This invention relates to a length adjustment device for adjusting the length of a component with which it is associated. By way of example, the length adjustment device may be incorporated or integrated into the component to form an integral part thereof, or it may be attached to, for example, an end thereof.

There are a number of applications in which it is desired to be able to adjust the length of a component. By way of example, in the automotive industry, where dampers are used as part of a vehicles suspension system, it is desirable in such circumstances to be able to adjust the rest length of the damper in order to be able to increase or decrease the ride height of the vehicle.

A number of dampers for use in vehicle suspension applications are known which permit adjustment of the rest length thereof, to permit ride height adjustment, but in such dampers such adjustment typically results in the maximum permitted travel of the damper in either the extending or retracting direction to be restricted, and this is undesirable.

Whilst the description herein relates primarily to automotive applications, it will be appreciated that the invention is not restricted in this regard and may be employed in a range of other applications. By way of example, the invention may be used to adjust a rest length of an actuator used in, for example, aerospace applications or in a wide range of other applications.

It is an object of the invention to provide a length adjustment device whereby at least some of the disadvantages associated with known arrangements may be overcome or of reduced impact. According to the present invention there is provided a length adjustment device comprising a drive member provided with an external thread of one handedness and with an internal thread of an opposite handedness, a first adjustment member including an internally threaded region in threaded engagement with the external thread of the drive member, and a second adjustment member including an externally threaded region in threaded engagement with the internal thread of the drive member, the first and second adjustment members being supported against rotation relative to one another, and a drive arrangement whereby the drive member can be driven for rotation.

It will be appreciated that, in use, rotation of the drive member causes axial movement of the first adjustment member in one direction and axial movement of the second adjustment member in an opposite direction, thereby causing extension or retraction of the length adjustment device. A relatively great level of extension or retraction can be achieved using a device of relatively small dimensions. The device can continue to bear loads whilst length adjustment is being undertaken.

The first adjustment device may incorporate mounting means to allow it to be connected to another device, and the second adjustment device may form part of a damper or actuator housing, for example comprising a damper body. It will be appreciated that the length adjustment device may thus allow the rest length of the damper or actuator with which it is used to be adjusted without impacting upon the normal operation of the damper or actuator. By way of example, where used with a damper, the maximum travel of the damper in the extending or retracting direction is not impacted by adjustment of the rest length thereof. Whilst the second adjustment device may form part of a damper or actuator housing as mentioned above, it will be appreciated that this need not always be the case and that the invention may be used in other arrangements and applications. By way of example, the second adjustment device could be attached to or form part of a shaft of a damper or actuator.

Preferably, the length adjustment device comprises a housing within which the drive member is located and supported for rotation, at least the first adjustment member preferably being keyed to the housing to resist rotation of the first adjustment member relative thereto. The second adjustment member may be keyed or otherwise connected to the housing to avoid or restrict relative rotation therebetween.

The drive arrangement preferably comprises a drive gear arranged to cooperate with a thread formation provided on the drive member. The drive gear is preferably rotatable about an axis substantially perpendicular to the axis of rotation of the drive member. The drive gear conveniently takes the form of a worm gear. Such an arrangement is advantageous in that unauthorised adjustment of the adjustment device is restricted. In particular, the drive arrangement resists adjustment of the length of the adjustment device resulting from the application of axially directed loads to the adjustment device. Such resistance arises, in part, from the gear ratio between the drive gear and the drive member, and the pitch of the worm gear formation.

The drive arrangement conveniently further comprises an electrically operated motor operable to drive the gear, and hence the drive member for rotation. It will be appreciated, however, that the invention is not restricted in this regard and that the drive arrangement may take a range of other forms. By way of example, it could be of hydraulic or pneumatically operated form, or could be of manually adjustable form.

The first adjustment member is preferably releasably connected to the mounting means. Conveniently, the first adjustment member can be secured to the mounting means in a range of angular orientations. By way of example, the first adjustment member may be provided with a plurality of angularly spaced fastener openings, and a threaded fastener associated with the mounting means may cooperate with a selected one of the fastener openings to secure the first adjustment member to the mounting means in a desired angular orientation.

