JP3066616B2 - Electric power steering device - Google Patents

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 apparatus for assisting a steering force of a steered wheel.

[0002]

2. Description of the Related Art An electric power steering apparatus detects a torque applied to a steering shaft by operating a steered wheel, and drives a DC motor that rotates the steering shaft with a drive current corresponding to the detected torque to reduce the steering force. It is configured to assist.

FIGS. 1 and 3 are block diagrams of a motor drive circuit in a conventional electric power steering apparatus. The motor drive circuit shown in FIG. 1 is for forward rotation (reverse rotation) so that a bridge circuit BR is constituted by a pair of forward rotation power transistors T ₁ and T ₂ and one pair of reverse rotation power transistors T ₃ and T ₄ . A power transistor T ₁ (T ₃ ) and a reverse (forward) power transistor T ₄ (T ₂ ) are connected in series, and a series circuit of a forward power transistor T ₁ and a reverse power transistor T ₄ and a reverse circuit use power transistor T ₃ and the forward rotation power transistor T
_Two series circuits are connected in parallel. A flywheel diode FD is connected in anti-parallel to each of the power transistors T ₁ , T ₂ , T ₃ and T ₄ .

A direct current motor M for assisting the steering force is provided between a connection between the forward rotation power transistor T ₁ and the reverse rotation power transistor T _{4 and} a connection between the reverse rotation power transistor T ₃ and the forward rotation power transistor T _2. Is interposed. Connecting portions BRa the forward rotation power transistor T ₁ and the reverse rotation power transistor T ₃ is connected to the positive electrode of the DC power source B consisting of a battery, connected to the reverse rotation power transistor T ₄ and the forward rotation power transistor T ₂ Department
BRb is connected to the negative electrode of the DC power supply B via the current detection resistor R. The flywheel diode FD is
The power transistors T ₁ , T ₂ , T ₃ , and T ₄ are protected from the back electromotive force induced in the DC motor M.

[0005] Forward (reverse) power transistor T
₁ (T ₃ ) gate has PWM (pulse width modulation) signal PWM
, And the forward (reverse) power transistor T
_The DC signal DC is given to the gate of ₂ (T ₄ ).

Next, the operation of the motor drive circuit will be described. When the DC motor M is driven to generate torque in the forward (reverse) direction to assist the steering force, forward (reverse)
The power transistor T ₁ (T ₃ ) is turned on and off according to the PWM signal, and the power transistor T
₂ (T ₄ ) is kept in the ON state. Then, every time the forward (reverse) power transistor T ₁ (T ₃ ) is turned on, the drive current I _M flows from the DC power supply B to the DC motor M as shown by the solid line arrow _LL ( _LR ), The DC motor generates torque in the forward (reverse) direction.

FIG. 2 shows a PWM for driving the DC motor M.
It is a waveform diagram showing the relation between signal PWM and the direct current signal DC and the driving current I _M of the DC motor M. Forward rotation as shown in Fig. 2 (a)
PWM signal supplied to the gate of the (reverse) for the power transistor T ₁ (T ₃₎ is I rise, forward (reverse) for the power transistor T ₁ (T ₃₎ is turned on, the forward (reverse)
2 (b) at the gate of the power transistor T ₂ (T ₄ )
When the direct current signal DC shown in (1) is given and the forward (reverse) power transistor T ₂ (T ₄ ) is turned on, the direct current motor M is transmitted via the forward (reverse) power transistor T ₁ (T ₃ ).
DC motor M driving current I _M is the flow shown in FIG. 2 (a) to generate a torque in the forward (reverse) direction.

On the other hand, when the PWM signal PWM falls and the forward (reverse) power transistor T ₁ (T ₃ ) turns off,
The drive current I _M is cut off and connected in parallel to the forward (reverse) power transistor T ₂ (T ₄ ) and the reverse (forward) power transistor T ₄ (T ₂ ) which are kept on. Dashed line through flywheel diode FD
Flowing regenerative current I _R shown by (see FIG. 1). The DC motor M is also driven by the regenerative current I _R.

The motor drive circuit shown in FIG. 3 has the same configuration as the motor drive circuit shown in FIG. 1, and has the gates of the power transistors T ₁ and T ₂ for normal rotation and the power transistors T ₃ and T ₄ for reverse rotation. Is provided with a PWM signal PWM.

