JP2004122992A - Fault detection method for steering system - Google Patents

Abstract

A steering device failure detection method capable of simply and accurately detecting a failure of a steering device without using a motor terminal voltage Vm and a rotation speed Nm.
Two motors (19A, 19B) that apply force in a direction in which a steered wheel (steering wheel) is steered are PWM-driven motors, and a duty value of a PWM signal applied to the two motors is obtained. Further, an absolute value of a difference between the two duty values is obtained, and a failure of the steering device (electric power steering) 10 is detected on condition that the absolute value of the difference is larger than a predetermined value.
[Selection diagram] FIG.

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a failure detection method for a steering system, and more particularly, to a failure detection method for a steering system in which two motors are provided in a steering system and, for example, steering force assistance is provided to the steering system.
[0002]
[Prior art]
Examples of the steering device include an electric power steering device and a steer-by-wire system (for example, see Patent Document 1). For example, an electric power steering device is a support device that assists a steering force by linking a motor when a driver operates a steering wheel (steering wheel) while driving a car. In the electric power steering device, motor control is performed by using a steering torque signal from a steering torque detection unit that detects a steering torque generated on a steering shaft by a driver's steering operation, and a vehicle speed signal from a vehicle speed detection unit that detects a vehicle speed. The driving of an assisting motor that outputs an auxiliary steering force based on the control operation of a control unit (ECU) is controlled to reduce the driver's manual steering force (for example, see Patent Document 2). In the control operation of the motor control unit, a target current value of a motor current to be supplied to the motor is set based on the steering torque signal and the vehicle speed signal, and a signal (a target current signal) relating to the target current value is actually transmitted to the motor. A difference from a motor current signal fed back from a motor current detector for detecting a flowing motor current is obtained, a proportional / integral compensation process (PI control) is performed on the difference signal, and a PWM signal for driving and controlling the motor is obtained. Is occurring.
[0003]
Conventionally, electric power steering devices have been mainly developed for small vehicles. In recent years, however, it has become particularly necessary to equip large vehicles (such as 2000cc class or more passenger vehicles) with a view to saving fuel consumption and expanding the vehicle control range. Has arisen. When the electric power steering device is applied to a large vehicle, the weight of the vehicle is large, so that a configuration using one motor requires a large motor that outputs a large assisting force. For this reason, the size of the motor becomes large, the mounting layout (mounting ability) on an actual vehicle is deteriorated, and a large motor other than a standard product and a dedicated motor control drive unit are required, thereby increasing the manufacturing cost. Become. Therefore, conventionally, a configuration using two support motors has been proposed as a configuration suitable for the electric power steering device for a large vehicle as described above (for example, see Patent Documents 1 to 3).
[0004]
[Patent Document 1]
Japanese Unexamined Patent Publication No. 2001-525292 (FIG. 1)
[Patent Document 2]
JP 2001-260908 A (paragraphs 0040 and 0041, FIG. 1)
[Patent Document 3]
JP 2001-151125 A (FIG. 1)
[0005]
[Problems to be solved by the invention]
In the case where the electric power steering apparatus is provided with two assisting motors as described above, even if one of the motors fails, the steering force manually operated by the driver by the other motor and the auxiliary steering force by the motor are reduced. There is also an advantage in this respect, since it is possible to reduce the light emission from the case of no light emission. Here, the failure detection of the steering device becomes a problem.
[0006]
FIG. 12 is a block diagram showing an internal configuration of a motor drive control unit 100 in a conventional electric power steering device including one motor. The motor drive control unit 100 includes a gate drive circuit 110, a motor drive circuit 120, and an inter-terminal differential voltage output amplifier 130. The gate drive circuit 110 causes the motor drive circuit 120 to perform a switching operation based on the duty value of the PWM signal. The motor terminal voltage Vm is a voltage measured from a portion where the motor drive control unit 100 and the motor 140 are connected. The measured motor terminal voltage Vm is input to the gate drive circuit 110 via the terminal differential voltage output amplifier 130. In a conventional electric power steering apparatus including one motor 140, a failure is detected by measuring a motor terminal voltage Vm because the following relational expression holds.
