Electric steering system with sensors for acquiring steering tie rod force

Abstract

An electric steering system for a motor vehicle is described, the electric steering system comprising a steering tie rod (1) and an electric actuator, wherein the electric actuator acts on the steering tie rod (1) to cause it to move laterally, wherein a steering tie rod (2) is fixed at at least one end of the steering tie rod (1), wherein a steerable wheel is deflected by the steering tie rod (2), wherein a sensor (5) is arranged between the steering tie rod (1) and the steering tie rod (2), the sensor being used to determine the steering tie rod force.

Description

Technical Field

[0001] The present invention relates to an electric steering system for motor vehicles having at least one sensor for obtaining steering tie rod force. Background Technology

[0002] Electric power steering systems for motor vehicles typically have a steering housing in which a rack is supported in a longitudinally movable manner. A pinion rotatably supported in the steering housing meshes with the teeth of the rack and causes lateral movement of the rack, which in turn causes deflection of the steering wheels of the motor vehicle via the steering tie rod and the shaft diameter. As an alternative to the pinion, a ball screw drive is used, in which a driven ball nut moves the steering tie rod.

[0003] In conventional steering systems with a mechanical connection to the steering column, the tie rod has teeth because the rotational motion of the steering shaft is transmitted to the rack via a pinion. In steering systems based on the principle of steer-by-wire, the mechanical connection to the steering column is eliminated. Therefore, the tie rod in a steer-by-wire system no longer has teeth for the steering pinion, but only teeth for the steering drive mechanism or a ball screw.

[0004] For a steering system with a central adjuster, i.e., a steering drive mechanism for two steerable wheels, a steering tie rod is installed at each end of the steering drag link, through which the wheels are deflected. For a steering system with a distributed, translational adjuster, i.e., a single-wheel adjuster (in which each steerable wheel has a steering drive mechanism), a steering drag link can be arranged at each wheel, which deflects the wheel via a steering tie rod.

[0005] Because this invention can be used in conventional steering systems, but also in steer-by-wire systems with central or distributed adjusters, the following description refers to the steering tie rod.

[0006] In such electric steering systems, sensors for measuring the steering tie rod force have not been used to date. Instead, the steering tie rod force is estimated. Parameters such as the current in the motor or the position of the steering tie rod are used in this estimation, referencing values ​​from a rotor position sensor. Such estimations cannot be sufficiently accurate for certain driving techniques. The cause of this inaccuracy is particularly due to frictional effects within the steering gear during slow movements. Examples of these internal frictional effects include stick-slip effects, friction within the ball screw drive, and friction in belt drives.

[0007] As described, the estimation is made specifically using data from the motor, i.e., the structural unit, which is relatively far from the system boundaries of the steering gear relative to the force path. Therefore, friction within the steering gear has a significant impact on the estimated steering tie rod force. Thus, the object of the present invention is to obtain, as accurately as possible, the resultant steering tie rod force and external forces individually at the wheel level, in order to, for example, achieve or improve steering feel and other functionalities at the wheel level.

[0008] Advantages of the present invention The present invention relates to an electric steering system for motor vehicles having the characteristic features of the independent claims.

[0009] At least one sensor is placed at the steering tie rod, thereby enabling direct measurement of the steering tie rod force. The sensor's measurement data is processed in the control unit and advantageously used, for example, to significantly improve steering feel.

[0010] Because the steering tie rod force is measured near the system limits, greater friction can be tolerated within the steering gear. This means that larger tolerances are possible in the components, allowing them to be manufactured more cost-effectively.

[0011] This invention proposes placing a sensor between the steering tie rod and the steering drag link. The steering drag link typically consists of an inner joint and an outer joint. The inner joint is screwed into a drilled hole in the steering tie rod for fixation. According to this invention, the steering tie rod and the inner joint no longer touch at their end faces, but instead leave a defined gap. Force flux is now measured through the sensor module positioned there.

