TECHNICAL FIELD OF THE INVENTION

The invention relates to a hydraulic device comprising a piston and a cylinder for a vehicle. The device is suitable to be used in heavy vehicles, e.g a lorry or the like, and may be used for connecting a chassis or frame of the vehicle with a cab for carrying out

tilting of the cab or to function as hydraulic dampers.

In particular, the invention is suitable for a vehicle comprising a chassis which supports a cab where the cab is intended, in the event of collision from the front, to be displaced backward. BACKGROUND OF THE INVENTION

For the purpose of reducing the force stress for driver and passenger (s) and for the purpose of reducing the aggressiveness of the vehicle in relation to external objects in the event of collision, use is made of

deformation structures. Deformation structure means a structure which is intended to be deformed at a given load when exposed to an impulse, for example generated by a collision. Deformation structures are used in

order to make rigid structures softer from a collision aspect and where appropriate in order to separate two elements fastened to one another at a given force. This invention relates to a deformation structure which is intended to separate two elements fastened to one

another at a given force.

JP 0828346 discloses an example of a vehicle comprising a deformation structure which is used in a tiltable

driver cab. The vehicle comprises a cab which is supported by a frame via an upper bracket which is fastened to the cab and is connected rotatably to a lower bracket fastened to the frame. The lower bracket has a break indication and the cab is freed from the frame during a collision and the cab may move rearwards until the bracket reaches a stop element a stop

element. However, the cab is completely disconnected at the attachment of the upper and lower brackets.

Still another deformation structure for a tiltable cab is described in WO 03 / 101 809. The vehicle described therein comprises in a conventional manner a chassis and a cab which is supported on said chassis and at its lower end has a bearing plate which is fastened to a cab bracket. Cab bracket means a bracket which supports the cab. The cab bracket is arranged with a swivel joint. The cab bracket and the bearing plate are anchored to one another via, in the direction of the vehicle, a front rigid joint and at least one rear deformable joint, said cab being intended, in the event of collision in the direction from the front, to be displaced backward while rotation of the cab bracket around its swivel joint and deformation of the at least one rear deformable joint take place. The rear

deformable joint comprises a bolt which is fastened to said bracket and passes through a lead-through arranged in a deformable area of said bearing plate, where the geometry of the lead-through is such that it fixes said bolt in a radial direction at right angles to a

longitudinal axis through the bolt, where said bolt has a projection, in the form of a head, washer or nut, which bears against said deformable area of the plate for fixing the plate in the axial direction. The breakage of the desired attachments will allow the cab to move relatively the frame due to the overall

construction of the frame and cab connection while the rigid attachment will remain intact and avoid an undesired, total release of the cab from the bearing plate.

Even though the structures disclosed in WO 03 / 101 809 provides an efficient impact absorbing function there is still a desire of an improved collision energy absorbing structure providing an improved energy absorption while still controlling the relative

movement of the cab and frame structure in the case of a collision.

DESCRIPTION OF THE INVENTION

An object of the invention is to provide a device which reduces force stresses in the event of an accident related to equipment or machinery comprising a

hydraulic device. The device may for example be used for improved impact energy absorbing properties in vehicles and the device is intended to allow an

efficient absorption of impact energy in the event of a collision in a controlled manner. The invention is in particular suitable for a vehicle comprising a tiltable cab and having a deformable joint between the cab and the frame and another hydraulic connection between the cab and the frame which may be modified in a simple way in order to obtain the intended impact energy absorbing characteristics .

The above stated objects may be achieved by a hydraulic device according to claim 1 wherein a hydraulic device is described. The hydraulic device comprises a cylinder and a piston fitted at least partly in the cylinder. The piston is arranged to be able to move back and forth in the cylinder such that the overall length of the hydraulic device, comprising the cylinder and piston, may be varied. The piston comprises a piston rod and a piston disc. The piston disc divides the cylinder in the longitudinal extension in a first chamber and a second chamber. By increasing

respectively decreasing the volumes of these chambers by supplying respectively withdrawing hydraulic liquid to and from the chambers it is possible to control the movement of the piston in the cylinder and thus the length of the hydraulic device. In the case of the present hydraulic device will an increase of the volume in the first chamber of the cylinder, which corresponds to the space located at the distal end beyond the piston and the piston disc, and a corresponding

decrease of the volume of the second chamber, through which the piston extends, imply an extension of the overall length of the hydraulic device by pushing the piston rod such that a longer part of the piston is extending out of the cylinder while a decrease of the volume in the first chamber and an accordingly increase of the volume of the second chamber corresponds to a pulling of the piston rod into the cylinder such that the part of the piston extending out of the cylinder is shortened. The control of the position of the piston rod is made by controlling the flow of hydraulic liquid to and from the first and second chambers. The

