JPH0248271A - Motor operated power steering device - Google Patents

Abstract

PURPOSE:To arrange so as to be able to respond immediately to the sudden change of a steering torque, by adding to a reference electric current value a corrected electric current value calculated according to a steering torque variation, and making its result the drive electric current value of a motor generating a steering supporting torque. CONSTITUTION:The size and direction of the steering torque of a steering system are detected by means of a steering torque detecting means, and a reference electric current value based upon these steering torque detection values, is determined by means of a reference electric current value determining means. And, at a reference electric current value limiting means, its size is limited so that the reference electric current value may not surpass a predetermined electric current value. Meanwhile, a steering torque variation detecting means detects the variation of the steering torque, and at the same time, a corrected electric current value which is in accordance with this steering torque variation detection value, is determined by a corrected electric current value determining means. And at a drive electric current value determining means, a drive electric current value is determined by the reference electric current value and the corrected electric current value being added or the like, and a drive means drives a motor according to this drive electric current value. As a result, a steering supporting torque is generated at the steering system, and the operation of steering can be conducted lightly.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electric power steering device that applies steering assist torque to a steering system using the output of an electric motor, and in particular, is designed to provide a stable steering feeling. be.

[Conventional technology]

Examples of conventional electric power steering devices include:
The one described in Japanese Unexamined Patent Publication No. 62-29465 is known.

This conventional technology operates an electric motor connected to a steering system by adding a reference current value calculated based on the steering torque of the steering system and a corrected current value calculated based on the differential value of the steering torque. By driving with the determined drive current value, a steering assist torque is applied to the steering system so that the steering operation can be performed easily.

Since a correction current value based on the differential value of the steering torque is added to the reference current value based on the steering torque, it can immediately respond to sudden changes in the steering torque due to disturbances at the start of steering or during steering. Torque fluctuations could be quickly stabilized to a steady state, and a stable steering feel could be obtained.

[Problem to be solved by the invention]

However, in the above conventional technology, the performance of the motor and motor drive circuit was not taken into consideration in the process of calculating the drive current value, so the standard current value and the corrected current value were It was necessary to perform control so that the drive current value obtained by adding the above does not exceed the maximum current value that can be applied to the motor or the motor drive circuit.

Therefore, even if the reference current value has already exceeded the maximum current value and the steering torque increases and the corrected current value becomes positive, or if the steering torque decreases and the corrected current value becomes negative, If the magnitude is smaller than the difference between the reference current value and the maximum current value, the effect of the correction current value will not appear on the drive current value (steering assist torque), and the reference current value will exceed the maximum current value. Even when the current value is not corrected, if the sum of the reference current value and the correction current value exceeds the maximum current value, the reference current value was not corrected correctly according to the change in steering torque. There has been an unresolved problem in that it is not possible to generate a steering assist torque that immediately responds to actual steering torque fluctuations, and as a result, automatic vibrations are likely to occur in the steering system, impairing the steering feel.

This invention was made by focusing on the unresolved problems of the prior art described above, and has a low risk of burning out the electric motor.
Another object of the present invention is to provide an electric power steering device that can correctly correct a drive current value according to changes in actual steering torque.

[Means to solve the problem]

In order to achieve the above object, the electric power steering device of the present invention, as shown in the basic configuration diagram of FIG. a steering torque detecting means for detecting the magnitude of the steering torque; a reference current value determining means for determining a reference current value of the electric motor based on a steering torque detection value of the steering torque detecting means; and a steering torque detecting means for detecting the amount of change in the steering torque. torque change amount detection means; correction current value determination means for determining a correction current value based on the steering torque change amount detection value of the steering torque change amount detection means; a reference current value limiting means for limiting;
drive current value determining means for determining a drive current value of the motor based on the reference current value limited by the reference current value limiting means and the corrected current value; and a drive for driving the motor according to the drive current value. equipped with means.

[Operation] The direction and magnitude of the steering torque of the steering system are detected by the steering torque detection means, and a reference current value based on the detected steering torque value is determined by the reference current value determination means. Then, in the reference current value limiting means, the magnitude of the reference current value is limited so that it does not exceed a predetermined current value (for example, a maximum current value that can be applied to the motor).

On the other hand, the steering torque change amount detection means detects the change amount of the steering torque, and the correction current value determination means determines a correction current value according to the steering torque change amount detection value.

