JP4967682B2 - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of performing the consistent control of a steering assist force by preventing a fuse from being blown in advance. <P>SOLUTION: The motor current command value Ir in which the future current value of an on-vehicle battery 17 is within a predetermined current limit value I<SB>th</SB>is calculated based on at least the detected torque value T, and an electric motor 12 is drive-controlled based on the motor current command value Ir. When the actual battery current I<SB>bat</SB>exceeds the current limit value I<SB>th</SB>, the limit control to limit the motor current command value Ir is performed, and not only the battery current I<SB>bat</SB>but also the temperature (FET temperature) of an element of a motor drive circuit is incorporated in the returning condition from the limit control to the normal control. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an electric power steering apparatus that applies a steering assist force to a steering system, and more particularly, to an electric power steering apparatus that suppresses a blown fuse caused by a battery current exceeding a limit value.

Conventionally, a power limit value corresponding to the remaining battery level is calculated, and the drive motor target torque is limited so that the power does not exceed the power limit value. 2. Description of the Related Art An electric vehicle drive control device that prevents a chute from occurring is known (see, for example, Patent Document 1).
Further, in a power supply device to which a plurality of electric loads are connected, a change in the power supply voltage is predicted based on the battery state and the operating state of the electric load, and when the predicted power supply voltage is smaller than a predetermined minimum voltage, It is known that the voltage is reduced in the power supply system even when a large-capacity electric load is applied by limiting the current (for example, Patent Document 2).

Furthermore, the priority of power supply for a plurality of electric loads is changed based on the vehicle state including the state of the electric load, and the total supply power supplied to each electric load can be supplied based on the priority. A vehicle load drive control device that distributes power to each electric load so as not to exceed power is known (for example, Patent Document 3).
Further, in a vehicle power supply apparatus comprising: a battery that supplies power to a plurality of electrical loads through a power line; and a generator that supplies power to the battery and each of the electrical loads through the power line, a voltage command value range of the power line It is known that the charging / discharging power range of the battery corresponding thereto is predicted, and the generated power of the generator or the power consumption of each electric load is adjusted so that the actual charging / discharging power falls within this charging / discharging power range. (For example, Patent Document 4).
JP 2003-259509 A JP 2004-194364 A JP 2004-194495 A JP 2004-249900 A

  However, in each of the above conventional devices, only the feedforward control is performed to design the current command value so that the battery current does not exceed the design target value, and the actual battery current is not monitored. If the battery current exceeds the design target value due to environmental conditions, it may not be possible to prevent the fuse from being blown beforehand.

  Accordingly, an object of the present invention is to provide an electric power steering apparatus that can perform stable steering assist force control by preventing a fuse from being blown beforehand.

In order to solve the above problems, an electric power steering apparatus according to claim 1, an electric power steering in g apparatus comprising an electric motor for applying a steering assist force to reduce the steering load of a driver to a steering system, Steering torque detection means for detecting steering torque, and a drive command value for calculating a drive command value for the electric motor such that a future current value of the in-vehicle battery is within a predetermined current limit value based on at least the steering torque Calculation means; motor control means for driving and controlling the electric motor based on the drive command value; current detection means for detecting or estimating an actual current value of the in-vehicle battery; and battery current value detected by the current detection means when There is exceeded the current limit value, a command value limiting means for limiting the driving command value, temperature for detecting the temperature of the element of the driving circuit of the electric motor When the temperature detected by the detection means and the temperature detection means is lowered to a temperature lower than the temperature at the time when the restriction of the drive command value by the command value restriction means is started by the command value restriction means, And a restriction releasing means for releasing the restriction of the current command value .

Furthermore, the electric power steering in g apparatus according to claim 2, in the invention according to claim 1, and a voltage detecting means for detecting a voltage value of the battery, the battery voltage value detected by said voltage detecting means to a predetermined voltage And a second restriction release means for releasing the restriction of the current command value by the command value restriction means when boosted.

