JP2577555B2 - Electric power steering device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention keeps the output torque of an electric motor properly,
The present invention relates to an electric power steering device that enables stable steering operation.

2. Description of the Related Art A device of this type, which is conventionally known, has a pinion at a tip end of an input shaft connected to a handle, and this pinion is engaged with a rack connected to wheels.

The rack is also engaged with a pinion linked to an electric motor, but the electric motor and the pinion are linked via an electromagnetic clutch.

Further, a torque sensor for detecting the torque of the input shaft, a vehicle speed sensor for detecting the vehicle speed of the vehicle, and an axial force sensor for detecting the axial force of the rack are provided, and these sensors are linked to the control device. .

The control device as described above controls the output of the electric motor according to the output signal of each of the sensors, and has a control unit that turns on and off the electromagnetic clutch as a main element. And an abnormality detection circuit for detecting an abnormality of each sensor.

If an abnormality occurs in any of the sensors, the control unit operates to turn off the electromagnetic clutch and put the electric motor in a free state.

(Problems to be Solved by the Present Invention) In the conventional device as described above, since the electromagnetic clutch is used, there are the following problems in addition to the problem that the entire device is expensive.

That is, when an abnormality occurs in the vehicle speed sensor, the electric motor is immediately brought into a free state, and the mode is switched to the manual steering. However, when the power steering is suddenly switched to the manual steering, there is a problem that the steering feeling is wrong.

Further, in this conventional device, even if the temperature of the electric motor rises due to high-load operation or the like, it does not have a function of detecting the temperature.Therefore, until the motor is disconnected or locked due to the rise in temperature, There was a problem that the abnormality could not be checked.

It is an object of the present invention to reduce costs by omitting an electromagnetic clutch and gradually reduce the output of an electric motor,
Moreover, it is an object of the present invention to solve the problem caused by the temperature rise of the electric motor.

(Means for Solving the Problems) In order to achieve the above object, the present invention relates to a rack in which knuckle arms connected to wheels are linked to both ends, and a rack connected to a steering input shaft and an electric motor. It is assumed that an electric power steering device is formed by engaging a pinion and configured to control the electric motor by a motor control device.

A torque sensor for detecting a steering torque, a vehicle speed sensor for detecting a vehicle speed, and a temperature sensor for detecting a temperature of the electric motor are connected to the motor control device. An abnormality detection circuit that detects an abnormality of, and a control unit to which a signal detected from each of the sensors and a signal from the abnormality detection circuit are input,
This control unit controls the electric motor in accordance with the steering torque and the vehicle speed, and executes a main program that gradually reduces the output of the electric motor after a certain period of time when the temperature of the electric motor exceeds the allowable temperature. Moreover, when an abnormality signal from the abnormality detection circuit connected to the torque sensor is input, a program for setting the output of the electric motor to zero is executed, and an abnormality signal from the abnormality detection circuit connected to the vehicle speed sensor or the temperature sensor is executed. Is entered,
The feature is that the output of the electric motor is gradually reduced after a certain period of time after returning to the main program.

(Operation of the Present Invention) With the above configuration, the control unit of the motor control device executes the main program and controls the electric motor according to the steering torque and the vehicle speed. However, in this main program, when the temperature of the electric motor exceeds a preset allowable temperature, the output of the electric motor is gradually reduced after a certain period of time.

Further, an abnormality detection circuit for detecting an abnormality of the sensor itself is connected to each sensor.

Then, when an abnormality occurs in the torque sensor, the control unit executes a program for immediately reducing the output of the electric motor to zero.

On the other hand, when an abnormality occurs in the vehicle speed sensor or the temperature sensor, the process returns to the main program, and the output of the electric motor is gradually reduced after a certain period of time as in the case of the temperature rise.

(Effect of the Present Invention) According to the electric power steering device of the present invention, when the temperature of the electric motor exceeds the allowable temperature, the output of the electric motor is reduced. Therefore, disconnection or locking of the electric motor due to a rise in temperature can be prevented. Moreover, at this time, the output of the electric motor is gradually reduced, so that the steering feeling does not suddenly change. Furthermore, since the output of the electric motor is reduced after a certain period of time, for example, when an incorrect temperature is output from the temperature sensor for a moment due to circuit noise or the like, the output of the electric motor is also immediately reduced. Can be returned to the output.

