WO1999045280A1

WO1999045280A1 - Double-acting hydraulic cylinder, in particular for tilting a cab of a vehicle

Info

Publication number: WO1999045280A1
Application number: PCT/NL1999/000088
Authority: WO
Inventors: Johannes Bernardus Gerhardus Rikhof
Original assignee: Applied Power Inc
Current assignee: Enerpac Tool Group Corp
Priority date: 1998-03-04
Filing date: 1999-02-18
Publication date: 1999-09-10
Anticipated expiration: 2000-09-04
Also published as: NL1008475C2; DE19983013T1

Abstract

Double-acting hydraulic cylinder (20) comprising a cylinder tube (21), which is closed off at its axial ends by a cylinder base (22) and a cylinder head (23), respectively, thus delimiting a cylinder space (24), a piston/piston rod assembly which can move to and fro in the axial direction inside the cylinder space (24), forms two variable chambers (28, 29) in the cylinder space and the piston rod (26) of which projects outwards through an associated bore (31) in the cylinder head (23), an associated connection (32, 33) for a hydraulic-liquid line being provided for each chamber, and furthermore bypass means being provided, with at least one bypass passage between a first bypass opening (40) which is connected to the cylinder space (29) and a second bypass opening (37) which is connected to the cylinder space (28), which bypass openings lie at an axial distance from one another, in such a manner that hydraulic liquid can be exchanged between the two chambers via the bypass passage if the bypass openings are connected to different chambers. The bypass means comprise a bypass tube (35) which is disposed in the cylinder space and the piston/piston rod assembly is provided with an axial bore (36) for receiving the bypass tube (36).

Description

Double-acting hydraulic cylinder, in particular for tilting a cab of a vehicle.

The present invention relates to a double-acting hydraulic cylinder according to the preamble of claim 1, in particular for tilting a tiltable cab of a vehicle.

It is known, for example from EP-0 101 129 and GB- 2 079 378, to support the cab of a vehicle, in particular a lorry, via a spring suspension on the chassis in order to improve the comfort of the driver. In order to be able to carry out maintenance work on the vehicle engine which is often positioned beneath the cab, the cab can be tilted with respect to the chassis. For this purpose, there is a hydraulic tilting device with a hydraulic cylinder, sometimes a number of hydraulic cylinders, arranged between the chassis and the tiltable cab. In order to prevent the cylinder interfering with the operation of the suspension which allows the movement of the cab with respect to the chassis, hydraulic cylinders which exhibit the so-called "lost-motion effect" are used. In a cylinder of this nature, there is a bypass passage which, over a certain section of the axial travel of the piston/piston rod assembly, forms a connection between the two chambers of the cylinder, so that hydraulic liquid can flow from one chamber to the other chamber via the bypass passage. Hydraulic cylinders of this nature are known, for example, from EP-0 101 129, EP-0 784 159 and GB-2 079 378. In order to obtain the lost-motion effect, in the cylinder which is known from EP-0 101 129, the inner wall of the cylinder space is provided, in the vicinity of the cylinder base, with bypass grooves over part of its axial length, so that hydraulic liquid can move past the seal arranged around the piston via these grooves.

In EP-0 784 159, part of the cylinder space, in the vicinity of the cylinder base, has a larger diameter, and in that part there is a bush which on the inside is smooth and has the same diameter as the rest of the cylinder space - 2 - and on the outside is provided with axial grooves . These grooves extend between first bypass openings in the vicinity of the cylinder base and second bypass openings on that edge of the bush which faces towards the cylinder head.

