JPH1111331A - Electric power steering control device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] A conventional electric power steering control device comprises:
A relay was used to stop energizing the motor when a failure was detected. However, this relay has been an obstacle to downsizing the control device. SOLUTION: As a semiconductor switching element constituting a bridge circuit 44A, a power MOS with an overheat cutoff function is provided.
By using the FETs Q1A to Q4A, when at least one semiconductor switching element detects an overheating state, the semiconductor element shuts off and prevents the switching element from being short-circuited, so that the relay 46 can be removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering control device for assisting a steering device of an automobile by the rotational force of a motor, and more particularly to a power MOS with an overheat cutoff function.
The present invention relates to an electric power steering control device using an FET.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram partially showing a general electric power steering control device in a block diagram. 3, a motor 40 that outputs an auxiliary torque to a steering wheel (not shown) of a vehicle is driven by a motor drive current IM supplied from a battery 41.

The motor drive current IM has a large capacity (1000
The ripple component is absorbed by a capacitor 42 of about μF to 3600 μF) and detected by a shunt resistor 43. The motor drive current IM is switched by a bridge circuit 44 including a plurality of semiconductor switching elements (for example, FETs) Q1 to Q4 according to the magnitude and direction of the auxiliary torque.

[0004] One end of the capacitor 42 is grounded by a conductive line L1. The semiconductor switching elements Q1 to Q4 are bridge-connected by wiring patterns P1 and P2 to form a bridge circuit 44. The wiring patterns P1 and P2 connect the bridge circuit 44 to the shunt resistor 43. The output terminal of the bridge circuit 44 is constituted by the wiring pattern P3.

The motor 40 and the battery 41 are connected to a bridge circuit 4 by a connector 45 comprising a plurality of connection terminals.
4 is connected. The motor 40, the battery 41, and the connector 45 are connected by the external wiring L2. The motor drive current IM is interrupted as necessary by a normally open relay 46. The relay 46, the capacitor 42, and the shunt resistor 43 are connected by a wiring pattern P4. The connector 45 is grounded by the wiring pattern P5. The wiring pattern P3 serving as an output terminal of the bridge circuit 44 is connected to the connector 45.

The motor 40 includes a switching control circuit 47
, And is driven via a bridge circuit 44 controlled by the switching. The switching control circuit 47
Drives the relay 46. Switching control circuit 47
Supplies a control signal to the bridge circuit 44 via the conductive line L4. The motor drive current IM is the shunt resistor 4
3, and is detected by the motor drive current detecting means 48. The switching control circuit 47 and the motor drive current detecting means 48 constitute a peripheral circuit element of a microcomputer 55 described later.

The steering torque T of the steering wheel is determined by a torque sensor 5
0, and the vehicle speed V of the vehicle is detected by the vehicle speed sensor 51. Microcomputer 55 (ECU: EL
The ECTRONIC CONTROL UNIT calculates the assist torque based on the steering torque T and the vehicle speed V, and feeds back the motor drive current IM from the shunt resistor 43 to generate a drive signal corresponding to the assist torque, and controls the bridge circuit 44. The rotation direction command D _O and the current control amount I _O for performing the operation are output to the switching control circuit 47 as drive signals.

The microcomputer 55 includes a motor 40
A motor current determining means 56 for generating a motor current command Im corresponding to the rotation direction command D _O and the auxiliary torque, and a current deviation モ ー タ between the motor current command Im and the motor drive current IM.
A subtraction means 57 for subtracting I and a correction amount of a P (proportional) term, an I (integral) term and a D (differential) term are calculated from the current deviation △ I and correspond to a PWM (pulse-width modulation) duty ratio. PID calculation means 5 for generating current control amount _IO
8 is provided.

Although not shown, the microcomputer 55 includes a well-known self-diagnosis function in addition to an AD converter, a PWM timer circuit, and the like. Occurs, all the semiconductor switching elements Q1 to Q4 constituting the bridge circuit 44 are turned off via the switching control circuit 47, and the relay 46 is opened to cut off the motor drive current IM. At the same time, when a failure is detected, the details of the failure are stored in a storage device (not shown) in the control device. The microcomputer 55 is connected to the switching control circuit 47 by a conductive line L5.

