Electric steering system comprising a sensor for determining the steering rod force

Abstract

The invention relates to an electric steering system for a motor vehicle, comprising a steering rod which pivots a steered wheel of the vehicle directly or via a track rod (2). A sensor module (3) is provided in the shaft region of the steering rod or the track rod (2), the sensor module (3) containing a plurality of strain gauges, and the sensor module (3) measures expansions and compressions of the steering rod or track rod (2), the steering rod force being determined using the sensor data.

Description

[0001] R.410507

[0002] Description

[0003] title

[0004] Electric steering system with a sensor to determine the steering force.

[0005] The present invention relates to an electric steering system for a motor vehicle with a sensor for determining the steering rod force according to the preamble of claim 1.

[0006] State of the art

[0007] Electric power steering systems for motor vehicles typically feature a steering housing in which a rack is mounted for longitudinal movement. A pinion, rotatably mounted within the steering housing, engages with the teeth of the rack, causing it to move laterally. This movement, in turn, transmits the steering input via tie rods and steering knuckles, resulting in the steering of the vehicle's steered wheels. Alternatively, a ball screw drive can be used instead of the pinion, in which a driven ball nut moves the steering rod.

[0008] In conventional steering systems with a mechanical connection to the steering column, the steering rod has a toothed section, as the rotational movements of the steering shaft are transmitted to the rack via a pinion. In steer-by-wire steering systems, the mechanical connection to the steering column is eliminated.

[0009] In steering systems with a central actuator, i.e., a steering system with one steering drive for both steerable wheels, a tie rod is mounted at each end of the steering column, via which the wheels are pivoted. In steering systems with decentralized, translational actuators, i.e., individual wheel actuators, where each steerable wheel has its own steering drive, a tie rod can only be attached to one end of the steering column, which then pivots the wheel carrier. In alternative designs, the steering column of the individual wheel actuator can be directly connected to the wheel carrier.

[0010] Since this invention can be used in conventional steering systems as well as in steer-by-wire systems with central or decentralized actuators, the following description refers to a steering rod. R.410507

[0011] Currently, no sensor is used to measure the steering rod force in such electric steering systems. Instead, the steering rod force is calculated based on system-internal parameters. These parameters include, among others, the motor current and the steering rod position. Such a calculation may not be sufficiently accurate for certain driving maneuvers. The inaccuracies are primarily caused by internal steering disturbances during slow movements. These include, for example, elasticity, friction, and / or play in the mechanical components.

[0012] As described, the calculation is based, among other things, on data regarding motor dimensions, i.e., a component that, relative to the force path, is located relatively far from the point of force application. Consequently, internal steering system frictions have a significant influence on the calculated steering rod force. The object of the invention is therefore to determine the steering rod force as accurately as possible in order to, for example, improve steering feel and enable further functionalities at the vehicle level.

[0013] Advantages of the invention

[0014] The present invention relates to an electric steering system for a motor vehicle with the characterizing features of the independent claim.

[0015] By arranging sensor modules in the shaft area of ​​the steering rod or tie rods, the steering rod force can be measured directly. The sensor data is processed in the control unit and is used to significantly improve, for example, the steering feel.

[0016] According to the invention, it is proposed to arrange sensor modules containing strain gauges on the steering rod or tie rods. During steering operation, axial tensile forces act on the steering rod or tie rod, causing elongation. Similarly, compressive forces cause compression of the steering rod or tie rod. One aspect of the invention is to measure the elongation and compression using strain gauges. It is further proposed to embed the strain gauges in a housing that protects them from moisture and electromagnetic interference (EMI). The housing also serves to press the strain gauges against the steering rod or tie rod so that the elongations and compressions are accurately transmitted to the strain gauges. R.410507

[0017] - 3 -

[0018] Furthermore, the housing should allow for easy mounting of the sensor module to the steering rod or tie rod.

[0019] Cables must be routed from the sensor modules to the control unit. Since the steering rod or tie rod moves relative to the steering housing during operation, at least the section of cable leading from the sensor module to the steering housing must be secured to allow movement.

[0020] The sensor signals are transmitted via cables to the steering control unit. In the control unit, the signals from the sensor modules are evaluated, calculated, and thus a resulting total steering force is determined.

[0021] For easy and quick installation, the sensor module housing can be divided into two halves. These halves are placed around the tie rod and then screwed or clamped together for secure attachment. Installation can be further simplified if the two housing halves are connected by a hinge and then screwed together on only one side. Instead of screws, other fastening methods such as riveting or welding are also possible.

[0022] One of the two housing halves of the sensor module can contain evaluation electronics that evaluate the signals from the strain gauges and convert them into a signal format suitable for the control unit.

[0023] In an initial version, the sensor module uses two grooved sheet metal parts as mounts for the strain gauges. When the two housing halves are bolted together, the grooves of the sheet metal parts are pressed against the tie rod. This ensures that the strains and compressions are reliably transmitted to the strain gauge mounting plates.

