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, the electric steering system comprising a Y-shaped steering rod (2), a servo unit which displaces the steering rod (2) by means of a ball screw drive, and a Y-shaped pressure element (3) which presses against the steering rod (2), wherein a pressure-element film (4) is arranged between the steering rod (2) and the pressure element (3), the pressure-element film enabling low-friction movement of the steering rod. At least two sensor modules (5), by means of which loads in the steering system can be detected, are arranged beneath the pressure-element film (4), thereby enabling the total steering-rod force to be determined.

Description

[0001] R.410504

[0002] - 1 -

[0003] Description

[0004] title

[0005] Electric steering system with a sensor to determine the steering force.

[0006] 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.

[0007] State of the art

[0008] Electric power steering systems for motor vehicles typically feature a steering housing in which a rack is mounted for longitudinal movement. A pinion, connected to the steering shaft and 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 wheels. To amplify the force applied by the driver, a servo unit with a ball screw drive can be used, in which a driven ball nut moves the steering rod.

[0009] In conventional steering systems with a mechanical connection to the steering column, the steering rod has splines because 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, and therefore so are the splines.

[0010] 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 linkage, 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 steering rod can be directly attached to each wheel carrier, which pivots the wheel; thus, an additional tie rod is no longer necessary.

[0011] 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.410504

[0012] 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.

[0013] 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.

[0014] Advantages of the invention

[0015] The present invention relates to an electric steering system for a motor vehicle with the characterizing features of the independent claim.

[0016] By arranging sensor modules on the steering column's pressure piece, 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.

[0017] A spring-loaded pressure piece presses against the back of the steering rod. Opposite the pressure piece, a pinion can engage with a toothed section on the steering rod, so that the pressure piece, via a compression spring, presses the steering rod toothing against the pinion toothing with minimal play. Alternatively, in a steer-by-wire steering system, a bearing can be used instead of the toothed section and pinion. Corresponding to the Y-shape of the steering rod, the pressure piece is also Y-shaped and serves as an anti-rotation device. R.410504

[0018] The servo unit is designed in the form of a ball screw drive. The torque of the steering drive sets the steering rod into rotation, or rather, generates a torque around the steering rod axis.

[0019] This torque must be counteracted by anti-rotation devices, such as the Y-type pressure piece. Depending on the direction of the torque, one side of the Y-type pressure piece is subjected to pressure while the other side is relieved. Furthermore, the radial components of the tie rod forces also result in a compressive load on the surfaces of the pressure piece.

[0020] On the steering rod side of the pressure piece, a pressure piece film is located, which is fixed to the pressure piece and allows for low-friction movement of the steering rod, thus improving the sliding properties on the pressure piece. According to the invention, it is proposed to place sensor modules under the pressure piece film, enabling the detection of the described loads. The total steering rod force can then be determined from these loads.

[0021] A sensor module is positioned on each side between the pressure piece foil and the pressure piece body. Any pressure load acting on the pressure piece foil is detected by the corresponding sensor module. By using one sensor module on each side of the Y-shaped pressure piece, the torsional torques acting on the steering rod can also be determined based on the measured pressure forces. Since the direction of the axial forces and torsional torques acting on the steering rod are related to each other, the described evaluation method can determine not only the absolute value of the total steering rod force but also its direction.

[0022] Various measurement principles can be used in the sensor modules.

[0023] The electronics required for evaluating the signals from the sensor modules can be housed in a sleeve within the pressure piece. The cables leading from the respective surfaces of the sensor modules are brought together in the sleeve and evaluated by the electronics inside. The sleeve advantageously protects the evaluation electronics from, for example, moisture and electromagnetic interference (EMI). Furthermore, the sensor modules and sleeve are designed as a single assembly. R.410504

[0024] In a first implementation, a capacitive measurement is performed. A two-layer flexible printed circuit board (FlexiPCB) is applied to the pressure piece body (e.g., glued or laid on top), acting as a plate capacitor. The pressure piece foil is then placed onto the pressure piece as usual, bringing the foil and the flexible printed circuit board (FlexiPCB) into contact. When the pressure piece's spring travel is adjusted, the surfaces of the flexible printed circuit board are subjected to a preload. Changes in capacitance at the plate connections can be evaluated when the pressure piece is loaded and unloaded against the loads caused by this preload, allowing the force applied to be calculated.

