WO2000000378A1

WO2000000378A1 - Hydraulic tilting device for tilting a vehicle cab and vehicle provided with such a tilting device

Info

Publication number: WO2000000378A1
Application number: PCT/NL1999/000345
Authority: WO
Inventors: René Hendrikus Plechelmus SCHOLTEN; Peter Bernhard Hulzebos; Willem Herman Masseling
Original assignee: Applied Power Incorporated
Priority date: 1998-06-26
Filing date: 1999-06-03
Publication date: 2000-01-06
Also published as: AU4292699A; DE19983312T1; NL1009507C2

Abstract

Hydraulic tilting device for tilting a cab of a vehicle between a driving position and a tilted position. The tilting device has a double-action hydraulic tilting cylinder (5) for tilting the cab, having a piston/piston rod assembly (8, 9) which forms in the cylinder space (7) a pull chamber (12), which, when hydraulic fluid is fed to it, draws in the piston/piston rod assembly, and a push chamber (13), which, when hydraulic fluid is fed to it, pushes out the piston/piston rod assembly. In addition, a lost-motion duct (30) is present in the ports (31, 32) emerging in the cylinder space, which lost-motion duct interconnects the pull chamber (12) and the push chamber (10) in a lost-motion mode of the tilting device. A hydraulically operated lost-motion valve (40) has a slide body, which is displaceable between a closed position, in which the first (42) and second (43) valve ports are closed off from each other, and an open position, in which the first (42) and second (43) valve port are interconnected. The lost-motion valve is provided with a spring means (48), which pressurizes the slide body in the direction of the closed position thereof. The closing-control surface of the lost-motion valve (53) processes an OR-valve having a first (53a) and a second (53b) inlet port, which are respectively connected to the cylinder space (12) and to a line (55) extending between the push terminal (15) of the tilting cylinder and a pressure port (4) of the pump (2). The outlet port (53c) is connected to the closing-control surface (51) of the lost-motion valve (40).

Description

Hydraulic tilting device for tilting a vehicle cab and vehicle provided with such a tilting device.

The present invention relates to a hydraulic tilting device for tilting a cab of a vehicle between a driving position and a tilted position.

From the prior art, it is generally known to mount a cab of a (motor) vehicle by hinge means tiltably on the chassis of the vehicle so that the cab is tiltable between a driving position, in which the vehicle can be driven, and a tilted position, in which, for example, maintenance can be carried out on the engine lying beneath the cab. It is further generally known, for example, from GB 2 079 378, DE 42 29 842 and EP 0 101 129, to support this kind of tiltable cab in the driving position by spring means on the chassis for the comfort of the occupants, especially the driver, during travel. For tilting a spring-mounted cab of this kind, hydraulic tilting devices are known having one or more tilting cylinders which are mounted between the chassis and the tiltable cab. In order to prevent the tilting cylinder (s) from disturbing the movement of the cab in the driving position relative to the chassis, the cab-tilting device in such a vehicle has a "lost-motion mode". Included amongst this type of tilting device are the tilting devices described in GB 2 079 378 and DE 42 29 842. These known tilting devices have common to them that they comprise components named in the identical preamble of claims 1 and 2.

In the lost-motion mode of these known tilting devices, the pump is inactive and the piston is between the two ports of the lost-motion duct. If now a movement of the cab during travel causes the piston rod to extend, then hydraulic fluid will flow via the lost-motion duct from the pull chamber to the push chamber. If the piston rod is pressed in as a result of a movement of the cab, the hydraulic fluid is delivered to the reservoir, since the hydraulic pressure in the push chamber acts upon the opening-control surface of the lost-motion valve and then displaces the slide body thereof counter to the spring force into the opened position. The object of these known tilting devices is therefore that the piston/piston rod assembly, within a range defined by the ports of the lost- motion duct, should be able to slide in and out virtually unhindered.

In practice, the above named tilting devices known from GB 2 079 378 and DE 42 29 842 prove to have the drawback that the lost-motion movement of the piston/piston rod assembly does still produce an unwelcome disturbance of the movement of the cab.