Next, the operation of the electric power steering control device will be described with reference to FIG. The microcomputer 55 takes in the steering torque T and the vehicle speed V from the torque sensor 50 and the vehicle speed sensor 51, and also feeds back the motor drive current IM from the shunt resistor 43 to obtain the rotational direction command _DO and the auxiliary torque amount of the power steering. A corresponding current control amount I _O is generated and output to the switching control circuit 47 via the conductive line L5.

In a steady driving state, the switching control circuit 47 operates a normally open relay 46 according to a command via the conductive line L3.
Is closed, the rotation direction command D _O and the current control amount I
_{When O} is input, a PWM drive signal is generated and the conductive line L
4 is applied to each of the semiconductor switching elements Q1 to Q4 of the bridge circuit 44.

Thus, the motor drive current IM is supplied from the battery 41 to the external wiring L2, the connector 45, the relay 4
6, power is supplied to the motor 40 via the wiring pattern P4, the shunt resistor 43, the wiring pattern P1, the bridge circuit 44, the wiring pattern P3, the connector 45, and the external wiring L2. The motor 40 is driven by the motor drive current IM and outputs a required amount of auxiliary torque in a required direction.

At this time, the motor drive current IM is detected via the shunt resistor 43 and the motor drive current detection means 48, and the subtraction means 5 in the microcomputer 55
7, the control is performed so as to coincide with the motor current command Im. Further, the motor drive current IM includes a ripple component due to the switching operation at the time of the PWM drive of the bridge circuit 44, but is smoothed and suppressed by the large-capacity capacitor 42.

[0014]

By the way, in this type of electric power steering control device, a relay 46 is conventionally used to cut off the power supply to the motor 40 when a failure is detected. However, this relay 46 has 20
Since a large current of A to 60 A flows, the outer shape becomes large, which has been an obstacle to downsizing the control device. Also, since the relay 46 performs a mechanical ON / OFF operation,
There is a problem that the reliability and the life are inferior to the case where a semiconductor switching element is used.

When the control device detects a failure, each of the semiconductor switching elements Q1 to Q4
Is turned off, the energization from the battery 41 can be cut off and the energization to the motor can be stopped without turning off the relay 46. However, each semiconductor switching element Q
If one of the combinations of Q1 and Q4 or Q2 and Q3 of any one of Q1 to Q4 has a failure in which both switching elements are short-circuited, the relay 46 must be turned off unless the relay 46 is turned off. There is a problem in that the current continues to flow through 40. Therefore, the relay 46
Could not be removed.

Each of the semiconductor switching elements Q1 to Q
4, when a failure occurs in which one of the semiconductor switching elements is short-circuited, the motor 40 is short-circuited by resistance (the sum of the short-circuit resistance of the switching element and the forward resistance of the parasitic diode). ,
As a result, the steering wheel becomes heavy and steering cannot be performed. As a cause of a failure in which each of the semiconductor switching elements Q1 to Q4 is short-circuited, for example, when a wiring to the motor 40 is grounded on the way, an overcurrent flows through the element, resulting in overheating and short-circuit. Further, as described above, when the control device detects a failure, it is necessary to store the details of the failure so that the repair can be reliably performed. Therefore, if a short-circuit fault due to overheating of each of the semiconductor switching elements Q1 to Q4 can be distinguished from a fault due to another cause, it is convenient to quickly identify a fault location.

The present invention has been made in order to solve the above-mentioned problems. As a semiconductor switching element constituting the bridge circuit 44, a power MO with an overheat cutoff function is provided.
By adopting the SFET, the semiconductor switching element itself is shut off when an overheat state is detected, and a failure detection function that detects an abnormality generated as a result of the self-interruption shuts off all remaining semiconductor switching elements,
An object of the present invention is to provide an electric power steering control device in which the relay 46 is eliminated by adopting a structure for preventing a short circuit of each semiconductor switching element, thereby realizing a miniaturized control device and improved reliability.

