The invention relates to a device for steering a multi-axle vehicle, which vehicle has on each axle at least two wheels arranged on either side of the vehicle, wherein the wheels of at least two axles are steerable, and wherein the steering device comprises on at least one side of the vehicle at least one steering rod connecting the steerable wheels to each other. Such a steering device is known, for instance from applicant’s earlier patent EP 2540595 Bl.

In multi-axle vehicles with steerable wheels on a plurality of axles the problem occurs that it is not easy to have all wheels perform a purely circular movement around the same centre during travel through a bend. This is because the steering deflections of the different wheels have to be adapted to each other for this purpose. This is not always the case in practice, whereby the wheels of some axles not only roll in the travel direction over the road surface but are also pulled sideways thereover when the vehicle negotiates a bend. This sideways slipping movement over the road surface results on the one hand in additional wear of the tyre and also causes additional loads on the wheel and the surrounding construction.

The problem of wheels slipping over the road surface occurs particularly in vehicles in which the steerable wheels can be placed at different positions, such as vehicles with an adjustable length or modular vehicles which can be assembled from different numbers of modules, but in vehicles of a fixed length not all wheels will perform a purely circular movement around a common bend centre either in practice. Extendable or modular vehicles are in practice mainly pulled vehicles, so trailers or semi-trailers, and the distance between the steerable wheels and the coupling between the pulled and the pulling vehicle are important for the steering behaviour in bends. This distance is after all different at each set length in the case of extendable or modular vehicles. The bend radius and the position of the centre of the bend, the so-called momentary centre, hereby also differ at a determined angular displacement of the pulling vehicle relative to the trailer or semi-trailer. The ratio of the steering deflections of the steerable wheels of the pulled multi-axle vehicle and the angular displacement of the pulling vehicle relative to the pulled vehicle will thus be optimal only at a determined distance between the coupling, the steerable wheels and optionally present non-steerable wheels. At all other distances, so when the multi-axle vehicle is lengthened or, conversely, shortened relative to this optimal state, this ratio will represent a compromise.

In order to resolve this problem it is already known in pulled modular vehicles to modify the positions of the steering rods in the different modules to the length of the assembled vehicle and the location of the wheels therein. Connected for this purpose to each wheel is a plate provided with a large number of openings. Using a manual a user can then find, for each length of the assembled vehicle, a combination of holes in which the ends of the steering rods must be mounted in order to arrive at the best possible compromise. This solution has the drawback that repositioning all the steering rods is a great deal of work, which is moreover made more difficult because the steering rods are usually arranged on the inner side of the vehicle, and so are difficult to access. The chance of errors during placing of the steering rods is moreover considerable in view of the large number of possible combinations of holes in the plates, while the end result remains a compromise, as stated.

Already described therefore in the above stated patent EP 2540595 B 1 is a steering device wherein a steering rod is connected displaceably to the wheel of one of the axles by means of a transmission element connected pivotally to a suspension part of said wheel. In this older steering device the ratio of the movement of the steering rod and the resulting steering deflection of the wheel, the transmission ratio, can be varied without the steering rod having to be manually removed and displaced.

The invention now has for its object to provide a steering device for a multi-axle vehicle which is simpler use than the heretofore known steering devices and wherein the steerable wheels perform a purely circular movement around the momentary centre even more accurately during travel through a bend. This is achieved according to the invention in that the at least one steering rod is adjustable in the length on at least one side of the vehicle during travel. By adjusting the length of the steering rod in suitable manner while the vehicle travels, the transmission ratio can be continuously varied in relatively simple manner. The steering deflection of the wheels on the associated axle can thus be adapted better than previously to the bend radius and the position of the momentary centre.

This principle can be applied in any type of steering, from rigid axles with Ackermann steering to pivoted axles with slewing rings and independently suspended wheels with axial pivot steering. The desired variation of the transmission ratio can already be achieved with a slight adjustment of the length of the steering rod, for instance in the order of 75 mm to both sides of a starting length. The adjustment of the length of the steering rod thereby requires relatively little energy. It is further important that the adjustability relates to a passive part of the steering device, i.e. the steering rods. The adjustability does not affect the active components of the steering device, such as the steering cylinders, and thereby does not affect the reliable operation of the steering device either.

In an embodiment of the steering device wherein the steerable wheels on either side of the vehicle are individually steerable the steering device can comprise on each side of the vehicle at least one length-adjustable steering rod.

When the wheels of more than two axles are steerable and the steering device comprises on each side of the vehicle a plurality of steering rods mutually connecting the steerable wheels, at least one of the plurality of steering rods is preferably length-adjustable on each side of the vehicle. A close approximation of a perfect bend is thus achieved in structurally simple manner. For an optimal cornering performance all steering rods on either side of the vehicle can be length-adjustable.

In addition to optimizing the cornering performance, the adjustability of steering rods also provides other possibilities, such as placing all wheels mutually parallel and so enabling a lateral displacement.

Each length-adjustable steering rod is preferably provided with a controllable actuator co-acting therewith. Using such actuators, the lengths of the steering rods, and thereby the transmission ratio(s) can be set in rapid and simple manner. The setting can moreover take place here while the vehicle is travelling.

