JPH03227769A - Electrically driven power steering device - Google Patents

Abstract

PURPOSE:To enable correct identification of a fault by providing a main and a sub sensors as two torque sensors, making difference in detection values of both torque sensors during a predetermined stop state of a vehicle a steady state deviation, and performing fault identification of the torque sensors with the steady state deviation taken into consideration. CONSTITUTION:An electrically driven power steering apparatus 1 has a worm gear 13 which is rotated by a dc motor 11 via an electromagnetic clutch 12 engaged with a worm wheel 14 which is fixed to an output shaft 3a so as to reinforce a steering torque, while the dc motor 11 is controlled according to outputs of a steering angle sensor 20 and a torque sensor 23. In this case a main and a sub sensors are provided as two torque sensors 23 wherein difference in detection values of both torque sensors is calculated as a steady state deviation when vehicle speed and steering speed are both zero as well as the detection value of the main sensor is a first specific value or less. When an absolute value of a value wherein the steady-state deviation is subtracted from the difference in the detection values of both torque sensors at the time of steering is a specific value or more, identification that the torque sensor is defective is made.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electric power steering device, and more particularly to an improved failure determination means for a torque sensor that detects steering torque.

[Prior art]

2. Description of the Related Art Conventionally, power steering devices with various mechanisms for reducing the operating force of a steering wheel of a vehicle have been put into practical use.

Hydraulic power steering devices have been widely put into practical use, but they require complex control valves and various sealing mechanisms to seal the hydraulic pressure, and the overall number of parts is large. It becomes expensive.

Therefore, recently, electric power steering devices in which an electric motor generates an assist force according to the steering torque detected by a torque sensor are being put into practical use, especially for light vehicles.

In the above electric power steering device, a steering angle sensor and a torque sensor are incorporated in the steering wheel shaft, and a DC electric motor with an electric clutch is provided to rotationally drive the output shaft portion of the steering wheel shaft via a worm gear mechanism. Assist torque is determined using steering torque, vehicle speed, steering angle, steering angle speed, steering angle acceleration, etc. as parameters, and the direction and magnitude of the drive current of the DC electric motor is controlled by the control device so that the assist torque is generated. It has become.

In this type of electric power steering device, erroneous control may occur if the torque sensor fails, so as a fail-safe measure, two sets of torque sensors are generally provided as torque sensors, and the output is based on the output of the two sets of torque sensors. It is designed to determine if the torque sensor is malfunctioning.

For example, in the electric power steering device described in Japanese Patent Application Laid-Open No. 63-82875, when there is a difference in the rate of change in the detected values of two sets of torque sensors, the torque sensor that shows the smallest rate of change is selected. It employs a torque sensor abnormality determination technology that determines that the torque sensor is abnormal, or determines that the torque sensor is abnormal when the detected value exceeds a predetermined range.

[Invention] (Problem to be solved)

The above-mentioned torque sensor is often composed of a torsion bar that is elastically twisted and deformed by the steering torque, and a potentiometer that electrically detects the torsion angle of the torsion bar. Not only can failures occur due to broken wires or poor contact, but they can also deteriorate due to changes in the characteristics of the potentiometer's electrical resistance wires during long-term use.

Here, the two sets of torque sensors may not have exactly the same characteristics due to product variations including manufacturing errors.
Although it is inevitable that steady-state deviations occur in the detected values of these torque sensors, the device disclosed in the above publication does not take the above-mentioned steady-state deviations into account, but simply determines the magnitude of the change rate of the detected value of the 2M torque sensor and the fluctuation of the detected value. Since the abnormality of the torque sensor is determined from the width, it may be determined that the torque sensor is abnormal even though it is not abnormal, or that the torque sensor is determined to be normal even though it is abnormal.

An object of the present invention is to provide an electric power steering device that can accurately determine abnormality of a torque sensor by taking into consideration the steady-state deviation of two sets of torque sensors.

