UTILITY VEHICLE STEERING SYSTEM

Abstract

A utility vehicle steering system has a steering gear for transmitting a manual torque that is applied to a steering wheel to a pitman arm. The steering gear has an electric motor for providing an auxiliary torque. The electric motor is arranged around a steering shaft. In addition, the electric motor has a stator with at least two electrically separated winding groups, each of which is controlled by a separate electronic control device. An especially compact utility vehicle steering system results, which enables the provision of large auxiliary torques by way of a single electric-motor drive while a limited installation space is achieved. The drive can be operated from a vehicle electrical system by a supply voltage of 24 V.

Claims

1-10. (canceled)

11. A utility vehicle steering system, comprising: a steering gear for transmitting a manual torque applied to a steering wheel to a steering pitman arm, said steering gear having a steering shaft and an output element with a shaft with a given axis of rotation; said steering gear having an electric motor for providing an auxiliary torque disposed around said steering shaft or around said shaft of said output element; and said electric motor having a stator with at least two electrically separate winding groups that are each actuated by a respective, dedicated electronic control device.

12. The utility vehicle steering system according to claim 11, which comprises a speed reduction gear stage coupling said steering shaft to said steering pitman arm, said speed reduction gear stage converting an input-side rotational movement into an output-side rotational movement in a single-stage such that an input-side axis of rotation and an output-side axis of rotation of said gear stage intersect one another or are skewed relative to one another.

13. The utility vehicle steering system according to claim 11, wherein said electric motor is a single electric motor configured to provide steering assistance alone, and exclusively electrically, over an entire operating range.

14. The utility vehicle steering system according to claim 11, which comprises a speed reduction gear stage coupling said steering shaft to said steering pitman arm, said gear stage having a variable transmission ratio such that, in a range encompassing a central position of the steering system, steering movements at the steering wheel give rise to smaller wheel steer angles than steering movements in a range remote from the central position.

15. The utility vehicle steering system according to claim 11, which comprises a speed reduction gear stage coupling said electric motor to said steering shaft, said speed reduction gear stage axially adjoining said electric motor and being arranged around said steering shaft.

16. The utility vehicle steering system according to claim 15, wherein said electric motor is arranged axially between a torque sensor and said speed reduction gear stage that couples said electric motor to said steering shaft.

17. The utility vehicle steering system according to claim 11, which comprises a speed reduction gear stage coupling said electric motor to said steering pitman arm and being disposed around an axis of rotation of said steering pitman arm.

18. The utility vehicle steering system according to claim 11, wherein said electric motor has two separately actuated partial motors, said partial motors having windings that are nested one inside the other.

19. The utility vehicle steering system according to claim 11, wherein said electric motor has a central connector ring for contacting all windings of said winding groups and electrical contact devices for a connection of said electronic control devices.

20. The utility vehicle steering system according to claim 11, wherein: said steering shaft is accommodated rotatably in a steering gear housing and has a connector for mounting a steering wheel or a steering column; said steering pitman arm is arranged on an output shaft projecting out of said steering gear housing; said electric motor and a first gear stage coupled between said electric motor and said steering shaft are accommodated in said steering gear housing; a second gear stage is arranged between said steering shaft and said steering pitman arm; wherein a manual torque imparted to said steering shaft by a driver of the vehicle is subjected to a speed reduction with a transmission ratio of the second gear stage, and an auxiliary torque provided by said electric motor is subjected to a speed reduction with a transmission ratio of said first gear stage and with the transmission ratio of said second gear stage.

21. The utility vehicle steering system according to claim 20, wherein said second gear stage is accommodated in said steering gear housing together with said electric motor and said first gear stage.

Description

[0030] The invention will be discussed in more detail below on the basis of exemplary embodiments illustrated in the drawing, in which:

[0031] FIG. 1 shows a schematic view of a first exemplary embodiment of a utility vehicle steering system according to the invention,

[0032] FIG. 2 shows a schematic view of the arrangement of a utility vehicle steering system according to the invention on a utility vehicle,

[0033] FIG. 3 shows a longitudinal sectional view of a second exemplary embodiment of a utility vehicle steering system according to the invention,

[0034] FIG. 4 is an exploded illustration of the second exemplary embodiment,

[0035] FIG. 5 shows a sectional view along the line V- in FIG. 3,

[0036] FIG. 6 shows a sectional view along the line VI-VI in FIG. 3,

[0037] FIG. 7 shows a side view of the stator of the electric motor, and

[0038] FIG. 8 shows a view of the stator of the electric motor in section.

