A steering gear arrangement and a steering system with such a steering gear arrangement

Abstract

The present invention relates to a steering gear arrangement for a ground vehicle steer-by-wire steering system (100) comprising a rack and pinion steering arrangement with a rack arrangement (7) connected to respective inner ends of a first and second tie rod (5A,5B), first and second actuation motors (9A,9B) via first and second pinions (8A,8B) connected to the rack arrangement (7). The rack arrangement (7) comprises a first and a second rack element (70A,70B) aligned such that an outer end of the first rack element (70A) is connected to the first tie rod (5A) and an outer end of the second rack element (70A) is connected to the second tie rod (5B). The first actuation motor (9A) via first pinion (8A) is connected to the first rack element (70A), the second actuation motor (9B) via second pinion (8B) is connected to the second rack element (70B) for separate controlling / driving of the first and second rack elements (70A,70B). The first and second rack elements (70A,70B) are independently movable with respect to one another to a limited extent.

Description

[0001] Title:

[0002] A STEERING GEAR ARRANGEMENT AND A STEERING SYSTEM WITH SUCH A

[0003] STEERING GEAR ARRANGEMENT

[0004] TECHNICAL FIELD

[0005] The present invention relates to a steering gear arrangement having the features of the first part of claim 1. The invention also relates to a steering system with such a steering gear arrangement having the features of the first part of claim 13.

[0006] BACKGROUND

[0007] Traditionally the steering system of e.g. a road vehicle comprises a mechanical connection between the steering wheel and the steerable wheels. Other steering systems, not having a mechanical connection, are also known, so called SbW, steer-by-wire, systems. In a SbW, steer-by-wire, system, one or more sensors register physical properties, e. g. forces and movements of the steering wheel or other steering input device, such as a yoke or joystick or other means, and generate signals. These signals of the registered physical properties can be provided to an ECU, Electronic Control Unit, and transformed by the ECU into a desired action to be provided on the steerable wheels. A power assisted steering actuator that is electrically connected to the ECU and mechanically linked to the steerable wheels will then execute the desired action and apply desired forces to the said steerable wheels. Feedback to the driver is typically provided by means of an electric motor, creating forces and / or movements to the steering wheel, otherwise transmitted via the mechanical connection.

[0008] SbW systems offer advantages compared to conventional mechanical steering, such as allowing energy absorption in collisions, flexible location of steering wheel, handling of left- and right-hand drive variants, removable steering wheel, variations in steering input devices, autonomous drive and advanced driving aid being some examples. Also, SbW offer several opportunities for the driving experience itself, e.g. variable steering ratio and immunity to road disturbances.

[0009] To obtain a desired feedback force, a feedback actuator, typically an electric motor, must be able to deliver a certain torque, either directly or via a gear. If there is a failure in the steering system, a desired functionality, or even a legal requirement, is that the vehicle still shall be controllable. An example of providing such a functionality is through the steering having a self-centring effect. When the steering wheel is connected mechanically to the steerable wheels of the vehicle, the self-centring forces are transmitted from the tyres via the suspension geometry to the steering wheel. When the force in the steering wheel is solely dependent on a feedback motor, the self-centring effect will be lost if the motor fails.

[0010] For ground vehicles, cars in particular, but also e.g., trucks, buses etc., with two steered wheels on a same axle, wherein the vehicle can have more than one steered axle, toe-in or toe-out on an axle has a large effect on vehicle behaviour. Toe-in and toe-out are important in describing the alignment of the wheels of a ground vehicle in relation to its longitudinal axis, i.e. alignment of the axis of a wheel with respect to the longitudinal axis of the vehicle seen from above and define an angle at which the wheels are oriented with respect to one another viewed from above.

[0011] I.e. at toe-in the front edges of the tires point slightly inward, and for a front steered axle will improve the steering response, zero toe-in is beneficial for low rolling resistance, whereas at toe- out, the front edges of the tires point slightly outward and can be used to improve stability during braking.

[0012] Thus, appropriate toe alignment is crucial among other things for the stability of the ground vehicle, safe driving, for tire wear and vehicle steering precision.

[0013] However, only one value of toe-in can be set when building a vehicle, resulting in a compromise of the many contradicting attributes referred to above as well as other not explicitly mentioned herein.