[Means to solve the problem]

An electric power steering device according to a first aspect of the present invention includes a torque sensor that detects at least a steering torque, and outputs an assist force according to the steering torque detected by the torque sensor. A main torque sensor and a sub-torque sensor are provided as and a steady-state deviation calculation means that reads the output of the sub-torque sensor and calculates the difference between the detected values of these two torque sensors as a steady-state deviation, and a steady-state deviation calculating means that calculates the difference between the detected values of both the torque sensors in the steering state by subtracting the steady-state deviation. and first failure determination means that determines that the torque sensor is in failure when the absolute value is greater than or equal to a predetermined set value.

The electric power steering device according to a second aspect of the present invention is the electric power steering device according to the first aspect, which determines that the torque sensor is malfunctioning when the steady-state deviation calculated by the steady-state deviation calculation means is equal to or larger than a second predetermined value. It is equipped with a second failure determination means.

[Function] The electric power steering device according to the first aspect basically assists steering by outputting an assist force according to the steering torque detected by the torque sensor.

Here, in order to prevent failures of the torque sensor, a main torque sensor and a sub-torque sensor are provided as torque sensors, but due to product variations including manufacturing errors of these two torque sensors, the detected values of both torque sensors There is a steady deviation between them.

Therefore, when the vehicle speed is zero, the steering angular velocity is zero, and the detected value of the main torque sensor is less than or equal to the first predetermined value, that is, when the vehicle is stopped and not being steered, The difference between the detected values of both torque sensors is calculated as a steady deviation 2 and stored. Since the steady-state deviation is determined by reading the outputs of both torque sensors under the above-mentioned static conditions, this steady-state deviation takes into account product variations between the two torque sensors and differences in the degree of deterioration between the two torque sensors. become.

The first failure determination means reads the detection values of both torque sensors during the steering state, calculates the absolute value of the difference between these detection values minus the steady-state deviation, and calculates the absolute value of the value obtained by subtracting the steady-state deviation from the difference between these detection values. Sometimes it is determined that the torque sensor is malfunctioning.

That is, when both torque sensors are normal, the difference between the detection values of both torque sensors in the steering state is equal to the steady-state deviation, so the above absolute value becomes zero. On the other hand, in the main torque sensor, if the sub torque sensor fails, the above absolute value becomes larger than the steady deviation (increases according to the steering torque), so it is difficult to accurately detect abnormalities in the torque sensor. I can do it. In this way, it is possible to accurately and reliably detect an abnormality in the torque sensor by eliminating the influence of the steady-state deviation between the detected values of both torque sensors.

In the electric power steering device according to the second claim, basically the same effect as the first claim can be obtained. In addition, the second failure determination means determines that the torque sensor is malfunctioning when the steady-state deviation calculated by the steady-state deviation calculation means is equal to or greater than a second predetermined value.

In other words, when both torque sensors are normal, the steady-state deviation will not become very large, but if the main torque sensor or sub-torque sensor fails, the steady-state deviation may become considerably large. Based on this, it is possible to detect an abnormality in the torque sensor. In this manner, since the second failure determination means determines a failure using a different determination criterion from that of the first failure determination means, the reliability of failure detection of the torque sensor is increased.

In this way, the first failure determination means and the second failure determination means perform failure determination using doubly different determination criteria, thereby increasing the reliability of the apparatus.

〔Effect of the invention〕

According to the electric power steering device according to the first aspect, as explained in the above [Operation] section, the torque sensor is Accurately identify abnormalities
It can be detected reliably.

According to the electric power steering device according to the second claim, in addition to basically obtaining the same effects as in the first claim, failure detection of the torque sensor is provided by providing the second failure determination means. It is possible to increase the reliability of the system and improve the reliability of the device.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

This embodiment is an example in which the present invention is applied to an electric power steering device for a light vehicle.

As shown in FIGS. 1 and 2, an electric power steering device 1 for an automobile M includes a steering wheel 2 for steering, a steering shaft 3 extending downward from the steering wheel 2, and a steering shaft 3.
, a lower steering shaft 3B connected to the output shaft 3A via a universal joint 5, and a gear box 7 connected to the lower end of the lower steering shaft 3B via a universal joint 6. A pinion (not shown) housed in the rack shaft 9, a rack shaft 9 that meshes with the pinion and is housed in a rank shaft case 8 that is integrally fixed to the gear box 7, A pair of left and right tie rods 10 are connected to both ends of a shaft 9 via pole joints, and each tie rod 1 has an outer end connected to a knuckle arm of a front wheel support member.
0 is provided, and furthermore, the following sensors and a DC motor 11 for generating assist force are provided.