[0039] The exemplary embodiments each relate to a utility vehicle steering system 10 of a block steering system type, which is suitable for front-axle loads of 2.5 t and higher. FIG. 2 shows, in a schematic illustration, the arrangement thereof in a utility vehicle.

[0040] The utility vehicle steering system 10 has a steering gear 11 which is intended and designed for transmitting a manual torque imparted by the driver at a steering wheel 12 to a steering pitman arm 13. For this purpose, the steering wheel 12 is coupled via a steering column 14 to an input element of the steering gear 11. The steering pitman arm 13, which is coupled to an output element of the steering gear 11, is connected for example via a track rod linkage 15 to the wheels 16, which are to be steered, of the motor vehicle, in order to transmit a pivoting movement of the steering pitman arm 13 to the wheels 16 and thus effect a steer angle at said wheels.

[0041] The steering gear 11 has a steering gear housing 17, in which steering shaft 18 is arranged so as to be rotatable about an axis of rotation A. The steering shaft 18 is acted on at the input of the steering gear 11 by the steering column 14, with the manual torque generated by the driver, so as to correspondingly rotate.

[0042] Furthermore, in the steering gear housing 17, there is accommodated an electric motor 19, which is arranged around the steering shaft 18. The electric motor 19 is preferably designed as a hollow-shaft motor, the axis of rotation of which is coaxial with respect to the axis of rotation A of the steering shaft 18.

[0043] A drive torque provided by the electric motor 19 is transmitted by means of a first gear stage 20 to the steering shaft 18 in order to assist the driver when steering. The first gear stage 20 is preferably in the form of a high-ratio coaxial gear, which couples a rotor of the electric motor 19 to the steering shaft 18. In particular, said first gear stage may be designed as a single-stage or multi-stage planetary gear set of two-shaft construction, as a cycloid gear, as a harmonic drive or as a combination of these. It is thus possible to realize speed reduction transmission ratios in the range from 1:15 to 1:400.

[0044] The electric motor 19 is actuated in a manner dependent on a driver steering command and possibly further vehicle parameters. In particular, the electric motor 19 may be actuated in a manner dependent on the manual torque imparted to the steering wheel 12 by the driver.

[0045] In the present case, the auxiliary force that assists the driver is generated exclusively electrically, and by a single electric motor 19 alone. In order, in a utility vehicle steering system, to generate adequate steering forces for the track rod linkage 15 from an on-board electrical system voltage of 24 V, the electric motor 19 has a stator 22 with at least two electrically separate winding groups 23a and 23b, which are each actuated by a dedicated electronic control device 24a and 24b, such that the two winding groups 23a and 23b are supplied with electrical current independently of one another from the on-board electrical system. In this way, the electric motor 19 is capable of providing a relatively high drive torque.

[0046] The steering shaft 18 is coupled by means of a second gear stage 25 to the steering pitman arm 13. For this purpose, the latter is fastened to an output element of the second gear stage 25 or to an output shaft 26 connected to said output element.

[0047] The second gear stage 25 is preferably a speed reduction gear stage. In particular, said gear stage may be designed such that an input-side rotational movement is converted into an output-side rotational movement in single-stage fashion. Here, the input-side axis of rotation, that is to say the axis of rotation A of the steering shaft 18, and the output-side axis of rotation B of the second gear stage 25 intersect one another, or are skewed relative to one another. By means of the second gear stage 25, the auxiliary torque acting at the steering pitman arm 13 is increased further, such that high steering forces track rod linkage 15 can be with a small, high-speed electric motor 19.

[0048] The second gear stage 25 may be designed for example as a worm drive, a bevel wheel stage or a hypoid gear stage. Here, as already mentioned, it is possible to realize a further considerable speed reduction transmission ratio with a transmission ratio in the range from 1:2 to 1:100, preferably in the range from 1:5 to 1:30.

[0049] The coaxial arrangement of the electric motor 19 around the steering shaft 18 yields a very compact and thus space-saving configuration of the steering gear 11.

[0050] A manual torque imparted to the steering shaft 18 by the driver is subjected to a speed reduction with the transmission ratio of the second gear stage 25, whereas the auxiliary torque provided by the electric motor 19 is subjected to a speed reduction with the transmission ratio of the first gear stage 20 and with the transmission ratio of the second gear stage 25.

[0051] In a modification of the first exemplary embodiment illustrated in FIG. 1, the first gear stage 20 may also be arranged around the axis of rotation B of the steering pitman arm 13, in particular coaxially with respect to the output shaft 26.