Next, the operation of the motor drive circuit will be described. When the DC motor M is rotated forward (reverse rotation) to assist the steering force, the power transistor T for forward rotation (reverse rotation) is used.
₁ (T ₃ ) and forward (reverse) power transistor T ₂
(T ₄ ) is turned on and off according to the PWM signal PWM. Then, the power transistor T ₁ (T
₃ ) and forward (reverse) power transistor T
₂ Each time both (T ₄ ) are turned on, the solid arrow L
_As indicated by _L (L _R ), a drive current I _M flows from the DC power supply B to the DC motor M, and the DC motor M generates a torque in the forward (reverse) direction.

FIG. 4 is a diagram showing the PWM when the DC motor M is driven.
A signal is a waveform diagram showing the relationship between the driving current I _M of the DC motor M. As shown in FIG. 4A, the PWM signal PWM applied to the gate of the forward (reverse) power transistor T ₁ (T ₃ ) rises, and as shown in FIG. 4B, the forward (reverse) power transistor PW given to the gate of T ₂ (T ₄ )
When the M signal PWM rises, the forward (reverse) power transistors T ₁ (T ₃ ) and T ₂ (T ₄ ) turn on, and the forward (reverse) power transistors T ₁ , T ₂ (T ₃₎ , T ₄ ), the drive current I _M flows to the DC motor M, and the DC motor M generates a torque in the forward (reverse) direction. FIG. 4
(a), as shown in (b) PWM signal PWM falling, the driving current I _M of the DC motor M and the forward (reverse) for power transistors _{T 1, T 2 (T 3} , T 4) are both turned off Will be shut off. When both the forward (reverse) power transistors T ₁ and T ₂ (T ₃ and T ₄ ) are off, the regenerative current does not flow through the DC motor M.

[0012]

In the former motor drive circuit, a forward (reverse) power transistor T ₁ (T ₃ )
There immediately after turning off flow to the DC motor M regenerative current I _R from the DC motor M to the driving current I _M in the same direction, the driving force for assisting a steering force by the regenerative current I _R is produced.
Therefore, even when the duty ratio of the PWM signal PWM is small, the steering force can be sufficiently assisted, and a wide range can be adjusted from the small duty ratio. However, normal rotation
The power transistor T ₁ (T ₃ ) for (reverse rotation) is off and the power transistor T ₂ (T ₄ ) for normal rotation (reverse rotation)
When the steering wheel is returned while the switch is turned on, the DC motor M is rotated by the return operation force to generate a reverse starting force. There is a problem that a braking force acts on the returning operation and the returning operation is hindered.

On the other hand, in the latter motor drive circuit,
Since (reverse) for power transistors T ₁ and (T ₃₎ and the forward (reverse) for a power transistor T ₂ (T ₄₎ is turned off at the same time, does not flow to the rotating current I _R is the DC motor M by the DC motor M , the DC motor M is driven only by the driving current I _M. Therefore, when the duty ratio of the PWM signal PWM is small, the driving force for assisting the steering force is insufficient, and in order to obtain the same driving force, it is necessary to increase the duty ratio in the former motor drive circuit. As a result, the minimum value of the duty ratio that can assist the steering force increases, and the duty ratio cannot be adjusted over a wide range, and the current ripple increases.

Further, the regenerative current generated by the DC motor M may flow to the DC power supply B. In such a case, there is a problem that noise is generated in a car radio or the like using the DC power supply B as a power supply. In view of such a problem, the present invention can adjust the driving force for assisting the steering force in a wide range, does not act on the braking force at the time of returning the steered wheels, and further generates noise on the car radio or the like due to the regenerative current by the DC motor. It is an object of the present invention to provide an electric power steering device that does not occur.

[0015]

An electric power steering apparatus according to the present invention includes a DC motor connected to bridge a bridge composed of a pair of forward switching elements and a pair of reverse switching elements. A motor driving circuit for rotating the DC motor forward or backward by selective conduction of the switching element pair at the opposing position, driving the DC motor by PWM controlling the motor driving circuit, and assisting the steering force with the driving force. In the electric power steering apparatus, the duty ratio of the pulse applied to the other switching element is different from the duty ratio based on the duty ratio of the pulse applied to one of the pair of switching elements. The ratio is determined.