[0018]

An electric power steering control device according to the present invention is configured such that a steering torque signal from a torque sensor, a vehicle speed signal from a vehicle speed sensor, and a motor drive current from a motor drive current detecting means are input to the motor. A microcomputer that calculates the driving torque of the
By controlling a switching circuit including a semiconductor switching element having an overheat cutoff function based on a signal output from the microcomputer, the motor outputs a driving torque calculated by the microcomputer in a predetermined driving direction. And a motor drive circuit for supplying a motor drive current to the motor via the switching circuit.

Further, the electric power steering control device according to the present invention provides a power MOS having an overheat cutoff circuit as a semiconductor switching element having an overheat cutoff function.
This is one using an FET.

Further, the electric power steering control device according to the present invention, when at least one semiconductor switching element detects an overheated state, shuts off itself,
A semiconductor switching element having an overheat cutoff function for outputting an overheat state detection signal to a microcomputer is provided.

Further, the electric power steering control device according to the present invention is provided in any one of a motor drive circuit comprising a microcomputer and / or a switching circuit and a switching control circuit for controlling the switching circuit, The operation of the drive circuit is constantly monitored, and when an abnormality is detected, all semiconductor switching elements are shut off to stop energization to the motor, and a failure state is maintained in which energization to the motor is stopped. And a blocking state holding means.

Further, the power steering control device according to the present invention is provided with a microcomputer provided with a failure diagnosis function for distinguishing and storing a failure of the semiconductor switching element into a failure due to overheating of the semiconductor switching element and a failure due to other reasons. It is provided with.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. Hereinafter, an embodiment of the electric power steering control device will be described with reference to FIGS. FIG. 1 is a circuit diagram including a partial block diagram illustrating an electric power steering control device according to Embodiment 1 of the present invention. FIG. 2 is a graph showing a shut-off characteristic of a power MOSFET with an overheat shut-off function, which is an example of a switching element used in the electric power steering control device according to the first embodiment and that shuts off when an overheat state is detected. Note that the same reference numerals in the drawings denote the same or corresponding components as those in the related art. The power steering control device according to the first embodiment has the same configuration as the conventional power steering control device shown in FIG. 3 except for the bridge 44A shown in FIG.

In FIG. 1, reference numeral 55 denotes a microcomputer which indicates a steering torque T applied to the steering wheel and a steering direction from the torque sensor 50 at the time of steering.
From 1 to the vehicle speed V, the motor drive current detection means 48 processes the motor drive current IM as an input signal, and outputs a rotation direction command D _O of the motor 40 and a current control amount I _O to the switching control circuit 47. This switching control circuit 47
Controls on / off of each switching element of a bridge circuit 44A provided with a power MOS FET with an overheat cutoff function as a semiconductor switching element;
The current supplied from the battery 41 in the bridge circuit 44 </ b> A switches the intermittent and polarity, and supplies the motor 40 as the motor drive current IM.

The motor drive current IM is detected by the shunt resistor 43 and is fed back to the subtraction means 57 provided in the microcomputer 55 via the motor drive current detection means 48. The motor current determination means 56 provided in the microcomputer 55 processes the steering torque T from the torque sensor 50 and the vehicle speed V from the vehicle speed sensor 51 and outputs the motor current Im corresponding to the auxiliary torque to the subtraction means 57. The subtraction means 57 calculates a current deviation ΔI from the motor drive current IM and the motor current Im transmitted from the motor current determination means 56, and outputs the current deviation ΔI to the PID calculation means 58. The PID calculation means 58 is also provided in the microcomputer 55.

The PID calculation means 58 calculates a correction amount of a P (proportional) term, an I (integral) term, and a D (differential) term from the current deviation ΔI, and calculates a current control amount I _O corresponding to the PWM duty ratio.
Generate The microcomputer 55 sends the current control amount I _O and the rotation direction command D _O to the switching control circuit 4.
7 is output.

The bridge circuit 44A employs a power MOS FET with an overheat cutoff function as a semiconductor switching element.
The gates of Q1A to Q4A are connected to the switching control circuit 47. Hereinafter, unless otherwise specified, a switching element is a power MOSF with an overheat cutoff function.
Shall mean ET. Switching control circuit 47
Controls on / off of each switching element by applying a voltage to the gate. If at least one of the switching elements Q1A to Q4A detects an overheat state, an overheat shutoff circuit inside the switching element self-interrupts the switching elements.

