JPH03182874A - Motor drive device in electrically driven power steering device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of current oscillation by employing 4 motor switching elements which are connected in an H-bridge pattern, controlling 2 pieces of the switching element of one arm in response to current deviation, and concurrently controlling 2 pieces of the switching elements of the other arm in response to polarity. CONSTITUTION:In a circuit wherein 2 each of switching element (FET) 1UL and 1LL; 1UR and 1LR are connected to each upper and each lower position of the right and left arms of an H-bridge in which motors 10 are connected to each middle point of the respective arms, the respective elements 1UL and 1LL and the respective elements 1UR and 1LR are controlled so as to be turned on and/or off by a left side drive arm 17 and the right side driven arm 18 respectively based on control signals from a drive logic circuit 16. Namely, the deviation Id between the current command value 1D and motor current IM is made 12 to be an absolute value, and the polarity of the deviation is concurrently judged 15. The control signal is then outputted based on the PWM pulse and the result of polarity judgement obtained through the comparison 14 of a magnitude signal with a chopping wave signal.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor drive device in an electric power steering device that assists steering force with the rotational output of a motor.

Prior Art and Its Problems In a conventional electric power steering device, a steering assist (auxiliary) motor is controlled based on a detected steering torque value and a detected vehicle speed value to generate steering assist torque. inertia of the motor and steering mechanical system;
Some perform inertia compensation, viscosity compensation, etc. that take into account viscosity, friction, etc.

In any case, it is necessary to control the assist motor according to the assist command value. One of the motor control technologies is 4.
PWM (Pulse WidthModu I a
Some motors are driven and controlled by a chopper operation using pulses (t ton). As shown in Figure 7, this driving method uses two switching elements (for example, FETs) on the upper (upper) and lower (lower) left arms of the H-bridge.
) IUL, ILL.

Two switching elements IUR and ILR are connected to the upper and lower parts of the right arm, respectively, and a motor 10 is connected between the midpoints of each arm. For example, to rotate the motor forward, switching element IUL is turned on (indicated by a circle), and switching elements ILL and IUR are turned off (indicated by a circle).
(indicated by an x mark), and turns on/off the switching element ILR (indicated by an SW mark). As shown in FIG. 8, the switching element ILR is turned on for a predetermined time T 2 every PWM carrier period T. This on-time T is determined according to the deviation (4) between the fed-back motor current detection value IM and the assist current command value ID. Therefore, only when the switching element ILR is turned on, current flows through the motor IO as shown by A. When the motor reverses, the switching element IUR
, ILR is turned off.

Control is performed using switches ILL and IUR.

Such a motor drive device has the following problems.

Let the voltage of the battery 35 be VBAT, and the induced starting pressure due to the rotation of the motor be E. vBAT≧Ea〉(T
/T) At the time of VBAT, a current tries to flow as shown by the broken line Bn in FIG. 7, but since the switching element IUR is off, this current cannot flow (the broken line Bn in FIG. 8). ). Since the switching element ILR is also off in the time zone n other than T, no current flows in this circuit as well (when it is on, a flywheel current flows). Therefore, when the motor rotates, as shown in FIG. 9, nonlinear characteristics occur near the current deviation (6) of 0.

In FIG. 9, ω is the rotational angular velocity of the motor.

In power steering, the motor terminal short circuit mode occurs when the motor is rotating and Id is small, or when there is no motor polarity reversal command, such as when steering or returning after letting go of the steering wheel.

A current IM expressed by L (d I /d t)+RIM-Ea flows. This current IM will be controlled by a current feedback loop while oscillating.

Such an oscillating current gives undesirable results in feedback control. This can cause malfunctions, especially in those in which motor drive is controlled by software.

On the other hand, when considering estimating the motor rotation angle, 2 rotations, angular velocity, 2 rotations, acceleration, etc. based on the motor current, and using this to perform viscosity compensation and inertia compensation, it is possible to estimate the oscillating current by using the observer as described above. If it is given, it will cause erroneous estimation.

Furthermore, switching loss increases during oscillation.

Furthermore, in inertia compensation control (acceleration control), current deviation i,
Since high-precision motor drive is required when 0 is around 0, it is not preferable to have the above-mentioned nonlinear characteristics.

SUMMARY OF THE INVENTION OBJECTS OF THE INVENTION An object of the present invention is to provide a device that can perform motor control suitable for an electric power steering device.

Structure 1 of the Invention Functions and Effects This invention provides a steering assist system that operates an assist current command value based on detected steering torque, detected vehicle speed, etc., and generates a steering assist torque in accordance with this assist current command value.
In the device that controls the motor, there are four assist motor control switching elements connected in an H-bridge type, two upper and lower on the first arm, two upper and lower on the second arm, and the above-mentioned current. When controlling the switching elements using the pulse width modulation method according to the magnitude of the deviation between the command value and the detected motor current and the polarity of the current command value, the two switching elements on one arm are controlled by the pulse width modulation method. Within the modulation period, the two switching elements in the other arm are controlled to be complementary on and off at a time depending on the magnitude of the deviation.