Then, in the drive current value determining means, the reference current value whose magnitude has been limited by the reference current value limiting means and the correction current value determined by the correction current value determining means are added, for example, to generate a drive current. Since the value is determined and the drive means drives the electric motor in accordance with this drive current value, a steering assist torque is generated in the steering system, making it possible to perform a light steering operation.

Furthermore, since the reference current value is limited by the reference current value limiting means so that it does not exceed a predetermined current value, there is no need to further limit the magnitude of the drive current value determined by the drive current value determining means. The influence of the correction current value according to the amount of torque change reliably appears on the drive current value. Then, since the steering assist torque immediately responds to sudden changes in the steering torque due to disturbances at the start of steering or during steering, fluctuations in the steering torque are quickly settled to a steady state.

In this case, even if the drive current value exceeds the predetermined current value, it will only momentarily exceed the predetermined current value according to the amount of change in steering torque, and if the amount of change in steering torque becomes negative, the drive current value will immediately change to the predetermined current value. Since the value is below this value, there is almost no risk of the motor burning out.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIGS. 2 to 8 show an embodiment of the present invention.

First, to explain the configuration, in Fig. 2, the universal joint 2
A steering shaft 1 is constituted by an upper shaft 1a and a lower shaft 1b connected via a steering wheel 3.
is fixed thereto, and a pinion shaft 5 is connected to the lower end of the lower shaft 1b via a universal joint 4.

Furthermore, a pinion provided at the lower end of this pinion shaft 5 is engaged with a rack of a rank shaft 7 inside a steering gear box 6, and these steering wheels 3
．． Steering shaft 1° universal joint 2, 4. The pinion shaft 5 and the rank shaft 7 constitute a steering system.

The pinion shaft 5 is connected to a rotating shaft 9a of an electric motor 9 via a reduction gear mechanism 8. This reduction gear mechanism 8 includes drive gears 8b that mesh with each other within a casing 8a.
The driven gear 8C is fixed to the pinion shaft 5, and the drive gear 8b is fixed to the rotating shaft 9a. The electric motor 9 is composed of, for example, a DC servo motor, and includes an electromagnetic clutch 9b and a rotating shaft 9a.
The rotational force is transmitted to the reduction gear mechanism 8 via.

Further, the steering shaft l is provided with a steering torque sensor 10 as a steering torque detection means for detecting the magnitude and direction of the steering torque input to the steering shaft l. The steering torque sensor 10 is composed of, for example, a strain gauge fixed to the steering shaft 1, and is configured to measure the steering torque according to the direction and magnitude of twisting that occurs in the steering shaft 1 when the driver steers the steering wheel 3. It outputs a detection signal DT.

A vehicle speed sensor 11 detects, for example, the rotational speed of an output shaft of a transmission, and outputs a vehicle speed detection signal DV consisting of a periodic pulse signal corresponding to the rotational speed.

Reference numeral 19 denotes a control device, which includes a control circuit 20 shown in FIG. 3 and a drive circuit 30 shown in FIG.
Each detection signal DT, 6v is supplied from the steering torque sensor 10 and the vehicle speed sensor 11, and control signals 81 to S3 and electromagnetic clutch 9b control the electric motor 9 based on these signals.
The drive circuit 30 is supplied with the control signals 31 to S3, and drives the electric motor 9 based on the control signals 31 to S3.

Then, the control circuit 20, as shown in FIG.
Converter 21. It includes a microcomputer 22 and a D/A converter 23.

The microcomputer 22 includes an input circuit 22a as an interface circuit, an output circuit 22b, and an arithmetic processing unit 2.
2c and a storage device 22d, the input circuit 2
The vehicle speed detection signal DV of the vehicle speed sensor 11 is directly supplied to the vehicle speed sensor 2a, and the steering torque detection signal DT of the steering torque sensor 10 is supplied via the A/D converter 21, and the output circuit 22b outputs the steering assist torque. A corresponding motor drive control signal S1 is outputted via the D/A converter 23, and control signals 82 to S4 are outputted directly.

Based on the steering torque detection signal DT supplied to the input circuit 22a, the arithmetic processing unit 22c executes predetermined arithmetic processing to determine the drive current value I1. Motor drive control signals 81 to S3 that calculate l and control the electric motor 9 based on the calculation result.
On the other hand, when the magnitude of the steering torque is less than the predetermined setting value α, generation of the steering assist torque by the electric motor 9 is stopped.