According to the electric power steering apparatus of the present invention, the actual battery current is monitored in addition to the feedforward control for setting the current command value of the electric motor so that the future battery current is within the predetermined current limit value. Thus, the feedback control for limiting the current command value of the electric motor is performed, so that it is possible to prevent the fuse from being blown and to perform stable steering assist force control. In addition, since the temperature of the element of the drive circuit of the electric motor is taken into the return condition from the restriction control of the current command value of the electric motor to the normal control, it is possible to efficiently supply power and suppress battery current consumption. Thus, the battery current can be more effectively suppressed below the current limit value.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram showing an embodiment of an electric power steering apparatus according to the present invention.
In the figure, reference numeral 1 denotes a steering wheel, and a steering force applied to the steering wheel 1 from a driver is transmitted to a steering shaft 2 having an input shaft 2a and an output shaft 2b. The steering shaft 2 has one end of the input shaft 2a connected to the steering wheel 1 and the other end connected to one end of the output shaft 2b via a torque sensor 3 as steering torque detecting means.

  The steering force transmitted to the output shaft 2 b is transmitted to the lower shaft 5 via the universal joint 4 and further transmitted to the pinion shaft 7 via the universal joint 6. The steering force transmitted to the pinion shaft 7 is transmitted to the tie rod 9 via the steering gear 8 and steers steered wheels (not shown). Here, the steering gear 8 is configured in a rack and pinion type having a pinion 8a connected to the pinion shaft 7 and a rack 8b meshing with the pinion 8a, and the rotational motion transmitted to the pinion 8a is linearly moved by the rack 8b. It has been converted to movement.

A steering assist mechanism 10 for transmitting a steering assist force to the output shaft 2b is connected to the output shaft 2b of the steering shaft 2. The steering assist mechanism 10 includes a reduction gear 11 coupled to the output shaft 2b, and an electric motor 12 coupled to the reduction gear 11 and generating a steering assist force with respect to the steering system.
The torque sensor 3 detects a steering torque applied to the steering wheel 1 and transmitted to the input shaft 2a, and a torsional angle displacement of a torsion bar (not shown) in which the steering torque is interposed between the input shaft 2a and the output shaft 2b. The torsional angular displacement is detected by, for example, a potentiometer. The torque detection value T output from the torque sensor 3 is input to the controller 15.

The controller 15 operates by being supplied with power from a vehicle-mounted battery 17 (for example, the rated voltage is 12V). The negative electrode of the battery 17 is grounded, and the positive electrode is connected to the controller 15 via an ignition switch 18 and a fuse 19 for starting the engine.
Further, the electric motor 12 of the present embodiment is, for example, a three-phase brushless motor, and as shown in FIG. 2, one end of the U-phase coil Lu, the V-phase coil Lv, and the W-phase coil Lw are connected to each other to form a star connection. The other ends of the coils Lu, Lv, and Lw are connected to the controller 15, and motor drive currents Iu, Iv, and Iw are individually supplied. The electric motor 12 includes a rotor position detection circuit 13 that includes a resolver, an encoder, and the like that detect the rotational position of the rotor.

  As shown in FIG. 2, the controller 15 receives the steering torque T detected by the torque sensor 3 and the vehicle speed detection value V detected by the vehicle speed sensor 16, and the rotor detected by the rotor position detection circuit 13. A motor drive current detection value Iud output from the current detection circuit 22 that receives the rotation angle θ and further detects the motor drive currents Iu, Iv, and Iw supplied to the phase coils Lu, Lv, and Lw of the electric motor 12. Ivd and Iwd are input. In addition, the temperature of a field effect transistor (FET), which will be described later, detected by a temperature sensor 26 as temperature detecting means is also input to the controller 15.

  The controller 15 executes a current command value calculation process, which will be described later, and a motor that is a drive command value of the electric motor 12 for generating a steering assist force according to the steering torque T and the vehicle speed detection value V by the electric motor 12. For example, a control arithmetic unit 23 configured by a microcomputer that outputs a current command value Ir, a motor drive circuit 24 configured by a field effect transistor (FET) that drives the electric motor 12, and a control arithmetic unit 23 output the current command value Ir. And an FET gate drive circuit 25 that executes a pulse width modulation (PWM) control process based on the motor current command value Ir and controls the gate current of the field effect transistor of the motor drive circuit 24.

