Electric power steering control device, electric power steering device, vehicle, and electric power steering control system

Abstract

Provided is a control device for electric power steering, the control device controlling output torque of a motor that outputs assist torque on the basis of a steering torque signal from a torque sensor that detects steering torque applied to a steering wheel by a user. The control device controls the output torque using, as a current command corresponding to a command value of the output torque, a signal obtained by adding a correction signal obtained by passing a steering torque signal through a second compensator to an assist torque signal that is approximately proportional to a compensated steering torque signal obtained by passing the steering torque signal through a first compensator. In each of the first compensator and the second compensator, at least two stages of primary or secondary low-order filters are connected in series.

Description

[Technical Field]

[0001] The present disclosure relates to an electric power steering control device, an electric power steering device, a vehicle, and an electric power steering control system. [Background technology]

[0002] In an electric power steering device that applies an assist torque from a motor in accordance with the steering torque applied to the steering wheel by a user (i.e., a driver) of a vehicle such as an automobile, the assist torque is determined to be approximately proportional to the steering torque, and the torque proportional gain, which is the amplification factor of this proportional relationship, is set to be large, thereby reducing the driver's steering force and suppressing vibrations such as oscillations in the control system that occur as the torque proportional gain increases, thereby improving the driver's feeling.

[0003] For example, Patent Documents 1 to 3 disclose examples of control of conventional electric power steering devices. Patent Document 1 discloses an example in which the output torque of a motor is controlled using, as an assist torque command value, a result of adding a series-path signal, which is the result of multiplying a signal of a steering torque detection value passed through a first compensator by a torque proportional gain, and a parallel-path signal of a steering torque detection value passed through a second compensator. Patent Document 2 discloses a configuration in which, as a parallel-path compensator, compensators whose denominator and numerator polynomials have the maximum degree of first order are connected in series in multiple stages. Patent Document 3 discloses a configuration in which, as a series-path compensator, compensators whose denominator and numerator polynomials have the maximum degree of second order are arranged. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5642272 [Patent Document 2] Patent No. 5160663 [Patent Document 3] Patent No. 4412006 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, vehicles that use electric power steering devices have tended to become heavier due to their larger size and electrification. In order to apply electric power steering to these vehicles, it is necessary to increase the gradient of the assist map, which represents the amount of assistance for the steering by the user (driver), i.e., the torque proportional gain.

[0006] However, Patent Document 1 does not disclose specific structures for the series path and parallel path compensators, making it unclear whether the performance required to increase the gradient of the assist map can be achieved. Furthermore, Patent Documents 2 and 3 disclose specific examples of compensators, but apply the compensator only to either the series path or the parallel path, limiting the degree of freedom of the controller. This makes it difficult to maximize performance, and there is a problem that there is an upper limit to the gradient of the assist map that can be achieved. This makes it difficult to apply electric power steering to large vehicles.

[0007] The present disclosure has been made in consideration of the above-mentioned circumstances, and one of its objects is to provide an electric power steering control device, an electric power steering device, a vehicle, and an electric power steering control system that can apply electric power steering even to large vehicle models. [Means for solving the problem]

[0008] The electric power steering control device according to the present disclosure is an electric power steering control device that controls the output torque of a motor that outputs an assist torque based on a steering torque signal from a torque sensor that detects the steering torque applied to the steering wheel by a user, and controls the output torque by using a signal obtained by adding a correction signal obtained by passing the steering torque signal through a second compensator to an assist torque signal that is approximately proportional to a compensated steering torque signal obtained by passing the steering torque signal through a first compensator, as a current command equivalent to the command value of the output torque, and the first compensator and the second compensator each have at least two or more stages of first-order or second-order low-order filters connected in series.

[0009] The electric power steering control device according to the present disclosure is an electric power steering control device that controls the output torque of a motor that outputs an assist torque based on a steering torque signal and a motor speed signal from a torque sensor that detects the steering torque applied to the steering wheel by a user, and controls the output torque by using a signal obtained by adding a composite correction signal, which is the result of adding a torque-based correction signal, which is the result of passing the steering torque signal through a second compensator, and a motor-speed-based correction signal, which is the result of passing the motor speed signal through a fourth compensator, to an assist torque signal that is approximately proportional to an assist torque calculation signal that is the result of adding a compensated steering torque signal, which is the result of passing the steering torque signal through a first compensator, and a compensated motor speed signal, which is the result of passing the motor speed signal through a third compensator, as a current command equivalent to the command value of the output torque, and the first compensator, the second compensator, the third compensator, and the fourth compensator each have at least two or more stages of first-order or second-order low-order filters connected in series.

[0010] The electric power steering device according to the present disclosure includes a torque sensor that detects the steering torque applied to the steering wheel by a user, and the above-mentioned electric power steering control device, and the output torque is controlled by the electric power steering control device based on the steering torque detected by the torque sensor.

[0011] The vehicle according to the present disclosure includes a vehicle speed detection unit that detects the speed of the vehicle, and the electric power steering device described above in which the output torque is controlled based on the vehicle speed detected by the vehicle speed detection unit and the steering torque.

[0012] The electric power steering control system according to the present disclosure is an electric power steering control system including a steering wheel, a motor that outputs an assist torque based on a steering torque signal from a torque sensor that detects the steering torque applied to the steering wheel by a user, and a control device that controls the output torque of the motor, wherein the control device controls the output torque by using a signal obtained by adding an assist torque signal that is approximately proportional to a compensated steering torque signal that has been passed through a first compensator to a correction signal that has been passed through a second compensator to the steering torque signal as a current command equivalent to the command value of the output torque, and the first compensator and the second compensator each have at least two or more stages of first-order or second-order low-order filters connected in series.

