JPH0478662A - Motor-driven power steering - Google Patents

Abstract

PURPOSE:To enable the positive abnormality detection of a torque sensor by forming a torque sensor in such a way that signals from its detecting parts are amplified so as to be outputted as the first and second output and the amplitude of each output differs. CONSTITUTION:A torque sensor 3 has a detecting part 20 provided with a detecting converter part for outputting a detecting signal Sa and a compensating converter part for outputting a compensating signal Sb. The detecting signal Sa is inputted into the first input terminals of two differential amplifier circuits 25, 26 through a first clamping circuit 21 and a first peak holding circuit 23, and the compensating signal Sb is inputted into the second input terminals of two differential amplifier circuits 25, 26 through a second clamping circuit 22 and a second peak holding circuit 24. Both signals Sa, Sb are then outputted as the first and second output V1, V2 from the respective differential amplifier circuits 25, 26. The first output V1 is used for the control of auxiliary steering force quantity or the like by the computer 6 of a controller 5, and the second output V2 is used for the abnormality detection of a torque sensor 3 or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an electric power steering device for, for example, an automobile.

BACKGROUND OF THE INVENTION For example, it is known that an electric power steering device for an automobile includes a torque sensor for detecting steering torque and an electric motor for assisting steering force that is driven based on the detected value of the torque sensor. In this type of conventional torque sensor for electric power steering devices, the signal from the detection section is amplified with the same amplification degree, and is output as two outputs, for example, a first output for control and a second output for abnormality detection. It was outputting.

Furthermore, the two outputs of the torque sensor were current outputs so as not to be affected by the contact resistance of the connector.

Problems to be Solved by the Invention In the electric power steering device as described above, an abnormality in the torque sensor is detected by comparing two outputs of the torque sensor, or whether the two outputs have the same amplification degree. Since the signals are of the same magnitude, if an abnormality such as voltage drop occurs in the power supply of the torque sensor, the two outputs will decrease in the same way and become the same magnitude, so the two outputs will be the same. Abnormalities cannot be detected just by comparing the outputs.

In addition, since the two outputs are current outputs, two voltage-current conversion circuits are required on the torque sensor side, and two current-voltage conversion circuits are required on the other side that uses the output of the torque sensor, which reduces the number of parts. In addition, high-precision parts are required for both the torque sensor side and the other side, which increases costs.

An object of the present invention is to provide an electric power steering device that solves the above problems.

Means for Solving the Problems An electric power steering device according to the present invention includes: a torque sensor that detects steering torque; and an electric motor for assisting steering force that is driven based on the detected value of the torque sensor. In the torque steering device, the torque sensor amplifies the signal from the detection section and outputs the amplified signal as a first output and a second output, and the amplification degree of the first output and the second output is set to be different. It is characterized by the fact that

Furthermore, means for calculating the first output calculation value from the second output based on the ratio of the amplification degree of the first output and the amplification degree of the second output of the torque sensor; The present invention is characterized by comprising a monitoring means for detecting an abnormality in the torque sensor when the difference is greater than or equal to a predetermined value, and a means for stopping steering force assistance by the electric motor when an abnormality is detected by the monitoring means. It is something.

Preferably, the first and second outputs of the torque sensor are voltage outputs.

Since the amplification degrees of the first output and the second output of the working torque sensor are set to be different, the relationship between the two outputs in an abnormal state is different from that in a normal state.

and calculating a first output calculation value from the second output based on the ratio of the amplification degree of the first output and the amplification degree of the second output, and checking the difference between the first output and this first output calculation value. Therefore, even if the two outputs fall in the same way due to a voltage drop in the power supply, this can be easily and reliably detected.

When the first and second outputs of the torque sensor are made into voltage outputs, two voltage-current conversion circuits on the torque sensor side and two current-voltage conversion circuits on the other side, which were required in the case of conventional current outputs, are replaced. becomes unnecessary.

