Control device for a motor-driven power steering system

Abstract

Control device for a motor-driven power steering system (MDPS), wherein the control device comprises: a torque sensor (10) configured to measure the steering torque applied by a driver to a steering wheel and to output a steering torque signal, a steering angle sensor (40) configured to measure a steering angle of the steering wheel, a variable notch filter (20) configured to reduce torque ripple for the steering torque signal as a function of a steering angle velocity, which is a rate of change of the steering angle with respect to time, a vehicle speed sensor (50) configured to measure vehicle speed, and a control device (30) configured to receive the steering angle, steering torque signal and vehicle speed respectively from the steering angle sensor (40), the variable notch filter and the vehicle speed sensor (50) and to control the drive of a drive motor (60) in accordance with the vehicle speed, wherein the variable notch filter (20) reduces torque ripple at a preset order.

Description

Background of the invention

[0001] The present invention relates to a control device for a motor-driven power steering system (MDPS) and in particular to a control device for an MDPS which is able to selectively remove humming vibrations that occur depending on the steering angle speed in order to reduce steering vibrations.

[0002] In general, an MDPS is understood to be a system that uses an electric motor to provide auxiliary torque along a direction in which a driver steers a vehicle, thereby simplifying handling.

[0003] Such an MDPS automatically controls the operation of the electric motor in accordance with the vehicle's driving conditions, thus differing from an existing hydraulic power steering system (HPS). The MDPS can therefore improve steering performance and steering feel.

[0004] The MDPS determines a driving condition of the vehicle using a torque sensor to measure the steering torque exerted by a driver on a steering wheel, a steering angle sensor to measure the steering angle of the steering wheel and a vehicle speed sensor to measure the vehicle speed, and provides an auxiliary torque by means of the electric motor in accordance with the steering torque exerted by the driver on the steering wheel.

[0005] Furthermore, the MDPS applies an auxiliary torque proportional to the steering torque, uses proportional amplification to maintain this proportional relationship, and reduces or smooths out any steering effort required by the driver. Simultaneously, the MDPS suppresses torque ripples generated by the electric motor or vibrations such as road disturbances to improve the driving experience for the driver.

[0006] To suppress torque ripples or vibrations generated by the electric motor, such as ground disturbances, the MDPS uses a hybrid filter comprising a low-pass filter (LPF) and a high-pass filter (HPF). It extracts a steering component using the LPF to control the power steering torque. Simultaneously, the MDPS extracts high-frequency vibration components, such as torque ripples, using the HPF and controls these components with a separate control unit, distinct from a control unit for low-frequency vibrations.

[0007] Furthermore, the MDPS extracts the rotational speed of the electric motor or the angular velocity vibration component of the steering angle using a bandpass filter (BPF), reduces a signal obtained by adding a gain to the vibration component of a target current, calculates a new target current and performs negative control for the angular velocity to reduce the vibration.

[0008] From EP 1 399 348 B1, a speed compensation control system for electric power steering systems is known. A control device is described that provides electric power steering assistance, as well as a torque sensor that detects the torque applied to the steering wheel by the driver and outputs a variable torque signal. Furthermore, it is mentioned that a control unit of the device receives a vehicle speed signal, and that a position sensor is provided for measuring a control pinion angle. A notch filter is also described as an example of a so-called torque compensator. This notch filter is intended to maintain the stability of the torque control of the electric power steering system.

[0009] From DE 10 2010 025 197 A1, a method and a device for filtering a setpoint signal are known. This device is connected to a control torque sensor, a vehicle speed sensor, a steering angle sensor, and a steering angle velocity sensor. The sensor signals are transmitted to a filter. Examples of such a filter include a notch filter, a high-pass filter, and a low-pass filter. It is disclosed that the filter is parameterized based on a so-called driving situation. Such a driving situation is characterized, for example, by the vehicle speed and / or the steering angle and / or the steering angle velocity.

[0010] The vibration caused by torque ripples is removed by the hybrid filter or the BPF. However, the MDPS has the problem that it cannot correctly handle humming vibrations caused by a worm gear, which depend on the steering angle speed. Explanation of the invention

[0011] The object of the invention is to selectively remove humming vibrations that can occur depending on the steering angle speed and thereby reduce steering vibrations.