Further, according to the electric power steering device of the present invention, the abnormality detection circuit is connected to each sensor.

When an abnormality occurs in the torque sensor, the abnormality detection circuit detects the abnormality and immediately sets the output of the electric motor to zero. That is, when an abnormality occurs in the torque sensor, the torque before the abnormality occurs is maintained, and the electric motor may be locked. In this way, the urgency is required when the torque sensor is abnormal, so that the output of the electric motor is immediately set to zero.

On the other hand, when an abnormality occurs in the vehicle speed sensor or the temperature sensor, the output of the electric motor is gradually reduced after a certain period of time. That is, even if an abnormality occurs in the vehicle speed sensor or the temperature sensor and the vehicle speed or the temperature is maintained, the electric motor is not locked. Therefore, the output of the electric motor is not immediately reduced to zero, but is gradually reduced to prevent a sudden change in the steering feeling. Further, similarly to the case where the temperature of the electric motor rises, when an erroneous signal is output for a moment due to circuit noise or the like, the output of the electric motor can be immediately returned to the original output.

Further, according to the present invention, the electromagnetic clutch is not required for the control when the sensor is abnormal, so that the cost can be reduced accordingly.

(Embodiment of the Present Invention) The illustrated embodiment is a steering input shaft 2 connected to a steering wheel H.
And the pinion 3 is engaged with the rack 4. Both sides of the rack 4 are connected to knuckle arms 6 of the wheels 1 via side rods 5.

Further, a speed reducer 7 is connected to the electric motor m which can be rotated forward and backward. A pinion 8 is provided on the output shaft side of the speed reducer 7, and the pinion 8 is engaged with the rack 4.

Further, a torque sensor 9 for detecting a steering torque acting on the input shaft 2 and a vehicle speed sensor for detecting a vehicle speed of the vehicle.
10 and a temperature sensor 11 for detecting the temperature of the electric motor m. These sensors are connected to a motor control device a.

The torque signal Tin detected by the torque sensor 9 is input to a torque signal processing circuit 12 and a torque sensor abnormality detection circuit 13 provided in the motor control device a.

The aforementioned torque signal processing circuit 12, but are connected to the phase correction circuit 14, in the phase correction circuit 14, the signal V ₂ has proceeded its phase by differentiating the output signal V ₁ of the from the torque signal processing circuit 12 Is output. The reason why the phase is advanced in this way is to improve the response.

The output signal V ₂ from the phase correction circuit 14 is input to a forward / reverse direction determination circuit 15 for determining the direction of the torque, and a torque forward / reverse signal T output from the determination circuit 15 is output.
_0, input to the input port A ₁ of the microprocessor P.

The output signal V ₂ from the phase correction circuit 14 is also input to an absolute value circuit 16 where it is converted into an absolute value. The absolute value | V ₂ | Is converted to This digital value converted torque level signal T ₁
Is input to the input port A ₂ of the microprocessor P. When the torque level signal T ₁ is, for example, 8 bits,
| V ₂ | = 0 corresponds to zero, and | V ₂ | = max corresponds to 256.

The vehicle speed signal v detected by the vehicle speed sensor 10 is transmitted to the vehicle speed signal processing circuit 18 of the motor control device a and the vehicle speed sensor abnormality detection circuit.
Enter 19 and so on. The signal processed by the vehicle speed signal processing circuit 18 is sent to an interrupt port of the microprocessor.
Input to INT1.

Note that the vehicle speed signal processing circuit 18 outputs a pulse train corresponding to the vehicle speed, for example, 0 pulses / sec when the vehicle speed is 0 km / h, 40 km / sec.
A pulse train of 40 pulse / sec at h and 100 pulse / sec at 100 km / h is output. When the pulse signal rises or falls, an interrupt is generated at the interrupt port INT1.