[0013] The electric power steering control system according to the present disclosure is an electric power steering control system including a steering wheel, a motor that outputs an assist torque based on a steering torque signal and a motor speed signal from a torque sensor that detects the steering torque applied to the steering wheel by a user, and a control device that controls the output torque of the motor, wherein the control device controls the output torque by using a signal obtained by adding a composite correction signal that is the sum of a torque-based correction signal that is the sum of a torque-based correction signal that is the sum of a motor speed-based correction signal that is the sum of a motor speed signal that is the sum of a torque ... motor speed-based correction signal that is the sum of a motor speed signal that is the sum of a motor speed-based correction signal that is the sum of a motor speed signal that is the sum of a motor speed-based correction signal that is the sum of a motor speed-based correction signal that is the sum of a motor speed-based correction signal that is the sum of a motor speed-based correction signal that is the sum of a motor speed-based correction signal that is the sum of a motor speed-based correction signal that is the sum of a motor speed-based correction signal that is the sum of a motor speed-based correction signal that is the sum of a motor speed-based correction signal that is the sum of a motor speed-based correction signal that is the sum of a motor speed-based correction signal that is the sum of a motor speed-based correction signal that is the sum of a [Effects of the Invention]

[0014] The electric power steering control device according to the present disclosure can be applied to electric power steering even in large vehicle models. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a configuration diagram showing an example of an electric power steering device according to a first embodiment. [Figure 2] FIG. 2 is a schematic block diagram showing an example of the configuration of a control device according to the first embodiment. [Figure 3] FIG. 3 is a diagram showing an example of an assist map according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing an example of transfer characteristics of a first compensator according to the first embodiment. [Figure 5] FIG. 4 is a diagram showing an example of the transfer characteristic of a second compensator according to the first embodiment. [Figure 6]FIG. 2 is a diagram showing a first example of the structure of a low-order filter according to the first embodiment. [Figure 7] FIG. 4 is a diagram showing a second example of the structure of the low-order filter according to the first embodiment. [Figure 8] FIG. 10 is a diagram showing a third example of the structure of the low-order filter according to the first embodiment. [Figure 9] FIG. 10 is a diagram showing a fourth example of the structure of the low-order filter according to the first embodiment. [Figure 10] FIG. 4 is a diagram showing an example of the maximum value of the torque proportional gain versus the order of the compensator according to the first embodiment. [Figure 11] FIG. 4 is a graph showing an example of disturbance suppression performance versus the order of the compensator according to the first embodiment. [Figure 12] FIG. 10 is a schematic block diagram showing an example of the configuration of a control device according to a second embodiment. [Figure 13] FIG. 10 is a configuration diagram showing an example of the configuration of a vehicle according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments will be described with reference to the drawings. First Embodiment First, the first embodiment will be described.

[0017] [Configuration of electric power steering device] FIG. 1 is a configuration diagram showing an example of an electric power steering device according to this embodiment. In FIG. 1, the electric power steering device 100 includes a steering wheel 51, a steering shaft 53, a rack and pinion gear 54, wheels 55, a tie rod 56, a knuckle arm 57, a motor 1, a control device 2, a motor rotation angle sensor 23, and a torque sensor 22. The hardware configuration of the electric power steering device 100 shown in this figure is similar to that of conventional electric power steering devices, and is mass-produced for installation in vehicles. However, the software portion implemented in the control device 2 differs from existing devices. Details of these different elements from existing devices will be described later.

[0018] The steering shaft 53 is composed of an input shaft 53a connected to the steering wheel 51 side and an output shaft 53b connected to the rack and pinion gear 54 side. The input shaft 53a and the output shaft 53b are connected to each other by a torsion bar (not shown). The torsion bar is disposed inside the torque sensor 22 and passes through the torque sensor 22 in the axial direction. The torsion bar generates a twist in response to the steering torque applied to the steering wheel 51 by the driver (not shown), who is the user of the vehicle, operating the steering wheel. The torque sensor 22 detects the direction and amount of this twist. Note that hereinafter, the steering wheel 51, the steering shaft 53, and the torsion bar will be collectively referred to as the steering.

[0019] Next, the operation of the electric power steering device 100 will be described. In Fig. 1, steering torque applied to a steering wheel 51 by a driver's steering operation is transmitted through a torsion bar in a torque sensor 22 and a steering shaft 53, and further transmitted to a rack (not shown) in the rack-pinion gear 54 via a rack-pinion gear 54. The rack and wheels 55 are connected via tie rods 56 and knuckle arms 57.

[0020] Therefore, when steering torque is transmitted to the rack by operating the steering wheel, the tie rod 56 pushes the knuckle arm 57 of the wheel 55 on one side, and the tie rod 56 pulls the knuckle arm 57 of the wheel 55 on the opposite side, giving the wheel 55 a steering angle and causing the wheel 55 to turn.

[0021] On the other hand, the output torque generated by the motor 1 is transmitted to the steering shaft 53 as a steering assist force, reducing the steering torque applied by the driver when steering. The motor 1 is configured to include, for example, an AC motor such as a permanent magnet synchronous motor or an induction motor, or a DC motor.

[0022] Torque sensor 22 detects the steering torque applied to the torsion bar when the driver turns steering wheel 51. When steering torque is applied, a twist approximately proportional to the steering torque occurs in the torsion bar. Torque sensor 22 detects this twist angle and converts it into a steering torque signal. Motor rotation angle sensor 23 is attached to the rotating shaft of motor 1, detects the rotation angle of the rotating shaft, and outputs a motor rotation angle signal.