At the bottom of the steering shaft 3, there are two sets of known steering angle sensors 20 (a first steering angle sensor 21 and a second steering angle sensor 20) that electrically detect the steering angle of the steering shaft 3 using a sliding resistance transducer. An angle sensor (referred to as an angle sensor 22) is fixedly provided on the steering column 4, and the steering torque applied from the steering wheel 2 is applied to the output shaft portion 3A and a portion near the lower end of the steering shaft 3 above the output shaft portion 3A by sliding the torsion bar. Two sets of known torque sensors 23 electrically detected by dynamic resistance transducers (these are
A main torque sensor 24 and a sub-torque sensor 25) are provided. In this torque sensor 23, a portion near the lower end of the steering shaft 3 and an output shaft portion 3A
are connected via a torsion bar, and a relative rotational displacement occurs between the lower end vicinity and the output shaft section 3A through elastic torsional deformation of the torsion bar due to steering torque.
The angular displacement is configured to be electrically detected by a sliding resistance transducer.

Further, a DC motor 11 and an electromagnetic clutch 12 are controlled by a control unit C, which will be described later, to apply assist torque AT to the output shaft portion 3A of the steering shaft 3.
is attached to the casing 4A on the lower end side of the steering column 4, and the electromagnetic clutch 1 is driven by the DC motor 11.
A worm gear 13, which is rotatably driven through a worm gear 2, is meshed and connected to a worm wheel 14 that is externally fitted and fixed to the output shaft portion 3A. Therefore, by driving the motor 11 in forward or reverse rotation with the electromagnetic clutch 12 turned on, the output shaft portion 3
It is possible to add an assist torque AT that rotates A in the right turning direction or left turning direction.

Next, the control system of the electric power steering device 1 will be explained.

As shown in FIG. 3, the first and second steering angle sensors 21 and 22, the main and sub torque sensors 24 are used as sensors and switches for inputting various signals to the control unit C that has a built-in microcomputer. - In addition to 25, at least a vehicle speed sensor 26, a crank angle sensor 27, and a reverse switch 28 are provided.

The vehicle speed sensor 26 is a sensor that electrically detects, for example, the rotational speed of the automatic transmission output shaft (that is, the rotational speed of the propeller shaft), but may also detect the rotational speed of the front wheels or rear wheels.

The reverse switch 28 is a switch that is installed in the automatic transmission and turns on when the gear is switched to reverse J.The crank angle sensor 27 is installed in conjunction with the distributor or crankshaft of the engine. There are some that electrically detect the rotational speed of the crankshaft.

The reverse signal from the reverse switch 28 is input to a waveform shaping circuit 31 via a digital buffer 30, where it is converted into a pulse signal and converted into a pulse signal.
Input to U33, and also output side terminal 2 of the alternator
The generated voltage signal from 9 is input to the waveform shaping circuit 32 via the digital buffer 30.
The vehicle speed signal from the vehicle speed sensor 26 and the crank angle signal from the crank angle sensor 27 are converted into pulse signals and input to the CPU 33 via a digital buffer 30.
33.

The steering angle signals from the first and second steering angle sensors 21 and 22 and the torque signals from the main and sub torque sensors 24 and 25 are input to an A/D converter 37 via an analog buffer 36, and this A/D converter 37, it is converted into a digital signal and input to the CPU 33.

The CPU 33 is connected to the ROM 34 and RAM 35 via the bus.
The ROM 34 stores in advance a control program that will be described later for controlling the DC motor 11 and the electromagnetic clutch 12, and the RAM 35 stores various memories (registers, flag memory, soft counter memory, etc.) necessary for the control arithmetic processing. etc.) are provided.

The battery 38 as a power source is connected to the ignition switch 39
is connected to the constant voltage circuit 40 via the constant voltage circuit 4.
A predetermined constant voltage (for example, 5V) is supplied from 0 to the CPU 33, and in order to detect the voltage of the battery 38, the output voltage of the output terminal of the battery 38 is converted into a digital signal by the A/D converter 37 and sent to the CPU 33. It has been entered.

