of a piezo crystal (A). The exciter side of this tuning fork is
set to a resonance of 11 kHz with the aid of an alternating current. The measuring side of
the tuning fork features a resonance frequency of 11.33 kHz and therefore does not vibrate
(B). Since, under influence of an external accelerating force, a vibrating mass reacts slower
than a comparable mass that is not vibrating, the tuning fork twists within itself with
rotational movement being imparted on the sensor (C). This rotation results in a change in
the charge distribution in the Piezo element, which is subsequently picked up and converted
into an electronic signal by electronics integrated into the sensor. This electronic signal is
then sent to the ESP module. The ESP module evaluates these data and takes into account
the other input data (vehicle speed, wheel speed) before deciding whether the ESP function
is required.
Item Description
1 Tuning fork exciter
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