GB2057604A

GB2057604A - Hydrostatic Operating System for Gear-change Boxes

Info

Publication number: GB2057604A
Application number: GB8027536A
Authority: GB
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1979-09-01
Filing date: 1980-08-26
Publication date: 1981-04-01
Also published as: IT1154074B; JPS5642751A; AR221776A1; BR8005515A; DE2935377A1; FR2464414A1; IT8046876A0; IT8046876A1

Abstract

A hydrostatic operating system for a gear change box in which movement of the gear shift lever (1) in one direction (A/B) for selection of the gear train and another direction (C/D) for engagement of the desired gear is transmitted to actuating means (4, 4', 5, 5') in the gear box by transfer circuits (6, 7, 8, 9) and means are provided to effect pressure and leak oil equalisation in the transfer circuits, the means comprising a piston pump (11) equipped with a reserve tank (12) and operable by the actuating pedal (18) of a clutch device. The output of the piston pump is connected to the transfer circuits, preferably through back pressure valves (14-17). If the clutch device (K) is also to be operated hydrostatically, and if a single hydrostatic medium can be used, then the two hydrostatic circuits can be connected together, both operated by the actuating pedal of the clutch device. If a different hydrostatic medium must be used the two circuits can still be connected through a pressure transfer device. <IMAGE>

Description

SPECIFICATION Hydrostatic Operating System for Gear-change Boxes The invention relates to a hydrostatic operating system for gear-change boxes, in particular for motor vehicles.

Hydrostatic transfer of operating forces from the gear shift lever in the driver's cab to actuating means in the gear-change box via transmitter and receiver cylinders has proved particularly useful in cases where the gearbox is relatively distant from the driver's cab or where a purely mechanical transfer would be particularly complicated, e.g. in the case of tiltable driver's cabs or where the operating forces to be transferred are especially large.

Hydrostatic operating systems of this kind are operated without outside energy, i.e. without the aid of a pressure medium pump, so that special measures are required to equalise the inevitable leak oil losses incurred during constant running and the pressure differentials occurring between the cylinders after the piston has completed its stroke. In a previous proposal, these measures have included arresting means for arresting the gear lever in its end positions and gear levels, a pressure medium tank and pressure medium lines between the tank and the cylinders with associated facilities for dpening or closing the pressure medium lines.

Such a system must operate not only automatically but must also be maintenance-free over as long a period as possible. The pressure in the reserve/pressure tank is built up during commissioning and should remain stable during the entire lifetime of the system. In practice this cannot be ensured.

The invention provides a hydrostatic operating system for a gear-change box, the system comprising a gear-shift lever movable in a first direction for selection of the gear train and in a second direction for engagement of the desired gear, the movements in the first and second directions being transferred to actuating means in the gear-change box by first and second transfer circuits, a clutch device, and a device for pressure and leak oil equalisation in which the pressure for effecting pressure and leak oil equalisation is built up by operating an actuating pedal of the clutch device just prior to changing gear, the build-up taking place in a piston pump equipped with a reserve tank.

By connecting the regenerating system with the actuating pedal of the clutch device it is possible to build up pressure for effecting pressure and leak oil equalisation just prior to each gear-changing operation, since the clutch has to be operated prior to each gear-changing operation.

This arrangement eliminates altogether the need for a pressure medium tank and a closed pressure system. It provides an easy solution through the use of a piston pump with a pressureless reserve tank for building up pressure, the piston being virtually maintenance-free.

Preferably each of the first and second transfer circuits comprises a pair of transfer lines and the piston pump output is connected to all four pressure transfer lines by way of four back pressure valves1 one for each pressure transfer line.

If the clutch device is also to be operated by hydrostatic means and if the same transfer medium can be utilized, then it is possible to connect the two systems in a single hydraulic circuit. Even if due to special reasons different transfer media are required for the hydrostatic operation of the clutch and the hydrostatic operation of gear-change system, the two hydrostatic systems may still be connected through a pressure-transfer device such as a piston and cylinder device.