In the present embodiment, in addition to the feedforward control for setting the motor current command value so that the future battery current does not exceed the current limit value, the control arithmetic device 23 detects or estimates the actual battery current and It is assumed that feedback control is performed to limit the motor current command value so that the battery current does not exceed the current limit value.
In FIG. 2, the motor drive circuit 24 and the FET gate drive circuit 25 correspond to the motor control means.

  FIG. 3 is a flowchart showing a current command value calculation processing procedure executed by the control calculation device 23. This current command value calculation process is executed as a timer interrupt process at predetermined intervals. First, in step S1, it is determined whether or not a motor current command value limiting process is being executed. Here, it is determined whether or not the limit processing flag FL is set to “1” indicating that the motor current command value is being limited. When FL = 0, the motor current command value is limited. If it is determined that it is not broken, the process proceeds to step S2. If FL = 1, the process proceeds to step S10 described later.

In step S2, the control arithmetic unit 23 reads various data and proceeds to step S3. Specifically, the torque detection value T detected by the torque sensor 3, the vehicle speed detection value V detected by the vehicle speed sensor 16, the motor drive current detection values Iud, Ivd and Iwd detected by the current detection circuit 22, and the rotor position detection circuit 13 The rotor rotation angle θ detected in is read.
In step S3, the control arithmetic unit 23 calculates a motor current command value Ir based on the various data read in step S2.

Specifically, first, referring to a characteristic diagram showing the correspondence between the torque detection value T, the vehicle speed detection value V, and the motor current, the motor current command value Ir ₀ is set based on the torque detection value T and the vehicle speed detection value V. To do. Here, in the above characteristic diagram, the motor current command value Ir ₀ increases as the vehicle speed V decreases, and the motor current command value Ir ₀ increases as the steering torque T increases. When the steering torque T exceeds a certain value, the motor current command value Ir ₀ increases. The current command value Ir ₀ is set so as not to increase any more.

Then, a differential value Id for feed forward control by differentiating the motor current command value Ir _0, the current deviation ΔI between the motor current command value Ir ₀ and the motor drive current detection value I, proportional calculation processing a current deviation ΔI A proportional value ΔIp for proportional compensation control and an integral value ΔIi for integral compensation control obtained by integrating the current deviation ΔI are calculated. Next, the motor current command value Ir ₁ (= Id + ΔIp + ΔIi) is calculated by adding the differential value Id, the proportional value ΔIp, and the integral value ΔIi.

Then, the motor current command value Ir ₁ and compared with the command value limiting value Ir _th, when the motor current command value Ir ₁ is the command value larger than the limit value Ir _th is command value limiting value Ir _th the motor current is set as the command value Ir, if the motor current command value Ir ₁ is equal to or less than the command value limiting value Ir _th sets a motor current command value Ir ₁ as a motor current command value Ir.
Here, the command value limit value Ir _th is set so that, for example, the power supplied to the battery 17 does not exceed the suppliable power (power limit value) of the battery 17 determined by the operating state of the steering assist force control, etc. This is the limit value of the motor current command value Ir.

That is, here, the battery current consumption is determined by performing the feedforward control and setting the motor current command value Ir. In other words, the motor current command value Ir is set so that the future battery current I _bat is suppressed within the current limit value I _th at which the battery 17 operates stably without causing the fuse to blow.
Next, in step S4, the control arithmetic unit 23 obtains the motor rotation speed ω based on the rotor rotation angle θ, and proceeds to step S5.

In step S5, the control arithmetic unit 23 estimates the battery current _Ibat . Here, it is assumed that the battery current I _bat is estimated based on the relational expression of the energy balance of the battery power shown in the following equation.
V _bat · I _bat = I _bat ² (R _h + R _dc ) + (3/2) ( _id ² + i _q ² ) (R _m + R _ac + R _acme ) + i _q K _m ω + P _loss (1)
Here, as shown in FIG. 4, V _bat is the battery voltage, R _h is the battery harness resistance, R _dc is the ECU internal DC circuit resistance, i _d is the motor d axis current, and i _q is the motor q axis current (weakening electromagnetic wave). ), R _m is motor terminal resistor, R _ac is AC circuit resistance of the internal ECU, R _acme the motor harness resistance, K _m is the torque constant, P _loss is an energy loss such as iron loss of the motor.