Embodiments Hereinafter, embodiments in which the present invention is applied to an electric power steering device for an automobile will be described with reference to the drawings.

FIG. 1 shows a schematic configuration of an electric power steering device.

This device uses an electric motor (1) to assist the steering force.
, an electromagnetic clutch (2) provided between the motor (1) and the steering system, a torque sensor (3) for detecting the input torque of the steering shaft, a vehicle speed sensor (4) for detecting the vehicle speed, and These sensors (3
) and a controller (5) that controls the motor (1) and the clutch (2) based on the output of (4).

The controller (5) is a microcomputer (6)
, 5V regulator (7), 8V regulator (8)
, motor drive main circuit (9), main circuit drive circuit (10)
, a current detection circuit (11) of the main circuit (9), a clutch drive circuit (12), a relay drive circuit (151,), a fail relay (5), etc.

The two regulators (7) (8) are connected to the key switch (
13) is connected to the battery (main power supply) (+4). The output of the 5V regulator (A) is connected to a computer (6), and the output of the 8V regulator (8) is connected to a current detection circuit (11) and a torque sensor (3).

The motor (1) is connected to the main circuit (9),
are the main circuit drive circuit (10) and the current detection circuit (+1)
It is connected to the computer (6) via. The clutch (2) is connected to the computer (6) via a clutch drive circuit (12). The main circuit (9) and the clutch drive circuit (12) are connected to the battery (+4) via the fail relay (15).
) is connected to the computer (
6). The main circuit drive circuit (10) is connected to a battery (14). Although not shown,
The main circuit (9) includes a bridge circuit consisting of four power elements (power transistors), and each power element is connected to the computer (6) via the main circuit drive circuit (10).
) is controlled by The motor (1) is PWM controlled to save power.

Battery (14) key switch (+3), torque sensor (3), vehicle speed sensor (4) and alternator (+6)
) or via the interface (17) to the computer (
6).

The computer (6) controls the main circuit drive circuit (10) etc. based on the detected torque of the torque sensor (3), the detected speed of the vehicle speed sensor (4), etc., and thereby controls the motor (
1) controls the amount of steering force assistance.

Figure 2 shows an example of a torque sensor (3) and a controller (
5) is shown in detail.

This torque sensor (3) is a 3-terminal regulator (18
), an oscillation circuit (19), a detection unit (20), a first clamp circuit (21) and a second clamp circuit (22), a first peak hold circuit (23) and a second peak hold circuit (24), and a first peak hold circuit (23) and a second peak hold circuit (24). 1 differential amplifier circuit (25) and a second differential amplifier circuit (26).

The three-terminal regulator (18) is connected to the 8V regulator (8) of the controller (5).

Although not shown, the detection section (20) includes a detection conversion section that outputs a detection signal Sa and a compensation conversion section that outputs a compensation signal sb. The detection signal Sa is transmitted through the first clamp circuit (21) and the first peak hold circuit (23).
The signal is then input to the first input terminals of two differential amplifier circuits (25) and (26). The compensation signal sb is input to the second input terminals of the two differential amplifier circuits (25) (2G) via the second clamp circuit (22) and the second peak clamp circuit (24). The amplification degrees of the two differential amplifier circuits (25) (2B) are different, the amplification degree of the first differential amplifier circuit (25) is A, and the amplification degree of the second differential amplifier circuit (26) is Alx (
χ≠1). The first differential amplifier circuit (25) differentially amplifies the difference between the output voltages of the two peak hold circuits (23) and (24) with an amplification degree A, and outputs this as a first output V1. The second differential amplifier circuit (26) differentially amplifies the difference between the output voltages of the two peak hold circuits (23) and (24) with an amplification degree of A/χ, and outputs this as a second output V2.