In order to control the direction and magnitude of the DC current supplied to the DC motor 11, a D/A converter 4 receives a digital motor drive current control signal from the CPU 33 and converts it into D/A.
1, an analog control signal supplied from the D/A converter 41, and an analog current detection signal supplied from the current detector 45 so that the current has the direction and magnitude specified by the control signal. A current control circuit 42 feedback-controls the motor drive current using PWM, a driver 43 that receives and amplifies an analog command signal supplied from the current control circuit 42, and a power supply line 46 connected to the output terminal of the battery 38. A power circuit 44 is connected to the motor 1 and supplies a motor drive current to the motor 11 in accordance with an amplified command signal supplied from the driver 43. In addition, current detector 4
5 is interposed in the ground line from the power circuit 44 to the ground, detects the direction and magnitude of the motor drive current, and supplies the analog detection signal to the current control circuit 42 and the A/D converter 37.

In order to control the 0N10FF and magnitude of the excitation current supplied to the electromagnetic clutch 12 incorporated in the motor 11, the CP
A current control circuit 48 receives a control signal from the CPU 33 and is connected to the input line 51 of the constant voltage circuit 40 via the power supply line 47 and to the input terminal of the solenoid 12a of the electromagnetic clutch 12, and receives a control signal from the CPU 33. A drive circuit 49 that is connected to the output terminal of the solenoid 12a and turns on or off an excitation current according to a control signal, and a monitor circuit 50 that monitors the excitation current of the solenoid 12a and supplies a monitor signal to the CPU 33 are provided. . Note that when the constant voltage circuit 40 becomes unable to output a predetermined constant voltage due to a drop in battery voltage, etc.
Since the operation of the PU33 is no longer guaranteed, in this case, the helicent signal R8T is transmitted from the constant voltage circuit 40 to the current control circuit 48.
is output, the exciting current is switched OFF, and the electromagnetic clutch 12 is switched OFF (disconnected state).

Next, a control routine executed by the control program stored in the ROM 34 of the control unit C will be explained based on the flowcharts of FIGS. 4 to 6. In the figure, 5i (i=positive integer) indicates each routine or each step.

As shown in FIG. 4, when control is started in response to turning on the ignition switch 39, necessary initial settings are first performed (Sl), and then in 810 the torque sensor 2
A steady-state deviation calculation processing routine (see Fig. 5) for calculating the steady-state deviation of 4.25 is executed, then a control routine for the motor 11 and clutch 12 (see Fig. 6) is executed at 320, and from then on this control routine is executed. The routine is executed repeatedly.

As shown in FIG. 5, when the steady-state deviation calculation processing routine is started, the vehicle speed signal V from the vehicle speed sensor 26, the steering angle signal θ1 from the first steering angle sensor 21, and the main torque sensor 2
The torque signal Tm from 4 is read (Sll), but it is read a plurality of times in a predetermined minute time. Next, when the vehicle speed ■=0, the absolute value of the torque Tm is less than a predetermined small constant 01, and the steering angular speed θ9=0 (312 to 515), the main and sub torque sensor 24
・Torque signals Tm and Ts from 25 are read (S16
), then the steady-state deviation ΔTd between the detected values of both torque sensors 24 and 25 is calculated by ΔTd=(Tm-Ts) (S17).

In this way, the steady state deviation Δ is calculated by reading the torque signals Tm and Ts when the vehicle is substantially stopped and not being steered.
By calculating Td, both torque sensors 24 and 25
The product variation and the difference in the degree of deterioration can be determined as the steady-state deviation ΔTd.

Next, a control routine for the motor 11 and clutch 12, which is executed after the steady-state deviation calculation processing routine described above, will be explained based on the flowchart shown in FIG.

When this control routine is started, it is determined whether the absolute value of the steady-state deviation ΔTd obtained as described above is greater than or equal to a predetermined constant 02 (S21), and if Yes, both torque sensors 2
4.25 (since one of them is faulty, it is determined that the torque sensor is faulty (S22), and a clutch OFF control signal to switch the electromagnetic clutch 12 OFF is output to the drive circuit 49 and the motor 11 is stopped. A motor stop control signal is output to the D/A converter 41, and an alarm output control signal is output to the drive circuit for the alarm lamp and alarm buzzer (the path shown) (S22), and then S22 is repeated.

