JPH069968B2 - Motor drive type power steering control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor-driven power steering control device for assisting a steering device of an automobile with a motor rotational force.

[Conventional technology]

Conventionally, this type of power steering device assists the driving force of a motor to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer.

[Problems to be solved by the invention]

The conventional power steering device as described above has a problem that, when continuously used in a portion having a large steering assist force, the motor and the power element for controlling the motor are destroyed due to temperature rise due to heat generation.

The present invention has been made to solve the above-mentioned problems, and prevents the power element from being destroyed due to a temperature rise,
Moreover, it is an object of the present invention to obtain a highly reliable and highly safe power steering control device with less discomfort in steering.

[Means for solving problems]

A motor-driven power steering apparatus according to the present invention is a steering torque measuring means for measuring a steering torque by an input from a torque sensor, a vehicle speed measuring means for measuring a vehicle speed, and an on-state voltage across a power element for controlling a motor current. And a power element ON resistance calculation means for calculating the ON resistance of the power element from the current measured by the current sensor,
Power element over temperature determination means for determining an over temperature state from the power element on resistance by the power element on resistance corresponding to the power element temperature, and motor current for determining the motor current according to the output of this determination means and the steering torque. Determining means, power element control means for controlling the power element based on the output of the motor current determining means, power element section for controlling the direction and current value of the motor current based on the output of the power element control means, and this power element And a current sensor for measuring the value of the current flowing through the section.

[Work]

The power steering control device according to the present invention determines the power element temperature from the power element ON resistance, and controls the motor current so that the temperature falls within a predetermined value to prevent the motor and the power element section from being destroyed. In addition, since the motor current is continuously reduced in accordance with the temperature rise time constant of the power element, the power steering has less feeling of strange steering.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. First
In the figure, 1 is a steering wheel that receives a steering rotational force, 3 is a torque sensor that outputs a signal according to the rotational force applied to the steering wheel 1, 4a is a first universal joint, and 4a
b is the second universal joint, 2a is the handle 1
A second steering shaft connecting the torque sensor 3 and the first universal joint 4a, and a second steering shaft connecting the torque sensor 3 and the first universal joint 4a.
2c is a third steering shaft connecting between the first universal joint 4a and the second universal joint 4b, 5 is a first pinion shaft connected to the second universal joint, and 6 is a first pinion shaft. A rack shaft having a first rack tooth portion 6a and a second rack tooth portion 6b that mesh with the pinion shaft 5, 7a is one ball joint that connects one of the tie rod 8a and one of the rack shafts 6, and 7b is the other. This is the other ball joint that connects the tie rod 8b and the other of the rack shaft 6. Reference numeral 9 is a control unit, 10 is a vehicle speed sensor for detecting a vehicle speed, 11 is a vehicle battery, 12 is a key switch, 13 is a DC motor having a shunt winding or a magnet field, and is driven from the battery 11 via the control unit 9. Reference numeral 14 is a worm shaft that is connected to the output shaft of the motor 13 and forms a speed reducer, and 15 is a worm wheel shaft that is meshed with the worm shaft 14.
Reference numeral 16 is an electromagnetic clutch for connecting or disconnecting the mechanical connection between the wheel shaft 15 and the second pinion shaft 17 meshing with the second rack tooth portion 6b of the rack shaft 6 according to the instruction of the control unit 9. .

FIG. 2 shows a block circuit diagram of the control unit 9. 9a is a steering torque measuring means for measuring a steering torque by an input from the torque sensor 3, and 9b is a vehicle speed sensor 10.
Vehicle speed measuring means for measuring the vehicle speed by the input from, 9c when ON of the power element 9h ₁ ~9h ₄ for controlling the current of the motor 13, the power element 9h ₁ ~9h ₄ measured by the voltage across the current sensor 9i Power element is turned on from the flowing current
Power element ON resistance calculation means for calculating a resistance, 9d than corresponding relationship of the power element 9h ₁ ~9h ₄ ON resistance and the power element temperature, the power element over temperature determining determines an over temperature condition of the power element 9h ₁ ~9h ₄ Means, 9e is a motor current determining means for determining a motor current according to the output of the over temperature determining means 9d and steering torque, and 9f is an electromagnetic clutch for performing control for connecting or disconnecting the electromagnetic clutch 16 under a condition determined at least by the vehicle speed. Control means, 9g is a power element section control means for controlling the power element section 9h based on the output of the motor current determining means 9e, and 9h is this control means 9g.
Based on the output, the power element portion consisting of the first to fourth power element 9h ₁ ～9H ₄ to control the direction and the current value of the motor current, 9i is a current sensor for measuring the current flowing through the power element portion 9h is there.