The first output v1 of the torque sensor (3) is output from the controller (5
) first filter circuit (27) and AD transformer 2B
) is input to the computer (6>) and is used for controlling the aforementioned steering force assistance amount.Torque sensor (
The second output V2 of 3> is input to the computer (6) via the second filter circuit (29) of the controller (5) and the AD converter (28), and is used to detect abnormalities in the torque sensor (3). used for.

The above torque sensor has the first output ■1 and the second output v2.
Since the amplification degrees of the two outputs V1 and +2 are set to be different, even if the two outputs Vl and +2 fall in the same way due to a voltage drop in the power supply, this can be easily and reliably detected.

Next, the reason will be explained with reference to FIGS. 3 and 4. Note that, as mentioned above, the amplification degree of the first output V1 is A
1 Since the amplification degree of the second output V2 is Alx, the amplification degree of the first output v1 is χ when the amplification degree of the second output 2 is set to 1.

FIG. 3 shows the relationship between the torque and the two outputs of the torque sensor in a normal state and FIG. 4 in an abnormal state. In these drawings, the horizontal axis represents torque T1, and the vertical axis represents first output V1 and second output (2). Also, the neutral point is torque or 0
It represents the magnitude of the torque to the left of the neutral point or in the counterclockwise rotation direction, and the magnitude of the torque to the right or clockwise rotation direction of the neutral point.

As shown in Figure 3, under normal conditions, the first
Output ■15 2nd output ■2 Both are V.

becomes. This VO is constant and will be referred to as the neutral point output. The following relationship exists between the first output V1 and the second output v2 during normal operation.

Vl −x (V2−Vo) 10Vo,, −=・−
mThe first output V1 during normal operation is V1 o sThe second output ■2
Assuming that V2o is V2o, the above equation (1) can be rewritten as follows.

Vlo−χ (V2o−Vo)+Vo・・・・・・
・(2) Furthermore, the value of the first output V1 (first output calculation value) calculated using the second output V2 according to equation (1) is expressed as Via
Then, Via becomes as follows.

Vla-X (V2-Vo) + Vo
-. (3) Under normal conditions, it is V2-V2o, so if this is substituted into equation (3) and Via is calculated, the following is obtained.

Vla=χ(V2o−Vo)→−V o −= −−
(4) Since the right sides of equation (2) and equation (4) are equal, V l
o −Vla. Also, under normal conditions, Vl −Vl
o, so Vl-vta. In this way, under normal conditions, the first output calculation value Vi calculated using the second output
a and the first output V1 are always equal, and their difference S (=
V], -Via,) is always O.

FIG. 4 shows a case where the same amount of output fluctuation ΔV occurs in the first output V1 and the second output V2. For example, due to a voltage drop in the power supply, the first output V1 and the second output V2
Assuming that V drops to V, these become as follows.

Vl -Vlo-AV... (5) V2-
V2o-AV・・・・・・・・・(6) ■2 of formula (6)
When Via is calculated by substituting into equation (3), the result is as follows.

V la = x f (V 2o - AV) - Vo
) +■.

=x (V2o-Vo) +Vo -1Δ■
... (7) From equation (2), equation (7) becomes as follows.

Via-Vlo-χ AV (8) 1st of equation (5). Output ■1 and the first output calculation value V of equation (8)
The difference S from ia is calculated as follows.

5=Vl −Vl, a = (Vl, o −AV) −(Vlo−x Δ■)
-(χ-1)AV (9) In equation (9), since χ≠1, χ-1≠0. When there is an output fluctuation ΔV, ΔV≠0, so S≠0. On the other hand, if there is no output fluctuation Δ■, then ΔV-0, so S-0. This is clear from the fact that Vl -Via occurs during normal operation as described above.

Therefore, by constantly checking the difference S between the first output V1 and the first output calculation value Via calculated using the second output V2, abnormalities such as output fluctuations can be reliably detected.

The flowchart in FIG. 5 shows an example of abnormality detection processing of the torque sensor (3) by the computer (6). Note that this program is repeatedly executed at fixed time intervals.