This can be achieved in structurally simple manner when each length-adjustable steering rod comprises two parts connected movably to each other by the controllable actuator.

In order to adapt the settings of the different steering rods to each other the steering device advantageously comprises a controller connected to each of the actuators for the purpose of determining a desired length for each length-adjustable steering rod.

The steering device can further be provided with a first detector connected to the controller for detecting a mode of use of the vehicle, wherein the controller is configured to determine on the basis of the detected mode of use the desired lengths for the length-adjustable steering rods. The transmission ratio can thus in each case be set depending on a mode of use of the vehicle.

When a length of the vehicle can vary, the first detector is preferably configured to detect the momentary length of the vehicle. The mode of use forming the basis for the setting of the steering rods can be the degree of extension in the case of a telescopically extendable vehicle or, in the case of a modular vehicle, the number of coupled modules and their length. The length of the vehicle, and thereby the distance between the associated axle and the coupling to the pulling vehicle, determines the transmission ratios in the steering system.

A travelling speed of the vehicle can additionally or instead vary, and the first detector can be configured to detect the momentary travelling speed of the vehicle. A speed- dependent adjustment of the steering angles can thus be achieved, whereby a greater degree of drift at higher speeds can for instance be compensated for.

In order to be able to give the length-adjustable steering rods a compact form, the or each controllable actuator can be a hydraulic actuator. A hydraulic actuator can exert a relatively great force and fits in well with the rest of the steering device, which takes a largely hydraulic form. Other types of actuator, such as for instance electromechanical or pneumatic actuators, can however likewise be envisaged. Electromechanical actuators have the advantage that they are relatively compact and electrical conduits are simpler to install than hydraulic conduits. The powers required for adjusting the lengths of the different steering rods however lie in the order of just several hundreds of Watts because only a slight extension or shortening is required for each steering rod, in the order of 60-75 mm to both sides, calculated from a neutral position.

The or each controllable actuator is advantageously configured to transmit information regarding the set length of the associated steering rod to the controller. Such feedback enables the steering to be optimized. This information can be collected by means of suitable sensors.

In a preferred embodiment of the steering device the or each controllable actuator can be configured to return the associated steering rod to an established length in case of a malfunction. By returning the steering rods to a predetermined length in the case of a malfunction the steering device maintains its alignment in the straight position and the vehicle remains steerable under all circumstances. For this purpose the actuators can be provided with biasing means, for instance in the form of a mechanical or hydraulic -pneumatic spring.

When the steering device is provided with a track rod connecting the steerable wheels on either side, this track rod can likewise be length-adjustable. The steering angles of the wheels on the left-hand side and right-hand side of the vehicle can hereby be varied relative to each other, whereby an even greater degree of adjustability is achieved.

When the multi-axle vehicle is a vehicle pulled by a pulling vehicle, the steering device preferably comprises a second detector for detecting a steering movement of the pulling vehicle and converting it into a steering signal. On the other hand, the vehicle can also be a self- propelling vehicle, in which a steering signal is generated by turning a steering wheel, or an autonomous vehicle which receives a steering signal generated at a distance.

The invention also relates to a multi-axle vehicle which has on each axle at least two wheels arranged on either side of the vehicle, wherein the wheels of at least two axles are steerable, and which is provided with a steering device as described above.

Such a multi-axle vehicle can be provided with a chassis adjustable in longitudinal direction. Owing to the presence of the above described steering device the steering deflection of the wheels of one or more axles can then be adapted to the set length of the chassis. When a multi axle vehicle is adjustable in the width, the above described steering device can also be used to adapt the steering deflection of one or more axles to the set width of the chassis.

It is on the other hand also possible to envisage the multi-axle vehicle forming a module and being provided with means for coupling thereof to another vehicle module. The steering deflection can then also be adapted to the length of the finally assembled vehicle which is determined by the number of modules coupled to each other and the length of each module.

In a preferred embodiment of the multi-axle vehicle according to the invention the wheels of at least a part of the axles are embodied as pivoted axle wheel sets. It is precisely in the case of pivoted axle wheel sets that the adjustability of the steering deflection provides great advantages, since it is here that the consequences of wheels slipping in transverse direction over the road are relatively great.

The invention also relates to a method for steering a multi-axle vehicle, which vehicle has on each axle at least two wheels arranged on either side of the vehicle, wherein the wheels of at least two axles are steerable and the steerable wheels on at least one side of the vehicle are connected to each other by steering rods, comprising of generating a steering signal and transmitting the steering signal via the steering rods to the steerable wheels. Such a method is characterized according to the invention in that a length of at least one steering rod on the at least one side of the vehicle is set such that steering lines of the steerable wheels display a desired course.

In a variant of this method the length of at least one steering rod on the at least one side of the vehicle can be set such that the steering lines of the controllable wheels intersect each other substantially in a common point when the vehicle travels through a bend. The adjustability of the steering rods can thus be used to reduce wear as a result of wheels slipping in transverse direction over the road.