Next, the operation will be described with reference to FIGS. FIG. 3 is a control characteristic diagram of steering torque versus motor current, FIG. 4 is a control characteristic diagram of vehicle speed versus motor current and electromagnetic clutch applied voltage, and FIG. 8 is a flow chart showing a control program of the control unit 9.

First, when the key switch 12 is turned on when the engine is started, the electromagnetic clutch 16 is turned on, and the worm wheel shaft 15 and the second pinion shaft 17 are mechanically connected.
When a torque is applied to the handle 1 in this state, the control unit 9 controls the current of the motor 13 as shown in FIG. In FIG. 3, when the steering torque is increased to the right, the motor 13 is moved to the first and second power elements 9h ₁ and 9h at point a.
In order to reduce the influence of the inertia of the motor and mechanical system by turning on the h ₂ or the 3rd and 4th power elements 9h ₃ and 9h ₄ ,
A motor current of I _OF (about 2 to 10 A) is passed. Further, the steering torque is increased, and the motor current is linearly increased with respect to the steering torque from the point b to 100% current at the point c. On the contrary, the torque is reduced and the motor current decreases from the steering torque point c to the motor current value I _{OF at} the point b. When the torque further decreases to point a, the motor turns off.
The same control is performed in the leftward direction. The relationship between the transmission torque and the motor current is proportional. Therefore, when the torque increases in FIG. 3, the motor is turned on at the point a and the motor current of I _OF flows. When the torque is further increased, the motor current is controlled to be gradually increased from the point b. Therefore, the output torque to the worm shaft 14 is gradually increased, and the auxiliary torque according to the driver's force applied to the steering wheel 1 is increased. It is transmitted to the second rack tooth portion 6b via the worm wheel shaft 15, the electromagnetic clutch 16, and the second pinion shaft 17. Therefore, the handle 1 becomes lighter. The above is the operation of this device when the vehicle is stopped.

Next, when the vehicle is in a running state, the motor current is controlled by the vehicle speed d point (vehicle speed = V ₂ ) I as shown in FIG.
The current is reduced to _OF , and is made zero with the applied voltage of the electromagnetic clutch 16 at the vehicle speed at point e (vehicle speed = V ₁ ). Therefore, the worm wheel shaft 15 and the second pinion shaft 17 are disengaged from each other, so that the steering wheel is not assisted by the driver turning the steering wheel. By the way, when the state where the steering assist force is large, such as the steering when the vehicle is stopped, the control is performed as shown in the flow charts of FIGS. 6 and 8.
FIG. 5 shows an element temperature vs. ON resistance characteristic diagram of the power MOS FET, and there is a correlation between the element temperature θ _P of the power MOS FET and the ON resistance R _ON . Therefore, when the second power element 9h ₂ or the fourth power element 9h ₄ is turned on, the terminal voltage (drain-source voltage) and the second or fourth power element 9h ₂ detected by the current sensor 9i, The power element ON resistance is obtained from the 9h ₄ current, and the power element temperature θ _P is estimated from this ON resistance. FIG. 6 shows a motor current characteristic diagram with respect to time when the power element temperature is controlled within a predetermined temperature. In this figure, the power element (9h _{1 to} 9h ₄ ) temperature θ _P obtained by the above method is a predetermined value. Temperature θ _A (Power element breakdown limit temperature, for example, 100 to 1
50 ° C.) or higher, the motor current is reduced to control the temperature to be kept within the predetermined temperature θ _A , and it is possible to prevent the motor 13 and the power elements 9h _{1 to} 9h _{4 from} being destroyed.

