GB2530182A - Heavy vehicle power steering gear correction system - Google Patents

Abstract

A device is provided for compensating a steering bias in a power steering system of a heavy vehicle, for example a 44 tonne articulated lorry. The power steering system comprises a steering box (120, Figure 1) for transferring rotation of a steering wheel (100, Figure 1) to vehicle wheels (150a, 150b, 160a, 160b, Figure 1) using an actuator piston (280, Figure 1) comprised in the steering box and a drop arm 420 fixedly attached to the steering box and cooperating with a drag link (200, Figure 2) associated with at least one steering arm for turning the vehicle wheels. The device comprises a counterweight 400 located at an attachment point between steering box 120 and the at least one steering arm, and directly opposes an effect of the steering bias at the attachment point. Preferably counterweight 400 has a mass of between 3 kg and 12 kg and is located on a lever arm 410 of length about 21 cm. The device is particularly suitable for right-hand drive vehicles based on left-hand drive designs and avoids the need for continuous left bias correction.

Description

DEVICE, SYSTEM, POWER STEERING SYSTEM AND METHOD FOR HEAVY

VEHICLE POWER STEERING COMPENSATION

Field of the invention

The present invention relates to the field of heavy vehicles, in particular to trucks and lorries with a weight greater than 7.5 metric tonnes (or 7500kg), comprising a power steering system. Moreover, the present invention concerns a device and a system for compensating a steering bias in a power steering system of a heavy vehicle and a power steering system of a heavy vehicle. Further the present invention relates to a method for heavy vehicle power steering compensation.

Background of the invention

In countries where (left hand drive, LHD) vehicles are driven on the right hand side of the road, such as France, The Netherlands, Sweden etc., the road is generally suitably cambered to the right to allow water drainage. This right camber causes vehicles to drift to the right. The drift effect is different for various types of vehicles, depending on design, steering setup and weight of the vehicle. Manufacturers (sometimes) implement various strategies into the basic vehicle design to take account of the right drift phenomenon.

In particular, vehicles such as trucks (for example, trucks with a weight ranging from 7.5 metric tonnes to 44 metric tonnes, for normal vehicles, and even up to heavier vehicles such as those of the STGO class) are arranged with an inherent slight opposing wheel camber set in the axles. Vehicle weights are referred to herein in terms of Gross Vehicle Weight, GVW. The steering system of the heavy vehicle can also provide a corrective effect e.g. by means of the weight of a piston, or an effective weight of a piston, present in a steering box, as it "falls" or presses down during the course of its normal action. (The steering box is also known as a steering gear box). The combined effect of wheel camber and piston weight assists the straight-line stability and handling of the vehicle and reduces the need for power-assisted corrections from the steering system. Essentially, these left hand drive (LHD) vehicles are given a left bias to compensate for the right camber.

Roads in countries such as the United Kingdom (UK), are arranged so that (right hand drive, RHD) vehicles drive on the left hand side of the road. Said roads comprise a left camber instead of a right camber, again to facilitate water to flow away from the centre of the road to the edge without passing across the path of oncoming traffic. There is thus a natural tendency for these right hand drive vehicles to drift to the left as a result of the left camber. This can also be (partially) compensated for by means of vehicle design, as explained above.

When a left hand drive vehicle, designed to compensate right road camber, especially a vehicle of significant weight such as a truck, is driven on the left hand side of a road with inherent left camber, the left bias of said vehicle acts in addition to the left camber of the road. Manufacturers are aware of this issue and frequently apply an opposite wheel camber (as above) when providing RHO models of an essentially LHD vehicle design, for normal use in countries where roads have a left camber, e.g. UK.

This leads to a situation where steering correction for a left road camber is applied by provision of wheel camber (opposing and to the right). The piston weight and physical positioning of elements of the (power) steering system of the vehicle usually remain largely unchanged.

Thus the currently applied solution has been recognised as not entirely adequate, as the pressure of the left road camber is released on(to), i.e. applied to, the steering rack of the RHD vehicle as well as other components. This causes the steering wheel and steering rack to turn slightly to the left while the vehicle is in motion, as gravity pulls the steering piston downwards (e.g. on the worm gear ball-race of the steering shaft). This slight left turn must be opposed by the driver, in order to correct it and maintain the vehicle driving in a straight-line.

Such a continuous effort by the driver is fatiguing and over a longer time period may lead to injury. Further, the vehicle is not optimised in design to be subject to a continuous left pull correction. Thus, the vehicle is in a more active state than normal over a longer time period, which may result in accelerated wear on vehicle components, such as tyres, power steering components. The heightened activity of the power steering during the required correction for the left pull may also decrease the efficiency of fuel use, the RHD vehicle then requiring relatively more fuel than would be expected for a LHD vehicle over a similar distance (under normal driving conditions on the type of right cambered roads for which said LHD vehicle was designed). T *l$ødetr1rflertaIHWith re.spet The problem of alleviating the need for continuous left pull correction, or left bias steering correction, in RHD vehicles must therefore be addressed.

Summary of the invention

The present invention seeks to provide an improved power steering for heavy vehicles, preferably comprising compensation for a steering bias, particularly a steering bias resulting from road camber issues.