[0016]

When the pair of switching elements are both turned on,
A drive current flows through the DC motor, and the DC motor is driven. When one of the pair of switching elements is turned off first, the drive current is cut off. When the drive current is cut off, a regenerative current in the same direction as the drive current flows through the DC motor via the other switching element and the flywheel diode, which remain on, to drive the DC motor.
When the other of the pair of switching elements is turned off, the regenerative current flowing from the DC motor to the DC motor via the flywheel diode is cut off, and the driving of the DC motor is stopped. Accordingly, the DC motor is driven by the drive current and the regenerative current, so that the DC motor can be driven even with a drive current having a small duty ratio, and the duty ratio of the drive current can be adjusted over a wide range from a small value to a large value. Since the regenerative current of the DC motor can be cut off, no braking force acts when the steered wheels are returned.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 5 is a schematic block diagram showing a configuration of a motor drive circuit in the electric power steering device according to the present invention. A PWM signal PWM ₁ from a PWM signal generator (not shown) is input to one input terminal of each of the AND circuits A ₁ and A ₂ . Forward rotation command signal S _L serving DC signal from the rotation direction command unit (not shown) is inputted to the other input terminal of the AND circuit A _2, A _4, serving likewise the DC signal reverse rotation command signal S _R AND circuit A ₁ and A _{3 are} input to the other input terminals.

The duty ratio greater than the PWM signal PWM ₂ of the PWM signal PWM ₁ is inputted to the AND circuit A _3, A ₄ each of one input terminal. AND circuit A ₁ (A ₂ , A ₃ ,
The output signal of A ₄ ) is a driving circuit D ₃ (D ₁ , D ₄ ,
D ₂ ). The driving circuit D ₁ (D ₂ , D ₃ ,
The output signal of D ₄ ) is a power transistor T ₁ (T ₂ , T ₂ ) as a switching element forming a bridge circuit BR.
₃ , T ₄ ) are individually input to the gates.

A DC motor M is interposed between the connection between the power transistors T ₁ and T _{4 and} the connection between the power transistors T ₃ and T ₂ . Each power transistor T ₁ , T ₂ , T ₃ , T ₄ has a flywheel diode F
D is connected in anti-parallel. Flywheel diode FD
Protects the power transistors T ₁ , T ₂ , T ₃ , T ₄ from the back electromotive force generated in the DC motor M. One side connection BRa of the bridge circuit BR is connected to the positive electrode of the DC power supply B composed of a battery, and the other side connection BRb is connected to the negative electrode of the DC power supply B via a current detection resistor R, thereby providing a motor drive circuit. Is configured.

Next, the operation of the motor drive circuit will be described with reference to FIG. 6 showing a waveform diagram of a PWM signal. Now, FIG.
PWM signal PWM ₁ shown in (a) are inputted to the AND circuit A _1, A ₂ each of one input terminal, the PWM signal PWM ₂ is AND shown in duty ratio is greater than 6 of the PWM signal PWM ₁ (b)
Circuits A ₃ , A _{4 are} inputted to respective one-side input terminals and, for example, normal rotation command signals S _L composed of DC signals are supplied to AND circuits A ₂ , A 4
_{4 When} the signal is input to the other input terminal, the PWM signals PWM ₁ and P
AND when the WM ₂ rises, the normal rotation command signal S _L is up standing
The logic of the circuits A ₂ and A ₄ is established, and the respective output signals are input to the drive circuits D ₁ and D ₂ .

The driving circuit D _1, D ₂ and outputs a gate signal by amplifying the input signal, the gate signal is input to the gate of the power transistors T _1, T _2, the power transistor T _1, T ₂ Turn on at the same time. Thereby, the DC power supply B switches the power transistor T ₁ , the DC motor M,
A circuit extending from the power transistor T ₂ to the DC power supply B through the current detection resistor R to the DC power supply B applies a solid line arrow L _L to the DC motor M.
The driving current I _M shown in FIG. 5 flows, and the DC motor M generates a torque in the forward direction. Thereafter, PWM signals PWM ₁ duty ratio is small becomes earlier and falls when logic unsatisfied AND circuit A ₂ as shown in FIG. 6 (a), the power transistors T ₁ and its output signal is extinguished is turned off Drive current I
_M is shut off.