[0052] In a further modification, the second gear stage 25, by means of which the steering shaft 18 is coupled to the steering pitman arm 13, has a variable transmission ratio. In a range encompassing the central position of the steering system, steering movements at the steering wheel 12 give rise to smaller wheel steer angles than steering movements in a range remote from the central position.

[0053] On the basis of FIGS. 3 to 8, in the context of a second exemplary embodiment, but expressly without restriction thereto, a further specific possible implementation for a utility vehicle steering system 10 will be discussed in more detail. Here, components corresponding to the first exemplary embodiment are denoted by the same reference designations.

[0054] The steering gear 11 of the second exemplary embodiment comprises a steering gear housing 17 with a pot-shaped receiving section 17a, which is closed off axially by a cover 17b.

[0055] In the steering gear housing 17, a steering shaft 18 is mounted so as to be rotatable about an axis of rotation A. The steering shaft comprises a hollow-shaft section 18a, through which a torsion bar 18b extends. Via a steering column section 14a, the manual torque from the driver is introduced into a first end section of the torsion bar 18b, which at its second end section is connected rotationally conjointly to the hollow-shaft section.

[0056] The manual torque from the driver, which acts at the input side on the steering gear 11, can be detected, for the purposes of actuating the electric motor 19 that is likewise accommodated in the steering gear housing 17, by means of a torque sensor 27 that interacts with the steering shaft 18.

[0057] The electric motor 19 is arranged coaxially around the steering shaft 18 and is coupled to the latter by means of a first gear stage 20, which in the present case is for example designed as a high-ratio coaxial gear in the form of an eccentric gear, for example a cycloid gear. Instead of a cycloid gear of said type, it is however also possible to use the gear types already mentioned above, specifically planetary gears or harmonic drives.

[0058] The first gear stage 20 is connected at the input side to a rotor 21 of the electric motor 20, whereas the output element of the first gear stage 20 is fastened rotationally conjointly on the hollow shaft section 18a.

[0059] The first gear stage 20 effects a speed reduction of the rotational speed of the electric motor 19 with a transmission ratio in the range from 1:15 to 1:400. In the second exemplary embodiment illustrated, said first gear stage is arranged around the steering shaft 18, and axially adjoins the electric motor 19.

[0060] As shown in FIGS. 3 and 4, during the assembly process, the first gear stage 20 is introduced axially into the receiving section 17a of the steering gear housing 17 first, followed by the electric motor 19 and subsequently the torque sensor 27 and furthermore a cabling circuit board 28, before the steering gear housing 17 is closed off by means of the cover 17b. The electric motor 19 is thus arranged axially between the torque sensor 27 and the first gear stage 20, which couples the electric motor 19 to the steering shaft 18. This yields a highly compact structural unit with a large axial spacing for the bearing points 29a and 29b of the steering shaft 18.

[0061] The steering shaft 18 of the second exemplary embodiment furthermore has a spindle section 18c, which serves as an input element 25a of a second gear stage 25. The spindle section 18c meshes with a worm wheel 25b of the second gear stage 25, which worm wheel rotates about an axis of rotation B perpendicular to the axis of rotation A of the steering shaft 18. The worm wheel 25b, which may also have a toothing only in the form of segments, is coupled rotationally conjointly to the steering pitman arm 13, whereby the manual torque and the auxiliary torque give rise to a pivoting movement of the steering pitman arm 13 about the axis of rotation B.

[0062] In the illustrated second exemplary embodiment, the steering shaft 18 projects with the spindle section 18c out of the steering gear housing 17. The second gear stage 25 is also arranged outside the steering gear housing 17. It is however possible for the second gear stage 25 to also be accommodated in the steering gear housing 17. It is furthermore possible for the assembly illustrated in FIG. 3, aside from the steering pitman arm 13, to be enclosed by an additional outer housing (not illustrated in any more detail).

[0063] The electric motor 20 and the contacting thereof are illustrated in more detail in FIGS. 5 to 8. Said electric motor has a stator 22 which is fixed in the steering gear housing 17 and in which a rotor 21, which is connected to the input side of the first gear stage 20, is rotatably arranged.

[0064] As already discussed above in conjunction with the first exemplary embodiment, the stator 22 has at least two, that is to say two or more, electrically separate winding groups. In the illustrated second exemplary embodiment, by way of example, only two electrically independent winding groups 23a and 23b are illustrated, which in the present case are arranged at two different diameters about the axis of rotation A.