Moreover, the present invention seeks to provide an improved power steering for heavy vehicles comprising vehicles with a (GVW) weight greater than 7.5 metric tonnes (or 7500kg), comprising a (power) steering system.

According to a first aspect of the present invention, there is provided a device as claimed in appended claim 1: there is provided a device, for compensating a steering bias in a power steering system of a heavy vehicle, said power steering system comprising * a steering box, for remotely receiving a turning movement of a steering wheel and arranged to translate said turning movement to the vehicle wheels by means of at least, o an actuator piston comprised in the steering box, o a drop arm fixedly attached to the steering box and arranged in cooperation with, * a drag link, the drag link being further arranged in association with at least one steering arm arranged to influence a turning orientation of the vehicle wheels, wherein, the device comprises a counterweight, said counterweight being arranged located at an attachment point between the steering box and the at least one steering arm, so as to directly oppose an effect of the steering bias at the attachment point.

Optionally, the counterweight is arranged to balance a weight of the steering box actuator piston AND/OR an effective weight of the drag link, to a point of equilibrium for use on left or right cambered roads.

Optionally, the attachment point is arranged proximate to the steering box OR on the steering box OR on the steering box drop arm OR on the rear second steer drop arm, preferably to a first end of the rear second steer drop arm proximate to the drag link OR on the forward second steer drop arm, preferably to a second end of the forward second steer drop arm proximate to ground.

Optionally, the counterweight weighs between 1.5kg and 15kg, preferably between 3kg and 12kg, even more preferably around 3kg or 6kg or 9kg or 12kg.

Optionally, the device further comprises a lever arm such that the counterweight is located at a first end of a lever arm, a second end of the lever arm being attached to the attachment point.

Optionally, the lever arm forms an angle between 150 and 45°, preferably around 30° with respect to the steering box drop arm in situ OR an angle between 20° and 30°, preferably 25°, in situ, with respect to the a horizontal plane substantially parallel to the ground, and in a positive or negative sense when mounted on the rear second steer drop arm or forward second steer drop arm, respectively.

Optionally, the lever arm comprises a length up to a maximum of 30cm, preferably a length of around 21cm.

Optionally, the lever arm comprises a curved shape OR a straight shape over its length.

Optionally, the counterweight is formed integral with the lever arm OR is arranged as fixedly attachable to the lever arm.

Optionally, the counterweight comprises a single piece of material OR multiple sheets of material arranged co-located on the lever arm.

Optionally, a material of the counterweight comprises mild steel OR steel OR stainless steel OR brass.

Optionally, a lever arm material comprises mild steel OR steel OR stainless steel OR brass.

According to a second aspect of the invention, there is provided a system for a heavy vehicle, as claimed in appended claim 13: the system, for compensating a steering bias in a power steering system of a heavy vehicle, comprises a plurality of devices as claimed in any of the above claims.

Advantageously, the provision of a plurality of devices (counterweights) facilitates distribution of the correcting effect of the present invention over various points of attachment of the vehicle. This allows the individual devices to be made less heavy than a corresponding single device, which may be advantageous given the restrictions of space or clearance in the vehicle design or in terms of ease of fitting.

By provision of this aspect of the invention, the opposing effect as provided by embodiment of the present invention to effect a correction to a steering bias can be provided by redistributing the correction weight split over a plurality of devices According to a third aspect of the invention, there is provided a power steering system for a heavy vehicle, as claimed in appended claim 14 the power steering system of a heavy vehicle comprises a device and/or a system according to an embodiment of the present invention.

According to a fourth aspect of the present invention, there is provided a method of calculating a weight of a device according to embodiments of the present invention, as claimed in appended claim 15. The method comprises the steps of:- * identifying a first weight of the actuator piston comprised in the steering box; AND/OR, * identifying an angular deflection of at least one steering arm associated with a vehicle wheel in situ and resulting from a second weight of the drag link effective on said at least one steering arm; AND, * determining a first and/or second effective force associated with said first and second weights, respectively; * estimating a set of first and/or second effective moments capable of compensation for said first and/or second effective force, respectively, to a desired point of equilibrium; * arranging a device weight and length and shape in accordance with the set of first and/or second effective moments.

It will be appreciated that features of the invention are susceptible to being combined in any combination without deparling from the scope of the invention as defined by the appended claims.

Description of the diagrams

Embodiments of the present invention will now be described, by way of example only, with reference to the following diagrams wherein: FIG. 1 is a schematic illustration of components of a power steering system for a heavy vehicle; FIG. 2A is a schematic illustration of a drag link and forward and rear drop arm arrangements of the steering system of FIG. 1; FIG. 2B is a schematic illustration of an actuator piston and quarter gear, as comprised in the steering system of FIG. 1; FIG. 3 is a schematic illustration of various embodiments of a device according to the present invention, presented in parts FIG. 3A, FIG. 3B and FIG. 3C; FIG. 4 is a schematic illustration of a device according to an embodiment of the present invention comprising a counterweight and lever arm and mounted on a drop arm of a steering box; FIG. 5 is an illustration of an embodiment according to the present invention suitable for attachment to the steering box drop arm; FIG. 6A is an illustration of an embodiment according to the present invention, suitable for attachment to the rear second steer drop arm; FIG. 6B is an illustration of an embodiment according to the present invention, suitable for attachment to the rear second steer drop arm; FIG. 7 is an illustration of an embodiment according to the present invention, suitable for attachment to the forward second steer drop arm; and, FIG. 8 illustrates a method according to an embodiment of the present invention.

