GB2079378A

GB2079378A - Hydraulic tipping apparatus for tipping the driving cabs of lorries

Info

Publication number: GB2079378A
Application number: GB8118281A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-07-02
Filing date: 1981-06-15
Publication date: 1982-01-20
Also published as: IT1142546B; SE8103234L; FR2493255A1; FR2493255B1; IT8148629A0; NL8102539A

Abstract

A hydraulic tipping apparatus for tipping the driving cabs of lorries from tipped to non-tipped positions comprises a pump (at 10), a pressure fluid tank (at 7), a double-acting piston/cylinder unit (2/1) wherein the piston rod (3) and cylinder (1) are respectively connected to the driving cab and the chassis frame structure. In the bottom dead-centre position of the piston (2), the two cylinder chambers (4, 5) are connected together by way of a conduit (11). The lower cylinder chamber (4) which is connected to the first pressure fluid conduit (6, 7) is connected to the pressure fluid tank by way of a valve (16) which is opened by the piston (2) after passing over the port (12), and an orifice (24'). A conduit check valve (15) which opens towards the lower cylinder (4) is disposed in the connecting conduit (11). <IMAGE>

Description

SPECIFICATION Hydraulic tipping apparatus The invention relates to hydraulic tipping apparatus for tipping the driving cabs of lorries and is concerned with hydraulic tipping apparatus as set forth in the classifying, i.e. non-characterising, portion of Claim 1.

A hydraulic tipping apparatus for lorry driving cabs, of that kind, is known (DOS NO. 20 30 450). In the known apparatus, however, the connecting conduit is formed only as a groove of short length, which is provided at the inside wall surface of the cylinder, in the interior thereof, in the direction of movement of the piston; however, when pressure fluid is introduced into the pressure fluid chamber for moving the piston outwardly and thus tipping the driving cab, the above-indicated arrangement is disadvantageous insofar as the groove forms a communication to the upper cylinder chamber which is connected to the pressure fluid tank, and this therefore results in an ineffective partial circuit which makes it difficult to extend the piston in the region of the connecting conduit in the form of the groove.

Therefore, a further aparatus is known in which the two cylinder chambers of the cylinder are connected together by way of an outer connecting conduit (DOS NO. 23 56 249). By virtue of the connecting conduit between the upper and the lower cylinder chambers, it can perform a free oscillating stroke movement in the bottom dead-centre position between the two ports at which the connecting conduit opens into the cylinder, so that the spring means of the driving cab can freely perform their functions and are not impaired for example by the cylinder. However, for the purposes of tipping the driving cab, the connecting conduit necessitates the use of so-called differential switching, in which the pressure fluid is introduced into the upper and the lower cylinder chamber at the same pressure, this being achieved by way of the connecting conduit.

Because of the different cross-sectional surface areas on the two sides of the piston - one one side, the effective cross-sectional area is reduced by the piston rod secured to the piston -the application of the same pressure in the two cylinder chambers produces a resultant force by means of which the piston can be moved into its extended position, in spite of the connecting conduit. However, so that the piston can operate with a sufficiently large force, against the total weight of the driving cab, the cross-sectional area ofthe piston rod must be of suitably large magnitude as ultimately it is the piston rod cross-sectional area which determines the effective resultant force.

A disadvantage with these known apparatuses is the fact that, after pressure actuation in the upper cylinder chamber is terminated, when the piston reaches or passes beyond the one (upper) port at which the connecting conduit opens into the cylinder, when the driving cab is being tipped back, a differential switching action occurs, whereby the piston abruptly drops through. This in turn results in the driving cab taking up all the movement of its spring suspension arrangement until reaching a condition of being supported on abutment buffers, and is particularly undesirable in air-suspension lorries because, in a repair situation, it is not always possible to ensure that there is sufficient system pressure in the air suspension arrangement.

Afurther disadvantage with the known apparatus is that a certain amount of pressure fluid is always being moved back and forth in the connecting conduit during the oscillating stroke movement with the piston in the corresponding dead-centre position. Because of this, and the friction which is always present, the spring suspension properties of the driving cab are falsified by this damping action of the piston.

The invention is based on the problem of so designing an apparatus as set forth in the classifying portion of Claim 1 that sudden dropping movement is no longer possible when the driving cab is being tipped back.