The device is characterized by comprising means for controlling the device to maintain either the on or off state within the pulse width modulation period depending on the polarity.

According to this invention, one of the two switching elements of one arm that is controlled to be on and off in a complementary manner is always on, so that flywheel current and motor induction in the opposite direction Both voltage and current flow. This prevents current oscillations from occurring either during steering or when the steering wheel is released and returned. Therefore, this motor current detection value can be used as an input to an observer or a current loop configured as a software servo. Furthermore, since perfect linear characteristics can be obtained, highly accurate inertial control is also possible.

DESCRIPTION OF THE EMBODIMENTS FIG. 1 is a block diagram functionally showing the entire motor drive device in an electric power steering device according to the present invention. FIG. 2 is a configuration diagram showing an example of a power steering mechanical system. FIG. 3 is a block diagram showing the entire electrical configuration of the electric power steering device.

In these drawings, the same parts are denoted by the same reference numerals, and the relationship between FIG. 1 and FIG. 3 is as follows. That is, the functions of blocks 11 to 16 shown in FIG. 1 are realized by the CPU 31 and memory 34 in FIG. Some of these blocks 11 to 16 are C
It may be realized by the PU 31, and the others may be realized by a hardware circuit. In FIG. 1, the motor voltage detection circuit 3 shown in FIG.
9 is omitted.

First, the power steering mechanical system shown in FIG. 2 will be explained.

The rotational force of the steering handle 21 is transmitted to the steering gear 22 including a pinion gear via the handle shaft, and further transmitted to the rack shaft 24 by the pinion gear.
The wheel 25 is turned through the knuckle arm and the like. Further, the rotational force of the steering assist motor (DC motor) 10 controlled and driven by the control device 30 is transmitted to the rack shaft 24 through the meshing between the steering gear 23 including a pinion gear and the rack shaft 24, and the rotational force is transmitted to the rack shaft 24 through the engagement of the steering gear 23 including a pinion gear. I will be assisting. Handle 21 and motor lO
The rotating shafts of the rotary shafts are mechanically connected by gears 22, Ll, and rack shafts 24. Steering torque is detected by the steering torque sensor 42, and vehicle speed is detected by the vehicle speed sensor 43, and the control device 30 controls the motor 10 based on these detected torque and vehicle speed, as will be described later. Operating power is supplied to the control device 30 and the motor 1O from a battery 35 mounted on the vehicle.

In FIG. 3, pulses of a frequency corresponding to the vehicle outputted from the vehicle sensor 43 are counted by a counter 33 and are outputted from the CP.
Given to U31. Further, the torque detected by the steering torque sensor 42 is converted into a digital quantity by the A/D converter 32 and is provided to the CPU 81. Furthermore, the steering assist motor
The current flowing through O and the voltage applied to motor 10 are detected by motor current detection circuit 19 and motor voltage detection circuit 39, respectively, and converted into digital quantities by A/D converters 38 and 37, respectively, and provided to CPU 31. C
The PU 31 generates an assist command value based on the input detected vehicle speed and detected torque, and adds a viscosity compensation value and an inertia compensation value to this as necessary to create a current command value ID.

For example, the assist command value is determined according to the detected steering torque.
For steering torque within a certain range, a motor current approximately proportional to the steering torque flows, and when the above range is exceeded, a certain motor current IN flows, and depending on the detected vehicle speed, when the vehicle speed is high, the motor It is created so that the motor IO can be controlled so that the current IM is decreased and the motor current IM is increased when the vehicle speed is slow.

A viscosity compensation value is calculated based on the steering angular speed (rotational speed of the assist motor 100) detected or estimated by the observer as described later, and, if necessary, the detected vehicle speed. This viscosity compensation value is added (or subtracted) from the assist command value. This suppresses the instability that tends to occur when the vehicle is released and returns at high speeds, and works to compensate for reducing viscosity at low vehicle speeds, reducing the sense of activation of the steering wheel and providing a good feeling. You will be able to do it.

The inertia compensation value is used to control the motor as if the rotor inertia at 0 had become smaller.It eliminates the weight caused by the motor lO not following the rotation of the steering wheel when the steering wheel is suddenly turned, and increases the return speed when the driver releases the steering wheel. It acts to speed up the process.

was detected. Alternatively, as described later, an inertia compensation value is calculated based on the steering angle acceleration (rotational acceleration of the motor 10) estimated by the observer. The calculated inertia compensation value is added to the assist command value.

In this way, the viscosity compensation value and the inertia compensation value are added to the assist command value to obtain the current command value ID.

