Steering for a motor vehicle

Abstract

A steering system (1) for a motor vehicle comprises a steering gear housing (20a), a steering rod (22) which is guided in the steering gear housing (20a) so as to be movable in the direction of its longitudinal axis (A) and is supported against rotation about the longitudinal axis (A), wherein a distance sensor (26) is arranged on one of the steering rod (22) and the steering gear housing (20a) and a touch surface (27) is provided longitudinally to the steering rod (22) on the other of the steering rod (22) and the steering gear housing (20a). Over a maximum travel of the steering rod (22) in the direction of the longitudinal axis (A), the distance of the touch surface (27) from the distance sensor (26) is a bijective function of the travel of the steering rod (22) in the direction of the longitudinal axis (A).

Description

The invention relates to a steering system for a motor vehicle, comprising a steering gear housing and a steering rod which is guided in the steering gear housing so as to be movable in the direction of its longitudinal axis and is supported against rotation about the longitudinal axis, wherein a distance sensor is arranged on one of the steering rod and the steering gear housing and a contact surface is provided on the other of the steering rod and the steering gear housing along the steering rod.In steer-by-wire steering systems, because of the lack of a mechanical coupling between a steering handle on the one hand and a steering rod on the other hand, information about the position and / or movement of the steering rod is required in order, for example, to model feedback from the roadway on the steering handle for the driver. Such information should be available already when the vehicle is switched on.A large number of approaches for determining the position of the steering rod are already known from the prior art.In conventional steering systems with steering pinions, the steering rod position can be transmitted to the steering wheel via the steering pinion linked to the steering rod and measured there, or a measurement takes place directly on the steering pinion with the aid of steering angle sensors arranged there.Further, a steering angle may be measured via the rotations of a ball screw nut or via the rotations of an assist motor.In steer-by-wire steering, however, the possibilities via a steering pinion in meshing engagement with the steering rod are eliminated.If the steering rod position is measured indirectly, measurement errors can result from pitch errors in the ball screw or from translation errors between the steering pinion and the steering rod.For many indirect measuring methods, sensors are used which have to be combined with transmission stages on the basis of the large measuring range required at a vehicle steering system and the required high resolution. This means a high production-related outlay, in particular when mounting these sensors. Furthermore, in the case of sensors which are multiturn capable, a correspondingly expensive control device must be installed.Furthermore, it must be ensured that the correct rack position is also detected in the switched-off state, which means a high amount of software outlay.A steering system of the generic type for a motor vehicle is known from DE 10 2017 207 716 B4. For detecting the position of the steering rod, it is proposed there that the steering rod, viewed in the longitudinal extension, has at least one change in its cross section, namely a local, step-shaped reduction in its diameter, wherein a first sensor device is designed to detect this change in diameter. This first sensor device can be a Hall sensor, for example. A jump in diameter thus creates a reference position from which, starting for example, the current position of the steering rod can be determined by means of a second sensor device in the form of a rotor position sensor. The reference position can preferably be matched to a central position of the steering system, so that the latter is generally traveled over shortly after the vehicle is switched on. However, if a motor vehicle is parked with the steering system turned on, the position of the steering rod is not immediately available from the sensor signals when it is switched on.Furthermore, DE 10 2017 207 716 B4 proposes providing a plurality of jumps in diameter on the steering rod, which jumps have different distances from one another in the longitudinal direction of the steering rod. From the detection of these distances, it is also possible to infer the position of the steering rod in the longitudinal direction thereof.On the basis of this, the invention is based on the object of demonstrating alternatives for detecting the absolute position of the steering rod of a steering system for a motor vehicle, which alternatives can be realized with little manufacturing and manufacturing effort and are also suitable for supplying precise information about the position of the steering rod when the motor vehicle is switched on.This object is achieved by a steering system having the features of patent claim 1. The steering system according to the invention is characterized in particular in that, over a maximum movement path of the steering rod in the direction of the longitudinal axis, the distance of the sensing surface from the distance sensor is a bijective function of the movement path of the steering rod in the direction of the longitudinal axis.According to the invention, the distance of the distance sensor from the touch surface over the maximum movement path unambiguously correlates with the position of the steering rod. In other words, there is exactly one distance value for each position of the handlebar and vice versa. If this distance value is known by measurement by means of the distance sensor, the position of the steering rod is simultaneously also known. When the vehicle is switched on, this value is available directly and without delay by reading out the distance sensor.It should be pointed out at this point with reference to DE 10 2017 207 716 B4 that there is no objectiveity of the assignment because of the jump in diameter points. Moreover, DE 10 2017 207 716 B4 aims at detecting distances in the longitudinal direction of the handlebar, whereas in the solution according to the invention distances are read out substantially transversely to the longitudinal direction of the handlebar.Particular embodiments of the invention are the subject of