[0012] The problem is solved using the features of claim 1.

[0013] Embodiments of the invention relate to a control device for an MDPS which is able to selectively remove humming vibrations that may occur depending on the steering angle speed and thereby reduce steering vibrations.

[0014] In one embodiment, a motor-driven power steering system (MDPS) comprises: a torque sensor configured to measure the steering torque applied by a driver to a steering wheel and to output a steering torque signal; a steering angle sensor configured to measure the steering angle of the steering wheel; a variable notch filter configured to reduce torque ripple in the steering torque signal as a function of the steering angle velocity, which is the rate of change of the steering angle with respect to time; and a vehicle speed sensor configured to measure the vehicle speed.and a control unit configured to receive the steering angle, steering torque signal and vehicle speed from the steering angle sensor, variable notch filter and vehicle speed sensor respectively, and to control the drive of a drive motor in accordance with a vehicle speed.

[0015] According to the embodiment of the present invention, the control device of the MDPS can selectively remove the humming vibration caused by the worm gear in a rapid steering situation by means of the variable notch filter, which is operated depending on the steering angle speed. The control device can thus reduce steering vibration by removing the humming vibration in a rapid steering situation without affecting the steering feel in a general steering situation.

[0016] The variable notch filter can reduce torque ripple at a preset order.

[0017] The preset order of the variable notch filter can correspond to the number of teeth of a worm gear for transmitting the drive of the drive motor to the steering wheel.

[0018] The preset order can include the 20.5th order and the 41st order.

[0019] The variable notch filter can have a notch width that varies with increasing steering angle speed.

[0020] The notch of the variable notch filter can be varied linearly at a steering angle speed of 1 U / s to 2 U / s.

[0021] The variable notch filter can have a notch of 41 Hz when the steering angle speed is 1 U / s, and a notch of 82 Hz when the steering angle speed is 2 U / s.

[0022] The variable notch filter can be operated when the steering angle speed is equal to or greater than a preset speed.

[0023] The preset speed can be 1 revolution / s (360 degrees / s).

[0024] The variable notch filter can have a transfer function defined as follows: X(s)Y(s)=s2+2ζα+α2(s+αβ)(s+αβ)

[0025] where α = order × 2 × π × θ̇, β represents the depth of a notch, ζ represents the width of the notch, and θ̇ represents the steering angular velocity. Brief description of the drawings Fig. Figure 1 is a block diagram showing the configuration of a control device of an MDPS according to an embodiment of the present invention. Fig. Figure 2 is a curve diagram showing the characteristic curve of a variable notch filter in the control device of the MDPS according to the embodiment of the present invention. Fig. Figure 3 is a curve diagram showing the results obtained by simulating the characteristic curve of the variable notch filter in the control device of the MDPS according to the embodiment of the present invention. Fig. 4A and Fig. Figure 4B are curve diagrams that illustrate the operating state of the variable notch filter in a general steering situation when the control device of the MDPS is used according to the embodiment of the present invention. Fig. 5A and Fig. Figure 5B are curve diagrams that illustrate the operating state of the variable notch filter in a fast steering situation when the control device of the MDPS is used according to the embodiment of the present invention. Description of specific embodiments

[0026] Various embodiments of the invention are described in detail below with reference to the accompanying drawings. It should be noted that the drawings are not to scale and that line thicknesses or component sizes may be exaggerated to illustrate the invention.

[0027] Furthermore, the terms used here are defined with reference to the functions of the invention and may be interchanged according to the custom or intention of users or operators. The meaning of the terms must therefore be understood within the context of the entire description given here.

[0028] Fig. Figure 1 is a block diagram showing the configuration of a control device for a motor-driven power steering system (MDPS) according to an embodiment of the invention. Fig. Figure 2 is a curve diagram showing the characteristic curve of a variable notch filter in the control device of the MDPS according to the embodiment of the present invention. Fig. Figure 3 is a curve diagram showing the results obtained by simulating the characteristic curve of the variable notch filter in the control device of the MDPS according to the embodiment of the present invention.