Hydraulic lost-motion cylinders according to the preamble of claim 1 have also been disclosed, for example by DE 23 56 249, with a bypass line which is disposed outside the cylinder tube and has a first bypass opening to the cylinder space in the vicinity of the cylinder base and a second bypass opening at an axial distance therefrom. These known lost-motion cylinders have various drawbacks. For example, arranging grooves in the cylinder wall has proven to be relatively complex, and the same applies to the design with the additional bush around the outside of the cylinder tube. The solution with the bypass line arranged on the outside has the drawback that the line is fragile and undesirably increases the external dimensions of the cylinder. The object of the present invention is to provide an improved hydraulic cylinder with features for obtaining the lost-motion effect which is of compact design, is not susceptible to damage from outside and can be produced easily. The present invention provides a double-acting hydraulic cylinder according to the preamble of claim 1, which is characterized in that the bypass means comprise a bypass tube which is disposed in the cylinder space, and in that the piston/piston rod assembly is provided with an axial bore for receiving the bypass tube. In other words, the invention proposes to realize the connection between the cylinder chambers which is necessary for the lost-motion effect by arranging in the cylinder space a bypass tube which extends in the axial direction and along which the piston/piston rod assembly can slide to and fro. Advantageous embodiments of the drive cylinder according to the invention are described in the claims and the following description which is given with reference to the drawing. The-' present invention furthermore relates to a - 3 - hydraulic tilting device for tilting a tiltable vehicle cab and to a vehicle which has a tiltable cab and is provided with a tilting device having a hydraulic cylinder of this nature . In the drawing : Figure 1 shows a side view of the front part of a vehicle with a tiltable driver's cab,

Figure 2 shows a longitudinal section through a first exemplary embodiment of the double-acting hydraulic cylinder according to the invention, Figure 3 shows a longitudinal section through a second exemplary embodiment of the double-acting hydraulic cylinder according to the invention, and

Figure 4 shows a longitudinal section through a preferred embodiment of the double-acting hydraulic cylinder according to the invention.

Figure 1 shows the front part of a vehicle 1 with a tiltable driver's cab 2. As is customary, the cab 2 is arranged on chassis 3 and is connected to the chassis 3 via pivot means 4. The pivot means 4 are designed in such a way that the cab 2 can be moved through an angle with respect to the chassis 3 about a pivot axis which is defined by the pivot means 4, between a driving position and a tilted-forward position which is shown in Figure 1. In the tilted position of the cab 2 , maintenance work can be carried out on the vehicle 1, in particular on its engine. The pivot means 4 and suspension means, which are known per se, are not shown here and support the cab 2 in the driving position, are designed in such a manner that the cab 2, in the driving position, can move up and down, in a sprung manner, with respect to the chassis 3 so as to increase the comfort of the driver.

In order to tilt the cab 2 forwards and back, there is a hydraulic tilting device with a double-acting hydraulic cylinder 6 according to the invention, the piston/piston rod assembly 7 of which is connected to the cab 2 and the cylinder tube 8 of which is connected to the chassis 3. The tilting device can be used to exert a force on the cab 2 which is able to tilt the cab 2 forwards from the driving position and back again. As is known per se, the tilting device may comprise a second hydraulic tilting cylinder and, furthermore, a hydraulic pump (not shown here) which can be driven manually and/or electrically and has a reservoir for hydraulic liquid, as well as, if appropriate, one or more associated hydraulic valves for feeding pressurized hydraulic liquid to the cylinder 6 and discharging it to the reservoir.

Figure 2 shows the first exemplary embodiment of a double-acting linear hydraulic cylinder 20 according to the invention in detail. The cylinder 20 is suitable for arrangement at the location of cylinder 6 in Figure 1.

The cylinder 20 has an elongate cylinder tube 21 which is closed off at its axial ends by a cylinder base 22 and a cylinder head 23, respectively, thus delimiting a cylinder space 24. The cylinder 20 furthermore comprises a piston/piston rod assembly which can move to and fro in the axial direction inside the cylinder space 24 and has a piston 25 and a piston rod 26 which is fixedly connected thereto. The piston 25 has a round cross section and is provided with a sealing ring 27 around the outer circumference, which sealing ring bears, in a sealing manner, against the inner wall of the cylinder tube 21. As a result, the piston 25 divides the cylinder space 24 into two variable chambers, namely a head-side or pulling chamber 28 and a base-side or pushing chamber 29. The piston rod 26 projects outwards through a bore 31, which is provided with a seal 30, in the cylinder head 23 and is provided with an external attachment eyelet or the like. For ea,ch chamber 28, 29, the cylinder 20 has an associated connection 32, 33 respectively, for a hydraulic-liquid line which leads to an associated pump unit for the purpose of supplying and discharging hydraulic liquid. In order to obtain the lost-motion effect, the cylinder 20 is provided with a bypass tube 35 which is disposed in the cylinder space 24 , is arranged centrally on the cylinder base 22 and extends towards the cylinder head 23 in the a.-5ial direction of the cylinder 20. This bypass - 5 - tube 35 projects into an axial bore 36 in the piston/piston rod assembly, which bore 36 extends as far as into the piston rod 26 and is open on the side of the cylinder base 22. The piston rod 26 is provided, in the vicinity of the piston 25, with connecting bores 37 which connect the central axial bore 36 to the cylinderhead-side chamber 28 of the cylinder 20.