In the accompanying diagrams, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing.

Description of embodiments of the invention

Referring to FIG. 1, which is a schematic illustration of components of a power steering system for a heavy vehicle, here shown as a twin steer heavy vehicle (front of the vehicle at left hand side of page), the steering system comprises a steering wheel 100, linked by a steering column 110 to a steering box 120. Further components of the steering system comprise front and rear track rods 130 140 which are arranged to direct steering impulses between pairs of wheels 150a 150b and 160a 160b, respectively, and may be adjustable. The wheels 150a 150b 160a 160b comprise the steering wheels of the heavy vehicle truck. Optionally, the truck may be fitted with an extra pair of wheels (not shown) to provide drive to the vehicle. The steering system also comprises a plurality of drag links e.g. three are shown in FIG.1 170a 170b 170c. These drag links transfer steering impulses to the wheels by means of steering arms (not shown).

The steering box 120 is physically connected to a steering box drop arm 180. Both the steering box 120 and the steering box drop arm 180 are suitable to comprise attachment points for devices according to embodiments of the present invention.

The steering box 120 is also commonly referred to as a steering gear box.

The steering system comprises a drag link 200 (which can also be referred to as the main drag link) and forward 210 and rear 220 second steer drop arm arrangements of the steering system, as further explained in FIG. 2 and below. Both the forward 210 and rear 220 second steer drop arms (also known as idler arms) are suitable to comprise attachment points for devices according to embodiments of the present invention.

A steering bias, as explained above, can be introduced to the steering system e.g. due to road camber. The driver must compensate the steering bias actively by a rotation of the steering wheel 100 in an appropriate direction to neutralise the bias and maintain the heavy vehicle in a correct (usually straight) orientation. By implementation of embodiments of the present invention, the steering bias can be corrected for and, in an optimal implementation of embodiments of the present invention, the driver is no longer required to make active correction to the steering of the vehicle in response to the steering bias.

The effects of a steering bias may be dependent on vehicle type. For a 4x2 vehicle, the steering bias can predominantly arise from steering box 120 effect. For a 6x2 vehicle, a drag link 200 contribution to the steering bias may overtake the effect of the steering box 120 contribution to such an extent that the bias may be split into a two-thirds to one-third contribution, drag link 200 to steering box 120, respectively, which thereby suggests a larger correction for the drag link effect by means of the rear (preferably) and/or forward second steer drop (or idler) arms as an efficient step.

A further correction could then be applied to the steering box drop arm, in such circumstances, if desired. Embodiments and implementation of the present invention are detailed below.

Referring now to FIG. 2A: FIG. 2A is a schematic illustration of a drag link and forward and rear second steer drop arm arrangements of the steering system of FIG. 1, as comprised in a heavy vehicle. (Note the drop arm may also be referred to as an idler arm). The illustration looks from the side of the vehicle, in the same manner as for FIG. 1. In this particular example, the heavy vehicle is a 6x2 tractor unit of an articulated lorry weighing around 40 metric tonnes and capable of towing a trailer with or without a payload (not shown). An example of such a heavy vehicle would be a Scania R series of Gross Vehicle Weight (GVW), approximately, 44 metric tonnes.

The steering system here comprises a steering box (not shown) and a drag link 200, the drag link 200 being further arranged in association with a remote steering arm (not shown) arranged to influence a turning orientation of the vehicle wheels. (This drag link may also be optionally referred to as the main drag link). The drag link 200 runs from the front of the vehicle to the rear, between components relating to the first and second sets (or pairs) of wheels (not shown) of the 6x2 vehicles responsible for the steering of the vehicle. In this example, the drag link 200 weighs approximately 56kg and is approximately 3m long. The driving wheel set (not shown) is located to the rear of the vehicle behind the two front pairs of wheels.

In this example, a counterweight may be mounted proximate to or on the steering box: this is an optional addition to any further counterweights according to embodiments of the invention to be described in the context of FIG. 2A and located between the drag link and forward or rear drop arms arm associated with the wheels.

FIG. 2A shows a forward second steer drop arm 210 and a rear second steer drop arm 220 associated with the front wheel and the rear wheel, respectively, on one side of the vehicle. The front of the vehicle relates to the left hand side of the drawing. In the case of a RHD drive vehicle suitable for use in e.g. UK, the drop arms 210 220 are likely to be positioned on the nearside of the vehicle, closest to the kerb. Each of the second steer drop arms 210 220 comprise a pivoting point 210a 220a, an upper section 210b 220b and a lower section 210c 220c. The offset (here approximately 4cm and 6cm for front and rear drop arms, respectively), between the upper sections of the front 21Db and rear 220b second steer drop (or idler) arms and their respective -10-pivots 210a 220a determine a lever ratio for each drop arm, here around 11-12% for the forward 210 and 21-22% for the rear 220 drop arms 210 220. Each drop arm experiences a component of the weight of the drag link, approximately half each corresponding in this example to around 28kg, as illustrated by arrows 230a 23Db. In this particular example, the lengths of the front second steer drop arm 210 upper 21Db and lower 201c section components are 14cm and 35cm, respectively, (measured vertically to end points from the pivot 210a centre) : for the rear second steer drop arm 220, the upper 220b and lower 220c measurements are 29cm and 28cm, respectively, from pivot 220a.