[0029] As in Fig. As shown in Figure 1, the control device of the MDPS according to the embodiment of the present invention comprises a torque sensor 10, a steering angle sensor 40, a variable notch filter 20, a vehicle speed sensor 50 and a control unit 30.

[0030] The torque sensor 10 is configured to measure a steering torque caused by a rotation of the steering wheel (not shown) when a driver operates the steering wheel, and to generate a steering torque signal.

[0031] The steering angle sensor 40 is configured to measure a steering angle as a function of steering input by the driver and to provide the measured steering angle.

[0032] The vehicle speed sensor 50 is configured to measure the vehicle's driving speed and to provide the measured speed.

[0033] The variable notch filter 20 is configured to reduce torque ripple for the steering torque signal based on a steering angle velocity, which is a rate of change for the measured steering angle with respect to time, at a preset order.

[0034] The steering angle speed can be calculated based on changes in the steering angle, which is measured by the steering angle sensor 40.

[0035] In the present embodiment, the variable notch filter 20 is set to remove a humming vibration caused by a 41st order torque ripple that occurs in a fast steering situation when the steering angle speed is high.

[0036] The torque ripple at the 41st order is a humming vibration caused by a worm gear (not shown) to transmit the drive of the drive motor 60 to the steering wheel, where the number 41 corresponds to the number of teeth of the worm gear.

[0037] Therefore, if the number of teeth of the worm gear is 41, the torque ripple component at the 41st order excites the frame and steering mechanism of the vehicle, thereby producing a humming vibration.

[0038] To remove the torque ripple component at the 41st order, the variable notch filter 20 removes the torque ripple component at the 41st order in a fast steering situation to eliminate the humming vibration.

[0039] For this operation, the transfer function of the variable notch filter 20 can be expressed by the following equation 1. X(s)Y(s)=s2+2ζα+α2(s+αβ)(s+αβ)

[0040] where α = 41 (order) x 2 × π × θ̇, β represents the depth of a notch, ζ represents the width of the notch, and θ̇̇ represents the steering angular velocity.

[0041] To determine whether the notch filter should be operated or not, β can be used as in Fig. Figure 2 shows that the notch filter should be operated at a steering angular velocity of 1 revolution per second (360 degrees per second) or higher, rather than at a steering angular velocity of 1 revolution per second or higher. Filtering can then be performed while the notch is linearly enlarged until the steering angular velocity reaches 2 revolutions per second.

[0042] This means that the notch is set to 41 Hz at a steering angle speed of 1 revolution / s and to 82 Hz at a steering angle speed of 2 revolutions / s.

[0043] Furthermore, ζ is a value for setting the width of the notch of the notch filter, which is set to a constant value regardless of the steering angle speed.

[0044] If the variable notch filter 20 is simulated with such a transfer function characteristic in accordance with the steering angle velocity, the simulation result can be as shown in Fig. 3 will be shown and received.

[0045] If, as in Fig. As shown in Figure 3, if the steering angle velocity is less than 1 revolution per second, the notch filter is not operated and no filtering takes place. However, if the steering angle velocity is equal to or greater than 1 revolution per second, the notch filter is operated for filtering and the point of the notch is changed.

[0046] For example, if steering is performed at a steering angle speed of 0.5 revolutions per second, the notch filter is not activated. If steering is performed at a steering angle of 1 revolution per second, a notch filter is applied to remove 41 Hz, and if steering is performed at a steering angle of 1.5 revolutions per second, a notch filter is applied to remove 61.5 Hz.

[0047] And if ζ is varied in accordance with the steering angle speed to provide optimal steering feel, the width of the notch can also be adjusted.

[0048] The control unit 30 receives the steering angle, steering torque signal and vehicle speed from the steering angle sensor 40, the variable notch filter 20 and the vehicle speed sensor 50, controls the drive of the drive motor 60 in accordance with the vehicle's driving speed, provides an auxiliary torque for the steering wheel operated by the driver and assists the driver in operating the steering wheel gently at a low speed or forcefully at a high speed, thereby ensuring driving stability.

