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 (1) which can be moved by a servomotor; at least one tie rod, via which the steering rod (1) pivots a steerable wheel; a pressure piece (4) which presses against the back of the steering rod (1). The pressure piece (4) is guided in a sensing sleeve (5), wherein the sensing sleeve (5) consists of a housing (11), wherein a sensing film (6) is integrated on the inner surface of the sensing sleeve (5) and serves to measure radial forces on the pressure piece (4).

Description

[0001] R.415853

[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, rotatably mounted within the steering housing and mechanically connected to the steering shaft, 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 to the vehicle's steered wheels. A second pinion, driven by a servo motor, engages with a second set of teeth on the rack. Alternatively, a ball screw drive can be used, in which a driven ball nut moves the steering rod.

[0009] In steering systems based on the steer-by-wire principle, the mechanical connection to the steering column is eliminated.

[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 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 steering column can be connected to a wheel carrier via a tie rod.

[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.415853

[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] The present invention provides an electric steering system for a motor vehicle with a steering rod for pivoting at least one wheel. The steering system also includes a pressure piece which presses against the back of the steering rod to guide it.

[0017] The pressure piece is guided in a sensing sleeve. According to this invention, a sensing sleeve is understood to be a sleeve in which a sensor film is integrated on its inner surface. This allows radial forces on the pressure piece to be measured.

[0018] One aspect of the present invention is to measure radial forces acting on the steering rod. In a steering system where a tie rod is arranged at each end of the steering rod, the total tie rod force is divided into radial (lateral forces) and horizontal components. These components depend on the tie rod angle and thus on the steering rod position. Therefore, to determine the steering rod force, it may be necessary to determine the steering rod position in addition to the signals from the sensing sleeve. R.415853

[0019] This allows conclusions to be drawn about the tie rod angle, which in turn allows force values ​​to be assigned to the steering rods corresponding to the signals from the sensing sleeve.

[0020] Since the radial forces are measured on the main body of the pressure piece using the sensing foil, pressure pieces with a Y or U profile are suitable for this sensing principle.

[0021] A sensing sleeve is arranged between the pressure piece body and the steering housing. The sensing sleeve accommodates the pressure piece body and its end cap. Similar to conventional pressure pieces, the pressure piece body can move up and down within the sensing sleeve housing. The end cap can be adjusted relative to the pressure piece body by means of a thread in the sensing sleeve housing.

[0022] The sensing sleeve is fixedly installed in the steering housing, for example, by screws. A sensing film is integrated into the sensing sleeve housing, which can detect compressive forces. A compressive load acting perpendicular to the axis of the pressure piece is detected by the sensing surfaces. Various measurement principles can be used in the sensing surfaces, such as capacitive measurement, measurement based on the piezoelectric effect, or a piezoresistive measurement principle.

[0023] The required evaluation electronics for the sensing surfaces are housed in the sensing sleeve. The sensing sleeve housing can be equipped with a cover to facilitate easy installation of the evaluation electronics. Additionally, the housing can be fitted with a connector, allowing the sensor information to be transmitted to the control unit via cable. The sensor film and sleeve can be designed as a single assembly. The cables leading from the respective surfaces of the sensor film are converged within the sensing sleeve housing and then processed by the evaluation electronics. The sleeve protects the evaluation electronics from external media and electromagnetic interference (EMI).

[0024] One embodiment is explained with reference to the figures. These show:

[0025] Fig. 1 shows a schematic representation of a steering system according to the invention.

[0026] Fig. 2 shows an exploded view of the pressure piece assembly according to the invention.

[0027] Fig. 3 shows a sectional view of the pressure piece assembly R.415853 according to the invention.

[0028] Figure 1 schematically depicts a steering system according to the invention in an exploded view. The steering rod 1 has a toothed section on the left side and a ball screw drive 2 on the right side for servo assistance. A pinion 3 meshes with the toothed section of the steering rod 1, thereby moving the steering rod in a known manner with the assistance of the servo motor. The steering housing and tie rods are not shown.

[0029] A pressure piece 4 is arranged on the back of the steering rod, which is guided in a sensing sleeve 5 according to the invention.

[0030] Figure 2 shows an exploded view of the pressure piece assembly according to the invention. The sensing sleeve 5 consists of a housing 11, which guides the pressure piece 4. The housing 11 also has an enlarged chamber 10 in which the evaluation electronics are housed. The sensing sleeve 5 further comprises a sensing foil 6, which is integrated into the inner surface of the sensing sleeve 5. The pressure piece 4 is pre-tensioned by a spring in the usual manner. The housing 11 is closed by a screwed-in cap 7, with one opening of the cap 7 being sealed by a plug 8. The enlarged chamber 10 of the housing 11, in which the evaluation electronics are housed, is equipped with a cover 9, which has an outlet for a connector.

[0031] Figure 3 shows a sectional view of the pressure piece assembly according to the invention. The sensing sleeve 5 guides the pressure piece 4. The sensing sleeve 5 further comprises a sensing foil 6, which is integrated into the inner surface of the sensing sleeve 5. The pressure piece 4 is pre-tensioned by a spring in the usual manner. The housing 11 of the sensing sleeve 5 is closed by a screwed-in cap 7, with one opening of the cap 7 being closed by a plug 8.

Claims

R.415853 - 5 - Claims 1. Electric steering system for a motor vehicle, comprising a steering rod (1) which can be moved by a servomotor; at least one tie rod via which the steering rod (1) provides a steerable wheel; a pressure piece (4) which presses against the back of the steering rod (1), characterized in that the pressure piece (4) is guided in a sensing sleeve (5), wherein the sensing sleeve (5) consists of a housing (11) wherein a sensing film (6) is integrated on the inner surface of the sensing sleeve (5), which serves to measure radial forces on the pressure piece (4).

2. Electric steering system according to claim 1, characterized in that pressure loads acting transversely to the axis of the pressure piece are detected in the sensing sleeve (5) by the sensing surfaces of the sensing foil (6).

3. Electric steering system according to claim 1 or 2, characterized in that the determination of the pressure loads by means of the sensing film (6) is carried out by a capacitive measurement or a measurement according to the piezo effect.

4. Electric steering system according to one of claims 1 to 3, characterized in that the angles of the tie rods, which are determined by measuring the steering rod position, and the signals of the sensing sleeve (5) are included in the calculation of the steering rod force.

5. Electric steering system according to one of claims 1 to 4, characterized in that an extended space (10) extends on the housing (11) of the sensing sleeve (5) in which an evaluation electronics is housed. R.415853 - 6 - 6. Electric steering system according to one of claims 1 to 5, characterized in that the sensing foil (6) and the sensing sleeve (5) are configured as a assembly are carried out, and that the cables leading from the sensing foils (6) are brought together in the housing (11) of the sensing sleeve (5) and are then contacted with the evaluation electronics.

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