GB2126657A

GB2126657A - Hydrostatic drive

Info

Publication number: GB2126657A
Application number: GB08318522A
Authority: GB
Inventors: Gerhard Fuchs
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1982-09-04
Filing date: 1983-07-08
Publication date: 1984-03-28
Also published as: DE3232903A1; IT1167370B; FR2532694A1; IT8322727A0; GB8318522D0; FR2532694B1; GB2126657B

Abstract

The drive comprises an adjustable positive-displacement pump, which may be a rotary one of the sliding vane type (as shown), and a pressure-limiting device. The adjusting element of the pump may be a cam ring (3) and is displaceable by a control device (9) from a position of maximum delivery to a non-delivery position. The control device and the pressure-limiting device (10), which are oppositely disposed in alignment, abut the adjusting element. The control device may comprise a fluid- pressure operated piston (17) and the pressure-limiting device may include an adjustable spring (11). <IMAGE>

Description

SPECIFICATION Hydrostatic drive This invention relates to a hydrostatic drive of the kind comprising a pressure-limiting device and an adjustable positive-displacement pump, in particular an adjustable vane-type pump, with an adjusting element having an effect on the delivery and being slidable by virtue of a control device between a position of maximum delivery and an idle-stroke position of substantially no delivery.

Hydrostatic drives are drives composed of a hydropump and one or several hydromotors, with hydropump and hydromotor being able to be combined in an open or in a closed circuit.

Adjustable positive-displacement pumps are provided in the event of a requirement for an infinitely variable driving speed. A pressurelimiting device for the working pressure is arranged for between the hydropump and the hydromotor.

In known hydrostatic drives with variable driving speed, the pressure-limiting device is designed as a separate, complicated valve arrangement.

According to the invention in its broadest aspect a hydrostatic drive of the kind referred to is characterised in that the control device and the pressure-limiting device, which are oppositely disposed in alignment, abut on the adjusting element of the pump. To this end, the pressurelimiting device will favourably be a construction unit adapted to be integrated into the positivedisplacement pump. There is no need for additional lines and screw couplings so that both the mounting effort and the risk of leakage will be reduced.

In another advantageous embodiment, it is arranged for that the adjusting element is a cam ring, on the peripheral surface of which abut the control device and the pressure-limiting device, the latter being oppositely disposed in alignment.

Favourably, the pressure-limiting device is a spring assembly located between the cam ring and the pump housing, the cam ring being slidable into the idle-stroke position in opposition to the force of the spring assembly.

A control unit that is movable mechanically, for example by thread means, or with the assistance of auxiliary energy is particularly simple and entails low costs. Hydraulically or electrically actuatable control devices allow remote adjustment of the flow rate and the adjustment in dependence upon predetermined reference inputs.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawing which shows an adjustable vane-type pump for fitting into a hydrostatic drive with a mechanical control device assisted by auxiliary energy.

A pump housing designated by reference numeral 1 accommodates a rotor 2 and a cam ring 3 surrounding the rotor 2. Arranged over the axial length of the rotor 2 are radially extending slots 4 in which working vanes 5 are radiallyslidably located. The working vanes 5 abut with their radially outer ends on the inner periphery of the cam ring 3 and, together with two laterally disposed lateral discs, define working compartments of variable volume. The lateral discs contain an inlet opening 6 and an outlet opening 7 for the pressure fluid supply and discharge, respectively.

Whilst being laterally supported by a supporting device 8, the cam ring 3 is slidable in relation to the rotor 2 from a position of maximum eccentricity into a position which is substantially coaxial of the rotor 2. The almost coaxial position will be referred to as idle-stroke position.

Displacement of the cam ring 3 takes place pressure-responsively, on the one hand, as a result of the pressure conditions developing within the working compartments. On the other hand, displacement can be simultaneously effected by a control device 9.

The pressure-responsive displacement of the cam ring 3 takes place in opposition to the force of a spring assembly acting as a pressure-limiting device 10. The spring assembly comprises a compensator spring 11 which, on the one hand, bears via an adjusting screw 1 2 against a casing 13 screwed to the pump housing 1 and which, on the other hand, bears via an intermediate element 14 against the cam ring 3. As a result of increasing pressure, the cam ring 3 is displaced until it assumes the idle-stroke position, while the flow rate decreases and the pressure increases until attainment of the preadjustable maximum pressure which limits the pressure range. The maximum pressure can be set by the preload of the compensator spring 11 which is adapted to be defined by means of the adjusting screw 12.

Disposed diametrally opposite to the pressure limiting spring assembly is the control device 9 for the displacement of the cam ring 3 and thus for the adjustment of the flow rate. A casing 1 5 secured to the pump housing 1 contains a bore 1 6 slidably accommodating an adjusting piston 17. The adjusting piston 17 comprises an extension 1 8 by which it abuts on the cam ring 3.

In the adjusting piston 17 is a stepped bore 30 which starts from the end opposite to the extension 1 8. The initial portion, intermediate portion and end portion of the stepped bore 30 are of like diameter and guide a control slider 19.

Disposed between the initial portion and the intermediate portion as well as between the intermediate portion and the end portion are two larger-diameter areas 20, 21 of the stepped bore 30 which communicate via bores 22, 23 with the end faces of the adjusting piston 1 7. A pressure fluid port 24 terminates into the intermediate portion of the stepped bore 30. The control slider 1 9 has an annular necked-down portion whose axial length corresponds to the axial length of the intermediate portion so that two control edges 25, 26 are formed thereby. The end faces of the adjusting piston 1 7 are via non-illustrated ports connected to a pressure fluid source, while the pressure fluid port 24 of the intermediate portion leads to a return reservoir. Upon displacement of the control slider 1 9 into either of the two directions indicated by the arrows, the pressure conditions will cause the adjusting piston 1 7 to be displaced into the position desired. By virtue of the displacement of the cam ring 3 resulting therefrom the flow rate will be changed.

Both the control device 9 and the pressurelimiting device 10 abut on the cam ring 3; this enables one continuously to adjust the required flow rate of the vane-type pump, with the pressure-limiting device being effective at all times.

Claims

1. A hydrostatic drive of the kind comprising a pressure-limiting device and an adjustable positive-displacement pump in particular an adjustable vane-type pump, with an adjusting element having an effect on the delivery and being slidable by virtue of a control device between a position of maximum delivery and an idle-stroke position of substantially no delivery, characterised in that the control device (9) and the pressure-limiting device (10), which are oppositely disposed in alignment, abut on the adjusting element (3) of the pump.

2. A drive as claimed in claim 1, characterised in that the adjusting element is a cam ring (3), on the peripheral surface of which abut the control device (9) and the pressure-limiting device (10), the latter being oppositely disposed in alignment.

3. A drive as claimed in claim 2, characterised in that the pressure-limiting device (10) is a spring assembly arranged between the cam ring (3) and the pump housing (1), the cam ring (3) being slidable to assume the idle-stroke position in opposition to the force of the spring assembly.

4. A drive as claimed in any one or in several of the preceding claims, characterised in that the control device (9) is actuatable mechanically, hydraulically or electrically.

5. A hydrostatic drive unit substantially as described with reference to the accompanying drawings.