[0007]
(Equation 1)
Vm = Im · Rm + Nm · Ke
[0008]
The motor terminal voltage Vm is a product of the voltage Vdd of the motor drive circuit 120 and the duty value D of the PWM signal duty provided to the motor drive circuit 120. Further, Im is a motor current, Rm is a motor internal resistance, Nm is a rotation speed of the motor, and Ke is an induced voltage constant of the motor. In an electric power steering apparatus including one motor, a failure of the apparatus is determined based on whether the above equation is satisfied. However, since the voltage Vm between the motor terminals is measured by the microcomputer through the primary filter, it is difficult to detect the voltage Vm with high accuracy. In addition, since the rotation speed Nm is a parameter that is not directly measured, a failure in consideration of the rotation speed Nm is considered. Judgment was difficult.
[0009]
On the other hand, as described above, in recent years, an electric power steering equipped with two motors has been developed in order to reduce a driver's steering burden on a large vehicle or the like. However, it is not easy to effectively solve the problem based on the motor terminal voltage Vm and the rotation speed Nm as long as the failure detection is performed in the conventional electric power steering having one motor. Therefore, from the knowledge that the above relational expression holds for the two motors, a method of detecting a failure without using the inaccurate motor terminal voltage Vm and the rotational speed Nm is considered.
[0010]
An object of the present invention is to solve the above problem effectively in view of the above problem, and to simply and accurately detect a failure of a steering device without using a motor terminal voltage Vm and a rotation speed Nm. It is an object of the present invention to provide a method for detecting a failure of a steering device which is capable of detecting a failure.
[0011]
Means and action for solving the problem
The steering device failure detection method according to the present invention is configured as follows to achieve the above object.
[0012]
A first method for detecting a failure of a steering device (corresponding to claim 1) is a steering device in which two motors for applying a force in a direction in which a steered wheel is steered are provided. And a step of obtaining a duty value of the PWM signal given to the two motors and a step of detecting a failure of the steering device based on the obtained two duty values.
[0013]
In the steering device failure detection method described above, the duty values of the PWM signals applied to the two motors are determined, and the failure of the steering device is detected based on the determined two duty values. Without using the number Nm, it is possible to detect a failure of the steering device by a digital element based on the duty value of the PWM signal.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
[0015]
The configurations, shapes, sizes, and arrangements described in the embodiments are merely schematically shown to the extent that the present invention can be understood and implemented. Therefore, the present invention is not limited to the embodiments described below, and can be modified in various forms without departing from the scope of the technical idea described in the claims.
[0016]
A representative configuration of an electric power steering device will be described as an example of a steering device according to the present invention with reference to FIGS. FIG. 1 is a view conceptually showing basic components (only one of the two motors is shown) of an electric power steering apparatus of a two-motor type, and FIG. 2 shows two motors and a gear box. FIG. 3 is a diagram showing an external appearance layout of an actual device of a rack shaft provided.
[0017]
The electric power steering device 10 is mounted on, for example, a passenger vehicle. The electric power steering device 10 is configured to apply auxiliary steering torque to a steering shaft 12 and the like connected to a steering wheel 11. An upper end of the steering shaft 12 is connected to the steering wheel 11, and a pinion gear (or pinion) 13 is attached to a lower end. Here, a portion of the lower end of the steering shaft 12 to which the pinion gear 13 is attached is referred to as a pinion shaft 12a. Actually, the upper steering shaft 12 and the lower pinion shaft 12a are connected by a universal joint (not shown). A rack shaft 14 provided with a rack gear 14a that meshes with the pinion gear 13 is disposed. A rack and pinion mechanism 15 is formed by the pinion gear 13 and the rack gear 14a.
[0018]
A rack and pinion mechanism 15 formed between the pinion shaft 12a and the rack shaft 14 is housed in a first gear box 24A. The appearance of the gear box 24A is shown in FIG.