The temperature signal detected by the temperature sensor 11 is transmitted to the temperature signal processing circuit 20 of the motor control device a and the temperature sensor abnormality detection circuit 21.
To enter. Then, the temperature signal processing circuit signal V ₃ treated with 20 is converted into a digital signal by the A / D conversion circuit 22 is input to the input port A ₃ of the microprocessor P as a temperature signal X.

Further, the output signal of the above-described torque sensor abnormality detection circuit 13 is input to the interrupt port INT2 of the microprocessor P via the OR gate 23, and the output signal of the vehicle speed sensor abnormality detection circuit 19 is directly input to the interrupt port INT3, The output signal of the sensor abnormality detection circuit 21 is also directly input to the interrupt port INT4.

From the output port C ₁ of the microprocessor P,
Output by the forward and reverse signals M ₀ to identify the rotational direction of the electric motor m, and inputs the forward and reverse signals M ₀ to the motor drive circuit 24. From the output port C _2, the output level signal M ₁ of the digital value is output, the output level signal M ₁ is, D / A conversion circuit 2
The signal is converted into an analog signal at step 5 and input to the motor drive circuit 24.

Then, in the motor driving circuit 24, the forward and reverse signal M ₀ and the output level signal M ₁ by controlling the electric motor m.
From the output port C _{3 of the} microprocessor P,
A power ON-OFF signal is output, and the ON-OFF signal is input to the port drive circuit 24.

When the output level signal M ₁ and the power-on signal to the motor drive circuit 24 is inputted, the electric motor m
There operates in accordance with the output signal of the output level signal M _1. On the other hand, when the power-off signal is input to the motor drive circuit 24, even if the output level signal is input,
The electric motor m is not driven, and is maintained in a free rotation state.

From the output port C _4, but outputs a pulse indicating that the program is running normally, the OR gate output signal via the watchdog processor 26
23 is to be entered.

Thus, the microprocessor P has a third to an eighth.
It operates according to the flowchart in the figure.

That is, when the ignition switch for starting the engine is turned on, the main program starts in synchronization with the ignition switch.

When the main program starts as described above, in step 1, the output level signal M ₁ = 0 is output to the output port C _2.
It causes outputs from, to output the power-on signal from the output port C ₃ in step 2.

Then, in step 3, the vehicle speed pulse
The count register is set to the maximum value (corresponding to vehicle speed = 0), the flag F for checking the temperature of the electric motor is set to 0 in step 4, and the maximum output level M of the electric motor m is set in step 5 and _{M 1} max = C M is set to ₁ max constant C _M, to complete the operation preparation.

When the preparation is completed as described above, the process shifts from step 6 to step 8 in order.

Then, the is input to the input port A ₃ temperature signal X In step 6, the flag F is to determine whether the zero in step 7. If the flag F is 0, the temperature of the electric motor m is considered to be normal when the temperature is equal to or lower than a certain value.

When the flag F is 0, the process proceeds to step 8, and it is determined whether or not the temperature X exceeds the maximum allowable temperature Xmax.

If the temperature X exceeds the maximum allowable temperature Xmax, it is determined that an abnormality has occurred in the electric motor m, and the process proceeds to step 9, the flag F is set to 1, and the process proceeds to step 14. I do.

If the flag F has already been set to 1 in step 7, the motor temperature can be determined to be abnormal by itself. In this case, steps 7 to 14 are performed.
Migrate directly to.

If it is determined in step 8 that the temperature of the electric motor m is equal to or lower than the maximum allowable temperature, the operation is considered to be normal, and the process proceeds to a normal motor control step of step 10 and subsequent steps.

Therefore, the control steps for the case where the temperature of the electric motor m exceeds the allowable temperature will be described first, and then the normal control steps after step 10 will be described.

When the temperature of the electric motor m exceeds the maximum allowable temperature Mmax in step 8 as described above, the process proceeds to step 9 and the flag F is set to 1.

When the flag F is set to 1 in this manner, the step
At 14 the timer A starts.

In step 14, the time, determines whether a predetermined inside certain time t _1, if if this predetermined time t ₁ within a, the process proceeds to step 18 following normal motor control step .