In another variant of this method the length of at least one steering rod on the at least one side of the vehicle can be set such that the steering lines of the steerable wheels are substantially parallel. In this way the vehicle can be moved laterally, so at an angle to the longitudinal axis.

Further variants of this method form the subject-matter of the dependent claims

21-29.

The invention will now be elucidated on the basis of a number of embodiments, wherein reference is made to the accompanying drawing in which corresponding components are designated with reference numerals increased in each case by 100, and corresponding components on the left- and right-hand side of the vehicle are designated with L and R, and in which:

Figure 1A is a schematic top view of a combination of a prior art eight-axle pulled vehicle and a pulling vehicle during travel in a bend, wherein the steerable wheels of the eight-axle vehicle lie relatively closely behind the pulling vehicle and each have a steering deflection set for this situation,

Figure IB is a view corresponding to Figure 1A of the combination in a bend when the steerable wheels of the eight-axle pulled vehicle lie relatively further behind the pulling vehicle and each once again have a steering deflection set for this situation,

Figure 2A is a schematic top view of a combination of a pulling vehicle and a vehicle pulled thereby with a steering device according to the invention, with two axles with steerable wheels at the front and five axles with steerable wheels at the rear, wherein the wheels are in their straight position and wherein a distance between the front and rear axles is minimal,

Figure 2B is a view corresponding to Figure 2A of the combination when the distance between the front and rear axles is maximal,

Figure 3A is a view corresponding to Figure 2A of the combination in a bend when the distance between the front and rear axles is minimal, wherein the length of steering rods connecting the steerable wheels is set such that steering lines of the steerable wheels intersect in a common point,

Figure 3B is a view corresponding to Figure 2B of the combination in a bend when the distance between the front and rear axles is maximal, wherein the length of the steering rods of the steerable wheels are set to a different length, such that the steering lines once again intersect in a common point,

Figure 4 is a view of a length-adjustable steering rod for use in a vehicle according to the invention;

Figure 5 is a bottom view of a six-axle pulled vehicle with a steering device according to the invention, wherein all wheels are steerable and have been placed in a mutually parallel position for a lateral displacement of the vehicle,

Figure 6 is a perspective bottom view of the vehicle of Figure 5,

Figure 7 is a schematic representation of a controller, two detectors and a number of adjustable steering rods of the steering device according to the invention,

Figure 8 is a flow diagram showing the most important steps of the method according to the invention,

Figure 9 is a schematic top view of a four-axle vehicle with so-called Ackermann steering, wherein the steering system according to the invention is applied, and

Figure 10 is a detail view on enlarged scale according to the arrow X in Figure 3B. When a vehicle having a plurality of axles with steerable wheels negotiates a bend, sideways slipping of the steerable wheels over the ground can only be prevented when all steerable wheels describe a purely circular path around a common centre of the bend. For this purpose so- called steering lines of the wheels, i.e. lines forming the produced part of the axles of wheels in the direction of the bend, all intersect each other in the bend centre, or momentary centre. This is known as the so-called Ackermann principle. When the vehicle also has an axle with non-steerable wheels in addition to axles with steerable wheels, the momentary centre must in any case lie on the produced part of the axle with non-steerable wheels, since these wheels would otherwise slip over the ground. Ideally, a steering deflection must therefore be imparted to all steerable wheels of a multi-axle vehicle such that their wheel axles are all directed toward the momentary centre. Where reference is made here to “wheels”, this is understood to mean not just individual wheels, but also wheel sets, consisting of one or more wheels with associated wheel suspension and steering. These can for instance be pivoted axle wheel sets, independently suspended wheels or wheel sets mounted on a rigid axle, both single- and dual-tyre. The invention is applicable in steering devices on the basis of slewing rings, axial pivot steering and Ackermann steering.

Figures 1A and IB show that an extendable, multi-axle vehicle 1 according to the prior art, in this case a semi-trailer with eight axles 21-28 which is pulled by a pulling vehicle 3, describes a bend in respectively its retracted and extended state. This is a vehicle 1 with an adjustable steering system as described in EP 2540595 Bl, wherein at least one of the steering rods is displaceably connected on each side of the vehicle to one of the wheels in order to optimize the steering behaviour in bends. In this steering system the wheels of each axle 21-28 are individually mounted pivotally in the chassis (not shown here) on either side of vehicle 1. The pivotable wheels of adjacent axles 21-28 on each side of vehicle 1 are all mutually connected by steering rods 10-16, and are steered collectively. Functioning as input signal for the steering in this system is the angular displacement of pulling vehicle 3 relative to semi-trailer 1, which can be measured at the position of rotating dish 7 which forms the connection between these vehicles 1, 3. When the pulled vehicle is a trailer, the angular displacement of the drawbar relative to the trailer could function as input signal.

