Electric power steering apparatus, control device for electric power steering apparatus, and program

Abstract

The electric power steering system (100) includes: an electric motor (110) that imparts a driving force to the wheels for operation of the steering wheel; and a control device (10) that estimates the degree of gradient in the transverse direction of the road on which the vehicle is traveling, determines a correction current for correcting the target current required to generate the driving force of the electric motor based on the estimated degree of gradient, and controls the drive of the electric motor by correcting the target current using the correction current.

Description

Technical Field

[0001] This invention relates to an electric power steering system, a control device for an electric power steering system, and a program. Background Technology

[0002] In recent years, electric power steering systems have been proposed that incorporate electric motors into vehicle steering systems, using the power of the electric motors to assist the driver's steering force and thus steer the wheels.

[0003] Furthermore, it is known that if the road on which a vehicle travels has a slope in the direction that crosses the road, then a phenomenon known as vehicle body slip will occur when the vehicle is in motion. A technique for suppressing this vehicle body slip using an electric power steering system has been proposed.

[0004] For example, the control device for the electric power steering system described in Patent Document 1 includes: an electric motor that applies an auxiliary force to the steering wheel of a vehicle; a steering angle sensor that detects the steering angle of the steering wheel; and a control device. The control device performs normal control of the driving force of the electric motor based on the steering torque of the steering wheel. Furthermore, when the steering wheel is held in a position other than neutral, the control device corrects the driving force based on the steering angle deviation between an estimated steering angle estimated based on the rotational speed of the vehicle's wheels and a detected steering angle detected by a steering angle detection unit, making the driving force greater than that under normal control. On the other hand, the control device does not correct the driving force when steering the steering wheel to turn the vehicle.

[0005] Prior art literature

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2017-177950 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] However, in the existing technology, since the driving force of the electric motor is corrected by using the steering angle of the steering component, the actual state of the vehicle is not taken into account, and the driver's steering feel may sometimes be worse.

[0010] The purpose of this invention is to provide an electric power steering device, etc., which takes into account the vehicle's state parameters to correct the driving force of the electric motor, thereby improving the driver's steering feel.

[0011] To achieve the above objectives, the present invention provides an electric power steering device comprising: an electric motor that imparts a driving force to the wheels for operation of a steering wheel; and a control unit that estimates the degree of gradient in the transverse direction of the road on which the vehicle is traveling, determines a correction current for correcting a target current required to generate the driving force of the electric motor based on the estimated degree of gradient, and controls the driving of the electric motor by correcting the target current using the correction current.

[0012] Furthermore, the present invention is a control device for an electric power steering system, comprising: a slope estimation unit that estimates the degree of slope in the transverse direction of the road on which the vehicle travels; a correction current determination unit that determines a correction current for correcting the target current required to generate the driving force of the electric motor based on the estimated degree of slope; and a target current determination unit that determines a target current based on the determined correction current.

[0013] Invention Effects

[0014] The present invention can provide an electric power steering device, etc., which corrects the driving force of the electric motor by taking into account the state variables of the vehicle, thereby improving the driver's steering feel. Attached Figure Description

[0015] Figure 1 This is a diagram showing the schematic structure of the electric power steering device according to this embodiment.

[0016] Figure 2 This is a schematic diagram of the control device for the steering system.

[0017] Figure 3 This is a schematic diagram of the target current calculation unit and the control unit.

[0018] Figure 4 This is a block diagram illustrating an example of the functional structure of the correction current calculation unit in the first embodiment.

[0019] Figure 5 This is a diagram illustrating the centripetal acceleration acting on a vehicle.

[0020] Figure 6 It is a diagram showing the various accelerations acting on a vehicle.

[0021] Figure 7 This is a control block diagram representing the processing performed by the slope estimation unit.

[0022] Figure 8 This is a control block diagram representing the processing performed by the correction current determination unit.

[0023] Figure 9 This is a control block diagram representing the processing previously performed in the correction current determination section.

[0024] Figure 10 This is a block diagram illustrating an example of the functional structure of the correction current calculation unit in the second embodiment.

[0025] Figure 11 This is a control block diagram illustrating the processing performed by the correction current determination unit in the second embodiment.

[0026] Figure 12 This diagram illustrates the axial force load on the rack shaft due to the slope of the road crossing the road.

[0027] Figure 13 It is a diagram showing the structure around the wheel.

[0028] Figure 14 It is a diagram showing the structure around the wheel.

[0029] Figure 15 This is a diagram illustrating the length of the tow distance.

[0030] Figure 16 This is a control block diagram illustrating the processing performed by the correction current determination unit in the third embodiment. Detailed Implementation

[0031] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0032] <Overall Description of the Electric Power Steering System>

[0033] Figure 1 This is a diagram showing the schematic structure of the electric power steering device 100 according to this embodiment.

[0034] The electric power steering system 100 (hereinafter, sometimes simply referred to as "steering system 100") is a steering device for arbitrarily changing the direction of travel of a vehicle. In this embodiment, a structure applied to a vehicle is illustrated.