[0019]
Tie rods 16 are provided at both ends of the rack shaft 14, and a front wheel 17 is attached to an outer end of each tie rod 16. The front wheels 17 function as steered wheels of the vehicle.
[0020]
A motor 19A is further provided to the pinion shaft 12a via a power transmission mechanism 18. The power transmission mechanism 18 includes a worm gear provided on an output shaft (worm shaft) 19A-1 of the motor 19A, and a worm wheel fixed to the pinion shaft 12a. The power transmission mechanism 18 is incorporated in the gear box 24A.
[0021]
The steering shaft 12 is provided with a steering torque detector 20. The steering torque detector 20 detects a steering torque applied to the steering shaft 12 when the steering torque generated by the driver operating the steering wheel 11 is applied to the steering shaft 12. The steering torque detector 20 is also incorporated in the gear box 24A. Reference numeral 21 denotes a vehicle speed detection unit that detects a vehicle speed of the vehicle, and reference numeral 22 denotes a control device (ECU) configured by a computer system using a microcomputer or the like. The control device 22 takes in the steering torque signal T output from the steering torque detection unit 20 and the vehicle speed signal V output from the vehicle speed detection unit 21, etc., and controls the motor 19A and the like based on information related to the steering torque and the vehicle speed. A drive control signal SG1 for controlling the rotation operation is output. The motor 19A and the like are provided with a motor rotation angle detector 23. A signal SG2 related to the rotation angle (electrical angle) of the motor rotation angle detection unit 23 is input to the control device 22.
[0022]
In the electric power steering apparatus according to the present embodiment, another motor (19B in FIG. 2) having the same performance as the motor 19A is attached, and is configured as a two-motor type. Another motor 19B is shown in FIG. The motor 19B has the same configuration as the motor 19A, and is controlled by the control device 22.
[0023]
As shown in FIG. 2, the rack shaft 14 is further provided with a second gear box 24B in addition to the above-described first gear box 24A. Like the first gear box 24A, the gear box 24B includes a rack gear formed on the rack shaft 14, a pinion gear that meshes with the rack gear, and a pinion shaft to which the pinion gear is fixed and rotatably supported. Have been. Another motor 19B is attached to the second gear box 24B via a power transmission mechanism 18. The output shaft of the motor 19B has a transmission shaft (worm shaft) as described above, and a worm gear is provided on the transmission shaft, while a worm wheel that meshes with the worm gear is fixed to the pinion shaft.
[0024]
The configuration of the gear box 24B is basically the same as that of the gear box 24A. When the motor 19B is driven, a driving force is transmitted to the rack shaft 14 via an output shaft, a worm gear, a worm wheel, a pinion shaft, a pinion gear, and a rack gear.
[0025]
As described above, the electric power steering apparatus 10 according to the present embodiment includes the two motors 19A and 19B as assisting motors, and is configured to assist the manual steering force. In the above description, the electric power steering device 10 has a steering torque detecting unit 20, a vehicle speed detecting unit 21, a control device 22, a first and a second two gear boxes 24A and 24B, The motors 19A and 19B are provided with two power transmission mechanisms 18 attached thereto.
[0026]
In the above configuration, when the driver operates the steering wheel 11 to perform steering in the traveling direction during traveling of the automobile, the rotational force based on the steering torque applied to the steering shaft 12 is reduced by the lower pinion shaft 12a and the rack. It is converted into linear motion in the axial direction of the rack shaft 14 via the pinion mechanism 15, and further attempts to change (steer) the running direction of the front wheel 17 via the tie rod 16. At this time, at the same time, the steering torque detector 20 attached to the pinion shaft 12a detects a steering torque corresponding to the steering by the driver on the steering wheel 11 and converts it into an electric steering torque signal T. The steering torque signal T is output to the control device 22. The vehicle speed detection unit 21 detects the vehicle speed of the vehicle, converts the vehicle speed into a vehicle speed signal V, and outputs the vehicle speed signal V to the control device 22. The control device 22 generates a motor current for driving the two motors 19A and 19B based on the steering torque signal T and the vehicle speed signal V. The motors 19A and 19B driven by the motor current apply auxiliary steering torque to the rack shaft 14 via the power transmission mechanisms 18 and the gear boxes 24A and 24B, respectively. As described above, the driver's steering force applied to the steering wheel 11 is reduced by driving the two motors 19A and 19B.