On the other hand, when 1ΔTdl<C2, both torque sensors 2
Since 4.25 is normal, the memory data of the steady-state deviation ΔTd stored in the memory of the RAM 35 is updated with the current data (323), and then the vehicle speed signal ■, the steering angle signal θ, and the torque signal Tm are read. Rarely (S24), and the vehicle speed V is not too high and is equal to or higher than the predetermined value 03 (S25: Yes)
, and the absolute value of the steering angle θ8 is equal to or greater than the small predetermined value 04 (S26: Yes), and the absolute value of the torque Tm is equal to or greater than the predetermined value 05 (S27: Yes), that is, the vehicle is in a running state and the steering is not performed. When the torque signal T m s T s is in the state of
This is executed by determining whether dl≧C6 (where C6 is a predetermined set value) (S29), and if YES, it is determined that the torque sensor has failed and the process moves to S22.

In other words, to give a supplementary explanation, the main and sub torque sensors 2
When 4.25 is operating normally, (Tm - Ts) using the torque signals Tm and Ts read in 528 should be substantially equal to the steady-state deviation ΔTd, in which case l(
Tm-Ts)-ΔTd1#0. However, when one of both torque sensors 24 and 25 fails (Tm-T
s) becomes significantly larger or smaller, I (
TmTs)-ΔTdl≧C6.

When both torque sensors 24 and 25 are normal (S29:
No), motor 1 is set by steps 530-336.
1 and clutch 12 are controlled.

First, the vehicle speed signal ■, the steering angle signal θ, and the torque signal Tm are read (S30), and then the basic assist torque is set to XT.
m is calculated (S31). In the above basic assist torque, XTm is preset to the characteristics shown in Fig. 7 using vehicle speed ■ and detected steering torque Tm as parameters, and K1 is a function of vehicle speed ■ and torque Tm, (V, Tm). , whose function K(V, Tm) is, for example? , is stored in the ROM 34 in the form of a map, and the basic assist torque XTm is calculated using the value read from the map. Here, as shown in Fig. 7, the basic assist torque is XTm
The torque T decreases as the vehicle speed increases.
It is set to increase as m increases.

Next, the current steering angle θ and the previous steering angle θ are used to calculate the steering angular velocity θ9, and the steering angular velocity θ1 is used to calculate the steering angular velocity correction term Xθ□ (S32). In this correction term,
and the function of the steering angular velocity θ□ is 2(V, θ,), and the number between them is 2(V, θ,), for example, as RO in the form of a map.
Since it is stored in M34, 2×θ is calculated for the steering angular velocity correction term using the value read from the map.

Note that 2Xθ□ in this correction term is intended to correct the assist torque AT to the decreasing side to ensure steering stability especially when the steering angular velocity θ is large.

Next, the steering angle acceleration θ is calculated using the current steering angular velocity θ and the previous steering angular velocity θ, and 3Xθ is calculated as the steering angle acceleration correction term (S33).

In this correction term, Xθ is set to a characteristic as shown in FIG. 9 using the steering angle acceleration θi as a parameter, and 3 is a predetermined constant. In this correction term, Xθ is intended to correct a response delay due to the inertia of the rotor of the motor 11 at the start of steering.

Next, 4×θ8 is calculated as a steering angle correction term using the steering angle θ given by the steering angle signal θ9 (S34). This correction term, 4×θ□, is set to the characteristic shown in FIG. 10 using the steering angle θ□ as a parameter, and is calculated using a predetermined calculation formula. still,
4×θH is added to this correction term to add a return torque to return the steering wheel 2 to the center position, and hunting is prevented by providing a dead zone (see FIG. 10).

Next, the basic assist torque is XTm and the four correction terms are 2×θH, Ki xθ□, K4×θ, and the motor 1
1, the assist torque AT that assists the steering shaft 3 is AT=, XTm- is 2×θ, and + is 3Xθ.
It is calculated using the formula HK4Xθ8 (S35), and then the motor drive current control signal (this is a signal that commands the direction and magnitude of the current) corresponding to the assist torque AT is D.
/A converter 41, and a clutch ON control signal for switching clutch 12 to ON is output to drive circuit 4.
9 (S36), and then steps 821 to S36 are repeated.