Next, in step S6, the control arithmetic unit 23 determines whether or not the battery current I _bat estimated in step S5 is smaller than the current limit value I _th . When I _bat <I _th , it is determined that the battery current I _bat is within the current limit value I _th and it is not necessary to limit the current command value Ir, and the process proceeds to step S7, where I _bat ≧ I _th If so, the process proceeds to step S8 described later.

In step S7, the control arithmetic unit 23 outputs the current command value Ir to the FET gate drive circuit 25, and ends the current command value calculation process.
In step S8, the control arithmetic unit 23 sets the limit process flag FL to “1” indicating that the current command value limit process is being performed, and proceeds to step S9.
In step S9, the control arithmetic unit 23 performs a process of limiting the current command value Ir, and proceeds to step S7. Here, it is assumed that the current command value Ir is limited by a predetermined amount (for example, 10%).

In step S10, the control arithmetic unit 23 reads the FET temperature inside the ECU detected by the temperature sensor 26, and proceeds to step S11.
In step S11, the control arithmetic unit 23 determines whether or not the FET temperature has dropped below a predetermined temperature after starting the current command value limiting process. Here, the predetermined temperature is set to, for example, 5 ° C. lower than the temperature at which the current command value limiting process is started. When it is determined that the temperature is lower than the predetermined temperature, the process proceeds to step S12. When it is determined that the temperature is not lower than the predetermined temperature, the process proceeds to step S9.

In step S12, the control arithmetic unit 23 estimates the battery current I _bat as in step S5, and _proceeds to step S13.
In step S13, as in step S6, the control arithmetic unit 23 determines whether or not the battery current I _bat is smaller than a preset current limit value I _th . If I _bat <I _th , step S14 is performed. If I _bat ≧ I _th , the process proceeds to step S9.

In step S14, the control arithmetic unit 23 resets the limit process flag FL to “0” indicating that the current command value limit process is not being performed, and proceeds to step S3.
In FIG. 3, the process of step S3 corresponds to the drive command value calculating means, the processes of steps S5 and S12 correspond to the current detecting means, the processes of steps S6, S8 and S9 correspond to the command value limiting means, The processes of S11, S13, and S14 correspond to the restriction releasing unit.

Next, the operation and effect of the first embodiment will be described.
Assume that the host vehicle is turning on a curved road. In this case, steering assist force control for generating a steering assist force according to the torque detection value T detected by the torque sensor 3 and the vehicle speed detection value V detected by the vehicle speed sensor 16 is performed. At this time, the control calculation device 23 calculates a motor current command value Ir for generating the steering assist force by the electric motor 12 in step S3 of FIG. The motor current command value Ir calculated here is a value designed by feedforward control so that the battery current does not exceed the current limit value. Then, to estimate the current battery current I _bat at step S5, when the battery current I _bat is assumed not to exceed the current limit value I _th, the process proceeds from step S6 to step S7, calculated in step S3 The motor current command value Ir is output to the FET gate drive circuit 25.

Therefore, in the FET gate drive circuit 25, a pulse width modulation (PWM) control process is executed based on the motor current command value Ir, and the drive current supplied to the electric motor 12 is controlled. As a result, the torque generated by the electric motor 12 is converted into the rotational torque of the steering shaft 2 via the reduction gear 11, and the driver's steering force is assisted.
Thus, since the motor current command value Ir is designed so that the battery current I _bat does not exceed the current limit value I _th by feedforward control, it is possible to prevent the fuse from being blown and perform stable steering assist force control. it can.

By the way, feedback control is performed based on the deviation between the battery current I _bat and the current limit value I _th to set the motor current command value Ir so that the battery current I _bat is within the current limit value I _th. In this case, however, there is a possibility that overshoot occurs in the battery current I _bat due to a delay in response, and the time until the battery current I _bat does not exceed the current limit value I _th may be increased.

