Acura NSX 1991 Manual page 523

Main Menu
Anti-lock Brake System (ABS) Description
Features/Construction/Operation (cont'd)
Pressure Switch
The pressure switch monitors the pressure accumulation (pressure from the pump) in the accumulator and is turned off
when the pressure becomes lower than a prescribed level. When the pressure switch is turned off, the switching signal is
sent to the ABS control unit. Upon receiving the signal, the ABS control unit activates the pump motor relay to operate
the motor. If the pressure doesn't reach the prescribed value, the ABS indicator light is turned on.
Operation
When the pressure in the accumulator rises, the Bourdon tube in the pressure switch deforms outwards. When the free
end of the Bourdon tube moves more than the prescribed amount, the micro-switch is activated by the force of the spring
attached to the sensing lever. When the pressure in the accumulator decreases due to anti-lock brake system operations,
the Bourdon tube moves in the direction opposite to the one described above, and the micro-switch is eventually turned
off. Upon receiving this signal, the ABS control unit activates the motor relay to operate the motor.
Power Unit
The power unit consists of a motor and a plunger-type pump. This unit transmits the revolution of the motor to the
plunger by way of an eccentric bearing and supplies high-pressure brake fluid to the accumulator by the effect of the
reciprocating movement of the plunger.
When the pressure in the accumulator drops below the prescribed pressure level, the pressure switch gives an OFF-
signal. The ABS control unit turns the motor relay ON to start the operation of the pump, upon the reception of this signal
and a signal from the wheel sensor that the vehicle is running at a speed greater than 6 mph (10 km/h). When the
pressure in the accumulator attains the prescribed pressure, the ABS control unit turns the motor relay OFF approximate-
ly three seconds after the unit receives an ON-signal from the pressure switch. By this, the high-pressure in the acc-
mulator is maintained.
The ABS control unit turns the pump off and lights the system indicator light if the accumulator pressure does not reach
the prescribed level after the pump has run continuously for 120 seconds.
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