JP4380362B2 - Vehicle steering device - Google Patents

Description

  The present invention relates to a vehicle steering apparatus including an electric motor that generates power for steering steered wheels.

Conventionally, for example, as shown in Patent Document 1 below, three electric motors have been provided in order to provide redundancy in the steering control of steered wheels, and the steered wheels are generated using the power generated by the three electric motors. A steering device for a vehicle to be steered is known.
JP 2003-200840 A

  And when using several electric motors as mentioned above, in order to avoid simultaneous failure of several electric motors, it is common to use several types of electric motors. Further, in this type of electric motor, it is normal to stop the operation of each electric motor at the time of overheating due to the operation of each electric motor to protect each electric motor from overheating. However, if the type of electric motor is different, the heat generation characteristics of each electric motor are different. Specifically, when the electric motor is energized and driven, the temperature of the electric motor rises due to the internal resistance of the electric motor. This temperature rises almost in proportion to the drive current and frequency (excitation frequency). That is, if the type of the electric motor is different, the internal resistance of the electric motor is also different, so that the temperature increase rate is different even at the same current value. Hereinafter, the difference in heat generation characteristics means that the temperature increase rate due to the internal resistance of the electric motor is different, and furthermore, the fact that the heat generation characteristics are high means that the temperature increase rate due to the internal resistance of the electric motor is high. . Due to such a difference in heat generation characteristics, it is difficult to accurately protect each electric motor from overheating, and this accurate heating protection has been conventionally desired. In particular, it is necessary to avoid a situation where a plurality of electric motors are stopped simultaneously for overheat protection.

The present invention has been made in order to cope with the above-described problems. The features of the present invention include three types including at least two types of electric motors that generate power for turning the steered wheels and have different heat generation characteristics. In the vehicle steering apparatus comprising the above-described electric motor and an overheat protection device that protects each electric motor from overheating by stopping the operation of each electric motor during overheating due to the operation of each electric motor, the heating protection device is: Based on the heat generation characteristic of the electric motor having the highest heat generation characteristic among the three or more electric motors and the temperature of each electric motor calculated from the operation state of each electric motor, overheat protection for the operation state of each electric motor is performed. It is in that.

  In this case, the overheat protection device includes, for example, operating state detecting means for detecting the operating state of each electric motor, and the heat generating characteristic of the electric motor having the highest heat generating characteristic with respect to the detected operating state of each electric motor. And applying temperature calculation means for calculating the temperature corresponding to the electric motor having the highest heat generation characteristic for each electric motor, and when any of the calculated temperatures is higher than a predetermined threshold, It is good to comprise with the stop control means which stops the action | operation of the electric motor corresponding to temperature higher than a predetermined threshold value. The operating state of the electric motor corresponds to, for example, the power generated by the electric motor, and is defined by the magnitude of the drive current flowing through the electric motor.

  In the present invention configured as described above, when an abnormality occurs in the electric motor having a low heat generation characteristic or its control device, the electric motor is stopped before being stopped by overheat protection according to the heat generation characteristic. It is possible to minimize the influence on other electric motors due to abnormal operation or stoppage of the same electric motor, especially the electric motor with the highest heat generation characteristics. Can be prevented. Specifically, when an abnormality occurs in the electric motor having a low heat generation characteristic or its control device and an abnormal current flows through the electric motor, when the operation of the electric motor is stopped according to the heat generation characteristic of each electric motor, In an electric motor in which an abnormal current flows, the operation stop is delayed due to low heat generation characteristics. For example, when an electric motor with a drive current flowing in the opposite direction stops due to overheat protection, the influence of abnormal operation of the electric motor tends to appear in other electric motors, particularly those with the highest heat generation characteristics. . When other electric motors are stopped for overheat protection in addition to the electric motor through which the abnormal drive current flows, a situation in which a plurality of electric motors are controlled to stop simultaneously occurs. On the other hand, in the present invention, the heat protection device applies the heat generation characteristic of the electric motor having the highest heat generation characteristic to the operating state of each electric motor, and the electric motor having the highest heat generation characteristic for each electric motor. Each of the temperatures corresponding to the motor is calculated, and when any of the calculated temperatures is higher than a predetermined threshold, the operation of the electric motor corresponding to the temperature higher than the predetermined threshold is stopped. The operating electric motor can be stopped early. As a result, the possibility of avoiding simultaneous stopping of a plurality of electric motors by avoiding the influence on the electric motor that is not operating abnormally increases.

a. First Embodiment Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall schematic diagram of a vehicle steering apparatus according to the present invention.