[0065] Each of the two winding groups 23a and 23b has three phases (I.sub.i, II.sub.i, III.sub.i). FIG. 8 shows a total of 12 coils per winding group 23a and 23b, such that, for each winding group 23a and 23b, the number of pole pairs is 2. The rotor 21 (not illustrated in any more detail) is accordingly formed with in each case six phase laminations. It is however also possible to provide winding groups 23a and 23b with smaller or greater numbers of pole pairs.

[0066] It is furthermore possible for the winding groups 23a and 23b to be arranged offset with respect to one another in a circumferential direction, such that the phases are also offset in the circumferential direction, as illustrated in FIG. 8. However, the offset of the phases between the windings of the two winding groups 23a and 23b may also be greater than the spatial offset of the windings.

[0067] All of the windings have been contacted by means of a common connector ring 30, which has corresponding conductors 31 which are electrically insulated with respect to one another. Said conductors are connected to electrical contact devices 32a and 32b which are likewise arranged on the connector ring, and which may be formed for example as plug connectors. A dedicated electrical contact device 32a and 32b is provided for each winding group 23a and 23b.

[0068] The electrical contact devices 32a and 32b are each connected by means of further electrical conductors 33a and 33b to an associated electronic control device 24a and 24b, such that each winding group 23a and 23b is actuated by a dedicated control device 24a and 24b and is supplied separately with electrical current from the vehicle on-board electrical system. This thus yields two electric sub-motors, which are nested one inside the other.

[0069] The electronic control devices 24a and 24b are preferably likewise accommodated in the steering gear housing 17, and for example attached to a circuit board 28 arranged axially in front of a face side of the electric motor 19.

[0070] The exemplary embodiments discussed above make it possible to realize a particularly compact utility vehicle steering system, which permits the provision of high auxiliary torques by means of a single electromotive drive in a limited structural space. Said drive can in particular be operated from a vehicle on-board electrical system with a supply voltage of 24 V.

[0071] With regard to the electromotive assistance, the steering gear 11 forms, by means of at least two sub-motors integrated into a common stator-rotor assembly, a redundant system that can continue to be operated in the event of a failure of one sub-motor.

[0072] The transmission ratios of the gear stages may possibly be set such that the steering system remains steerable manually even in the event of a total failure of the electric motor 19.

[0073] Owing to the use of an electric motor 19 with a high power output, a hydraulic power assistance arrangement can be omitted entirely. As a result of the arrangement of the electric motor 11 around the steering shaft 18, the steering gear 11 nevertheless remains surprisingly compact. This is further enhanced by means of a high-ratio gear stage connected downstream of the electric motor 11.

[0074] The utility vehicle steering system according to the invention is moreover characterized by relatively easily producible components.

[0075] The invention has been discussed in more detail above on the basis of various exemplary embodiments and further modifications. In particular, technical individual features that have been discussed above in the context of further individual features may be realized independently of these and in combination with further individual features, even if this is not expressly described, as long as this is technically possible. The invention is therefore explicitly not restricted to the described exemplary embodiments, but rather encompasses all refinements defined by the patent claims.

LIST OF REFERENCE SYMBOLS

[0076] 10 Steering system [0077] 11 Steering gear [0078] 12 Steering wheel [0079] 13 Steering pitman arm [0080] 14 Steering column [0081] 14 Steering column section [0082] 15 Track rod linkage [0083] 16 Vehicle wheel [0084] 17 Steering gear housing [0085] 17a Receiving section [0086] 17b Cover [0087] 18 Steering shaft [0088] 18a Hollow shaft section [0089] 18b Torsion bar [0090] 18c Spindle section [0091] 19 Electric motor [0092] 20 First gear stage [0093] 21 Rotor [0094] Stator [0095] 23a Winding group [0096] 23b Winding group [0097] 24a Electronic control device [0098] 24b Electronic control device [0099] 25 Second gear stage [0100] 25a Worm shaft section [0101] 25b Worm wheel [0102] 26 Output shaft [0103] 27 Torque sensor [0104] 28 Circuit board [0105] 29a Bearing point of the steering shaft [0106] 29b Bearing point of the steering shaft [0107] 30 Connector ring [0108] 31 Conductor [0109] 32a Electrical contact device [0110] 32b Electrical contact device [0111] 33a Further conductor [0112] 33b Further conductor [0113] A Axis of rotation of the steering shaft and of the electric motor [0114] B Axis of rotation of the output element of the steering gear and of the steering pitman arm