However, if the time of the timer A exceeds the predetermined time t _1, the process proceeds to step 16, slightly down the maximum output level of the motor, and _{M 1 max = M 1 max-} ΔM 1.

Then, in step 17, the timer A is started again, and the process proceeds to step 18, a normal control step.

However, in this normal control step, the electric motor m
Is controlled as M ₁ max = M ₁ max−ΔM ₁ .

Determining the elapsed normal control step 18 as described above, at step 19, the output level M ₁ of the electric motor m at that time, whether greater than the M ₁ max.

Then, the output level M ₁ is, since if smaller is no problem than M ₁ max, the process proceeds to step 21. Conversely, the output level M _1, when M ₁ max greater than, Step 20
In the M ₁ is set to be equal to the M ₁ max.

After setting the maximum output level of the electric motor as described above, the output port an output forward and reverse signal M ₀ in step 21
Is outputted from the C _1, at step 22, the output level signal M ₁ is outputted from the output port C ₂ and to operate the motor drive circuit 24 in response to Korare signal M ₀ and M ₁ of the signal, the electric motor m
Control the output of

If the above steps have been completed, the apparatus is considered to be operating normally.
In, to output a pulse for watchdog from the output port C _4, and inputs the output signal to the OR gate.

In step 24, the above M ₁ max is compared with a constant Ca which is a predetermined minimum value.

When it is determined that M ₁ max> Ca, the electric motor m
Go to step 15 again to power down
The above-mentioned routine is passed. By repeating the process of shifting from step 24 to step 15, the maximum output of the electric motor m is reduced by ΔM ₁ at step 16, which is the process of the routine, and the output is set to the value determined by the constant Ca. It will be controlled as follows.

Next, the input / vehicle speed response routine in steps 10 and 18 will be described with reference to FIG.

When this routine starts,
With the torque forward and reverse signal T ₀ is input to the input port A ₁ at 71, a torque level signal T ₁ at step 72 is input to the input port A _2.

With such the respective signals to the two input ports A ₁ and A ₂ are inputted, in step 73, selects the torque constant C _T according the torque constant table the torque T _1. In step 74, a vehicle speed constant CV corresponding to the vehicle speed signal _V is extracted from the vehicle speed constant table.

Then, in step 75, in order to make the output torque sensitive to the vehicle speed, the torque constant C _T is multiplied by the vehicle speed constant C _V and shifted right by n bits. To this manner is shifted to the right by n bits, obtaining the output level M ₁ as _{^{(1/2 n) × C V ×}} C T.

If the bit is not shifted to the right by n bits as described above, for example, if C _V is 4 bits, _CT is 8 bits, and the D / A conversion circuit 25 is 8 bits, the result of the multiplication becomes 11 bits. , Exceeding the capability of the D / A conversion circuit. Therefore, in this case, n = 4 bits are shifted to the right, and a maximum of 8
The number of bits is set so as not to exceed the capability of the D / A conversion circuit.

In step 76, an output forward and reverse signals M _0, the torque forward and reverse signals
The same Lay the T _0, is outputted from the output port C ₁ its output forward and reverse signal M ₀ in step 20. Then, the output level signal M ₁ is outputted from the output port C ₂ in step 21, these output forward and reverse signal M ₀ and the output level signal M _1, controls the electric motor m.

FIG. 5 shows a routine of an interruption process by a vehicle speed pulse. In other words, a pulse signal having a different pulse width is always output from the vehicle speed sensor according to the vehicle speed. An interrupt is generated when the pulse signal rises or falls.

When a pulse signal is input to the interrupt port INT1 as described above, the value of the pulse counter at that time is set in the register V in step 31, and the pulse counter is cleared in step 32 to start counting.

In this way, for example, the time from the rising of the pulse to the next rising is counted.
The pulse interval is proportional to the count number, and the vehicle speed v is inversely proportional to the count number.
Therefore, the vehicle speed v can be grasped by looking at the value of the register V at this time. Upon completion of the above operation, the program returns to the main routine at the time when the interrupt occurred.