In this known steering system the steering signal is transmitted hydraulically or mechanically to a steering member 8 which is close to the rear of vehicle 1 and which is connected by means of steering arms 9 to the wheels of the rearmost axle 28 on either side of vehicle 1. From this axle 28 the steering signal is transmitted to the wheels of the axles 21-27 located further forward by means of steering rods 10-16. These steering rods 10-16 are each connected pivotally to the suspension of an associated wheel. Because the position of the connection between each steering rod 10-16 and the corresponding wheels varies from axle to axle, the steering deflection becomes smaller as the steering signal is transmitted from the rear axle 28 forward by the steering rods 12-16. At the two foremost axles 21, 22 the position is conversely chosen such that the steering deflection increases again there.

In this steering system the second and third steering rods 11, 12 are connected on either side to the wheels of the third axle 23 via a pivotable transmission element. The steering movement is thereby reversed at the position of the third axle 23 when the wheels of third axle 23 are locked in their straight position relative to the chassis (Fig. 1 A). This reversal of the steering movement, whereby the wheels of the foremost axles 21, 22 counter-steer, results in a substantially optimal steering when the axles 21-28 lie relatively close to rotating dish 7, so when vehicle 1 is retracted to its minimal length FI. When vehicle 1 is extended to its maximal length L2, and axles 21-28 therefore he relatively far from rotating dish 7, the wheels of second axle 22 can be locked in their straight position. In that case the wheels of first axle 21 are also straight, and the steering deflection of the wheels of third axle 23 is limited in that the pivotable transmission element transmits the steering deflection of fourth axle 24 with reduced effect. The course of the steering deflection per axle shown in Figure IB is thereby achieved, this resulting in a substantially optimal steering in the fully extended state of vehicle 1.

Figures 1A and IB show that the steering device according to EP 2540595 B1 results in a very close approximation of the optimal steering angles. In this embodiment the rearmost two axles 53, 54 of pulling vehicle 3 are provided with non-steering wheels 63, 64, while the foremost two axles 51, 52 are provided with steering wheels 61, 62. The momentary centre M must here thus lie on the produced part of a line between axles 63, 64. As can be seen, the steering angles to be obtained represent a compromise determined on the one hand by the requirement that the length of multi-axle vehicle 1 can vary over a wide range and on the other by the rigid connection between the wheels on each side of vehicle 1 as a consequence of the presence of the steering rods 10L-16L, 10R-16R. The intersecting points between the steering lines S1L-S8L, S1R-S8R of axles 21-28 therefore do not intersect in a single point, the momentary centre, but he in an area M. This area M determined by the individual intersecting points is relatively small in the steering device according to EP 2540595 Bl, particularly in the retracted or short state of vehicle 1, whereby sideways slipping over the ground of the wheels during travel through a bend will be limited.

Figures 2 A and 2B show an extendable multi-axle vehicle 101 according to the invention - in this case a semi-trailer with a front dolly 104 with two axles 121, 122 with steerable wheels 141, 142 and a rear dolly or rear axle set 105 with five axles 123-127 with steerable wheels 143-147 - in respectively its retracted and its extended state. In the shown embodiment the extendable multi-axle vehicle 101 is a pulled vehicle which is connected to a pulling vehicle 103. The pulling vehicle 103 here has a front axle 151 with steering wheels 161 and two rear axles 152, 153 with non-steering wheels 162, 163.

The pulled vehicle 101 has on its front side a gooseneck 102 which rests pivotally on the rear side of pulling vehicle 103 via a rotating dish (not shown here). The axis P about which vehicle 101 is pivotable lies between the two non-steering axles 152, 153. The vehicle 101 has here between the front dolly 104 and the rear dolly 105 a loading floor 106, which can for instance be a lowered floor when the vehicle 101 is a (semi-)low-loader. The distance between front dolly 104 and rear dolly 105 can be varied by lengthening or shortening the loading floor 106. For this purpose one or more chassis beams (not shown here) of vehicle 101 can for instance take a telescopic form. The difference between the length LI of vehicle 101 in fully retracted state and the length L2 in fully extended state is such that the optimal steering angles of the steerable wheels 141-147 in the retracted state clearly differ from the optimal steering angles in the extended state.

Arranged on both the front side and the rear side of vehicle 101 in this embodiment is a pair of steering cylinders, respectively 108L, 108R and 109L, 109R, each imparting a steering deflection to a wheel, respectively 141 L, 141R and 146L, 146R, of respectively foremost axle 121 and second-to-last axle 126. The wheels, respectively 141, 142 and 143-147, of the successive axles, respectively 121, 122 and 123-127, on each side of vehicle 101 are mutually connected by respective steering rods 110 and 111-114. In addition, the steerable wheels 141R-147L, 141R-147R on either side of vehicle 101, which are in principle steerable independently of each other, are mutually connected by one or more track rods, here two track rods 133, 134. Each of these track rods 133, 134 enables the steering movements to be transmitted from the one side of vehicle 101 to the other side in the event that one of the steering cylinders, respectively 108L, 108R and 109L, 109R, were to fail unexpectedly. Each track rod 133, 134 can co-act with the same axle on which the steering cylinders 108, 109 also engage. In the shown embodiment the first track rod 133 is arranged at the position of the foremost axle 121, while the second track rod 134 mutually connects the wheels 146L, 146R of the second-to-last axle 126.