[0023] [Control device configuration] Next, the configuration of the control device 2 will be described in detail. 2 is a schematic block diagram showing an example of the configuration of the control device 2 according to this embodiment. The control device 2 shown in FIG. 2 includes a first compensator 3, a second compensator 4, an assist map 5, a current control unit 6, a drive circuit 7, and a current detection unit 8.

[0024] The control device 2 receives the steering torque signal, which is the output of the torque sensor 22, as an input, and obtains an assist torque signal by multiplying the compensated steering torque signal, which is obtained by passing the steering torque signal through a first compensator 3, by a torque proportional gain determined by an assist map 5. The control device 2 also obtains a current command by adding a correction signal, which is obtained by passing the steering torque signal through a second compensator 4, to the assist torque signal.

[0025] The current control unit 6 performs control so that the current command matches the current detection value output by the current detection unit 8. To achieve this, the current control unit 6 outputs a voltage command signal, such as a PWM signal, to the drive circuit 7, which includes, for example, an H-bridge circuit or an inverter circuit. The drive circuit 7 applies a voltage corresponding to the voltage command signal to the motor 1. The motor 1 generates an output torque according to the voltage applied by the drive circuit 7. Furthermore, the current detection unit 8 detects the current flowing through the drive circuit 7 or the motor 1 in response to the voltage applied to the motor 1.

[0026] The features of the control device 2 configured as described above will be described below. FIG. 3 is a diagram showing an example of the assist map 5. The assist map 5 sets the relationship between the steering torque and the current corresponding to the assist torque, and the gradient of the assist map is calculated as the torque proportional gain. The assist map 5 may be variable depending on the vehicle speed. In the example of FIG. 3, the assist map 5 has two maps, one corresponding to a low vehicle speed and the other corresponding to a high vehicle speed, and for vehicle speeds between the low and high vehicle speeds, the torque proportional gain is calculated by interpolating between the two maps.

[0027] Next, the characteristics required of the first compensator 3 and the second compensator 4 will be described. The assist map 5 corresponds to the characteristics of the steering assist force relative to the steering torque. In the frequency band caused by the driver's steering, it is required to accurately realize the characteristics of the steering assist force set in the assist map 5. Therefore, in the frequency band caused by the driver's steering, it is required that the steering torque signal and the compensated steering torque signal match. For this reason, for example, the gain of the first compensator 3 at 0 Hz may be set to approximately 0 dB. However, the gain of the first compensator 3 at 0 Hz does not need to be strictly 0 dB, and may be within a range that allows the desired steering assist force to be output.

[0028] FIG. 4 is a diagram showing an example of the transfer characteristics of the first compensator 3. The horizontal axis plots frequency, and the vertical axis plots gain. As shown in FIG. 4, the first compensator 3 exhibits a characteristic of nearly 0 dB up to about 5 Hz. In addition, in the frequency range above 5 Hz, the first compensator 3 is adjusted to suppress vibrations due to disturbances and ensure stability of the feedback loop.

[0029] Note that Fig. 4 shows the characteristics of only the first compensator 3, and the assist torque signal is the result of multiplying the compensated steering torque signal, which is obtained by passing the steering torque signal through the first compensator 3, by the torque proportional gain determined by the assist map 5. Therefore, the transfer characteristics from the steering torque signal to the assist torque signal change depending on the magnitude of the torque proportional gain.

[0030] Next, the second compensator 4 will be described. The main role of the second compensator 4 is to improve performance in the region where the torque proportional gain is small. Under operating conditions where the torque proportional gain is large, the effect of feedback through the serial path from the steering torque signal to the assist torque signal reduces the influence of disturbances. On the other hand, under operating conditions where the torque proportional gain is small, the effect of feedback through the serial path decreases, and the influence of disturbances increases.

[0031] Since the parallel path from the steering torque signal to the correction signal is not affected by the torque proportional gain, under operating conditions where the torque proportional gain is small, the effect of the feedback of the parallel path reduces the influence of disturbances, thereby improving the performance of the control device 2.

[0032] However, because the basic steering assist force is determined by the series path, if the parallel path functions in the frequency band where the driver steers, it may have a negative effect on the driver's steering feel. Therefore, the parallel path must have a characteristic that reduces the gain in the frequency band where the driver steers, so that it does not affect steering. Since the highest frequency at which the driver steers is generally around 5 Hz, the gain must be reduced at frequencies lower than this.

[0033] Fig. 5 is a diagram showing an example of the transfer characteristics of the second compensator 4. As shown in Fig. 5, the characteristics are differential in the low frequency range of 10 Hz or less, and it can be seen that the gain decreases in the frequency range corresponding to the steering by the driver.

[0034] Next, we will explain the configurations of the first compensator 3 and the second compensator 4. At least one of the first compensator 3 and the second compensator 4 has multiple first- or second-order low-order filters connected in series. Note that a low-order filter refers to a filter in which the highest order of the denominator polynomial and numerator polynomial of the transfer function is first or second order.

[0035] The following equations (1) and (2) are examples of second-order low-order filters. The denominator polynomial and numerator polynomial each have a damping coefficient ζ and a natural angular frequency ω, so the transfer characteristics are determined by a total of four parameters.

[0036]

number

[0037]

number

[0038] Moreover, the following equation (3) is the result of connecting the compensators expressed by the equations (1) and (2) in series, and the highest order is the fourth order.