FIG. 6 shows a routine of an interruption process by an abnormal signal.

That is, when an abnormal signal from either the torque sensor abnormality detecting circuit 13 or the watchdog processing circuit 26 is input to the OR gate 23, the abnormal signal is input to the interrupt port INT2. With such abnormality signal to interrupt port INT2 is interrupted, and outputs a power-off signal to the output port C ₃ in step 41, the output port C ₂ output level M ₁ = 0 in step 42
To stop the electric motor m and maintain the state.

Thus output the power-off signal, moreover if the output level M ₁ is 0, the rotational force of the steering input shaft 2 rack 4
Is transmitted directly to the vehicle, and the vehicle enters a state of manual steering.

FIG. 7 shows a routine when an abnormality occurs in the vehicle speed sensor 10.

That is, when an abnormality signal from the abnormality detection circuit 19 is input to the interruption port INT3, the interruption port INT1 is masked in step 51 and the flag F is set to 1 in step 52 in order to stop counting the vehicle speed pulse. ,
Return to main routine.

If the process returns to the main routine with the flag F set to 1, the output of the electric motor m is gradually powered down in the same routine as when the motor temperature rises.

FIG. 8 shows a routine when an abnormality occurs in the temperature sensor 11.

When an abnormality occurs in the temperature sensor 11, an abnormality signal is output from the abnormality detection circuit 21, and the abnormality signal is output to the interrupt port IN.
Input to T4. When the signal is input to the interrupt port INT4 as described above, the flag F is set to 1 in step 61, and the process returns to the main routine at the time when the interrupt occurs. If the process returns to the main routine in a state where the flag F is set to 1, the output of the electric motor m is gradually powered down in the same routine as when the motor temperature rises.

In addition, according to this device, since the vehicle is of a vehicle speed sensitive type, as shown in FIG. 9, the steering torque and the output level change according to the vehicle speed.

[Brief description of the drawings]

1 to 9 show an embodiment of the present invention.
FIG. 2 is a block diagram of a motor control device, FIG. 3 is a diagram showing an example of a flow chart of a control program, FIG. 4 is a flow chart showing an input / vehicle speed sensitive processing routine, and FIGS. FIG. 9 is a flowchart showing an interrupt processing routine, and FIG. 9 is a graph showing the relationship between the output level and the steering torque. 1 ... wheels, 2 ... steering input shaft, 3, 8 ... pinion,
4 ... rack, 6 ... knuckle arm, m ... electric motor, a ... motor control device, 9 ... torque sensor, 10 ...
... Vehicle speed sensor, 11 ... Temperature sensor, 13 ... Torque sensor abnormality detection circuit, 19 ... Vehicle speed sensor abnormality detection circuit, 21 ...
Temperature sensor abnormality detection circuit, P ... A microprocessor as a control unit.

Continuation of the front page (56) References JP-A-61-205556 (JP, A) JP-A-61-254829 (JP, A) JP-A-60-80967 (JP, A) , U)

Claims (1)

(57) [Claims] A pinion connected to a steering input shaft and a pininone linked to an electric motor are engaged with a rack having knuckle arms connected to both ends of the wheel linked to both ends, and the electric motor is controlled by a motor control device. In the electric power steering device configured to be controlled by
A torque sensor for detecting a steering torque, a vehicle speed sensor for detecting a vehicle speed, and a temperature sensor for detecting a temperature of the electric motor are connected to the motor control device. And a control unit to which a signal detected from each of the sensors and a signal from the abnormality detection circuit are input. The control unit controls the electric motor according to the steering torque and the vehicle speed. When the temperature of the electric motor exceeds the allowable temperature, the main program that gradually reduces the output of the electric motor after a certain period of time is executed, and an abnormality signal from the abnormality detection circuit connected to the torque sensor is input. Sometimes, a program to reduce the output of the electric motor to zero is executed, and an abnormality is detected from an abnormality detection circuit connected to the vehicle speed sensor or temperature sensor. No. When you enter is returned to the main program, an electric power steering apparatus being characterized in that the gradually reducing constitutes the output of the electric motor from at a certain time.