[0027]
FIG. 3 is a block diagram showing the internal configuration of the control device. Control device 22 sets a target current based on motor drive control unit 31A for motor 19A, motor drive control unit 31B for motor 19B, failure detection unit 40, steering torque signal T and vehicle speed signal V, and sets target current signals MA, MB. Is output from the target current setting unit 50. The motor drive control unit 31A includes a gate drive circuit 32A and a motor drive circuit 33A, and the motor drive control unit 31B includes a gate drive circuit 32B and a motor drive circuit 33B. The above-described motor current is provided from the motor drive control unit 31A to the motor 19A based on the target current signal MA relating to the target current set by the target current setting unit 50. The gate drive circuit 32A of the motor drive control unit 31A outputs a PWM signal according to a target current signal MA related to a target current set based on the steering torque signal T and the vehicle speed signal V, and outputs a PWM signal based on the duty value of the PWM signal. The switching operation of the motor drive circuit 33A is performed based on this. As a result, the motor current is supplied to the motor 19A. Also in the motor drive control unit 31B for the motor 19B, the gate drive circuit 32B and the motor drive circuit 33B similarly operate according to the target current signal MB related to the target current set based on the steering torque signal T and the vehicle speed signal V. .
[0028]
Here, assuming that the equation (formula 1 described above) that generally holds for the motors is independently established for the two motors 19A and 19B, the following equation is obtained.
[0029]
(Equation 2)
D1 = Im1 · a1 + Nm1 · b1
D2 = Im2 · a2 + Nm2 · b2
[0030]
Here, (Rm1 / Vdd) was set to a1, and (Ke1 / Vdd) was set to b1. D1 is the duty value of the PWM signal duty1 output from the gate drive circuit 32A, Im1 is the motor current value flowing through the motor 19A, Rm1 is the motor internal resistance value of the motor 19A, Nm1 is the motor rotation speed of the motor 19A, and Ke1 is This is the induced voltage constant of the motor 19A. The same applies to the expression corresponding to the motor 19B. The motor internal resistance Rm and the induced voltage constant Ke depend on the motor, and are hereinafter referred to as motor characteristics. Note that the duty value of the PWM signal is a value obtained by dividing the on-time or off-time of one cycle of the PWM signal by the sum of the on-time and the off-time which is one cycle.
[0031]
Further, the gear ratio of the two motors can be expressed by the following equation.
[0032]
[Equation 3]
Nm1 = cNm2
[0033]
From the above relational expression regarding the rotation speed, the theoretical duty value D2 ′ of the duty value D2 of the PWM signal output from the gate drive circuit 32B can be expressed by the following expression according to the duty value D1.
[0034]
(Equation 4)
D2 ′ = Im2 · a2 + (b2 / b1) · c · D1-a1 (b2 / b1) · c · Im1)
[0035]
This general formula is based on the premise that the two motors 19A and 19B are independent, and therefore can be applied to the case where the two motor characteristics (motor internal resistance Rm, induced voltage constant Ke, etc.) are different. Further, assuming that motors having the same performance and characteristics are used (a1 and a2 are the same and b1 and b2 are the same) and two motors apply an auxiliary steering force to the same rack shaft (c is 1), The theoretical duty value D2 'can be expressed by an equation.
[0036]
(Equation 5)
D2 '= D1 + a. (Im2-Im1)
[0037]
Here, since the motor characteristics are the same, a1 and a2 are set to a. Next, on the premise of the above-described formula of the theoretical duty value D2 ', a failure detection method in the case where the load torque applied to the two motors is the same as the first embodiment, and a load torque applied to the two motors as the second embodiment will be described. The following describes a failure detection method in the case where. FIG. 4 is a diagram showing the relationship between load torque and motor current. The vertical axis shows the motor current, and the horizontal axis shows the load torque. MB1 and MB2 each indicate the value of the load torque. It can be seen that when the load torque is different, the motor current is also different.
