JP2001191933A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device having a current suppression function accurately deciding an overload state likely to cause overheat of a motor by lock end steering maintenance or the like to properly suppress a current flowing through an assist motor. SOLUTION: In this steering device, when the current flowing through the assist motor 11 is above a prescribed value and when a state that a rotation speed of the assist motor 11 is below a prescribed value continues until a loss integrated value of the assist motor 11 becomes above a prescribed value, a control circuit 13 executes a current suppression control to reduce the current flowing through the assist motor 11 (steps S1-S5).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric motor having a current suppressing function for accurately judging an overload state in which there is a possibility of overheating of a motor caused by lock-end steering and the like, and precisely suppressing an electric current of an assist motor. It relates to a power steering device.

[0002]

2. Description of the Related Art In general, an electric power steering apparatus used in a small vehicle such as a mini car detects a steering torque generated on a steering shaft by operating a steering wheel with a torque sensor, and is attached to the steering shaft or the like accordingly. An electric current flows from a battery of a vehicle to an assist motor (hereinafter, sometimes simply referred to as a motor in some cases) to generate a steering assist torque. To control the current of the assist motor, four F
Using an H bridge circuit composed of an ET (field effect transistor), the assist motor is driven through the H bridge circuit under the control of a control unit including a microcomputer.
It is driven by the M (pulse width modulation) method.

In this electric power steering apparatus, when an operation is performed to further rotate the steering wheel in the same direction at the maximum steering angle position in any direction (for example, when a so-called lock-end steering operation is performed). )
In the case where the steering wheel is rotated in the direction in which the tire is restrained while the tire is restrained, the steering torque becomes abnormally large, and a current corresponding to the steering torque is simply supplied to the motor. If only control is performed, overheating of the motor and excessive consumption of electric power may occur. For this reason, a current suppression function for judging such an overload state based on the steering torque, the steering speed, and the like to reduce the motor current more than usual is provided from the viewpoint of preventing the motor from overheating. For example, Japanese Patent Application Laid-Open No. H11-43059 discloses an electric power steering that reduces a current supplied to a motor when a state in which a steering torque is equal to or more than a predetermined value and a steering speed is equal to or less than a predetermined value continues for a predetermined time. An apparatus is disclosed.

[0004] In order to surely prevent the motor temperature from rising above the heat-resistant temperature and causing an accident such as motor burnout, the motor temperature rise is monitored, and if it is determined that the temperature rise is remarkable, For example, a fail-safe function (motor protection function) for forcibly stopping the supply of current to the motor is provided in this type of device in the same manner as a general motor drive device. However, once this fail-safe function has been activated, normal assist cannot be performed at all until the motor temperature drops, and the steering torque borne by the driver increases, causing the driver to feel discomfort or malfunction of the device. There is a problem that it is mistakenly determined that Therefore, when the overload state as described above occurs, the occurrence of this state is quickly determined and the current is suppressed in advance, so that the fail-safe function is not operated as much as possible. Is a practical role. In other words, it is the above-mentioned fail-safe function that finally protects the assist motor from overheating and reliably prevents the motor from burning, etc., but also ensures that the driver's comfort is not impaired. In addition, it is an ideal of the current suppressing function that the current of the motor is appropriately suppressed to prevent the motor from being overheated preventively, and that the steering assist torque is always generated as much as possible.

[0005]

However, the current suppressing function of the conventional electric power steering apparatus described above considers variations and fluctuations in the resistance value of the motor and changes over time in the current value of the motor in determining the overload state. Therefore, an overload state that causes overheating of the motor cannot always be accurately determined. For this reason, when the overload state as described above occurs, the operation of the fail-safe function is reliably avoided, and the current suppression function unnecessarily works even when the overload state does not occur as described above. There has been a problem that it is difficult to reliably prevent such malfunctions with high reliability. This is because the amount of heat generated by the motor naturally changes depending on the motor resistance even when the current is the same, and the larger the motor resistance, the larger the amount of heat generated by the motor. In addition, the motor resistance varies from one motor to another, and also fluctuates depending on the motor temperature and the ambient temperature (in general, the motor resistance increases at high temperatures). Further, since the thermal state of the motor actually depends on a change in the resistance value and the current value of the assist motor with time, it is difficult to accurately determine only the temporary current value. For this reason, in the above-described determination of the overload state, it is necessary to take into consideration such a variation and fluctuation of the motor resistance value or a change with time of the motor current (or a steering torque that is a value corresponding to the current). It is difficult to always operate the assist motor at a normal current value and to minimize the occurrence of the malfunction, up to the limit where the assist motor does not become overheated (near the limit where the fail-safe function does not operate). Because.