hydraulic device is arranged with at least a first inlet opening in the first chamber to which hydraulic liquid may flow via a first, push pipe and to a second inlet opening in the second chamber via a second, pull pipe. Hence, the hydraulic device serving as the basic hydraulic element for the present invention is intended to be an ordinary hydraulic cylinder which may be controlled by the flow of hydraulic liquid to retract respectively to extend. In addition to the features of the hydraulic device described above is the device according to the invention provided with an instant pressure relief arrangement. The arrangement is intended to react to an external force above a certain limit acting to extend or retract the piston rod or some other parts indicating the need of a pressure relief. The pressure relief arrangement may for example either be directly influenced by a sudden change of the pressure or a certain pressure value in the hydraulic device and thus be actuated directly by this pressure change or pressure, to be actuated by a triggering signal indicating the need of instant pressure relief in the hydraulic device or to be directly influenced by a relative movement of the parts connected by the hydraulic device. Such a signal may be triggered by some kind of safety system for the system comprising the hydraulic device indicating the need or desire of relieving the pressure instantly so as to allow the piston and cylinder to move essentially without any hydraulic forces acting to keep them in a specific position relatively each other.

In case the pressure is acting directly as the

triggering function for the pressure relief safety mechanism, the pressure may be chosen as desired.

However, the pressure should of course be chosen such that no other part of the hydraulic device is deformed or breaks before the pressure relief mechanism or be chosen so low that the pressure release mechanism will be released during ordinary use of the device. The piston disc of the hydraulic device may be adapted to break or rupture when subjected to a certain

pressure or a sudden pressure impulse. The breakage of the piston disc will allow the hydraulic liquid to pass easily between the first and second chambers and there will be essentially no force acting to keep the piston in a certain position. The piston may thus move more or less freely relatively the cylinder. An advantage with this arrangement is that there is no leakage of

hydraulic liquid out of the cylinder. Hence, there will be a relief of the pressure from the hydraulic forces keeping the piston rod in its position and the freed piston rod may move easily.

Another way of providing the hydraulic device with a pressure relief mechanism is to provide the first, push pipe and /or the second, pull pipe with a pressure release arrangement such that there is a controlled breakage of the first, push pipe and /or the second, pull pipe as a direct consequence of an increased pressure in the pipe or pipes or triggered by some safety mechanism. Hence, it will be possible to control where the pipe will leak and the hydraulic liquid will be drained at a known location such that the liquid may be taken care of in an appropriate way. A pressure relief of the first, push pipe by breakage of the pipe will allow the piston rod to easily move into the cylinder and a correspondingly breakage of the second, pull pipe will allow the piston rod to be extended further with low resistance forces.

The hydraulic device may be provided with a pressure release valve located in the first, push pipe and/or the second, pull pipe in order to provide a pressure relief of the hydraulic device. By relieving the pressure of the first, push pipe there will be a low resistance for retraction of said piston rod, i.e. the piston may easily move in a direction into the

cylinder, while the activation of a pressure relief valve in the second, pull pipe will allow the piston to easily be further exetended with no or low hydraulic forces working to counteract such an extension.

As is evident, all the above described pressure relief mechanisms of the hydraulic device may be actuated directly in response to an increased pressure or a pressure impulse in the hydraulic device. Hence, it is the pressure increase or pressure pulse which directly influence the pressure relief mechanism.

The pressure relief mechanism in the hydraulic devices may also be actuated by a signal indicating the need of instant pressure relief. Still another possible way of actuating the pressure relief mechanism may be a mechanical arrangement which effects a force upon a desired part of the hydraulic system as consequence of large forces causing a change of the overall

configuration of the structure in which the hydraulic device is a part.

The hydraulic device may form part of a hydraulic system of a vehicle and may for example be used as hydraulic suspensions or an actuator for tilting or lifting desired parts of the vehicle.

The hydraulic device may be located on a vehicle comprising a chassis and a cab supported on said chassis wherein said hydraulic device forms a first connection between said cab and said chassis. In this case, the vehicle may further comprise a second

connection between said chassis and cab which is adapted to deform in the event of a collision in the direction from the front so as to allow the cab to move relatively said chassis in a direction towards the rear end of the chassis. These connections may be arranged such that said second connection is able to pivot and said first connection formed by said hydraulic device is adapted to raise and lower said cab relatively said chassis such that said first and second connections together form a tilting structure for the cab

relatively said chassis. The hydraulic device described herein may for example be a part of the cab tilting arrangement described in WO 03 / 101 809, e.g. the use of the hydraulic device for the hydraulic tilting of a cab arranged on a chassis.