Since the power element ON resistance corresponds to the power element temperature θp, it is possible to reliably detect overtemperature. At this time, since the power element ON resistance is calculated from the current value and the terminal voltage using a normal current sensor, an expensive sensor element such as a temperature sensor is not required, and the cost is not particularly increased.

Further, since the power element ON resistance is calculated by directly detecting the current value of the power element section 9h to be protected, the over temperature state of the power element can be detected reliably without being affected by the ambient temperature or the like. be able to.

FIG. 7 shows a cutoff characteristic diagram of the motor current with respect to time when the power element temperature θ _P exceeds a predetermined value θ _{A. When the} temperature of the power elements 9h _{1 to} 9h ₄ exceeds the predetermined temperature θ _A , Even if the steering assist force is controlled to zero for a predetermined time _Td (for example, 0.5 to 1 second), the same effect as above can be obtained.

〔The invention's effect〕

As described above, according to the present invention, the power element is turned on.
The power element temperature is obtained from the resistance, and the motor current is controlled to decrease so that this temperature falls within a predetermined value.
Since the motor current is continuously reduced according to the temperature rise time constant of the power element, the power steering is highly safe with less discomfort in steering.

Moreover, the power element can be turned on by using an ordinary current sensor without using an expensive sensor element such as a temperature sensor.
Since the power element temperature is estimated by calculating the resistance, there is no particular increase in cost. Furthermore, since the current value of the power element to be protected is directly detected,
The temperature state of the power element can be reliably detected without being affected by the ambient temperature and the like.

[Brief description of drawings]

1 is a block diagram of a motor drive type power steering control device according to an embodiment of the present invention, FIG. 2 is a block circuit diagram of a control unit, FIG. 3 is a control characteristic diagram of steering torque vs. motor current, and FIG. Is a control characteristic diagram of vehicle current vs. motor current and electromagnetic clutch applied voltage. Fig. 5 shows power MO
S FET element temperature vs. ON resistance characteristic diagram, FIG. 6 is a motor current characteristic diagram with respect to time when the power element temperature is controlled within a predetermined temperature, and FIG. 7 is a motor when the power element temperature exceeds a predetermined value. FIG. 8 is a flow chart of a control program, which is a cutoff characteristic diagram of current with respect to time. 1 ... Steering wheel, 3 ... Torque sensor, 9 ... Control unit, 9a ... Steering torque measuring means, 9b ... Vehicle speed measuring means, 9c ... Power element ON resistance calculating means, 9
d ... Power element over temperature determination means, 9e ... Motor current determination means, 9f ... Electromagnetic clutch control means, 9g ... Power element section control means, 9h ... Power element section, 9i ...
Current sensor, 10 ... Vehicle speed sensor, 11 ... Battery,
13 ... motor, 16 ... electromagnetic clutch. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (2)

[Claims] 1. A vehicle speed sensor for detecting a vehicle speed, a torque sensor provided in the middle of a steering shaft for detecting a turning force of a steering wheel, a control unit for inputting signals of the vehicle speed sensor and the torque sensor, and the control from a vehicle-mounted battery. A direct-current motor driven via a unit, wherein the control unit measures a steering torque by an input from the torque sensor, and a vehicle speed measuring means by which a vehicle speed is measured by an input from the vehicle speed sensor. And a monitor-driving power steering control device including a power element section including a plurality of power elements for controlling a direction and a current value of a motor current of the DC motor, wherein a current value flowing in the power element section is measured. A current sensor is provided, and the control unit is A power element ON resistance calculation means for calculating a power element ON resistance based on the current value and a voltage across the power element section when the power element is ON; and an overtemperature of the power element section from the power element ON resistance. Power element over temperature determination means for determining the state, and a motor current determination means for determining the motor current according to the output of the power element over temperature determination means and the steering torque, the power element control means, A motor drive type characterized in that the power element is controlled based on the output of the motor current determination means, and the power element section controls the direction and current value of the motor current based on the output of the power element control means. Power steering control device. 2. The motor-driven power steering control device according to claim 1, wherein the power element section is a power MOSFET.