In FIG. 5, first, it is checked whether the timer has timed up (step 1). This timer is used to determine the time interval for abnormality detection processing, and if this timer has not timed up, it means that the time for abnormality detection processing has not arrived, and the processing should be terminated and the timer should be set to time up. For example, the abnormality detection processing in step 2 and subsequent steps is performed.

In step 2, the first output v1 of the torque sensor (3) is read from the AD converter (28). Next, the AD converter (2
Read the second output V2 of the torque sensor (3) from 8) (
Step 3), using this ■2, the first
An output calculation value Via is calculated (step 4). Next, V
Calculate the difference S between l and Via (Step 5) and check whether its absolute value 1sI is smaller than a predetermined threshold (
Step 6).

If IsI is less than the threshold in step 6, then
It is determined that there is no abnormality, the NG timer is cleared (step 7), and the process is terminated.

If IsI is not smaller than the threshold value in step 6, it is determined that there is a possibility of an abnormality, and the NG timer is incremented by 1 (step 8). Next, it is checked whether or not the NG timer has timed up (step 9), and if the time has not expired, the process is terminated. If the NG timer times up in step 9, this means that the state in which IsI is equal to or higher than the threshold value has continued for a certain period of time or more, so it is determined that there is an abnormality and fail-safe processing is performed (step 10). That is, the fail relay (15) is turned off and steering force assistance by the motor (1) is stopped.

As mentioned above, if there is no abnormality in the torque sensor (3), the result is S-0, but if an abnormality such as output fluctuation occurs due to a voltage drop in the power supply, S≠O. Therefore, by comparing IsI with the threshold value as described above, it is possible to reliably detect an abnormality in the torque sensor (3).

In the flowchart of FIG. 5, the first output calculation value Via
Since χ and neutral point output VO in equation (3) for calculating are constant and known in advance, they can be calculated by computer (
6).

The neutral point output Vo is also expressed by the equation (1) as follows.

Vo −(Vl −χV2 ) / (1−χ) ・(
10) As mentioned above, since χ is constant and known in advance, the first
The neutral point output Vo can be calculated using equation (1o) using the output V] and the second output V2.

For example, it is possible to measure Vl and V2 when the power is turned on, use these to calculate Vo, and set this in the computer (6).

When an abnormality occurs in the torque sensor (3), the calculated value of VO calculated by equation (10) changes. Therefore, it is also possible to detect an abnormality by always measuring Vl and V2, calculating VO, and monitoring this.

Since the two outputs Vl and V2 of the torque sensor (3) are voltage outputs, two voltage-current conversion circuits and a controller (5) on the torque sensor (3) side, which were necessary in the case of conventional current output, are required. The two current-voltage conversion circuits on the side become unnecessary. Therefore, the number of parts is reduced, and high precision parts are not required on either the torque sensor (3) side or the controller (5) side.

In the above electric power steering device, 8V
A regulator (8) is used to generate an 8V voltage using the battery (14) as an input, and this is supplied as a power source to operational amplifiers such as a torque sensor (3) and a current detection circuit (11). Further, the power for driving the power element of the main circuit (9) is directly supplied from the battery (14). However, when the voltage of the battery (14) decreases, the main circuit (9)
) power elements are not driven sufficiently and losses increase,
This may lead to damage to the power element. Moreover, depending on the voltage drop of the battery (14), the 8V power supply voltage of the 8V regulator (8) also drops, which adversely affects the output of the torque sensor (3) and the operational amplifier.

For this reason, the computer (6) constantly monitors the voltage of the battery (14), and when it falls below a predetermined threshold,
Fail-safe processing is performed to reduce the steering force exerted by the motor (1). Also, this threshold is
In order to guarantee the operation of each part that operates with an 8V power supply voltage, we have taken into account variations in internal voltage drop, etc.
The voltage is set to a value slightly higher than V, for example, 9V.

Instead of monitoring the voltage of the battery (14) with the computer (6), the output of the 8V regulator (8) is input to the computer (6) via the interface (17), as shown by the dashed line in FIG. This 8V regulator (8
), the output of the torque sensor (3) can be monitored.
It is also possible to directly monitor the power supply voltage of an operational amplifier.

FIG. 6 shows another example of the electric power steering device. In addition, in this figure, the same parts as in FIG. 1 are given the same reference numerals.

This device is designed to reduce the influence of the voltage drop of the battery (14) as described above, and the controller (5)
The booster circuit (30) is used instead of the 8V regulator (8).
It is equipped with 20 The booster circuit (30) takes as input the 5V power supply voltage of the 5V regulator (7), boosts it to, for example, 24V, and transfers it to the torque sensor (3), the main circuit drive circuit (10), the current detection circuit ( 11) and other operational amplifiers.

The output of the booster circuit (30) is held at 24V as long as the output of the 5V regulator (7) does not fall below 5V.
The output of the regulator (7) is maintained at 5V unless the voltage of the battery (14) falls below a value slightly higher than 5V, for example 6V. That is, as long as the voltage of the battery (14) does not drop below 6V, the output of the booster circuit (30) is maintained at 24V, and the torque sensor 3), power element, operational amplifier, etc. operate normally. Therefore, compared to the one in FIG. 1, the operable voltage range of the battery (j4) is expanded, and the operating rate of the device is improved.

In addition, in the case of FIG. 6 as well, as shown by the broken line, the booster circuit (
30) can be input to the computer (6) via the interface (17) to monitor the output of the booster circuit (30).

Effects of the Invention According to the electric power steering device of the present invention, as mentioned above, the relationship between the two outputs when the torque sensor is abnormal is different from that when it is normal, so the two outputs may be the same due to a voltage drop in the power supply, etc. Even if there is a significant drop, this can be easily and reliably detected.

By prohibiting steering force assistance by the electric motor when an abnormality in the torque sensor is detected, it is possible to prevent accidents due to abnormality in the torque sensor.

In addition, by making the first and second outputs of the torque sensor into voltage outputs, the two voltage-current conversion circuits on the torque sensor side and the two currents on the other side, which were required in the case of conventional current outputs, can be used. -A voltage conversion circuit is no longer required, which in turn reduces the number of parts and eliminates the need for high-precision parts.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an electric power steering device showing an embodiment of the present invention, Fig. 2 is a block diagram showing a part of the torque sensor and controller in Fig. 1 in detail, and Fig. 3 shows the torque during normal operation. FIG. 4 is a graph showing the relationship between the torque and the first output and the second output during an abnormality. FIG. 5 is a graph showing the relationship between the torque and the first output and the second output. FIG. A flowchart showing an example, and FIG. 6 is a block diagram showing another example of an electric power steering device. (3)...torque sensor, (20)...detection section, (
25) (26)...Differential amplifier. Above Figure 3 Figure 4

Claims (3)

[Claims] (1) An electric power steering device comprising a torque sensor that detects steering torque, and an electric motor for assisting steering force that is driven based on the detected value of the torque sensor, wherein the torque sensor detects the steering torque. What is claimed is: 1. An electric power steering device characterized in that a signal from a power steering section is amplified and outputted as a first output and a second output, and the degree of amplification of the first output and the second output is set to be different. (2) means for calculating the first output calculation value from the second output based on the ratio of the amplification degree of the first output and the amplification degree of the second output of the torque sensor; A claim characterized by comprising a monitoring means for detecting an abnormality in the torque sensor when the difference is greater than or equal to a predetermined value, and a means for prohibiting steering force assistance by the electric motor when the abnormality is detected by the monitoring means. The electric power steering device according to item (1). (3) The electric power steering device according to claim (1), wherein the first output and the second output of the torque sensor are voltage outputs.