[0038]
The failure detection method according to the first embodiment when the load torque applied to the two motors is the same will be described below with reference to FIGS. In the first embodiment, since the load torques applied to the two motors are the same, the motor currents are the same as shown in FIG. Therefore, from the equation (5), if the two motors 19A and 19B are operating normally, the theoretical duty value D2 'and the duty value D1 are always the same. Here, when a failure occurs in one of the motors, the load torque applied to the motor changes, and the motor current also changes. As a result, the duty value of the PWM signal determined by feeding back the motor current also changes. Therefore, if a failure occurs in the motor, the theoretical duty value D2 'differs from the duty value D1. From this, it can be seen that the failure determination can be performed by looking at the relationship between the duty values of the PWM signals.
[0039]
FIG. 5 is a block diagram showing the internal configuration of the failure detection unit 40. The failure detection unit 40 includes a reception unit 41 that receives the PWM signal duty1 from the gate drive circuit 32A, a D1 calculation unit 42 that calculates a duty value D1 from the received PWM signal duty1, and a PWM signal duty2 from the gate drive circuit 32B. Receiving section 43, a D2 calculating section 44 for calculating the duty value D2 from the received PWM signal duty2, a comparing section 45 for comparing the duty values D1 and D2, and a failure based on the result of the comparing section 45. It is composed of a judgment unit 46 for making a judgment. The receiving unit 41 transmits the PWM signal duty1 to the D1 calculating unit 42. The D1 calculator 42 calculates the duty value D1 from the PWM signal duty1 and transmits the calculated value to the comparator 45. Here, since the load torques applied to the two motors are the same, the duty value D1 has the same meaning as the above-described theoretical duty value D2 ′ from the equation (5). The receiving unit 43 transmits the PWM signal duty2 to the D2 calculating unit 44. The D2 calculation unit 44 calculates a duty value D2 from the PWM signal duty2, and transmits the duty value D2 to the comparison unit 45. The comparison unit 45 compares the duty value D1 with the duty value D2, and transmits a signal H according to the comparison result to the determination unit 46. The determination unit 46 determines the failure of the steering device according to the signal H related to the received comparison result.
[0040]
FIG. 6 is an operation flowchart of the failure detection unit 40. The failure detection unit 40 receives the PWM signal duty1 from the gate drive circuit 32A and the PWM signal duty2 from the gate drive circuit 32B (step S101). The D1 calculator 42 calculates the duty D1 from the PWM signal, and the D2 calculator 44 calculates the duty D2 from the PWM signal (step S102). In the comparing section 45 of the failure detecting section 40, the absolute value of the difference between the duty value D1 and the duty value D2 is calculated and compared with a predetermined value α (Step S103). When the difference between the duty value D1 and the duty value D2 is equal to or smaller than the predetermined value α, the PWM signal duty1 and the PWM signal duty2 are received again assuming that the difference is not large enough to make a failure determination (NO in step S103). When the difference between the duty value D1 and the duty value D2 is larger than the predetermined value α (YES in step S103), the determination unit 46 determines that the steering device has failed (step S104).