In this embodiment the steering signal for the steering cylinders 108, 109 is also derived from a steering movement of pulling vehicle 103. For this purpose the steering device is provided with a detector, referred to hereinafter as second detector, which registers the steering movement of pulling vehicle 103 and converts it into a steering signal. The second detector can for instance comprise two cylinders (not shown here), one end of which is in each case connected to the pulling vehicle and the other end to the vehicle, and which are incorporated in joint hydraulic circuits with the steering cylinders, as will be elucidated below with reference to figure 9. It is however also possible to embody the second detector as electrical or optical sensor which generates a steering signal which activates for instance a hydraulic pump connected via valves to the steering cylinders 108, 109 and which also controls the position of the valves.

In contrast to the above discussed prior art, each steering rod 110-114 is mounted at a fixed position on the two wheels, respectively 141, 142 and 143-147, connected thereby.

Figure 10 shows that a first end 156 of a steering rod 111L, 111R is mounted on a steering element 120L, 120R relatively closer to a rotation point of a wheel set 144L, 144R than a second end 157 of a subsequent steering rod 112L, 112R. In order to still be able to achieve an optimal steering angle for each wheel 141-147 the provision is made according to the invention that at least one of the steering rods on each side of vehicle 101 is adjustable in the length. In the shown embodiment all steering rods 1 lOL-114L, 1 lOR-114R on either side of vehicle 101 are length-adjustable. The ratios between the steering deflections of the successive wheels, respectively 141, 142 and 143- 147, which are mutually connected by the steering rods, respectively 110 and 111-114, can thus be set such that a determined steering deflection of the wheels, respectively 141 L, 141R and 146L, 146R, which are steered by the steering cylinders, respectively 108L, 108R and 109L, 109R, automatically results in a steering deflection of all other steerable wheels, respectively 142L, 142R and 143L-145L, 143R-145R, 147L and 147R, optimally suited thereto.

Each steering rod - one of the foremost steering rods 110 is shown by way of example in Figure 4 - has here a first end 156 which is connected to a rear one 142 of two wheels, and a second end 157 which is connected to a wheel 141 placed upstream thereof. Each end 156, 157 has here a bolt 158, 159 whereby the steering rod 110 can be mounted on the wheel, and a bearing 160, 161 in which the mounting bolt 158, 159 is pivotally mounted. A distance D between first end 156 and second end 157, which determines the effective length of steering rod 110, can be increased or reduced, whereby the ratio between the steering deflections of the two wheels 141,

142 connected by the steering rod 110 can be varied. In order to increase or reduce the length of steering rod 110 it is provided with a controllable actuator 166, in this case in the form of a hydraulic cylinder 167. This cylinder 167 is mounted on a part 110A of the steering rod close to the second end 157, while a piston rod 168 movable in cylinder 167 is mounted on a part 110B of the steering rod which comprises first end 156.

The hydraulic cylinder 167 is here a double-action cylinder which has two connections 169, 170 for the feed and discharge of hydraulic fluid. The actuator 166 can be connected to the hydraulic system of the vehicle 101, which is also used for damping and height control of the chassis and for retracting and extending the chassis. The actuator 166 here further has a connection 171 for a connecting cable 172 running to a controller 173 (figure 7). Valves (not shown here) can be opened on the basis of a command from controller 173, whereby hydraulic fluid flows from a feed conduit to one of the two connections 169, 170 and hydraulic fluid is pressed via the other connection from cylinder 167 to a return conduit. Piston rod 168 can thus be extended (arrow E) or retracted (arrow R), whereby the length of steering rod 110 is increased or reduced. In this way the ratio between the steering movements of the wheels 141, 142 connected by steering rod 110 can be continuously varied. This can even take place while vehicle 101 is travelling.

Although a hydraulic actuator 166 is shown and discussed here, it will be apparent that another type of controllable actuator could also be applied, for instance an electromagnetic actuator such as a servomotor or a screw spindle, or a pneumatic actuator. Electromagnetic actuators are compact, particularly at the low powers - in the order of several hundred Watts - required to extend or shorten each steering rod, and can be incorporated in a steering device in relatively simple manner. It must be considered here that the maximum stroke required of the actuator is relatively small, for instance 60-80 mm around a neutral position. An important aspect of actuator 166 is that it is configured to return the steering rod 110 to its original length when a malfunction occurs in the steering device. For this purpose each actuator 166 is configured to return to its neutral position in the event of a malfunction. For this purpose actuator 166 can be provided with a (mechanical or hydraulic-pneumatic) biasing spring (not shown here). When one of the actuators 166 has been returned to its neutral position due to malfunction, this position will be fed back to the controller 173. In this case the controller 173 can generate a command whereby the other actuators 166 are also returned to their starting positions. In the case of hydraulic actuator 166 this therefore means that the piston rod 168 is retracted if it was extended, or is conversely extended if it was retracted. In the event of a malfunction the vehicle 101 thus maintains the alignment in the straight position and remains steerable as normal, wherein the steering rods 110-114 act as rigid elements. Although the steering behaviour in bends is then not optimal, the functionality of vehicle 101 is preserved. This is of great importance, since vehicles for special transport in particular are difficult to replace if they were to drop out due to a defect.