Similarly, the second adjustment member is preferably securable to the housing in a range of angular orientations. By way of example, the second adjustment member and/or the housing may be provided with a plurality of angularly spaced key slots, and a key member may be located within a selected one or ones of the slots to secure the second adjustment member to the housing in a desired angular orientation.

The ability to adjust the angular orientations of the first and second adjustment members relative to the housing is advantageous in that it can be ensured that the adjustment device is assembled in such a fashion as to permit the range of extending and retracting movement thereof to be maximised.

Where used in a vehicle ride height adjustment application, a length adjustment device in accordance with the invention is preferably associated with each damper of a vehicle. In such an arrangement, the length adjustment devices may be independently controlled. Alternatively, a pair of length adjustment devices may be interconnected by a drive shaft connected to a common motor such that both length adjustment devices are adjusted simultaneously. Such an arrangement may permit independent ride height control over the front and rear wheels of a vehicle in a relatively simple and convenient manner.

The invention may be employed in an active ride height control arrangement, for example adjusting the ride height depending upon vehicle speed and/or the nature of the surface over which the vehicle is being driven. If desired, the arrangement could include one or more sensors operable to detect the spacing of parts of a vehicle from the ground and to adjust one or more of the length adjustment devices in response to the detected spacing falling outside of a predetermined range. It will be appreciated that such active ride height control arrangements adjust the vehicle ride height substantially in real time to tune the vehicle suspension to the conditions and/or manner in which the vehicle is being driven, thereby allowing vehicle performance, control and/or safety to be enhanced.

The invention also relates to a vehicle suspension component comprising a damper incorporating or to which has been fitted a length adjustment device of the type set out hereinbefore. By way of example, the second adjustment member of the length adjustment device may form the body of the damper. According to another aspect of the invention there is provided a drive member adapted for use in the length adjustment device described hereinbefore, the drive member including an external thread of one handedness and with an internal thread of an opposite handedness.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic exploded view illustrating a length adjustment device in accordance with an embodiment of the invention;

Figure 2 is an assembled view illustrating the device of Figure 1;

Figure 3 illustrates the device of Figure 1 incorporated into a damper of a vehicle suspension system;

Figure 4 illustrates the device of Figure 1 in an example in use configuration; and

Figures 5 and 6 illustrate a modification to the device of Figures 1 and 2.

Referring firstly to Figures 1 to 3, a length adjustment device 10 forming part of a damper 12 of a vehicle suspension system is illustrated. Although described herein in relation to a damper 12 of a vehicle suspension system, it will be appreciated that the length adjustment device 10 may be employed in a range of other applications, both in the automotive field and in other technologies. By way of example, it may be used with or form part of an actuator such as used in the aerospace industry to drive component parts for movement, the length adjustment device 10 serving to allow adjustment of a rest length of the actuator. The length adjustment device 10 comprises a housing 14 that, in this embodiment, is of generally cylindrical form. Located within the housing 14 is a rotatable drive member 16. The drive member 16 is of hollow cylindrical form and includes, on its outer surface, a screw thread formation of a first handedness. The drive member 16 further includes, on its inner surface, a screw thread formation of a second, opposite handedness. By way of example, the external thread formation may be of left handed form, and the internal screw thread formation may be of right handed form. An externally toothed gear 18 is rigidly connected to the drive member 16, for example by drive pins 20. It will be appreciated that other connection techniques may be used and that, if desired, the gear 18 could be formed integrally with the drive member 16.

The drive member 16 is supported in such a fashion that axial movement thereof within the housing 14 is not permitted or is restricted.

The housing 14 is shaped to define a pocket 22 within which a drive gear in the form of a worm gear 24 is supported for rotation, the worm gear 24 cooperating with the teeth of the gear 18 such that rotation of the worm gear 24 drives the gear 18 and drive member 16 for rotation relative to the housing 14. The gear 18 and worm gear 24 together thus form part of a drive arrangement for driving the drive member 16 for rotation.