[0035] The steering device 100 includes a wheel (disc) shaped steering wheel (handle) 101 for driver operation and a steering shaft 102 integrally mounted on the steering wheel 101. The steering shaft 102 is connected to the upper connecting shaft 103 via a universal joint 103a, and the upper connecting shaft 103 is connected to the lower connecting shaft 108 via a universal joint 103b.

[0036] Furthermore, the steering device 100 includes: a steering knuckle arm 121 and a steering knuckle 125, which are respectively connected to the left and right wheels 150, which are rotating wheels, and rotate about a steering pin 124; a tie rod 104 connected to the steering knuckle arm 121; and a rack shaft 105 connected to the tie rod 104. The steering knuckle arm 121 and the tie rod 104 are rotatably engaged about a coupling 123. In addition, the tie rod 104 and the rack shaft 105 are rotatably engaged about a coupling 122.

[0037] In addition, the steering device 100 includes a pinion 106a that, together with the rack teeth 105a formed on the rack shaft 105, constitutes a rack and pinion mechanism. The pinion 106a is formed at the lower end of the pinion shaft 106.

[0038] Additionally, the steering system 100 has a steering gearbox 107 that houses the pinion shaft 106. The pinion shaft 106 is connected to the lower connecting shaft 108 via a torsion bar in the steering gearbox 107. Inside the steering gearbox 107 is a torque sensor 109 that detects the steering torque T of the steering wheel 101 based on the relative angle between the lower connecting shaft 108 and the pinion shaft 106.

[0039] Additionally, the steering device 100 includes: an electric motor 110 supported on a steering gearbox 107; and a reduction mechanism 111 that reduces the driving force of the electric motor 110 and transmits it to the pinion shaft 106. In this embodiment, the electric motor 110 is a three-phase brushless motor. The magnitude and direction of the actual current flowing through the electric motor 110 are determined by the motor current detection unit 33 (see reference 100). Figure 3 ) detection.

[0040] Furthermore, the steering system 100 includes a control device 10 for controlling the operation of the electric motor 110. The control device 10 is input to the output value of the torque sensor 109 (torque signal Td), the output value of the vehicle speed sensor 170 (vehicle speed signal v) which detects the vehicle's movement speed (vehicle speed Vx), and the lateral acceleration G of the vehicle. ySens The output value of the lateral acceleration sensor 180, i.e., the lateral acceleration signal Gy, and the output value of the yaw rate sensor 190, i.e., the yaw rate signal γs, which detects the yaw rate γ of the vehicle, are also present. In this embodiment, the control device 10 functions as a control unit (a control device for an electric power steering system) that controls the drive of the electric motor 110. The control device 10 estimates the degree of gradient in the transverse direction of the driving road and controls the drive of the electric motor 110 based on the estimated degree of gradient, as detailed later.

[0041] The steering device 100, configured as described above, uses a torque sensor 109 to detect the steering torque T applied to the steering wheel 101. Based on this detected torque, it drives an electric motor 110, which then transmits its generated torque to a pinion shaft 106. Thus, the torque generated by the electric motor 110 assists the driver in applying steering force to the steering wheel 101. In other words, the electric motor 110 generates a driving force, or auxiliary force, to steer the wheels 150 in response to the operation of the steering wheel 101. This auxiliary force is applied to the wheels 150 via a rack and pinion shaft 105 that transmits the auxiliary force.

[0042] <Description of Control Device 10>

[0043] Next, the control device 10 will be described.

[0044] Figure 2 This is a schematic structural diagram of the control device 10 of the steering device 100.

[0045] The control device 10 is an arithmetic logic operation circuit composed of CPU, ROM, RAM, backup RAM, etc.

[0046] The control device 10 is input with respect to: a torque signal Td obtained by converting the steering torque T detected by the torque sensor 109 into an output signal; a vehicle speed signal v obtained by converting the vehicle speed Vx detected by the vehicle speed sensor 170 into an output signal; and a lateral acceleration G detected by the lateral acceleration sensor 180 based on the lateral acceleration of the vehicle. ySens The lateral acceleration signal Gy is obtained by converting it into an output signal; and the yaw rate signal γs is obtained by converting the yaw rate γ detected by the yaw rate sensor 190 according to the vehicle's rotational speed into an output signal. The yaw rate γ is the rotational speed about the vertical axis passing through the vehicle's center of gravity.

[0047] Furthermore, the control device 10 includes: a target current calculation unit 20, which calculates the target torque based on the torque signal Td and calculates the target current required for the electric motor 110 to supply the target torque; and a control unit 30, which performs feedback control based on the target current calculated by the target current calculation unit 20.

[0048] <Explanation of the target current calculation unit 20 and the control unit 30>

[0049] Next, the target current calculation unit 20 and the control unit 30 will be described in detail.

[0050] Figure 3 This is a schematic structural diagram of the target current calculation unit 20 and the control unit 30.