According to the invention, hydraulic tipping apparatus for tipping the driving cabs of lorries into a tipped assembly position and from that position into a tipped-back driving position of the driving cab, comprises a pump, a pressure fluid tank, a doubleacting stroke cylinder, of which the piston or piston rod and cylinder are respectively connected to the driving cab and the chassis frame structure, pressure fluid conduits for pressure actuation, which open into the upper and lower cylinder chambers separated by the piston and which can be selectively connected to the pump or the pressure fluid tank, wherein, in the dead-centre position of the piston which corresponds to the tipped-back position of the driving cab, the two cylinder chambers are connected together by way of a connecting conduit, the ports at which the connecting conduit opens into the cylinder determining the oscillating stroke movement of the piston, and a check valve which is controllable by the piston passing over the port and which is arranged in the first pressure fluid conduit which leads to the pressure fluid tank when the driving cab is tipped back, characterised in that the lower cylinder chamber which is connected to the first pressure fluid conduit is connected to the pressure fluid tank by way of a valve which is opened by the piston after passing over the port, and an orifice, and that a conduit check valve which opens towards the lower cylinder chamber is disposed in the connecting conduit.

If therefore the check valve in the first pressure fluid conduit which leads to the pressure fluid tank, that check valve in accordance with the invention preferably being pressure-controlled by way of the pressure in the upper cylinder chamber, is closed for example shortly before the piston reaches the bottom dead-centre position, after passing over the port at which the connecting conduit opens into the cylinder, the valve connected to the lower cylinder chamber opens, in accordance with the teaching of the invention, and provides a communication to the pressure fluid tank by way of an orifice incorporated into the first pressure fluid conduit.Desirably, the controlled valve is connected to the first pressure fluid conduit between the orifice and the controlled check valve so that the pressure fluid which is displaced out of the lower cylinder chamber when the driving cab is being tipped back is always discharged by way of the orifice and therefore in a damped mode.

In an advantageous development and embodiment of the invention, a conduit check valve which opens towards the lower cylinder chamber is also arranged in the connecting conduit, which has the advantage that a differential switching action cannot occur and the piston cannot therefore drop through because, when the check valve in the first pressure fluid conduit is closed, in contrast to the state of the art, pressure fluid cannot be displaced from the lower cylinder chamber into the upper cylinder chamber in the downward movement of the piston, which is advantageous insofar as the pressure fluid which is displaced into the pressure fluid tank by way of the controllable valve and the orifice and a suction blocking valve for preventing fluid from being sucked along afterwards (check valve) is removed from the system.If, as a result of random movement while the vehicle is being driven, the piston of the double-acting cylinder moves slightly upwardly, pressure fluid is displaced into the lower cylinder chamber from the upper cylinder chamber and the conduit check valve. There is no possibility of fluid being sucked out of the pressure fluid tank, because of the suction blocking valve in the first pressure fluid conduit. In the subsequent random downward movement of the piston while the vehicle is being driven, the pressure fluid which is displaced from the upper cylinder chamber into the lower cylinder chamber is in turn conveyed into the pressure fluid tank by way of the first pressure fluid conduit so that a vacuum is gradually developed, which permits unimpeded oscillation ofthe piston in the oscillating stroke movement length, that is to say, between the ports at which the connecting conduit opens into the cylinder, without being accompanied by displacement of pressure fluid, with the resulting damping action and falsification in respect of the spring suspension qualities of the driving cab.

Advantageous developments and embodiments of the invention are characterised in the subsidiary