The weight of the drag link acting through the steering mechanisms and under influence of the left road camber causes a steering bias, which is being compensated by the driver under the prevailing driving conditions. Embodiments of the invention suitable for implementation to compensate for this steering bias are attached to one or both of the drag links 210 220. This then eliminates the need for the driver of the vehicle to actively correct the steering to account for the steering bias.

The attachment point for each of the drag arms 210 220 can be optimised for effect and for ease of positioning within the mechanical setup and design of the vehicle.

For the forward second steer drop arm 210 the device according to an embodiment of the invention is placed proximate to the end of the lower section 210c and indicated at position 240. For the rear second steer drop arm 220, the device according to an embodiment of the invention is placed proximate to the drag link 200 at a top end of the upper section 22Db and indicated at position 250. These positions should not be considered as limiting, however, as it is possible to place devices according to the present invention on other parts of the drop arms, according to available space and effect.

Where the device attached comprises a lever arm, the lever arm is optimally directed dependant on the attachment point being located on front or rear second steer drop arms 210 220. For a forward drop arm 210 attachment, a lever arm pointing downwards to ground level is preferred. In this instance, it is also advantageous that the lever arm is arranged to comprise a narrower clamp at point of attachment to vehicle than would be suitable for an attachment to a rear drop arm 220. This accommodates design features and clearance requirements for movement of the lever arm when the vehicle is under a turning influence. A lever arm attached at the rear second steer drop arm 220 is preferably attached directed upwards towards the drag link 200. The lever arms are angled with respect to a vertical perpendicular to ground level with an acute angle.

In this specific example, the effective device counteracts the unwanted bias forces, here shown in terms of weight, as 3kg on the forward second steer drop arm, as indicated by arrow 260 and 6kg on the rear second steer drop arm, as indicated by arrow 270.

Referring now to FIG. 2B, which is a schematic illustration of an actuator piston and quarter gear, as comprised in the steering system of FIG. 1, arranged in cooperation with the steering box 120. The drop arm 180 of the steering system is shown in FIG. 2B and comprises two ends 180A 180B. Also shown in FIG. 2B is an actuator piston 280. Normally such an actuator piston 280 weighs between 9.5 and 10.1kg, more usually around 9.8kg. The weight of the actuator piston 280 acts under gravity downwards to ground level, as indicated by arrow 280A.

The actuator piston 280 and the drop arm 180 engage at the quarter gear assembly 290. The quarter gear assembly 290 comprises a pair of interlocking gear teeth 290A 290B cooperating such that gear teeth 290A are arranged as located on the actuator piston 280 and gear teeth 290B are arranged as located on the drop arm 180.

A steering impulse from the steering wheel (not shown) is translated along the power steering system to the actuator piston 280, whose responsive movement causes the gear teeth 290A on the actuator piston to actively engage with the gear teeth 290B thereby initiating a movement of the drop arm 180. A lever effect through the shaft of the drop arm causes the drop arm end 180B to move, as indicated in this instance by arrow 180C. Movement of the drop arm end 180B translates the steering impulse to the rest of the steering system and, eventually, to the wheels (not shown) of the heavy vehicle (not shown). -12-

The actuator piston 280 comprises a weight such that the weight is capable of initiating (at least a part) of a steering bias in the steering system of the heavy vehicle. The actuator piston 280 weight moving (i.e. as a result of road camber) as indicated by arrow 280A is capable of causing a resultant movement of the drop arm end 180B in a similar way to a steering impulse (described above), thereby initiating a steering bias which is translated to the wheels (not shown) and which requires driver correction. This steering bias can be corrected by means of various embodiments of the present invention so that the driver no longer has to actively correct and can drive a more balanced vehicle.

Referring now to FIG. 3, in FIG. 3, parts A, B and C, various embodiments of the device according to the present invention are shown. The device comprises a counterweight, which may optionally be attached to a point of attachment located between the steering box and the steering arm of a (power) steering system for a heavy vehicle by means of a connection such as a holder, clamp, screw or bolt attachments or by indirect attachment by means of a lever arm (not shown). The schematic drawings of FIG. 3 (all parts) are designed to illustrate possible forms of the counterweight but should not be regarded as limiting. Optionally, the counterweight could also be attached to or be part of an arm extended from and/or manufactured as an integral part of the drop arm. (In one example, an embodiment of the counter weight device is shown in FIG. 4 400). Weights associated with the counterweights as quoted herein, are generally quoted in terms of the weight of the individual counterweight. Should the counterweight be attached to a lever arm, for example, the weight of the lever arm itself would be additional and could be taken into consideration of the overall effect associated with embodiments of the present invention.

FIG. 3A shows the device in the form of a rod, which is designed to be attachable at one end to the attachment point. The rod has a constant radius throughout its length.