When at least one of the switching elements Q1A to Q4A constituting the bridge circuit 44A detects an overheated state and shuts off itself, the switching function does not operate. Further, it goes without saying that the motor 40 cannot be properly controlled even if a part of the circuit in the control device is grounded. The failure detection function constantly monitors the operation state of the motor drive circuit composed of the bridge circuit 44A and the switching control circuit 47 for controlling the bridge circuit 44A, and when any abnormality is detected, all the switching elements constituting the bridge circuit 44A are activated. It shuts off and stops the power supply to the motor 40. The failure detection function may be provided in the microcomputer 55, or may be provided in a part of the motor drive circuit.

In the conventional general electric power steering control device, the interruption of the circuit due to the detection of the failure and the stop of the power supply to the motor 40 are performed by the relay 46 shown in FIG. 46
And the conductive line L3 connecting the switching control circuit. However, power MOSF with overheat cutoff function
By employing ET as the switching element, it is possible to prevent the switching element from being short-circuited, so that the relay 46 can be eliminated and the device can be downsized.

Incidentally, the power MOS FE with the overheat cutoff function of the electric power steering control device according to the present invention.
When the TQ1A to Q4A detects an overheated state, the TQ1A to Q4A shuts off and outputs an overheated state detection signal to the microcomputer 5.
5 is output. The microcomputer 55 receives the overheat state detection signal, and has a failure diagnosis function of discriminating and storing a failure due to the overheat state detection and a failure due to another cause. By providing this failure diagnosis function,
It is possible to quickly determine the cause of the failure as to whether it is an interruption failure due to overheating of the switching element or a failure due to other causes such as a failure caused as a result of a ground fault in a part of the circuit, and further facilitate identification of a failure part. Note that this failure diagnosis function does not necessarily need to be provided in the microcomputer 55, similarly to the failure detection function described above.

As described above, when the failure detection function provided in the electric power steering control device according to the present invention detects at least one failure, the bridge circuit 44A is configured to prevent a short circuit of each switching element. All the switching elements Q1 to Q4
The power supply to the motor 40 is stopped. However, there may be a case where it is desired to maintain the state in which the power supply to the motor 40 is interrupted even after the fault state is restored to the normal state. In such a case, by providing the shut-off state holding means in the control device, the key switch (not shown) is turned off and the motor 4 is turned on until it is turned on again.
It is also possible to keep the power supply cutoff state to zero.

FIG. 2 is a graph showing the shut-off characteristics of a power MOS FET with an overheat cutoff function, which is an example of a semiconductor switching element with an overheat cutoff function used in the electric power steering control device according to the first embodiment. FIG.
[A] is a graph showing the cutoff characteristics of the latch-type current cutoff method, where the vertical axis represents the drain current and the horizontal axis represents the channel temperature. Assuming that the magnitude of the drain current is ID,
Until the channel temperature reaches 170 ° C., current can be supplied at that value. When the channel temperature reaches 170 ° C., the overheat state is detected and the current is cut off.
Instantaneously becomes zero. This is indicated by the downward arrow. On the other hand, when the channel temperature becomes 170 ° C. or lower, the current is supplied again, and the drain current ID returns. This is indicated by the upward arrow. On the other hand, FIG. 2B is a graph showing the cutoff characteristics of the hysteresis type current cutoff method. In the hysteresis type current cut-off method, the return temperature at which the cut-off state returns to the energized state has a width of about 10 degrees as compared with the latch type current cut-off method. By having this width,
The switching element is prevented from repeating the cutoff / return state.

[0033]

As described above, according to the electric power steering control device of the present invention, the driving of the electric motor is performed by using the semiconductor switching element having the overheat cutoff function, specifically, the power MOS FET having the overheat cutoff function. By configuring the motor drive circuit to be controlled, when at least one of the semiconductor switching elements detects an overheated state and self-interrupts, the other semiconductor switching elements can be shut off and the power supply to the motor can be stopped. Therefore, by removing the relay provided in the conventional electric power steering control device in the present invention, the electric power steering control device can be downsized and the reliability of the switching circuit can be increased.