[0049] The auxiliary torque is inversely proportional to the drive speed.

[0050] Fig. 4A and Fig. Figure 4B are curve diagrams that illustrate the operating state of the variable notch filter in a general steering situation when the control device of the MDPS is used according to the embodiment of the present invention. Fig. 5A and Fig. Figure 5B are curve diagrams that illustrate the operating state of the variable notch filter in a fast steering situation when the control device of the MDPS is used according to the embodiment of the present invention.

[0051] Fig. 4A, Fig. 4B, Fig. 5A and Fig. Figure 5B shows a steering torque signal based on the steering angle, the torque FFT-converted for the steering torque signal at each order, and a steering angle velocity based on time, both when the variable notch filter 20 is not applied and when the variable notch filter 20 is applied.

[0052] Fig. 4A and Fig. Figure 4b shows a test result in a general steering situation where the steering angle speed is 0.5 revolutions / s. As in Part A of Fig. 4A shown, in which the variable notch filter 20 is not applied, and in part A of Fig. Figure 4B shows that when the variable notch filter 20 is applied, the vibration components increase slightly at the 20.5th and 41st orders. However, because no hum vibrations occur in this state, the notch filter is not operated.

[0053] Fig. 5A and Fig. Figure 5B shows a test result in a fast steering situation where the steering angle speed is 1 revolution / s. As in Part A of Fig. 5A shown, in which the variable notch filter 20 is not applied, and in part B of Fig. As shown in Figure 5B, where the variable notch filter 20 is applied, the vibration components increase slightly at the 0.5th and second order in part B of Fig. 5B, however, have no effect on the steering feel.

[0054] As in Part A of Fig. As shown in Figure 5A, where the variable notch filter 20 is not applied to a fast steering situation, a fairly large vibration component occurs at the 41st order. As shown in Part A of Fig. Figure 5B shows that, with the variable notch filter 20 applied, the variable components are removed at the 20.5th and 41st orders.

Claims

[1] Control device for a motor-driven power steering system (MDPS), wherein the control device comprises: a torque sensor (10) configured to measure the steering torque applied by a driver to a steering wheel and to output a steering torque signal, a steering angle sensor (40) configured to measure a steering angle of the steering wheel, a variable notch filter (20) configured to reduce torque ripple for the steering torque signal as a function of a steering angle velocity, which is a rate of change of the steering angle with respect to time, a vehicle speed sensor (50) configured to measure vehicle speed, and a control device (30) configured to receive the steering angle, steering torque signal and vehicle speed respectively from the steering angle sensor (40), the variable notch filter and the vehicle speed sensor (50) and to control the drive of a drive motor (60) in accordance with the vehicle speed, wherein the variable notch filter (20) reduces torque ripple at a preset order. [2] Control device according to claim 1, wherein the preset order of the variable notch filter (20) corresponds to the number of teeth of a worm gear for transmitting the drive of the drive motor (60) to the steering wheel. [3] Control device according to claim 2, wherein the preset order comprises the 20.5th order and the 41st order. [4] Control device according to one of the preceding claims, wherein the variable notch filter (20) has a notch width which is varied with the increase of the steering angle speed. [5] Control device according to claim 4, wherein the notch of the variable notch filter (20) is varied linearly with a steering angular velocity of 1 U / s to 2 U / s. [6] Control device according to claim 5, wherein the variable notch filter (20) has a notch of 41 Hz when the steering angular velocity is 1 RPM and has a notch of 82 Hz when the steering angular velocity is 2 RPM. [7] Control device according to one of the preceding claims, wherein the variable notch filter (20) is operated when the steering angle speed is equal to or greater than a preset speed. [8] Control device according to claim 7, wherein the preset speed is 1 revolution / s (360 degrees / s). [9] Control device according to one of the preceding claims, wherein the variable notch filter (20) has a transfer function defined as follows: X(s)Y(s)=s2+2ζα+α2(s+αβ)(s+αβ) where α = order × 2 × π × θ̇̇ is, β represents the depth of a notch, ζ represents the width of the notch, and θ̇̇ represents the steering angular velocity.

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