In case a vehicle is provided with a hydraulic device comprising a pressure relief arrangement, and the vehicle is provided with crash detecting arrangement intended to detect a crash situation, the pressure relief arrangement may be connected to the crash detecting arrangement and using relevant data from the crash detecting arrangement to trigger an actuator of the pressure relief arrangement. In case it is a vehicle having a chassis and cab connected to the chassis by a first hydraulic device as described herein and a second connection adapted to deform in the event of crash, said pressure relief arrangement in said hydraulic device could be arranged to be triggered by deformation of the second connection between the cab and the chassis. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 Describes a hydraulic device suitable for the invention Fig . 2 Describes a hydraulic device comprising a pressure relief arrangement according to a first embodiment of the invention

Fig. 3 Describes a hydraulic device comprising a

pressure relief arrangement according to a second embodiment of the invention

Fig. 4 Describes a hydraulic device comprising a

pressure relief arrangement according to a third embodiment of the invention

Fig. 5 Describes a hydraulic device according to the invention mounted on a vehicle

DETAILED DESCRIPTION OF THE DRAWINGS

In fig. 1 is a hydraulic device 1 suitable for the present invention generally described and the same reference numbers are used for the same features in the 3 different embodiments of the invention described in figures 2-4. A hydraulic device 1 suitable for the invention comprises a cylinder 2 and a piston 3 located in the cylinder 2. The piston 3 is arranged to be able to move back and forth in the cylinder 2. The piston 3 comprises a piston rod 4 and a piston disc 5 provided at the central end of the piston rod 4, i.e. the end of the piston rod 4 provided in the cylinder 2. The piston rod further comprises a distal end 14 provided outside the cylinder 2. The cylinder 2 comprises a central end 15 which is provided with a hole through which the piston rod 4 extends and a distal end 13 located at the opposite end of the cylinder. The piston disc 5 divides the cylinder 2 in the longitudinal extension in a first chamber 6 and a second chamber 7 whereof the first chamber 6 is defined by the piston disc 5, walls of the cylinder 2 and the distal end 13 of the cylinder 2 while the second chamber 7, through which the piston rod 4 extends, is defined by the piston disc 5, walls of the cylinder 2 and the central end 15 of the

cylinder. Hence, an increase of the volume in the first chamber 6, and an accordingly decrease of the volume of the second chamber 7, which is effectuated by moving the piston disc 5 attached to the piston rod towards the central end 15 of the cylinder 2, corresponds to an extension of the length of the part of the piston rod 4 outside the cylinder 2 and thus an extension of the overall length of the hydraulic device 1. A decrease of the volume in the first chamber 6, and an accordingly increase of the volume of the second chamber 7, which is effectuated by moving the piston disc 5 attached to the piston rod 4 towards the distal end 13 of the cylinder corresponds to a retraction of the length of the part of the piston rod 4 outside the cylinder 2 and thus a shortening of the overall length of the

hydraulic device 1. The control of the position of the piston rod 4 relatively the cylinder 2 is made by controlling a flow of hydraulic liquid by a pump 12 to a first inlet opening 8 in the first chamber 6 via a first, push pipe 9 and to a second inlet opening 10 in the second chamber 7 via a second, pull pipe 11. When hydraulic liquid is flowing through the first inlet opening 8 into the first chamber 6 of the cylinder 2 via the first, push pipe 9, the piston disc 5, and the thereto attached piston rod 4, will be pushed so as to extend the overall length of the hydraulic device 1 while the volume of the first chamber 6 increases.

There is of course also a flow out of the second chamber 7 simultaneously as the volume of the second chamber decreases. On the contrary, when hydraulic liquid is flowing through the second inlet opening 10 into the second chamber 7 of the cylinder 2 via the second, pull pipe 11, the piston disc 5, and the thereto attached piston rod 4, will be pulled so as to shorten the overall length of the hydraulic device 1 while the volume of the second chamber 7 increases and a simultaneous decrease of the volume of the first chamber 6 as hydraulic liquid flows from the first chamber. When there is no flow, and there is an

equalized pressure in both the first and second

chambers 6, 7, the overall length of the hydraulic device 1 will be constant and kept in its position by the pressurized hydraulic liquid in the chambers 6, 7 acting on opposite sides of the piston disc 5.

In case of an emergency, it may be desired to release the pressure in the hydraulic device 1 such that there is a low resistance for adjusting the overall length of the hydraulic device 1. It may be desired to provide this safety feature to allow a low resistance for either shortening or extension or for both shortening and extension of the overall length of the hydraulic device 1.