[0039]

number

[0040] As described above, a high-order compensator can be realized by connecting multiple stages of low-order filters in series. Note that while the above example shows two stages of second-order low-order filters connected, three or more stages of low-order filters can also be connected. In this case, the amount of calculation increases, but the degree of freedom in the characteristics that can be expressed by the first compensator 3 and the second compensator 4 increases, which may improve the performance of the control device.

[0041] Furthermore, a compensator with the above configuration may be applied to both the first compensator 3 and the second compensator 4, or a compensator with the above configuration may be applied to only one of the first compensator 3 or the second compensator 4. As an example of applying a compensator with the above configuration to only one of the compensators, a configuration in which a high-order compensator is applied to the second compensator 4 and the first compensator 3 has a characteristic of passing the steering torque signal as is can be considered. Compared to the case in which high-order compensators are applied to both, there is a possibility that the performance of the control device 2 will be reduced, but the calculation load and software capacity can be reduced.

[0042] Although equations (1) and (2) express the low-order filter in a continuous-time system, from the perspective of software implementation, it is necessary to express it in a discrete-time system as shown in equations (4) and (5) below. Also, as with the continuous-time system, the low-order filters of equations (4) and (5) connected in series are shown in equation (6).

[0043]

number

[0044]

number

[0045]

number

[0046] Moreover, the transfer functions shown in equations (4) and (5) can be realized with a number of structures. Figure 6 shows an example of the structure of a low-order filter that realizes the calculation of equation (4). Note that the structure refers to a block diagram representation of a transfer function converted into a state equation format that can be implemented in software.

[0047] Here, z in the figure -1 is a delay block that means a delay of one cycle of the calculation process. Note that the parameters written in the gain block in Fig. 6 correspond to the parameters b10 to b12 and a10 to a12 in equation (4).

[0048] 7 is a diagram showing an example of another structure for realizing the calculation of equation (4). The gains A to E shown in the gain block of FIG. 7 are calculated by converting the parameters b10 to b12 and a10 to a12 of equation (4) as shown in equations (7) to (11).

[0049]

number

[0050]

number

[0051]

number

[0052]

number

[0053]

number

[0054] Up to this point, we have shown examples where the order of the low-order filter is second order, but the order of the low-order filter may also be first order. The following equations (12) and (13) show examples where the order of the low-order filter is first order. Furthermore, the following equation (14) shows an example where two first-order low-order filters are connected in series.

[0055]

number

[0056]

number

[0057]

number

[0058] Moreover, when formulas (12) to (14) are expressed in a discrete time system, the following formulas (15) to (17) are obtained.

[0059]

number

[0060]

number

[0061]

number

[0062] Also, as in the example where the order of the low-order filter is second, there are multiple possible structures of low-order filters that realize the calculations shown in equations (15) and (16), such as the structures shown in Figures 8 and 9. The structure shown in Figure 8 is equivalent to the structure in Figure 6 where a12 and b12 have been removed. Also, the structure shown in Figure 9 is equivalent to the structure in Figure 7 where B and C have been removed. Therefore, the features of each structure shown in Figures 8 and 9 are similar to the examples of the structures shown in Figures 6 and 7.

[0063] Next, the configurations and features of the first compensator 3 and the second compensator 4 will be described. Elements that make up a compensator include the structure of the low-order filter, the order of the low-order filter, and the number of connected low-order filters. As for the number of connected low-order filters, as mentioned above, the degree of freedom in the characteristics that can be expressed by the compensator increases as the number of connected stages increases. Therefore, it is possible to improve the performance of the control device 2 by increasing the number of low-order filters connected in series.

[0064] Furthermore, if at least one of the first compensator 3 and the second compensator 4 is configured with low-order filters of the same structure, the processing of a single low-order filter can be made into a function and reused, which has the advantage of facilitating software implementation. The amount of calculation and ease of parameter adjustment for low-order filters also differ depending on the structure. For example, the low-order filter structure shown in Figure 6 makes it easy to grasp the correspondence between the transfer functions of the continuous-time system and the discrete-time system, making it easy for the adjustment technician to change parameters and adjust the transfer characteristics. Therefore, if you want to manually adjust the compensator of a low-order filter, the low-order filter structure shown in Figure 6 is effective.

[0065] Furthermore, the low-order filter structure shown in Figure 7 requires that the parameters of the discrete-time transfer function be converted to calculate each gain. This makes it difficult to grasp the effect that parameter changes have on the transfer characteristics, and it is relatively difficult to manually adjust the parameters. However, this can be achieved with half the number of delay blocks compared to the structure in Figure 6, which is advantageous in terms of the computational load.

[0066] As described above, the amount of calculation and ease of parameter adjustment differ depending on the low-order filter structure. Therefore, for example, it is effective to apply the low-order filter structure shown in Fig. 6 to a compensator that requires manual parameter adjustment, and to apply the low-order filter structure shown in Fig. 7 to a compensator that does not require parameter adjustment.

[0067] Furthermore, if the low-order filters constituting at least one of the first compensator 3 and the second compensator 4 are all of the same order, the upper and lower limit values ​​of the parameters set in each low-order filter or the settings for fixed-point conversion can all be set in common. This is effective for simplifying the setting of the search range or the search process when exploratory design of low-order filter parameters that achieve desired transfer characteristics. This is particularly effective when there are many parameters to be designed, such as when configuring a compensator by connecting three or more low-order filters in series.

[0068] On the other hand, when the low-order filters constituting at least one of the first compensator 3 and the second compensator 4 are realized with different orders, it may be possible to optimize the compensator in terms of the calculation load. For example, if the desired characteristics can be realized by a compensator in which a second-order low-order filter and a first-order low-order filter are connected in series, the amount of calculation can be reduced compared to when a compensator is constituted by connecting two second-order low-order filters in stages.