The invention is illustrated by the drawings, of which: Figure 1 is a hydrostatic gear-changing system illustrated with the clutch pedal in the operating position.

Figure 2 is a regenerating system for operation by the clutch, and using two different media.

Figure 3 is an illustration of the regenerating system with the clutch pedal in the inoperative position.

With reference to Figure 1, a hydrostatic gearchanging system comprises a gear-shift lever 1 arranged proximate to a driver of a vehicle (not shown) in which the system is mounted, a transmitted cylinder 2, 2' for selecting the gear train (A/B), a transmitter cylinder 3, 3' for the gear-changing movement (C/D), and corresponding receiver cylinders 4, 4' and 5, 5' arranged proximate to or within the gearbox (not shown).

The connections between the transmitter and receiver cylinders 2 and 4, 2' and 4', 3 and 5 and 3' and 5' are made by pressure transfer lines 6 to 9. A regenerating system - pressure and leak oil equalisation system - 10 comprises a piston pump 11, a reserve tank 12 and a line 13 extending from the piston pump 11 and branching four ways through back pressure valves 14 to 1 7 to connect with each of the pressure transfer lines 6 to 9.

In this arrangement the piston pump 11 for building up the static pressure in the link line 13 is operated by the clutch pedal 1 8 of a mechanical clutch (not illustrated) of the vehicle.

However, if the clutch of the vehicle is to be operated hydrostatically, then its actuation source is the piston pump 11 of this system acting via line 19, to the clutch K.

If, as a result of practical considerations -- e.g.

low temperature problems concerning the operation of the clutch - it is decided to operate this facility with brake oil and the gear-changing system with mineral oil, then this can be achieved in a simple way by fitting a pressure transfer device 20 comprising a cylinder 21 and a piston 22 into the line 1 3 ahead of the back pressure valves 14 to 1 7 (see Figure 2).

Whilst the clutch is in the inoperative position, as illustrated in Figure 3, a quantity of oil may leak from the reserve tank 12 into the non-pressurized pressure chamber 1 a of the piston pump 11. As the clutch pedal 18 is operated, the first thing to happen is the closure of the line from the reserve tank 12. Once this has been done, pressure is built up to effect pressure and leak oil equalisation in the hydrostatic gear-changing system and possibly operation of the clutch K via the line 19.

Instead of using a piston and cylinder device as a pressure transfer device, it is, for example possible to utilize a pressure transfer box with a diaphragm. It is also possible to use two piston pumps operated jointly by the clutch pedal instead of a pressure transfer device.

Claims

1. A hydrostatic operating system for a gearchange box, the system comprising a gear-shift lever movable in a first direction for selection of the gear train and in a second direction for engagement of the desired gear, the movements in the first and second directions being transferred to actuating means in the gear-change box by first and second transfer circuits, a clutch device, and a device for pressure and leak oil equalisation in which the pressure for effecting pressure and leak oil equalisation is built up by operating an actuating pedal of the clutch device just prior to changing gear, the build-up taking place in a piston pump equipped with a reserve tank.

2. A hydrostatic operating system according to claim 1 in which each of the first and second transfer circuits comprises a pair of transfer lines and the piston pump output is connected to all four pressure transfer lines by way of four back pressure valves, one for each pressure transfer line.

3. A hydrostatic operating system according to claim 1 or claim 2 zn which the transfer circuits are connected to a hydrostatic circuit for operation of the clutch device.

4. A hydrostatic operating system according to claim 3 in which the connection of the transfer circuits to the hydrostatic circuit for operation of the clutch device is by way of a piston and cylinder pressure transfer device.

5. A hydrostatic operating system for a gearchange box, the system being substantially as described herein with reference to Figures 1 and 3 of the drawings.

6. A hydrostatic operating system according to claim 5 modified substantially as described herein with reference to Figure 2 of the drawings.