[0014] In addition, the so called Ackerman is another steering phenomenon. In low speed manoeuvring it is desired to have a high degree Ackermann e.g. to minimize tyre wear, rolling resistance and not to upset nicely made gravel driveways etc. In higher speeds it is beneficial with a low, or even slightly negative Ackermann to increase grip levels during evasive manoeuvres. The degree of Ackermann is determined by steering and suspension geometry and is typically also a compromise of the attributes referred to above, but Ackerman is also limited by packaging constraints.

[0015] To some degree, toe changes, e. g. small wheel angles, can be designed to come from longitudinal forces and lateral forces and from vertical wheel travel and thus assist in having effect on the vehicle behaviour as described above. However, usually, this effect is quite limited and involves many constraints, e.g. when braking in curve it is desired to have a small steer angle to the left on the outer wheel (left if it is a turn to the right), and vice versa, to stabilise the vehicle, but when braking on split-mu, with a good grip on the left side, it is desirable to have a small steer angle to the right.

[0016] There are known steer-by-wire steering gears comprising a steering rack in a housing with two electric motors giving force to the steering rack via gears and a pinion on each side of the steering rack. However, the setting of toe is restricted to the fabrication stage, flexibility is low and the building in of elements, e.g. locations of inner and outer tie rods, is inflexible upon construction, fabrication liberty is severely restricted, as well degree of Ackermann steering is restricted and inflexible. Also, safety is not as desired if one of the motors (particularly electric) is malfunctioning or would brake rather than drive, or even fall out completely, and vehicle behaviour is not optimal under different varying conditions.

[0017] SUMMARY

[0018] It is therefore an object of the present invention to provide a steering gear arrangement for a steer- by-wire steering system and a steer-by-wire steering system respectively through which one or more of the above-mentioned problems can be solved and through which one or more of the shortcomings can be overcome.

[0019] It is an object of the present invention to provide an improved steering gear arrangement for a wired or a wireless steering system.

[0020] It is a particularly an object to provide a steering gear arrangement for a steer-by-wire steering system through which steering safety can be enhanced. More particularly it is an object to provide a steering gear arrangement for a steer-by-wire steering system for a ground vehicle with two steered wheels on a same axle through which a certain amount of steering safety can be upheld also when an actuation motor falls out or doesn’t work properly.

[0021] Further it is a particular object to provide a steering gear arrangement for a steer-by-wire steering system through which vehicle manoeuvring can be facilitated at driving under varying driving conditions.

[0022] Another particular object is to provide a vehicle steering gear arrangement for a steer-by-wire steering system through which the dependence on, at fabrication stage, pre-set toe-characteristics can be reduced.

[0023] Yet another particular object is to provide a steering gear arrangement for a steer-by-wire steering system for a ground vehicle through which driving stability and steering response can be improved.

[0024] It is also a particular embodiment to provide a steering gear arrangement for a steer-by-wire steering system for a ground vehicle through which through which tyre wear and energy consumption can be reduced.

[0025] Another object is also to provide a steering gear arrangement for a steer-by-wire steering system for a ground vehicle through which a larger advantage of pre-set toe-characteristics and Ackermann angle can be taken than with hitherto known steering arrangements.

[0026] Another particular object is to provide a steering gear arrangement for a steer-by-wire steering system for a ground vehicle which provides an enhanced freedom in building a steering system and allows a larger, flexible, freedom in the location e.g. for inner and outer tie rods and also other elements or components, in relation to link arms and knuckle.

[0027] Still another particular object is to provide a vehicle steering gear arrangement for a steer-by-wire steering system which is easy to fabricate and build in. A most particular object is to provide a SbW steering system arrangement through which one or more of the above-mentioned objects can be achieved.

[0028] It is particularly an object to provide a SbW steering system with such a steering gear arrangement through which one or more of the above mentioned objects can be achieved.

[0029] Therefore a steering gear arrangement as initially referred to is provided which has the characterizing features of claim 1. Therefor also a steering system having the characterizing features of claim 13 is therefore also provided.

[0030] Advantageous embodiments are given by the appended dependent claims.

[0031] It will be appreciated that features of the invention are susceptible to being combined in any combination without departing from the scope of the invention as defined by the accompanying claims.

