Park Lock - GPA40 rear axle



The Park Lock is a parking brake mechanism located above the GPA40 rear axle. It is designed to immobilise the tractor in complete safety. The Park Lock is easily controlled via a pushbutton located to the left of and below the steering wheel. This pushbutton enables the operator to select the Park Lock engaged position (A) or the disengaged position (B) while seated in the operator's seat.


The Park Lock mainly comprises three parts:
a hydraulic part
The hydraulic part is located above the rear axle inside the Park Lock unit (7)/cover plate (20) assembly. It comprises:
- two "O" rings (12) and (13)
- a piston (2), which is returned by a set of eight


Belleville washers (14). The effect of the load exerted on the piston (2) by the Belleville washers may be cancelled by fully screwing the special hexagonal head screw (5). Cancelling the load exerted by the Belleville washers is useful if:
- it is necessary to disassemble the Park Lock
- a hydraulic and/or electronic problem occurs, which hinders tractor mobility.
• an electrical part
The electrical part comprises:
- two solenoid valves (21) and (22)
- two switches (18) and (19)
The solenoid valves and switches are screwed onto the Park Lock unit (7) and the cover plate (20) respectively. They are managed by the tractor's electronic system and via the connectors (TR5), (TR6), (TR7) and (TR8).
• a mechanical part
The mechanical part of the Park Lock uses the components and the operating principle which are an extension of the hand brake mechanism. Here is a reminder of the components used:
- Actuator lever
- Discs
- Intermediate plates
- Mechanism

Parts list 
(1) Park Lock (2) Piston (3) Pin (4) Wedge (5) Special screw (manual disengagement) (6) "O" ring (7) Park Lock unit (8) Actuator lever (9) Screw (10) Push rod (11) Pushrod (12) "O" ring (13) "O" ring
(14) Belleville washers (15) Screw (16) Cover plate (17) Screw (18) Switch (19) Switch (20) Cover plate (21) Solenoid valve (22) Solenoid valve (23) 17 or 21 bar union (24) Mecanindus pin (25) Circlip (26) Tie rod (27) Screw (28) Stud (29) Washer/nut (M) Hand brake mechanism


Operation

Engaged position: mechanical action 


The movement of the piston (2) caused when the Belleville washers (14) are released forces the actuator lever (8) to tilt, compressing the hand brake discs splined in rotation with the pinion. The rear axle is then blocked and the tractor is immobilised.

Disengaged position: hydraulic action 


In this configuration, the Park Lock mechanism receives a 17 or 21 bar oil supply via two different solenoid valves. The piston (2) then compresses the Belleville washers and releases the push rod (10), the mechanism (M) and the hand brake discs via the actuator lever (8) and the hand brake tie rod (26). One of the two solenoid valves secures the Park Lock disengaged position in the event of a fault. The principle consists of maintaining the oil chamber of the piston (2) under pressure by shutting off its return line. A switch screwed onto the cover plate (20) and a second switch located on the Park Lock unit (7) check the hand brake disc wear and operation of the Park-Lock respectively via indicator lights. Each electrical component is controlled by the tractor's electronic system.

Manual disengagement and engagement of the Park Lock

Manual disengagement (C) 


If manual disengagement is necessary
The Park Lock must be disengaged manually:
- if the rear axle is to be removed for dismantling
- to provide tractor mobility in the event of a failure on the 17 or 21 bar hydraulic system or a fault on the electronic management system

Procedure
Using the remote control (1) linked to the special screw (5) on the cover plate, manually disengage the Park Lock by fully screwing in the special screw (5) until it no longer turns.

Description of the mechanical reaction during manual disengagement
When the special screw (5) is screwed in, the wedge (4) moves. This beveled wedge mechanically pulls the piston (2) upwards, compressing the set of Belleville washers (14). The load which had been applied to the push rod (10) is cancelled. The mechanism (M) and the hand brake discs are then released to make the tractor mobile.

Manual engagement (D) 

Procedure
If for whatever reason the Park Lock has been disengaged, using the remote control (1), completely unscrew the special screw (5) until it comes into contact with a "hard" point. This procedure restores the Park Lock original functions:
disengagement (hydraulic function) and engagement (mechanical function).