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ESP SYSTEM
(1) System Overview
When equipped with ABS, the braking force at each wheel will be controlled with 3-channel 4-
sensor method. And when equipped with ESP, 4 wheels will be controlled independently with 4-
channel method. (When controlling ABS system only, it will be operated with 3-channel
method.) When compared to the vehicle equipped with ABS/EBD only, the internal hydraulic
circuit has a normally-open separation valve and a shuttle valve in primary circuit and in
secondary circuit. When the vehicle brakes are not applied during engine running or when
applying the non-ABS operating brakes, the normally-open separation valve and the inlet valve
are open, whereas the normally-closed shuttle valve and the outlet valve are closed. When the
ESP system is operating, the normally-open separation valve will be closed by the solenoid
valve operation and the hydraulic circuit will be established by the shuttle valve. Then, the inlet
and outlet valves will be
closed or open depending on the braking pressure increase, decrease or unchanged
conditions.
<0d96007b008f008c0047009e00880099009500900095008e004700930088009400970047008a00960094008c009a004700960095004700880095008b0047009e00880099009500900095008e00470089008c008c00970047009a0096009c0095008b009a00
47009e008f008c00950047009b008f008c0047006c007a0077> is operating
▶Driving feeling when the ESP is operating
<0d96007500960090009a008c004700880095008b0047009d0090008900990088009b0090009600950047009b008f0088009b0047008b00990090009d008c00990047009a008c0095009a008c009a0047009e008f008c00950047009b008f008c0047006c00
7a007700470090009a004700960097008c00990088009b0090>ng When the ESP operates during vehicle movement, the ESP warning lamp on the instrument
panel flickers and beep comes on every 0.1 seconds. The ESP operation shows that the
vehicle stability is extremely unstable and it is used to warn the driver. The ESP system is just a
supplementary system for the vehicle motion and it cannot control the vehicle when it exceeds
the physical limits. Do not solely rely on the system but be advised to drive the vehicle safely.
When the ESP system activates, the driving feeling can be different depending on vehicle
driving conditions. For example, you will feel differently when the ESP system is activated
during when ABS is operating with the brakes applied and when brakes are not applied on a
curve. Thus, the ESP system would make the driver feel more abruptly when the brakes are
applied during the ESP system activation.
The ESP system may transfer noise and vibration to the driver due to the pressure changes
caused by the motor and valve operations in a very short period of time. Extreme cornering will
trigger the ESP operation and this will make the driver feel noise and vibration due to sudden
brake application. Also, the ESP system controls the engine output. So, the driver may notice
the engine output decrease even when the accelerator pedal is being applied.
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ESP SYSTEM
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▶Hydraulic Diagram of HBA
The above figure shows one front and one rear wheel and the same hydraulic circuit forms as
in the ESP operation.
When HECU recognizes that it is an emergency and it is required for hard braking, depending
on the pressure value of the brake pressure sensor and pressure changes caused by the
pressure sensor timing, it operates the pump immediately to apply the brake pressure at the
wheels.
Then, the pressure in the pump increases until just before the corresponding wheel gets locked.
The motor still keeps rotating and the outlet valve and the separation valve are will stay closed.
When the wheel starts to lock, the HBA function cancels and switches to ABS operation.
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ABS SYSTEM
1. COMPONENTS AND LOCATION
Newly introduced ABS has a different shape of integrated hydraulic modulator and HECU
(Hydraulic and Electronic Control Unit) compared to existing ABS. And, the wheel speed senso
r
uses different method to detect wheel speed. The basic function of the ABS that maintains the
vehicle stability by controlling the steerability of the vehicle when braking has not been
changed.
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ABS SYSTEM
Pressure Decreases in the Circuit when ABS is Operating ▶
Pressure Increases in the Circuit when ABS is Operating ▶
Even when the hydraulic pressure on each circuit is stable, the wheel can be locked as the
wheel speed decreases. This is when the ABS ECU detects the wheel speed and the vehicle
speed and gives the optimized braking without locking the wheels. In order to prevent from
hydraulic pressure increases, the inlet valve is closed and the outlet valve is opened. Also, the
oil is sent to the low pressure changer and the wheel speed increases again. The ABS ECU
operates the pump to circulate the oil in the low pressure chamber to the master cylinder. This
may make the driver to feel the brake pedal vibration and some noises.
As the wheel speed increases, the inlet valve opens and the wheel’s pressure increases
due to the master cylinder pressure. The oil in the low pressure chamber circulates to the wheel
by the pump and the wheel speed decreases as the hydraulic pressure at wheel increases. This
operation continues repetitively until there are no signs that the ECU is locking the wheels.
When the ABS hydraulic pressure control takes place, there may be some vibration and noises
at the brake pedal.