Interrelated power delivery controls – including engine control – Transmission control – Transmission controlled by engine
Patent
1996-10-18
1998-09-22
Ta, Khoi Q.
Interrelated power delivery controls, including engine control
Transmission control
Transmission controlled by engine
477148, 477125, 477 83, 74336R, F16H 5904, B60K 2000
Patent
active
058106910
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a hydraulic changing device for a multi-ratio vehicle transmission according to the preamble of claim 1.
DE-A 40 11 033 (corresponding to U.S. Pat. No. 5,172,611) has disclosed a hydraulic changing device for a multi-ratio vehicle transmission of the related type. To prevent inadmissible downshifts, the changing device contains a pilot valve and a control valve. The pilot valve is connected, by a gearshift valve, with a servopump or a container. The individual gears of the vehicle transmission are changed by another connection to actuator devices. The control valve is connected, via a line, with a low-pressure pump whose operation depends on the engine speed. Both possible switching positions of the pilot valve are dependently affected by the engine speed-by the control valve. If, in order to engage the low gear, the gearshift valve is actuated while the high gear is engaged at an engine speed above a specific limiting value, while the pilot valve is held in its momentary switching position and thus a downshift is prevented. Said downshift only takes place when the engine speed has reached the specific limiting value at which the control valve changes its switching position. Said downshift blockage prevents an over-speed of the prime mover which would occur if the vehicle transmission were downshifted from the high gear to the low gear while the prime mover is at high speed.
SUMMARY OF THE INVENTION
The problem on which this invention is based is to simplify, practically and structurally, the existing hydraulic changing device.
The problem on which the invention is based is solved by a hydraulic changing device according to the main claim. Claims 2 to 6 refer to advantageous embodiments of the object according to the main claim.
Other features, essential to the invention and the advantages resulting therefrom, are to be understood from the description that follows of one embodiment of a hydraulic changing device in the example of a two-gear vehicle transmission for a mobile excavator or loader.
BRIEF DESCRIPTION OF THE DRAWING(S)
In the drawings:
FIG. 1 is a diagrammatic partly cut away view, of a hydraulic changing device, when the low gear is engaged; and
FIG. 2 to FIG. 4 depict the hydraulic changing device of FIG. 1 in different changing positions according to existing operating conditions.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
A servopump 10 conveys pressure medium, via a gear-change valve 2, from a tank 11 to a stop valve 1. For this purpose, the gear-change valve 2 is attached, via a first work line 12 and a second work line 13, to a first annular duct 14 and to a second annular duct 15. A third annular duct 18 communicates with the first annular duct 14 and a fourth annular duct 19 communicates with the second annular duct 15.
A connecting line 17 leads from the third annular duct 18 to a gear actuator 4 (first gear) of the vehicle transmission, not shown.
A connecting line 16 leads from the fourth annular duct 19 to a gear actuator 3 (second gear).
One control slide 26 of a stop valve 1 is axially movably situated in a valve cylinder 27. The valve cylinder 27 is locked by a screw 28.
The control slide 26 can be converted to two switching positions by adjusting forces which act upon its front faces.
As depicted in top of the drawings, the upper front face of the control slide 26 exerts an adjusting force dependent on the pressure prevailing in a low-pressure chamber 23.
The opposite front face abuts a control spring 33 which exerts an adjusting force directed opposite to the hydraulic adjusting force mentioned above.
The low-pressure chamber 23 communicates, via a low-pressure duct 24, with a low-pressure pump 20. The low-pressure pump is driven in dependence on the engine speed and an oil pressure is produced dependent on the input speed. The maximum delivery pressure of the low pressure 20 is limited by a pressure-limiting valve 7. If the low pressure pump reaches a maximum value, the pressure-limiting valve 7 opens and, as can b
REFERENCES:
patent: 3682014 (1972-08-01), Magg et al.
patent: 3738198 (1973-06-01), Kell
patent: 3937107 (1976-02-01), Lentz
patent: 5172611 (1992-12-01), Eymuller et al.
patent: 5528949 (1996-06-01), Stainton et al.
patent: 5622080 (1997-04-01), Furukawa
Gebhard Wolfgang
Heilig Eduard
Ta Khoi Q.
ZF Friedrichshafen AG
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