The storage device 22d stores processing programs necessary for the arithmetic processing of the arithmetic processing unit 22c, storage tables representing various relationships as shown in FIGS. 6 and 7, etc. 22C calculation results etc. are stored sequentially.

As shown in FIG. 4, the drive circuit 30 has an input side supplied with a motor drive control signal S1 outputted from the control circuit 20 and a current feedback signal from a current detector 40 that detects the load current of the electric motor 9. a differential amplifier 31, a comparator circuit 33 as a pulse width modulation circuit whose differential amplified output and the sawtooth wave signal from the sawtooth wave generation circuit 32 are supplied to the input side; Right rotation signal S2 from control circuit 20. AN to which the left rotation signal S3 is supplied
D gate 34.35 and these AND gates 34.35
switching transistor 36.3 supplied with an output of
7 and flywheel diodes 38 and 39 that protect these from the inductive energy accumulated in the electric motor 9, and the collectors of the switching transistors 36 and 37 are connected to the clockwise rotation terminal R and the counterclockwise rotation terminal of the electric motor 9, respectively. is connected to chopper control the motor drive current.

Next, the operation of the above embodiment will be explained using the microcomputer 22.
This will be explained with reference to FIG. 5, which shows the processing procedure executed within the system.

The process shown in FIG. 5 is performed for a predetermined main program (not shown) for a predetermined time (for example,
c) is executed as a timer interrupt process every time.

First, in step (2), the vehicle speed detection signal DV supplied from the vehicle speed sensor 11 is read, and the process proceeds to step (2). The detected value ■ is determined and stored in a predetermined storage area of the storage device 22d.

Next, the process moves to step (3), and the steering torque sensor 17
The steering torque detection signal DT supplied from the controller is read, and the process proceeds to step (2), where the steering torque detection signal DT read in step (2) is stored as the steering torque detection value T in a predetermined storage area of the storage device 22d.

Next, the process proceeds to step (2), where it is determined whether the magnitude of the detected steering torque value T obtained in step (2) has reached a predetermined value α. Determine that auxiliary torque is not necessary and proceed to step (■).

In step (2), for example, by outputting the electromagnetic clutch control signal S4 with a logical value of "0", the electric motor 9 and the output shaft 9 are
The electromagnetic clutch 9b that is interposed between the electric motor 9 and the electric motor 9 and transmits rotational force is turned off, so that the rotational force of the electric motor 9 is not transmitted to the steering system.

Next, the process moves to step (2), where the right rotation signal S2 and the left rotation signal S3, which control the rotation direction of the electric motor 9, are set to a logical value r□.
, and then proceeds to step (3) where these control signals S2 and S3 are outputted to render the electric motor 9 in a state in which it cannot be driven, so that steering can only be performed by the driver's steering operation.

After completing the process of step (2), the process of FIG. 5 is repeated again from step (2).

Further, if the determination in step (2) is rNOJ, it is determined that steering assist torque by the electric motor 9 is necessary, and the process proceeds to step (2), where the electromagnetic clutch control signal S4 of logic 4fi' I J is output, for example. As a result, the electromagnetic clutch 9b is turned on, and the rotational force of the electric motor 9 is transmitted to the steering system.

Next, the process moves to step [phase], and based on the vehicle speed detection value (2) obtained in step (2) and the steering torque detection value T obtained in step (2), the data is stored in advance in the storage device 22d, for example, as shown in FIG. Steering torque detection value T with vehicle speed V as a parameter and reference current value for electric motor 9 ■
. The reference current value I is determined by referring to a storage table showing the relationship between the reference current value I and the reference current value I. Calculate.

Next, the process moves to step 0, and the steering torque T° obtained in the process a predetermined number of times before (for example, the previous process) is calculated from the steering torque T obtained in step (2) in the current process.
is subtracted to calculate the steering torque change amount ΔT. In addition,
Numerical differentiation may be performed using this steering torque change amount ΔT and a predetermined time based on the interruption time and the predetermined number of times, and the differential value may be set as the steering torque change amount ΔT.

Next, the process moves to step [phase], and based on the detected vehicle speed value (2) obtained in step (2) and the steering torque change amount ΔT obtained in step (2), the data is stored in advance in the storage device 22d, for example, as shown in FIG. The corrected current value (■) is calculated by referring to a storage table showing the relationship between the steering torque change amount ΔT and the corrected current value (I) using the vehicle speed (■) as a parameter.