[0012] The sensor is mounted on the steering tie rod. In one embodiment, the sensor is screwed onto the external thread of the steering tie rod until it reaches a stop. Then, the inner joint of the steering lateral tie rod is screwed into the steering tie rod. During this installation step, a predefined prestress is applied to the sensor module. Now, the force exerted from the steering lateral tie rod causes increased or slightly lower pressure in the sensor module.

[0013] In one advantageous implementation, the upsetting in the sensor module can be measured using a strain gauge. Alternatively, other measurement principles are also possible. Therefore, pressure can also be acquired using a capacitive pressure sensor. Similarly, sensors utilizing the piezoelectric or piezoresistive effects for measurement are also possible.

[0014] For common steering systems with a central adjuster, steering tie rods are fixed at both ends of the steering tie rod. A sensor module must also be placed on each side. The resultant force of the steering tie rods is then obtained using appropriate calculations of the forces measured by the two sensor modules.

[0015] For a single-wheel adjuster that operates in a translational manner, only one steering tie rod is fixed at the steering tie rod. Here, a sensor module can also be placed between the steering tie rod and the steering tie rod. In this way, the force can be measured individually at each wheel of the vehicle's single-wheel adjuster.

[0016] The acquired measurement data is then transmitted from the sensor module to the steering control unit or the vehicle's central control unit via cables. The control unit uses the data to generate lane feedback, for example, at the steering actuator in a steering-by-wire system. Furthermore, the data can be provided to other systems, such as the chassis control mechanism.

[0017] As already mentioned, in a preferred embodiment, the upsetting in the sensor module can be measured by means of a strain gauge. Here, the sensor module consists of an inner part and an outer part, with a pin arranged or pressed between the two parts. When the inner joint is screwed into the steering tie rod, the outer part is preloaded toward the inner part, wherein the pin is upset. A strain gauge for measuring the upsetting is placed on this pin.

[0018] It is capable of applying at least three strain gauges to pins distributed at the periphery. The desired axial force of the force exerted by the steering tie rod on the steering drag link is obtained by averaging the values ​​of all strain gauges in the sensor module.

[0019] The pin can be made into a cylinder. However, other suitable geometries are also possible. Furthermore, the pin and internal components can be integrally composed of a single unit. Alternatively, the pin and external components can be integrally constructed.

[0020] To protect the electrical components within the sensor module, the internal space of the sensor module must be properly sealed. This can be achieved, for example, by using O-rings in grooves within internal or external components.

[0021] Because the sensor consists of an outer part and an inner part, that is, it is made in two parts, the design must have a feasible way to transfer torque from the outer part to the inner part during installation.

[0022] In one embodiment, one or more slots are provided on the outer component and a corresponding synchronization profile is provided on the inner component. Thus, when the sensor module is mounted on the steering tie rod, torque is transmitted from the outer component to the inner component. Attached Figure Description

[0023] An embodiment of the invention is illustrated in the accompanying drawings, which are explained in detail in the following description of the drawings.

[0024] in: Figure 1 A side view showing the connection between the steering tie rod and the steering lateral tie rod and the sensor according to the invention; Figure 2 A side view of the sensor according to the invention in a preferred embodiment is shown; Figure 3 Another view of the sensor according to the invention, according to a preferred embodiment, is shown; Figure 4 An exploded view of the sensor according to the present invention is shown. Detailed Implementation

[0025] exist Figure 1 In the side view, the connection between the steering tie rod 1 and the steering lateral tie rod 2 and the sensor 5 according to the invention can be seen. An inner joint can be seen in the steering lateral tie rod 2, which is screwed into a drilled hole in the steering tie rod 1. Furthermore, the connection is surrounded by a bellows 3, which prevents water and dirt from entering.

[0026] The inner joint of the steering tie rod 2 no longer contacts the steering drag rod 1 with its end face 4, but instead leaves a defined gap 6. A sensor 5 is arranged at this position according to the present invention.

