JPH01297373A - Control of steering electric motor for four-wheel steering device - Google Patents

Abstract

PURPOSE:To protect an electric motor from being damaged by the generated heat, by controlling the electric conduction rate of the electric motor according to the electric current value which flows in an H-bridge circuit for driving a steering electric motor, in the constitution in which a rear wheel steering mechanism is driven by the steering electric motor. CONSTITUTION:The steering angle ratio is calculated in correspondence with the front wheel steering angle or car speed by a CPU 8 in a controller, and a rear wheel steering mechanism is controlled by the drive of a steering electric motor 2a according to the calculated steering angle ratio. An H-bridge circuit which is constituted of power transistors Q1-Q4 and drives the steering electric motor 2a is installed into the controller. The electric current which flows in the H-bridge circuit is detected by detecting the electric voltage which is generated in a resistance R1, and the electric conduction rate of an electric motor 1a is controlled according to the detected electric current value. Therefore, in case of the excessive electric current, etc. the need of immediately suspending the electric conduction of the electric moor 2a is obviated, and the control is continued for a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of controlling a steering electric motor that drives a rear wheel steering mechanism of a four-wheel steering device.

[Conventional technology]

In an electric four-wheel steering system in which the rear wheel steering mechanism is directly driven by an electric motor, when the electric motor is locked or the H bridge circuit is shorted,
When the motor is overloaded due to tires shining on curbs or falling into grooves, etc.
A large current flows through the H-bridge circuit that drives the motor when the direction of rotation of the motor changes, but conventional methods have only been able to cut the overcurrent.

[Problem to be solved by the invention]

However, the conventional measures such as cutting off overcurrent are not sufficient to protect the system when heat generation in the motor is taken into account.

[Means to solve the problem]

In order to solve such problems, a method for controlling a steering electric motor of a four-wheel steering system according to the present invention includes controlling the energization rate of the steering electric motor according to the value of the current flowing through the H-bridge circuit that drives the steering electric motor. This is what I did.

[Effect]

In the control method according to the invention, control of the steering electric motor is maintained as long as possible while protecting against damage due to heat generation.

〔Example〕

FIG. 2 is a configuration diagram showing a general four-wheel steering system.
In the figure, ■ is a front wheel steering device having a front wheel steering mechanism, 1a is a steering angle sensor, 1b is a column sensor, 2 is a rear wheel steering device having a rear wheel steering mechanism, 2a is a steering electric motor,
2b is a reduction gear; 2C is a steering angle sensor; 2d is a centering spring; 3 is a controller having a steering angle ratio calculation mechanism that calculates a steering angle ratio in accordance with the front wheel turning angle or vehicle speed;
4 is a safety relay as a relay for supplying power to the electric motor 2a, 5 is a fuse, 6 is an ignition switch, and T is a power terminal to which power from the battery is supplied.

In FIG. 2, the controller 3 has an H-bridge circuit that drives the steering electric motor 2a, and detects the value of the current flowing through the H-bridge circuit.

Next, the operation in response to overcurrent in the controller 3 will be explained. Figure 3 shows power transistors Q1 to Q4.
1 is a circuit diagram showing a detection system for a current value flowing through an H-bridge circuit configured with the following.

The current flowing through the H-bridge circuit flows through the resistor R1 regardless of whether the motor rotates forward or reverse. Therefore, by looking at the voltage generated across the resistor R1, it is possible to know the value I of the current flowing through the I]brifuji circuit. The voltage generated across the resistor R1 is amplified by the operational amplifier 7 and input to the A/D converter 9 of the CPU8. Here, the A/D converted current value I is taken into the CPU and processed by the program. Processing by the program includes calculation of allowable time and calculation of duty ratio limit rate. In FIG. 3, 4a is a contact point of the safety relay 4.

Next, calculation of duty ratio restriction rate will be described.

FIG. 4(a) is a graph showing the relationship between counter contents (count value) and duty ratio restriction rate. The contents of the counter indicate the integral value of the detected current value I when the detected current value I exceeds the threshold level TH, and indicate the thermal influence on the transistors Q1 to Q4 and the motor 2a. If the thermal influence is large, increase the duty ratio restriction rate. A high duty ratio restriction rate means that the duty ratio (current energization rate to the electric motor 2a) is small. For example, a duty ratio restriction rate of 100% means a duty ratio of θ%. Figure 4 (
b) shows the duty ratio with respect to the deviation, and the characteristic line shown in the figure is the characteristic line when the restriction rate is 0%.

An example of count values (counter contents) is shown in FIG. Fifth
Figure (a) shows the detected current value ■, where I-TH becomes the excess current B. Since I < TH until time ta, the count value shown in Fig. 5(b) is zero, but when I > TH, B > 0, and the count value becomes the integrated value of I - TH = B. Become. At time tb, I <TH again, but the counter still performs integration, and when the counter content becomes zero, the integration operation is stopped. Figure 5 (al
The broken line of (bl) indicates the case where the integral value of the excess current B is zero.

FIG. 1 is a flowchart for explaining the duty ratio limit rate calculation method. First, the content of the counter is set to zero (step 11), and after performing the main side <BA in step 12, the flow shifts to duty ratio limit rate calculation (steps 13 to 22).

In the flow of calculating the duty ratio limiting rate, first, the detected current value I output from the operational amplifier 7 is A/D converted (step 13), and the excess current B=I-TH is calculated (step 14). If the excess current B is positive, B7 is added to the counter contents (step 15.16). If the excess current B is zero or negative, proceed to step 17 and calculate the absolute value IB of B.
Compare the magnitude of I to the mth power and the counter contents, 1B1'''
〉In the case of counter contents, the counter contents are set to zero.

