GB2112910A

GB2112910A - Hydrostatic transmissions

Info

Publication number: GB2112910A
Application number: GB08300567A
Authority: GB
Inventors: Karlmann Hamma; Unal Gazyakan; Friedrich Ehrlinger
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1982-01-08
Filing date: 1983-01-10
Publication date: 1983-07-27
Also published as: DE3200329A1; IT8346804A0; GB2112910B; JPS58121348A; GB8300567D0; DE3200329C2; IT1174965B

Abstract

Overrun of an hydraulic motor (6) is detected by a valve (7) responsive to the pressure differential across the motor the valve serving to admit working fluid to the supply side of the motor. The fluid may be supplied from oil leak (4) by a valve (8) or an auxiliary pump, or it may be supplied by the main transmission pump (1). The motor is in open circuit with the main pump during forward and reverse drive as determined by reversing valve (5), the motor then being selectively braked by throttle (3). Upon overspeed of the motor the reversing valve is centred to establish a restricted short circuit across the motor. In other embodiments the pump is driven via a clutch and the motor is short-circuited when the clutch is disengaged. <IMAGE>

Description

SPECIFICATION Shift device for hydrostatic skew disc gears The invention relates to a shift device for hydrostatic skew disc gears having an open circuit, and wherein a directional valve is provided for controlling the direction of flow of the pressure fluid to and from the hydromotor.

In the operation of hydraulic skew disc machines in an open circuit, the hydromotors and their piston guide are subject to the risk of damage or destruction as a result of excess speeds or low pressure in the low pressure line if the power flow is reversed and the hydromotor acts as a pump as may take place, for example, in vehicle drives.

In German Offenlegungsschrift No. 30 10 913 a control device is disposed between the pump pressure line and the return line, which device supplies the pump pressure line with sufficient pressure fluid from the return line and prevents breakdown of the fluid flow in the case of drive reversal in which the hydrometer acts as a pump.

This control device operates as a delicate sensor and is therefore very sensitive. In addition this control device is prone to vibrations.

In accordance with the present invention, in the case of critical operating conditions, which may occur in the case of drive reversal, the hydromotor is shifted from an open to a closed circuit. This takes place via a control device which adjusts the directional valve, which determines the direction of the supply flow of the pressure fluid, as a function of the output speed of the hydromotor or the shift condition of the pump into the zero position. In order to ensure an adequate supply of the hydromotor with pressure fluid, a supply via a volume compensating valve or a supply circuit with a feed pump is additionally provided and is associated with a shift valve. In order to achieve a sufficient shift pressure throttles are connected upstream of the shift valve. In addition, both the hydropump circuit and the hydromotor circuit are protected by high pressure relief valves.

The device of the present invention enables the drawbacks of known mechanisms to be overcome as a control device is provided instead of an adjustment device, which control device comprises accurately determined shift positions, but no intermediate positions.

Some embodiments of the invention are exemplified with reference to the accompanying drawings, in which: Figure 1 shows the shift arrangement of a hydrostatic vehicle drive with a speed monitoring output on the hydromotor and a volume compensating valve; Figure 2 shows a similar arrangement to Figure 1 but with a supply circuit including a supply pump; Figure 3 shows a similar arrangement to Figure 1 but with subsequent supply of the hydromotor circuit by the hydropump; Figure 4 shows another shift arrangement, for example of a hydrostatic drive of a fan wheel only requiring one drive direction; and Figure 5 shows a similar arrangement to Figure 4 but is a drive for a winch or a pivot drive for construction machines.

In the hydrostatic arrangement of Figure 1 for a vehicle drive, an adjustable hydropump is designated by 1, which pump suctions oil from a tank 4 via a suction line 1.1 and supplies a 4/3 way valve 5 via a pressure line 1.2. The pressure in the pressure line 1.2 is determined by a pressure relief valve 2, which valve returns the excess oil back into the oil tank 4. The directional valve 5 serves to determine the direction of rotation of the output shaft and whether forward or reverse movement is required. As a result of this, two conduits 6.1 and 6.2 alternately form supply or return conduits. In accordance in each case with the direction of flow, a pressure relief valve 11.1 in a conduit 11.3 or a pressure relief valve 11.2 in a conduit 11.4 determines the pressure in the circuit of a hydromotor 6.A shift valve 7 is disposed parallel to the hydromotor 6, which valve is also formed as a 4/3-way valve and is shifted by the respective return pressure through conduits 7.2 and 7.3. The purpose of this shift valve 7 is, in the case of drive from the load, i.e. when the vehicle is travelling downhill and the hydromotor 6 has become the pump and therefore supplies more oil to the return than the supply provides, to supply more oil from the oil tank 4 to the supply line via the shift valve 7 and a volume compensating valve 8.

Assuming that the vehicle is travelling forwards, when the directional valve 5 is in the shaft position X, the conduit 6.1 is the supply and the conduit 6.2 is the return to the hydromotor 6.

In the case of accelerated downhili movement, the hydromotor 6 acting as a pump then supplies oil from the supply conduit 6.1 to the return conduit 6.2 and therefore causes a pressure decrease in the supply conduit 6.1. The shift valve 7 is therefore shifted to the right by the pressure in the conduit 7.3 so that a branched conduit 7.1 of the shift valve 7 connects the volume compensating valve 8 with a conduit 10.4 via a channel 8.1,which conduit 10.4 communicates with the supply conduit 6.1.

For reverse movement the directional valve 5 is in the shift position Y, whereby the conduit 6.2 is the supply and the conduit 6.1 is the return. If, in this shift position, the output shaft is also driven by the vehicle, the hydromotor 6 supplies from the supply conduit 6.2 to the return conduit 6.1.