[0069] The effects of the above-described configuration will be described based on the calculation results shown in Fig. 10 and Fig. 11. Fig. 10 is a diagram showing an example of the maximum value of the torque proportional gain versus the order of the compensator. The example shown in Fig. 10 is the result of calculation of the maximum value of the torque proportional gain that can be achieved according to the order of each compensator for a configuration having both the first compensator 3 and the second compensator 4 and a configuration having only the first compensator 3.

[0070] In these trial calculation results, all low-order filters had the same structure and were of second order, and the order of each compensator was changed by increasing the number of low-order filters connected in series. Also, in Fig. 10, in a configuration having first compensator 3 and second compensator 4, the maximum value of the torque proportional gain when the order of each compensator is sixth is used as the reference, and the maximum value of the torque proportional gain under other conditions is expressed. Note that the trial calculation of the torque proportional gain was carried out by exploratory design of the parameters of each low-order filter, with the constraints being that the characteristics required of each compensator described above are satisfied and a specified stability margin is realized.

[0071] The calculation results shown in Fig. 10 show that the maximum value of the torque proportional gain tends to improve as the order of each compensator increases. Furthermore, it can be seen that the maximum value of the torque proportional gain can be improved more effectively with a configuration that includes the second compensator 4 in addition to the first compensator 3 than with a configuration that includes only the first compensator 3.

[0072] Next, Figure 11 shows an example of disturbance suppression performance versus the order of the compensator. This indicates that the smaller the gain of the disturbance suppression performance, the less likely the torque input as a disturbance is to be transmitted to the steering wheel. The compensator used in the calculations had a configuration including a first compensator 3 and a second compensator 4, and all low-order filters had the same structure and were of second order, with the order of each compensator being changed by increasing the number of low-order filters connected in series. The results shown in Figure 11 show that a sixth-order compensator can achieve better disturbance suppression performance than the example in which the order of each compensator is second.

[0073] [Summary of the first embodiment] As described above, the control device 2 of the electric power steering according to this embodiment controls the output torque of the motor 1 that outputs assist torque based on the steering torque signal from the torque sensor 22 that detects the steering torque applied to the steering wheel 51 by the driver (user). For example, the control device 2 controls the output torque of the motor 1 by using, as a current command equivalent to a command value for the output torque, a signal obtained by adding a correction signal obtained by passing the steering torque signal from the torque sensor 22 through the second compensator 4 to an assist torque signal that is approximately proportional to a compensated steering torque signal obtained by passing the steering torque signal from the torque sensor 22 through the first compensator 3. The first compensator 3 and the second compensator 4 each have at least two or more stages of first-order or second-order low-order filters connected in series.

[0074] This makes it possible to improve the performance of the electric power steering control device 2, increase the gradient of the assist map that indicates the magnitude of the steering assist amount, and obtain a significant effect not previously seen in the past, that is, make it possible to apply electric power steering to large vehicles that require large steering assist force.In addition, the first compensator 3 and the second compensator 4 are configured by connecting low-order filters in multiple stages in series, making software implementation easy.

[0075] The first compensator 3 has a characteristic of being approximately 0 dB at 0 Hz, and the second compensator 4 has a characteristic of reducing low frequency components.

[0076] As a result, the electric power steering control device 2 generates a current command corresponding to the desired steering assist force using the first compensator 3, and the second compensator 4 does not affect the driver's steering, resulting in the effect of improving the disturbance suppression performance under operating conditions where the torque proportional gain is small.

[0077] For example, the low-order filters constituting at least one of the first compensator 3 and the second compensator 4 all have the same order.

[0078] This allows the electric power steering control device 2 to share constraints such as upper and lower limit values ​​for the parameters of each low-order filter that makes up each compensator and fixed-point settings, thereby reducing the amount of work required to design the parameters.

[0079] Furthermore, the low-order filters constituting at least either the first compensator 3 or the second compensator 4 all have the same structure.

[0080] As a result, the electric power steering control device 2 can realize the first compensator 3 and the second compensator 4 by utilizing the same calculation structure, which has the effect of reducing the number of steps required for software implementation.

[0081] In addition, the electric power steering device 100 according to this embodiment is configured to include a torque sensor 22 that detects the steering torque applied to the steering wheel 51 by the driver (user) and a control device 2, and the output torque of the motor 1 is controlled by the control device 2 based on the steering torque detected by the torque sensor 22.

[0082] As a result, the electric power steering device 100 can improve the performance of the control device 2, increase the gradient of the assist map that indicates the magnitude of the steering assist amount, and achieve the unprecedented and remarkable effect of making it possible to apply electric power steering to large vehicle models that require large steering assist force.

[0083] The electric power steering control system according to this embodiment also includes a steering wheel 51, a motor 1 that outputs an assist torque based on a steering torque signal from a torque sensor 22 that detects the steering torque applied to the steering wheel 51 by a driver (user), and a control device 2 that controls the output torque of the motor 1. For example, the control device 2 controls the output torque of the motor 1 by using, as a current command corresponding to a command value for the output torque, a signal obtained by adding a correction signal obtained by passing the steering torque signal from the torque sensor 22 through a second compensator 4 to an assist torque signal that is approximately proportional to a compensated steering torque signal obtained by passing the steering torque signal from the torque sensor 22 through a first compensator 3. The first compensator 3 and the second compensator 4 each have at least two or more stages of first-order or second-order low-order filters connected in series.