A seal 38 which engages in a sealing manner on the outside of the bypass tube 35 is arranged in the vicinity of the base-side end of the piston/piston rod assembly.

The bypass tube 35 has an internal bypass channel 39 and is provided, at a distance from the cylinder base 22 which amounts to a specific part of the length of the cylinder space 24, with one or more first bypass openings 40 which connect the bypass channel 39 to the outside of the bypass tube 35. At a greater distance from the cylinder base 22, the bypass channel 39 is closed off, in this case by a stop 41.

In the cylinder base 22, there is a bypass channel 42 which is connected to the bypass channel 39 in the bypass tube 35 and to one or more second bypass openings 43 which are arranged next to the bypass tube 35 in the cylinder base 22 and are in communication with the pushing chamber 29. The bypass tube 35 has a uniform external diameter along its length, the length being such that the bypass tube 35 fits into the seal 38 even in the completely extended position of the piston rod 26.

Due to the presence of the bypass tube 35 and the associated bypass openings 40, 43, there is a connection between the chambers 28 and 29 if the piston/piston rod assembly is situated in the vicinity of the cylinder base 22, with the result that a considerable volume of hydraulic liquid can be exchanged between the chambers 28, 29 via this connection. This possibility of liquid exchange remains for as long as the first bypass openings 40 open out into the blind bore 36 and consequently, via the connecting bores 37, into the pulling chamber 28. When the piston rod 26 has been extended further and the seal 38 has - 6 - moved past the first bypass openings 40, both the first and the second bypass openings 40, 43 open out into the chamber 29 and it is no longer possible for the hydraulic liquid to flow past the piston 25. Figure 3 shows a second exemplary embodiment of a double-acting linear hydraulic cylinder 50 according to the invention. The cylinder 50 is suitable for arrangement at the position of cylinder 6 in Figure 1.

The cylinder 50 has an elongate cylinder tube 51 which is closed off at its axial ends by a cylinder base 52 and a cylinder head 53, respectively, thus delimiting a cylinder space 54. The cylinder 50 furthermore comprises a piston/piston rod assembly which can move to and fro in the axial direction inside the cylinder space 54 and has a piston 55 and a piston rod 56 which is fixedly connected thereto. The piston 55 has a round cross section and is provided with a sealing ring 57 around the outer circumference, which sealing ring bears, in a sealing manner, against the inner wall of the cylinder tube 51. As a result, the piston 55 divides the cylinder space 54 into two variable chambers, namely a head-side or pulling chamber 58 and a base-side or pushing chamber 59. The piston rod 56 projects outwards through a bore 61, which is provided with a seal 60, in the cylinder head 53. For each chamber 58, 59, the cylinder 50 has an associated connection 62, 63 respectively, for a hydraulic-liquid line for supplying and discharging hydraulic liquid.

In order to obtain the lost-motion effect, the cylinder 50 is provided with a bypass tube 65 which is disposed in the cylinder space 54 and is arranged between the cylinder base 52 and the cylinder head 53, eccentrically and parallel with respect to the axis of the cylinder 50. For this purpose, the cylinder head 53 is provided with an insertion bore and the cylinder base 52 is provided with an introduction opening for the bypass tube 65, into which a stop 66 is screwed so that the tube 65 is fixed in place. This bypass tube 65 projects into an axial bore 67 which is arranged next to the piston rod 56 in the piston 55. A seal - 7 -

68 seals the gap between the bypass tube 65 and the piston 55.