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention will in the following be further described, in a non-limiting manner, and with reference to the accompanying drawings, in which:

[0034] Fig. 1. is a schematic illustration of a state-of-the art ground vehicle steering system showing two wheels and a steering gear with a steering rack,

[0035] Fig. 2. is a schematic illustration of a ground vehicle steering system showing two wheels and a steering arrangement comprising a steering gear with a steering rack arrangement,

[0036] Fig. 3. is an enlarged, schematic view of a section of the steering rack arrangement of the steering arrangement shown in Fig. 2,

[0037] Fig. 4. is an enlarged, schematic view of a section of a steering rack arrangement of a steering arrangement as shown in Fig. 2 according to an embodiment wherein the steering rack arrangement comprises a spring for balancing compression forces in the rack elements, e.g. a contraction or tension spring,

[0038] Fig. 5 is an enlarged, schematic view of a section of a steering rack arrangement of a steering arrangement as shown in Fig. 2 according to another embodiment wherein the steering rack arrangement comprises a spring for balancing tension forces in the rack elements, e.g. a compression spring arranged to compress when the rack arrangement elongates,

[0039] Fig. 6 is an enlarged, schematic view of a section of a steering rack arrangement of a steering arrangement as shown in Fig. 2 according to still another embodiment wherein the steering rack arrangement comprises a compression spring acting as a bi-directional spring, i.e. compresses when the rack arrangement contracts as well as when it elongates,

[0040] Fig, 6A is a cross-sectional view taken through the steering rack arrangement in Fig. 6,

[0041] Fig. 7 is an enlarged, schematic view of a section of a steering rack arrangement of a steering arrangement as shown in Fig. 2 according to yet another embodiment wherein the steering rack arrangement comprises hydraulic damping arrangement.

[0042] DETAILED DESCRIPTION

[0043] Fig. 1 is a very schematic view of a known Steer by Wire vehicle steering system lOOo of a ground vehicle having two steered wheels, left wheel 1 Ao and right wheel IBo, a steering gear comprising a steering rack 7o with a left side rack portion 7Ao connected to the left wheel, a right side rack portion 7Bo connected to the right wheel and a central rack portion lOo as discussed above. The steering rack 7o comprises a single rack element arranged in a housing (not shown). In Fig. 1 also left and right kingpin shafts 2Ao,2Bo, left and right steering arms 3 Ao,3Bo, left and right tie rods 5Ao,5Bo and left and right inner tie rod ends 6Ao,6Bo are illustrated. Two electric servo motors, left side electric motor 9Ao and right side electric motor 9Bovia gears on the rack and left and right side pinions 8AQ,8BQ respectively are provided for displacing the steering rack 7o. Fig. 2 is a schematic view of a vehicle steering system 100 for a ground vehicle according to the present invention. As illustrated for the state of the art steering system above, it comprises, here, two steered wheels, left wheel 1 A and right wheel IB, a steering gear comprising a steering rack arrangement 7 comprising a first, here left side, rack element 70A with an outer rack end portion 7 A’ and a second, here right side, rack element 70B with an outer rack end portion 7B’. The first rack element 70A is here connected to the left wheel 1 A and the second rack element 70B is here connected to the right wheel IB.

[0044] Thus, the steering rack arrangement 7 is split up in a first rack element 70A and a second rack element 70B.

[0045] In Fig. 2 also left and right kingpin shafts 2A,2B, left and right steering arms 3 A,3B, left and right tie rods 5A,5B and left and right inner tie rod ends 6A,6B are illustrated. Two electric servo or actuator motors 9A, 9B are via gears on the respective rack elements 70A,70B and first and second (here left and right side) pinions 8A,8B provided for powering the steering rack arrangement 7 rack elements 70A,70B. Other parts of a steering system are not shown for not playing any significant role for the inventive concept, or being the same as in known steering systems.