Therefore each part of the rod along its length contributes to the counterbalance effect, that is to say the moments of the rod calculated from its centre of gravity (C of G). The length of the rod can be adjusted to fit into the space available at the point of -13-attachment as well as adjusted to provide the appropriate weight for the counterbalance effect. The rod can be fashioned in a variety of materials dependent on the weight required and the strength required. Advantageously, this embodiment of the present invention is easy to manufacture and may even be implemented from standard materials i.e. available lengths of metal.

The rod may also be tailored in shape to resemble e.g. a cone such that the radial dimension alters gradually along the length of the rod.

The lever arm may be straight or curved at an angle, advantageously shaped for correct fitting at a desired point of attachment.

FIG. 3B shows the device in the form of a counterweight of rectangular form. The rectangular form may comprise a square. Various edge effects may be implemented as desired, such as the rounding of corners. This embodiment of the present invention is designed to be used in association with a lever arm (not shown).

Attachment of the counterweight device to the lever arm is facilitated by means of a bolt system (not shown). The rectangular form can be a solid block or comprise a plurality of independent layers, which are co-located at one end of the lever arm by means of the bolt system. The latter device advantageously permits adjustment of the actual weight of the counterweight by addition or removal of layers. Other attachment methods can be used, such as a holder, said holder optionally being formed integral with the lever arm.

FIG. 3C shows the device in the form of a circular counterweight, here seen directly from above. The circular shape may comprise an oval or ellipse, for example. This device is also susceptible to implementation in the form of layers and in association with a lever arm and/or holder, as described for FIG. 3B.

All shapes shown in FIG. 3 (parts A, B and C) are capable of being implemented with various surface patterning which optionally may be introduced to facilitate fixing or to ease the manufacturing process. -14-

The individual counterweights comprise a broad weight range but preferably weigh between 3kg and 12kg, mounted in association with a lever arm of around 21cm length (as measured centre to centre, on the poles or ends, of the lever arm). The overall lever arm length should preferentially lie in a range of between 18cm and 23cm. This length permits correct clearance of the lever arm in situ, when the vehicle is at rest, and in motion, when the vehicle is under a turning influence of the steering to facilitate wheel turn. The lever action of the lever arm is designed to produce an effective weight of the counterweight, used to compensate for the unwanted steering bias. Thus the combination of counterweight and lever arm length is important. A shorter arm would require a bigger weight to produce an equivalent effective weight and compensating force of the device. Similarly for practical purposes, the counterweight should be heavy enough to produce an effect but not so heavy that it damages, or is inappropriate with respect to the strength of, the lever arm on which it is mounted. Too small a counterweight, conversely, may not produce sufficient effective weight unless mounted on a lever arm too long to be accommodated in the vehicle architecture. Advantageously, by standardising a lever arm length and/or design, counterweights can be chosen appropriate to that arm length. This avoids production of two kinds of lever arms, one for forward implementation and the other for rearward implementation. An arm length of around 21cm (centre to centre and between the mounting points provided in the drop arm for facilitating connection to other components of the steering system, said mounting points frequently being fashioned as round machined holes, optionally threaded internally) as described above, is suitable for implementation in association with both forward and rear second steer drop arms.

Referring now to FIG. 4: FIG. 4 is a schematic illustration of a device according to an embodiment of the present invention comprising a counterweight 400 and lever arm 410 and mounted on a drop arm 420 of a steering box (not shown). The steering box is comprised in the power steering system of a heavy vehicle. The drop arm of FIG. 4 420 is equivalent to the drop arm of FIG. 1 180. Note that the lever arm and/or counterweight assembly may optionally be formed as part of said drop arm 420 180. -15-

It should be noted that in this figure the drop arm 420 is shown in situ in a vertical position. That is to say, the drop arm would be substantially perpendicular to the plane of the ground. The drop arm moves according to steering input to translate the driver input to guide the vehicle wheels. The device for compensating a steering bias, according to an embodiment of the present invention, is rigidly fixed to the drop arm 420 by attachment of a first end of the lever arm 410 of the device, which is angled at an acute angle indicated by arrow 430 with respect to the drop arm 420. In situ, i.e. when the attachment is complete and the heavy vehicle is at rest with no steering influence on the steering system of the vehicle, the lever arm forms said angle with the drop arm. Said angle 430 lies in an angular range between 20° and 45°, most preferably having a value of around 3Q°. While in motion the angular range of the drop arm 420 is around 1000. By positioning the lever arm 410 at the correct angle with respect to the drag arm 420, the device does not interfere with e.g. the chassis mounting or other mechanical components of the vehicle. In addition, the angle of implementation of the device and/or the sizing in terms of length of lever arm, facilitates a proper clearance of the device within the mechanical environment.

The embodiment of the present invention shown in FIG. 4 is implemented in a RHD vehicle being driven on left cambered (UK roads). In this embodiment therefore, in order to achieve the correct counterbalance effect and optimal positioning in the mechanical set up, the lever arm 410 points directly backwards towards the rear of the vehicle and is comprised in a vertical plane also comprising the drop arm. The actual direction and orientation of implementation of embodiments of the present invention are arranged so as to oppose an effect of the steering bias at the attachment point. This may require specific implementations depending on the type of vehicle and design.