The bypass tube 65 has an internal bypass channel

69 along at least part of its length and is provided, at a distance from the cylinder base 52 which amounts to a specific part of the length of the cylinder space 54, with one or more first bypass openings 70 which connect the bypass channel 69 to the outside of the bypass tube 65. The bypass channel 69 is closed off at a greater distance from the cylinder base 52.

In the vicinity of the cylinder base 52, the bypass tube 65 is provided with one or more second bypass openings 71 which are in communication with the pushing chamber 59. The bypass tube 65 has a uniform external diameter along its length. Due to the presence of the bypass tube 65 and the associated bypass openings 70, 71, there is a connection between the chambers 58 and 59 if the piston/piston rod assembly is situated in the vicinity of the cylinder base 52, with the result that a considerable volume of hydraulic liquid can be exchanged between the chambers 58, 59. This possibility of liquid exchange remains for as long as the first bypass openings 70 open out into the chamber 58. When the piston rod 56 has been extended further and the seal 68 has moved past the first bypass openings 70, both the first and the second bypass openings 70, 71 open out into the chamber 59 and it is no longer possible for the hydraulic liquid to flow past the piston 55. It will be clear that it is also possible for a plurality of bypass tubes 65 to be disposed in the cylinder space.

Figure 4 shows the preferred embodiment of a double-acting linear hydraulic cylinder 80 according to the invention in detail. The cylinder 80 is suitable to be arranged at the location of cylinder 6 in Figure 1. The cylinder 80 has an elongate cylinder tube 81 which is closed off at its axial ends by a cylinder base 82 and a cylinder head 83, respectively, thus delimiting a cylinder space 84. The cylinder 80 furthermore comprises a piston/piston rod assembly which can move to and fro in the - 8 - axial direction inside the cylinder space 84 and has a piston 85 and a piston rod 86 which is fixedly connected thereto. The piston 85 has a round cross section and is provided with a sealing ring 87 around the outer circumference, which sealing ring bears, in a sealing manner, against the smooth, cylindrical inner wall of the cylinder tube 81. As a result, the piston 85 divides the cylinder space 84 into two variable chambers, namely a head-side or pulling chamber 88 and a base-side or pushing chamber 89. The piston rod 86 projects outwards through a bore 91, which is provided with a seal 90, in the cylinder head 83.

For each chamber 88, 89, the cylinder 80 has an associated connection 92, 93 respectively, for a hydraulic-liquid line for supplying and discharging hydraulic liquid. In this design, both connections 92, 93 are arranged in the base part 82 of the cylinder 80, the connection 93 being connected directly to the chamber 89 via an internal passage 94 in the base part 82. In this case, a special tube assembly is used for the connection between the connection 92 and the chamber 88 and to obtain the lost-motion effect. This tube assembly comprises a tube 100 which is disposed in the cylinder space 84 and is arranged centrally on the cylinder base 82. The tube 100 extends towards the cylinder head 83 in the axial direction of the cylinder 80. The tube 100 projects into a central axial bore 101 in the piston/piston rod assembly, which bore 101 extends as far as into the piston rod 86. The tube 100 has a central channel 102, the bottom part of which is delimited by an inner tube 104 which is arranged coaxially in the tube 100 and has an external diameter which is smaller than the internal diameter of the tube 100, resulting in an annular bypass channel 105 between the tube 100 and the inner tube 104. At a distance from the cylinder base 82, this bypass channel 105 is closed off by closure 106.

On the base side, the central channel 102 is connected to the connection 92. One or more first bypass openings 108, which connect the bypass channel 105 to the - 9 - outside of the tube 100, are formed in the tube 100 at a distance from the cylinder base 82 which amounts to a specific part of the length of the cylinder space 84.