further claims.Thus, the function is preferably continuous over the maximum movement path of the steering rod in the direction of the longitudinal axis.According to a particular embodiment of the invention, for the purpose of simple evaluation, the function over the maximum movement path of the steering rod in the direction of the longitudinal axis can be linear.The gradient of the sensing surface can be selected to match the sensor resolution. In particular, a suitable distance sensor can be selected, which transmits its signal, for example, to a control device of the steering system. The distance sensor can be in mechanical contact with the sensing surface, but can also sense the distance contactless as a non-contact sensor. Suitable measurement principles include, without limitation, measurement probes, ultrasonic sensors, optical sensors, capacitive sensors, inductive sensors, etc.Furthermore, the sensing surface can be designed to extend as a groove base in a groove. Such a groove can be introduced, for example, into the steering rod or else also into the steering gear housing or a structure fastened to the steering gear housing or to the steering gear housing.Alternatively, the sensing surface can be formed as a comb surface of a protrusion. Here too, a formation or attachment on the steering rod or on the steering gear housing is again possible.According to a further particular embodiment of the invention, the steering gear housing has a guide bushing for the longitudinal guidance and torque support of the steering rod, wherein the steering rod extends with the sensing surface through the guide bushing and the distance sensor is fixed to the guide bushing. Since the spacing signal is tapped in the region of the guide of the steering rod, adverse effects on the measurement signal as a result of deflection effects of the steering rod can be minimized.The attachment of the distance sensor to a stationary component is advantageous for the wiring of such a distance sensor, since any wear effects on the wiring as a result of relative movements are avoided.Furthermore, the guide bush can form a recess pointing towards the sensing surface, wherein the distance sensor extends at least in sections into this recess. As a result, the distance sensor can be accommodated in a particularly space-saving and protected manner.In a modification thereof, however, it is also possible to fix the distance sensor on the steering rod, so that when the steering rod moves in the longitudinal direction thereof, the distance sensor interacts with a sensing surface which is stationary on the steering gear housing.The invention is explained in more detail below with reference to exemplary embodiments shown in the drawing. The drawing shows in: FIG. 1 shows a schematic illustration of a steering system for a motor vehicle in the form of a steer-by-wire steering system according to one exemplary embodiment of the invention, FIG. 2 shows a schematic illustration of the steering gear or wheel actuator of the steering system illustrated in FIG. 1, FIG. 3 shows a side view of a steering rod and guide bushing of the steering system from FIGS. 1 and 2, FIG. 4 shows a further side view of the steering rod and guide bushing of the steering system from FIGS. 1 and 2, and FIG. 5 shows a further exemplary embodiment of a steering system according to the invention.FIGS. 1 to 4 show a schematic representation of a possible example of a steering system 1 for a motor vehicle, in particular for a passenger motor vehicle or light commercial vehicle.The steering system 1 of the first exemplary embodiment is designed here as a steer-by-wire steering system, for example. It can be divided into a steering column module 10 for inputting a steering command on the driver side and a steering gear module (also wheel actuator) 20, which are mechanically decoupled from one another.The steering column module 10 comprises a steering handle 11 for inputting the steering command by a driver of the motor vehicle. The steering handle 11 is, for example, a steering wheel as illustrated, but may be another input means such as a joystick or the like. In the case of a steering wheel, the steering command is a steering wheel angle. In addition, the steering wheel angular speed and / or steering wheel angular acceleration can optionally be taken into account in the steering command.Furthermore, the steering column module 10 of the steering system 1 comprises a haptic actuator (also force feedback actuator) 12 which is mechanically coupled to the steering handle 11. The haptic actuator 12 serves to simulate a steering reaction for the driver at the steering handle 11. This is manifested in a resistance during steering and, if appropriate, also an active return of the steering handle 11 into a neutral position corresponding to straight-ahead travel on level ground.The haptic actuator 12 comprises a motor 13 which is mechanically coupled to the steering handle 11 by means of a shaft 14. In addition, a control unit 3 awhich is not shown in more detail in FIG. 1 is provided on the steering column module 10 for controlling the motor 13 of the haptic actuator 12.The steering gear module 20 of the steering system 1 forms a wheel actuator for setting a steering angle at steerable vehicle wheels 2 of the motor vehicle and has an electric motor 21 which drives a steering rod 22 coupled to the vehicle wheels 2 and which is in turn arranged in a steering gear housing 20 a. The steering rod 22 is guided in the steering gear housing 20 ain such a way that it can be moved in the direction of its longitudinal axis A and is supported against rotation about the longitudinal axis A. A further control unit 3 bmay be provided on the steering gear module 20.In the present case, there is no mechanical coupling between the steering gear module 20 and the steering handle 11 and the haptic actuator 12 for linking the steering gear module 20 to the steering handle 11 and the haptic actuator 12, the steering 1 comprises a control device 3 which is configured in such a way as to cause the steering gear module 20 to effect a steering actuation of the vehicle wheels 2 as well as to cause the haptic actuator 12 to generate a steering reaction at the steering handle 11 as a function of a steering command on the driver side. The linking can be carried out electrically wired or wirelessly.The control device 3 of the steering system 1 can be concentrated in a central control unit or, as illustrated in the