In figure 2 is described an arrangement which will allow the hydraulic device 1 to extend or contract when the pressure release mechanism is actuated. The piston disc 5 used herein is in the form of a rupture disc. This disc is arranged to break or rupture in the case of an emergency such that there will be communication between the first and second chamber 6, 7. Even though the hydraulic liquid in the cylinder 2 may be still pressurized after the breakage or rupture of the disc 5, there will be no, or small, forces acting to keep the piston in its original location and the piston may move either way, i.e. the overall length of the

hydraulic device may easily be shortened or extended. In figure 3 is another pressure release mechanism shown in which a breakage of the second, pull pipe 11 is effectuated in case of the need for emergency pressure release. By releasing the pressure in the pull pipe 11, the pressure in the second chamber 7 will be lowered and the piston disc 5 will thus easily move in a direction towards the central end 15 of the cylinder 2 such that the piston rod 4 attached to the piston disc 5 will extend further through the cylinder 2 and the overall length of the hydraulic device will increase. The arrangement disclosed in figure 4 represents a third embodiment of the invention. In this embodiment has the second, pull pipe 11 been provided with

pressure release pipe 16 extending between the pull pipe 11 and an oil reservoir in the pump 12. The pressure release pipe 16 is provided with a pressure relief valve 17 adapted to break when there is a need for a pressure relief in the pull pipe 11 and thus a pressure relief in the second chamber 7 and there will be essentially the same effect of this arrangement as described for the arrangement in figure 3.

It shall be noted that it could also be possible to place the pressure relief valve 17 directly in the pull pipe 11 (or push pipe 9) instead of arranging the valve 17 in a separate release pipe 16. However, in order to avoid additional friction losses during normal use of the hydraulic device 1 while having a control flow of hydraulic liquid in the pull pipe 11, it may be

advantageous to use a separate pressure release pipe even though more pipes will be needed. It is evident for both the embodiment described in figure 3 as well as for the embodiment described in figure 4 that if the first, push pipe 9 should be provided with the same pressure release arrangement, actuation of that arrangement should allow the overall length of the hydraulic device to be shortened with no or low outer forces working on the hydraulic

arrangement. Hence, depending on what safety feature that is desired in the hydraulic device, i.e. a

pressure relief allowing extension and/or contraction of the overall length of the hydraulic device, the pressure release arrangement may be provided at desired locations, i.e. connected so as to be able to influence the pressure in the the pull pipe 11 and/or in the push pipe 9.

The above described pressure release arrangements may be actuated by being directly influenced by pressure or in response to a signal indicating the need of instant pressure relief whereby an actuator activates the pressure relief arrangement.

In figure 5 is described a vehicle 101 comprising a hydraulic device 1 provided with a pressure release arrangement such as for example described in any of the embodiments described in association with figures 2 - 4. The vehicle exemplified in fig. 5 comprises a chassis 102 and a cab 103 supported on said chassis 102. The hydraulic device 1 forms a first connection 104 between the cab 103 and the chassis 102. The vehicle 101 further comprises a second connection 105 between said chassis 102 and cab 103. The second connection 105 is adapted to deform in the event of a collision in the direction from the front so as to allow the cab 103 to move relatively said chassis 102 in a direction towards the rear end of the chassis 102. The second connection 105 is further able to pivot. The first connection 104 formed by said hydraulic device 1 is adapted to raise and lower said cab 103 relatively said chassis 102 by controlling the flow of hydraulic liquid to and from the hydraulic device 1 such that said first and second connections 104, 105 together form a tilting structure for the cab 103 relatively said chassis 102. The vehicle also comprises a crash detecting arrangement comprising a control unit 106 and sensors 107 a, b. The signals from the sensors, which in this case are exemplified as a crash sensor 107 b in the front of the vehicle and a deformation detecting sensor 107 a for detecting deformation of the second connection 105, may be used as input to the control unit 106 which uses the information from the sensors 107 a, b for deciding if a triggering signal shall be sent to an actuator 108 for activation of the pressure relief arrangement of the hydraulic device 1. There may of course be further inputs to the control unit 106 in order to trigger the activation of the pressure relief arrangement or it may be sufficient with only one sensor, e.g. to only use the deformation sensor 107 a for the activation of the pressure relief arrangement. Even though it is disclosed the use of a control system comprising sensors 107 a, b and a control unit 106 in order to activate the pressure relief arrangement in the vehicle in fig. 5, it is of course possible to use a pressure relief arrangement which need no sensors but is directly actuated by a pressure limit or pressure change in the hydraulic system for the activation of the pressure relief arrangement and the use of such a crash detecting system is optional. It is also obvious that the hydraulic safety release arrangement may be used in other kind of vehicles than the one described herein and the hydraulic device may be used for other purposes than for the hydraulic tilting of a cab arranged on a chassis, e.g. hydraulic suspensions .