  This vehicle steering apparatus includes a steering shaft 12 connected to a steering handle 11 so as to integrally rotate at an upper end thereof, and a pinion gear 13 is connected to a lower end of the shaft 12 so as to integrally rotate. The pinion gear 13 meshes with rack teeth formed on the rack bar 14 to constitute a rack and pinion mechanism. Left and right front wheels FW1 and FW2 are connected to both ends of the rack bar 14 so as to be steerable. The left and right front wheels FW1 and FW2 are left and right according to the axial displacement of the rack bar 14 as the steering shaft 12 rotates about the axis. It is steered to.

  The rack bar 14 is driven in the axial direction by the first and second electric motors 21 and 22 for turning assist, and the steering shaft 12 is driven around the axis by the third electric motor 23 for turning assist. It has become. The rotations of the first and second electric motors 21 and 22 are decelerated by the screw feed mechanisms 24 and 25 and converted into a linear motion of the rack bar 14. The rotation of the third electric motor 23 is decelerated by a reduction mechanism 26 made up of a plurality of gears and transmitted to the steering shaft 12. In this case, the first and second electric motors 21 and 22 are configured identically, and their heat generation characteristics are higher than those of the third electric motor 23. Specifically, when the same axial force is generated on the rack bar 14 in the first electric motors 21, 22 and the third electric motor 23, there is a difference in structural heat generation characteristics or the magnitude of the driving current that flows. Because of the difference, as shown in FIG. 2, the temperatures of the first and second electric motors 21 and 22 rise faster than the temperature of the third electric motor 23. 2 indicates a limit temperature Tth as a threshold value for stopping the operation of the first to third electric motors 21 to 23 for heat protection by a process described later.

  The operation and stop of the first to third electric motors 21 to 23 are controlled independently by assist electronic control units 31 to 33 (hereinafter simply referred to as assist ECUs 31 to 33). The assist ECUs 31 to 33 have a microcomputer composed of a CPU, ROM, RAM and the like as main components, and operate the first to third electric motors 21 to 23 by executing the assist control programs shown in FIG. And the first to third electric motors 21 to 23 are protected by executing the first to third heating protection programs shown in FIGS. And these assist ECU31-33 comprises the overheat protection apparatus of this invention in order to aim at the heat protection of the 1st thru | or 3rd electric motors 21-23.

  In order to control the first to third electric motors 21 to 23, drive circuits 34 to 36 are interposed between the assist ECUs 31 to 33 and the first to third electric motors 21 to 23, respectively. . The drive circuits 34 to 36 flow drive currents to the first to third electric motors 21 to 23 in accordance with instructions from the assist ECUs 31 to 33. The drive circuits 34 to 36 include drive current sensors 34a to 36a that detect the drive currents I1 to I3 flowing through the first to third electric motors 21 to 23 and supply them to the assist ECUs 31 to 33, respectively.

  A steering wheel angle sensor 37 and a vehicle speed sensor 38 are also connected to the assist ECUs 31 to 33, respectively. The steering wheel steering angle sensor 37 detects a rotation angle around the axis from the reference position of the steering shaft 12, and outputs the rotation angle as a steering wheel steering angle θ. Note that the steering angle θ of the steering wheel represents the steering angle of the left and right steering wheels by positive and negative. The vehicle speed sensor 38 detects the vehicle speed V.