Although omitted in the above explanation, in the routine of FIG. 5, the steady deviation is also calculated for the steering angle signals θ8 and θ'9 from the first and second steering angle sensors 21 and 22 in the same way as for the torque signals Tm and Ts. It is also possible to determine the failure of both side angle sensors 21 and 22 using the same method as in S21 and S29, and to proceed to S22 when the steering angle sensor 2o fails. It is also conceivable to set 4 in FIG. 10 as 4 (V) as a function of the vehicle speed.

Incidentally, the crank angle sensor 27 is provided as a countermeasure against a failure of the vehicle speed sensor 26, and the crank angle sensor 27 is provided as a countermeasure against a failure of the vehicle speed sensor 26.
Since there is generally a certain correlation between the two, the vehicle speed is estimated based on the crank angle signal when the vehicle speed sensor 26 fails. In addition, the reverse switch 28
When the reverse signal is turned on, control is performed to reduce the assist torque AT by a predetermined percentage. Furthermore, when the voltage generated by the alternator is below a predetermined value, control is executed to turn off the motor 11 and clutch 12.

Next, the operation of the electric power steering device 1 will be explained.

As can be seen from steps S12 to S15, S16, and S17, the steady deviation ΔTd is calculated by reading the torque signals Tm and Ts when the vehicle is stopped and in a static state in which no steering is being performed. ΔTd can be determined accurately.

When the torque sensor 23 fails, the steady-state deviation ΔT
Since the absolute value of d reliably increases, the failure of the torque sensor 23 can be reliably detected by step 321, and moreover, it can be detected before the automobile M starts running.

In addition, as can be seen from the steps 325 to S27, when the torque sensor 23 is out of order in the running state and the steering state, l(Tm-Ts)ΔTdi definitely increases, so the torque sensor 23 is broken in the step S29. 23 can be reliably detected, and can be detected without the influence of the steady-state deviation ΔTd.

Since the steps S21 and S29 perform a double failure determination based on different criteria, the reliability of the failure determination can be improved.

Incidentally, as a mechanism for applying assist 1-lux AT to the steering shaft 3 by the DC motor 11, a structure as shown in FIG. 11 may be adopted.

That is, the steering angle sensor 20 and the torque sensor 23 are assembled to the lowest steering shaft 3C connected to the lower steering shaft 3B via a universal joint, and the output shaft 3D is connected to the shaft 3C via a torsion bar.
A pinion 16 that meshes with the disc member 15 and the rack 9 is fixed to the disc member 15 , and a pinion 17 that meshes with a gear on the upper surface of the disc member 15 is rotationally driven by a DC motor 11 via an electromagnetic clutch 12 . It should be noted that the structure other than this is the same as that of the previous embodiment, so a description thereof will be omitted.

[Brief explanation of drawings]

The drawings show embodiments of the present invention, and FIG. 1 is similar to FIG. 4. Figure 5 No. 9 figure Figure 10 Figure 11

Claims (2)

[Claims] (1) In an electric power steering device that has at least a torque sensor that detects steering torque and outputs an assist force according to the steering torque detected by the torque sensor, a main torque sensor and a sub-torque sensor are provided as the torque sensor. , when the vehicle speed detected by the vehicle speed sensor is zero, the steering angle speed detected by the steering angle sensor is zero, and the detected value of the main torque sensor is less than or equal to a first predetermined value, read the outputs of the main and sub torque sensors and use these. A steady-state deviation calculation means that calculates the difference between the detected values of the two torque sensors as a steady-state deviation, and when the absolute value of the value obtained by subtracting the steady-state deviation from the difference between the detected values of the two torque sensors in the steering state is greater than or equal to a predetermined set value. a first failure determination means for determining that the torque sensor is in failure;
An electric power steering device characterized by being equipped with. (2) The device according to claim 1, further comprising second failure determination means for determining that the torque sensor is at fault when the steady-state deviation determined by the steady-state deviation calculation means is equal to or greater than a second predetermined value. electric power steering device.