[0051] The target current calculation unit 20 includes: a base current calculation unit 21, which calculates a base current Ib as a reference for setting the target current; an inertia compensation current calculation unit 22, which calculates an inertia compensation current to offset the moment of inertia of the electric motor 110; a vibration damping compensation current calculation unit 23, which calculates a vibration damping compensation current to limit the rotation of the motor; and a correction current calculation unit 24, which calculates a correction current Ia to correct the target current. Furthermore, the target current calculation unit 20 includes the base current calculation unit 21, the inertia compensation current calculation unit 22, the vibration damping compensation current calculation unit 23, and a target current determination unit 25 that determines the target current It based on the value calculated by the correction current calculation unit 24.

[0052] In addition, the target current calculation unit 20 inputs torque signal Td, vehicle speed signal v, lateral acceleration signal Gy, yaw rate signal γs, and speed signal Nms obtained by converting the speed Nm of the electric motor 110 into an output signal.

[0053] The base current calculation unit 21 calculates the base current Ib based on the torque signal Td and the vehicle speed signal v from the vehicle speed sensor 170, and outputs a base current signal Imb containing information about the base current Ib.

[0054] The inertia compensation current calculation unit 22 calculates the inertia compensation current for offsetting the inertia moment of the motor 110 and the system based on the torque signal Td and the vehicle speed signal v, and outputs an inertia compensation current signal Is containing information about the current.

[0055] The damping compensation current calculation unit 23 calculates the damping compensation current that limits the rotation of the electric motor 110 based on the torque signal Td, the vehicle speed signal v, and the rotational speed signal Nms of the electric motor 110, and outputs a damping compensation current signal Id containing information about the current.

[0056] The correction current calculation unit 24 estimates the degree of slope in the transverse direction of the travel road and determines the correction current Ia based on the estimated degree of slope. The correction current calculation unit 24 will be described later.

[0057] The target current determination unit 25 determines the target current supplied to the electric motor 110. The target current determination unit 25 determines the target current based on the base current signal Imb calculated by the base current calculation unit 21, the inertia compensation current signal Is calculated by the inertia compensation current calculation unit 22, the damping compensation current signal Id calculated by the damping compensation current calculation unit 23, and the correction current Ia calculated by the correction current calculation unit 24, and outputs a target current signal IT containing information about the current.

[0058] The control unit 30 includes: a motor drive control unit 31 that controls the operation of the electric motor 110; a motor drive unit 32 that drives the electric motor 110; and a motor current detection unit 33 that detects the actual current flowing through the electric motor 110 and outputs the actual current detection signal Im to the motor drive control unit 31.

[0059] The motor drive control unit 31 includes: a feedback (F / B) control unit 40, which performs feedback control based on the deviation between the target current (value shown by the target current signal IT) ultimately determined by the target current calculation unit 20 and the actual current supplied to the electric motor 110 (value shown by the actual current detection signal Im) detected by the motor current detection unit 33; and a PWM signal generation unit 60, which generates a PWM (pulse width modulation) signal for PWM driving the electric motor 110.

[0060] The feedback control unit 40 includes: a deviation calculation unit 41, which calculates the deviation between the target current finally determined by the target current calculation unit 20 and the actual current detected by the motor current detection unit 33; and a feedback (F / B) processing unit 42, which performs feedback processing to make the deviation zero.

[0061] [First Implementation Method]

[0062] Next, the method for determining the aforementioned correction current Ia will be described in detail. Here, firstly, a first embodiment of the method for determining the correction current Ia will be described. In the first embodiment, the correction current calculation unit 24 estimates the degree of gradient in the transverse direction of the driving road based on the vehicle's state variables, and determines the correction current Ia based on the estimated degree of gradient.

[0063] <Explanation of Correction Current Calculation Unit 24>

[0064] Figure 4 This is a block diagram showing an example of the functional structure of the correction current calculation unit 24 in the first embodiment.

[0065] As shown in the figure, the correction current calculation unit 24 includes an acquisition unit 241, a slope estimation unit 242, a correction current determination unit 243, and a correction current output unit 244.

[0066] The acquisition unit 241 acquires the vehicle speed signal v from the vehicle speed sensor 170. In addition, the acquisition unit 241 acquires the lateral acceleration signal Gy from the lateral acceleration sensor 180 and the yaw rate signal γs from the yaw rate sensor 190.

[0067] The slope estimation unit 242 estimates the degree of slope in the transverse direction of the driving road based on the centripetal acceleration (lateral G) acting on the vehicle when it is traveling on the driving road. Here, "driving road" refers to the road on which the vehicle travels, such as a street. Furthermore, the "transverse direction of the driving road" is a direction perpendicular to the direction in which the driving road extends. For example, since roads need to guide rainwater falling onto the road surface to side channels, a slope is sometimes provided in this transverse direction. Therefore, the cross-section of the driving road in the transverse direction sometimes has a so-called fish cake shape, high in the middle and low towards the shoulders at both ends. The slope in the transverse direction of the driving road is sometimes also called the transverse slope. Additionally, "degree of slope" is an indicator of the steepness of the slope. The degree of slope is, for example, the angle of the slope. However, it is not limited to this; it is not particularly limited as long as the degree of slope can be expressed. For example, the degree of slope can be expressed in five levels, from 1 to 5. In this case, for example, it can be set such that the slope is minimum when the slope level is 1, and maximum when the slope level is 5.