[0006] For example, in the device disclosed in the above-mentioned publication, when the state where the steering torque is equal to or higher than the predetermined value and the steering speed is equal to or lower than the predetermined value continues for a predetermined time (for example, 3 seconds to 10 seconds), the excessive It is determined that the vehicle is in the load state, and the current supplied to the assist motor is reduced. In other words, regardless of the variation or fluctuation of the motor resistance value and the time-dependent change of the current value (or the steering torque), the current suppression function is activated when the above state continues for a predetermined time. Therefore, when the set value of the predetermined time is set to a large value so as to correspond to, for example, a case where the motor resistance value is small (for example, a case where the motor temperature rising speed is small under a low temperature condition), Although the malfunction that the suppression function works unnecessarily is prevented, in the case of a high-temperature condition, the operation of the current suppression function may be delayed and the above-described fail-safe function may work before the current suppression function works. . Conversely, when the set value of the predetermined time is a large motor resistance value (for example,
If the value is set to a small value so as to correspond to the case where the motor temperature rise rate is high under high temperature conditions), it is possible to eliminate the possibility that the above-mentioned fail-safe function is activated before the current suppression function is activated. In a low-temperature condition, there is a risk of malfunction in which the current suppression function works unnecessarily without the risk of overheating of the motor.

Also, depending on the change with time of the steering torque (or the current value of the motor) after the start of the clocking of the above-mentioned predetermined time, the current suppression function can be realized even though the motor does not actually overheat. There is a risk of malfunction such as unnecessary work. This is because, assuming that the lock-end steering is maintained in the determination of the set value of the predetermined time, the set value of the predetermined time is taken into consideration in consideration that the steering torque further increases after exceeding the predetermined value. Has to be set for a fairly short time. However, in practice, for example, as in the case of slow steering operation on a rough road with a heavy steering wheel, the steering torque slightly exceeds the above-mentioned predetermined value, but changes while maintaining a relatively low value, and the motor may overheat. It may take a long time until the motor is overheated. This is because the current suppression function works. As described above, the current suppression function of the conventional electric power steering apparatus considers variations and fluctuations in the resistance value of the assist motor and changes over time in the current value (or steering torque) of the assist motor in determining the overload state. Therefore, it has not been possible to always accurately determine an overload state that may cause overheating of the assist motor. Therefore, the present invention provides an electric power steering apparatus having a current suppression function for accurately determining an overload state in which there is a risk of overheating of a motor due to lock-end steering or the like and accurately suppressing the current of the assist motor. It is an object.

[0008]

An electric power steering apparatus according to the present invention has an assist motor connected to a steering system of a vehicle to generate a steering assist torque, and the assist motor is provided in accordance with the steering torque of the steering system. In the electric power steering device that controls the current of the steering motor to generate the steering assist torque according to the steering torque, the current of the assist motor or the steering torque is equal to or more than a predetermined value, and the rotational speed of the assist motor or the When the state where the steering speed of the steering system is equal to or less than a predetermined value continues until the integrated loss value of the assist motor becomes equal to or more than a predetermined value,
A current suppression control unit for performing current suppression control for reducing the current of the assist motor is provided.