[0084] As a result, the electric power steering control system can improve the performance of the control device 2, increase the gradient of the assist map that indicates the magnitude of the steering assist amount, and obtain a significant effect not previously seen in the past, that is, make it possible to apply electric power steering to large vehicles that require large steering assist force.In addition, the first compensator 3 and the second compensator 4 are configured by connecting low-order filters in multiple stages in series, which makes software implementation easy.

[0085] <Second embodiment> Next, a second embodiment will be described. In the first embodiment described above, the steering torque is used as an input to the input / output device. In contrast, this embodiment differs from the first embodiment in that the motor rotation speed is used in addition to the steering torque, but the rest is the same.

[0086] Fig. 12 is a schematic block diagram showing an example of the configuration of a control device 2A according to this embodiment. The control device 2A shown in Fig. 2 further includes a third compensator 9, a fourth compensator 10, and a motor speed calculation unit 11 in addition to the configuration shown in Fig. 2 of the first embodiment. The motor speed calculation unit 11 calculates the motor speed of the motor 1 from the output of a motor rotation angle sensor 23 that detects the rotation angle of the motor 1. The third compensator 9 and the fourth compensator 10 are connected to the output of the motor speed calculation unit 11.

[0087] The compensated motor speed signal, obtained by passing the motor speed calculated by motor speed calculation unit 11 through third compensator 9, is added to the compensated steering torque signal, obtained by passing the steering torque signal through first compensator 3, to generate a signal for calculating the assist torque. Also, the motor speed-based correction signal, obtained by passing the motor speed calculated by motor speed calculation unit 11 through fourth compensator 10, is added to the torque-based correction signal, obtained by passing the steering torque signal through second compensator 4, to generate a composite correction signal.

[0088] Furthermore, the current command is obtained by adding the combined correction signal to an assist torque signal, which is obtained by multiplying the assist torque calculation signal by the torque proportional gain calculated in the assist map 5. The processing after the generation of the current command is the same as in the first embodiment.

[0089] As described above, the control device 2A according to this embodiment is obtained by adding a motor speed feedback loop to the control device 2 described in the first embodiment. The motor speed calculated from the output of the motor rotation angle sensor 23 can generally be detected up to a higher frequency range than the detected value of the steering torque. Therefore, by adding the motor speed feedback loop, it becomes easier to ensure a stability margin and it becomes possible to sufficiently suppress vibrations such as oscillations.

[0090] Furthermore, since the stability of the feedback loop does not depend on the torque sensor 22, it is easy to adapt to various torque sensors. For example, it is not affected by factors that reduce stability due to problems specific to the torque sensor, such as the spring constant of the torsion bar, phase lag of the detected value, communication delay, etc.

[0091] Next, the characteristics of the third compensator 9 and the fourth compensator 10 will be explained. The third compensator 9 and the fourth compensator 10 have characteristics that decrease the gain in the low frequency range in order to reduce the steering frequency component contained in the motor speed signal. Note that, since the frequency at which the driver steers is generally 5 Hz or less, it is sufficient to have characteristics that decrease the gain at 5 Hz or less.

[0092] Furthermore, noise is superimposed on the motor speed signal during the detection process, and this noise is generally in the 200 to 500 Hz band. Therefore, the third compensator 9 and the fourth compensator 10 may have a characteristic that reduces the gain in the low frequency range of 5 Hz or less, as well as a characteristic that reduces the gain in the 200 to 500 Hz range to reduce the impact of detection noise. By using compensators with such characteristics, it is possible to realize a compensator that suppresses the viscous feeling in response to steering in the steering frequency range without unnecessarily increasing the impact of noise.

[0093] In this embodiment, the characteristics of the first compensator 3 and the second compensator 4 may be set to satisfy the same requirements as those in the first embodiment. The structures and orders of the third compensator 9 and the fourth compensator 10 may be set from the same viewpoints as those in the first embodiment.

[0094] [Summary of the second embodiment] As described above, the control device 2A of the electric power steering according to this embodiment controls the output torque of the motor 1, which outputs an assist torque, based on the steering torque signal and the motor speed signal from the torque sensor 22, which detects the steering torque applied to the steering wheel 51 by the driver (user). For example, the control device 2A controls the output torque of the motor 1 by using, as a current command corresponding to an output torque command value, a signal obtained by adding a combined correction signal obtained by adding a torque-based correction signal obtained by passing the steering torque signal through the second compensator 4 and a motor-speed-based correction signal obtained by passing the motor speed signal through the fourth compensator 10 to an assist torque signal that is approximately proportional to an assist torque calculation signal that is the sum of a compensated steering torque signal obtained by passing the steering torque signal from the torque sensor 22 through the first compensator 3 and a compensated motor speed signal obtained by passing the motor speed signal through the third compensator 9. The first compensator 3, the second compensator 4, the third compensator 9, and the fourth compensator 10 each include at least two or more stages of first-order or second-order low-order filters connected in series.

[0095] As a result, the electric power steering control device 2A according to this embodiment adds a motor speed feedback loop, increasing the degree of freedom in the transfer characteristics that can be expressed by the control device 2A, thereby improving the performance of the control device 2A. Therefore, the electric power steering control device 2A can increase the gradient of the assist map, which represents the magnitude of the steering assist amount, resulting in a significant effect of enabling electric power steering to be applied to large vehicles that require large steering assist force. Furthermore, because the motor speed can be detected up to a higher frequency range than the detected value of steering torque, disturbance suppression performance can be improved compared to when only steering torque is used. Furthermore, the first compensator 3, second compensator 4, third compensator 9, and fourth compensator 10 are configured by connecting multiple low-order filters in series, facilitating software implementation.