The present invention aims to eliminate the abovementioned drawback, so that in the lost-motion mode of the tilting device the tilting cylinder (s) can repeatedly slide smoothly in and out. The present invention further aims to make sure that if the piston/piston rod assembly is slid out beyond the "lost-motion range", a reliable "hold- function" is obtained, that is to say that the tilting cylinder is secured against unwelcome sliding-in, for example if the pump is stopped in a position of the cab which is not tilted fully forwards and the cab then rests upon the tilting cylinder (s) .

The present invention achieves these objects by providing tilting devices according to claims 1 and 2.

The tilting devices according to claims 1 and 2 are based upon the following common insight. In the tilting devices known from GB 2 079 378 and DE 42 29 842, it is exclusively the spring pressing against the slide body of the lost-motion valve which, in a number of commonly occurring situations, forces the slide body into the closed position and holds it in this closed position so that the lost-motion valve is and remains closed. In order to ensure that the lost-motion valve remains closed in these cases, the slide body has to be forced into the closed position with a specific minimum closing force. In the known tilting devices, this requires that the spring of the lost-motion valve shall be of stiff construction, i.e. having a high spring constant . A stiff construction of this spring has proved to have the drawback however that in the lost-motion mode of these tilting devices a considerable pressure has to be applied to the opening-control surface of the slide body in order to open the lost-motion valve counter to the force of the stiff spring. The result of this is that in lost-motion mode the lost-motion valve opens only under a considerable hydraulic pressure, which hinders the movement of the piston/piston rod assembly and thus disturbs the movement of the spring-mounted cab connected thereto . At the same time, the stiff spring means that the pressure in the cylinder space during the lost-motion mode always remains at an undesirably high level, which likewise hinders the lost-motion movement.

The invention, as described in claims 1 and 2, provides measures whereby the spring which forces the slide body into its closed position can be constructed considerably less stiff than in the known tilting devices. The solutions according to claims 1 and 2 are commonly based upon increasing, relative to the known tilting devices, the hydraulic force which forces the slide body into its closed position. A weaker, less stiff spring or similar spring means is thereby admissible in the lost- motion valve without the closing force necessary in specific situations, by which the slide body is held in its closed position, being adversely diminished.

Advantageous embodiments of the tilting device according to the invention will be described below with reference to the drawing, in which

Fig. 1 shows the hydraulic diagram of a first illustrative embodiment of the tilting device according to the invention,

Fig. 2 shows in longitudinal cross section a preferred embodiment of the lost-motion valve which can be used in the diagram of Figure 1, Fig. 3 shows the hydraulic diagram of a second illustrative embodiment of the tilting device according to the invention, and

Fig. 4 shows in longitudinal cross section a preferred embodiment of the lost-motion valve which can be used in the diagram of Figure 3.

The hydraulic tilting devices shown in the drawing are designed to tilt the driver's cab of a vehicle, especially of a lorry. Such cabs are conventionally fitted to the chassis of the vehicle and are tiltably connected by hinge means to the chassis. The hinge means are constructed such that the cab can be tilted between a driving position, in which the vehicle can be driven, and a tilted position, generally forwards, in which, for example, maintenance can be carried out on the vehicle, especially on its engine located wholly or partially beneath the cab.

Such vehicles are further conventionally provided with cab support means, which support the cab in the driving position such that the cab in the driving position can perform a motion up and down relative to the chassis in order to increase the comfort of the driver.

To tilt the cab forwards and back again, a hydraulic tilting device is provided.

Figure 1 shows diagrammatically a hydraulic tilting device of this kind. This tilting device comprises a reservoir 1 for hydraulic fluid and a preferably electrically driven pump 2 with reversible pump direction, which pump 2 has a first port 3 and a second port 4. Depending on the direction of rotation of the drive motor, the one port is a suction port for the intake of fluid and the other port a pressure port for delivering fluid under pressure .