Next, the process moves to step 0, and the reference current value I obtained in the step [phase] is determined. The absolute value of is the predetermined current value r, 4A
Determine whether it exceeds X. In this case, the predetermined current value I Then, the reference current value I0 is set to the predetermined current value 1, AX (however, if Ioo is negative, 10=INAX). Further, if the determination in step 0 is "NO", the reference current value I. Since there is no need to change , the process in step (■) is not executed.

Then, the process moves to step (2), and the reference current value (2) set in the step [phase] or the step (2) is set. and the corrected current value I obtained in step @ above, and the calculation result is set as the drive current value Ia of the motor 9.

Next, the process moves to step [phase], and the step [phase]
Based on the polarity of the drive current value ■8 calculated in , it is determined whether or not the current steering direction is turning to the right. If it is determined that the steering direction is turning to the right, the process moves to step O and the steering direction is turned to the right. The rotation control signal S2 is set to the logical value "1", and the left rotation control signal S3 is set to the logical value "0", and if it is determined that the turning is to the left, the process moves to step [phase] and the turning is to the right. The rotation control signal S2 is set to logical value "0" and the left rotation control signal S
Let 3 be the logical value "1".

Then, the process moves to step @, where the control signals S2 and 33 set in step O or step @ are output, and the electric motor 9 is driven in a predetermined rotational direction.

Next, the process moves to step [phase], and the step [phase]
Or the drive current value ■ set in step ■ above.

The absolute value of is output as the motor drive control signal S1.

In this way, when the motor drive control signal S1 is output,
This is converted into an analog current by the D/A converter 23, and this is supplied to the drive circuit 30.

Therefore, in the drive circuit 30, if the electric motor 9 is in a stopped state, the detection signal of the load current detector 40 that detects the load current is zero, so the differential amplifier 31 supplies the signal from the control circuit 20. A comparatively high level differential amplification output is output according to the drive current value (2). Therefore, the comparison circuit 33 outputs a pulse modulation signal with a large duty ratio (the width of the on state is larger than the width of the off state), which is output from the AND gate 34.
35. At this time, assuming that the driver is turning the steering wheel to the right (or left), the output circuit 22b outputs a clockwise rotation signal S2 (or counterclockwise rotation signal S3) with a logic value of "1". An output corresponding to the pulse modulation signal is obtained from the AND gate 34 (or 35), and the switching transistor 34 (or 35) is thereby controlled to be turned on or off. As a result, the electric motor 9
starts rotating to the right (or left), and the rotational torque is transmitted to the pinion shaft 5 of the steering system via the electromagnetic clutch 9as and the reduction gear mechanism 8.

When the electric motor 9 starts rotating, the load current detection value of the load current detector 40 increases, so the output of the operational amplifier 31 decreases, and the duty ratio of the pulse width modulation signal from the comparator circuit 33 also decreases accordingly. As a result, the drive current value of the motor 9 is output from the control circuit 20! Since the steering system is rotationally driven so as to add a steering assist torque corresponding to (a) to the steering system, the steering assist torque is generated in the steering system and the steering operation can be performed lightly.

Here, the processing of step [phase] and the memory table shown in FIG. 6 correspond to the reference current value determining means, the processing of step (2) corresponds to the steering torque change amount detection means, and the processing of step @ and the storage table shown in FIG. The memory table shown in FIG. 7 corresponds to the correction current value determining means, the processing of step 0 and step (2) corresponds to the reference current value limiting means, and the processing of step [phase] corresponds to the driving current value determining means. However, the processing of the steps [phase] to step [phase] and the drive circuit 30 shown in FIG. 4 correspond to the drive means.

In this way, in the above embodiment, the reference current value I is calculated according to the steering torque T. The correction current value (■), which is calculated according to the steering torque change amount ΔT, is set as the reference current value (■). , and the addition result is the drive current value I1. of the electric motor 9. It is set as I.

Therefore, the drive current value 1. Due to the action of the correction current value I included in the steering system, the steering assist torque generated in the steering system immediately responds to sudden changes in steering torque due to disturbances at the start of steering or during steering, so steering torque fluctuations are quickly brought to a steady state. Since the steering angle is set to , a stable steering feeling can be obtained.