In the vicinity of the piston 85, the piston rod 86 is provided with one or more connecting bores 109 which connect the central axial bore 101 to the cylinder-head- side chamber 88 of the cylinder 80.

In the vicinity of the base-side end of the piston/piston rod assembly there is a seal 110 which acts in a sealing manner on the outside of the tube 100.

In the cylinder base 82 there is a bypass channel 112 which is connected to the bypass passage 105 and to one or more second bypass openings 113 which are arranged next to the tube 100 in the cylinder base 82 and are in communication with the pushing chamber 89.

The tube 100 has a uniform external diameter along its length, the length being such that the tube 100 fits into the seal 110 even in the completely extended position of the piston rod 86. In order to connect the connection 92 and the chamber 88, the tube 100 is provided with one or more openings 115 in the vicinity of the cylinder head 83 , at a position which is such that the connection 92 is always in communication, via the tube 100 and the associated opening (s) 115, with the bore 101 and therefore, via the connecting openings 109, with the chamber 88.

Due to the presence of the bypass passage 105 and the associated bypass openings 108, 113, there is a connection between the chambers 88 and 89 if the piston/piston rod assembly is situated in the vicinity of the cylinder base 82, with the result that a considerable volume of hydraulic liquid can be exchanged between the chambers 88, 89. This possibility of liquid exchange remains for as long as the first bypass openings 108 open out into the axial bore 101 and consequently, via the connecting bores 109, into the pulling chamber 88. When the piston rod 86 has been extended further and the seal 110 has moved past the first bypass openings 108, both the first and the second bypass openings 108, 113 open out into the chamber.89 and it is no longer possible for the - 10 - hydraulic liquid to flow past the piston 85.

The hydraulic drive cylinder 80 shown in Figure 4 is of very compact design, is without external bypass lines or feed lines, and has the further advantage that the two connections 92 , 93 are arranged in the cylinder base 82. It will be clear that if the piston/piston rod assembly of the cylinders described here moves towards the cylinder base during the lost-motion movement, more hydraulic liquid is forced out of the pushing chamber than it is possible to accommodate in the pulling chamber. In this regard, it is known, for example from GB-2 079 378, to provide an additional connection between the bypass passage and one of the two pump unit connections to the chambers of the cylinder, in which additional connection one or more hydraulic valves are accommodated. This connection and the associated valve or valves may, as is known, be fully integrated in the cylinder base.

Claims

- 11 - CLAIMS

1. Double-acting hydraulic cylinder comprising a cylinder tube, which is provided at its axial ends with a cylinder base and a cylinder head, respectively, thereby delimiting a cylinder space in the cilinder tube, a piston/piston rod assembly which can move to and fro in the axial direction inside the cylinder space, forms two variable chambers in the cylinder space and the piston rod of which projects outwards through an associated bore in the cylinder head, an associated connection for a hydraulic-liquid conduit being provided for each chamber, and furthermore bypass means being provided, with at least one bypass passage between a first bypass opening which is connected to the cylinder space and a second bypass opening which is connected to the cylinder space, which first and second bypass openings lie at an axial distance from one another, such that hydraulic liquid can be exchanged between the chambers in the cilinder space via the bypass passage if the first bypass opening is connected to one of these chambers and the second bypass opening is connected to the other chamber, characterized in that the bypass means comprise a bypass tube which is disposed in the cylinder space, and in that the piston/piston rod assembly is provided with an axial bore for receiving the bypass tube.

2. Cylinder according to claim 1, in which the bypass tube is fixed on the cylinder base and, from there, extends in the axial direction towards the cylinder head.

3. Cylinder according to claim 1 or 2, in which the axial bore for receiving the bypass tube is provided next to the piston rod in the piston, so that the bypass tube extends along the piston rod.

4. Cylinder according to claim 3, in which the bypass tube extends between the cylinder base and the cylinder head and is fixed thereto.

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- 14 - the cab can be tilted through an angle with respect to the chassis about a pivot axis which is defined by the pivot means, between a driving position and a tiltedforward position, and in which a drive cylinder according to one or more of the preceding claims is provided for the purpose of tilting the cab.