Parking brake, function description

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L120F Volvo Arvika 27544 99999

The parking brake is a spring-loaded disc brake that is applied when there is no hydraulic pressure to overcome the spring force. The
hydraulic pressure is needed to release the parking brake.

Figure 1
Parking brake

1. Adjustment screw, outer brake pad

2. Spring disc
3. Piston
4. Piston and magnetic assembly
5. Adjustment screw, inner brake pad

The parking brake construction includes two adjustment screws that facilitates the setting of the right clearance between the brake
disc and the inner brake pad.
For more information, see: Parking brake, adjusting
When there is no oil entering the connection port the disc springs push the piston into the lining and carrier assembly which
squeezes the brake disc. (parking brake applied)
Figure 2
Hydraulic connection to the parking brake

1. Brake disc
2. Connection port
3. Hydraulic hose
4. Brake pads

Figure 3
SW5501
The parking brake is applied and released with switch SW5501. When the upper end of SW5501 is pressed in, the parking brake is
applied. To release the parking brake, the catch on SW5501 must be released.
Regardless of the position of switch SW5501, the parking brake is applied when the engine is turned off.
See also Wiring diagram 501 and Hydraulic diagram, complete.

Figure 4
 1. Central valve
2. Accumulator block, service brakes
3. Parking brake

Application of parking brake

When the upper end of SW5501 is pressed in or if the engine is turned off, MA5501 becomes de-energised. The oil from the
hydraulic pumps (via the central valve and brake accumulator block) cannot pass through the parking-brake valve to the parking
brake, but is drained to tank, which means that the parking brake becomes applied because of the spring force. SE5503 senses no
pressure and sends signal to the V-ECU about this, which will cause the control lamp for the parking brake to light up (if the ignition is
on).
Releasing parking brake
When the catch on SW5501 is released, MA5501 receives current. The oil from the hydraulic pumps (via the central valve and brake
accumulator block) can pass through the parking-brake valve and the parking brake is pressurised. The hydraulic oil pressure then
overcomes the spring force and the parking brake is released. Also SE5503 registers pressure and sends signal about this to the V-
ECU whereby the control lamp for the parking brake is extinguished.
If the operator selects directional gear forward or reverse, even though the parking brake is applied, a warning will be shown on the
operator display unit. If the warning is ignored, the parking brake will be released automatically, when the engine speed exceeds
1600 rpm.
Software

Electric parking brake

Input signals Conditions for output functions Output functions
Machine stationary
¡ Ignition switch, ¡ Parking brake applied “ON”.
SW3301 ¡ Engine Off MA5501 de-energised and
¡ Speed, SE4307 ¡ Speed < 0.5 km/h (0.3 mph) SE5503 without pressure.
¡ Parking brake ¡ Ignition switch in position 0
applied
¡ Engine speed, Machine in starting position
SE2701 ¡ Parking brake applied “ON”.
¡ Engine On/Off ¡ Engine Off MA5501 de-energised and
¡ Directional gear ¡ Speed < 0.5 km/h (0.3 mph) SE5503 without pressure.
¡ Switch, parking ¡ Directional gear in position Neutral ¡ Warning lamp, parking brake
brake, SW5501 ¡ Ignition switch in position 1

Machine in operation with directional gear in position Neutral

¡ Parking brake applied “ON”.
¡ Engine On MA5501 de-energised and
¡ Switch, parking brake in position Applied SE5503 without pressure.
¡ Directional gear in position Neutral ¡ Warning lamp, parking brake

Machine in operation with directional gear in position Forward

or Reverse ¡ Parking brake applied “ON”.
MA5501 de-energised and
¡ Engine On SE5503 without pressure.
¡ Switch, parking brake in position Applied ¡ Warning lamp, parking brake
¡ Directional gear in position Forward or Reverse ¡ Red central warning
¡ Warning
Applied parking brake

Release of parking brake, when the machine is in operation

and the parking brake is applied with the parking brake switch ¡ Parking brake applied
“OFF”. MA5501 energised
¡ Engine On and SE5503 pressurised.
¡ Switch, parking brake in position Released
¡ Directional gear in position Neutral

Safety function “Releasing parking brake” when the parking

brake is applied. ¡ Parking brake applied
“OFF”. MA5501 energised
¡ Engine On and SE5503 pressurised.
¡ Switch, parking brake in position Applied
¡ Directional gear in position Forward or Reverse
 ¡ Engine speed above 1600 rpm

Application of parking brake

¡ Logic diagnostics ¡ Check
¡ When MA5501 becomes de-energised, SE5503 should Parking brake failure
be without pressure within 3 seconds Check at next stop

Release of parking brake

¡ When MA5501 becomes energised, SE5503 should

become pressurised within 10 seconds

The following applies in case of incorrect input signals:

Input signal Assumed value in case of a fault

Engine “On”
Ignition switch, SW3301 “ON”
Engine speed, SE2701 <1600 rpm
Directional gear "Neutral"
Speed, SE4307 0 km/h (0 mph)

Parking brake alarm

Input signals Conditions for output functions Output functions
General conditions for the function
¡ VCADS Pro ¡ Red central warning
parameter HWU “ ¡ VCADS Pro parameter HWU “ON” ¡ Warning
¡ Parking brake Park brake NOT applied
applied
¡ Engine On/Off ¡ Engine On
¡ Load operator seat, ¡ Parking brake applied “OFF”
SE8502 ¡ Loading on operator seat ON for more than 3 seconds

The following applies in case of incorrect input signals:

Input signal Assumed value in case of a fault

Engine “On”
Parking brake applied “ON”
Load operator seat Function turned off
VCADS Pro parameter HWU “OFF”

Parking brake applied

Input signals Conditions for output functions Output functions

¡ Parking brake ¡ SE5503 without pressure ¡ Parking brake applied “ON”

pressure, SE5503

¡ SE5503 pressurised ¡ Parking brake applied “OFF”