Figure 1 further shows a double-action linear hydraulic tilting cylinder 5 for tilting the vehicle cab (not shown) . The cylinder 5 comprises a cylinder housing 6 incorporating a cylinder space 7 in which a piston/piston rod assembly can be moved to and fro. The piston/piston rod assembly comprises a piston 8 and a piston rod 9 fixedly connected thereto. Around the piston 8 lies a sealing ring 10, whilst the piston rod 9 projects outwards from the cylinder housing 6 through a seal 11. The cylinder 5 is conventionally mounted between the cab and the chassis of the vehicle, the cylinder housing 6 generally being pivotably connected to the chassis and the end of the piston rod 9 generally being pivotably connected to the cab.

The piston/piston rod assembly forms in the cylinder space 7 a pull chamber 12, which, when hydraulic fluid is fed to it, draws in the piston/piston rod assembly, and a push chamber 13, which, when hydraulic fluid is fed to it, pushes out the piston/piston rod assembly. For the pull chamber 12 and the push chamber 13, an associated pull terminal 14 and push terminal 15 are respectively provided.

The pull terminal 14 is connected by a first hydraulic line 16 to the first port 3 of the pump 2. In the first line 16 there are accommodated two non-return valves 17, 18, which work in the opposite direction and are placed in parallel and which together form a suction-blocking device to prevent unhindered intake of fluid through the line 16.

The push terminal 15 is connected by a second hydraulic line 20 to the second port 4 of the pump 2. In the second line 20 there is accommodated a non-return valve

21, which closes in the direction of the pump 2. The nonreturn valve 21 is of the hydraulically operated type and can be opened by means of a control signal, this here being realized by hydraulic control line 22, which transmits the pressure obtaining in the first line 16 to a control surface of the non-return valve 21.

The reservoir 1 is connected by a suction shuttle valve 24 both to the first line 16 and to the second line 20. The suction shuttle valve 24 has a bore having at each end thereof a seat for an associated close-off member, in this case a ball, the bore accommodating a spacer, the effect of which is that only one of the close-off members fits in its seat and the other close-off member is thus forced from its seat. The spacer fits with clearance in the bore, so that the reservoir 1 is always connected to the first line 16 or the second line 20 by a line 25 which emerges in the bore .

In order to prevent excessively high pressure of the fluid in the hydraulic circuit, excess pressure valves 27 and 28 are provided, which are placed respectively between the first line 16 and the reservoir 1 and the second line 20 and the reservoir 1.

The tilting device additionally comprises a lost- motion duct 30 having two ports emerging in the cylinder space 7, denoted by 31 and 32 respectively, the port 31 coinciding in this example with the push terminal 15 of the cylinder 5.

The lost-motion duct 30 is represented diagrammatically in Figure 1 and can be constructed in various ways. For instance, it is possible for the lost- motion duct 30 to be formed by a lost-motion line lying outside along the cylinder housing 6. It is also however conceivable for the lost-motion duct to be fitted in the cylinder housing 6. In yet another variant, the lost-motion duct 30 is fitted in a pipe directed up from the bottom of the cylinder housing 6 into the cylinder space.

The lost-motion duct 30 connects the pull chamber 12 to the push chamber 13 if the piston 8 is between the two ports 31, 32 of the duct 30, which is the case whenever the piston/piston rod assembly is in a position pertaining to the driving position of the cab. Whilst the vehicle is driven, the pump 2 is inactive and the tilting device functions in its "lost-motion mode". In the lost-motion duct 30 there is a non-return valve 33, which closes in the direction of he port 32, which port 32, in the lost-motion mode of the tilting device, emerges in the pull chamber 12.