[0041]
Next, a description will be given of a failure determination method for determining that a failure has occurred in the steering device when a time during which the value obtained by the comparison deviates from the predetermined range is equal to or longer than a predetermined time. This failure determination is performed with the same configuration as the configuration shown in FIG. FIG. 7 is an operation flowchart of the failure detection unit 40 in the failure determination method for determining that the steering device has failed when the time during which the value obtained by comparing the duty values deviates from the predetermined range is equal to or longer than a predetermined time. When the failure detection unit 40 operates, first, the failure determination frequency S is set to zero (step S201). Next, the failure detection unit 40 receives the PWM signal duty1 from the gate drive circuit 32A and the PWM signal duty2 from the gate drive circuit 32B (step S202). The D1 calculator 42 calculates the duty D1 from the PWM signal, and the D2 calculator 44 calculates the duty D2 from the PWM signal (step S203). In the comparing section 45 of the failure detecting section 40, the absolute value of the difference between the duty value D1 and the duty value D2 is calculated and compared with a predetermined value α (step S204). If the difference between the duty value D1 and the duty value D2 is equal to or smaller than the predetermined value α, it is determined that the difference is not large enough to make a failure determination, and the number of failure determinations S is set to zero, and the reception of the PWM signal duty1 and the PWM signal duty2 again. This is performed (NO in step S204). If the difference between the duty value D1 and the duty value D2 is larger than the predetermined value α (YES in step S204), the value obtained by comparison is added to the number of failure determinations S out of the predetermined range by one (step S205). The number of failure determinations S after the addition is compared with a predetermined number β (step S206). If the failure determination number S is equal to or less than the predetermined number β, the reception of the PWM signal duty1 and the PWM signal duty2 is performed again (NO in step S206). If the number of failure determinations S is greater than the predetermined number β (YES in step S206), the determination unit 46 determines that the steering device has failed (step S207). Here, the number of times S is used, but the number of times corresponds to time, and the predetermined number of times corresponds to a predetermined time. Therefore, one addition means that a certain time has elapsed.
[0042]
Next, with reference to FIGS. 8 to 11, a failure detection method according to the second embodiment when two motors have different load torques will be described. In the second embodiment, since the load torques applied to the two motors are different, the motor currents are also different as shown in FIG. Therefore, according to the above equation 5, if the two motors 19A and 19B are operating normally, the theoretical duty value D2 'is the sum of the duty value D1 and a · (Im2-Im1). In other words, the theoretical duty value D2 ′ for the other motor 19B is obtained by combining the duty value D1 for the one motor 19A, the current value Im2 supplied to the other motor 19B to a constant a that depends on the motor characteristics, and the one motor It is the sum of the value obtained by multiplying the difference of the current value Im1 supplied to 19A. Therefore, it can be seen from the duty value D1 relating to one motor 19A, the current value Im2 supplied to the other motor 19B and the current value Im1 supplied to the one motor 19A that a failure determination can be made.
[0043]
FIG. 8 is a block diagram showing the internal configuration of the control device 22. In addition, the same reference numerals are given to substantially the same elements as those shown in FIG. 3 of the control device 22 of the first embodiment, and the description will be appropriately omitted. In the failure detection method according to the second embodiment when the load torques applied to the two motors 19A and 19B are different, it is necessary to look at the current Im1 of the current flowing through the motor 19A and the current Im2 of the current flowing through the motor 19B. Therefore, current value detection units 34A and 34B for detecting the current flowing to the motors 19A and 19B are provided. The detected current values Im1 and Im2 of the current flowing through the motors 19A and 19B are input to the failure detection unit 40.
[0044]
FIG. 9 is a block diagram of the internal configuration of the failure detection unit 40. Note that the same reference numerals are given to substantially the same elements as those shown in FIG. 5 of the failure detection unit 40 of the first embodiment, and description thereof will be omitted as appropriate. The failure detection unit 40 receives the current value Im1 and the current value Im2 from the reception unit 41 that receives the PWM signal duty1 from the gate drive circuit 32A, and calculates D1 and the current values Im1 and Im2 calculated from the PWM signal duty1. A theoretical D2 calculator 47 for calculating a theoretical duty value D2 ′, a receiver 43 for receiving the PWM signal duty2 from the gate drive circuit 32B, a D2 calculator 44 for calculating D2 from the PWM signal duty2, and a duty value D1, The comparison unit 45 includes a comparison unit 45 that compares D2 and a determination unit 46 that determines a failure based on the result of the comparison unit 45. The theoretical D2 calculation unit 47 calculates a theoretical duty value D2 ′ from the duty value D1, the current value Im1, and the current value Im2 by the equation (5).