[0046] The first and second rack elements 70A,70B are aligned with each other and so arranged that a movement is allowed between the first and second rack elements 70A,70B the amount of which movement being mechanically restricted. The first rack element 70A free or outer end portion 7 A’ comprises a recess or a cut-out portion, the depth of which exceeds the size of the radius of the rack element 70A (if the rack element has a circular cross-section, otherwise, or in general, it slightly exceeds half of the dimension of the transverse dimension such that engagement with another rack element is allowed without affecting the outer cross-sectional dimensions and such that they can be arranged to be moved with respect to each other in a longitudinal direction to a limited, predetermined maximum extent) and extends longitudinally a predetermined, first, distance towards the end of the rack element end portion, but ending a distance from the end such that a protruding, gripping or claw, portion 71 A (see Fig.3) is formed, protruding from the bottom of the recess, here perpendicularly to the longitudinal extension of the rack element, having a length somewhat shorter than the radius of the rack element 70A. Correspondingly the second rack element 70B free or outer end portion 7B’ comprises a recess or a cut-out portion, the depth of which exceeds the radius or correspondingly of the rack element 70B, and extends longitudinally a predetermined, first, distance towards the end of the rack element end portion, but ending a distance from the end such that a protruding, gripping or claw, portion 7 IB (see Fig.3) is formed, protruding from the bottom of the recess, here perpendicularly to the longitudinal extension of the rack element 70B, having a length somewhat shorter than the radius of the rack element 70B. However, the recess of the second rack element 70B is disposed oppositely with respect to the recess of the first rack element 70A and the protruding, gripping or claw, portions 71 A, 7 IB of the first and second rack elements 70A,70B are thus oppositely directed such that a movement between the rack elements will be limited (maximum extension) when respective inner wall portions of the protruding, gripping or claw, portions 71A,71B come into engagement, and (maximum compression) when outer end walls (perpendicular to the longitudinal extension of a respective rack element) of the protruding, gripping or claw, portions 71A,71B come in engagement with an inner wall of the recess of the respective other rack element 70B,70A respectively. Thus, the first and second rack elements 70A,70B, controlled by each a respective actuator motor 9A,9B, can move freely with respect to one another, to a limited extent as given by the mechanical design, e.g. the length (longitudinally in relation to the respective rack element) and the widths (in a longitudinal direction) of the protruding, gripping or claw, portions 71 A,71B, and they can be controlled independently. DI in Fig.2 illustrates the rack 7 contraction leeway whereas d2 illustrates the rack arrangement 7 elongation leeway.

[0047] Through rack arrangement being divided and comprising two separate rack elements 70A,70B, which also are independently controlled by each a separate actuation motor 9A,9B, such that they can move to a certain extent independently from one another, both wheels 1A,1B are allowed to be steered by one of the actuator motors 99A,9B, e.g. in case of failure of the other actuator motor, although with a reduced steering precision, but to such an extent that it will at least be possible to drive with steering precision limitations, e.g. to a workshop or to a safe stop or similar, which enhances safety. It also becomes possible to make small, individual, steer angles to the steered wheels. This improves directional stability, steering response, reduces tyre wear and contributes in lowering energy consumption. It should be clear that the rack can be split up, i.e. comprise two separate rack elements, in many different ways, that the rack element end portions can be differently shaped and adapted to each other such that a mechanically restricted movement is allowed between them; they do not have to comprise recesses end protruding portions as described above, but many variations are possible. Also the contraction and elongation leeways may be set in many different ways and to different measures or lengths.

[0048] Fig.3 is an enlarged view of the mid sections rack 10 described with reference to Fig.2 showing the protruding, gripping or claw, portions 71 A,71B and the leeways dl,d2 more clearly.

[0049] Fig.4 is an enlarged view of a mid-section of a rack arrangement 7’ of a steering arrangement as shown in Fig. 2 according to an embodiment of the invention. The rack arrangement T here comprises a first rack element 70A’ and a second rack element 70B’ which are interconnected by means of a preloaded contraction or tension spring 723, wherein the movement between the first and second rack elements 70A’,70B’ is limited by means of a stroke limiter 722 disposed on an end portion of rod in a guideway determining the rack contraction leeway dl’ and the rack elongation leeway d2’ respectively, the movement of the stroke limiter being limited by opposed walls of an opening in one of the rack elements, here rack element 70A’. In this embodiment the spring, e.g. a contraction or tension spring, or any other appropriate spring, serves the purpose of balancing the compressive force in the rack arrangement 7’ e.g. to minimize the energy consumption of the actuator, servo, motors; not shown, which are arranged as in Fig.2. The contraction or tension spring may comprise an eye or a loop on each end.