On the other hand, in this embodiment, by designing the motor current command value Ir so that the battery current I _bat is within the current limit value I _th by feedforward control, the responsiveness is improved and the battery current I _bat is increased. The overshoot is prevented from occurring.
However, if the motor current command value Ir is simply designed by performing Ford forward control, the battery current I _bat may exceed the current limit value I _th depending on environmental conditions. in addition to the design of the motor current command value Ir according to the actual motor current command value Ir feedback correction by monitoring the battery current I _bat, the battery current I _bat reliably current limit value I _th within suppress so in the To.

That is, when the normal steering assist force control is performed without performing the feedback correction, if the battery current I _bat exceeds the current limit value I _{th due} to environmental conditions, the control arithmetic unit 23 will 3 from step S6 to step S8, the restriction process flag FL is set to “1” which means that the restriction process of the motor current command value is performed. In step S9, the motor current command value Ir is limited (for example, limited by 10%). In step S7, the limited motor current command value Ir is output to the FET gate drive circuit 25. Thereby, limit control of the motor current command value is started.

Thus, estimates or detects the actual battery current I _bat, so limiting the motor current command value Ir is when the actual battery current I _bat exceeds the current limit value I _th, the battery current I _bat Thus, it is possible to reliably prevent the fuse from being blown due to the battery current I _bat exceeding the current limit value I _th .
Thereafter, assuming that the FET temperature of the motor drive circuit falls below a predetermined temperature after starting the limit process of the motor current command value, and the battery current I _bat returns to within the current limit value I _th , in step S11 Yes, it is determined Yes in step S13, the restriction process flag FL is reset to “0” in step S14, and the restriction process of the motor current command value is released. Therefore, the control returns to the normal steering assist force control based on the unrestricted motor current command value Ir calculated in step S3.

When the FET temperature is lowered, the harness resistance value and the resistance value inside the ECU are lowered, so that consumption of the battery current I _bat can be reduced. Accordingly, by incorporating not only the battery current value but also the FET temperature into the return condition from the limit control state of the motor current command value to the normal control, the battery current I _bat is more effectively suppressed to the current limit value I _th or less. It will be.

  As described above, in the first embodiment, in addition to the feedforward control for determining the consumed battery current based on the motor current command value, the feedback control for monitoring the actual battery current and limiting the motor current command value is performed. Thus, the battery current can be reliably suppressed below the current limit value and the fuse capacity can be suppressed within the design value, and the fuse blow can be surely prevented and stable steering assist force control can be realized. In addition, accuracy can be improved while ensuring high responsiveness.

In addition, since the FET temperature is taken into the return condition from the limit control of the motor current command value to the normal control, the power supply can be efficiently performed and the consumption of the battery current can be suppressed, and the battery current is more effectively limited. It can be suppressed below the value.
Furthermore, since the battery current is estimated by the relational expression of the energy balance of the battery power, it is not necessary to provide a current sensor or the like for detecting the battery current, and the cost can be reduced.

Next, a second embodiment of the present invention will be described.
In the second embodiment, the FET temperature is set as a return condition to normal steering assist force control in the first embodiment described above, whereas the battery voltage is set as a return condition to normal steering assist force control. It is what you do.
That is, as shown in FIG. 5 in the command value limiting process procedure executed by the control arithmetic device 23 of the second embodiment, step S10 is detected in the command value limiting process shown in FIG. 3 is executed except that step S11 is replaced with step S22 for determining whether or not the battery voltage has been boosted to a predetermined voltage. Therefore, steps that execute the same processing as in FIG. 3 are given the same step numbers, and the description will focus on the different portions of the processing.

In step S21, the control arithmetic unit 23 detects the battery voltage V _bat with a voltage sensor or the like, and _proceeds to step S22.
In step S22, the control arithmetic unit 23 determines whether or not the battery voltage _Vbat detected in step S21 has been boosted to a predetermined voltage (for example, 12V). When it is determined that the voltage has been boosted to a predetermined voltage, the process proceeds to step S12. When it is determined that the voltage has not been boosted to the predetermined voltage, the process proceeds to step S9.

In FIG. 5, the process of step S21 corresponds to the voltage detection means, and the processes of steps S22, S13, and S14 correspond to the second restriction release means.
Next, operations and effects of the second embodiment will be described.
Assuming that the host vehicle is turning on a curved road, the electric motor 12 is driven based on a motor current command value Ir for generating a steering assist force according to the torque detection value T and the vehicle speed detection value V. By being controlled, a steering assist force that assists the steering force of the driver is applied to the steering system, and normal steering assist force control is performed.