The shown hydraulic tilting device further comprises a hydraulically operated lost-motion valve 40 of the two-way/dual-position 2/2 type, an illustrative embodiment of which valve 40 is shown in Figure 2. This lost-motion valve 40 has a housing 41 having a first valve port 42, which is connected to the push chamber 13 of the cylinder 5, and a second valve port 43, which, at least in the lost-motion mode, is connected to the reservoir 1. The lost-motion valve 40 further has a slide body 44, which can be moved to and fro in a bore in the housing 41. The slide body 44 is displaceable between a closed position shown in Figure 2, in which an axial end of the slide body 44 bears in sealing manner against a seat 45 in the connection between the first valve port 42 and second valve port 43, and an opened position, in which the slide body 44 is located at a distance from the seat 45, and the first valve port 42 and the second valve port 43 are interconnected. In Figure 2, it is apparent that a fluid pressure obtaining at the first valve port 42 acts upon an opening-control surface 46 of the slide body 44 even when the valve 40 is in the closed position, so that a hydraulic pressure in the push chamber 13 acts upon the opening-control surface 46 so as to force the slide body 44 into the opened position. In the diagram of Figure 1, this is represented by a control- pressure line 47.

That side of the slide body 44 which lies opposite the opening-control surface 46 is acted upon by a light biassing spring 48, which urges the slide body 44 in the direction of its closed position. That side of the slide body 44 which faces away from the seat 45 further forms a closing-control surface 50. The housing 41 is provided with a control line terminal 51, to which a control line 52 connects which control line is connected to the closing- control surface 50. The control line 52 connects to an outlet 53c of an OR-valve 53, also referred to as a shuttle valve. This OR-valve 53 has a first inlet 53a, which connects to a control line 54 connected to that part of the lost-motion line 30 connecting to the port 32. The OR-valve 53 further has a second inlet 53b, which connects to a control line 55 which in turn connects to the second hydraulic pressure line 20. The working of the tilting device now described is as follows. In order to push out the piston rod 9 from the position shown in Figure 1 and hence tilt the cab forwards, hydraulic fluid is fed via the port 4 and the second line 20 to the push chamber 13. The non-return valve 33 hereupon closes off the lost-motion line 30. At the same time the lost-motion valve 40 remains closed, because the hydraulic pressure upon the closing-control surface 50, together with a slight loading of the spring 48, is stronger than the hydraulic pressure upon the opening-control surface 46, which opening-control surface 46 is smaller than the closing-control surface 50.

When, during forward-tilting of the cab, the operation is stopped and the cab, under the influence of its own weight, threatens to tilt back again into the driving position, then the non-return valve 21 closes. If the piston 8 is above the port 32 at the moment of stopping, the valve 40 also remains closed, because then the hydraulic pressure in the push chamber 13 acts via the control line 54 and shuttle valve 53 upon the closing- control surface 50 of the slide body 44. In this way, the slide body 44 is pressed firmly against the seat 45 and the piston/piston rod assembly is held reliably in place, which is of great importance to the safety of the persons who then make their way beneath the cab or are present there . When the cab has to be tilted from the tilted position into the driving position, and hence the piston rod 9 has to be retracted, fluid is fed via the first port 3 to the pull chamber 12. The pressure in the first line 16 causes the non-return valve 21 to open and allows fluid to flow out of the push chamber 13. If the return tilting is interrupted in a position in which the piston 8 is above the port 32, the pressure in the lost-motion line, which acts via the line 52 upon the body 44 of the lost-motion valve 40, keeps the valve 40 closed. At the same time, the valve 21 closes, so that the cab then remains stationary. If, when the cab is being tilted back into the driving position, the piston 8 has already passed the port 32, then the pressure in the part of the lost-motion duct 30 between the valve 33 and port 32 drops. Consequently the pressure in line 52 also drops and the lost-motion valve 40 is opened by the pressure obtaining in line 47. The fluid is thereby able to flow out of the push chamber 13 into the reservoir 1 and the cab can also tilt back unhindered into the driving position, an orifice possibly being provided to limit the speed of the movement of the cab. This "free" tilting movement of the cab is in many cases desirable in order to allow the cab to lock with one or more cab locking devices which are fitted to the chassis and secure the cab in the driving position. For the mutual engagement of the cab and such locking devices, a relatively fast tilting movement of the cab is advantageous .