At least a part of the steering rods 110-114 is in this embodiment otherwise also provided with an additional adjusting mechanism 174, which can only be operated when vehicle 101 is stationary and which can be used to set a neutral or straight position of the steering. The part of the steering rod 110 connected to piston rod 168 is for this purpose itself also embodied in two parts. These two parts are provided at their mutually facing ends 175A, 175B with screw thread with opposing pitch, while the adjusting mechanism 174 further comprises a nut 176 which can be twisted by a user when vehicle 101 is stationary. The two screw thread ends 175A, 175B are hereby moved toward each other (arrow T) or apart (arrow F). The parts on either side of adjusting mechanism 174 are each provided with a pinching member 190A, 190B whereby adjusting mechanism 174 can be locked against unintended rotation. Each wheel can thus be accurately straightened after mounting of the steering rods.

Not only the steering rods 110L-114L, 110R-114R on either side of vehicle 101 are length-adjustable in the shown embodiment, but so are the two track rods 133, 134 on the front and rear side. Because the optimal steering angles of the respective left-hand and right-hand wheels 141 L, 141R and 146L, 146R of an axle 121, 126 will differ during travel through a bend, a rigid connection between these wheels by a track rod 133, 134 is undesirable. By making the track rods 133, 134 length-adjustable they form no impediment to setting of the optimal steering transmission on the left hand-side and right-hand side of vehicle 101, but can be adapted thereto. The track rods 133, 134 can take the same structural form as the steering rods 110-114, and so can have the construction shown in Figure 4.

The representation of the track rods 133, 134 is otherwise slightly simplified in this embodiment, since the Figures 2 and 3 suggest that the track rods 133, 134 engaged directly on the respective wheel sets 121L, 121R, 126L, 126R. Because the left-hand wheels 141L and 146L are incorporated in a different hydraulic circuit than the right-hand wheels 141R, 146R, adjustment of the track rods 133, 134 would result in conflicts between the two hydraulic circuits in such a direct engagement. Each track rod 133, 134 is therefore in practice connected to the respective wheel sets 121L, 121R, 126L, 126R, in each case via a separate, pivotally mounted steering part (not shown here).

As stated, each actuator 166 of a steering rod 110-114 is controlled on the basis of commands coming from a controller 173 via a signal line. In the shown embodiment the signal line consists of a central conduit or bush 177L, 177R, to which are connected lines 172, 178, 179 leading to the individual actuators 166 of the steering rods 110-114. In the shown embodiment the actuator 166 of the rear track rod 134 is connected via a separate signal line 180 to the controller 173, but could also be connected to a bush 177, as well as the actuator (not shown here) of the foremost track rod 133. In the shown embodiment each actuator 166 also generates a signal which is representative of its momentary state, and this state signal is fed back to controller 173 via the corresponding signal line 177, 180. The state signal can for instance be generated by a sensor which detects the position of the piston rod 168 relative to the cylinder 167, or by a sensor which measures the length of the steering rod 110.

The controller 173 is here configured to determine for each wheel 141-147 an optimal steering angle on the basis of a mode of use of vehicle 101. This mode of use can for instance be the momentary length L of vehicle 101, when vehicle 101 is extendable or modular. The optimal steering angle then depends on the position of the wheel 141-147 relative to the steering wheels 161 of pulling vehicle 103. In practice the controller 173 receives a signal from a first detector 183 which detects the momentary length L of vehicle 101. The first detector comprises for instance an encoder 183A which detects an extending or retracting movement of vehicle 101. In the case of a modular vehicle the first detector can determine the number of modules from which the vehicle is assembled. The relative position of each wheel 141-147 relative to for instance the rotating dish and the rotation point P determined thereby can be determined from this momentary length L and from the known position of each wheel 141-147 in vehicle 101. This position is associated with an optimal steering angle, which can for instance be calculated or read from a table. For this purpose controller 173 is provided with a central processing unit 181 which can run through a program in order to determine the optimal steering angle. Controller 173 can also be provided with a memory 182 in which is stored a table with optimal values of the steering angle for different positions of the wheels 141-147.

Because the wheels of a single axle will normally not lie on a common steering line during travel through a bend (except in the case of a vehicle with Ackermann steering), the optimal steering angles for the wheels 141L-147L on the left-hand side of vehicle 101 will differ from those for the wheels 141R-147R on the right-hand side. Each wheel 141L-147L, 141R-147R will thus have its own optimal steering angle, and in order to achieve it the lengths of the steering rods 1 lOL-114L, 1 lOR-114R have to be set separately on the left and on the right.

Another mode of use of vehicle 101 which can affect the optimal steering angle is the speed. Depending on the speed, vehicle 101 will drift to some extent in a bend, and in order to ensure an ideal steering deflection for each wheel 141L-147L, 141R-147R it may be necessary to compensate for the drift angle. For this purpose the first detector can also comprise a speed sensor 183B which sends a speed signal to controller 173.