The length adjustment device 10 further includes a first adjustment member 26 that includes an eye 28 to allow the length adjustment device 10 to be connected to, for example, a vehicle suspension body mounting (not shown). The first adjustment member 26 is provided with external, axially extending ribs 30, and is telescopically fitted within the housing 14 such that the ribs 30 are located within corresponding guide channels 32 formed in the housing 14. The first adjustment member 26 is provided with an internal screw thread which mates with the external thread of the drive member 16. It will be appreciated that the cooperation of the ribs 30 within the guide channels 32 prevents or restricts rotation of the first adjustment member 26 relative to the housing 14. Accordingly, rotation of the drive member 16 causes, by virtue of the threaded engagement between the drive member 16 and the first adjustment member 26, telescoping movement of the first adjustment member 26 relative to the housing 14.

In addition, the length adjustment device 10 further comprises a second adjustment member in the form of a cylindrical damper body 34. The damper body 34 includes an externally threaded region that is in threaded engagement with the internal thread of the drive member 16. The damper body 34 is also held against rotation relative to the housing 14. Accordingly, rotation of the drive member 16 drives the damper body 34 for telescoping movement. For a given direction of rotation of the drive member 16, the first adjustment member 26 and the damper body 34 undertake telescoping movement in opposite directions. Accordingly, depending upon the direction of rotary movement of the drive member 16, the overall length of the length adjustment device 10 will either increase or reduce.

Seal members are provided to restrict the ingress of contaminants into the housing 14.

The damper body 34 defines an internal cylindrical chamber containing a piston which divides the chamber into two sections. The piston is connected to a piston rod 36 that includes a mounting eye 38 on the free end thereof for connection to, for example, a lower suspension wishbone of a vehicle. A spring 40 urges the piston rod 36 for extending movement. The damper is designed in such a way that fluid is able to pass around the piston at a controlled rate, thus the damper serves to control the rate at which the piston and rod 36 are able to move. The operation of the damper 12 is thus largely conventional and will not be described herein in further detail.

In use, with the damper fitted to a vehicle, the weight of the vehicle causes compression of the spring 40, and the design of the damper 12 is preferably such that under normal conditions, the piston is located approximately centrally within the cylindrical chamber. To adjust the ride height of the vehicle, the drive arrangement is operated to cause rotation of the drive member 16. As described above, depending upon the direction of rotation, this causes an increase or decrease in the length of the length adjustment device 10, increasing or decreasing the ride height as required. In conventional ride height adjustment arrangements, adjustment of the ride height adjusts the rest position of the piston within the cylindrical chamber, and so reduces the permitted range of travel of the piston in one or other direction, and so negatively impacts upon the performance of the suspension arrangement. It will be appreciated that, through the use of the invention, adjustment of the ride height does not impact upon the distance through which the piston can travel and so the operation of the suspension system is not negatively impacted through adjustment of the ride height.

As shown in Figure 3, the drive arrangement may include an electrically operated motor 42 operable to drive the worm gear form rotation. However, other techniques may be used to drive the worm gear for rotation. By way of example, manual arrangements are possible, as are hydraulically or pneumatically operated arrangements.

It will be appreciated that the length adjustment device 10 allows adjustment to be undertaken whilst the device 10 is in a load bearing condition, and the gearing of the drive arrangement is selected to permit this. The pitches of the threads are selected such that frictional forces within the length adjustment device 10 are sufficient to hold the device 10 at a selected length when the drive motor 42 is not being operated. Undesirable or uncontrolled changes in the length of the adjustment device 10 are thus avoided, adjustment only occurring as a result of rotation of the worm gear 18 under the control of the motor 42.