Here, "the current of the assist motor or the steering torque is equal to or more than a predetermined value" means that the current value of the assist motor or the value of the steering torque that is a value corresponding to this current value indicates that the assist motor is overheated. It means that the state is out of the allowable range which is unlikely (or unlikely) to be reached. Specifically, for example, the current value of the assist motor may be equal to or more than a reference value based on the rated current value. Also,
"The rotational speed of the assist motor or the steering speed of the steering system is equal to or less than a predetermined value" means that the rotational speed of the assist motor or a steering speed that is a value corresponding to this rotational speed becomes a lock end steering state or the like. It means that the value is as small as expected. Specifically, for example, the rotational speed of the assist motor may become zero or close to zero. Further, the “loss integrated value of the assist motor” is, for example, from the time when the current or the steering torque of the assist motor is equal to or more than the predetermined value, and the rotation speed or the steering speed of the assist motor is equal to or less than the predetermined value. , The integrated value of the assist motor loss. Here, the loss of the assist motor means that when the resistance of the assist motor is R and the current flowing through the assist motor is I, RI
² or a value equivalent to RI ² (for example, the product of the terminal voltage V and the current I of the assist motor). Further, “the integrated loss value of the assist motor is equal to or more than a predetermined value” means that the integrated loss value of the assist motor is a value estimated to cause overheating of the assist motor (a value estimated to operate the fail-safe function described above). ).

According to the present invention, the motor resistance value of the assist motor is set as a condition for executing the current suppression control as an integrated loss value of the assist motor (that is, a condition for determining an overload state).
The time condition for executing the current suppression control changes according to the motor resistance value of the assist motor. That is, for example, when the motor temperature is high and the motor resistance value increases accordingly, or when the motor resistance value varies to a large value, the current value of the motor is maintained at the same value as the predetermined value or more. Even if it does, the loss integrated value increases earlier by that amount, and the current suppression control is easily executed. On the other hand, when the motor temperature is low and the motor resistance value is correspondingly reduced, or when the motor resistance value varies to a small value, the motor current value is equal to or greater than the predetermined value. Even if it is maintained, the loss integrated value increases later by that much, making it difficult to execute the current suppression control. In other words, the temporal condition under which the current suppression control is executed changes according to the difference in the amount of heat generated by the assist motor due to the fluctuation or variation in the motor resistance value.

Similarly, the time-dependent change in the current value of the assist motor is also incorporated into the condition for executing the current suppression control as the integrated loss value of the assist motor. The time condition for executing the suppression control changes. For this reason, current suppression control can be performed on the condition that accurate determination of an overload state is performed in consideration of fluctuations and variations in the resistance value of the assist motor and changes over time in the current value of the assist motor. Normal current can always be driven up to the limit just before the function is activated.Conversely, in the case of an overload state where the fail-safe function may be activated, the current suppression control can be executed reliably to suppress the overload state . That is, it is possible to reliably prevent a failure in which the above-described fail-safe function is activated before the current suppression control is activated and a malfunction in which the current suppression control is activated unnecessarily.

In a further preferred aspect of the present invention, the current suppression control means calculates an estimated value of a rotational speed of the assist motor or a steering speed of the steering system from a current and a voltage of the assist motor. The current suppression control is performed based on the estimated value. With such a configuration, since a sensor for detecting the rotation speed or the steering speed of the assist motor is not required, there is an advantage that the size and cost of the device can be reduced accordingly.

[0013] Further, a more preferable configuration of the present invention is that the current suppression control means decreases the current of the assist motor stepwise or continuously according to the magnitude of the integrated loss value of the assist motor. To change it. With such a configuration, fine-grain current suppression according to the degree of the overload state can be performed, and the above-mentioned fail-safe function can be reliably avoided with the minimum possible current suppression. An auxiliary torque can be generated. For this reason, for example, even if the motor current increases and the steering speed decreases due to some factor even if the lock end steering state is not set, the current suppression control is executed. Within the range in which the activation of the fail-safe function can be avoided, a steering assist torque having a value as close to normal as possible according to the degree of the overload state can be generated. The degree of sudden heaviness can be minimized.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. First, an example of a hardware configuration of the electric power steering device will be described with reference to FIG. The device includes an assist motor 11 (hereinafter, sometimes simply referred to as a motor 11 in some cases) that is connected to a steering system of a vehicle and generates a steering assist torque, a control circuit 13 that controls the motor 11 via a drive circuit 12, The vehicle includes a power supply circuit 15 for supplying predetermined power to the control circuit 13 based on an output of a power supply (battery) 14 of the vehicle, and a torque sensor 16 for detecting a steering torque of the steering system. Here, the control circuit 13 corresponds to the current suppression control means of the present invention.