[0025] In a second version, measurement is performed using the piezoelectric effect, or a piezoresistive measuring principle. A metal frame with a vapor-deposited piezoelectric layer is placed on the pressure piece foil. When the pressure piece is loaded and unloaded, the coating generates a measurable electrical voltage between the ground connection and the crystal layer, allowing conclusions to be drawn about the force acting on the pressure piece.

[0026] The invention will now be briefly explained using the figures. These show:

[0027] Figure 1 shows a section of a steering gear

[0028] Figure 2 shows the pressure piece according to the invention in an exploded view.

[0029] Figure 3 shows the pressure piece according to the invention in an assembly drawing

[0030] Figure 4 shows the flexible printed circuit board according to the first embodiment of the invention.

[0031] Figure 5 shows the piezoelectric construct according to the second embodiment of the invention.

[0032] Figure 1 shows a cross-sectional view of a steering gear. A pinion 1 meshes with the steering rod 2. The Y-shaped steering rod 2 is pressed against the pinion 1 by a pressure piece 3. A pressure piece foil 4 is located between the pressure piece 3 and the rack 2. This foil is fixed to the pressure piece 3 and allows for low-friction movement of the steering rod 2. R.410504

[0033] - 5 - Figure 2 shows an exploded view of the pressure piece 3 according to the invention. Sensor modules 5 are arranged between the pressure piece foil 4 and the pressure piece 3. A pressure load acting on the pressure piece foil 4 is detected by the sensor modules 5. The necessary electronics for evaluating the signals from the sensor modules 5 are housed in a sleeve 6. The cables leading from the sensor modules 5 (not shown) are brought together in the sleeve 6 and evaluated therein by electronics. Furthermore, the pressure piece 3 has an O-ring 7, which is arranged in a groove.

[0034] Figure 3 shows the described printed piece 3 again in an assembly drawing.

[0035] Figure 4 shows the sensor modules 5 as a flexible printed circuit board according to the first embodiment of the invention. The first embodiment is based on capacitive measurement. A two-layer flexible printed circuit board (Flexi PCB), which functions as a plate capacitor, is bonded to the pressure piece 3. When the spring travel of the pressure piece 3 is adjusted, the surfaces of the flexible printed circuit board are subjected to a preload. During loading and unloading of the pressure piece 3, changes in capacitance at the plate terminals 8 can be evaluated, from which the applied force can then be calculated.

[0036] Figure 5 shows the piezoelectric construct according to the second embodiment of the invention. The second embodiment is based on a measurement using the piezoelectric effect. A metal frame 10 with a vapor-deposited piezoelectric layer is placed on the pressure piece foil 4. When the pressure piece 3 is loaded and unloaded, the coating generates a measurable electrical voltage between the ground connection 11 and the crystal layer 12, allowing the force acting on the pressure piece 3 to be determined.

Claims

R.410504 - 6 - Claims 1. Electric steering system for a motor vehicle, comprising a Y-shaped steering rod (2), a servo unit which displaces the steering rod (2) by means of a ball screw drive; a Y-shaped pressure piece (3) which presses against the steering rod (2); wherein a pressure piece foil (4) is arranged between the steering rod (2) and the pressure piece (3), which enables low-friction movement of the steering rod, characterized in that at least two sensor modules (5) are arranged under the pressure piece foil (4), with which loads in the steering system can be detected, whereby the total steering rod force can be determined.

2. Electric steering system according to claim 1, characterized in that the determination of the loads in the sensor modules (5) is based on a capacitive measurement or a measurement according to the piezo effect.

3. Electric steering system according to claim 2, characterized in that sensor modules (5) are attached to the pressure piece (3), which are designed as two-layer flexible printed circuit boards, wherein the printed circuit boards are used as plate capacitors, wherein the changes in capacitance are evaluated according to the loads on the pressure piece (3) in order to calculate force effects.

4. Electric steering system according to claim 2, characterized in that a metal frame (10) with a vapor-deposited piezo layer is placed on the pressure piece film (4), wherein the coating generates an electrical voltage according to the loads on the pressure piece (3), with which the force acting on the pressure piece (3) can be determined.

5. Electric steering system according to one of claims 1 to 4, characterized in that electronics for evaluating the sensor signals are housed in a sleeve (6) which contains the outgoing cables of the sensor modules (5) R.410504 - 7 - joined together, wherein the sleeve (6) is arranged in a recess in the pressure piece (3).

6. Electric steering system according to one of claims 1 to 5, characterized in that a first sensor module (5) is located on one side of the pressure piece. (3) is arranged and a second sensor module (5) is arranged on the radially opposite side of the pressure piece (3).

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