Electromechanical motor vehicle steering

Abstract

Electromechanical motor vehicle steering (1), comprising a rack (3), a steering pinion (4) which is rotatable about a pivot axis (B) and engages with the rack (3), an electric motor (5) with a motor rotation axis (A), and a gearbox (6) that couples the electric motor (5) to the steering pinion (4) in order to introduce a drive torque from the electric motor (5) into the steering pinion (4), wherein the motor axis of rotation (A) runs parallel to the axis of rotation (B) of the steering pinion (4), the transmission (6) is single-stage and has a first gear (11) which is rotatable about the motor axis of rotation (A) and a second gear (12) which is coaxially mounted on the steering pinion (4) and is rotatable about the axis of rotation (B) of the steering pinion (4), characterized by the fact that the transmission (6) has a gear ratio greater than 15.

Description

[0001] The invention relates to an electromechanical motor vehicle steering system according to the respective preamble of claims 1 and 4.

[0002] Electromechanical power steering systems are becoming increasingly common due to their fuel-saving potential. Different types exist, depending on the arrangement of the electric motor and transmission.

[0003] In one type of steering system, the electric motor's drive torque is transmitted to the steering column (EPSc - "column"). However, the maximum drive torque is limited due to the transmission via the steering column. Since the electric motor and transmission are typically located in the upper part of the steering column, close to the driver, this presents particular challenges regarding crash performance.

[0004] A second option is to place the electric motor and gearbox directly on the steering pinion (EPSp - "pinion" or "single pinion"). This allows for higher steering performance than with an EPSc-type steering system. However, the packaging options, i.e., the possibilities for high compactness, are limited due to the direct placement on the steering pinion, especially since a torque sensor is also typically located in this area. Such a steering system is used, for example, in Fig. 21 and Fig. 22 of EP 1 545 959 A1 describes a design where a motor-driven worm gear drives a worm wheel located on the steering pinion. The motor's axis of rotation runs transversely to the steering pinion's axis of rotation. This design is also mentioned in JP 2017 7414 A.

[0005] In a third steering type, the electric drive unit, consisting of an electric motor and gearbox, is mounted on a second pinion that meshes with the rack in addition to the steering pinion (EPSdp - "double pinion"). Accordingly, two toothed sections must be formed on the rack for the two pinions, making it more complex compared to an EPSp-type steering system.

[0006] Instead of using a second pinion, the force generated by the electric motor can be transmitted to the rack by a combination of a ball screw drive and a toothed belt drive (EPSapa - “axle parallel”).

[0007] From DE 10 2013 010 362 A1, an electromechanical motor vehicle steering system is known in which the drive torque of a steering-assisted electric motor is distributed to two steering pinions, which mesh with a steering rod on both sides. A gear stage consisting of two gears ensures opposite, but otherwise synchronous, rotation. The drive from the electric motor rotor is transmitted via a further gear stage to the gear of the first steering pinion. The latter is connected to a steering column via a pinion shaft and is coaxial with the electric motor. The second steering pinion is connected to the second gear and arranged axially parallel to the first steering pinion. However, such a design is complex.

[0008] An electromechanical vehicle steering system of type EPSp with the features of the preamble of claim 1 as well as of claim 4 is known from JP 2010 280381 A.

[0009] The present invention aims to demonstrate alternatives for an electromechanical vehicle steering system of the EPSp type, in which the electric drive unit, consisting of an electric motor and gearbox, engages directly with the steering pinion. In particular, the invention aims to achieve a more economical package for such a steering system while simultaneously minimizing the manufacturing effort.

[0010] This problem is solved by an electromechanical motor vehicle steering system with the features of claim 1 and further by an electromechanical motor vehicle steering system with the features of claim 4. Special embodiments are the subject of further claims.

[0011] This allows for a very compact design of the electric drive unit with minimal manufacturing effort.

[0012] The electric motor and gearbox can be housed within a very narrow cylindrical space around the axis of rotation of the steering pinion. The longitudinal axis of this cylindrical space can coincide with the axis of rotation of the steering pinion or be offset parallel to it.

[0013] Since the gearbox only has one gear stage, the manufacturing effort is limited. The engine speed is directly reduced via this single gear stage to a slower speed of the steering pinion.

[0014] In the case of an electromechanical motor vehicle steering system according to claim 1, the transmission can also have a gear ratio greater than 20. A cycloidal gear ratio can also be provided between the first and second gears of the transmission.

[0015] In another variant, the electric motor 5 and the gearbox 6 are provided to be housed within a cylindrical space 15, which encloses the axis of rotation B of the steering pinion 4, wherein the diameter D R of the cylindrical space 15 smaller than the sum of the outer diameter D M of the electric motor 5 and the tip circle diameter D Z of the second gear 12 is.

[0016] Furthermore, the outer diameter D can M of the electric motor 5 smaller than the tip circle diameter D Z of the second gear 12.

[0017] The solution according to the invention makes it possible to reserve smaller clearances for the vehicle steering system when designing the front end of motor vehicles. This applies to the size, shape, and orientation of the clearance. This reduces the coordination effort required with adjacent components in the vehicle when using the same steering system type in vehicles with different layouts.

