Linde 350 Series Service Training page 40

Section 2
Service Training
Page 14
FUNCTIONAL DESCRIPTION
When the engine is running and the brake pedal is depressed, the solenoid of the release valve (2) is de-
energised. Boost pressure is applied from port F to nozzle (6); the passage behind the nozzle, however, is
connected to tank via the open release valve (2) and is thus without pressure.
The spool (7) is connected to port F on both sides via the pilot valve (10), the way valve (9) and the servo
circuit nozzles (8), thus holding the variable pump (1) in the hydraulic neutral position.
After the electronic controller has released the switching signal to the release valve (2), the valve closes the
connection to tank so that boost pressure also rises behind the nozzle (6). The two way valves (5) are set
to the open position so that boost pressure from passage F is applied to the unactuated proportional valves
(4). Simultaneously, the way valve (9) is shifted from the throttled to the unthrottled position.
Depressing an accelerator pedal controls the respective solenoid (3) with a pedal-dependent signal. A
pressure corresponding to the signal value of the solenoid is applied through the downstream proportional
valve (4) to the spool (11). The spool (11) moves and pushes the oil flowing off at the opposite end of the
spool through the respective proportional valve (4) into the tank. The operation of the spool (11) adjusts the
pilot valve (10) through which the spool (7) is supplied with pressure and the pump starts delivering.
Releasing the accelerator pedal towards zero stroke reduces the signal at the solenoid. As a result, the
proportional valve reduces the pressure going to the spool, the pump reduces the swashplate angle and the
truck is braked.
When the electronic controller detects an error in the speed control, the truck must be brought to a controlled
stop, independent of the position of the accelerator pedal.
To do this, the release valve (2) is de-energised so that the pressure behind the nozzle (6) will drop to 0 bar.
The way valves (5) move to the closed position, thus removing the boost pressure going to the proportional
valves (4). This action also shifts the proportional valve (4), which is controlled by the solenoid (3),
mechanically to the home position and the pressure applied to the spool (11) is removed. The piston is pushed
mechanically to the zero position, which also shifts the pilot valve (10) to the zero position. The opening of
the release valve (2) and the concomitant pressure drop to 0 bar also switches the way valve (9) from the
unthrottled to the throttled position.
The reset time for the spool (7), and therefore also for the braking deceleration, is metered with the servo
circuit nozzles (8) and the throttling with the way valve (10). This arrangement prevents sudden braking.
EMERGENCY STOP WITH THE BRAKE PEDAL
If, due to a fault, the truck can no longer be braked with the accelerator pedals, it is possible to make an
emergency stop with the brake pedal.
Depressing the brake pedal actuates the microswitches in the pedal console. This cuts off the power to the
release valve (2) and the truck is brought to a controlled stop as with a fault in the controller. The brake release
pressure at the disc brakes is also reduced and the truck is thus also braked mechanically.