Patent ID: 12240536

DETAILED DESCRIPTION

Before describing example embodiments of the present disclosure, the discoveries made by the present inventors and the technical background thereof will be described.

In the conventional control device, an assist controller and an angle controller are provided as individual controllers. The assist controller sets a target value of assist torque necessary for manual driving, and the angle controller sets a target value of torque necessary for angle control. An angular deviation depending on an input state of the driver indicating manual driving or automatic driving is input to a shared controller as input information. The shared controller calculates a weighting factor for performing weighted addition based on the target value set by the assist controller and the angle controller, and outputs target assist torque. However, according to this method, it is necessary to simultaneously process the functions of both the assist controller and the angle controller, and a large operation load is applied to the arithmetic circuit. As a result, there is a problem that an expensive arithmetic circuit having a large data processing amount is required.

According to the study of the present inventors, in the control device of an electric power steering apparatus, it is effective to make the gain of the integrator that performs the I control in the PI control variable according to the input target steering wheel angle, and to perform switching between enabling and disabling of the integrator. As a result, the present inventors have found that both functions of the assist controller related to manual driving and the angle controller related to automatic driving can be realized by one angle controller, and have completed the present disclosure.

With reference to the accompanying drawings, hereinafter, a specific description will be given on example embodiments of a control device and a control method for an electric power steering apparatus of the present disclosure as well as an electric power steering apparatus including the control device. However, a specific description more than necessary will not be given in some cases. For example, detailed descriptions of well-known matters and duplicate description of substantially the same configuration may be omitted. This is to avoid unnecessary redundancy of the following description and to facilitate the understanding of those skilled in the art.

The following example embodiments are illustrative, and the control device and the control method for an electric power steering apparatus according to the present disclosure are not limited to the following example embodiments. For example, the numerical values, the steps, the order of the steps, and the like illustrated in the following example embodiments are only illustrative, and various modifications can be made unless any technical inconsistency occurs. The example embodiments described below are illustrative, and various combinations are possible unless any technical inconsistency occurs.

FIG.1is a diagram schematically illustrating a configuration example of an electric power steering apparatus1000according to the present example embodiment.

The electric power steering apparatus1000(hereinafter, referred to as an “EPS”) includes a steering system520and an assist torque mechanism540which generates an assist torque. The EPS1000generates the assist torque for assisting the steering torque of the steering system generated when a driver operates a steering wheel. The assist torque reduces the operation load on the driver.

The steering system520includes a steering wheel521, a steering shaft522, universal joints523A and523B, a rotary shaft524, a rack and pinion mechanism525, a rack shaft526, right and left ball joints552A and552B, tie rods527A and527B, knuckles528A and528B, and right and left steered wheels529A and529B, for example.

The assist torque mechanism540includes a steering torque sensor541, a steering angle sensor542, an electronic controller (ECU)100for automobiles, a motor543, a deceleration gear544, an inverter545, and a torsion bar546, for example. The steering torque sensor541detects a steering torque in the steering system520by detecting the amount of torsion of the torsion bar546. The steering angle sensor542detects a steering angle of the steering wheel. Incidentally, the steering torque may be an estimated value derived from calculation, not a value of the steering torque sensor. The steering angle can also be calculated based on the output value of the angle sensor.

The ECU100generates a motor driving signal based on the detection signals detected by the steering torque sensor541, the steering angle sensor542, a vehicle speed sensor (not illustrated) mounted on a vehicle, and the like to output the motor driving signal to the inverter545. For example, the inverter545converts direct-current power into three-phase alternating-current power having A-phase, B-phase, and C-phase pseudo sine waves in accordance with the motor driving signal, and supplies the power to the motor543. The motor543is, for example, a surface permanent-magnet synchronous motor (SPMSM) or a switched reluctance motor (SRM), and is supplied with the three-phase alternating-current power to generate assist torque corresponding to the steering torque. The motor543transmits the generated assist torque to the steering system520via the deceleration gear544. Hereinafter, the ECU100will be referred to as a control device100for the EPS.

The control device100and the motor are modularized and manufactured and sold as a motor module. The motor module includes the motor and the control device100and is suitably used for the EPS. Alternatively, the control device100may be manufactured and sold as a control device to control the EPS independently of the motor.

FIG.2is a block diagram illustrating a typical example of a configuration of the control device100according to the present example embodiment. The control device100includes a power supply circuit111, an angle sensor112, an input circuit113, a communication I/F114, a drive circuit115, a ROM116, and a processor200, for example. The control device100can be realized as a printed circuit board (PCB) on which these electronic components are implemented.