present case by way of example, distributed or arranged in another way over different control units 3 aand 3 bon the haptic actuator 12 and on the steering gear module 20.The steering gear module 20 of the steering system 1 is shown in more detail in FIG. 2. In addition to the already mentioned electric motor 21 and the steering rod 22, this further comprises a transmission 23 for converting a rotational movement of the electric motor 21 into a translatory movement of the steering rod 22.The transmission 23 comprises a toothed belt drive in the present case, as is illustrated by way of example in FIG. 2. In this case, a first toothed belt wheel 23.1 on the transmission input side is coupled in a rotationally fixed manner to a drive shaft 21.1 of the electric motor 21, while a second toothed belt wheel 23.2 on the output side is coupled in a drive-driven manner to the steering rod 22, for example via a ball screw 24. Said toothed belt wheels 23.1 and 23.2 are in turn coupled to one another in terms of drive via a toothed belt 23.3, so that a torque applied by the electric motor 21 can be brought to act as a longitudinal force on the steering rod 22.In order to determine the position of the steering rod 22 with respect to its movement path in the longitudinal direction A of the steering rod 22, a sensor device is provided in the present case, which interacts directly with the steering rod 22.For this purpose, a distance sensor 26 is arranged on one of the steering rod 22 and the steering gear housing 20 a, while a sensing surface 27 is arranged along the steering rod 22 on the other of the steering rod 22 and the steering gear housing 20 a.In the example shown in FIG. 2, the distance sensor 26 is located on a component in the form of a guide bushing 20 b, which is connected in a stationary manner to the steering gear housing 20 a, but can also be arranged at another location in the steering gear housing 20 a, next to the steering rod 22.In the example in FIG. 2, the sensing surface 27 is located on the steering rod 22, but it is also possible to interchange the arrangement of distance sensor 26 and sensing surface 27 with respect to the steering rod 22 and the steering gear housing 20 a.The arrangement of distance sensor 26 and sensing surface 27 is such that over a maximum movement path of the steering rod 22 in the direction of the longitudinal axis A, the distance of the sensing surface 27 from the distance sensor 26 is a bijective function of the movement path of the steering rod 22 in the direction of the longitudinal axis A. This results in an individual distance from the distance sensor 26 substantially transversely to the longitudinal axis A for each location on the sensing surface 27, so that the relevant location on the sensing surface 27 can be unambiguously identified if the distance is known.The mathematical function of the distance over the path of movement of the steering rod 22 in the direction of the longitudinal axis A is continuous at least over the maximum path of movement of the steering rod 22 in the direction of the longitudinal axis A, which corresponds to the maximum steering angle of the steering system 1. In particular, this function can be a linear function. The sensing surface 27 is produced in this case as an oblique plane.FIGS. 3 and 4 show a possible arrangement of distance sensor 26 and sensing surface 27 in more detail with respect to one another.The sensing surface 27 represents a groove base which runs in a groove 28 formed on the steering rod 22.However, it is also possible to form the sensing surface 27 as a comb surface of a projection. A corresponding structure may be fastened to the steering rod 22, for example.Furthermore, FIGS. 3 and 4 show the guide bushing 20 bfor longitudinal guidance and torque support of the steering rod 22, which is part of the steering gear housing 20 a, in particular can be attached thereto.The steering rod 22 preferably extends with the sensing surface 27 through the guide bushing 20 b. At the same time, the distance sensor 26 can be fixed to the guide bushing 20 bto measure the distance to the sensing surface 27. By integrating the distance sensor 26 into the guide bushing 20 b, measurement errors which can result from a possible bending of the steering rod 22 can be practically eliminated.The guide bush 20 bmay form a recess 20 cfacing the sensing surface 27 in order to accommodate the distance sensor 26. In particular, the distance sensor 26 can extend at least in sections into this recess 20 c, whereby the distance sensor 26 can be accommodated in a space-saving and protected manner.FIG. 5 illustrates a second embodiment for illustrating the reversal of the arrangement of the distance sensor 26 and the touch surface 27. The sensing surface 27 is, on the other hand, located on a projection 29 which is arranged on an inner wall section of the steering gear housing 20 a. However, the sensing surface 27 can likewise also be accommodated in a groove 27 as in the first exemplary embodiment above.Corresponding structures can also be fastened as separate components separately to the steering gear housing 20 a.The invention has been explained in more detail above with reference to exemplary embodiments and further modifications. The embodiments and the modifications serve to demonstrate the feasibility of the invention. Technical features which have been explained above in the context of further features can also be realized independently of these and in combination with further features, even if this is not expressly described, as long as this is technically possible. The invention is therefore expressly not restricted to the specifically described exemplary embodiments, but rather comprises all the configurations defined by the patent claims.List of reference characters1 Steering 2 Vehicle wheel 3 Control 3 aControl device on the side of the steering column module 3 bControl device on the side of the steering gear module 10 Steering column module 11 Steering handle 12 Haptic actuator 13 Motor 14 Shaft 20 Steering gear module 20 a Lenkgetriebe gear housing 20 b Führungsbuchse bushing 20 c Ausnehmung 21 Electric motor 22 Steering rod 23 Gear 23.1 First toothed belt wheel 23.2 Second toothed belt wheel 23.3 Toothed belt 24 Ball screw 25 Rotor position sensor 26 Distance sensor 27 Touch surface 28 Groove 29 Projection A Longitudinal axis of the steering rodReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2017 207 716 B4 [0010, 0011, 0015]