  Next, the operation of the embodiment configured as described above will be described. The assist ECUs 31 to 33 each execute the assist control program of FIG. 3 every predetermined short time. The assist control program is started in step S10, and the steering wheel steering angle θ is input from the steering wheel steering angle sensor 37 and the vehicle speed V is input from the vehicle speed sensor 38 in step S11. In step S12, the assist torque table stored in the ROM is referred to, and the target assist torque Tr * corresponding to the steering angle θ and the vehicle speed V is calculated. As shown in FIG. 7, the assist torque table stores a target assist torque Tr * that increases as the steering wheel steering angle θ increases and increases as the vehicle speed V decreases. Instead of using the assist torque table, a function indicating the relationship between the steering angle θ, the vehicle speed V, and the target assist torque Tr * is prepared in advance, and the target assist torque Tr is obtained using the function. * May be calculated. Further, instead of or in addition to calculating the target assist torque Tr * according to the steering angle θ and the vehicle speed V, the target assist torque Tr * is calculated by detecting the steering torque (steering torque), the yaw rate, and the like. You may do it.

  After calculating the target assist torque Tr *, the assist ECUs 31 to 33 drive and control the first to third electric motors 21 to 23 via the drive circuits 34 to 36 in step S13, and assist control in step S14. Each program execution is temporarily terminated. In this drive control, the assist ECUs 31 to 33 receive the drive currents I1 to I3 detected by the drive current sensors 34a to 36a, respectively, and the first to third electric motors 21 to 23 receive the target assist torque Tr *. The drive circuits 34 to 36 are controlled so as to be generated. Under these controls, the drive circuits 34 to 36 cause the drive currents I1 to I3 corresponding to the target assist torque Tr * to flow through the first to third electric motors 21 to 23, respectively. The motors 21 to 23 are driven. In this case, since the first and second electric motors 21 and 22 are different from the third electric motor 23, the drive control of the first and second electric motors 21 and 22 by the assist ECUs 31 and 32 and the first and second electric motors 23 and 22 by the assist ECU 33 are performed. 3 The driving control of the electric motor 23 is different in respect of the magnitude of the driving current.

  By such drive control of the first to third electric motors 21 to 23, the first and second electric motors 21 and 22 transmit power to the rack bar 14 via the screw feed mechanisms 24 and 25, thereby the rack bar. 14 is linearly driven in the axial direction. The third electric motor 23 transmits power to the steering shaft 12 via the speed reduction mechanism 26 and rotationally drives the steering shaft 12 about the axis. Thus, when the driver turns the steering handle 11 to steer the left and right front wheels FW1 and FW2, the first to third electric motors 21 to 23 cause the driver to turn the steering handle 11. Assisted, the driver can steer the left and right front wheels FW1, FW2 with a small steering force.

  Next, overheat protection of the first to third electric motors 21 to 23 will be described. The assist ECUs 31 to 33 execute the first to third overheat protection programs shown in FIGS. 4 to 6 every predetermined short time in parallel with the assist control program shown in FIG. The execution of the first overheat protection program is started in step S20 of FIG. 4, and the assist ECU 31 inputs the first drive current I1 from the drive current sensor 34a in step S21. In step S22, the temperature T1 of the first electric motor 21 that changes over time is calculated using the drive current I1. If a little explanation is added about calculation of this temperature T1, temperature T1 is decided by the balance of the emitted-heat amount by energization of drive current I1 of the 1st electric motor 21, and cooling by outside air. Since the heat generation amount is proportional to the square value of the drive current I1, the temperature T1 of the first electric motor 21 is a parameter that represents the square value of the drive current I1 and the heat generation characteristic of the first electric motor 21. It is calculated by executing a low-pass filter process, a first-order lag calculation process or a second-order lag calculation process (a kind of low-pass filter process).

  After calculating the temperature T1 corresponding to the drive current I1 related to the first electric motor 21, it is determined in step S23 whether the temperature T1 is higher than a predetermined limit temperature Tth. If the temperature T1 is equal to or lower than the limit temperature Tth, “No” is determined in step S23, and the execution of the first heating protection program is temporarily ended in step S25. Therefore, in this case, the first electric motor 21 continues to operate, and the turning operation of the steering handle 11 is assisted by the first electric motor 21.