This is because if IBI'>counter contents, even if the counter integrates, the result will be less than or equal to zero. I
If BI”<counter contents, IB1 from the counter contents.
Subtract the value of ``''. After the processing in steps 16 and 17 or 19 is completed, the process moves to step 20.

The above n and m are weights for the magnitude of the current.

For example, when considering the heat generation and heat dissipation time of a motor, the heat generation time during overload is much shorter than the heat dissipation time during light load. Therefore, by setting n>m, the heat generation of the motor can be suppressed to some extent.

Next, calculate the duty ratio restriction rate using the counter contents as shown in Figure 4 (a).
Step 20), calculate the duty ratio with a limit rate of 0% for the deviation according to FIG. 4(b).
Step 21). Next, the actual duty ratio is calculated from the limit rate retrieved in step 20 using the following equation (1), and the PWM signal of this actual duty ratio is output to the H bridge circuit (step 22.23).

Actual duty ratio=duty ratio of restriction rate 0%×(1-restriction rate/100) (1) Next, main control B is performed (step 24), and after completion, main control A is returned.

The CPU 8 repeats the operations from steps 11 to 24. Therefore, as long as the excess current B is generated, the count value increases, that is, the duty ratio limiting rate increases, and the energization rate to the power transistors Q1 to Q4 and the motor 2a decreases, and eventually the energization rate reaches zero, i.e. Power will be cut off.

By performing the control described above, it is possible to meet the demand for maintaining control as long as possible. That is, power transistors Q1 to Q4. Control is no longer abandoned due to temporary overcurrent to the motor 2a, and the power transistors Q1 to Q4. Energization can be reliably stopped before the electric motor 2a is damaged, and therefore, there is no need for an over-spec design and an economical design is possible.

Moreover, there is an effect that overload can be handled without using a temperature sensor.

FIG. 6 is a flow chart for explaining a second embodiment of the control method according to the present invention. Steps 31 to 39 are the same as steps 11 to 19 in FIG. 1, so their explanation will be omitted. After calculating the counter value, it is determined whether the counter value is greater than or equal to the allowable value, and if it is smaller than the allowable value, a PWM signal with a fixed duty ratio is output to the H-bridge circuit to drive the motor (step 40.41). If the counter value is greater than or equal to the allowable value, the motor is stopped (step 42).
). Thereafter, as in the case of FIG. 1, the process returns to the main control A of step 32 via the main control B of step 43.

FIG. 7 is a circuit diagram for explaining a third embodiment of a method for controlling a steering electric motor of a four-wheel steering system according to the present invention. In the same figure, R2 and R3 are current value detection resistors;
7a and 7b are operational amplifiers that amplify the current values detected by resistors R2 and R3. In FIG. 7, the same or equivalent parts as in FIG. 3 are given the same reference numerals. The circuit shown in FIG. 7 is a case in which two systems of current detection are provided, and has the effect of increasing the degree of freedom of calculation within the CPU. In other words, since the detected current value is detected separately for forward rotation and reverse rotation, it is easy to discover in which case excessive current has occurred.
Further, allowable time control and duty ratio limiting rate control can be performed for each forward rotation and reverse rotation.

〔Effect of the invention〕

As explained above, the method for controlling the steering electric motor of the four-wheel steering device according to the present invention controls the energization rate of the steering electric motor according to the value of the current flowing in the H-bridge circuit that drives the steering electric motor, thereby controlling the overcurrent. In such cases, there is no need to immediately stop energizing the steering assist electric motor, and the present invention has the advantage of being able to meet the need to maintain control as long as possible.

That is, the power transistor constituting the H-bridge circuit does not abandon control due to temporary overcurrent to the motor, and the power transistor described above.

Energization can be reliably stopped before the motor is damaged.
Therefore, there is an advantage that over-specification design is unnecessary and economical design is possible.

Another advantage is that overload can be handled without using a temperature sensor.

[Brief explanation of the drawing]

FIG. 1 is a flowchart for explaining an embodiment of a method for controlling a steering electric motor of a four-wheel steering device according to the present invention, FIG. 2 is a configuration diagram showing a general four-wheel steering device, and FIG. A circuit diagram showing a current value detection system to which an embodiment of the method according to the invention is applied, and FIGS. 4(a) and 4(b) are graphs showing the relationship between duty ratio limiting rate and counter contents and the relationship between deviation and duty ratio. , FIG. 5 is a time chart showing the relationship between the detected current value and the count value, FIG. 6 is a flow chart for explaining the second embodiment of the present invention, and FIG.
The figure is a circuit diagram showing a current value detection system to which a third embodiment of the present invention is applied. 1... Front wheel steering device, 1a... Steering angle sensor, ■b
...Column sensor 2...Rear wheel steering device, 2a...
Rear wheel steering electric motor, 2b... Reduction gear, 2C... Steering angle sensor, 2d... Centering spring, 3.
... Controller, 4... Safety relay, 4a.
...Contact, 5...Fuse, 6...Ignition switch, 7゜7a, 7b...Operation amplifier, 8...
CPU, 9... A/D converter, Q1-Q4... power transistor, R1-R3... resistor, T... power supply terminal.

Claims (1)

[Claims] The vehicle has a front wheel steering mechanism that steers the front wheels, a rear wheel steering mechanism that steers the rear wheels, and a steering angle ratio calculation mechanism that calculates a steering angle ratio corresponding to the front wheel steering angle or the vehicle speed, In an all-electric four-wheel steering system in which a rear wheel steering mechanism is directly controlled by a steering electric motor, the energization rate of the steering electric motor is controlled by the value of a current flowing through an H-bridge circuit that drives the steering electric motor. A method of controlling an electric motor for steering a device.