In FIG. 1, reference numeral 17 denotes an ignition switch of the vehicle, which functions as a start switch of the control circuit 13 in this device. The reference numeral 18 indicates the current of the motor 11 (hereinafter referred to as the current).
This is an electrolytic capacitor that backs up the power supply when the motor current (sometimes simply referred to as motor current) increases. Reference numeral 19 denotes a resistor connected to the ground side of the drive circuit 12, and a voltage corresponding to a voltage drop of the resistor 19 is input to the control circuit 13 via the input line 20. Since the voltage value input from the input line 20 is naturally proportional to the current value of the motor 11 (hereinafter simply referred to as the motor current value in some cases), the control circuit 1
3, the motor current value can be detected from this voltage value.
The resistor 19 and the input line 20 substantially constitute a current detecting means 21 for the motor current. 1 are terminal voltage input lines for the control circuit 13 to detect the voltage between the terminals of the motor 11 (hereinafter, sometimes simply referred to as the voltage between the motor terminals). The drive circuit 12, the control circuit 13, the power supply circuit 1,
5. The electrolytic capacitor 18 and the like constitute a control unit 24 of the power steering device.

Here, the drive circuit 12 comprises the above-described H-bridge circuit, and operates by a PWM drive signal output from the control circuit 13. The control circuit 13
Is constituted by a circuit including a microcomputer, and generates a steering assist torque corresponding to a value of the steering torque detected from the detection signal of the torque sensor 16 so as to generate a motor current corresponding to the steering torque. PW
In addition to the control function in the normal state (normal operating state that is not an overload state) for generating the M drive signal to control the drive circuit 12, the overload state is determined and the motor current is changed from the normal state in the overload state. Also, the function of the current suppression control for reducing the power consumption is realized. Further, the power supply circuit 15 changes the voltage of the battery 14 (normally, 12 V to 14 V) to a predetermined voltage (for example, 5 V).
V) and supplies it to the control circuit 13.

Next, an example of the control contents of the control circuit 13 (first embodiment) will be described. The control circuit 13 is activated when the ignition switch 17 as an activation switch is turned on, and performs a series of operations including the following processing.
For example, until the ignition switch 17 is turned off and the normal operation state of the control circuit 13 is stopped, the control circuit 13 is repeatedly executed, for example, at a constant cycle. First, the torque sensor 16
Is performed to calculate a target current value of the motor current according to the value of the steering torque detected from the detection signal of the above. In this calculation, a motor current value for generating a target steering assist torque corresponding to (for example, in proportion to) the steering torque is calculated as a target current value, but the target current value is calculated in consideration of parameters other than the steering torque. The current value (that is, the target steering assist torque) may be obtained. For example, even if the steering torque is the same, there may be a configuration in which the target current value varies depending on the vehicle speed, and the steering assist torque varies slightly depending on the vehicle speed. In recent years, since a means for detecting the vehicle speed is usually provided for every vehicle type, if a signal of the vehicle speed detecting means is also input to the control circuit 13, the control circuit 13 detects the vehicle speed and executes the above calculation. It is possible. Next, the control circuit 13 executes a process (to be described later) for current suppression control, and then generates a PWM drive signal having a duty ratio for realizing the target current value obtained in the processes up to that point, and generates a drive circuit. 12 is controlled. As a result, a current substantially equal to the target current value flows in a predetermined direction of the motor 11, and in a normal state, a steering assist torque in the same direction as the steering torque is generated with a magnitude corresponding to the steering torque, and the steering operation is assisted. Is done.