Setting the optimal steering ratios between wheels 141L-147L, 141R-147R of successive axles 121-127 using the above described steering device thus takes place as follows - see Figure 8:

The length F of vehicle 101 is first determined using the first detector 183 (block 801). The position of each wheel 141F-147F, 141R-147R relative to the rotating dish is then determined from the detected length F by the controller 173, and the optimal steering angle for each wheel 141F-147F, 141R-147R and therefore the optimal steering ratio and the optimal length of each steering rod 1 lOF-114F, 1 lOR-114R is determined therefrom (block 802). The steering rods 1 lOF-114F, 1 lOR-114R are then brought to the thus determined length by controlling the controllable actuators 166 (block 803). This takes place in principle while the vehicle travels. During and after control of the actuators 166 it is checked whether a malfunction is occurring anywhere (block 804).

If a malfunction were indeed detected, the actuators 166 are returned to their neutral position, whereby the steering rods 1 lOF-114F, 1 lOR-114R take on their original length and the wheels 141F-147F, 141R-147R are once again aligned straight when the vehicle travels forward (block 805). The vehicle 101 can then be steered in the manner of a conventional vehicle with non-adjustable steering. Although the steering behaviour will no longer be optimal in this situation, it is in any case acceptable, and vehicle 101 can be used safely until the malfunction can be rectified.

When no malfunction is found, the speed of the vehicle is determined using the first detector 183 (block 806). Controller 173 then determines for each wheel 141F-147F, 141R- 147R the optimal steering deflection at the measured speed, as well as the optimal steering ratio and therefore the optimal length of the steering rods 1 lOF-114F, 1 lOR-114R (block 807). It is then checked whether the previously set length of the steering rods 110F-114F, 110R-114R is equal to the now determined speed-dependent optimal length (block 808). When this is the case, the program will return to the check for any possible malfunctions in block 804. If the optimal length determined on the basis of the speed were to vary from the set length, the steering rods 1 lOF-114F, 1 lOR-114R will still be returned to this optimal length (block 809), after which the programme once again returns to the malfunction check.

This method 800 can be performed continuously during travel with vehicle 101, so that each wheel 141L-147L, 141R-147R has an optimal steering angle at all times.

The result of this method 800 is shown in figures 3A and 3B. As can be seen, with a suitable setting of the length of respectively the steering rods 110L, 110R of the front dolly 104, the steering rods 111L-114L, 111R- 114R of the rear dolly 105 and the track rods 133, 134 of the foremost and rearmost dollies or axle sets 104, 105 the steering ratios between the subsequent wheels are adapted such that each wheel 141L-147L, 141R-147R takes up an optimal steering angle for the degree of steering of the pulling vehicle 103, the length LI of vehicle 101 and the speed of the vehicle. The steering lines S101L-107L of the wheels 141L-147L on the left-hand side of the vehicle and the steering lines S101R-107R of the wheels 141R-147R on the right-hand side of vehicle 101 all intersect each other exactly in the bend centre or momentary centre M, which is defined by the steering line STF of the steering wheels 161L, 161R and the steering line STR of the non-steering wheels 162L, 162R and 163L, 163R of the pulling vehicle 103. This is the case both in the retracted state of vehicle 101 in Figure 3A, where the momentary centre is designated as MS, and in the extended state of Figure 3B with momentary centre ML.

Comparison of these figures shows that the steering angles of corresponding wheels differ slightly from each other in the retracted and extended state of vehicle 101. This is the case not only for the steering angles of the wheels 143-147 of the rear dolly 105, but also for the steering angles of the wheels 141, 142 of the front dolly 104. Although the distance of these front wheels 141, 142 relative to the rotation point P does not change along with the length of vehicle 101, the position of the bend centre or momentary centre does shift from the position MS (Figure 3A) to the position ML (Figure 3B). This is why the optimal steering angles of the front wheels 141, 142 also change when vehicle 101 is extended or conversely shortened.

As can further be seen in Figure 3B, in the extended state of vehicle 101 the respective steering lines S105L and S106L of the left-hand wheels 145L, 146L of the third-to-last and second-to-last axles 125, 126 almost coincide with the respective steering lines S106R and S107R of the right-hand wheels 146R, 147R of the third-to-last and second-to-last axles 126, 127. In the retracted state of vehicle 101 (Figure 3A) however, these steering lines are still clearly oriented differently.

Adjusting the lengths of the steering rods and the track rod(s) enables not only an optimal steering angle to be set for each wheel for travelling through a bend without sideways slipping over the ground, but also enables other directions of movement to be set. It is thus possible to place all wheels on either side of the vehicle parallel at an angle relative to a longitudinal axis of the vehicle with a suitable length adjustment of the steering rods and the track rod(s). This can be seen in Figures 5 and 6, where another embodiment of the vehicle 201 is shown, with six axles 221-226 on the rear side.