  On the other hand, if the temperature T1 is higher than the limit temperature Tth, “Yes” is determined in step S23, and the process proceeds to step S24. In step S24, the drive circuit 34 is controlled to stop the operation of the first electric motor 21. Thereby, the overheated first electric motor 21 is cooled by outside air, and the first electric motor 21 is protected from the overheating.

  Further, the assist ECU 32 continues to execute the second overheat protection program of FIG. 5 every predetermined short time. This second overheat protection program is composed of steps S30 to S35 similar to steps S20 to S25 of the first overheat protection program of FIG. 4, and is equivalent to the heat generation characteristic of the second electric motor 22 (the heat generation characteristic of the first electric motor 21). ), The temperature T2 related to the second electric motor 22 corresponding to the drive current I2 detected by the drive current sensor 35a is calculated, and the operation stop of the second electric motor 22 is controlled based on the temperature T2. That is, it is the same as the first overheat protection program. Therefore, the second electric motor 22 is protected from the overheating by executing the second overheating protection program.

  Further, the assist ECU 33 continues to execute the third overheat protection program of FIG. 6 every predetermined short time. In the third overheat protection program, after the execution of step S40 is started, the drive current I3 flowing from the drive current sensor 36a to the third electric motor 23 is input in step S41. In step S42, the low-pass filter process using the parameter representing the heat generation characteristic of the first electric motor 21 having the highest heat generation characteristic among the first to third electric motors 21 to 23, or the first-order lag calculation process or By executing a calculation such as a second-order lag calculation process (a kind of low-pass filter process), a temperature T3 ′ relating to the third electric motor 23 corresponding to the first electric motor 21 is calculated for the drive current I3. The temperature T3 ′ is estimated based on the assumption that the drive current I3 flowing through the third electric motor 23 flows through the first electric motor 21 having the highest heat generation characteristics. You can also think that you are doing. Further, since the heat generation characteristics of the first and second electric motors 21 and 22 are the same, low-pass filter processing using a parameter representing the heat generation characteristics of the second electric motor 22, or first-order lag calculation processing or second-order lag calculation. It is the same even if the temperature T3 ′ related to the third electric motor 23 is calculated by executing an operation such as processing (a kind of low-pass filter processing).

  In step S43, it is determined whether the temperature T3 'is higher than the limit temperature Tth. If the temperature T3 ′ is equal to or lower than the limit temperature Tth, “No” is determined in step S43, and the execution of the third overheat protection program is terminated in step S45. Therefore, the steering assist by the third electric motor 23 is performed. Continued. However, if the temperature T3 'is higher than the limit temperature Tth, "Yes" is determined in step S43, and the operation of the third electric motor 23 is stopped by the process of step S44.

  When an abnormality occurs in the third electric motor 21 having a low heat generation characteristic or its control device by executing the third overheat protection program, the overheat protection according to the heat generation characteristic of the third electric motor 23 is not performed. The abnormal operation of the third electric motor 23 can be stopped according to the heat generation characteristic of the first electric motor 21 (or the second electric motor 22) having the highest heat generation characteristic. Since the operation stop of the third electric motor 23 is executed earlier than the overheat protection according to the heat generation characteristic of the third electric motor 23, the first and second electric motors 21 due to the abnormal operation of the third electric motor 23 are executed. , 22 can be minimized, and a situation where a plurality of electric motors are stopped simultaneously can be prevented.

  Specifically, when an abnormality occurs in the third electric motor 23 or the drive circuit 36 having low heat generation characteristics and an abnormal current flows through the third electric motor 23, each of the first to third electric motors 21 to 23 is detected. If the operations of the first to third electric motors 21 to 23 are controlled to stop according to the heat generation characteristics, the operation stop of the third electric motor in which an abnormal current flows is delayed due to low heat generation characteristics. For example, in a state where the third electric motor 23 in which the drive current flows in the opposite direction is stopped due to overheat protection, the first and second electric motors 21 having high heat generation characteristics are affected by the abnormal operation of the third electric motor 23. 22 tends to appear. And when the 1st or 2nd electric motors 21 and 22 stop for overheat protection in addition to the 3rd electric motor 23 in which the abnormal drive current flows, the situation where a plurality of electric motors are stopped and controlled simultaneously Will occur. On the other hand, according to the first embodiment, when the temperature T3 ′ related to the third electric motor 23 becomes higher than the limit temperature Tth by the third overheat protection program, the abnormally operated third electric motor 23 is changed. Stop early. As a result, it is possible to avoid the influence on the first and second electric motors 21 and 22 not operating abnormally and to avoid simultaneous stopping of the plurality of electric motors.

