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BOU Tandem Master Cylinder
The outlets ports are connected to A7/3
(SBC hydraulic unit), which contains
separation valves y1 and y2.
When the travel sensor moves ~2mm, a
brake request signal is sent to A7/3.
A7/3 y1 and y2 are activated and
separate the master cylinder from the
rest of the brake system during normal
When y1 and y2 are energized, the fluid
cannot move from the master cylinder,
therefore the floating piston
compresses the fluid in the simulator
chamber causing a counter pressure
that the driver interprets to be normal
brake pressure feel.
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In the event of a SBC system failure
the front brakes are braked
hydraulically by the brake pedal
without power assist.
In this case both separation valves
are de-energized, allowing the brake
pressure to go to the calipers of the
This system meets the legally
mandatory minimum deceleration of
0.3 g with a foot pressure of 500 N.
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Traction System Hydraulic
Consists of:• SBC control module (A7/2n1)• High pressure charge pump
• Pressure reservoir
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Emergency Operation Circuit
A7/3b1, b3, and b4 are pressure sensors
that provide information to the SBC control
The left front dividing piston (7) and right
front dividing piston (8) are used to
isolate the emergency circuit from the
electronically controlled circuit.
The pistons are double sealed with the
dotted line representing that the brake
fluid would return to the reservoir in the
event of a seal failure.
During the emergency operation, the
pistons have reached their maximum
travel so that the caliper pistons will
apply the pressure to the rotors.
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Brake Pressure Supply
During normal operation pressure sensor b2
monitors the available stored pressure and turns
the charge pump on and off as needed to
maintain the reservoir pressure at ~160 bar.
The intake control valves (y6, y8, y10, y12)
prevent the pressure from reaching the calipers.