A vehicle speed sensor300mounted on the vehicle, the steering torque sensor541, and the steering angle sensor542are electrically connected to the processor200. The vehicle speed sensor300, the steering torque sensor541, and the steering angle sensor542transmit a vehicle speed v, steering torque Ts, and a steering angle θ to the processor200, respectively.

The control device100is electrically connected to the inverter545(seeFIG.1). The control device100controls switching operations of a plurality of switching elements (for example, MOSFETs) included in the inverter545. Specifically, the control device100generates control signals (hereinafter referred to as “gate control signals”) for controlling the switching operations of the respective switch elements and outputs the gate control signals to the inverter545.

The control device100generates a torque command value based on the vehicle speed v, the steering torque Ts, and the like, and controls torque and rotation speed of the motor543by means of, for example, vector control. The control device100can perform not only the vector control but also other closed-loop control. The rotation speed is expressed by the number of revolutions (rpm) at which a rotor rotates per unit time (for example, one minute) or the number of revolutions (rps) at which the rotor rotates per unit time (for example, one second). The vector control is a method in which current flowing through the motor is separated into a current component that contributes to generation of a torque and a current component that contributes to generation of a magnetic flux, and the current components orthogonal to each other are independently controlled.

The power supply circuit111is connected to an external power supply (not illustrated) and generates DC voltage required for each block in the circuit. The DC voltage to be generated is, for example, 3 V or 5 V.

The angle sensor112is, for example, a resolver or a Hall IC. Alternatively, the angle sensor112is also realized by a combination of an MR sensor having a magnetoresistive (MR) element and a sensor magnet. The angle sensor112detects a rotation angle of the rotor to output the rotation angle to the processor200. The control device100may include a speed sensor and an acceleration sensor for detecting the rotation speed and acceleration of the motor instead of the angle sensor112.

The input circuit113receives a motor current value (hereinafter, referred to as an “actual current value”) detected by a current sensor (not illustrated), converts the level of the actual current value into the input level for the processor200as needed, and outputs the actual current value to the processor200. A typical example of the input circuit113is an analog-digital conversion circuit.

The processor200is a semiconductor integrated circuit and is also referred to as a central processing unit (CPU) or a microprocessor. The processor200sequentially executes a computer program which is stored in the ROM116and describes a command set for controlling motor driving, and realizes desired processing. The processor200is widely interpreted as a term including a Field Programmable Gate Array (FPGA), an Application Specific Integrated Circuit (ASIC), or an Application Specific Standard Product (ASSP) equipped with a CPU. The processor200sets a target current value in accordance with, for example, the actual current value and the rotation angle of the rotor to generate a PWM signal, and outputs the PWM signal to the drive circuit115.

The communication I/F114is an input/output interface for transmitting/receiving data in conformity with an in-vehicle control area network (CAN), for example.

The drive circuit115is typically a gate driver (or a pre-driver). The drive circuit115generates a gate control signal in accordance with the PWM signal and gives the gate control signal to gates of the plurality of switching elements included in the inverter545. There is a case where a gate driver is not necessarily required when a driving target is a motor that can be driven at a low voltage. In that case, the functionality of the gate driver may be implemented in the processor200.

The ROM116is electrically connected to the processor200. The ROM116is a writable memory (for example, a PROM), a rewritable memory (for example, a flash memory or an EEPROM), or a read-only memory, for example. The ROM116stores a control program including a command set for causing the processor200to control motor driving. For example, the control program is temporarily expanded to a RAM (not illustrated) at boot time.

FIG.3is a functional block diagram that illustrates functional blocks, to be implemented on the processor200, of the EPS controller230according to an example embodiment of the present disclosure. The processor200in the example embodiment of the present disclosure can be realized by an EPS controller230having an angle controller231, a current controller232, and a pulse width modulation (PWM) modulation unit233as functional blocks. Typically, the processes (or tasks) of the functional blocks corresponding to the respective units are described in the computer program on a software module basis, and are stored in the ROM116. However, in the case where an FPGA or the like is used, all or some of the functional blocks may be implemented as hardware accelerators.

In the case in which each functional block is implemented as software (or firmware) in the control device100, a device that executes the software may be the processor200. In one aspect, the control device according to the present disclosure includes the processor200and a memory that stores a program that controls the operation of the processor200. The processor200executes, according to the program, (1) calculation of the target assist torque Trby performing PI control based on the target steering wheel angle and the steering angle θg, and (2) control of the motor based on the target assist torque Tr. Controlling the motor based on the target assist torque Trincludes calculating the command voltage Vr by performing current control based on the target assist torque Tr, and performing PWM modulation on the command voltage Vr to generate a PWM signal. Here, the gain of the integrator used for the I control of the PI control is variable.