And the reference current value I. is the predetermined current value I. The drive current value IN is executed to limit it so that it does not exceed AX.
There is no need to further limit the size of . Then, for example, a steering torque T as shown in FIG. 8(a) is detected,
In accordance with this steering torque T, a reference current value I exceeds a predetermined current value INAX. Even if (see FIG. 8(b)) is calculated, the upper limit of the reference current value I0 at this time is the predetermined current value! .
The correction effect is fully visible. As a result, similar to the above, the steering torque fluctuation quickly settles to a steady state, so that a stable steering feeling can be obtained without generating self-excited vibrations.

Further, since the correction current value l is determined based on the steering torque change amount ΔT, the drive current value IN is set to the predetermined current value I.
A predetermined current value 1 is applied to the motor 9 and drive circuit 30 beyond NAX.
．． A large current of 4AX or more flows for a very short time, and if the steering torque change amount ΔT becomes negative, the drive current value I
Since N immediately becomes less than the predetermined current value 1□8, the motor 9
There is almost no risk that the drive circuit 30 will be burnt out.

In the above embodiment, a case has been described in which the reduction gear mechanism 8 is configured with a spur gear train, but it is not limited to this. For example, it may be configured with a worm gear and a worm wheel, or a beher gear etc. It is also possible to apply

Further, in the above embodiment, a case has been described in which the microcomputer 22 is applied as the control circuit 2o, but the invention is not limited to this. You can also.

Furthermore, in the embodiment described above, the reference current value I is determined by the steering torque T. , and when determining the corrected current value ■ from the steering torque change amount ΔT, the case where a preset memory table is used has been described, but the present invention is not limited to this. A function representing the relationship between values may be set, and the above determination may be made in accordance with that function.

〔Effect of the invention〕

As explained above, in the electric power steering device of the present invention, a means is provided to limit the reference current value calculated according to the detected steering torque value so that it does not exceed a predetermined current value, and the steering torque The corrected current value calculated according to the amount of change is added to the reference current value, and the addition result is used as the motor drive current value, so it can immediately respond to sudden changes in steering torque due to disturbances at the start of steering or during steering. Therefore, it is possible to quickly settle the steering torque fluctuation to a steady state and obtain a stable steering feeling, and there is no need to further limit the magnitude of the drive current value, so the addition of the reference current value and the correction current value Even if the result exceeds the specified current value,
This has the effect that the drive current value can have a sufficient correction effect and automatic vibration can be prevented.

In addition, since the correction current value is determined based on the amount of change in steering torque, the drive current value exceeds the predetermined current value and a large current greater than the predetermined current value flows through the motor or drive circuit in an extremely short period of time. Moreover, if the amount of change in steering torque becomes negative, the drive current value immediately falls below the predetermined current value, so there is almost no risk of burning out the motor or drive circuit.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the basic configuration of the present invention, Fig. 2 is a block diagram showing an embodiment of the invention, Fig. 3 is a block diagram showing the structure of the control circuit applied in this embodiment, and Fig. 4 The figure is a block diagram showing the drive circuit applied in this embodiment, Figure 5 is a flowchart showing an example of the processing procedure executed in the microcomputer, and Figure 6 is the steering torque and reference current value with vehicle speed as a parameter. 7 is a graph showing the relationship between the amount of change in steering torque and the corrected current value, and FIG. 8 is a graph showing the relationship between the steering torque change amount and the corrected current value. It is a time chart showing the relationship between values. 1... Steering shaft, 3... Steering wheel, 5... Pinion shaft, 7... Rack shaft, 8... Reduction gear mechanism, 9 ...Electric motor, 10...
・Steering torque sensor (steering torque detection means), 11...
-Vehicle speed sensor, 19...control device, 20...control circuit, 30...drive circuit. Figure 6 Figure 7 <->

Claims (1)

[Claims] (1) an electric motor that generates a steering assist torque in a steering system; a steering torque detection means that detects the direction and magnitude of the steering torque of the steering system; a reference current value determining means for determining a reference current value; a steering torque change amount detecting means for detecting the amount of change in the steering torque; and a correction current value based on the steering torque change amount detection value of the steering torque change amount detecting means. a correction current value determining means for determining a value; a reference current value limiting means for limiting the reference current value so that it does not exceed a predetermined current value; and a reference current value limited by the reference current value limiting means and the correction current. An electric power steering device comprising: drive current value determining means for determining a drive current value of the electric motor based on the drive current value; and drive means for driving the electric motor according to the drive current value.