[0050] Fig. 5 is an enlarged view of a mid-section of a rack arrangement 7” of a steering arrangement as shown in Fig. 2 according to another embodiment of the invention. The rack arrangement 7” here comprises a first rack element 70A” and a second rack element 70B” which are interconnected by means of a preloaded compression spring 723’, or any other appropriate spring, arranged to be compressed when the rack arrangement is elongated, the first rack element (here left side rack element) will pull on the right hand side of the spring 723’ wherein the movement between the first and second rack elements 70A”,70B” is limited by means of a stroke limiter 722” disposed on an end portion of rod in a guideway determining the rack contraction leeway dl” and the rack elongation leeway d2” respectively, the movement of the stroke limiter being limited by opposed walls of an opening in one of the rack elements, here rack element 70A’. In this embodiment the spring serves the purpose of balancing the tractive force in the rack arrangement 7” e.g. to minimize the energy consumption of the actuator, servo, motors; not shown, which are arranged as in Fig. 2.

[0051] Fig.6 is an enlarged view of a mid-section of a rack arrangement 7”’ of a steering arrangement as shown in Fig. 2 according to another embodiment. The rack arrangement 7”’ here comprises a first rack element 70A’” and a second rack element 70B’” which are interconnected by means of a preloaded compression spring 733 arranged to be compressed irrespectively of whether the rack arrangement 7”’ is elongated or contracted, i.e. acts as a bidirectional spring, whereby the first and second rack elements 70A”’,70B”’ can move together. When the compressive force or the tractive force exceeds the preloading of the bi-directional spring 733, the first and second rack elements 70A”’,70B”’ are allowed to move individually or independently. This will e.g. be the case if the actuator motors 9A,9B (not shown in this Fig.) are driven differently, with different power, to achieve a toe difference between the right and the left side or due to differences in force from the wheels or the tie rods. In Fig. 6 the (here) left contraction spring seat 731 A , the, here, right, contraction spring seat 73 IB, the, here, left, elongation spring seat 732A, and the, here, right, elongation spring seat 732B are illustrated.

[0052] The rack contraction leeway dl’” is illustrated.

[0053] Fig, 6A is a cross-sectional view along the lines A-A taken through the steering arrangement in Fig-6.

[0054] With a divided rack arrangement, each rack element being driven by an actuation motor, the motor will have to supply power in normal driving forwards, all the time, which is a considerable drawback, the energy losses not being insignificant. Through using pre-loaded springs as discussed above, e.g. energy can be saved, and the losses at least partly being compensated for through designing and dimensioning or preloading the springs such that e.g. driving forwards within predetermined speed range will represent a normal state, the actuation motors being required to supply power to deviate from this normal state, e.g. compress or extend the spring, e.g. during braking, driving in curves or during other more temporary driving manoeuvres not corresponding to the majority of the driving cycle.

[0055] Fig.7 is an enlarged view of a mid-section of a rack arrangement 7”” of a steering arrangement as shown in Fig. 2 according to yet another embodiment. The rack arrangement 7”” here comprises a first rack element 70A”” and a second rack element 70B”” between which a hydraulic damping arrangement comprising a contraction pressure chamber 747 and an elongation pressure chamber 748 is arranged. The hydraulic damping arrangement comprises a tube 741 fixed to the first, here, left rack element 70A””, a piston 742 moving with the second, here right, rack element 70B"", a piston rod 743 and a ring seal 744. A dividing wall 745 moves with the first, here left, rack element 70A’ ” ’ .

[0056] The first and the second rack elements can move freely with respect to one another, to a limited extent as given by the mechanical design, and / or the mechanical design in combination with one or more spring arrangements or springs and / or one or more damping arrangement(s).

[0057] The spring arrangements may alternatively comprise any other appropriate springs.

[0058] In some embodiments the rack arrangement comprises means or is adapted such that the independent relative movement between the rack elements is fixedly or adaptably controllable or variable, and the rack elements are allowed to move at least partly independently from each other to a fixed or adaptable extent.

[0059] The first and the second rack elements are in different embodiments allowed to move individually to the same or to different extents. For example may the first and the second rack elements each be allowed to move maximally about 25 mm, particularly about 20 mm or less, more particularly about 10-15 mm.

[0060] In some implementations the first and the second rack elements are allowed to move individually e.g. each about 10-15% (or to each a different extent within that range) of an allowed total stroke length of a rack arrangement. Of course, the above figures are merely given for exemplifying reasons to which the invention by no means is limited; they may be larger as well as smaller.

[0061] An advantage of using a spring arrangement and / or a hydraulic damping arrangement is that in case of a faulty actuator motor, the arrangement and / or a hydraulic damping arrangement will provide a force making a wheel align at a certain predetermined position.