In another aspect, the processor200executes, according to the program, (1) calculation of the target assist torque Trby performing PI control based on the target steering wheel angle and the steering angle θg, (2) switching between enabling and disabling of an integrator used for I control of the PI control in response to a trigger, and (3) control of the motor based on the target assist torque Tr. Examples of the trigger include a hands-on and hands-off command indicating a hands-on state or a hands-off state, a signal that changes according to a magnitude relationship between a steering wheel torque or a torsion torque indicating an automatic driving signal and a threshold, and a mode command output from a host device. An example of the host device is a host electronic controller (ECU). Details of the trigger will be described later.

In the case where each functional block is implemented in the control device100as software and/or hardware, in another aspect, the control device100of the present disclosure includes: an angle controller that calculates target assist torque Trby performing PI control based on a target steering wheel angle and a steering angle θg; a current controller that calculates a command voltage Vr by performing current control based on the target assist torque Tr; and a PWM modulation unit that generates a PWM signal by applying PWM modulation to the command voltage Vr. Here, the gain of the integrator used for the I control of the PI control is variable. In still another aspect, the control device100includes: an angle controller that calculates a target assist torque Trby performing PI control based on the target steering wheel angle and the steering angle θg, and is capable of switching between enabling and disabling of an integrator used for I control of the PI control in response to a trigger; a current controller that calculates a command voltage Vr by performing current control based on the target assist torque Tr; and a PWM modulation unit that generates a PWM signal by performing PWM modulation on the command voltage Vr.

The EPS controller230calculates the target assist torque Trby performing PI control based on the target steering wheel angle and the steering angle θg. The target steering wheel angle in the example embodiments of the present disclosure may include a manual steering wheel angle θdand an automatic target steering wheel angle θr. In the present specification, the manual steering wheel angle θdor the automatic target steering wheel angle θrmay be referred to as a target steering wheel angle.

The EPS control device200according to the example embodiment of the present disclosure can be regarded as one angle controller. The EPS controller230according to the example embodiment of the present disclosure includes an angle controller231, a current controller232, and a PWM modulation unit233. The automatic target steering wheel angle θr, the manual steering wheel angle θd, and the steering angle θgare input to the EPS controller230as input signals. The EPS controller230switches the control between the manual driving mode and the automatic driving mode by switching the command value related to the angle including the automatic target steering wheel angle θrand the manual steering wheel angle θdand adjusting the integral term.

The angle controller231calculates and outputs the target assist torque Trbased on the automatic target steering wheel angle θror the manual steering wheel angle θdand the steering angle θg. The manual steering wheel angle θdindicates the angle of the steering wheel moved by the driver in the manual driving mode. The automatic target steering wheel angle θrindicates a target value of a steering wheel angle derived from a sensor such as a camera in the automatic driving mode. In the example embodiment of the present disclosure, a gain of an integrator that performs I control in PI control changes according to a target steering wheel angle, and enabling and disabling of the integrator are switched.

In the manual driving mode, the angle controller231performs power assist control while causing the steering angle θgto follow the manual steering wheel angle θd. The residual deviation in the power assist control is the steering torque. On the other hand, in the automatic driving mode, the angle controller231performs control to cause the steering angle θgto follow the automatic target steering wheel angle θrto eliminate the residual deviation. In this manner, both the functions of the assist control involved in the manual driving and the angle control involved in the automatic driving are implemented in one angle controller. The difference in the control between the manual driving mode and the automatic driving mode is the difference in the command value related to the angle, and the presence or absence of an integrator used for I control to be described later.

In the example embodiment of the present disclosure, the EPS controller230generally has a manual driving mode and an automatic driving mode, but can further divide the above two modes into four control modes based on a combination of a target steering wheel angle input to the angle controller231, validity and invalidity of the I control, and a variable gain. Four control modes are listed below. In the following second to fourth control modes, the steering feeling felt by the driver can be appropriately adjusted by changing the gain in the I control according to the target steering wheel angle.

The first control mode is a mode for causing the processor to execute P control based on the manual steering wheel angle θd. This mode corresponds to the manual driving mode. The driver can feel the residual deviation of the steering angle with respect to the manual steering wheel angle in the steering as a steering feeling.

The second control mode is a mode for causing the processor to perform PI control based on the manual steering wheel angle θd. This mode corresponds to the manual driving mode, but torque is assisted by adding I control. Therefore, the driver is less likely to feel fatigue.