b. Second Embodiment Next, a second embodiment of the present invention will be described. FIG. 8 is an overall schematic diagram of the vehicle steering apparatus according to the second embodiment. In this steering apparatus, instead of the second electric motor 22 and the screw feed mechanism 25 of the first embodiment, the second electric motor 41, a speed reduction mechanism 42 including a plurality of gears, and an output shaft of the speed reduction mechanism 42 are fixed. A mechanism comprising a pinion gear 43 and a rack tooth 44 provided on the rack bar 14 and meshing with the pinion gear 43 is used. The second electric motor 41 is different from the first and third electric motors 21 and 23 of the first embodiment, and the heat generation characteristics thereof are the heat generation characteristics of the first electric motor 21 and the third electric motor as shown in FIG. It is set between the heat generation characteristics of the motor 23. Since other configurations are the same as those in the first embodiment, the same reference numerals as those in the first embodiment are used for the same portions, and descriptions thereof are omitted.

  Also in the second embodiment, the assist ECUs 31 to 33 execute the first electric motor 21 and the second through the drive circuits 34 to 36 by the execution of the assist control program of FIG. 3 similar to the first embodiment. The electric motor 41 and the third electric motor 23 are driven and controlled. Therefore, also in the second embodiment, the driver's steering operation is assisted as in the first embodiment.

  In parallel with the execution of the assist control program, the assist ECUs 31 and 33 execute the first overheat protection program of FIG. 4 and the third overheat protection program of FIG. The overheat protection of the first electric motor 21 and the third electric motor 23 is executed. On the other hand, the assist ECU 32 executes the second overheat protection program of FIG. The second overheat protection program is the same as that in the first embodiment except that the processing in steps S32 and S33 in FIG. 5 is changed to the processing in steps S32 'and S33'.

  In step S32 ′, a low-pass filter process using a parameter representing the heat generation characteristic of the first electric motor 21 having the highest heat generation characteristic among the first to third electric motors 21 to 23, or a first-order lag calculation process or 2 A temperature T2 ′ relating to the second electric motor 41 corresponding to the first electric motor 21 is calculated for the drive current I2 by executing a calculation such as a next delay calculation process (a kind of low-pass filter process). The temperature T2 ′ is estimated based on the assumption that the drive current I2 flowing through the second electric motor 41 flows through the first electric motor 21 having the highest heat generation characteristics. You can also think that you are doing.

  In step S33 ', it is determined whether the temperature T2' is higher than the limit temperature Tth. If the temperature T2 ′ is equal to or lower than the limit temperature Tth, “No” is determined in step S33 ′ and the execution of the second overheat protection program is terminated in step S35. Will continue. However, if the temperature T2 'is higher than the limit temperature Tth, it is determined "Yes" in step S33', and the operation of the second electric motor 41 is stopped by the process of step S34.

  In the second embodiment that operates as described above, when an abnormality occurs in the second electric motor 41 or the drive circuit 35, the overheating protection is not performed according to the heat generation characteristic of the second electric motor 41, but the heat generation characteristic is the highest. The abnormal operation of the second electric motor 41 can be stopped according to the high heat generation characteristic of the first electric motor 21. As for the third electric motor 23, as in the case of the first embodiment, when an abnormality occurs in the third electric motor 23 or the drive circuit 36, the heat generation characteristics of the third electric motor 23 are followed. The abnormal operation of the third electric motor 23 can be stopped according to the heat generation characteristic of the first electric motor 21 having the highest heat generation characteristic, not overheat protection. Therefore, also in the second embodiment, when the operation of the second or third electric motor 41, 23 is abnormal, the operation of the second or third electric motor 41, 23 is stopped. The first and third electric motors 21 and 23 or the first and second electric motors 21 due to the abnormal operation of the second or third electric motors 41 and 23 are executed earlier than the overheat protection according to the heat generation characteristics of the first and second electric motors 21 and 23. , 41 can be minimized, and a situation where a plurality of electric motors are stopped simultaneously can be prevented.