The lever arm 410 is here shown attached to the drop arm 420 by means of two bolts or threaded screws 440 and 450. The lever arm may optionally be attached by means of a specially formed connector. The counterweight 400 is attached to a end of the lever arm 410 remote from the drop arm 420 by means of four smaller bolts 460, 470, 480, 490. Many different forms of attachment are possible in both cases, depending on configuration, materials and manufacture. -16-

A counterweight 400 attached externally or integral to a lever arm 410 fixed or integral to the drop-arm 420 would compensate for the weight of the piston (e.g. approximately 10kg in this particular situation). Optionally, the counterweight may be provided in association with a cradle to support the counterweight and maintain the shape of the counterweight e.g. in the event that the material used to form the counterweight is relatively soft e.g. lead. The weight would be adjustable to balance the piston to a point of equilibrium for use on left or right cambered roads (E.g. UK or Europe). Or, more usefully, it would be set to overcome the piston weight for vehicles that are used solely on left camber roads (e.g. UK) This correcting force would reduce the need for a powered steering inputs to overcome the left camber.

The lever arm could be cast at the manufacturing stage as an extension of the drop arm 420 or retro fitted to older vehicles and fixed to the drop arm 420 by various means. The counterweight 400 could be fixed or removable and made from e.g. steel, lead or other materials.

The technical effect of this particular embodiment of the present invention is to compensate for the weight of the power steering gear actuator piston that is mounted vertically inside a power steering box, by retro fitting or otherwise a counterweight at the end of a lever arm to the power steering drop arm.

In a specific example of a device according to an embodiment of the present invention as implemented in a 4x2 vehicle. In this particular instance an embodiment is optimised for a vehicle in a weight range of 28 to 40 metric tonnes GVW. The counterweight is here attached to the steering drop arm and comprises a counterweight of between 1.5 to 3kg. The lever arm comprises a length of around 29cm.

Referring now to FIG. 5: FIG. 5 is an illustration of an embodiment of the present invention, mounted on a steering box drop arm. Where the device comprises components in common with the device shown FIG. 4, these components are labelled accordingly; specifically, a counterweight 400 and lever arm 410 410a, mounted on a drop arm 420 of a steering box (not shown), two bolts (preferably hex -17-bolts) or threaded screws 440 and 450. The two bolts 440 450 are designed to engage with a clamp 510.

The embodiment of FIG. 5 further comprises an attachment of the counterweight by means of screw thread (not shown) and pin 500. The pin 500 is optional. The screw thread is located at an end of the lever arm 410 remote from the drop arm 420 and is arranged in cooperation with a matching thread on the counterweight 400. Said counterweight is shown in FIG. 5 in an embodiment comprising a plurality of matching plates 400a to 400f which are further secured by the pin 500. The screw thread is optional and the plates 400a to 400f may be located by means of a machined slot in each of the plates and the pin 500. The plates 400a to 400f are shown in FIG. 5 as substantially identical but this should not be considered as limiting the plates within the set may be made of different materials, comprise different shapes, comprise different weights and/or comprise different densities.

Advantageously, the use of said plates allows for adjustment of the counterweight as desired. For example, should an adjustment be required following the addition of a second or third counterweight according to other embodiments of the present invention, then the counterweight provided on the steering box drop arm can be adjusted. By contrast, should a fully fixed weight be desired then it is also possible to form the counterweight and lever arm in one integral piece with the added advantage of strength and stability and ease of manufacturing.

For a correct fit and effective action, the lever arm 410 is preferably implemented comprising a gently curved shape (as indicated by the dashed line 410a) along its length. This provision avoids contact between the lever arm and other components of the vehicle in the vicinity of the lever arm attachment point.

Optionally, the device of FIG. 5 comprises 3 to 6 of 10mm plates, is fashioned from 10mm mild steel and weighs approximately 2.9kg, (ranging between 1.5kg and 4kg).

The lever arm length (centre to centre) is around 21cm, but no longer than 30cm. In this particular embodiment of the present invention, the lever arm weighs between 1.2kg and 3kg. This device is particularly suitable for a 4x2 heavy vehicle of (GVW) weight 44 metric tonnes. -18-

Optionally, the device of FIG. 5 comprises 2 to 5 of 15mm plates, is fashioned from 15mm mild steel and weighs approximately 3.1kg, (ranging between 1.5kg and 4kg).

The lever arm length (centre to centre) is around 21cm, but no longer than 30cm.

This device is particularly suitable for a 4x2 heavy vehicle of (GVW) weight 44 metric tones Preferably, the diameter of the plates should be around 10cm, preferably no larger than 12cm for the purposes of clearance.

Referring now to FIG. GA FIG. GA is an illustration of an embodiment according to the present invention, suitable for attachment at the rear second steer drop arm.

FIG. GA illustrates a counterweight 600 comprised of six plates 600a to 600f, arranged in cooperation with a lever arm 610, such that the plates are mountable on one end of the lever arm (remote from the mounting point of the lever arm on the rear second steer drop arm (not shown) and attachment means 640 650) and secured by a pin 500. Various specific embodiments of the device shown in FIG. 6A are possible, including those subject to the physical design considerations applicable to the device of FIG. 5, such as integral counterweight and lever arm for example.