[0062] Another advantage is that a spring load can be dialled in to counteract any static load coming from the wheel, thus relieving the electric actuator motor from load, which is beneficial for a lower power consumption.

[0063] An advantage of having a damping arrangement is that, if an actuator motor fails, the damping mechanism will provide a stabilising force to counteract any tendency of wobbling of the steered wheel.

[0064] It should be clear that the invention is not limited to the specifically illustrated embodiments, but that it can be varied in a number of ways within the scope of the appended claims, and features can be combined in any desired manner. The different spring and damping arrangements can be of many different kinds. The inventive concept is not limited to any specific dimensions of rack arrangements, they may have different lengths, thicknesses, cross-sectional shapes and may be made of different materials.

Claims

CLAIMS1. A steering gear arrangement for a ground vehicle steer-by-wire steering system (100), said steering gear arrangement comprising a rack and pinion steering arrangement with a rack arrangement (7;7’;7”;7”’;7””) adapted to, on each outer end, be connected to an inner end of a first and a second respective tie rod (5A,5B), and first and second actuation motors (9A,9B) via first and second pinions (8A,8B) being connected to the rack arrangement (7;7’;7”;7”’;7””) c h a r a c t e r i z e d i n t h a t the rack arrangement (7;7’;7”;7”’;7””) comprises a first rack element (70A;70A’;70A”; 70A”’;70A””) and a second rack element (70B;70B’;70B”’;70B””) aligned with each other such that an outer end of the first rack element (70A;70A’;70A”;70A”’;70A””) will be connected to the inner end of said first tie rod (5 A) and an outer end of the second rack element (70A;70A’;70A”;70A”’;70A””) will be connected to the inner end of said second tie rod (5B), that the first actuation motor (9A) via first pinion (8A) is connected to the first rack element (70A;70A’;70A”;70A”’;70A””) and the second actuation motor (9B) via second pinion (8B) is connected to the second rack element (70B;70B’;70B”’;70B””) for separate controlling and / or driving of the first and second rack elements (70A,70B;70A’,70B’;70A”,70B”; 70A’”, 70B’”; 70A””,70B””) via the respective actuation motor (9A,9B), that the first and second rack elements (70A,70B;70A’,70B’;70A” ,70B”; 70A’”, 70B’”; 70A””,70B””) are movable with respect to one another and in that the rack elements (70A,70B;70A’,70B’;70A”,70B”; 70A’”, 70B’”; 70A””,70B””) are allowed to move independently from each other to a fixed or adaptable extent, and in that the rack arrangement (7’;7”;7”’;7””) comprises a spring arrangement (722,723;722’,723’;733,731A,731B,732A,732B) and / or a hydraulic damping arrangement connected to or between the first and second rack elements (70A’,70B’;70A”,70B”; 70A’”, 70B”’;70A””,70B””) adapted to further control the movement between the first and second rack elements (70A’,70B’;70A”,70B”; 70A”’, 70B”’;70A””,70B””).

2. A steering gear arrangement according to claim 1, c h a r a c t e r i z e d i n t h a tthe independent relative movement between the first and second rack elements (70A,70B;70A’,70B’;70A”,70B”; 70A’”, 70B’”; 70A””,70B””) is fixedly defined by the first and second rack elements (70A,70B;70A’ ,70B’;70A” ,70B”; 70A’”, 70B’”; 70A””,70B””) having a mechanical design limiting at least maximum elongation of the rack arrangement (7;7’;7”;7”’;7””).

3. A steering gear arrangement according to claim 1 or 2, c h a r a c t e r i z e d i n t h a t the first and second rack elements (70A,70B;70A’,70B’;70A”,70B”; 70A’”, 70B’”; 70A””, 70B””) at least have a mechanical design limiting the movement between the first and second rack element, the movement being the same or different for the first and the second rack element (70A,70B;70A’,70B’;70A”,70B”; 70A’”, 70B’”; 70A””,70B””).