  Furthermore, the present invention is not limited to the first and second embodiments, and various modifications can be employed within the scope of the present invention.

  For example, in the first and second embodiments, the present invention is applied to a steering device for a vehicle including three electric motors 21 to 23 (or 21, 41, 23). However, four or more electric motors are used. The present invention can also be applied to a vehicle steering apparatus provided. In this case, the drive currents (operating states) of all the electric motors are detected, and the heat generation characteristics of the electric motor having the highest heat generation characteristics are applied to the detected drive currents to generate heat for each electric motor. When the temperature corresponding to the electric motor having the highest characteristic is calculated, and any one of the calculated temperatures is higher than a predetermined threshold, the operation of the electric motor corresponding to the temperature higher than the predetermined threshold is performed. What is necessary is just to make it stop.

  In the first and second embodiments, the present invention is applied to the electric motor for applying assist torque to the turning operation of the steering handle 11 of the vehicle. However, the present invention can also be applied to an electric motor that steers wheels in a steer-by-wire steering device. Further, the present invention is also applicable to a steering apparatus for a vehicle that steers steered wheels by a linear operation, such as a joystick, in addition to the steering handle 11.

1 is an overall schematic diagram of a vehicle steering device according to a first embodiment of the present invention. 4 is a graph showing heat generation characteristics of the first to third electric motors of FIG. 1. It is a flowchart of the assist control program each performed by each assist ECU of FIG. 1 and FIG. It is a flowchart of the 1st heating protection program performed by assist ECU for the 1st electric motor of FIG. 1 and FIG. It is a flowchart of the 2nd heating protection program performed by assist ECU for the 2nd electric motor of FIG. It is a flowchart of the 3rd heating protection program performed by assist ECU for the 3rd electric motor of FIG. 1 and FIG. It is a graph which shows the relationship between a steering wheel steering angle and a vehicle speed, and a target assist torque. It is a whole schematic diagram of the steering device of vehicles concerning a 2nd embodiment of the present invention. 9 is a graph showing heat generation characteristics of the first to third electric motors of FIG. 8. It is a flowchart of the 2nd heating protection program performed in assist ECU for the 2nd electric motor of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Steering handle, 12 ... Steering shaft, 13 ... Pinion gear, 14 ... Rack bar, 21-23, 41 ... Electric motor, 31-33 ... Assist ECU, 34a-36a ... Drive current sensor, 37 ... Steering wheel steering angle sensor, 38 ... Vehicle speed sensor.

Claims (3)

Three or more electric motors including at least two types of electric motors each generating power for turning the steered wheels and having different heat generation characteristics, and stopping the operation of each electric motor when overheating is caused by the operation of each electric motor In a vehicle steering device provided with an overheat protection device that protects each electric motor from overheating,
The heating protection device operates each electric motor based on the heat generation characteristic of the electric motor having the highest heat generation characteristic among the three or more electric motors and the temperature of each electric motor calculated from the operation state of each electric motor. A vehicle steering apparatus characterized in that the overheat protection for a state is performed. The overheat protection device,
Operating state detecting means for detecting the operating state of each electric motor;
Applying the heat generation characteristic of the electric motor having the highest heat generation characteristic to the detected operating state of each electric motor, and calculating the temperature corresponding to the electric motor having the highest heat generation characteristic for each electric motor. When,
The system according to claim 1, further comprising stop control means for stopping the operation of the electric motor corresponding to a temperature higher than the predetermined threshold when any of the calculated temperatures is higher than a predetermined threshold. The vehicle steering apparatus as described.   The vehicle steering apparatus according to claim 1 or 2, wherein an operating state of each electric motor is defined by a magnitude of a drive current flowing through each electric motor.

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