The counterweight associated with the rear second steer drop arm is usually arranged to be heavier than any of the counterweights associated with the steering box drop arm or forward second steer drop arm. This is because of the direct opposition to the drag link weight (without loss of force through the offset levers) vehicle clearances and ease of fitment, but such an arrangement should not be considered as limiting to the embodiments of the present invention.

Advantageously, a standardised lever arm, to be suitable for implementation on both forward and rear drop arms, is implemented so that the lever arm can be flipped or reversed for use on either of the two possible attachment points. Different weights of counterweight can be implemented on the standardised lever arm depending on point of use. Thus the lever arms of FIG 6A and 6B 610 and FIG 7 710 can be arranged as identical. The lever arms 610 710 are preferentially straight, rather than curved, along the length of the lever arm, when implemented in cooperation with a front or rear second steer drop arm. -19-

The device of FIG.6A is preferably implemented with a point of attachment on the rear second steer drop arm (or rear second steer idler arm) proximate to the drag link end of the rear second steer drop arm, as shown in FIG. 2 250.

Referring now to FIG. GB FIG. GB is an illustration of an embodiment according to the present invention, suitable for attachment to the rear second steer drop arm.

This embodiment differs from the embodiment of FIG. 6A in that the counterweight 600 comprises a circular weight in one piece attached to the lever arm 610 by attachment means 660 670 which comprise two bolts, here shown optionally mounted along a central long axis of the lever arm 610. The circular counterweight and attachment means shown in FIG. 6B may also be applied to the device of FIG. 7 for use in cooperation with a forward second steer drop arm.

Referring now to both FIG. GA and FIG. 6B: When mounted on the heavy vehicle, the lever arm 610 is arranged such that the lever arm points upwards, away from ground level, in a neutral position. The lever arm then rests (in situ) at an acute angle to the horizontal or ground level such that the counterweight end of the lever arm is higher than the attachment point. This angle is preferably arranged to be between 200 and 30°, even more preferably arranged to be 25°. During steering action, said lever arm 610 may move through an angular range of approximately 60°.

Further the lever arm is arranged such that the counterweight end is proximate to the front of the vehicle while the attachment point is proximate to the rear of the vehicle.

Preferred characteristics of the device comprise mild steel for the material, a centre to centre length of 21cm, up to a maximum of 28cm, an associated counterweight of diameter 10cm mounted at one end of the lever arm. Preferred attachment means to secure an end of the lever arm to the rear second steer drop arm include a clamp with hex bolt (or other suitable) fixings.

In a preferred application of embodiments of the present invention for 6x2 having vehicles of approximate weight (GVW) of around 44 metric tonnes, a standard lever arm length of 21cm is associated with a weight of 10-12kg counterweight attached -20 -proximate to the drag link on the rear second steer drop arm. A corresponding counterweight of 3-6kg is then associated with the forward second steer drop arm.

Referring now to FIG. 7: FIG. 7 is an illustration of an embodiment according to the present invention, suitable for attachment to the forward second steer drop arm (or idler arm). Further, FIG. 7 shows an embodiment according to the present invention, particularly suited to 6x2 vehicles.

When mounted on the (heavy) vehicle, the lever arm 710 is arranged such that the counterweight points downwards, towards ground level, in a neutral position. The lever arm then rests (in situ) at an acute angle to the horizontal such that the counterweight end of the lever arm is lower than the attachment point. This angle is preferably arranged to be between 200 and 300, even more preferably 25°. During steering action, said lever arm 710 may move through an angular range of approximately 1000. The front second steer drop arm 210 is offset (i.e. larger at the bottom than the top to reduce the movement of the steering box drop arm 180) and therefore the angular range of movement of the rear second steer drop arm 220 is consequently limited. Further the lever arm is arranged such that the counterweight end is proximate to the front of the vehicle while the attachment point is proximate to the rear of the vehicle.

Preferred characteristics, of a particular device according to an embodiment of the present invention, comprise mild steel for the material, a centre to centre length of 21cm, up to a preferred maximum of 28cm, an associated counterweight of diameter 10cm mounted at one end of the lever arm. Preferred attachment means to secure an end of the lever arm to the forward second steer drop arm include a clamp with hex bolt fixings.

In a preferred application of embodiments of the present invention for 6x2 vehicles of approximate weight (GVW) of around 44 metric tonnes, a standard lever arm length of 21cm is associated with a weight of 3-6kg counterweight attached proximate to the ground end of the forward second steer drop arm. A corresponding counterweight of 10-12kg is then associated with the rear second steer drop arm.

-21 -A further preferred embodiment of the present invention in this context comprises a lever arm in the form of a 100mm bar arranged in combination with a front counterweight of size lOxlOcm and weight 6kg and a rear counterweight of size lOxl7cm and weight 10.5kg. This particular embodiment of the invention distributes the front and rear counterweights more equally, thereby advantageously enabling easier handling of the counterweight devices during fitting to the heavy vehicle.