Claims

Steering system (1) for a motor vehicle, comprising a steering gear housing (20a), a steering rod (22) which is guided in the steering gear housing (20a) such that it can be moved in the direction of its longitudinal axis (A) and is supported against rotation about the longitudinal axis (A), wherein a distance sensor (26) is arranged on one of the steering rod (22) and the steering gear housing (20a) and a sensing surface (27) is provided on the other of the steering rod (22) and the steering gear housing (20a) along the steering rod (22), characterized in that the distance of the sensing surface (27) from the distance sensor (26) is a bijective function of the movement path of the steering rod (22) in the direction of the longitudinal axis (A) over a maximum movement path of the steering rod (22) in the direction of the longitudinal axis (A).Steering system (1) according to Claim 1, characterized in that the function is continuous over the maximum movement path of the steering rod (22) in the direction of the longitudinal axis (A).Steering system (1) according to Claim 1 or 2, characterized in that the function is linear over the maximum movement path of the steering rod (22) in the direction of the longitudinal axis (A).Steering system (1) according to one of Claims 1 to 3, characterized in that the sensing surface (27) runs as a groove base in a groove (28).Steering system (1) according to one of Claims 1 to 3, characterized in that the sensing surface (27) is designed as a comb surface of a projection (29).Steering system (1) according to one of Claims 1 to 5, characterized in that the steering gear housing (20a) has a guide bush (20b) for longitudinally guiding and torque supporting the steering rod (22), the steering rod (22) extends with the sensing surface (27) through the guide bush (20b) and the distance sensor (26) is fixed to the guide bush (20b).Steering system (1) according to Claim 6, characterized in that the guide bush (20b) forms a recess (20c) which points towards the sensing surface (27), and the distance sensor (26) extends at least in sections into this recess (20c).Steering system (1) according to one of Claims 1 to 5, characterized in that the distance sensor (26) is fixed on the steering rod (22).Steering system (1) according to one of Claims 1 to 8, characterized in that the distance sensor (26) detects a distance in the transverse direction to the steering rod (22).

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