The control circuit 13 executes a series of processes shown in FIG. 2A as a process for the current suppression control. In this case, these processes are executed as a subroutine to, for example, a main routine in the operation program of the control circuit 13. When this subroutine is started, first, in steps S1 to S3, it is determined whether or not an overload state is present. That is, first, in step S1, the motor current value IM detected by the current detecting means 21 is equal to or more than a predetermined value (hereinafter, referred to as a current reference value), and the rotation speed MV of the motor 11 is set in advance. Predetermined value (hereinafter referred to as rotation speed reference value)
It is determined whether or not the following conditions are satisfied. If these conditions are satisfied, the process proceeds to step S2. If not, the process proceeds to step S6 assuming that there is no overload state. Motor 11 used here
Of the motor current value IM detected by the current detecting means 21 and the terminal voltage input lines 22 and 2
Motor terminal voltage VM detected as a potential difference of 3.
And the resistance value RM of the motor 11 registered in advance based on an experimental value or a design value, the control circuit 13 obtains the resistance by the following equation (1). MV = VM−RM × IM (1) Note that the right side in the above equation (1) is strictly the value of the induced voltage, but since the induced voltage and the rotation speed of the motor have a fixed proportional relationship, The value is the rotation speed M of the motor 11
V.

The predetermined values (the current reference value and the rotation speed reference value) are in the lock-end steering state or the like as described in the section of the means for solving the problems.
Reference numeral 1 is a reference value for determining a state in which there is a risk of overheating. Among them, the current reference value is, for example, a constant value obtained by adding a slight margin to the rated current value of the motor 11, and The speed reference value is, for example, a constant value close to zero. However, these predetermined values (current reference value and rotation speed reference value) do not necessarily need to be set as constant values,
The value may be set by, for example, a data table (or an arithmetic expression) so that the value changes according to another parameter. For example, the smaller the rotation speed MV is, the higher the possibility of the lock end steering state or the like is.
The motor current reference value is set in advance so as to decrease as V is smaller, and it is easier to determine that the motor is overloaded as the rotation speed MV is smaller (that is, in this case, current suppression in step S4 described later is executed). (Easy).

In step S2, the motor loss is calculated and integrated. More specifically, first, the motor current value IM detected by the current detection means 21 at that time,
A product of the motor terminal voltage VM detected as the potential difference between the terminal voltage input lines 22 and 23 at that time is calculated, and this integration result is added to the motor loss integrated value one cycle before as the motor loss at that time. Further, the addition result is updated and registered as a new motor loss integrated value. In addition, 1
If step S6, which will be described later, is executed in the process before the cycle, the value of the motor loss integrated value has been reset to zero, and the value of the motor loss obtained as the above integrated result is directly updated as the motor loss integrated value. You will be registered. In addition, since the rotation speed MV of the motor terminal voltage VM is very small (the induced voltage is very small), the voltage drop in the motor 11 (the voltage of the motor 11) The product of the motor current value IM and the voltage VM between the motor terminals is, after all, the product of the motor current value IM and the motor terminal voltage VM. can be treated as a value) corresponding to RI ² mentioned in the description of the means.

Next, in step S3, it is determined whether or not the motor loss integrated value obtained in step S2 is equal to or greater than a predetermined value (hereinafter referred to as a loss reference value). The process proceeds to step S4 assuming that the vehicle is overloaded, and proceeds to step S7 if it is not overloaded. The loss reference value here is, for example, the motor 1
It is set to a constant value based on a value estimated to cause one overheating. Note that the value of the motor loss integrated value that is estimated to cause overheating of the motor 11 (that is, the value of the motor loss integrated value after the condition of step S1 is satisfied, is not satisfied if the thermal condition of the motor 11 Is actually a constant value, and the temperature of the motor 11 at the time when the determination of step S1 is changed from negative to affirmative and the integration of the motor loss is started is not performed. , At that time or thereafter depending on the ambient temperature. Therefore, when setting the loss reference value as a constant value, the loss reference value should be set on the safe side in consideration of such a fluctuation range. That is, for example, the motor 11 is set to a fixed value that is smaller by the margin than the lowest value of the integrated motor loss value estimated to cause overheating of the motor 11. However, the loss reference value here need not always be a constant value. For example, the optimum value of the loss reference value according to a parameter such as the rotation speed of the motor 11 is set in advance in the form of a data table or the like, and the optimum value of the loss reference value is selected at any time according to the value of this parameter. There may be a configuration used.