[0068] The gradient estimation unit 242 estimates the gradient based on the vehicle speed Vx and lateral acceleration G, according to the method described below. ySens And the degree to which the yaw rate γ estimates the gradient of the road in the transverse direction.

[0069] Figure 5 This is a diagram illustrating the centripetal acceleration Ay acting on the vehicle.

[0070] Here, vehicle S rotates around point O. At this time, the relationship between vehicle speed Vx, centripetal acceleration Ay, and yaw rate γ becomes the following equation (1). That is, the slope estimation unit 242 calculates the centripetal acceleration Ay based on the yaw rate γ acting on the vehicle and the vehicle speed Vx.

[0071] Ay=γ·Vx…(1)

[0072] in addition, Figure 6 This is a graph representing the various accelerations acting on vehicle S.

[0073] Here, θ Bank It is the slope angle in the transverse direction of the road. Furthermore, acceleration G is the acceleration due to gravity. And G' is the effect of the gravitational acceleration G caused by the slope of the road. If there is no slope (θ) in the transverse direction of the road... Bank =0), then the acceleration G' is 0. However, due to the slope on the road, the vehicle S appears to have a lateral acceleration G' due to the gravitational acceleration G.

[0074] At this time, θ BankThe relationship between acceleration G' and gravitational acceleration G is as follows (2).

[0075] G'=G·sin(θ Bank (2)

[0076] Furthermore, the actual centripetal acceleration Ay' acting on the vehicle in the lateral direction becomes the following equation (3). That is, the lateral acceleration G detected by the lateral acceleration sensor 180 is... ySens The acceleration G' differs from the centripetal acceleration Ay' by the amount of gravitational acceleration G.

[0077] Ay'=G ySens -G'…(3)

[0078] The slope angle θ in the transverse direction of the driving road Bank When the value is sufficiently small, the centripetal acceleration Ay is essentially the same as the centripetal acceleration Ay'. Therefore, the following equation (4) holds true.

[0079] Ay'≈Ay=γ·Vx…(4)

[0080] Therefore, θ Bank It becomes the following formula (5).

[0081] θ Bank =sin -1 (G′ / G)≈sin -1 ((G ySens -γ·Vx) / G)…(5)

[0082] At the slope angle θ Bank If the value is sufficiently small, sinθ≈θ, therefore if we use this approximation, then θ Bank This becomes equation (6). Therefore, the slope angle θ can be calculated using equation (6). Bank In this case, it can be said that the slope estimation unit 242 uses equation (6), based on the lateral acceleration G detected by the lateral acceleration sensor 180. ySens The degree of slope is estimated by the centripetal acceleration Ay (=γ·Vx).

[0083] θ Bank =(G ySens -γ·Vx) / G…(6)

[0084] Furthermore, at this time, the slope estimation unit 242 can also correct for the difference in lateral height of the vehicle caused by the slope in the transverse direction of the driving road and / or the vehicle's movement. That is, if there is a slope as described above on the driving road, the vehicle will tilt to the left and right depending on the slope of the driving road, thus the height of the vehicle in the left and right directions will be different. In addition, when the driving road is a curve, the vehicle will tilt, and similarly the vehicle body will tilt, thus the height of the vehicle in the left and right directions will be different. Taking into account such vehicle tilting, the slope estimation unit 242 corrects for the lateral height difference of the vehicle and calculates the slope angle θ. Bank In this case, the estimated slope angle θ Bank The accuracy will be further improved.

[0085] Figure 7 This is a control block diagram representing the processing performed by the slope estimation unit 242.

[0086] The slope estimation unit 242 calculates the centripetal acceleration Ay according to equation (1) based on the yaw rate γ obtained from the yaw rate signal γs acquired from the yaw rate sensor 190 and the vehicle speed Vx obtained from the vehicle speed signal v acquired from the vehicle speed sensor 170. Furthermore, the slope estimation unit 242 calculates the lateral acceleration G based on the lateral acceleration signal Gy acquired from the lateral acceleration sensor 180. ySens Find G in equation (6) ySens -γ·Vx. Then, the slope estimation unit 242 uses the gravitational acceleration G to calculate the slope angle θ using equation (6). Bank Furthermore, at this time, high-frequency components are removed by a noise removal filter 242a, which functions as a low-pass filter (LPF). Specifically, the slope angle θ, obtained through simulation, is removed due to unevenness or other factors on the road surface. Bank That is, the slope angle θ is determined by the unevenness or other features of the road surface. Bank It changes frequently, thus producing a slope angle θ. Bank It is considered to have high-frequency components. On the other hand, the slope angle θ generated by the actual slope. Bank It does not change frequently and is considered to have low-frequency components. Therefore, by removing high-frequency components and retaining low-frequency components, the slope angle θ resulting from the latter is preserved. Bank .