By using a power MOS FET with an overheat cutoff function as each of the semiconductor switching elements Q1 to Q4, even if a fault occurs such that an overcurrent flows through the switching element due to a ground fault in the wiring to the motor 40, Since the element itself detects the overheating state and shuts off the power supply itself, the element does not need to be short-circuited. Further, since each switching element detects an overheated state and shuts off itself, it is possible to prevent the occurrence of a trouble that the switching element is short-circuited and power supply to the motor cannot be stopped.

In addition, when at least one of the semiconductor switching elements having an overheat shut-off function detects an overheat state, the semiconductor element shuts off itself and outputs an overheat state detection signal to a peripheral device such as a microcomputer. , And a failure site and a failure cause can be quickly specified.

Further, by providing a failure detection function,
The operation of the control device is constantly monitored, and when an abnormal operation state is detected, the power supply to the motor is stopped by shutting off all the switching elements, thereby preventing a short circuit of the semiconductor switching elements. Further, by providing the cutoff state holding means for holding the cutoff state, it is possible to hold the state in which the power supply to the motor is stopped by shutting off the semiconductor switching element having the overheat cutoff function.

Further, since the interruption failure of the semiconductor switching element due to the detection of the overheat state and the interruption failure of the semiconductor switching element due to other causes can be identified and stored, the cause of the failure can be specified quickly.

[Brief description of the drawings]

FIG. 1 is a circuit diagram, partially including a block diagram, for explaining an electric power steering control device according to a first embodiment of the present invention.

FIG. 2 shows a power with an overheat cutoff function used in the power steering control device according to Embodiment 1 of the present invention.
4 is a graph showing a cutoff characteristic of a MOS FET.

FIG. 3 is a circuit diagram including a partial block diagram illustrating a conventional electric power steering control device.

[Explanation of symbols]

40 motor, 41 battery, 42 capacitor, 43 shunt resistor, 44 / 44A bridge circuit, 45 connector, 46 relay, 47 switching control circuit, 48 motor drive current detecting means,
50 torque sensor 51 vehicle speed sensor, 55 microcomputer, Q1 to Q4 semiconductor switching element, the semiconductor switching elements with Q1A~Q4A thermal shutdown function, IM motor drive current, Im motor current command, I _O current control amount, D _O rotational direction Command, T
Steering torque, V vehicle speed.

Claims (5)

[Claims] A microcomputer for calculating a motor driving torque by inputting a steering torque signal from a torque sensor, a vehicle speed signal from a vehicle speed sensor, a motor driving current from a motor driving current detecting means, and an output from the microcomputer. Controlling the switching circuit composed of a semiconductor switching element having an overheat cutoff function based on the signal, so that the motor outputs a drive torque calculated by the microcomputer in a predetermined drive direction. An electric power steering control device, comprising: a motor driving circuit that supplies a motor driving current to the motor via the motor. 2. A semiconductor switching element having an overheat cutoff function is a power MOS FET having an overheat cutoff function.
The electric power steering control device according to claim 1, wherein 3. A semiconductor switching element having an overheat cutoff function, wherein when at least one of the semiconductor switching elements with an overheat cutoff function detects an overheat state, the semiconductor switching element shuts off itself and outputs an overheat state detection signal to a microcomputer. Claim 1 or Claim 2
3. The electric power steering control device according to claim 1. 4. An electric motor driving circuit comprising a microcomputer and / or a switching circuit and a switching control circuit for controlling the switching circuit, wherein the operation of the electric motor driving circuit is constantly monitored to detect abnormalities. A failure detection unit that shuts off all the semiconductor switching elements to stop the current supply to the motor when the power supply is detected, and a cutoff state holding unit that holds the cutoff state in which the current supply to the motor is stopped. The electric power steering control device according to any one of claims 1 to 3. 5. The microcomputer according to claim 1, wherein the microcomputer has a failure diagnosis function for distinguishing and storing a failure due to overheating of the semiconductor switching element and a failure due to other reasons. 3. The electric power steering control device according to claim 1.