Next, in step S4, the value of the target current value coefficient used in step S5 described below is set to a value a less than 1.0.
(For example, 0.5 to 0.6). Where the value a
Is a predetermined constant value, for example. On the other hand, in step S6, the value of the motor loss integrated value is reset to zero. In step S7, the value of the target current value coefficient used in step S5 described later is set to 1.0. Then, in step S5, the aforementioned target current value of the motor current calculated according to the value of the steering torque is corrected with the latest target current value coefficient. That is, the target current value is integrated with the target current value coefficient set in step S4 or S7, and the integration result is updated and registered as a new target current value. By the way, when step S7 is executed without determining the overload state, the target current value coefficient is 1.0, so that the target current value is not substantially corrected.

According to the processing of FIG. 2, from the time when the determination result of step S1 changes from negative to affirmative, step S2 is executed every time the processing is repeated as long as the determination result is affirmative. Then, the motor loss is integrated (in other words, the integrated value of the motor loss is obtained). Then, when the motor loss integrated value, which is the result of the integration (or the result of the integration operation), is equal to or greater than the above-mentioned loss reference value, it is determined that an overload state has occurred, and steps S4 and S5 are sequentially executed via step S3. The target current value for control 11 is corrected downward. Thereby, the actual motor current value is also corrected in the decreasing direction, and the overload state of the motor 11 is suppressed. At this time, since the actual value of the resistance value of the motor 11 is substantially incorporated into the motor loss integrated in step S2, the influence of the fluctuation of the resistance value due to the temperature condition and the variation of the product is excessive. It is included in the determination of the load condition, and the current suppression control (here, step S
4, the time condition for executing S5) changes. That is, for example, the temperature of the motor 11 at the time when the determination in step S1 changes from negative to affirmative is high and its resistance increases accordingly. In this case, even if the motor current value is maintained at the same value equal to or higher than the current reference value, the value of the motor loss calculated as described above becomes a large value from the beginning. It increases quickly, and the result of the determination in step S3 tends to be positive in a short time, and the current suppression control is easily executed. On the other hand, when the motor 11 is at a low temperature and its resistance value is reduced accordingly, even if the motor current value is maintained at the same value equal to or higher than the current reference value, as described above, Since the value of the motor loss calculated in (1) becomes a small value from the beginning, the loss integrated value increases later by that amount, so that the determination result in step S3 tends to be negative for a long time, and the current suppression control becomes difficult to execute ( For example, if the motor current value returns below the current reference value on the way, the current suppression control will not be executed after all.

Similarly, the time-dependent change in the motor current value (the change in the magnitude of the motor current value after the time when the determination result in step S1 changes from negative to affirmative) is also determined in step S1.
The current suppression control (Steps S4 and S5) is incorporated in the conditions for executing the current suppression control as the integrated loss value of the motor 11 calculated in Step 2, and the current suppression control is executed in accordance with such a temporal change of the motor current value. Temporal conditions change. That is, when the motor current value further rises sharply beyond the current reference value, the motor loss calculated in step S2 naturally rises sharply, so that the result of the determination in step S3 becomes earlier accordingly. This changes affirmatively, and the current suppression control is easily executed early. Conversely, when the motor current value slightly exceeds the current reference value and is maintained at that value, the motor loss calculated in step S2 is naturally maintained at a relatively small value. Therefore, it is difficult for the determination result of step S3 to be affirmative even after a long time elapses (for example, if the motor current value returns to the current reference value or less in the middle, the current suppression control will not be executed after all).