When the cab is in the driving position and the tilting device is brought into the lost-motion mode, which here simply means that the pump 2 is switched off, then the working of the device shown in Figure 1 is as follows.

Whenever the cab makes a movement such that the piston rod 9 is drawn out of the cylinder housing 6, then fluid flows via the port 32 out of the pull chamber 12 and then makes its way via the line 30 through the opening nonreturn valve 33 into the push chamber 13. The lost-motion valve 40 hereupon remains closed.

Whenever the cab moves such that the piston rod 9 is forced into the cylinder housing 6, then fluid flows out of the push chamber 13 via the opened valve 40 to the reservoir 1. The lost-motion valve 40 opens in this situation, since a hydraulic pressure is applied via the control-pressure line 47 to the control-pressure-opening surface 46 of the slide body 44. At the same instant, there is no hydraulic pressure acting upon the closing surface 50, so that the opening of the lost-motion valve 40 is resisted only by the light spring 48.

The hydraulic diagram according to Figure 1 here described differs from the diagram shown in GB 2 079 378 especially in that connected to the terminal 51 of the valve 40, which terminal 51 is connected to the closing surface 50 of the valve 40, there is not only the lost- motion duct 30 but at the same time, via the intermediate OR-valve 53, also the line 20, which connects the pump 2 to the push chamber 13 of the cylinder 5. This additional hydraulic operation in the closing direction of the lost- motion valve 40, such as is proposed by the present invention, enables the spring 48 of this lost-motion valve 40 to be considerably weaker than in the lost-motion valve in the diagram of GB 2 079 378. The fact that the spring 48 can be a light spring means that the lost-motion valve 40 will easily open in the lost-motion mode of the device, so that the cylinder 5 disturbs the spring movement of the cab, and hence the comfort of the occupants, as little as possible. At the same time, the light spring 48 has the effect that the pressure in the cylinder 5 during the lost- motion mode is low, which is advantageous for a smooth continuous movement of the piston/piston rod assembly.

In Figure 2 it is further apparent that the slide body 44 of the lost-motion valve 40 is of stepped construction and has a larger outer diameter on the side of the closing surface 50 than on the side of the opening surface 46, the slide body 44 having an annular shoulder face 49 at the transition of the larger diameter to the smaller diameter. The bore in the housing 41 is also of stepped construction, having a smaller diameter on the side of the seat 45, into which the smaller-diameter part of the slide body 44 fits in sliding arrangement, and having a part of larger diameter, into which the larger-diameter part of the slide body fits in sliding arrangement. Both the smaller-diameter part and the larger-diameter part of the slide body 44 are provided with a sealing ring, 58 and 59 respectively, which seal against the bore in the housing 41.

The object of the measure to construct the slide body 44 with a stepped outer diameter, as is described above, is to increase the hydraulic force, which keeps the slide body 44 in its closed position, relative to conventional valves of this type, in which the slide body has the same diameter on the opening side and the closing side. By increasing the hydraulic closing force in this way, the spring 48 can once again be lighter, slacker than had been achieved with the previously described measure. As stated, that has a favourable effect upon the lost-motion behaviour of the cylinder 5 and hence upon the suspension of the cab.

Since a small quantity of fluid can make its way along the seals 58, 59, in the housing 41 of this lost- motion valve 40 an additional duct 60 is provided, which has a mouth 62 close to the shoulder face 61 of the bore for the slide body 44. The duct 60 is connected to the reservoir 1, so that no fluid can collect in the space between the shoulder faces of the bore and of the slide body 44. Any such accumulation of fluid would disturb the movement of the slide body 44. In place of the duct 60, an internal duct can also be provided in the slide body 44, extending between point 60a in Figure 2, which is connected to the terminal 43, and a point 60b close to the shoulder 49.

In a variant (not shown) of the diagram of Figure 1, the non-return valves 17 and 18 in the first line 16 are replaced by a hydraulically operated non-return valve, which just like the valve 21, closes in the direction of the pump. The control line of this non-return valve connects in this case to the second line 20.