In FIG. 1, the H-bridge connection configuration of switching elements IUL, ILL, IUR, :LLR in the motor drive circuit 40 is the same as that shown in FIG. The voltage VBAT of the battery 35 is applied to these switching elements via the main power relay contact 20. Switching elements IUL and ILL are left arm driver 17
Accordingly, switching elements IUR and ILR are controlled by right arm driver 18 based on control signals from drive logic circuit 16 in a manner to be described below.

Each is controlled on and off.

Connection blocks 11 to 1 inside the CPU 81 shown in FIG.
6 is actually realized by software (software servo), but is shown as a hardware configuration to make the explanation easier to understand. A subtracter 11 calculates a deviation I between the current command value ID and the motor current I detected by the motor current detection circuit 19. This deviation Id is converted into an absolute value by an absolute value circuit 12 on the one hand, and its polarity (positive or negative) is determined by a polarity determining circuit 15 on the other hand. The output of the absolute value circuit 12 is compared with the triangular wave output from the PWM carrier frequency triangular wave generation circuit 13 in the voltage comparison circuit 14, and is output as a PWM pulse. This PWM pulse and the polarity discrimination result of the polarity discrimination circuit 15 are applied to the drive logic circuit 16, and from this circuit 16, a signal for controlling the switching elements on and off is generated in the following manner.

Referring to FIGS. 4 and 5, when the motor (0) is rotated in the forward direction, the switching element IUR is held in the off state and the switching element ILR is held in the on state in one period T of the PWM carrier. IU
L is turned on for a time T corresponding to the deviation Id, and turned off during other time periods (T-on T). Further, the switching element n ILL is turned off during the time T and turned on during the other time period n (TT). In this way, the switching elements IUL and ILL of the left n-arm have their ON and OFF states reversed and operate in a complementary manner. At time T, current IN flows through motor 10n. At other times (T −T on), the flywheel current C flows through the switching element ILL which is on, and in particular v > Ea(
T/T) When VBAT, MoBAT
When the current is on, the current due to the induced voltage also flows through the switching element ILL which is on. In this way.

The waveform of current IN is as shown in Figure 5, and the characteristics are as shown in Figure 6.
As shown in the figure, it has linearity at all positions. During forward rotation, forward rotation power running mode I and forward rotation regeneration mode ■ operate.

At the time of reversal, the switching element IUL is kept off and the switching element ILL is kept on in the PWM carrier cycle period part, and the switching elements IUR and ILR of the right arm are controlled to be turned on and off in a complementary manner according to the time T.

As described above, since current oscillation does not occur, the current detected by the motor current detection circuit 19 can be fed back to the software servo by the CPU 31.

4. Furthermore, it is possible to estimate the steering angle position, steering angle velocity, steering angle acceleration, etc. by the observer using the detected current, and these estimated values can be used to perform the viscosity compensation and inertia compensation of the above-mentioned assist command.

Based on the current detected by the motor current detection circuit i9 and the voltage detected by the motor voltage detection circuit 39, the observer
Furthermore, the steering angle position, steering angle velocity, steering angle acceleration, etc. are estimated based on the detected current and the current command value.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram showing a motor drive device according to an embodiment of the invention. FIG. 2 is a configuration diagram showing an example of a power steering mechanical system. FIG. 3 is a block diagram showing the electrical configuration of the electric power steering device. 4 and 5 are a circuit diagram and a waveform diagram for explaining the operation of the motor drive circuit, respectively, and FIG. 6 is a graph showing current command value/motor current characteristics. 5. FIGS. 7 and 8 are a circuit diagram and a waveform diagram for explaining the operation of a conventional motor drive circuit, respectively, and FIG. 9 is a graph showing current command value/motor current characteristics. IUL, ILL, IUR, ILR...Switching elements. lO...Assist motor. 11... Reducer. 12... Absolute value circuit. 13...PWM carrier frequency triangular wave generation circuit. I4... Voltage comparison circuit. I5...Polarity discrimination circuit. 16...Drive logic circuit. 17, 18...Switching element driver. 19...Motor current detection circuit. 30...control device. 31...CPU. 40...Motor drive circuit. 42...Torque sensor. 6 43...Vehicle speed sensor. that's all

Claims (1)

[Scope of Claims] A steering assist device that creates an assist current command value based on detected steering torque, detected vehicle speed, etc., and controls a motor and a steering assist device that generates a steering assist torque according to the assist current command value, Four assist motor control switching elements connected in an H-bridge type, two upper and lower on the first arm and two upper and lower on the second arm, as well as the above current command value and detected motor current. When controlling the switching elements using the pulse width modulation method according to the magnitude of the deviation from the current command value and the polarity of the current command value, the two switching elements of one arm are controlled within the pulse width modulation period.
Complementary on/off control is performed at a time depending on the magnitude of the deviation, and the two switching elements on the other arm are turned on or off within the pulse width modulation period depending on the polarity. A motor drive device in an electric power steering device, comprising means for controlling the motor so as to maintain the motor.