[0087] return Figure 4The correction current determining unit 243 determines a correction current Ia based on the estimated degree of slope. This correction current Ia corrects the target current required to generate the auxiliary force for the electric motor 110. That is, when a vehicle is traveling on a road with a slope in the transverse direction, the vehicle tends to slide down the road due to gravity. This phenomenon is also known as vehicle slip. The driver corrects this by operating the steering wheel 101 in a way that makes the vehicle slide down the road. Specifically, the driver operates the steering wheel 101 in a direction opposite to the direction where the road slopes down due to the slope, relative to the left-right direction of the vehicle. At this time, the correction current determining unit 243 determines the correction current Ia to generate an auxiliary force to assist the driver's operation.

[0088] Figure 8 This is a control block diagram showing the process performed by the correction current determination unit 243.

[0089] The correction current determination unit 243 inputs a value representing the slope angle θ that has been pre-made and stored in ROM based on empirical rules. Bank The gradient current is calculated using a gradient current mapping that corresponds to the gradient current. Meanwhile, the correction current determination unit 243 substitutes a speed gain mapping, pre-created based on empirical rules and stored in ROM, representing the correspondence between vehicle speed Vx and speed gain, to calculate the speed gain. In this case, the larger the vehicle speed Vx, the larger the speed gain; if the vehicle speed Vx exceeds a pre-defined value, the speed gain becomes a constant value. Then, the correction current determination unit 243 multiplies the gradient current by the speed gain to obtain the correction current Ia.

[0090] Return to Figure 4 The correction current output unit 244 outputs the correction current Ia determined by the correction current determination unit 243 to the target current determination unit 25.

[0091] Then, in the target current determination unit 25, the target current is corrected based on the correction current Ia output from the correction current output unit 244, and the final target current It is determined.

[0092] Figure 9 This is a control block diagram showing the processing performed in the correction current determination unit 243 in the past.

[0093] The right front wheel speed, left front wheel speed, right rear wheel speed, left rear wheel speed, vehicle speed Vx, steering angle (i.e., steering rudder angle) of steering wheel 101, and steering torque applied to steering wheel 101 by the driver's operation of steering wheel 101 are input to the correction current determination unit 243. Then, the steering angle conversion gain is calculated based on the right front wheel speed, left front wheel speed, right rear wheel speed, and left rear wheel speed. Additionally, the vehicle speed adjustment ratio is calculated using a vehicle speed adjustment ratio mapping based on vehicle speed Vx, and the vehicle speed ratio is calculated using a vehicle speed ratio mapping. Furthermore, the steering angle ratio is calculated using a steering angle ratio mapping based on the steering rudder angle. Moreover, the torque ratio is calculated using a torque ratio mapping based on the steering torque. Then, the steering angle conversion gain is adjusted using the vehicle speed adjustment ratio, and a temporary correction current is calculated using a correction current mapping. Finally, the temporary correction current is adjusted using the steering angle ratio, torque ratio, and vehicle speed ratio to determine the final correction current.

[0094] In other words, the vehicle speed adjustment ratio, steering angle ratio, torque ratio, and vehicle speed ratio are adjustment terms. Conventionally, in this situation, the logic for calculating the correction current fails when the vehicle is in a special state, such as during sharp turns. Therefore, a greater number of adjustment terms are used to limit the calculation of the correction current. However, with such a large number of adjustment terms, the assist force can easily become discontinuous, sometimes worsening the driver's steering feel.

[0095] In this embodiment, the slope angle θ is calculated based on the vehicle's state variables. Bank According to the slope angle θ Bank Calculate the correction current Ia. In this case, the vehicle's state variables are the vehicle speed Vx and lateral acceleration G, as described above. ySens And the yaw rate γ. Thus, when using the vehicle's state parameters, the aforementioned adjustments are unnecessary, and the assist force is less likely to become discontinuous. As a result, the driver's steering feel becomes easier to improve.

[0096] Furthermore, in this embodiment, the slope angle θ is calculated. Bank And based on the slope angle θ Bank By calculating the correction current Ia, we can more directly determine the current that takes into account the slope angle θ. Bank The generated vehicle body slip correction current Ia. This makes it easier for the driver to feel the steering. Furthermore, the correction current determination unit 243 determines the correction current based on the slope angle θ. BankThe calculation of the correction current Ia is not complicated. Furthermore, in this embodiment, parameters such as the speeds of the right front wheel, left front wheel, right rear wheel, and left rear wheel, which are easily affected by road surface irregularities, are not used. Instead, the vehicle speed Vx is used. Therefore, the calculation of the correction current Ia is less affected by road surface irregularities. That is, the vehicle speed Vx is the average of the speeds of the right front wheel, left front wheel, right rear wheel, and left rear wheel, making it less susceptible to road surface irregularities. Additionally, it avoids the reduction in robustness caused by wheel slippage at 150.