In another variant of the diagram of Figure 1, between the port 43 of the lost-motion valve 40 and the reservoir 1 there is a non-return valve, which closes in the direction of the lost-motion valve 40 in order to prevent an unwelcome intake of hydraulic fluid.

In yet another variant, the lost-motion duct 30 runs via the OR-valve 53, which means that in the diagram of Figure 1 the non-return valve 33 connects on its seat side to the line 52 leading to the OR-valve 53. This variant can be realized in constructionally simple manner in a valve block. It will be evident that the OR-valve 53 can be designed in a number of ways known to the person skilled in the art to acquire the working described above.

The tilting device shown as a hydraulic diagram in Figure 3 is substantially the same as the diagram according to Figure 1 of DE 42 29 842 and additionally comprises a large number of components which have already been explained with reference to Figure 1 of the present application. In Figure 3, those components which conform to the components of Figure 1 are denoted by the same reference numeral and these will receive no further explanation.

In place of the reversible pump 2, a one- directional pump 65 is now provided, having a pressure port 66. A return line 67 to the reservoir 1 is additionally provided. An operable dual-position control valve 68 serves optionally to connect the pressure port 66 and the return line 67 to the first line 16 leading to the pull terminal 14 and to the second line 20 leading to the push terminal 15.

In Figure 3, a lost-motion valve 70 is further apparent, which is shown in detail in Figure 4. Just like the lost-motion valve 40, the lost-motion valve 70 is a hydraulically operated valve of the two-way/dual-position type, or 2/2 type. The lost-motion valve 70 is accommodated in the second line 20 between the valve 68 and the push terminal 15 of the push chamber 13 of the cylinder 5. The lost-motion valve 70 has a housing 71 having a first valve port 72, which is connected to the push chamber 13 of the cylinder 5, and a second valve port 73, which is connected to a port of the valve 68. The lost-motion valve 70 further has a slide body 74, which can be moved to and fro in first bore in the housing 71 and which is displaceable between a closed position shown in Figure 4, in which an axial end of the slide body 74 bears in sealing arrangement against a seat 75 in the connection between the first valve port 72 and second valve port 73, and an open position, in which the slide body 74 is located at a distance from the seat 75. The valve 70 further has a first control-pressure ter- minal 76 for a control line 77, which is connected to the first hydraulic line 16 between the valve 68 and the pull terminal 14. In the housing 71, a second bore 78 is present in the extension of the first bore, having a control piston 79 which is displaceable to and fro therein and which on one side is pressurized by the hydraulic pressure at the control-pressure terminal 76. The control-pressure piston 79 is constructed such that if the pump 2 feeds fluid to the first line 16, the slide body 74 is forced from its seat 75. In Figure 4, it is further apparent that a fluid pressure obtaining at the first valve port 72 acts upon an opening-control surface 80 of the slide body 74 even when the lost-motion valve 70 is in the closed position, so that a hydraulic pressure in the push chamber 13 acts upon the opening-control surface 80 so as to force the slide body 74 into the opened position. This is represented in the diagram of Figure 3 by the control-pressure line 81. The opening-control surface 80 is formed by that part of the conical point of the slide body 74 which is located in the bore. In addition, this point can also be provided with a ball, which can lie in sealing arrangement against the seat 75.

Just as in Figure 2, the slide body 74 of the lost- motion valve 70 is of stepped construction, likewise the associated first bore. The slide body 74 thereby has a smaller diameter on the side of the seat 75 than on the opposite side having an annular shoulder face 83 which forms the transition. The first bore is constructed in accordance with a shoulder face 84 between the parts of differing diameter. In the housing 71 a connecting duct 85 is formed, which connects to the terminal 73 and emerges in the first bore close to the shoulder face 84. This connecting duct 85 has the effect that if the pump 65 is active and is delivering fluid to the line 20, this hydraulic pressure acts both upon the surface of the slide body 74 covering the opening of the seat 75 and upon the annular shoulder face 83 of the slide body 74. This is represented diagrammatically in Figure 3 by the control line 87.