The third control mode is a mode for causing the processor to perform PI control based on the manual steering wheel angle θdand automatic target steering wheel angle θr. This mode corresponds to the semi-automatic driving mode. The driver has a sense that the steering wheel angle is further guided.

The fourth control mode is a mode for causing the processor to perform PI control based on the automatic target steering wheel angle θr. This mode corresponds to the full automatic driving mode. The driver can cause the vehicle to travel even in a state in which the driver is not on hand.

The function and operation of the angle controller231included in the EPS controller230will be described in detail with reference toFIGS.4A to6.

According to the EPS controller230in the present example embodiment, the gain of the integrator used for I control of PI control using a certain signal or command as a trigger is variable. The integrator used for I control in PI control is enabled.

FIG.4Ais a functional block diagram illustrating functional blocks of the angle controller231of the EPS controller230in a state where the integrator12cis enabled.FIG.4Bis a functional block diagram illustrating another configuration of functional blocks of the angle controller231in a state where the integrator12cis enabled.FIG.5is a graph illustrating a relationship between a gain or a weight of the integrator12cwith respect to the steering wheel torque Th.

As illustrated inFIG.4A, the angle controller231includes a subtractor10, a torsion bar rigid unit11, a P controller12a, a D controller12b, an I controller12c, and an adder13. Herein, the I controller may be described as an integrator, and the D controller may be described as a differentiator. The angle controller231calculates the target assist torque Trby performing PI control based on the target steering wheel angle and the steering angle θg.

In the example of the graph illustrated inFIG.5, a state in which the steering wheel torque This not present or a state in which the steering wheel torque This minute even if present is the hands-off state. This mode corresponds to the automatic driving mode. The EPS controller230operates in accordance with the fourth control mode. Here, the steering wheel torque Thindicates an automatic driving signal. In the fourth control mode, the gain of the integrator12cis maximized, and the gain indicates a constant value without depending on the steering wheel torque Th.

The state in which the steering wheel torque This constantly generated is the manual driving state. The EPS controller230operates in accordance with the second control mode. In the second control mode, the gain of the integrator12cdoes not become completely 0 and indicates a minute value. However, the value is constant.

An area located between the ranges of the steering wheel torque Thdefining the second and fourth control modes, that is, a transition period from the automatic driving to the manual driving, is the hands-on state. The EPS controller230operates in accordance with the third control mode. In the third control mode, as the steering wheel torque Thincreases, the gain of the integrator12ccontinuously decreases. However, the present disclosure is not limited to this example, and for example, the gain of the integrator12cmay decrease stepwise or may change non-linearly and continuously.

As illustrated inFIG.4A, the integrator12cis enabled regardless of the control mode. As the target steering wheel angle, at least one of the manual steering wheel angle θdand the automatic target steering wheel angle θris input to the angle controller231. In the second and third control modes, the deviation between the steering angle θgand the target steering wheel angle including the manual steering wheel angle θdand the automatic target steering wheel angle θroutput from the subtractor10is input to each of the P controller12a, the D controller12b, and the I controller12c. In the fourth control mode, the deviation between the steering angle θgand the automatic target steering wheel angle θroutput from the subtractor10is input to each of the controller12a, the D controller12b, and the I controller12c. The adder13adds the output values output from the P controller12a, the D controller12b, and the I controller12c, and outputs the target assist torque Tr. However, as illustrated inFIG.4B, the D controller12bis not an essential component, and the angle controller231may include at least the P controller12aand the I controller12c. By using the D controller12b, responsiveness to instantaneous disturbance can be improved.

The steering wheel torque Thcan be used to determine a hands-on state or a hands-off state. In the example ofFIG.5, the gain of the integrator12ccontinuously changes according to the value of the steering wheel torque Thwhen the third control mode is selected. By always enabling the integrator12c, the residual deviation that may remain only by the P control can be set to 0. As a result, it is possible to eliminate an error in the angle generated between the target steering wheel angle and the actual steering angle, and as a result, it is possible to travel along the target travel trajectory. As a modification, a value of the torsion torque Ttorcan be used instead of the steering wheel torque Th.

FIG.6is a graph illustrating a gain that changes according to a ratio between the manual steering wheel angle θdand the automatic target steering wheel angle θr. In one aspect, the gain of the integrator12cmay vary depending on the ratio between the manual steering wheel angle θdand the automatic target steering wheel angle θr. This ratio, that is, the inclination of the straight line can be determined according to the mode command output from the host device. In the example ofFIG.6, the ratio changes linearly, but is not limited thereto, and may change non-linearly or change stepwise.