[0018] Furthermore, the solution according to the invention enables simplified assembly in the front of the vehicle due to fewer interfering contours.

[0019] Furthermore, the solution according to the invention facilitates an improvement in crash behavior with regard to increasing occupant safety.

[0020] The invention will now be explained in more detail with reference to an embodiment illustrated in the drawing. The drawing shows: Fig. 1 a spatial view of an embodiment of an electromechanical motor vehicle steering system according to the invention in a front view, and Fig. 2 a view of the steering Fig. 1 in the direction of the axis of rotation of the steering pinion.

[0021] The embodiment shows an electromechanical motor vehicle steering system 1 of type EPSp with an electric drive unit acting directly on the steering pinion.

[0022] Steering 1 according to Fig. 1 includes, among other things, a steering column 2, a rack 3, a steering pinion 4 that couples the steering column 2 to the rack 3, and an electric drive unit with an electric motor 5, whose drive torque is introduced into the steering 1 via a gearbox 6 at the steering pinion 4.

[0023] Only an intermediate shaft extending towards a steering wheel (not shown in detail) is depicted on the steering column 2, to which the steering pinion 4 is connected. A torque measuring device 7 can be arranged on the input side of the steering pinion 4 in the coupling area between the steering column 2 and the steering pinion 4.

[0024] The steering pinion 4 is rotatably mounted in a steering housing (not shown) via corresponding bearings. The steering pinion 4 has a toothed section 8 which engages with a toothed section 9 of the rack 3. Furthermore, in Fig. 1 a pressure piece 10 is shown, which presses the rack 3 against the toothed section 8 of the steering pinion 4.

[0025] As already indicated, the electric drive unit comprises the electric motor 5 and a gearbox 6 downstream of it, which is designed as a single-stage unit.

[0026] The electric motor 5 and the gearbox 6 are arranged such that the motor's axis of rotation A is parallel to the axis of rotation B of the steering pinion 4. In other words, the motor's axis of rotation A is parallel to and offset from the axis of rotation B of the steering pinion 4.

[0027] The gearbox 6 has a first gear 11 and a second gear 12, which mesh with each other. The axes of rotation C and D of both gears 11 and 12 run parallel to each other and have the same offset as the motor axis of rotation A and the axis of rotation B of the steering pinion 4.

[0028] In particular, the motor axis of rotation A coincides with the axis of rotation C of the first gear 11 and the axis of rotation B of the steering pinion 4 coincides with the axis of rotation D of the second gear 12.

[0029] The first gear 11 is formed on or attached to a drive shaft 13 of the electric motor 5. The second gear 12 is located coaxially on the steering pinion 4.

[0030] This allows the electric motor 5 to be moved very close to the axis of rotation B of the steering pinion 4, if necessary. How Fig. 2 shows that, when viewed in the direction of the axis of rotation B of the steering pinion 4, the electric motor 5 overlaps the second gear 12.

[0031] In particular, the electric motor 5 and the gearbox 6 can be housed within a very narrow cylindrical space 15 around the axis of rotation B of the steering pinion 4. The longitudinal axis M of this cylindrical space 15 can coincide with the axis of rotation B of the steering pinion 4, or, as in Fig. 2 shown, be offset parallel to this.

[0032] Preferably the diameter D R of the cylindrical space 15 smaller than the sum of the outer diameter D M of the electric motor 5 and the tip circle diameter D Z of the second gear 12, i.e. D M < (D R + D Z ). Furthermore, the following is preferred: D M < 0.9 (DR + D Z ).

[0033] Furthermore, the outer diameter D can M of the electric motor 5 smaller than the tip circle diameter D Z of the second gear 12 be: D M < D Z and further preferred D M < 0.8 D Z .

[0034] With conventional spur gear stages featuring involute teeth, single-stage gear ratios i of a maximum of approximately 7 can be achieved. Such gear ratios are generally far too low to generate sufficiently high steering torques in a vehicle steering system using a compact electric motor. Therefore, worm gear stages are currently commonly used for speed reduction in EPSp-type vehicle steering systems. However, as explained earlier, these stages have packaging disadvantages due to the crossed arrangement of the motor axis of rotation A and the steering pinion axis of rotation B.

[0035] This problem is overcome by using a gear design that is unusual in steering systems, in which the first gear 11 has a helical tooth and / or a cycloidal toothing is provided between the first gear 11 and the second gear 12 of the gearbox 6.

[0036] This allows a single-stage transmission ratio i greater than 15, and preferably greater than 20, to be achieved. Maximum single-stage transmission ratios i up to 40 or even 100 are possible.

[0037] While comparable gear ratios can be achieved with planetary gears, cycloidal gears, or harmonic drive gears, these are very complex and expensive. Furthermore, they typically have coaxial input and output axes, meaning that an additional gear stage would be required in an EPSp-type automotive steering system to transmit the electric motor's drive torque to the steering pinion.

[0038] In contrast, with the solution according to the invention, which has a single-stage design of the gearbox 6 between the electric motor 5 and the steering pinion 4, the manufacturing and assembly effort of the steering system 1 remains very low.