4. A steering gear arrangement according to claim 2 or 3, c h a r a c t e r i z e d i n t h a t the first rack element (70A) has a free or outer end portion (7 A’) comprising a recess or a cut-out portion, the depth of which somewhat exceeds the radius or transverse dimension of the first rack element (70 A), and extends longitudinally in the direction of the rack arrangement, a predetermined, first, distance towards the end of the rack element end portion, but ending a distance from the end such that a protruding, gripping or claw, portion (71 A) is formed, protruding from the bottom of said first rack element recess, perpendicularly to the longitudinal extension of the first rack element (70A), having a total protruding length somewhat shorter than the radius of the first rack element (70A), and in that the second rack element (70B) has a free or outer end portion (7B’) comprising a recess or a cut-out portion, the depth of which somewhat exceeds the radius, or half the transverse dimension, of the second rack element (70B), and which extends longitudinally, in the direction of the rack element, a predetermined, first, distance towards the end of the second rack element (70B) end portion, but ending a distance from the outer end thereof such that a protruding, gripping, or claw, portion (7 IB) is formed, protruding from the bottom of the recess, here perpendicularly to the longitudinal extension of the second rack element (70B), having a length somewhat shorter than the radius, or half the transverse dimension, of the second rack element (70B), where the recess of the second rack element (70B)is disposed oppositely with respect to the recess of the first rack element 70A such that the protruding, gripping or claw, portions (71A,71B) of the first and second rack elements (70A,70B) will be oppositely directed such that a movement between the rack elements at least will be limited (maximum extension) when respective inner wall portions of the protruding, gripping or claw, portions (71A,71B) come into engagement, and (maximum compression) when outer end walls, perpendicular to the longitudinal extension of a respective rack element, of the protruding, gripping or claw, portions (71 A,71B) come in engagement with an inner wall of the recess of the respective other rack element (70B,70A) respectively.

5. A steering gear arrangement according to any one of the preceding claims, characterized in that the rack arrangement (7’) comprises a spring arrangement (722,723) which comprises a preloaded spring serving the purpose of balancing the tractive forces in the rack arrangement (7’), e.g. contraction or tension spring (723) with a contraction stroke limiter (722).

6. A steering gear arrangement according to any one of claims 1-4, characterized in that the rack arrangement (7”) comprises a spring arrangement (722”, 723’) which comprises a preloaded spring serving the purpose of balancing the compressive forces in the rack arrangement (7”), e.g. compression spring (723’) with an elongation stroke limiter (722”).

7. A steering gear arrangement according to any one of claims 1-4, characterized in that the rack arrangement (7’”) comprises a bi-directional spring arrangement(733 ,731A,731B,732A,732B) which comprises a compression spring (733) arranged to be compressed, irrespectively of whether the rack arrangement (7’”) is elongated or contracted, and in that when the compressive force or the tractive force exceeds the preloading of the bidirectional spring (733), the first and second rack elements (70A’”,70B’”) are allowed to move individually or independently.

8. A steering gear arrangement according to any one of claims 1-8,characterized in that the rack arrangement (7””) comprises a hydraulic damping arrangement arranged between the first rack element (70A””) and the second rack element (70B””), the hydraulic damping arrangement comprising a contraction pressure chamber (747) and an elongation pressure chamber (748), a tube (741) being fixed to the first rack element (70A””), a piston (742), with a piston rod (743), being arranged to move with the second rack element (70B""), and a dividing wall (745) being arranged to move with the first rack element (70A””).

9. A steering gear arrangement according to any one of the preceding claims, characterized in that the allowed amount of movement of the rack elements (70A,70B;70A’,70B’;70A”,70B”; 70A”’, 70B’”; 70A””,70B””) is independently set or controllable for each rack element.

10. A steering gear arrangement according to any one of the preceding claims, characterized in that the first and the second rack elements (70A,70B;70A’,70B’;70A”,70B”; 70A”’, 70B’”; 70A””,70B””) are allowed to move individually, the movement of the rack elements (70A,70B;70A’,70B’;70A”,70B”;70A”’,70B”’; 70A””,70B””) with respect to one another being controllable.

11. A steering gear arrangement according to claim 9 or 10, characterized in that the first and the second rack elements (70A,70B;70A’,70B’;70A”,70B”; 70A’”, 70B’”;70A””,70B””) each is allowed to move maximally about 25 mm, particularly about 20 mm or less, more particularly about 10-15 mm.

12. A steering gear arrangement according to any one of claims 9 -11, characterized in that the first and the second rack elements (70A,70B;70A’,70B’;70A”,70B”; 70A’”, 70B’”;70A””,70B””) are allowed to move individually e.g. each about 10-15% ,of an allowed total stroke length of the rack arrangement.

13. A steer-by-wire steering system (100) for a ground vehicle characterized in that it comprises a steering gear arrangement according to any one of claims 1-12.

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