[0045]
The calculated theoretical duty value D2 'is input to the comparing unit 45. The D2 calculation unit 47 calculates D2 from the PWM signal duty2 received by the reception unit 43 and outputs the D2 to the comparison unit 45. The comparing unit 45 compares the theoretical duty value D2 ′ with the duty value D2, and transmits a signal H according to the comparison result to the determining unit 46. The determination unit 46 determines the failure of the steering device according to the signal H related to the received comparison result.
[0046]
FIG. 10 is an operation flowchart of the failure detection unit 40. The failure detection unit 40 receives the PWM signal duty1 from the gate drive circuit 32A and the PWM signal duty2 from the gate drive circuit 32B (step S301). The theoretical D2 calculating unit 47 calculates a theoretical duty value D2 'from the duty value D1 calculated from the PWM signal duty1 (step S302). In the comparing section 45 of the failure detecting section 40, the absolute value of the difference between the duty value D1 and the theoretical duty value D2 'is calculated and compared with a predetermined value α (step S303). When the difference between the duty value D1 and the theoretical duty value D2 'is equal to or smaller than the predetermined value α, the PWM signal duty1 and the PWM signal duty2 are read again assuming that the difference is not enough to determine a failure (NO in step S303). . When the difference between the duty value D1 and the theoretical duty value D2 'is larger than the predetermined value α (YES in step S303), the determination unit 46 determines that the steering device has failed (step S304).
[0047]
Next, a description will be given of a failure determination method for determining that a failure has occurred in the steering device when a time during which the value obtained by the comparison deviates from the predetermined range is equal to or longer than a predetermined time. This failure determination is performed with the same configuration as the configuration shown in FIG. FIG. 11 is an operation flowchart of the failure detection unit 40 in the failure determination method for determining that the steering device has failed when the time during which the comparison value deviates from the predetermined range is equal to or longer than a predetermined time. When the failure detection unit 40 operates, the failure determination frequency S is first set to zero (step S401). Next, the failure detection unit 40 receives the PWM signal duty1 from the gate drive circuit 32A and the PWM signal duty2 from the gate drive circuit 32B (step S402). The theoretical D2 calculator 47 calculates a theoretical duty value D2 'from the duty value D1 (step S403). In the comparing section 45 of the failure detecting section 40, the absolute value of the difference between the duty value D1 and the theoretical duty value D2 'is taken and compared with a predetermined value α (step S404). If the difference between the duty value D1 and the theoretical duty value D2 ′ is equal to or smaller than the predetermined value α, it is determined that the difference is not large enough to make a failure determination, and the number of failure determinations S is set to zero. Reception is performed (NO in step S404). If the difference between the duty value D1 and the theoretical duty value D2 'is larger than the predetermined value α (YES in step S404), the value obtained by the comparison is added to the number of failure determinations S out of the predetermined range by one (step S405). . The number of failure determinations S after the addition is compared with a predetermined number β (step S406). If the failure determination frequency S is equal to or less than the predetermined frequency β, the PWM signal duty1 and the PWM signal duty2 are read again (NO in step S406). If the number of failure determinations S is greater than the predetermined number β (YES in step S406), the determination unit 46 determines that the steering device has failed (step S407). The number here corresponds to time as described above.
[0048]
Based on the description of the above embodiment, the subject of the steering device failure detection method according to the present invention can be further grasped as follows.
[0049]
A first failure detection method for a steering device is a steering device provided with two motors that apply a force in a direction in which a steered wheel is steered, wherein the two motors are PWM-driven motors, and If the load torques are the same, a step of obtaining a first duty value of the PWM signal applied to one motor, a step of obtaining a second duty value of the PWM signal applied to the other motor, This is a method for detecting a failure of the steering device by a step of obtaining an absolute value of a difference between the two duties and a step of determining a failure on condition that the absolute value of the difference is larger than a predetermined value.
[0050]
The second method for detecting a failure of a steering device is that in a steering device provided with two motors for applying a force in a direction in which a steered wheel is steered, the two motors are PWM-driven motors, and When the load torques are different, a step of obtaining a theoretical second duty value in accordance with the first duty value of the PWM signal applied to one motor; and a step of obtaining a second duty value of the PWM signal applied to the other motor. A method for detecting a failure of the steering device by a step of obtaining an absolute value of a difference between the theoretical second duty value and the second duty value, and a step of determining a failure on condition that the absolute value of the difference is larger than a predetermined value. is there.
