Spring Loaded Brake Test and Removal

Spring Loaded Brake Test and Removal

Brake function during operation

If the truck stops and the accelerator pedal is in the neutral position, the springloaded brake automatically applies after 5-120 seconds (adjustable, set to 8 sec. as standard). “Release brake solenoid” 7Y1 is de-energised by the hydraulic controller and the pre-tension pressure is directed to the reservoir. This discharges the spring-loaded brake and the brake is activated. If the accelerator is pressed again, output 2 of the hydraulic controller 2U9/pin2 is controlled, “Release brake solenoid” 7Y1 and simultaneously toggle valve 8Y4 is set to block. The steer pump is set to maximum speed. This produces the required increase in pressure in the steering circuit to pre-tension the brake cylinder against the spring assembly. After the brakes are released, the toggle valve 8Y4, controlled by the magnetic brake switch 7S21, is restored to free fl ow to allow for steering without pressure loss. The pre-tension pressure is kept in the system through non-return valves. When the pressure drops below the fi xed minimum level (RSP=Return switch point on the pressure switch), changeover valve 8Y4 is activated again and the pump speed increased to maximum until the holding pressure is attained again. This process lasts approx. 500ms.

Steer unit Steer cylinder Service brake

Toggle valve

Steering unit

Reservoir Release brake solenoid

Spring-loaded accumulator block

Service brake Spring-loaded brake

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When the seat switch opens, the truck brakes electrically at fi rst. The spring-loaded brake applies at a residual speed of approx. 2 km/h. The seat switch contact time can be adjusted. This condition is shown visually on the LCD display on the LISA or the Else Check.

The steering pump generally operates in standby mode when the seat switch is applied by the driver.

Handbrake switch and emergency braking

Set the handbrake switch (1) to the brake position. This de-energises “Release brake solenoid” 7Y1 and the spring-loaded brake applies. Braking takes place with the maximum delay.

This process can also be induced by pressing the Emergency Disconnect. A visual display is shown on the LCD as well as the LISA.

Travelling against the handbrake is inhibited.

Ramp function

If the truck stops on a ramp it is held in place electrically until the spring-loaded brake applies. When the truck sets off again on the ramp a drive moment builds up in the traction motor, after which the spring-loaded brake opens and the truck sets off.

This prevents the truck from rolling back on a ramp. Manual release of the spring-loaded brake

Manual release of the spring-loaded brake

Releasing the Brake

Travel position

- Travel disabled - No display message:

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fi g. 153b

If the truck is to be moved without an energy supply (e.g. shipping, towing), the spring-loaded brake must be mechanically/hydraulically released.

STOP

Suitable measures must first be taken to prevent the truck from rolling away.

• Set the lever to the left to the “release brake” position. “Release brake solenoid” 7Y1 is in the blocked position. Turn the steering wheel to the right. This generates a pressure in the hydraulic circuit until the brake is released. You can tell when this has happened as the spring-loaded piston extends by 20-25 mm, thereby releasing the handbrake lever.

The truck can be towed or loaded. The foot brake is functional.

STOP

You cannot brake the truck securely with the spring-loaded brake in this condition, only by applying the brake pedal.

The blocked position is monitored by an inductive proximity switch. When the lever and therefore the valve tappet are in the normal position (sensor activated), an LED on the sensor lights up. This means the switch is active and a possible broken wire will be indicated.

! Before starting the truck again, the locking lever “Release brake solenoid” 7Y1 must be reset to the travel position. The truck is ready for operation.

The spring-loaded brake now functions again automatically.