In this embodiment each axle 221-226 has two respective pivot axle wheel sets 241L-246L and 241R-246R. These wheel sets 241L-246L, 241R-246R are arranged on either side of a continuous chassis beam 288. Arranged in each case between two successive wheel sets 241L- 246L, 241R-246R on each side of vehicle 201 is a shore 284 which supports a loading floor 206 of vehicle 201. Each pivoted axle wheel set 241L-246L, 241R-246R has here a wheel support arm 285 with a rotating bearing 286 at an outer end, around which an axle body (not shown) with two wheels is pivotally mounted. Further arranged between the wheels is a brake cylinder 287. Each wheel set 241L-246L, 241R-246R is mounted in the chassis of vehicle 201 for pivoting about a vertical steering axle S and has a steering bracket 289, to which the first end 256 of a first steering rod 210-213 and a second end 257 of a second steering rod 211-214 are attached. In the shown embodiment the steering rods 210L-214L, 210R-214R are all length-adjustable steering rods according to the invention. Arranged between the left-hand and right-hand wheel set 241L, 241R of foremost axle 221 is a track rod 234, which in the shown embodiment is also length-adjustable.

A suitable setting of the lengths of the individual steering rods 210L-214L, 210R- 214R enables the steering ratio between successive wheels to be set such that all wheels 241L- 246L, 241R-246R have a substantially identical steering deflection. Vehicle 201 can hereby thus be driven at an angle to its longitudinal axis, also referred to as crabbing. This is particularly important when the vehicle 201 must manoeuvre in small spaces. To set the lengths of the steering rods 210L-214L, 210R-214R in order to enable this displacement a program which is run by the central processing unit 281 can be stored in the memory 282 of controller 273, although a table in memory 282 can also be read for this purpose.

This embodiment of vehicle 201 is otherwise likewise extendable. The chassis is divisible between the gooseneck 202 and a main part of the loading floor 206, and the rear part 288B of chassis beam 288 has a greater diameter than the front part 288A thereof. The front part 288A of chassis beam 288 thus continues over a determined length into the rear part 288B and is telescopically slidable therein, as shown schematically with broken lines. To move vehicle 201 at an angle to the longitudinal axis the length otherwise does not affect the steering, since all wheels 241L-246L, 241R-246R are oriented parallel. The length setting of steering rods 210L-214L, 210R-214R therefore does not depend in that case on the length of vehicle 201, nor for that matter on the travelling speed. Controller 273 can thus ignore the input from first detector 283.

In the variants of the steering system shown up to this point there were always wheels or wheel sets that were individually steerable on either side of the vehicle, such as pivoted axle wheels sets or wheels sets with axial pivot steering, and steering rods were also length- adjustable on either side of the vehicle. Figure 9 shows the application of the steering system in a vehicle 301 with a so-called “Ackermann steering”. The wheels 341L-344L, 341R-344R are here in each case mounted on opposite ends of a rigid axle 321-324, which is connected pivotally to the chassis of vehicle 301 by means of a rotating dish 317-320. The steerable axles 321-324 are mutually connected by steering rods 310-312 on only one side of vehicle 301. In accordance with the invention, these steering rods 310-312 are once again length-adjustable. The nominal steering ratios between the successive axles are determined by the length and angle of steering arms 349, 350, 355, which are mounted on the rotating dishes 317-320. Each steering rod 310-312 is mounted with one end on one of the steering arms 349, 350, 355 and with the other end on one of the rotating dishes 317-320.

This figure further shows that a second detector 336 converts a steering movement of a pulling vehicle (not shown here) into a steering signal for the vehicle 301. The second detector 336 is here incorporated in the gooseneck 302 and comprises two cylinders 337L, 337R, one end of which is in each case connected to the rotating dish 307 of the pulling vehicle, while the other end is connected to vehicle 301. These cylinders 337L, 337R are each incorporated in hydraulic circuit 338L, 338R, in which a steering cylinder 309L, 309R is also incorporated. In the shown embodiment corresponding connections of the two cylinders 337 and 309 are in each case connected to each other via hydraulic conduits designated as “red”, “yellow”, “blue” and “green”, so that extension of the detector cylinder 337 results in retraction of the steering cylinder 309 connected thereto, and vice versa. A steering movement of the pulling vehicle thus results in a pivoting movement of the rotating dish 307, whereby one of the cylinders 337 is retracted and the other extended. The flow of hydraulic fluid in the circuits 338L, 338R caused thereby results in an opposing movement of the associated steering cylinders 309L, 309R, and thereby in a counter steering movement of axle 323, which is transmitted via the steering rods 310-312 to the other axles 321, 322 and 324. The degree to which the axles 321, 322 and 324 follow the movement of axle 323 depends on the length of each of the steering rods 310-312, which is in turn determined by the controller (not shown here) on the basis of the input from the first detector (not shown here either).

The invention thus makes it possible with simple means to vary the transmission ratio between a steering signal and a resulting steering deflection per wheel in order to give each wheel an optimal steering angle at different lengths of a vehicle.

Although the invention has been elucidated above on the basis of a number of embodiments, it will be apparent that it is not limited thereto. The invention can be varied in many ways within the scope of the following claims.