[0051]
A third method for detecting a failure of a steering device is the method for detecting a failure of the second steering device, wherein the step of obtaining the theoretical second duty value includes the step of determining the first duty value of the PWM signal applied to the one motor and the one of the first motor. This is a method of obtaining from a given first current value and a second current value given to the other motor.
[0052]
The fourth method for detecting a failure in a steering device is the method for detecting a failure in a steering device according to any one of the first to third methods, wherein the time when the absolute value of the difference is larger than a predetermined value is equal to or longer than a predetermined time. This is a method having a step of determining a failure.
[0053]
According to the invention, when the load torques of the two motors are the same, the first duty value of the PWM signal applied to one motor and the second duty value of the PWM signal applied to the other motor are determined. When the absolute value of the difference between the first duty value and the second duty value is greater than a predetermined value, it is determined that the steering device has failed. Therefore, only the comparison of the digital elements based on the duty values of the PWM signals supplied to the two motors is performed. The failure of the steering device can be determined.
[0054]
When the load torques of the two motors are different, a theoretical second duty value is obtained according to the first duty value of the PWM signal applied to one motor, and the second duty value of the PWM signal applied to the other motor is obtained. Find the absolute value of the difference from the value. If the absolute value of the difference is larger than a predetermined value, it is determined that the steering device has failed. Therefore, even if the load torques for the two motors are different, the duty ratio is not used without using the motor terminal voltage Vm and the rotation speed Nm. The failure of the steering device can be detected by a digital element based on the value, and accurate failure determination can be made.
[0055]
Further, when the time during which the absolute value of the difference becomes larger than the predetermined value is equal to or longer than a predetermined time, it is determined that the steering device has failed. Therefore, it is possible to determine the failure of the steering device based on the determination result of the predetermined time. , Reliable.
[0056]
【The invention's effect】
As apparent from the above description, the present invention has the following effects.
[0057]
As described above, according to the steering device failure detection method of the present invention, the duty value of the PWM signal applied to the two motors that apply force in the direction in which the steered wheels are steered is obtained, and based on this duty value, Since the failure of the steering device is detected, the failure can be detected without using the inaccurate motor terminal voltage Vm and the rotational speed Nm.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the overall configuration of an electric power steering apparatus according to the present invention.
FIG. 2 is a diagram illustrating an external layout of an actual device of a rack shaft including a motor and a gear box.
FIG. 3 is a block diagram illustrating an internal configuration of a control device.
FIG. 4 is a diagram showing a relationship between load torque and motor current.
FIG. 5 is a block diagram showing the internal configuration of a failure detection unit.
FIG. 6 is an operation flowchart of a failure detection unit.
FIG. 7 is an operation flowchart of a failure detection unit.
FIG. 8 is a block diagram showing an internal configuration of a control device.
FIG. 9 is a block diagram showing the internal configuration of a failure detection unit.
FIG. 10 is an operation flowchart of a failure detection unit.
FIG. 11 is an operation flowchart of a failure detection unit.
FIG. 12 is a block diagram illustrating an internal configuration of a motor drive control unit in a conventional electric power steering device including one motor.
[Explanation of symbols]
10 Electric power steering device
18 Power transmission mechanism
19A, 19B motor
22 Control device
24A, 24B gear box
31A, 31B Motor drive control unit
32A, 32B Gate drive circuit
33A, 33B Motor drive circuit
34A, 34B Current value detector
40 Failure detector
41, 43 receiving unit
42 D1 calculator
44 D2 calculator
45 Comparison section
46 Judgment unit
47 Theoretical D2 'calculation unit

Claims (1)

In a steering device provided with two motors for applying a force in a direction to steer a steered wheel,
The two motors are PWM driven motors,
Obtaining a duty value of a PWM signal applied to the two motors;
Detecting a failure of the steering device based on the obtained two duty values.

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