[0039] The proposed drive concept breaks new ground in the field of automotive steering systems. Despite the advantages outlined above, it had not previously been considered by experts. Rather, it represents a surprisingly simple and elegant solution for the further development of EPSp-type automotive steering systems.

[0040] Numerous variations of the illustrated embodiment are possible.

[0041] For example, the first gear can have 11 additional helical teeth, resulting in a multi-turn helix.

[0042] Furthermore, the position of the second gear 12 arranged on the steering pinion 4 can be freely chosen, i.e., the second gear 12 can either be placed between the input side and the toothed section 8 of the steering pinion 4, as shown in Fig. Figure 1 shows. However, it is also possible to arrange the second gear 12 between the end 14 opposite the input side and the rack 3, i.e., at the free end section 14 of the steering pinion 4.

[0043] Instead of a cycloidal gear or the use of a first gear with a helical tooth, other engagement structures are also possible which, with the motor axis of rotation A running parallel to the axis of rotation B of the steering pinion 4, have a single-stage transmission ratio greater than 15 and preferably greater than 20 and allow an arrangement of the electric drive device in the cylindrical space 15 described above.

[0044] Finally, slight deviations from mathematically exact parallelism between the motor axis A and the axis of rotation B are permissible. In this case, deviations of + / - 5° can still be considered parallel.

[0045] The invention has been explained in more detail above with reference to an exemplary embodiment and further variations. The exemplary embodiment and the variations serve to demonstrate the feasibility of the invention. Individual technical features, which were explained above in the context of further individual features, can also be implemented independently of these features and in combination with other individual features, even if this is not expressly described, as long as it is technically possible. The invention is therefore expressly not limited to the specifically described exemplary embodiment and its variations, but encompasses all embodiments defined by the claims. Reference symbol list 1 electromechanical motor vehicle steering (short: steering) 2 Steering column 3 Rack and pinion 4 steering sprockets 5 electric motor 6 gearboxes 7 Torque measuring device 8. Gear section of the steering pinion 9 gear teeth 10 printed pieces 11 first gear 12 second gear 13 Drive shaft of the electric motor 14 Final Section 15 cylindrical rooms A motor axis B Axis of rotation of the steering pinion C axis of rotation of the first gear The axis of rotation of the second gear D M Outer diameter of the electric motor 5 D R Diameter of the cylindrical space 15 D Z Tip circle diameter of the second gear 12 M Central axis of the cylindrical space i Translation ratio (number of teeth of the second gear 12 to the number of teeth of the first gear 11 or motor speed to speed of the steering pinion 4)

Claims

[1] Electromechanical motor vehicle steering (1), comprising a rack (3), a steering pinion (4) which is rotatable about a pivot axis (B) and engages with the rack (3), an electric motor (5) with a motor rotation axis (A), and a gearbox (6) that couples the electric motor (5) to the steering pinion (4) in order to introduce a drive torque from the electric motor (5) into the steering pinion (4), wherein the motor axis of rotation (A) runs parallel to the axis of rotation (B) of the steering pinion (4), the transmission (6) is single-stage and has a first gear (11) which is rotatable about the motor axis of rotation (A) and a second gear (12) which is coaxially mounted on the steering pinion (4) and is rotatable about the axis of rotation (B) of the steering pinion (4), characterized by , that the transmission (6) has a gear ratio greater than 15. [2] Electromechanical motor vehicle steering (1) according to claim 1, characterized by, that the transmission (6) has a gear ratio (i) greater than 20. [3] Electromechanical motor vehicle steering (1) according to claim 1 or 2, characterized by , that a cycloidal toothing is provided between the first and second gear (11, 12) of the transmission (6). [4] Electromechanical motor vehicle steering (1), comprising a rack (3), a steering pinion (4) which is rotatable about a pivot axis (B) and engages with the rack (3), an electric motor (5) with a motor rotation axis (A), and a gearbox (6) that couples the electric motor (5) to the steering pinion (4) in order to introduce a drive torque from the electric motor (5) into the steering pinion (4), wherein the motor axis of rotation (A) runs parallel to the axis of rotation (B) of the steering pinion (4), the transmission (6) is single-stage and has a first gear (11) which is rotatable about the motor axis of rotation (A) and a second gear (12) which is coaxially mounted on the steering pinion (4) and is rotatable about the axis of rotation (B) of the steering pinion (4), characterized by , that A cycloidal toothing is provided between the first and second gear (11, 12) of the transmission (6). [5] Electromechanical motor vehicle steering (1) according to any one of claims 1 to 4, characterized by , that the electric motor (5) and the gearbox (6) are housed within a cylindrical space (15) which encloses the axis of rotation (B) of the steering pinion (4), wherein the diameter (D R ) of the cylindrical space (15) smaller than the sum of the outer diameter (D M ) of the electric motor (5) and the tip circle diameter (D Z ) of the second gear (12). [6] Electromechanical motor vehicle steering (1) according to any one of claims 1 to 5, characterized by that the outer diameter (D M ) of the electric motor (5) is smaller than the tip circle diameter (Dz) of the second gear (12).

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