By the way the duty ratio of the PWM signal PWM ₂ is larger than the duty ratio of the PWM signal PWM ₁ as shown in FIG. 6 (b), PWM when the PWM signal PWM ₁ fell standing
The signal PWM ₂ does not fall, and the power transistor T ₂ keeps on. Its for the DC motor M, the regenerative current I _R shown in FIG. 6 (a) through the DC motor M in the same direction as the driving current I _M. That be driven DC motor M by the PWM signal PWM ₁ duty ratio is small, a large driving force is obtained for flowing regenerative current I _R is the DC motor M. Then, when the PWM signal PWM ₂ falls as shown in FIG.
Becomes logic does not hold circuit A _4, the power transistor T ₂ is turned off by the output signal disappears, the regenerative current I _R shown by the broken line arrow marks in FIG. 5 is interrupted.

That is, the regenerative current I _R flowing through the DC motor M
Is cut off, and the DC motor M is forcibly rotated by the operating force at the time of the returning operation of the steered wheels. As a result, even when the back electromotive force is generated, no current flows due to the power generation, and at the time of the returning operation of the steered wheels, No braking force is applied.

Next, the PWM signal PWM ₁ is connected to the AND circuits A ₁ , A ₂
PWM signal PWM ₂ is ANDed
When the reverse command signal S _R composed of a DC signal is inputted to one input terminal of each of the circuits A ₃ and A ₄ and inputted to the other input terminal of each of the AND circuits A ₁ and A ₃ , the PWM signal PWM ₁ , P
When the WM ₂ rises, the logic of the AND circuits A ₁ and A ₃ is established, and the output signals thereof cause the power transistors T ₃ and T ₃ to operate.
₄ is turned on, the DC motor is the M power transistor T _3, the DC motor M, a power transistor T _4, driven by a circuit shown by the solid line arrow L _R passing through the current detection resistor R current I
_M flows, and the DC motor M generates torque in the reverse rotation direction.

[0025] Then, PWM signal PWM ₁ becomes a logic does not hold the AND circuit A ₁ when falls, the output signal disappears, the power transistor T ₃ is turned off, the driving current I _M is cut off. When the driving current I _M is cut off, the regenerative current flows in the DC motor M in the same direction as the driving current I _M, and a large driving force is obtained in the DC motor M. If then the PWM signal PWM ₂ is falls, the logic of the AND circuit A ₃ is not satisfied, the power transistor T ₄ whose output signal is extinguished to turn off.
Thereby is interrupted regenerative current I _R flowing through the DC motor M, is interrupted circuit of the regenerative current I _R flowing through the DC motor M, the braking force at the time of return operation of a steering wheel even during reverse rotation of the DC motor M does not act.

[0026] Since a large driving force is obtained in this way, the DC motor M even with a small duty ratio of the PWM signal PWM ₁ and, so that a small duty ratio can be adjusted extensively duty ratio. Further, even if a counter-electromotive force is generated in the DC motor M by mechanically rotating the DC motor by the returning operation of the steered wheels, the current generated by the power generation does not flow through the DC motor M, and the braking force acting during the returning operation can be eliminated.

FIGS. 7 and 8 are waveform diagrams showing the relationship between the duty ratios of the PWM signals PWM ₁ and PWM ₂ . As shown in FIG.
PWM signal PWM ₂ are predetermined duty to the PWM signal PWM ₁
Created by adding 0.5A. Fig. 7 (a) shows the PWM signal PWM ₁
FIG. 7B shows a case where the duty ratio of the PWM signal P is small.
FIG. 7C shows a case where the duty ratio of WM ₁ is increased.
This shows a case where the duty ratio of the M signal PWM ₁ is further increased. This relationship of the duty ratio, the pulse width of the PWM signal PWM ₁ in FIGS. 7 (a) If you A, the pulse width of the PWM signal PWM ₂ to 1.5A. When the pulse width of the PWM signal PWM ₁ is set to 2A as shown in FIG.
Set the pulse width of signal PWM ₂ to 2.5A. Further, when the pulse width of the PWM signal PWM ₁ is set to 2.5 A as shown in FIG.
M signal PWM ₂ is a continuous DC signal.