[0097] Furthermore, in this embodiment, parameters such as steering torque, which are affected by inertia, attenuation, and friction within the steering wheel 101, are not used. Therefore, the accuracy of the correction current Ia is further improved.

[0098] [Second Implementation]

[0099] Next, the second embodiment will be described. In the second embodiment, the control device 10 changes the control according to the condition of the road surface.

[0100] Figure 10 This is a block diagram illustrating a functional structure example of the correction current calculation unit 24 in the second embodiment.

[0101] The diagram shows the correction current calculation unit 24 and... Figure 4 Compared to the first embodiment shown, the difference is that it has a road surface determination unit 245, but otherwise it is the same.

[0102] Therefore, the following explanation will focus on the function of the road surface determination unit 245.

[0103] The road surface determination unit 245 determines the condition of the road surface of the driving road. Specifically, the road surface determination unit 245 determines whether the road surface is a paved road or an unpaved road (off-road). Then, if the road surface determination unit 245 determines that the road surface is a paved road, it controls the drive of the electric motor 110 according to the degree of slope, similar to the first embodiment. That is, the correction current determination unit 243 calculates the correction current Ia according to the degree of slope. In contrast, if the road surface is an unpaved road, this control is not performed. In this case, the correction current determination unit 243 will... Figure 8 The vehicle speed gain is set to 0, and therefore the correction current Ia is set to 0. That is, no correction of the target current is performed in the target current determination unit 25.

[0104] The road surface determination unit 245 determines the condition of the road surface of the driving road in the following manner, for example.

[0105] Road surface determination unit 245 for slope angle θ BankThe differential value is calculated. Then, the road surface determination unit 245 determines the slope angle θ. Bank The number of times the count exceeds a pre-defined first threshold is counted. Then, if the count exceeds a second threshold per unit time, it is determined to be an unpaved road (off-road). Conversely, if the count is below the second threshold per unit time, it is determined to be a paved road.

[0106] That is, on unpaved roads (off-road), vehicles will sway more from side to side; therefore, the calculated slope angle θ Bank The change becomes larger. Therefore, the road surface determination unit 245 uses a first threshold to detect the slope angle θ. Bank The road surface determination unit 245 determines that the driving road is an unpaved road (off-road) if this situation occurs frequently, based on a second threshold.

[0107] Figure 11 This is a control block diagram showing the processing performed by the correction current determination unit 243 in the second embodiment.

[0108] Figure 11 The control block diagram shown is similar to Figure 8 Compared to the control block diagram shown, the difference lies in the input of the road surface condition output by the road surface determination unit 245. Furthermore, when the road surface condition is paved, the correction current determination unit 243, similarly to the first embodiment, substitutes the vehicle speed Vx into the vehicle speed gain mapping to calculate the vehicle speed gain. In contrast, when the road surface condition is unpaved (off-road), vehicle speed gain mapping is not used, and the vehicle speed gain is 0. Therefore, the correction current Ia becomes 0.

[0109] In this scenario, the vehicle is, for example, an off-road vehicle. When an off-road vehicle travels on unpaved roads (off-road), such as grassland, sand, mud, or rocky terrain, the vehicle tilts to the left or right due to uneven surfaces, obstacles, or water accumulation. The resulting slope angle θ needs to be calculated. Bank In this situation, if the aforementioned correction is performed, it may result in an assist force that differs from the driver's intention. That is, on unpaved roads (off-road), the driver is required to adapt to the road conditions. In this case, performing the aforementioned correction would create unnecessary adjustments, potentially worsening the driver's steering feel. In this situation, on unpaved roads (off-road), setting the correction current Ia to 0 and not correcting the target current allows the driver's steering feel to easily improve. Furthermore, it does not affect the driver's experience of off-road driving enjoyment.

[0110] [Third Implementation Method]

[0111] Next, the third embodiment will be described. In the third embodiment, the rack shaft 105 (refer to...) is further considered based on the slope of the road in the transverse direction. Figure 1 The axial force load on the rack shaft 105 is used to calculate the correction current Ia. The axial force load on the rack shaft 105 is a load applied along the axial direction of the rack shaft 105 due to the existence of this slope.

[0112] Example of the functional structure of the correction current calculation unit 24 in the third embodiment Figure 4 The situation is the same as in the first embodiment shown.

[0113] Figure 12 This diagram illustrates the axial force load on the rack shaft 105 due to the slope of the road in the transverse direction.

[0114] Here, the vehicle S is schematically shown at a slope angle θ. Bank Imagine a vehicle S traveling on a road. If the weight of vehicle S is set to M, then M·G·sinθ will be applied to vehicle S in the direction along the road surface R. Bank The force acts as the axial load borne by the rack shaft 105.

[0115] The following explains the calculation method for the axial force load on the rack shaft 105.

[0116] Figure 13 as well as Figure 14 This is a diagram showing the structure around wheel 150. Additionally, Figure 15 This is a diagram illustrating the drag distance length Lt.

[0117] in, Figure 13 From Figure 1 The image shows the periphery of wheel 150 viewed from the XIII direction, while the image shows the periphery of wheel 150 viewed from the horizontal direction.