[0096] The first compensator 3 has a characteristic of being approximately 0 dB at 0 Hz. The second compensator 4, the third compensator 9, and the fourth compensator 10 each have a characteristic of reducing low frequency components.

[0097] As a result, the electric power steering control device 2A generates a current command corresponding to the desired steering assist force using the first compensator 3, and the second compensator 4, third compensator 9, and fourth compensator 10 do not affect the driver's steering, making it possible to improve the disturbance suppression performance and feedback loop stability under operating conditions where the torque proportional gain is small.

[0098] For example, the low-order filters constituting at least one of the first compensator 3, the second compensator 4, the third compensator 9, and the fourth compensator 10 all have the same order.

[0099] This allows the electric power steering control device 2A to share constraints such as upper and lower limit values ​​for the parameters of each low-order filter that makes up each compensator and fixed-point settings, thereby reducing the amount of work required to design the parameters.

[0100] Furthermore, the low-order filters constituting at least one of the first compensator 3, the second compensator 4, the third compensator 9, and the fourth compensator 10 all have the same structure.

[0101] As a result, the electric power steering control device 2A can realize the first compensator 3, second compensator 4, third compensator 9, and fourth compensator 10 by utilizing the same calculation structure, thereby reducing the amount of work required for software implementation.

[0102] The electric power steering control system according to this embodiment includes a steering wheel 51, a motor 1 that outputs an assist torque based on a steering torque signal and a motor speed signal from a torque sensor 22 that detects the steering torque applied to the steering wheel 51 by a driver (user), and a control device 2A that controls the output torque of the motor 1. For example, the control device 2A controls the output torque of the motor 1 by using a signal obtained by adding a combined correction signal obtained by adding a torque-based correction signal obtained by passing the steering torque signal through a second compensator 4 and a motor-speed-based correction signal obtained by passing the motor speed signal through a fourth compensator 10 to an assist torque signal that is approximately proportional to an assist torque calculation signal that is the sum of a compensated steering torque signal obtained by passing the steering torque signal from the torque sensor 22 through a first compensator 3 and a compensated motor speed signal obtained by passing the motor speed signal through a third compensator 9, as a current command corresponding to an output torque command value. The first compensator 3, the second compensator 4, the third compensator 9, and the fourth compensator 10 each include at least two or more stages of first-order or second-order low-order filters connected in series.

[0103] As a result, the electric power steering control system according to this embodiment adds a motor speed feedback loop, increasing the degree of freedom in the transfer characteristics that can be expressed by the control device 2A, thereby improving the performance of the control device 2A. Therefore, the electric power steering control system can increase the gradient of the assist map, which represents the magnitude of the steering assist amount, achieving the remarkable effect of enabling electric power steering to be applied to large vehicles that require large steering assist force. Furthermore, because the motor speed can be detected up to a higher frequency range than the detected value of the steering torque, disturbance suppression performance can be improved compared to when only the steering torque is used. Furthermore, the first compensator 3, second compensator 4, third compensator 9, and fourth compensator 10 are configured by connecting multiple low-order filters in series, facilitating software implementation.

[0104] <Third embodiment> Next, a third embodiment will be described. In this embodiment, a configuration of a vehicle equipped with the electric power steering device 100 described in the first and second embodiments will be described. The vehicle is, for example, an electric vehicle that uses electricity for power, such as a hybrid vehicle, a plug-in hybrid vehicle, an electric vehicle, or a hydrogen fuel cell vehicle. Note that the vehicle may also be a gasoline vehicle, a diesel vehicle, or the like.

[0105] 13 is a diagram showing an example of the configuration of a vehicle 200 according to this embodiment. The vehicle 200 includes a vehicle speed detection unit 30 and an electric power steering device 100. The vehicle speed detection unit 30 detects the speed of the vehicle 200 based on the rotation speed of wheels 55, for example.

[0106] The control device 2 of the electric power steering device 100 controls the output torque of the motor 1 based on the vehicle speed detected by the vehicle speed detection unit 30 and the steering torque (the steering torque signal from the torque sensor 22). The vehicle speed affects the characteristics of the assist map 5, as described with reference to FIG. 3. The control device 2 determines a torque proportional gain using an assist map corresponding to the vehicle speed detected by the vehicle speed detection unit 30, and multiplies the compensated steering torque signal by the torque proportional gain to obtain an assist torque signal. The control device 2 may be the control device 2A of the second embodiment shown in FIG. 12.

[0107] As such, the vehicle 200 according to this embodiment is equipped with a vehicle speed detection unit 30 that detects the speed of the vehicle 200, and an electric power steering device 100 in which the output torque of the motor 1 is controlled based on the vehicle speed and steering torque detected by the vehicle speed detection unit 30.

[0108] As a result, by installing the electric power steering device 100 in which the gradient of the assist map that indicates the magnitude of the steering assist amount is increased, the vehicle 200 can obtain a remarkable effect not seen in the past, in that the electric power steering can be applied even to large vehicle models that require large steering assist force.

[0109] Although the embodiments have been described above in detail with reference to the drawings, the specific configurations are not limited to these embodiments, and each embodiment can be modified or omitted as appropriate.

[0110] It is also possible to perform at least some of the processing of the control device 2 (2A) by recording a program for realizing at least some of the functions of the control device 2 (2A) on a computer-readable recording medium and having a computer system load and execute the program. Note that the term "computer system" here includes hardware such as an OS and peripheral devices.