Claims

claims. An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawing which is a diagrammatic view of a hydraulic circuit. With reference to the drawing, reference numeral 1 denotes a double-acting stroke cylinder/piston unit, comprising cylinder 1 having a piston 2 and a piston rod 3 which are secured to the driving cab and the chassis frame structure of a motor lorry (not shown). The cylinder/piston unit as drawn is intended to represent the tipped-back, bottom deadcentre position ofthe piston 2, below which is the lower cylinder chamber 4 and above which is the upper cylinder chamber 5. The lower cylinder chamber 4 is taken by way of a first pressure fluid conduit 6 generally in direction 7 of a pressure fluid tank (not shown). The second pressure fluid conduit 8 leads by way of an orifice 9 to the output of a pump (not shown), in the direction indicated by arrow 10.The first pressure fluid conduit 6 and the second pressure fluid conduit 8 are respectively connected to the pressure fluid tank and the pump, downstream of 7 and 10 respectively, by way of an actuating and change-over control means (not shown). The cylinder 1 also has a connecting conduit generally denoted by 11. The connecting conduit 11 connects the lower cylinder chamber 4 to the upper cylinder chamber 5 in the bottom dead-centre position of the piston 2, as illustrated in the drawing. The oscillating stroke movement 14 of the piston is fixedly predetermined by the ports 12 and 13 in the wall of the cylinder 1, at which the connecting conduit opens into the cylinder. A conduit check valve 15 is so arranged in the connecting conduit 11 that it blocks flow towards the upper cylinder chamber 5. In addition, a pressure-controlled two-way twoposition valve which is generally denoted by reference numeral 16 is connected to the connecting conduit 11 in the region between the check valve 15 and and the lower cylinder chamber 4. The valve 16 is closed in the illustrated position in which it is held in a rest condition by means of a spring 17. Afirst control conduit 18 of the valve 16 is connected to the lower cylinder chamber 4 by way of a first conduit 20, while a second control conduit 19 is connected only to the upper cylinder chamber 5, by way of the conduit 11, downstream of the check valve 15. In the operative position (not shown), the first conduit 20 of the controllable valve 16 is connected by way of a conduit 21 to the first pressure fluid conduit 6, at a point indicated by reference numeral 22. Provided between point 22 and the lower cylinder chamber 4 is a check valve 23 which is disposed in the first pressure fluid conduit 6 and which opens towards the cylinder chamber 4. A control conduit 24 of the check valve 23 is connected to the first pressure fluid conduit 8 or the upper cylinder chamber 5. Arranged between the check valve 23 and the pressure fluid tank (not shown), as indicated by arrow 7, is an orifice 24' and a suction blocking valve 25, the latter having a check valve which opens towards the pressure fluid tank in the direction indicated by arrow 7. CLAIMS

1. A hydraulic tipping apparatus for tipping the driving cabs of lorries into atipped assembly position and from that position into a tipped-back driving position of the driving cab, comprising a pump, a pressure fluid tank, a double-acting stroke cylinder, of which the piston or piston rod and cylinder are respectively connected to the driving cab and the chassis frame structure, pressure fluid conduits for pressure actuation, which open into the upper and lower cylinder chambers separated by the piston and which can be selectively connected to the pump or the pressure fluid tank, wherein, in the dead-centre position of the piston which corresponds to the tipped-back position of the driving cab, the two cylinder chambers are connected together by way of a connecting conduit, the ports at which the connecting conduit opens into the cylinder determining the oscillating stroke movement of the piston, and a check valve which is controllable by the piston passing over the port and which is arranged in the first pressure fluid conduit which leads to the pressure fluid tank when the driving cab is tipped back, characterised in that the lower cylinder chamber which is connected to the first pressure fluid conduit is connected to the pressure fluid tank by way of a valve which is opened by the piston after passing over the port, and an orifice, and that a conduit check valve which opens towards the lower cylinder chamber is disposed in the connecting conduit.

2. Apparatus according to Claim 1, characterised in that the orifice is arranged in the first pressure fluid conduit and the controllable valve is arranged in parallel to the pressure fluid conduit.

3. Apparatus according to Claim 1 or 2, characterised in that the controllable valve is in the form of a pressure-controlled two-way two-position valve, the first control conduit of which is connected to the lower cylinder chamber.

4. Apparatus according to Claim 3, characterised in that the second control conduit of the pressurecontrolled valve is connected to the upper cylinder chamber.

5. Apparatus according to any one of Claims 1 to 4, characterised in that the controlled valve has a rest position which is defined by means of a spring and in which the valve is blocked.

6. Apparatus according to any one of Claims 1 to 5, characterised in that the controllable valve is connected to the first pressure fluid conduit in parallel with the controllable check valve and in the direction towards the pressure fluid tank upstream of the orifice.

7. Apparatus according to any one of Claims 1 to 6, characterised in that the controllable check valve is a pressure-controlled valve.

8. Apparatus according to Claim 7, characterised in that the control line of the pressure-controlled check valve is connected to the upper cylinder chamber or the second pressure fluid conduit.

9. Hydraulic tipping apparatus substantially as hereinbefore described with reference to the accompanying drawing.