Although each length adjustment device 10 may have its own drive motor 42, where used in automotive applications, often it will be desired for the dampers associated with the front wheels to be set at the same ride height as one another, and similarly for the dampers associated with the rear wheels to be set at the same ride height as one another. Accordingly, as shown in Figure 4, the worm gears associated with the length adjustment devices for the front dampers may be connected to one another by a drive shaft driven by a single drive motor, and the worm gears of the length adjustment devices associated with the rear wheels may be similarly interconnected. In use, a control unit 44 may receive information relating to, for example, the vehicle speed, the terrain over which the vehicle is being driven, or other factors, and may use this information to derive a desired ride height. Appropriate control signals may then be sent to the drive motors 42 to achieve the desired ride height. Ride height adjustment may be undertaken substantially in real time. It will be appreciated that the control unit 44 may use the outputs from sensors used to measure a range of parameters, and that the invention is not restricted to the specific arrangement outlined hereinbefore.

Although the description hereinbefore is of a length adjustment device 10 integrated into a damper 12, it will be appreciated that the length adjustment device 10 may be fabricated as a separate component to be installed between, for example, an end of a damper and the mounting to which the damper would normally be fitted. Furthermore, whilst described in with reference to a specific type of damper, it will be appreciated that the invention is not restricted in this regard and may be used with other types of damper, for example those without a coil spring, or indeed may be used in non-damper related applications as mentioned hereinbefore.

With the arrangement described hereinbefore, in order to ensure that the range of extension and retraction of the device 10 is maximised, it is important to ensure that the screw threads provided on the first and second adjustment members 26, 34, and upon the drive member 16 are properly orientated when the device 10 is assembled, and depending upon the angular orientations of the threads it may not always be possible to achieve a proper orientation whilst having the eye 28, for example, in a desired orientation. If not properly orientated relative to one another, then the first adjustment member 26 may reach the end of its permitted range of extending or retracting movement before the second adjustment member 34 reaches the end of its permitted range of movement, or vice versa, forcing extension or retraction to terminate before the maximum level of extension or retraction of the device 10 has been achieved.

In order to address this, in the embodiment of Figures 5 and 6, the first and second adjustment members 26, 34 are angularly adjustable relative to the housing 14. Specifically, the first adjustment member 26 is formed as a separate component from a mounting component 28a upon which the eye 28 is formed. The mounting component 28a is keyed to the housing 14 by key members 28b slidable within slots 28c formed in the housing 14. The first adjustment member 26 is formed with a large number of angularly spaced fastener openings 26a arranged in a ring, and fasteners 26b in the form of bolts extending through openings provided in the mounting component 28a are received within selected ones of the fastener openings 26a to secure the first adjustment member 26 and mounting component 28a to one another in a desired relative orienation. It will be appreciated that, in this manner, the angular orientation of the first adjustment member 26 relative to the housing 14 may be selected or adjusted.

Similarly, the angular orientation of the second adjustment member 34 relative to the housing 14 is adjustable, in this case by providing the second adjustment member 34 and/or the housing 14 with a large number of angularly spaced key slots 34a, and locating key members 34b within selected aligned key slots 34a to secure the second adjustment member 34a to the housing 14 in a selected angular orientation.

During assembly, the first and second adjustment members 28, 34 and the drive member 16 can be introduced into the housing 14 with the second adjustment member 34 in a desired angular orientation relative to the housing 14, and adjusted relative to one another to ensure that the first and second adjustment members 28, 34 both reach their fully retracted conditions at substantially the same time. The mounting member 28a may then be fitted to the housing 14 and secured to the first adjustment member 28 in a desired angular orientation. In this manner, it can be ensured that the device 10 can be assembled in such a manner as to allow optimal adjustment of the length thereof, with Figure 5 showing the device 10 in its fully retracted position and Figure 6 illustrating the device 10 in its fully extended position.

Whilst specific embodiments of the invention have been described hereinbefore with reference to the accompanying drawings, it will be appreciated that a wide range of modifications and alterations may be made thereto without departing from the scope of the invention as defined by the appended claims.