Next, another embodiment (second embodiment) of the control contents of the control circuit 13 will be described. Note that the second embodiment has a feature in a part of the processing for current suppression control, and the other processing contents are the same as those of the first embodiment.
The same reference numerals are given to the same contents as those of the embodiment, and the duplicate description will be omitted. The control circuit 13 in the present embodiment performs the processing shown in the flowchart of FIG. 3 as the above-described subroutine processing for current suppression control. What is characteristic here is that after step S31, the motor loss integrated value is determined and evaluated stepwise, and the current suppression is performed stepwise.

First, in step S31, step S2
The motor loss integrated value obtained in step 1 is a predetermined value 1
(Hereinafter referred to as a loss reference value 1). If it is not less than the loss reference value 1, it is determined that a higher overload state is set, and the process proceeds to step S36. Proceed to S32. Next, in step S32, similarly, it is determined whether or not the value of the motor loss integrated value is equal to or greater than a predetermined value 2 (hereinafter referred to as a loss reference value 2). The process proceeds to step S37 assuming that the vehicle is in the overload state, and otherwise proceeds to step S33. Next, in step S33, similarly, it is determined whether or not the value of the motor loss integrated value is equal to or greater than a predetermined value 3 (hereinafter referred to as a loss reference value 3). It is determined that the vehicle is not overloaded, and the process proceeds to step S38.
Proceed to 34. Here, the loss reference values 1 to 3 are, for example, values set as constant values that are smaller by a predetermined margin than the lowest value of the motor loss integrated value estimated to cause overheating of the motor 11. Here, the loss reference values 1 to 3 need not necessarily be constant values. However,
In any case, the magnitude relation between the loss reference values 1 to 3 is as follows: loss reference value 1> loss reference value 2> loss reference value 3.

Next, in step S34, the value of the target current value coefficient used in step S35 described later is set to 1.0. On the other hand, in step S36, a later-described step S3
The value of the target current value coefficient used in 5 is set to a value a1 of less than 1.0.
(For example, 0.0), and in step S37, the value of the target current value coefficient is similarly set to a value a2 less than 1.0.
(For example, 0.5 to 0.6) and step S
At 38, the value of the target current value coefficient is set to a value a3 (for example, 0.7 to 0.8) smaller than 1.0. here,
The values a1 to a3 are, for example, predetermined constant values,
These magnitude relations are a1 <a2 <a3.
Then, in step S35, the aforementioned target current value of the motor current calculated according to the value of the steering torque is corrected with the latest target current value coefficient. That is, steps S34 and S3
The target current value coefficient set in any of 6 to S38 is integrated with the target current value, and the result of the integration is updated and registered as a new target current value.

According to the above-described processing of FIG. 3, the degree to which the current of the motor 11 is reduced changes stepwise in accordance with the magnitude of the integrated loss value of the motor 11, so that the first step shown in FIG.
In addition to the same operation as the embodiment, there are the following advantages. That is, it is possible to finely control the current in accordance with the degree of the overload state, and to avoid the above-mentioned fail-safe function operation with the minimum necessary current control as much as possible and to generate the steering assist torque as much as possible. Becomes possible.

It should be noted that the present invention is not limited to the embodiments described above, and various embodiments are possible. For example, in the processing content of the first embodiment shown in FIG. 2, the value a of the target current value coefficient in step S4 is obtained as, for example, a function of the motor loss integrated value, and is continuously determined according to the magnitude of the motor loss integrated value. May be changed. Also in this case, similarly to the above-described second embodiment, fine current suppression according to the degree of the overload state can be performed. Further, as a parameter of the determination condition in step S1 of FIG. 2, a steering torque equivalent to this can be used instead of the motor current, or a steering speed equivalent to this can be used instead of the motor rotation speed. Good. Further, in the first embodiment, the value of the motor rotation speed used in step S1 is obtained by calculation from the motor current value or the like as described above, but a sensor for detecting the motor rotation speed or the steering speed is provided, The detection value of this sensor may be used. However, in this case, it is necessary to provide wiring from the sensor to the control unit together with the sensor main body in a narrow vehicle space, which leads to an increase in the size and complexity of the device, and thus to a higher cost. From such a viewpoint, a configuration in which the rotational speed or the steering speed of the assist motor is obtained by the estimation calculation as in the first embodiment is excellent.