The PWM signal PWM ₂ shown in FIG.
Created by varying the duty to be added in accordance with the duty ratio of the PWM _1. 8A shows a case where the duty ratio of the PWM signal PWM ₁ is small, FIG. 8B shows a case where the duty ratio of the PWM signal PWM ₁ is increased, and FIG.
This shows a case where the duty ratio of PWM ₁ is further increased. And when the pulse width of the PWM signal PWM ₁ to A as shown in FIG. 8 (a), the pulse width of the PWM signal PWM ₂ to 2A. In the case that the 2A the pulse width of the PWM signal PWM ₁ as shown in FIG. 8 (b), the pulse width of the PWM signal PWM ₂ to 4A. Further when the pulse width of the PWM signal PWM ₁ to 2.5A as shown in FIG. 8 (c), a continuous direct current signal PWM signal PWM _2.

Such a PWM signal having a large duty ratio
To create the PWM ₂ in accordance with the duty ratio of the PWM signal PWM ₁ is increased, a larger duty, it can be created by adding the PWM signal PWM _1.
The duty ratio of the PWM signal PWM ₁ and the PWM signal
The relationship with the duty ratio of signal PWM ₂ is an example,
Signal the duty ratio of the PWM ₂ is good if the larger than the duty ratio of the PWM signal PWM _1, is not limited to this embodiment.

[0030]

As described above in detail, one according to the present invention
Given to one of the pair of switching elements
Pulse duty ratio and the other switching element
So that the duty ratio of the pulse given to the
The steering assist power is insufficient and the electric ripple is large
In addition to eliminating the disadvantages such as difficulty in driving, the regenerative current generated after the DC motor drive current is cut off is supplied to the DC motor, so the DC motor that controls the drive current is large even if the duty ratio of the PWM signal is small. The driving force can be obtained, and the duty ratio of the PWM signal can be adjusted in a wide range from a small value to a large value. If the DC motor is not driven, the circuit in which the current generated by the back electromotive force flows through the DC motor is cut off, so that the braking force does not act when returning the steered wheels. In addition, there is an excellent effect that an electric power steering apparatus can be provided in which a regenerative current does not flow into a DC power supply and noise does not occur in a car radio or the like.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a motor drive circuit in a conventional electric power steering device.

FIG. 2 is a waveform diagram of a PWM signal for controlling the motor drive circuit shown in FIG. 1, a drive current of a DC motor, and a regenerative current.

FIG. 3 is a configuration diagram of a motor drive circuit in another conventional electric power steering device.

FIG. 4 is a waveform diagram of a PWM signal for controlling the motor drive circuit shown in FIG. 3 and a drive current of a DC motor.

FIG. 5 is a schematic block diagram showing a configuration of a motor drive circuit in the electric power steering device according to the present invention.

6 is a waveform diagram of a PWM signal for controlling the motor drive circuit shown in FIG. 5, a drive current of a DC motor, and a regenerative current.

FIG. 7 is a waveform diagram showing a relationship between duty ratios of two PWM signals.

FIG. 8 is a waveform diagram showing another relationship between the duty ratios of two PWM signals.

[Explanation of symbols]

_{A 1, A 2, A 3} , A 4 AND circuit _{D 1, D 2, D 3} , D 4 drive circuits _{T 1, T 2, T 3} , T 4 power transistors M DC motor FD flywheel diode B DC power supply

Claims (1)

(57) [Claims] 1. A DC motor is connected so as to bridge a bridge composed of a pair of switching elements for normal rotation and a pair of switching elements for reverse rotation. An electric power steering apparatus, comprising: a motor drive circuit for rotating the motor forward or backward, PWM controlling the motor drive circuit to drive the DC motor, and assisting the steering force with the driving force. based on the duty ratio of the pulse applied to one of the switching elements of the switching elements, the du
An electric power steering apparatus, wherein a duty ratio of a pulse applied to the other switching element is determined so as to be different from the duty ratio.