That side of the slide body 74 lying opposite the opening-control surface 80 is acted upon by a light biassing spring 88, which urges the slide body 74 in the direction of the closed position thereof. Furthermore, that side of the slide body 74 facing away from the seat 75 forms a closing-control surface 89. The housing 71 is provided with a control- line terminal 90, to which a control line 91 connects which control line is connected to the closing-control surface 89. The control line 91 connects to the lost-motion line 30.

In Figure 4, it is additionally apparent that the slide body 74 is provided with a continuous bore 92, which extends between the closing-control surface 89 and the opening-control surface 80 of the slide body 74. The non- return valve 33 is placed in this bore 92.

An important difference between the device shown by way of Figures 3 and 4 and the device which is known from DE 42 29 842 lies in the stepped construction of the slide body 74 of the lost-motion valve 70, which slide body, in the known device, has the same diameter on both sides. The stepped construction of the slide body 74 means that the closing-control surface 89 is considerably larger in relation to the opening-control surface 80 than is the case with the known lost-motion valve. The spring 88 can consequently be considerably weaker than in the known lost- motion valve, which has those advantages for the lost- motion working of the cylinder 5 which have already described with reference to Figure 2. Furthermore, the presence of the connecting duct 85 has the effect that the valve 70, despite the extra large hydraulic force upon the slide body 74 in the closing direction, opens easily if the pump 2, via the line 20, delivers fluid under pressure. In a variant of the device according to Figure 3, an anti- intake device, just like the valves 17 and 18 in Figure 1, is accommodated at reference numeral 22.

It will be evident that the measure to construct the slide body of the lost-motion valve in stepped design is also advantageous in respect of the tilting device shown in GB 2 079 378, so that in this case also a light spring can suffice fcr the slide body.

Claims

1. Hydraulic tilting device for tilting a cab of a vehicle between a driving position and a tilted position, which tilting device comprises:

- a reservoir (1) for hydraulic fluid, - a pump (2) having at least one pressure port (3, 4) for delivering hydraulic fluid under pressure,

- a double-action hydraulic tilting cylinder (5) for tilting the cab, comprising a cylinder housing (6) incorporating a cylinder space (7) in which a piston/piston rod assembly (8, 9) can be moved to and fro, the piston rod (9) of which projects outwards from the cylinder housing, which piston/piston rod assembly forms in the cylinder space a pull chamber (12) , which, when hydraulic fluid is fed to it, draws in the piston/piston rod assembly, and a push chamber (13) , which, when hydraulic fluid is fed to it, pushes out the piston/piston rod assembly, for the pull chamber and the push chamber an associated pull terminal and push terminal (14, 15) respectively being provided, which can be optionally connected to the pressure port of the pump and to the reservoir, and a lost-motion duct (30) further being provided, having ports (31, 32) emerging in the cylinder space, which lost-motion duct (30) interconnects the pull chamber (12) and the push chamber (13) in a lost-motion mode of the tilting device, in which the piston/piston rod assembly is in a position pertaining to the driving position of the cab,

- a hydraulically operated lost-motion valve (40) , which valve (40) has a first valve port (42) , which is connected to the push chamber (13) , a second valve port (43) , which, at least in the lost-motion mode, is connected to the reservoir, and a slide body (44) , which is displaceable between a closed position in which the first and second valve port (42, 43) are closed off from each other and an open position in which the first and second valve port (42, 43) are interconnected, the lost-motion valve (40) being provided with a spring means (48) , which pressurizes the slide body (44) in the direction of the closed position thereof, and the slide body (44) possessing an opening- control surface (46) , which is connected to the push chamber (13) , so that a hydraulic pressure in the push chamber acts upon the opening-control surface to force the slide body into the open position, and a closing-control surface (50) , which is connected to the cylinder space (7) , so that a hydraulic pressure in the cylinder space (7) acts upon the closing-control surface to force the slide body into the closed position, characterized in that an OR-valve (53) pertaining to the closing-control surface (50) of the lost-motion valve (40) is provided with a first and a second inlet port (53a, 53b) , which are respectively connected to the cylinder space and to a line (20) extending between the push terminal of the tilting cylinder and a pressure port of the pump, which OR-valve has an outlet port (53c) , which is connected to the closing- control surface (50) of the lost-motion valve.

