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(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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96009a0090009b009000960095>
In this position, the separation valve and the inlet valve are open (normal open), the electrically
operated shuttle valve and the outlet valve are closed. When the brake is applied under these
conditions, the brake fluid will be sent to each wheel via the separation valve and inlet valve.
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▶When applied ABS (decreased pressure)
The pressure decreases just before the wheel speed drops and the wheels. The inlet valve
closes and the outlet valve opens as in the ABS HECU and the oil is gathered at the low
pressure chamber while no additional oil is being supplied.
Then the pump operates to allow fast oil drainage.
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▶When applied ABS (maintained pressure)
The Inlet valve and outlet valve will be closed to maintain the pressure in the hydraulic circuit
applied at the wheels. By closing the valves, the hydraulic pressure at the wheels will not be
lost or supplied any more. During ESP operation, the separation valve closes and only the
shuttle valve at the pump opens.
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▶When applied ABS (increased pressure)
The shuttle valve and inlet valve will be open and the separation valve and outlet valve will be
closed. Then, the pump is operated.
When ESP operates while the ABS is operating, the pressure will be increased continuously
until just before the corresponding wheel gets locked.
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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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4. ELECTRICAL CIRCUIT DIAGRAM
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4700730088009400970047004f00680069007a0056006c007a>P)
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530047006c007a007700470076006d006d0047007a009e0090>tch