If the battery current I _bat exceeds the current limit value I _th due to environmental conditions from this normal control state, the control arithmetic unit 23 determines No in step S6 of FIG. The processing flag FL is set to “1”. In step S 9, the motor current command value Ir corresponding to the torque detection value T and the vehicle speed detection value V is limited (for example, limited by 10%), and is output to the FET gate drive circuit 25. As a result, steering assist force control based on the limited motor current command value Ir is started.

Thereafter, when the battery voltage V _bat is gradually increased to reach a predetermined voltage (for example, 12 V) and the battery current I _bat is restored within the current limit value I _th , Yes in step S21 and Yes in step S13. In step S14, the restriction process flag FL is reset to “0”, and the restriction process for the motor current command value is canceled. Therefore, the control returns to the normal steering assist force control according to the unrestricted motor current command value Ir calculated in step S3.

When the battery voltage V _bat rises, naturally the consumption of the battery current I _bat can be reduced. Therefore, by incorporating the battery voltage value not battery current value only a return condition to the normal control from the restriction control state of the motor current command value, is more effectively battery current suppression below I _bat current limit value I _th Will be.
Thus, in the second embodiment, since the battery voltage is taken into the return condition to the normal control, it is possible to efficiently supply power and suppress the consumption of the battery current. It can be suppressed below the current limit value.

In each of the embodiments described above, the battery current I _bat has been described based on the relational expression shown in the equation (1). However, the motor current detection value (phase) via the A / D converter is described. It can also be calculated from the current peak hold value). Further, the battery current I _bat can be directly detected by a current sensor or the like.
In each of the above embodiments, the FET temperature is measured using the temperature sensor. However, the energization current is measured by the current sensor provided in the FET, and the FET temperature is estimated based on the current sensor value. You can also In this case, the thermal characteristics of the temperature rise value of the FET with respect to the energizing current may be tabulated in advance.

1 is a schematic configuration diagram of a vehicle in an embodiment of the present invention. It is a block diagram which shows the structure of the controller in this embodiment. It is a flowchart which shows the command value restriction | limiting process performed with the control arithmetic unit of 1st Embodiment. It is a conceptual diagram explaining a motor drive circuit and its peripheral parameters. It is a flowchart which shows the command value restriction | limiting process performed with the control arithmetic unit of 2nd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 2 ... Steering shaft, 3 ... Torque sensor, 10 ... Steering assist mechanism, 11 ... Reduction gear, 12 ... Electric motor, 15 ... Controller, 16 ... Vehicle speed sensor, 17 ... Battery, 18 ... Ignition switch, 19 ... Fuse, 22 ... Current detection circuit, 23 ... Control arithmetic unit, 24 ... Motor drive circuit, 25 ... FET gate drive circuit, 26 ... Temperature sensor

Claims (2)

The electric power steering in g apparatus comprising an electric motor for applying a steering assist force to reduce the steering load of a driver to a steering system,
Steering torque detection means for detecting steering torque, and a drive command value for calculating a drive command value for the electric motor such that a future current value of the in-vehicle battery is within a predetermined current limit value based on at least the steering torque Calculation means; motor control means for driving and controlling the electric motor based on the drive command value; current detection means for detecting or estimating an actual current value of the in-vehicle battery; and battery current value detected by the current detection means When the current exceeds the current limit value, the command value limiting means for limiting the drive command value, the temperature detection means for detecting the temperature of the element of the drive circuit of the electric motor, and the temperature detected by the temperature detection means However, when the temperature of the drive command value by the command value limiting means is reduced to a temperature lower than the temperature at the time when the limit of the drive command value is started, the current by the command value limiting means An electric power steering apparatus characterized by comprising a restriction canceling means for canceling the limitation of the decree value.   A voltage detection means for detecting a voltage value of the vehicle-mounted battery, and a second restriction release for releasing the restriction of the current command value by the command value restriction means when the battery voltage value detected by the voltage detection means is boosted to a predetermined voltage The electric power steering apparatus according to claim 1, further comprising: means.

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