FIG.3will be referred to again.

As input signals, for example, the target assist torque Tr, the motor angle θm, and the actual current value Imare input to the current controller232. The current controller232calculates the command voltage Vr by performing current control based on the target assist torque Tr, the motor angle θm, and the actual current value Im, in accordance with vector control for example. The PWM modulation unit233performs PWM modulation on the command voltage Vr to generate a PWM signal, and outputs the PWM signal to the drive circuit115.

According to the present example embodiment, since the control of the manual and automatic driving modes is realized by one angle controller, the amount of data to be processed by an arithmetic circuit such as a processor can be reduced as compared with the related art. As a result, the cost of the arithmetic circuit can be suppressed.

An EPS controller230according to a second example embodiment will be described with reference toFIGS.7A to9. Hereinafter, differences from the EPS controller230according to the first example embodiment will be mainly described.

FIG.7Ais a functional block diagram illustrating functional blocks of the angle controller231of the EPS controller230in the manual driving mode.FIG.7Bis a functional block diagram illustrating functional blocks of the angle controller231of the EPS controller230in the automatic driving mode.FIG.8Ais a functional block diagram illustrating functional blocks of the angle controller231in another configuration of the EPS controller230in the manual driving mode.FIG.8Bis a functional block diagram illustrating functional blocks of the angle controller231in another configuration of the EPS controller230in the manual driving mode.FIG.9is a graph illustrating a relationship between a gain of the integrator12cwith respect to the steering wheel torque Th.

The EPS controller230according to the present example embodiment switches enabling and disabling of the integrator12cused for the I control of the PI control by using a certain signal or command as a trigger. As illustrated inFIG.9, the control mode in the present example embodiment includes a first control mode and a fourth control mode. In a state where the steering wheel torque This not present or in a state where the steering wheel torque This minute even if present, that is, in the hands-off state, the EPS controller230operates in accordance with the fourth control mode. The integrator12cis enabled and its gain can be fixed to a constant value. As illustrated inFIG.7B, the angle controller231calculates the target assist torque Tr based on the automatic target steering wheel angle θr and the steering angle θg. However, as illustrated inFIG.8B, the differentiator12bis not essential.

In a state where the steering wheel torque This constantly generated, that is, in the hands-on state, the EPS controller230operates in accordance with the first control mode. The integrator12cis disabled completely, so that its gain is 0. As illustrated inFIG.7A, the angle controller231calculates the target assist torque Trbased on the manual steering wheel angle θdand the steering angle θg. However, as illustrated inFIG.8A, the differentiator12bis not essential.

Examples of the trigger are a hands-on and hands-off command indicating a hands-on state or a hands-off state, a mode command output from a host device, or a signal that changes according to a magnitude relationship between the steering wheel torque Thindicating an automatic driving signal and a threshold Vth. However, the value of the torsion torque Ttorcan be used instead of the steering wheel torque Th. As illustrated inFIG.9, the EPS controller230operates in accordance with the fourth control mode in a range in which the steering wheel torque This less than the threshold Vth, and the EPS controller230operates in accordance with the first control mode in a range in which the steering wheel torque This equal to or greater than the threshold Vth.

In the present example embodiment, the angle controller231selects one of the manual steering wheel angle θdand the automatic target steering wheel angle θras an input value used for PI control in response to a hands-on and hands-off command indicating a hands-on state or a hands-off state or a mode command output from a host device. The angle controller231switches enabling and disabling of the integrator12caccording to the selected input value. More specifically, the angle controller231selects the automatic target steering wheel angle θras the input value used for the PI control in response to the hands-on and hands-off command indicating the hands-off state, and enables the integrator12c. On the other hand, the angle controller231selects the manual steering wheel angle θdas the input value used for the PI control in response to the hands-on and hands-off command indicating the hands-on state, and disables the integrator12c.

According to the present example embodiment, similarly to the first example embodiment, since the control of the manual/automatic driving mode is realized by one angle controller, the amount of data processed by an arithmetic circuit such as a processor can be reduced as compared with the related art. As a result, the cost of the arithmetic circuit can be suppressed.

The example embodiments of the present disclosure can be used for a control device to control an EPS mounted on a vehicle.

Features of the above-described example embodiments and the modifications thereof may be combined appropriately as long as no conflict arises.

While example embodiments of the present disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present disclosure. The scope of the present disclosure, therefore, is to be determined solely by the following claims.