Referring now to FIG. 8: FIG. 8 illustrates a method according to an embodiment of the present invention. The method comprises the steps of:- * identifying a first weight of the actuator piston comprised in the steering box; AND/OR, * identifying an angular deflection of at least one steering arm associated with a vehicle wheel in situ and resulting from a second weight of the drag link effective on said at least one steering arm; AND, * determining a first and/or second effective force associated with said first and second weights, respectively; * estimating a set of first and/or second effective moments capable of compensation for said first and/or second effective force, respectively, to a desired point of equilibrium; * arranging a device weight and length and shape in accordance with the set of first and/or second effective moments.

It should be noted that the desired point of equilibrium in step four of the above method should be interpreted in terms of the application of embodiments of the invention. For a steering bias, it is preferable to compensate to equilibrium or as close to equilibrium as possible, thereby reducing any effects of the steering bias on the driver to a minimum by reducing the amount of active driver action required. It may be desired, however, in some uses and applications of embodiments of the present invention, to implement compensation to a desired point of equilibrium comprising over-or under-compensation as required. This may be dependent on other prevailing circumstances or setups of the vehicle.

-22 -In essence, a method according to an embodiment of the present invention comprises: * identifying the weight or force associated with the steering bias to be compensated; * calculating moments associated with the components comprising the identified weight or force; and, * designing the device characteristics to oppose the calculated moments.

It should also be noted that the moments or effective moments of the methods above may further comprise corrected moments. That is to say, corrected moments can also be implemented according to embodiments of the present invention to compensate for an offset lever associated with the first second steer drop arm.

The various embodiments of the present invention may be implemented in a variety of materials of suitable density and weight to achieve the required balancing force by weight. In particular, steel is a preferred material. Not only does (mild) steel have sufficient density and weight, it is also strong and relatively easy to process into counterweights with respect to machining and other processes. Stainless steel is another preferred material. Other examples of materials which can embody a counterweight according to the present invention, but which comprise issues which must be overcome in the implementation) include; lead (which is suitably weighty but is relatively soft, thereby being preferably implemented in association with a cradle or sleeve to contain or support the lead material), brass (which is strong but relatively expensive), iron (which is heavy and strong but which is difficult to work as the material becomes brittle with extensive processing). These materials are presented as examples only and do not form a comprehensive or limiting list, other materials being suitable for implementation.

Further, the basic material of the embodiments of the present invention may be coated with a protective layer of a suitable material comprising examples such as paint, galv (galvanising coating), powder coat etc. The layer thickness of these materials should be chosen according the clearances available for the component in use.

-23 -A clamping mechanism (arranged as a means of attachment between device and attachment point), comprising a clamp such as clamp 510, for example, may optionally comprise a threaded centre for extra security of attachment, the threaded centre being arranged to cooperate with matching threads on the counterweight or on the lever provided proximate to an end of the lever arm 410 610 710.

Although embodiments of the invention are described in the foregoing, it will be appreciated that the present invention is also susceptible to being implemented in other ways and, optionally, according to specific considerations. For example, it should be noted that a steering bias compensation of a 4x2 (also referred to as 4by2, two wheel drive vehicle with four wheels) and 6x2 (also referred to as 6by2, two wheel drive with six wheels), by means of embodiments of the present invention, may comprise a preference in implementation. Preferentially compensating to balance the steering box piston and/or an effective weight of the steering box piston may be considered as most effective for a 4x2 model, whereas for the 6x2 model, the preference may comprise a compensation to balance the drag link to a point of equilibrium. For various models, the relative effects of the steering box piston and drag link may differ.

The embodiment of the present invention illustrated in FIG. 7, for example, is particularly suitable for 6x2 vehicles.

Embodiments of the present invention are also suitable for implementation in other drive types of vehicles, e.g. 4x4, 6x4, 8x4 etc. In particular, it should be noted that vehicles that drive on the left side of the road that have a vertically mounted steering gear box and have a steering box counterbalance or (mechanical bias), according to embodiments of the present invention, fitted would benefit from; * Improved straight line stability and easier straight line handing.

* Increased road safety by reducing hard shoulder incursions (accidents).

* Reduced driver fatigue, generally.

-24 - * Reduced pain in the drivers hand and wrist from repetitive strain injury (RSI).

* Reduced musculoskeletal disorders (MSD's) from repeated exposure to low-intensity asymmetric loads over a long period of time (back pain).

* Reduced tyre wear.

S * Reduced power steering pump loads.

* Reduced steering rack and component wear.

SLt±:..advantages..resulting:.fr. m.:.the iètbibh h lOt ti IStFiàñdSàfétHd: the &iQèf Of the heavy vehicle but also for the environment Embodiments of the present invention are preferably implemented on a RHD vehicle, to correct a steering bias arising from a left road camber. It should be noted, however, that embodiments of the present invention are also suitable for inclusion and application on a LHD vehicle, especially a LHD vehicle to be driven in e.g. the UK on the left hand side of the road, to compensate for a steering bias. Additionally, embodiments of the present invention may also be implemented to compensate for steering bias arising from issues other than road camber, optionally with suitable weight modifications depending on the level of correction required.

Modifications to embodiments of the invention described in the foregoing are possible without departing from the scope of the invention as defined by the accompanying claims. Expressions such as "including". "comprising", "incorporating", "consisting of", "have", "is" used to describe and claim the present invention are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. Numerals included within parentheses in the accompanying claims are intended to assist understanding of the claims and should not be construed in any way to limit subject matter claimed by these claims.