2. Hydraulic tilting device for tilting a cab of a vehicle between a driving position and a tilted position, which tilting device comprises:

- a reservoir (1) for hydraulic fluid,

- a pump (2,-65) having at least one pressure port (3, 4,-66) for delivering hydraulic fluid under pressure,

- a double-action hydraulic tilting cylinder (5) for tilting the cab, comprising a cylinder housing (6) incorporating a cylinder space (7) in which a piston/piston rod assembly (8, 9) can be moved to and fro, the piston rod (9) of which projects outwards from the cylinder housing, which piston/piston rod assembly forms in the cylinder space a pull chamber (12) , which, when hydraulic fluid is fed to it, draws in the piston/piston rod assembly, and a push chamber (13) , which, when hydraulic fluid is fed to it, pushes out the piston/piston rod assembly, for the pull chamber and the pressure chamber an associated pull terminal and push terminal (14, 15) respectively being provided, which can be optionally connected to the pressure port of the pump and to the reservoir, and a lost-motion duct (30) further being provided, having ports (31, 32) emerging in the cylinder space, which lost-motion duct (30) interconnects the pull chamber (12) and the push chamber (13) in a lost-motion mode of the tilting device, in which the piston/piston rod assembly is in a position pertaining to the driving position of the cab,

- a hydraulically operated lost-motion valve (40;70), which valve (40;70) has a first valve port (42; 72), which is connected to the push chamber (13) , a second valve port (43;73), which, at least in the lost-motion mode, is connected to the reservoir, and a slide body (44;74), which is displaceable between a closed position in which the first and second valve port (42 , 43 ; 72 , 73) are closed off from each other and an open position in which the first and second valve port (42 , 43 ; 72 , 73) are interconnected, the lost-motion valve (40; 70) being provided with a spring means (48;88), which pressurizes the slide body (44;74) in the direction of the closed position thereof, and the slide body (44; 74) possessing an opening-control surface, which is connected to the push chamber (13), so that a hydraulic pressure in the push chamber acts upon the opening-control surface to force the slide body into the open position, and a closing-control surface (89) , which is connected to the cylinder space (7) , so that a hydraulic pressure in the cylinder space (7) acts upon the closing-control surface to force the slide body into the closed position, characterized in that the slide body (44,-74) is of stepped construction, having a first part boasting a first outer diameter on the side of the closing-control surface (50; 89) and a second part boasting a second outer diameter on the side of the opening-control surface (46;80), the first outer diameter being larger than the second outer diameter.

3. Device according to claim 2, in which the slide body (44; 74) has an annular shoulder face (49; 83) at the transition of the first part to the second part.

4. Device according to claims 1 and 2.

5. Device according to claim 4, in which the housing (41) of the lost-motion valve (40) is provided with an additional terminal (60) , which has a mouth (62) close to a shoulder face (61) of the bore for the slide body (44) and which, at least in the lost-motion mode, is connected to the reservoir (1) .

6. Vehicle comprising a tiltable cab, a chassis and hinge means which connect the cab to the chassis, in which the cab is tiltable through an angle relative to the chassis, about a hinge axis defined by the hinge means, between a driving position and a tilted position, and in which a hydraulic tilting device according to one or more of the preceding claims is provided for tilting the cab.

7. In combination a vehicle comprising a tiltable cab, a chassis and hinge means which connect the cab to the chassis, in which the cab is tiltable through an angle relative to the chassis, about a hinge axis defined by the hinge means, between a driving position and a tilted position, said combinatie further comprising a hydraulic tilting device according to one or more of the preceding claims for tilting the cab.