[0030]

According to the electric power steering apparatus of the present invention, the state in which the current of the assist motor or the steering torque is equal to or higher than a predetermined value and the rotational speed of the assist motor or the steering speed of the steering system is equal to or lower than the predetermined value is determined. A current suppression control means for performing current suppression control for reducing the current of the assist motor when the loss integrated value is continued to be equal to or more than a predetermined value is regarded as an overload state. According to the present invention, the motor resistance value (including the change with time) of the assist motor is incorporated in the condition for executing the current suppression control as the integrated loss value of the assist motor (that is, the condition for determining the overload state), The time condition for executing the current suppression control changes according to the motor resistance value. That is, for example, when the motor temperature is high and the motor resistance value increases accordingly, or when the motor resistance value varies to a large value, the current value of the motor is maintained at the same value as the predetermined value or more. Even if it does, the loss integrated value increases earlier by that amount, and the current suppression control is easily executed. On the other hand, when the motor temperature is low and the motor resistance value is correspondingly reduced, or when the motor resistance value varies to a small value, the motor current value is equal to or greater than the predetermined value. Even if it is maintained, the loss integrated value increases later by that much, making it difficult to execute the current suppression control. In other words, the temporal condition under which the current suppression control is executed changes according to the difference in the amount of heat generated by the assist motor due to the fluctuation or variation in the motor resistance value.

Similarly, the time-dependent change in the current value of the assist motor is also incorporated into the condition for executing the current suppression control as the integrated loss value of the assist motor. The time condition for executing the suppression control changes. For this reason, current suppression control can be performed on the condition that accurate determination of an overload state is performed in consideration of fluctuations and variations in the resistance value of the assist motor and changes over time in the current value of the assist motor. Normal current can always be driven up to the limit just before the function is activated.Conversely, in the case of an overload state where the fail-safe function may be activated, the current suppression control can be executed reliably to suppress the overload state . That is, it is possible to reliably prevent a failure in which the above-described fail-safe function is activated before the current suppression control is activated and a malfunction in which the current suppression control is activated unnecessarily.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of an electric power steering device.

FIG. 2 is a flowchart illustrating an example of processing contents of an electric power steering device.

FIG. 3 is a flowchart showing another example of the processing content of the electric power steering device.

[Explanation of symbols]

 Reference Signs List 11 assist motor 12 drive circuit 13 control circuit (current suppression control means) 16 torque sensor 24 control unit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B62D 119: 00 B62D 119: 00 F term (Reference) 3D032 CC26 DA13 DA15 DA23 DA63 DA64 DC02 DC32 DC34 DD02 DE02 EC23 GG01 3D033 CA16 CA19 CA20 CA21 CA31 5G044 AA01 AA07 AC05 AD01 CA01 CA11 CB01 CE04 5H571 AA03 BB07 CC04 DD01 EE03 GG04 HB01 HD03 HD10 JJ03 JJ22 KK06 LL14 LL16 LL22 LL23 LL29 LL50 MM04

Claims (3)

[Claims] An assist motor connected to a steering system of a vehicle to generate a steering assist torque; controlling an electric current of the assist motor according to a steering torque of the steering system;
In the electric power steering device that generates the steering assist torque according to the steering torque, the current of the assist motor or the steering torque is equal to or more than a predetermined value, and the rotation speed of the assist motor or the steering speed of the steering system is predetermined. Current suppression control means for performing current suppression control for reducing the current of the assist motor when the state of being equal to or less than the value continues until the integrated loss value of the assist motor becomes equal to or greater than a predetermined value. Electric power steering device. 2. The current suppression control unit calculates an estimated value of a rotation speed of the assist motor or a steering speed of the steering system from a current and a voltage of the assist motor, and based on the estimated value, calculates the current suppression. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus performs control. 3. The current suppression control means changes stepwise or continuously the degree of reduction of the current of the assist motor in the current suppression control according to the magnitude of the integrated loss value of the assist motor. The electric power steering device according to claim 1 or 2, wherein: