JPH0542705Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention relates to an electric power steering device that uses the power generated by an electric motor as auxiliary torque to reduce the steering force of the steering system. Regarding improvement.

(Prior art) A microcomputer or the like is used as the main control circuit to detect the amount of operation for the steering system, such as steering torque and steering rotation speed, and based on this amount of operation, the main control circuit generates the auxiliary torque necessary for the electric motor. Such an electric power steering device is known.

Some electric power steering devices of this type have a main control circuit that performs failure diagnosis before starting control. For example, a relay circuit including a relay having at least one normally open contact between the motor and the motor drive circuit and between the motor drive circuit and the power supply is provided, and this relay circuit can be turned on and controlled after the power is turned on. do. In addition, if there is an abnormality in the control system, a relay circuit is provided that opens the relay contacts of this relay circuit to disconnect the motor and the motor drive circuit, or to disconnect the motor drive circuit from the power source. In this case, if a failure is determined, the operation of the electric motor is stopped and the operation shifts to manual operation.

By the way, in order to diagnose the failure of the relay circuit itself, the relay circuit is turned off for a certain period of time after the power is turned on, and at this time, for example, the voltage or current is monitored to monitor the voltage drop across the relay contacts in the relay circuit. A detection circuit was installed to determine failure based on detected voltage or current abnormalities.

(Problems to be solved by the invention) As can be seen from the above, in diagnosing the failure of the relay circuit itself for circuit protection, it was necessary to provide a voltage detection circuit and the like as a separate component. but,
Electric power steering devices are also required to have improved reliability and simplified circuitry.

Therefore, it is an object of this invention to provide an electric power steering device equipped with an electrical system that enables highly reliable initial failure diagnosis with a simple circuit configuration.

(Means for solving the problem) In order to achieve this purpose, according to this invention,
an electric motor that generates an auxiliary torque determined by a main control circuit based on a manipulated variable acting on a steering system; a motor drive circuit that supplies power to the electric motor based on an output command of the main control circuit to generate the auxiliary torque; and a relay circuit having a relay that cuts off power supply to the motor in response to an abnormality detection signal from the main control circuit, and the motor drive circuit includes a bridge circuit in which two circuits each having two switching means connected in series are connected in parallel. the relay circuit supplies the power to the connection point of the two series circuits, and connects the connection point of the two switching means of each series circuit to the motor, and the relay circuit connects the power supply and the bridge circuit. In the electric power steering device, the main control circuit is interposed between the electric motor and the bridge circuit, and the main control circuit is interposed between the electric motor and the bridge circuit.
The presence or absence of current flowing through the bridge circuit is detected with the two relay circuits open and each of the switching means of one series circuit of the bridge circuit turned on for a predetermined time, and then the power supply is connected to the power supply. A relay circuit between the bridge circuit is closed, a relay circuit between the bridge circuit and the motor is opened, and the two switching means located diagonally of the bridge circuit are closed. A failure diagnosis of the relay circuit is performed by detecting the presence or absence of current flowing through the bridge circuit while the relay circuit is driven to the on state, or by turning each switching means of the bridge circuit to the on state in the reverse order. shall be.

(Function) The main control circuit controls two relay circuits to open states before starting the electric power steering device. Since the relay circuit is interposed between the power source and the bridge circuit or is in an open state, if the relay circuit is operating normally, power will not be supplied to the bridge circuit. In this state, the two switching means constituting one series circuit of the bridge circuit are both turned on, and it is detected whether or not current flows through the bridge circuit. If current flows, it can be determined that the relay circuit interposed between the power supply and the bridge circuit is malfunctioning.

Next, the main control circuit controls a relay circuit interposed between the power source and the bridge circuit to a closed state, and controls a relay circuit interposed between the bridge circuit and the electric motor to an open state. In this state, power is applied to the bridge circuit, but if the relay circuit interposed between the bridge circuit and the motor is operating normally, the electrical connection between the output side of the bridge circuit and the motor is off. Therefore, no current flows through the motor. Therefore, in this state, two diagonally located switching means from among the switching means constituting the bridge circuit are driven to the on state, and it is detected whether or not current flows through the bridge circuit. If current flows, it can be determined that the relay circuit interposed between the bridge circuit and the motor is malfunctioning.

(Example) Hereinafter, an example of this invention will be described according to the accompanying drawings. Note that the same reference numerals in each figure indicate similar objects.

FIG. 1 is a system diagram showing an electric power steering device according to an embodiment of this invention. In the figure, 1 is a detection circuit, 2 is a main control circuit of the motor that determines a motor control signal based on the detection output signal of detection circuit 1, 3 is a motor drive circuit that drives the motor, and 4 is an auxiliary to the steering system. An electric motor generates torque, and 5 is a power supply circuit. These components will be explained in detail below.

The detection circuit 1 includes a steering torque sensor 11 and a steering rotation sensor 12 that respectively detect the steering torque and the steering rotation speed applied to the steering system. These sensors 11 and 12 receive steering torque detection signals S ₁ and S ₂ and steering rotation detection signals S ₃ and S ₄ via interface circuits 13 and 14, respectively.
is input to the motor main control circuit 2. Outputs S ₁ , S ₂ of the steering torque sensor 11 and the steering rotation sensor 12,
S ₃ and S ₄ are as shown in FIG. 2 and FIG. 3, respectively. The main control circuit 2 includes an A/D converter 21 and a microcomputer unit (hereinafter referred to as MCU).
22, which determines and outputs a control signal for the electric motor 4. That is, the MCU 22 reads out the motor control duty D _T stored in the memory as shown in FIG. 4 based on the steering torque detection signal T (T=|S1-S2|). Similarly, based on the steering rotation speed N (N=|S3−S4|), the motor rotation speed control duty D _N stored in the memory as shown in FIG. 5 is read, and these duty signals D _T , T _N
The motor control signals T3 and T4 are determined and output.

The motor drive circuit 3 includes a drive unit 30
and field effect transistors (hereinafter simply referred to as FETs) 31, 32, 33, as switching means.
34 in combination as each arm, and a current detection circuit 40. In this bridge circuit, a series circuit of first and second FETs 31 and 32 connected in series adjacent to each other and a series circuit of third and fourth FETs 33 and 34 adjacent to each other also connected in series are connected in parallel. ing. Connection point 36 of these two series circuits
a and 36b are power supply terminals, and one connection point 36
Normally open contact 5 of relay circuit 54 of power supply circuit 5 is shown at a.
4a, and the other connection point is connected to the ground side of the drive power source via a resistor 38. The voltage across the resistor 38 is input to the current detection circuit 40 and processed by the MCU 22 as failure diagnosis data for the relay circuits 39 and 54. In addition, the first circuits adjacent to each other in each series circuit
and the connection point 37a of the second FETs 31, 32 and the third and fourth FETs 33, 3 adjacent to each other.
The connection point 37b of No. 4 is an output terminal, and the motor 4 is connected through the normally open contact 39a of the relay circuit 39. The detection signal _S5 of the current detection circuit 40 is as shown in FIG. 6, for example.

According to such a configuration, after confirming the operation of the relay circuits 39 and 54 through initial failure diagnosis, the relay circuits 39 and 54 are turned on, and the main control circuit 2
starts controlling the electric motor 4. That is, each
Drive unit 3 drives the gates of FETs 31 to 34.
By driving with an output signal having a predetermined duty value of 0, the FETs 31 to 34 are operated as switching elements to drive and control the electric motor 4. In addition, during normal operation, the relay circuits 39 and 54 each receive a control signal from the MCU 22 of O _R2 =1.
(high level), O _R1 = 1 is input to maintain the connection state, O _R2 = (low level), O _R1 =
When 0 is input, the circuit of the electric motor 4 is opened.

The power supply circuit 5 receives power from an on-vehicle battery 50 via a fuse circuit 51, a key switch 52 such as an ignition switch, and a fuse circuit 53.
It is supplied to a relay circuit 54 and a constant voltage circuit 55.
The relay circuit 54 is connected to the drive circuit 3 as described above.
This is to cut off the conduction of power to FETs 31 to 34, and is connected to the MCU 22 similar to the relay circuit 39.
Controlled by the output O _R1 . Constant voltage circuit 55 is MCU
This is for operating the 22 etc.

FIG. 7 is a longitudinal sectional view mainly showing the mechanical structure of the electric power steering device according to the embodiment of the invention. According to the figure, the electric power steering device of this embodiment uses a pinion shaft 71 as an input shaft for transmitting steering motion, and a rack shaft 72 for transmitting auxiliary torque generated by the electric motor 4 at a desired rotation speed. It has a rack-and-pinion configuration with the output shaft.

A pinion gear 711 is formed at one end of the input shaft 71, and a rack gear 711 of the output shaft 72, which will be described later, is formed at one end of the input shaft 71.
Mesh with 21. This input shaft 71 is connected via a seal member 712, bearings 713, 714, pinion case 715, and bearings 716, 717.
It is rotatably supported by a rack case 73. Here, the input shaft 71 meshes with a rack gear 721 via a pinion gear 711 and rotates as the steering wheel rotates, but the pinion case 715 is also rotatable within a certain range with respect to the rack case 73. The input shaft 71 is provided with a steering rotation sensor 12 that detects the rotation direction and rotation speed of the input shaft 71, and a steering torque sensor 11 that detects the rotation torque of the input shaft 71. Steering rotation sensor 1
2 is configured to transmit the rotation of a pulley 121 pivotally attached to an input shaft 71 to a generator (not shown) via a timing belt 122. The output voltage of this generator is used as detection signals S ₃ and S ₄ . That is, the absolute values of these signals S ₃ and S ₄ give the steering rotation speed, and the polarity of this output signal gives the rotation direction. It was mentioned above that this output signal corresponds to the curves S ₃ and S ₄ in FIG. Steering torque sensor 11
A movable core 114 is made of one primary coil 111, two secondary coils 112, 113, and a magnetic material, and is displaced as the input shaft 71 rotates.
constitute a differential transformer. Movable core 114
is a piston 1 which is held between coil springs 115 and 116 and is movable in the axial direction (horizontal direction in the drawing).
It is connected to 17. A recess 117a is formed in the middle of this piston 117, and this recess 117a
, the pin 118 is engaged. This pin 118
is fixed to the pinion case 715 slightly eccentrically from the central axis of the input shaft 71, and the amount of displacement in the axial direction is proportional to the rotational torque. Therefore, by inputting the alternating signal T1 from the control device 74 to the primary coil 111 and differentially extracting this signal by the secondary coils 112 and 113, the displacement of the movable core 114 and hence the steering torque can be detected as an electrical signal. It becomes possible to do so. This output signal corresponds to S ₁ and S ₂ in FIG. The electric motor 4 for generating auxiliary torque is connected to a pulley 7 of a reduction mechanism 76 disposed coaxially with the output shaft 72 via a pulley 741 and a cog belt 742.
The auxiliary torque is transmitted to 61. Reduction mechanism 76
is a ball screw 7 formed on a part of the rack shaft 72.
Bolt nut 764 through ball 763 to 62
It forms a so-called ball nut mechanism.

The operation of the electric power steering device as described above will be explained with reference to the flowcharts shown in FIGS. 8a and 8b. In the following explanation, the symbols P0 to P64 correspond to the numbers of each step in the flowchart. Further, the symbols P6-Y and P6-N, for example, indicate that the judgment of the judgment block P6 is positive and negative, respectively.

First, when the electric power steering device is started P0 by operating the ignition key, etc.
Initial settings are made for the MCU 22, etc., and P1 and initial failure diagnosis P2 are executed as subroutines. FIG. 9 shows a subroutine for initial failure diagnosis. This initial failure diagnosis will be explained below. When starting the initial diagnosis routine P2, first the relay circuits 39, 54 and FET
90, all of 31-34 are turned off. Next, both FETs 31 and 32 forming the bridge circuit are turned on (91). At this time, the current detection circuit 40 monitors 92 whether or not current flows through the resistor 38. If current flows, 92y, relay circuit 5
The main control circuit 2 determines that there is an abnormality in the relay circuit 54, executes the failure process 100, and ends the process for controlling the motor. 101 to do.
If no current flows, 92n is normal and the FET
93 which turns 31 and 32 off, and 94 which turns the relay circuit 54 on. Therefore, the electric drive circuit 3 is in a standby state in which it can operate.

Next, the main control circuit 2 includes FETs 31 and 31 disposed diagonally in the bridge circuit of the motor drive circuit 3.
95 to turn on 34; At this time, the current detection circuit 40 monitors 96 whether or not current flows through the resistor 38 as in the previous process. If the current flows, it is 96y, and the current flows even though the relay circuit 39 should be in the off state, so the main control circuit 2 determines that there is an abnormality in the relay circuit 39.
101 executes the failure process 100 and ends the process for controlling the electric motor; 96n when no current flows
is normal, and 97 turns the FETs 31 and 34 off and 9 turns the relay circuit 39 on.
8. Therefore, the motor drive circuit 3 and the motor 4 are electrically connected and enter a standby state in which the motor can be controlled. Therefore, the process returns to the main routine9.
9.

In addition, in the above, the failure processing 100 includes each of the corresponding FETs 31-34 and relay circuits 39, 5.
4 is turned off, and processes such as displaying a warning are performed. Also, instead of turning on FETs 31 and 32, FETs 33 and 34 may be turned on, and similarly, instead of turning FETs 31 and 34 on, FETs 32 and 33 can be turned on to perform the same fault diagnosis. It is easy to understand that. Each FET31-3
A control signal may be used as the signal for turning on and off 4, or a separate signal for fault diagnosis may be supplied from the main control circuit 2.

Next, the detection signals S ₁ and S ₂ of the steering torque sensor 11
Read P3 and execute the sensor failure diagnosis shown in the subroutine following step P40. Subsequently,
Calculate S ₁ and S ₂ to obtain the steering torque T shown in Figure 2, P5,
Conversion is performed to obtain the absolute value of this steering torque T, and a flag F of that sign is set in P6 to P9. The absolute value of the steering torque T obtained in this way is used as an address,
Access table 1 in the memory that stores the duty value characteristic curve D _T as shown in Figure 4.
P10. Next, the detection signal S ₃ of the steering rotation sensor 12,
_S4 is read and sensor failure diagnosis is performed in the subroutine shown at step P11 and step P40. Then, S ₃ and S ₄ are calculated at P13, and the absolute value conversion of the steering rotation speed N shown in FIG. 3 is performed, and its sign flag G is set at P14 to P17.
And the duty value characteristic curve as shown in Figure 5
P18 accesses table 2 in memory where D _N is stored. In this way, it is possible to obtain the duty value _DT of the torque control signal necessary to generate the rotational torque required of the electric motor 4, and the duty value _DN of the rotation speed control signal necessary to generate the rotational speed. These duty values _DT and _DN constitute the control signal _T4 .

In step P19, it is determined whether the flags F and G set when calculating the duty values _DT and _DN match each other. If they match, P14-Y determines that the steering wheel is in the forward operation state and outputs the duty value D _D = D _T + D _N and the duty value.
P20, 21 to calculate D _U =1. If not match P19
-N, P22 and 23 calculate the duty value D _D =D _T and the duty value D _U =1-D _N when it is determined that the steering wheel is in the return operation state. After this, it is determined whether steering torque is applied to the steering wheel, that is, whether D _D =0.
P24, P26 where R=L=0 when D _D =0.
If D _D =0, flag F is checked in P25. If F=1 then R=
0, L=1, P27, if F=1, then R=
1, P28 with L=0. Then, in step P29, a direction control signal T3 containing R and L is output,
Torque control signal consisting of D _D and D _U at step P30
T4 is output, a failure diagnosis of the motor system is performed in step P60, and the series of processes is repeated. Note that R and L are codes indicating the rotation direction of the rotation direction signal T3; for example, R indicates clockwise rotation, and L indicates counterclockwise rotation.
In addition, the above D _D and D _U are the duty values that are the contents of the torque signal T4. For example, when rotating clockwise,
_DU is applied to the FET 31, _DD is applied to the FET 34, and during left rotation, _DU is applied to the FET 33, and _DD is applied to the FET 32.

Next, the subroutine of sensor failure diagnosis P40 will be explained based on FIG. 8b. That is, it is determined whether it is a steering torque sensor or not, and if it is a steering torque sensor, the detection signal _S1 from the steering torque sensor 11 is placed in A and the detection signal _S2 is placed in B, respectively, in P42 and P43. . If it is not a steering torque sensor, the detection signal _S3 from the steering rotation sensor 12 is set to A,
P44 and P45 respectively place S ₄ in B. And (A+
B) Perform the calculation /2 and set this as d.P46, then this d
is within the range between the lower limit value a and the upper limit value b of each detection signal S ₁ to _{S 4} set in advance.
P47, P48. If it is within this range, the process returns to the next step P5 or P13, respectively. If not within this range, R = L = 0, D _D = D _U = 0 relay control signal O _R1 = 0, O _R2 = 0, P50 to P52, each signal R, L, D _D , D _U is output to the motor drive circuit 3,
Relay control signals O _R1 and O _R2 are sent to relay circuits 54 and 3.
9 and P53, and P54 to stop the control process. Then, by driving the relay circuit 54, the supply of power to the bridge circuit is stopped, and by driving the relay circuit 39, the connection circuit between the bridge circuit and the electric motor 4 is opened. Therefore, the drive of the motor drive circuit 3 and the motor 4 is stopped, and the steering shifts to manual steering.

Furthermore, in the subroutine P60 for diagnosing failure of the electric motor system, the detection signal S5 from the current detection circuit 40 is read in P61, and it is determined whether the torque control duty value D _T is within the allowable range C shown in FIG. PP62, P63. This allowable range C is preset around D _T as shown in the figure. If the detection signal S5 is within this allowable range, the process returns to the next step P3 and P64; if it is not within the allowable range, R=
P54 outputs each signal with L=0, D _D =D _U =0, O _R1 =0, O _R2 =0 and stops the control process. Therefore, the relay control signals O _R1 =0, O _R2 =0 cause the relay circuits 54 and 39 to be cut off, and the steering is shifted to manual steering in the same manner as described above.

In this way, according to the electric power steering device of this embodiment, even if any of the FETs 31 to 34 that constitute the bridge arm of the motor system, that is, the motor drive circuit, breaks down and becomes conductive, this FET will not break. is detected by the current detection circuit 40,
Since the formation of a closed circuit can be avoided by cutting off the relay circuit 39 by the MCU 22, there is no possibility that a braking current will flow through the electric motor 4, and the reliability of the device can be improved.

In the above embodiment, FETs are used for the switching means constituting the bridge circuit, but relay contacts or bipolar transistors may also be used as the switching means. Furthermore, although the case where the relay circuits are turned off (non-conducting) based on a fault diagnosis has been described, each relay circuit may be turned off actively by a manual switch or the like as necessary.

(Effect of the invention) According to this invention, the main control circuit 2
Prior to the start of motor control by the motor drive circuit 3, the relay circuits 39 and 54 are activated by the main control circuit 2.
In order to carry out the diagnosis, the bridge circuit of the existing motor drive circuit is activated in an appropriate manner and whether or not current flows through the bridge circuit is monitored, thereby requiring the separate preparation of special components. Therefore, it is possible to obtain an electric power steering device having a simple configuration and a highly reliable control system that can perform initial failure diagnosis without any trouble.

[Brief explanation of the drawing]

Fig. 1 is an electric system diagram of an electric power steering device according to an embodiment of this invention, Fig. 2 is a characteristic diagram showing a steering torque detection signal of the electric power steering device according to an embodiment of this invention, and Fig. 3 4 is a characteristic diagram showing the steering rotation detection signal of the electric power steering device according to the embodiment of this invention, and FIG. 4 shows the electric motor torque control calculated by the main control circuit 22 of the electric power steering device according to the embodiment of this invention. A characteristic diagram of the duty signal; FIG. 5 is a characteristic diagram of the motor rotation speed control duty signal calculated by the main control circuit 22 of the electric power steering device according to an embodiment of the invention; FIG. 6 is an embodiment of the invention. FIG. 7 is a mechanical configuration diagram of the electric power steering device according to an embodiment of the invention, and FIG. 8 is an embodiment of the invention. FIG. 9 is a flowchart showing a subroutine for initial failure diagnosis in the flowchart of FIG. 8. In the drawings, 1 is a detection circuit, 2 is a main control circuit, 3 is a motor drive circuit, 4 is a motor, 5 is a power supply circuit, 31 to 34 are field effect transistors (FETs) as switching means constituting a bridge circuit, and 38 39 is a current detection resistor, 39 is a relay circuit interposed between the motor and the bridge circuit, 40 is a current detection circuit, and 54 is a relay circuit interposed between the power source and the bridge circuit.

Claims (1)

[Claims for Utility Model Registration] An electric motor that generates an auxiliary torque determined by a main control circuit based on the amount of operation applied to the steering system; and a relay circuit having a relay that cuts off power supply to the motor in response to an abnormality detection signal from the main control circuit, and the motor drive circuit includes a circuit in which two switching means are connected in series. The relay circuit has two bridge circuits connected in parallel, supplies the power to the connection point of the two series circuits, and connects the connection point of the two switching means of each series circuit to the motor, and the relay circuit has two bridge circuits connected in parallel. , an electric power steering device interposed between the power source and the bridge circuit and between the electric motor and the bridge circuit, wherein the main control circuit controls the two
The presence or absence of current flowing through the bridge circuit is detected with the two relay circuits open and each of the switching means of one series circuit of the bridge circuit turned on for a predetermined time, and then the power supply is connected to the power supply. A relay circuit between the bridge circuit is closed, a relay circuit between the bridge circuit and the motor is opened, and the two switching means located diagonally of the bridge circuit are closed. A failure diagnosis of the relay circuit is performed by detecting the presence or absence of current flowing through the bridge circuit while the relay circuit is driven to the on state, or by turning each switching means of the bridge circuit to the on state in the reverse order. Electric power steering device.