[0024] At least two carrier plates for the strain gauges can be attached between the two sheet metal parts. A strain gauge is then bonded to one of the carrier plates. At least one carrier plate should be located in the upper housing half and at least one carrier plate opposite it in the lower housing half. This allows disturbances (temperature-induced strain, bending) to be advantageously detected and filtered out. Preferably, two carrier plates are located in the upper housing half.

[0025] The housing half and two support plates are arranged opposite each other in the lower housing half.

[0026] The assembly just described, consisting of sheet metal parts and support plates, is overmolded with a plastic coating, forming a protective housing. Additionally, seals can be provided at the contact points with the steering rod shaft or tie rod on the two housing halves.

[0027] In a second version, the strain gauges are attached directly to the tie rod, for example by gluing. A housing is also provided here to protect the strain gauges.

[0028] The invention will now be briefly explained using the figures. These show:

[0029] Fig. 1 shows the tie rod of a steering system with the sensor module according to the invention.

[0030] Fig. 2 the sensor module according to the invention

[0031] Fig. 3 shows the sensor module according to the invention in a further embodiment

[0032] Fig. 4 shows the lower half of the sensor module according to the invention.

[0033] Figure 1 shows the tie rod 2 of a steering system. The tie rod 2 is connected to a steering rod (not shown), with the connection being surrounded by a bellows 1. A sensor module 3 is attached to the tie rod 2.

[0034] Figure 2 shows the sensor module 3 according to the invention before mounting it on the tie rod 2. The sensor module 3 consists of an upper half 4 and a lower half 5. The upper half 4 can house evaluation electronics and two carrier plates with strain gauges (not shown). In the lower half 5, the strain gauges are mounted on two carrier plates 8. In this embodiment, the two housing halves 4 and 5 have bores on opposite sides by which the halves 4 and 5 can be screwed together.

[0035] Figure 3 shows a further development of the housing halves 4, 5. The housing halves 4, 5 are connected on one side by a hinge 6, whereby both housing halves 4, 5 R.410507 The housing halves 4 and 5 are held together. During assembly, they are placed around the tie rod 2 and then only need to be screwed together on one side. This further simplifies assembly. Furthermore, the electrical connection between the lower and upper housing halves can also be advantageously made during pre-assembly. This means that the strain gauges of the lower housing half are connected in advance to the evaluation electronics and the strain gauges of the upper housing half via cables that can be routed along the hinge.

[0036] Figure 4 shows the lower half 5 of the sensor module 3. Two curved sheet metal parts 7 serve to hold the support plates 8, on which the strain gauges are glued (not shown). The sheet metal parts 7 have grooves which are pressed against the tie rod when the two housing halves are screwed together.

[0037] The sheet metal parts 7 have holes at both ends to connect the two housing halves 4, 5, with the two ends protruding from the plastic casing 6.

Claims

R.410507 Claims 1. Electric steering system for a motor vehicle, comprising a steering rod which pivots a steered wheel of the vehicle directly or via a tie rod (2), characterized in that a sensor module (3) is arranged in the shaft area of ​​the steering rod or the tie rod (2), wherein the sensor module (3) contains several strain gauges; wherein the sensor module (3) measures strains and compressions of the steering rod or tie rod (2), and the steering rod force is determined using the sensor data.

2. Electric steering system according to claim 1, characterized in that the sensor module comprises a housing with two housing halves (4, 5).

3. Electric steering system according to claim 1 or 2, characterized in that the strain gauges are arranged on carrier plates (8), wherein the carrier plates (8) are pressed against the steering rod or tie rod (2) by sheet metal parts (7).

4. Electric steering system according to claim 3, characterized in that at least one carrier plate (8) with a strain gauge is arranged in each housing half (4, 5).

5. Electric steering system according to one of claims 2 to 4, characterized in that a housing half (4, 5) of the sensor module contains evaluation electronics, wherein the evaluation electronics direct the sensor signals to a steering control unit.

6. Electric steering system according to one of claims 3 to 5, characterized in that, R.410507 that the carrier plates (8) with the strain gauges and the sheet metal parts (7) are encased in a plastic (6) for protection.

7. Electric steering system according to claim 1 or 2, characterized in that the strain gauges are attached directly to the steering rod or tie rod (2).

8. Electric steering system according to one of claims 2 to 7, characterized in that the two housing halves (4, 5) are held together on one side by a hinge (6).

9. Electric steering system according to one of claims 1 to 8, characterized in that the steering system is a steer-by-wire steering system, wherein the steering system has a central steering actuator which simultaneously provides the two steerable wheels.

10. Electric steering system according to one of claims 1 to 8, characterized in that the steering system is a steer-by-wire steering system, wherein the steering system has at least two decentralized steering actuators, each of which pivots a steerable wheel.

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