In this case an over-pressure is produced in the channel 7.2, which overpressure displaces the shift valve 7 to the left and connects the volume compensating valve 8 with the conduit 6.2 via a conduit 10.3 in order to prevent an under pressure in the supply conduit. Throttles 10.1 and 10.2 in the conduits 10.3 and 10.4 facilitate the shifting of the shift valve.

The actuation of the directional valve, i.e.

selection of forward or reverse movement, takes place via a control device 9. a speed monitoring output device 9.1 is disposed on the output shaft of the hydromotor 6, the signals from which output device are supplied to the control device 9 via a line 9.2. When overspeed of the hydromotor 6 is ascertained, the position of the directional valve 5 set in the control device 6 is overridden and set to the zero position. For this purpose, solenoids 5.3 and 5.4 are provided and are connected with the control device via conduits 9.3 and 9.4. If the circuit of the hydromotor 6 is thus shifted into a closed circuit, the through-flow speed of the oil in this circuit is decelerated by a throttle 5.2 in the directional valve 5 and therefore the output shaft is also braked by the hydromotor 6.

The device of Figure 2 only differs from that of Figure 1 by a modified supply circuit in critical operating conditions. In this respect the branched conduit 7.1 of the shift valve 7 is connected with a supply pump 12 via a conduit 12.1, which pump supplies oil from the oil tank 4 to the supply conduit 6.1 or 6.2 if the output shaft of the hydromotor is driven by the vehicle weight.

In the device of Figure 3, a consequential supply of the hydromotor driven by the output shaft takes place directly via the hydropump 1.

For this purpose, a 6/3-way valve 14 is disposed between the hydropump circuit and the hydromotor circuit, which valve comprises, in addition to the connections for bypass channel 14.1, a branched conduit 14.3 which connects the pump pressure line 1.2 with the branched conduit 7.1 of the shift valve 7 via a line 1 5 in the zero position of the valve. In accordance with this shift arrangement, when the hydromotor 6 is driven by the load, the supply conduit 6.1 or 6.2, according to the direction of rotation, is supplied with pressure oil by the hydropump 1. The bypass channel 14.1, incorporated in the directional valve 14, is provided with solenoids 14.4 and 14.5 which are controlled by the control device 9 by the lines 9.3 and 9.4 in the manner described above. The remainder of this device corresponds to the devices shown in Figure 1 and 2.

Figure 4 shows a hydrostatic drive, for example of a fan wheel, wherein only one direction of rotation of the hydromotor is required. For this reason a 4/2-way valve is provided as the directional valve 1 7 which supplies pressure fluid via the pressure line 1.2 by means of a constant delivery pump 16.

The drive shaft of the hydropump 16 is connected to a clutch 16.1 which is actuated by a control device 1 8 which simultaneously serves to shift the directional valve 17. In the case of a closed clutch 1 6.1, the directional valve 1 7 is adjusted by the control device 1 8 into its shift position A in which the hydromotor is supplied with pressure oil. However, as soon as the clutch 1 6.1 is opened, i.e. the drive of the hydropump is discontinued, the control device 1 8 is caused, by a signal from the line 18.1, to adjust the directional valve 1 7 into its zero position via the line 1 8.2 to the solenoid 17.3.

The device of Figure 5 is also used to drive a working device, however with two directions of rotation, e.g. as required for a pivot drive for a construction machine. In this respect, a constant delivery pump 16 again supplies pressure oil to a directional valve 5, as in the case of Figures 1 and 2, although the drive shaft of the constant delivery pump 16 may be stopped by a clutch 16.1. In this case, with an open clutch 16.1, the control device 19 adjusts the directional valve 5 into its zero position under the action of a signal via line 19.1, by means of lines 19.2 to the solenoid 5.2 and lines 19.3 to the solenoid 5.4.

The shift arrangements of Figures 1, 2 and 3 also comprise an adjustable brake throttle 3 or a brake valve in the oil return conduit 1.3 between the directional valve 5 and the oil tank 4, which may also be used to brake the vehicle.

Claims

1. A shift device for hydrostatic skew disc gears is an open circuit, and wherein a directional valve is provided for controlling the direction of flow of the pressure fluid to and from a hydraulic motor, characterised by the following features: a) a mechanical, hydraulic, pneumatic or electrical control device is arranged for the actuation of the directional valve; b) a shift valve with a branched conduit for controlling supply into a respective supply conduit to the hydraulic motor is arranged to control the hydraulic motor as a function of the respective operating pressure; c) control means is disposed for ensuring supply pressure fluid supply to the branched conduit.

2. A shift device according to claim 1, wherein said control means is a volume compensating valve.

3. A shift device as claimed in claim 1, characterised in that a feed pump and a pressure relief valve are arranged for ensuring supply of fluid to the supply conduit.

4. A shift device as claimed in claim 1, characterised in that a 6/3-way valve having an additional branched conduit and a connecting line is disposed between the directional valve and the shift valve.

5. A shift device as claimed in claim 2, characterised in that the drive shaft of a constant delivery pump comprises a clutch which is controlled by a contol device for the directional valve.

6. A shift device as claimed in claim 5, characterised in that the control device is connected to the hydromotor output by means of a speed monitoring device in order to control solenoids of the directional valve.

7. A shift device as claimed in any one of the preceding claims, characterised in that throttles are disposed between the branched conduit of the shift valve and the supply and return conduits in order to produce shift pressure for controlling the shift valve.

8. A shift device as claimed in any one of the preceding claims, characterised in that a bypass channel closing the hydromotor circuit in the zero position of the directional valve comprises a throttle.

9. A shift device for hydrostatic skew disc gears substantially as hereinbefore described with reference to any one of the accompanying drawings.