[0111] Furthermore, the term "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into computer systems. Furthermore, the term "computer-readable recording medium" also includes devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs over networks like the Internet or communication lines like telephone lines, and devices that store programs for a fixed period of time, such as volatile memory within the computer systems that serve as servers or clients. The program may be a program that implements part of the aforementioned functions, or may be a program that can implement the aforementioned functions in combination with a program already stored in the computer system. The program may also be stored on a designated server and distributed (e.g., downloaded) over communication lines in response to requests from other devices.

[0112] Furthermore, some or all of the functions of the control device 2 (2A) may be realized as an integrated circuit such as an LSI (Large Scale Integration). Each function may be individually implemented as a processor, or some or all of the functions may be integrated into a processor. The integrated circuit method is not limited to LSI, and may be realized using a dedicated circuit or a general-purpose processor. Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology, an integrated circuit based on that technology may be used. [Explanation of symbols]

[0113] 1 motor 2,2A control device 3 First compensator 4 Second compensator 5 Assist Maps 6 Current control section 7. Drive circuit 8 Current detection section 9 Third compensator 10 Fourth compensator 11 Motor speed calculation unit 22 Torque sensor 23 Motor rotation angle sensor 51 Steering wheel 53 Steering shaft 54 Rack and pinion gear 55 wheels 56 tie rod 57 Knuckle Arm 100 Electric power steering device 200 vehicles

Claims

1. A control device for electric power steering that controls an output torque of a motor that outputs an assist torque based on a steering torque signal from a torque sensor that detects a steering torque applied to a steering wheel by a user, a signal obtained by adding a correction signal obtained by passing the steering torque signal through a second compensator to an assist torque signal that is approximately proportional to a compensated steering torque signal that is obtained by passing the steering torque signal through a first compensator, and the signal is used as a current command corresponding to the command value of the output torque to control the output torque; the first compensator and the second compensator each have at least two stages of first-order or second-order low-order filters connected in series; Electric power steering control device.

2. the first compensator has a characteristic of being approximately 0 dB at 0 Hz, the second compensator has a characteristic of reducing low-frequency components; The electric power steering control device according to claim 1.

3. low-order filters constituting at least one of the first compensator and the second compensator all have the same order; The electric power steering control device according to claim 1.

4. low-order filters constituting at least one of the first compensator and the second compensator all have the same structure; The electric power steering control device according to claim 1.

5. A control device for electric power steering that controls an output torque of a motor that outputs an assist torque based on a steering torque signal from a torque sensor that detects a steering torque applied to a steering wheel by a user and a motor speed signal, a signal obtained by adding a torque-based correction signal obtained by passing the steering torque signal through a second compensator and a motor-speed-based correction signal obtained by passing the motor speed signal through a fourth compensator to an assist torque signal that is approximately proportional to an assist torque calculation signal that is a sum of a compensated steering torque signal that has been passed through a first compensator and a compensated motor speed signal that has been passed through a third compensator, and the output torque is controlled using the resulting signal as a current command equivalent to the command value of the output torque; the first compensator, the second compensator, the third compensator, and the fourth compensator each include first-order or second-order low-order filters connected in series in at least two stages; Electric power steering control device.

6. the first compensator has a characteristic of being approximately 0 dB at 0 Hz, the second compensator, the third compensator, and the fourth compensator have a characteristic of reducing low-frequency components.

6. The electric power steering control device according to claim 5.

7. low-order filters constituting at least one of the first compensator, the second compensator, the third compensator, and the fourth compensator all have the same order; 6. The electric power steering control device according to claim 5.

8. low-order filters constituting at least one of the first compensator, the second compensator, the third compensator, and the fourth compensator all have the same structure; 6. The electric power steering control device according to claim 5.

9. a torque sensor that detects the steering torque applied to the steering wheel by a user; The electric power steering control device according to any one of claims 1 to 8, Equipped with The output torque is controlled by the control device of the electric power steering based on the steering torque detected by the torque sensor. Electric power steering device.

10. a vehicle speed detection unit that detects the speed of the vehicle; an electric power steering device according to claim 9, wherein the output torque is controlled based on the vehicle speed detected by the vehicle speed detection unit and the steering torque; A vehicle equipped with:

11. An electric power steering control system including a steering wheel, a motor that outputs an assist torque based on a steering torque signal from a torque sensor that detects a steering torque applied to the steering wheel by a user, and a control device that controls the output torque of the motor, The control device a signal obtained by adding a correction signal obtained by passing the steering torque signal through a second compensator to an assist torque signal that is approximately proportional to a compensated steering torque signal that is obtained by passing the steering torque signal through a first compensator, and the signal is used as a current command corresponding to the command value of the output torque to control the output torque; the first compensator and the second compensator each have at least two stages of first-order or second-order low-order filters connected in series; Electric power steering control system.

12. An electric power steering control system including: a steering wheel; a motor that outputs an assist torque based on a steering torque signal and a motor speed signal from a torque sensor that detects a steering torque applied to the steering wheel by a user; and a control device that controls the output torque of the motor, The control device a signal obtained by adding a torque-based correction signal obtained by passing the steering torque signal through a second compensator and a motor-speed-based correction signal obtained by passing the motor speed signal through a fourth compensator to an assist torque signal that is approximately proportional to an assist torque calculation signal that is a sum of a compensated steering torque signal that has been passed through a first compensator and a compensated motor speed signal that has been passed through a third compensator, and the output torque is controlled using the resulting signal as a current command equivalent to the command value of the output torque; the first compensator, the second compensator, the third compensator, and the fourth compensator each include first-order or second-order low-order filters connected in series in at least two stages; Electric power steering control system.

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