[0118] in addition, Figure 14 From Figure 13 The diagram showing the periphery of wheel 150 viewed from the XIV direction is a diagram showing the periphery of wheel 150 viewed from the vertical direction. That is, Figure 14 From and Figure 1 View the diagram around wheel 150 from the same direction.

[0119] and, Figure 15 From Figure 14 View the wheel 150 from the XV direction.

[0120] like Figure 13 and Figure 14As shown, a drive shaft 158 ​​is connected to the wheel 150, transmitting power from a power source such as an engine to propel the vehicle. Specifically, rotational force is transmitted from the drive shaft 158 ​​to the wheel 150, causing the wheel 150 to rotate and thus propelling the vehicle. The wheel 150 is connected to the vehicle body 159 via a steering knuckle 125 and a lower arm 153. The joint between the steering knuckle 125 and the lower arm 153 forms a steering pin 124. Furthermore, the steering knuckle 125 is connected to the vehicle body 159 via a vibration absorber 151. This vibration absorber 151 includes a shock absorber 151a and a coil spring 151b, and is connected to the vehicle body 159 via a ball bearing 151c located at its upper part. Through the shock absorber 151, the vehicle can absorb impacts from uneven road surfaces.

[0121] Furthermore, when the rack shaft 105 is moved in the direction of arrow A, the steering knuckle arm 121 and the steering knuckle 125 rotate around the steering pin 124, and the wheel 150 turns in the direction of arrow C. Conversely, when the rack shaft 105 is moved in the direction of arrow B, the steering knuckle arm 121 and the steering knuckle 125 rotate in the opposite direction around the steering pin 124, and the wheel 150 turns in the direction of arrow D.

[0122] At this point, consider the shaft connecting ball bearing 151c and steering pin 124, and designate it as steering pin shaft J. Furthermore, as... Figure 15 As shown, the point where the steering pin J intersects with the road surface R is designated as point Pc, and the point where the wheel 150 contacts the road surface R is designated as point Pw. The distance between point Pc and point Pw is defined as the trailing length Lt. Furthermore, the distance between the steering pin J and the contact point Pw is defined as L. The distance L is predetermined by the trailing length Lt and the caster angle θc. The distance L can also be described as the distance between the center of the steering pin 124 and the point where the wheel 150 contacts the road surface.

[0123] In addition, the length of the steering knuckle arm 121 is set as the steering knuckle arm length L. N Steering knuckle arm length L N It can also be described as the distance between the center of the joint 123 and the center of the steering pin 124.

[0124] Furthermore, if we define the weight of the vehicle borne by the front wheels as M... f Based on the slope of the road in the transverse direction, the axial force load F borne by the rack shaft 105 is... Gθ It can be expressed by the following equation (7).

[0125] F Gθ = (L·M f ·G·sinθ Bank ) / L N …(7)

[0126] Figure 16This is a control block diagram showing the processing performed by the correction current determination unit 243 in the third embodiment.

[0127] Figure 16 The control block diagram shown is similar to Figure 8 The control block diagram shown differs from the one shown in that it incorporates axial force load mapping instead of slope current mapping. Axial force load mapping represents the slope angle θ. Bank With axial force load F Gθ The mapping of the corresponding relationships. The axial force load mapping is pre-created based on empirical rules and stored in ROM. Furthermore, if the slope angle θ is... Bank Substituting into the axial force load mapping, the axial force load F can be calculated. Gθ It should be noted that, as shown in the figure, in the axial force load mapping, in the region with a small slope angle, the axial force load F... Gθ The slope angle is set to 0, thus creating a slope angle insensitive region. Therefore, the correction current Ia calculated by the correction current determination unit 243 becomes 0. This is because, in the region of small slope angle, the axial force load F... Gθ Therefore, even if the calculated correction current Ia is set to 0, there is no problem.

[0128] Then, the correction current determination unit 243 determines the axial force load F based on the thrust-to-current conversion coefficient. Gθ The current is converted into a current. Then, the correction current determination unit 243 multiplies the current obtained by the conversion with the vehicle speed gain to obtain the correction current Ia.

[0129] Furthermore, in the vehicle speed gain mapping used here, as shown in the figure, the gain is 0 in a predefined low-speed region. At this time, the correction current Ia becomes 0. This low-speed region is, for example, when the vehicle speed Vx is 0 km / h or higher and 60 km / h or lower. Additionally, in a predefined medium-speed region, the gain increases with vehicle speed. This medium-speed region is, for example, when the vehicle speed Vx is 60 km / h or higher and 80 km / h or lower. Further, in a predefined high-speed region, the gain remains constant regardless of the vehicle speed. This high-speed region is, for example, when the vehicle speed Vx is 80 km / h or higher. That is, the axial force load F... Gθ The problem only arises above the predetermined speed; therefore, in the low-speed region, there is no problem even if the correction current Ia calculated by the correction current determination unit 243 is set to 0. In contrast, in the medium-speed region and above, the correction current determination unit 243 calculates the current relative to the axial force load F... Gθ The corresponding correction current Ia

[0130] In the third embodiment, the axial force load F on the rack shaft 105 is also considered based on the slope of the road in the transverse direction. GθTo calculate the correction current Ia. Additionally, regarding the axial force load F acting on the rack shaft 105... Gθ The calculation takes into account the orientation of wheel 150. In this case, the correction current determination unit 243 uses the steering knuckle arm length L. N And the axial force load F is calculated using the towing distance length Lt. Gθ Therefore, the accuracy of the correction current Ia is further improved.

