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

Abstract

An electric steering system for a motor vehicle is described, comprising a steering rod (1), an electric actuator, wherein the electric actuator acts on the steering rod (1) in order to displace the latter laterally, wherein a track rod (2) is fastened at least at one end of the steering rod (1), wherein a steerable wheel is pivoted by the track rod (2), wherein a sensor (5) which serves to determine the steering rod force is arranged in each case between the steering rod (1) and the track rod (2).

Description

[0001]

[0002] Description

[0003] title

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

[0005] The present invention relates to an electric steering system for a motor vehicle with at least one sensor for determining the steering rod force.

[0006] State of the art

[0007] Electric steering systems for motor vehicles typically feature a steering housing in which a rack is mounted for longitudinal movement. A pinion, rotatably mounted in the steering housing, engages the rack's teeth and causes the rack to move laterally, which in turn pivots the vehicle's steered wheels via tie rods and steering knuckles. Alternatively to the pinion, a ball screw drive is used, 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 connection, as the rotational movement of the steering shaft is transmitted to the rack via a pinion. In steer-by-wire systems, the mechanical connection to the steering column is eliminated. Therefore, steering rods in steer-by-wire systems no longer have a toothed connection for the steering pinion, but only a toothed connection or a ball screw for the steering drive.

[0009] In steering systems with a central actuator, i.e., a steering system with a steering drive for both steerable wheels, a tie rod is mounted at each end of the steering rod, via which the wheels are pivoted. In steering systems with decentralized, translational actuators, i.e., individual wheel actuators, in which each steerable wheel has a steering drive, a tie rod can be mounted at each wheel, which pivots the wheel via a tie rod.

[0010] Since this invention can be used in classic steering systems, but also in steer-by-wire steering systems with central or decentralized actuators, the following description refers to a steering rod.

[0011] In such electric steering systems, no sensor is currently used to measure the steering rod force. Instead, the steering rod force is estimated. Parameters such as the current in the motors or the steering rod position, for which values ​​from the rotor position sensor are used, are used for the estimation. Such an estimate may not be sufficiently accurate for certain driving maneuvers. The main cause of the inaccuracies is friction effects within the steering system during slow movements. These include, for example, stick-slip effects, friction within the ball screw drive, and friction in the belt drive.

[0012] As described, the estimation is performed using, among other things, data from the motor, a component that, in terms of the force path, is relatively distant from the steering system boundaries. As a result, friction within the steering system has a noticeable influence on the estimated steering rod force. The object of the invention is therefore to determine the total steering rod force as well as the external forces for each individual wheel as accurately as possible, in order to, for example, enable or improve steering feel and other functionalities at the vehicle level.

[0013] Advantages of the invention

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

[0015] By placing at least one sensor on the handlebar, the steering force can be measured directly. The sensor's measured data is processed in the control unit and can be used to significantly improve steering feel, for example.

[0016] Because the steering rod force is measured close to the system boundary, greater friction can be tolerated within the steering system. This means larger tolerances are possible for the components, making them more cost-effective to manufacture.

[0017] The invention proposes arranging a sensor between the steering rod and the tie rod. The tie rod typically consists of an inner joint and an outer joint. The inner joint is screwed into a hole in the steering rod for attachment.

[0018] According to the invention, the steering rod and inner joint no longer touch at their end faces, but a defined gap remains. The force flow now occurs through a sensor module located there.

[0019] The sensors are mounted on the handlebar. In one embodiment, the sensor is screwed onto an external thread on the handlebar until it touches a stop. Then, the inner joint of the tie rod is screwed into the handlebar. During this assembly step, the sensor module is subjected to a defined preload. The forces acting from the tie rod now lead to increased or slightly decreased pressure in the sensor module.

[0020] In an advantageous embodiment, compression in the sensor module can be measured using strain gauges. Alternatively, other measurement principles are also possible. For example, compressive forces can also be determined using a capacitive pressure sensor. Sensors that utilize piezo or piezoresistive effects for measurement are also possible.

[0021] In a conventional steering system with a central actuator, a tie rod is attached to each end of the steering rod. A sensor module must also be installed on each side. The total steering rod force is then determined by appropriately calculating the forces measured by both sensor modules.

[0022] With translatory independent wheel actuators, only one tie rod is attached to a steering rod. Here, too, a sensor module can be placed between the steering rod and the tie rod. This allows the forces on each individual wheel actuator in a vehicle to be measured individually.

[0023] The measured data is then transmitted via cable from the sensor module to the steering control unit or the vehicle's central control unit. The control unit uses the data, for example, to generate road feedback to the steering actuator of the steer-by-wire system. The data can also be made available to other systems, such as the chassis control system.

[0024] As already mentioned, in a preferred embodiment, compression in the sensor module is measured using strain gauges. The sensor module consists of an inner part and an outer part, with bolts arranged or pressed in between these parts. When the inner joint is screwed into the steering rod, the outer part is preloaded toward the inner part, compressing the bolts. Strain gauges are placed on these bolts to measure the compression.

[0025] At least three strain gauges can be applied to the bolts distributed around the circumference. By calculating the average value of all strain gauges in a sensor module, the desired axial force acting from the tie rod to the steering rod is determined.

[0026] The bolts can be designed as cylinders. However, other suitable geometric shapes are also possible. Furthermore, the bolts and the inner part can be formed from a single component. Alternatively, the bolts and the outer part can be formed integrally.