[0027] This point is Figure 2 This is shown more clearly in the enlarged view. At the end of the steering tie rod 1, a shoulder is machined and an external thread 11 is created. First, the sensor is screwed onto the external thread 11 at the steering tie rod 1 until it touches the stop 10. Then, the inner joint of the steering tie rod 2 is screwed into the steering tie rod 1, thereby applying a defined prestress to the sensor module 5 in this installation step. The inner joint of the steering tie rod 2 consists of a ball thrust bearing and a threaded journal, which is used to screw the inner joint into the steering tie rod 1. The ball thrust bearing of the inner joint touches the sensor 5 axially with its end face 4, but does not touch the steering tie rod 1, leaving a defined gap 6.

[0028] The sensor module 5 consists of an inner component 7 and an outer component 9, with a pin 8 arranged or pressed between these components. When the inner joint is screwed into the steering tie rod 1, the outer component 9 is pre-tightened toward the inner component 7, wherein the pin 8 is upset. A strain gauge (not shown) for measuring the upset is placed on the pin 8.

[0029] To protect the electrical components in sensor module 5, the internal space of sensor module 5 must be properly sealed. This can be achieved, for example, by using O-rings (not shown in the accompanying drawings) in the grooves of the internal or external components 7 and 9.

[0030] exist Figure 3Another view of the sensor according to the invention is shown, in which the synchronizing element for installation is particularly highlighted. For this purpose, a slot 13 is provided at the outer part 9 and a synchronizing profile 12 is provided at the inner part 7. If a tool is placed at the outer part 9 during installation, torque can be transmitted from the outer part 9 to the inner part 7.

[0031] Figure 4 An exploded view of the sensor 5 according to the invention is shown again. The pin 8 is made as a cylinder.

Claims

1. An electric steering system for a motor vehicle, comprising a steering tie rod (1) and an electric actuator, wherein the electric actuator acts on the steering tie rod (1) to cause it to move laterally; A steering tie rod (2) is fixed at at least one end of the steering tie rod (1), through which the steerable wheel is deflected. Its features are, Sensors (5) are arranged between the steering tie rod (1) and the steering cross tie rod (2), respectively, and the sensors are used to determine the steering tie rod force.

2. The electric steering system according to claim 1, Its features are, The sensor (5) includes a strain gauge for measuring pressure load.

3. The electric steering system according to claim 1, Its features are, The sensor (5) is made as a piezoresistive, piezoelectric or capacitive pressure sensor in order to measure pressure load.

4. The electric steering system according to claim 2 or 3, Its features are, The sensor (5) includes an inner part (7), an outer part (9) and at least one pin (8), wherein the pin (8) is pre-tightened between the inner part (7) and the outer part (9), and wherein the strain gauge or pressure sensor is arranged at the pin (8).

5. The electric steering system according to claim 4, Its features are, The sensor (5) is screwed onto the external thread (11) of the steering tie rod (1) with its internal component (7), wherein the end face of the sensor (5) abuts against the ball thrust bearing (14) of the inner steering tie rod (2), wherein a defined gap (6) is left between the steering tie rod (1) and the ball thrust bearing (14).

6. The electric steering system according to claim 4 or 5, Its features are, The pin (8) is arranged circumferentially between the inner part (7) and the outer part (9).

7. The electric steering system according to any one of the preceding claims, Its features are, The sensor (5) has a mechanical synchronizing element, which enables the torque to be transmitted from the outer part (9) to the inner part (7) when the sensor module (5) is mounted on the steering tie rod (1).

8. The electric steering system according to claim 7, Its features are, For a mechanical synchronizing element, at least one groove (13) is provided at the outer part (9) and a corresponding synchronizing profile (12) is provided at the inner part (7), or at least one synchronizing profile (12) is provided at the outer part (9) and a corresponding groove (13) is provided at the inner part (7).

9. The electric steering system according to any one of the preceding claims, Its features are, Steering tie rods (2) are fixed at both ends of the steering tie rod (1), and sensors (5) are arranged between the steering tie rod (1) and the steering tie rod (2), wherein the rack resultant force is calculated from the forces obtained by the two sensors (5).

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