[0131] <Program Description>

[0132] Furthermore, the processing performed by the control device 10 in this embodiment is achieved through the cooperation of software and hardware resources. That is, a CPU (not shown) located inside the control device 10 executes programs that implement the various functions of the control device 10, thereby realizing these functions.

[0133] Therefore, the processing performed by the control device 10 can also be understood as a program for enabling the computer to perform the following functions: a slope estimation function, which estimates the degree of slope in the transverse direction of the road on which the vehicle travels; a correction current determination function, which determines a correction current Ia to correct the target current required to generate the driving force of the electric motor 110 based on the estimated degree of slope; and a target current determination function, which determines the target current based on the determined correction current Ia.

[0134] Furthermore, the program for implementing this embodiment can of course be provided via a communication unit, or it can be provided by storing it in a recording medium such as a CD-ROM.

[0135] The embodiments described above are for illustrative purposes only; however, the scope of the present invention is not limited to the scope described in the above embodiments. As can be seen from the claims, various modifications or improvements made to the above embodiments are also included within the scope of the present invention.

[0136] Symbol Explanation

[0137] 10: Control device; 20: Target current calculation unit; 24: Correction current calculation unit; 30: Control unit; 100: Electric power steering device; 101: Steering wheel (handle); 110: Electric motor; 105: Rack and pinion shaft; 121: Steering knuckle arm; 124: Steering pin; 150: Wheel; 170: Vehicle speed sensor; 180: Lateral acceleration sensor; 190: Yaw rate sensor; 241: Acquisition unit; 242: Slope estimation unit; 243: Correction current determination unit; 244: Correction current output unit; 245: Road surface determination unit; R: Road surface; S: Vehicle.

Claims

1. An electric power steering device, comprising: An electric motor, which provides the driving force to steer the wheels in response to steering wheel input; and The control unit estimates the gradient of the road the vehicle is traveling on in the transverse direction, determines a correction current based on the estimated gradient, and corrects the target current required to generate the driving force of the electric motor. The control unit then uses this correction current to correct the target current to control the drive of the electric motor. The control unit determines the condition of the road surface and adjusts the control accordingly. The control unit performs the control when the road surface is paved. When the number of times the differential value of the index representing the degree of the slope exceeds a predetermined first threshold exceeds a second threshold per unit time, the road surface is considered to be unpaved, and the control is not performed.

2. The electric power steering device according to claim 1, characterized in that, The control unit uses a slope current mapping that represents the correspondence between the estimated degree of the slope and the slope current to calculate the slope current, and calculates the correction current by multiplying the slope current by a vehicle speed gain determined by the vehicle speed.

3. The electric power steering device according to claim 1, characterized in that, The control unit estimates the degree of the slope based on the lateral acceleration detected by the lateral acceleration sensor and the centripetal acceleration calculated based on the yaw rate acting on the vehicle and the vehicle speed.

4. The electric power steering device according to any one of claims 1 to 3, characterized in that, The control unit performs the control by correcting for the difference in lateral height of the vehicle caused by the slope of the road crossing the direction of travel and / or the vehicle's movement.

5. The electric power steering device according to claim 1, characterized in that, The electric motor provides the driving force via a rack and pinion shaft. The control unit also performs the control based on the axial force load on the rack shaft due to the slope of the road crossing the direction of travel.

6. The electric power steering device according to claim 5, characterized in that, The control unit uses the steering knuckle arm length and the distance between the center of the steering pin and the point where the wheel contacts the road surface to calculate the axial force load.

7. A control device for an electric power steering system, comprising: The gradient estimation unit estimates the degree of gradient in the transverse direction of the road on which the vehicle is traveling; The road surface assessment unit determines the condition of the road surface during travel. The correction current determination unit determines a correction current to correct the target current required to generate the driving force of the electric motor, based on the condition of the road surface determined by the road surface determination unit and the estimated degree of the slope. as well as The target current determining unit determines the target current based on the determined correction current. The road surface determination unit determines that the road surface is an unpaved road when the number of times the differential value of the index representing the degree of slope exceeds a predetermined first threshold exceeds a second threshold per unit time; and determines that the road surface is a paved road when the number of times the differential value of the index representing the degree of slope exceeds the predetermined first threshold exceeds the second threshold per unit time. When the road surface is paved, the correction current determination unit determines the correction current based on the estimated slope; when the road surface is unpaved, the correction current is set to zero.

Images