[0027] To protect the electrical components in the sensor module, the interior of the sensor module is suitably sealed. This can be achieved, for example, with O-rings in grooves in the inner or outer part.

[0028] Since the sensor comprises an outer part and an inner part, i.e. is designed in two parts, the design must provide a way to transfer the torque from the outer part to the inner part during assembly.

[0029] In one design, one or more grooves are provided on the outer part and corresponding drive contours on the inner part. This transfers the torque from the outer to the inner part when the sensor module is mounted on the steering rod.

[0030] Short description of the drawings

[0031] An embodiment of the present invention is illustrated in the figures and explained in more detail in the following description of the figures.

[0032] It shows:

[0033] Fig. 1 a side view of the connection between the steering rod and the tie rod with a sensor according to the invention

[0034] Fig. 2 a side view of the sensor according to the invention in a preferred embodiment

[0035] Fig. 3 is a further view of the sensor according to the invention of the preferred embodiment

[0036] Fig. 4 an exploded view of the sensor according to the invention

[0037] Figure 1 shows a side view of the connection between the steering rod 1 and the tie rod 2, including a sensor 5 according to the invention. The inner joint of the tie rod 2 can be seen, which is screwed into a hole in the steering rod 1. Furthermore, the connection is surrounded by a bellows 3, which prevents the ingress of water and dirt.

[0038] The inner joint of the tie rod 2 no longer touches the steering rod 1 with its end face 4, but a defined gap 6 remains. According to the invention, the sensor 5 is arranged at this point.

[0039] This is shown more clearly in an enlarged view in Figure 2. At the end of the steering rod 1, a shoulder is machined off and an external thread 11 is created. First, the sensor 5 is screwed onto the external thread 11 on the steering rod 1 until it touches a stop 10. Then, the inner joint of the tie rod 2 is screwed into the steering rod 1, whereby the sensor module 5 is subjected to a defined preload during this assembly step. The inner joint of the tie rod 2 consists of a ball socket and a threaded pin with which the inner joint is screwed into the steering rod 1. is screwed. The ball socket of the inner joint axially touches the sensor 5 with its end face 4, but not the steering rod 1; instead, the defined gap 6 remains.

[0040] The sensor module 5 consists of an inner part 7 and an outer part 9, with bolts 8 arranged or pressed in between these parts. When the inner joint is screwed into the steering rod 1, the outer part 9 is preloaded toward the inner part 7, compressing the bolts 8. Strain gauges (not shown) are placed on these bolts 8 to measure the compression.

[0041] To protect the electrical components in the sensor module 5, the interior of the sensor module 5 is suitably sealed. This can be achieved, for example, by O-rings in grooves (shown without reference numerals) in the inner or outer parts 7, 9.

[0042] Figure 3 shows a further view of the sensor according to the invention, highlighting in particular the mechanical drive for assembly. For this purpose, a groove 13 is provided on the outer part 9 and a drive contour 12 on the inner part 7. When the tool is applied to the outer part 9 during assembly, the torque can be transferred from the outer part 9 to the inner part 7.

[0043] Figure 4 shows another exploded view of the sensor 5 according to the invention. The bolts 8 are designed as cylinders.

Claims

Claims 1. An electric steering system for a motor vehicle, comprising a handlebar (1) and an electric actuator, the electric actuator acting on the handlebar (1) to displace it laterally; a tie rod (2) being fastened to at least one end of the handlebar (1), a steerable wheel being pivoted via the tie rod (2), characterized in that a sensor (5) is arranged between the handlebar (1) and the tie rod (2), which sensor serves to determine the handlebar force.

2. Electric steering system according to claim 1, characterized in that the sensor (5) contains strain gauges to measure the pressure load.

3. Electric steering system according to claim 1, characterized in that the sensor (5) is designed as a piezoresistive, piezoelectric or capacitive pressure sensor in order to measure the pressure load.

4. Electric steering system according to claim 2 or 3, characterized in that the sensor (5) comprises an inner part (7), an outer part (9) and at least one bolt (8), wherein the bolts (8) are prestressed between the inner part (7) and the outer part (9), wherein the strain gauges or pressure sensors are arranged on the bolt (8).

5. Electric steering system according to claim 4, characterized in that the sensor (5) with its inner part (7) is mounted on an external thread (11) on the steering rod (1) is screwed on, whereby the sensor (5) with its front face on the ball socket (14) the inner tie rod (2), whereby a defined gap (6) remains between the steering rod (1) and the ball socket (14).

6. Electric steering system according to claim 4 or 5, characterized in that the bolts (8) are arranged in the circumferential direction between the inner part (7) and the outer part (9).

7. Electric steering system according to one of the preceding claims, characterized in that the sensor (5) has a mechanical drive, whereby the torque can be transmitted from the outer part (9) to the inner part (7) when the sensor module (5) is mounted on the steering rod (1).

8. Electric steering system according to claim 7, characterized in that for the mechanical driving, at least one groove (13) is provided on the outer part (9) and corresponding driving contours (12) are provided on the inner part (7) or at least one driving contour (12) is provided on the outer part (9) and corresponding groove(s) (13) are provided on the inner part (7).

9. Electric steering system according to one of the preceding claims, characterized in that a tie rod (2) is fastened to each of the two ends of the steering rod (1), a sensor (5) being arranged between each of the steering rod (1) and the tie rod (2), the total rack force being calculated from the forces determined by the two sensors (5).

Images