 |
Description  |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a motor driving apparatus
including an H-bridge circuit constituted by a plurality of transistors
some of which are driven under the control of a pulse-width modulated
signal of which duty ratio is controllable (hereinafter, such driving will
be referred to as the driving under PWM control or PWM-driving or the
like). More specifically, the invention is concerned with a motor driving
apparatus which is capable of continuing or stopping selectively and
effectively operation of an electric motor employed as a drive source in
dependence on abnormal conditions prevailing upon occurrence of a
short-circuit fault in a transistor circuit. The invention can profitably
find application to a motor-driven power steering system of a motor
vehicle, being understood, however, that the invention is never restricted
thereto.
2. Description of Related Art
For having better understanding of the invention, description will first be
directed to the technical background thereof. FIG. 4 is a block diagram
showing generally a circuit configuration of a conventional motor driving
apparatus known heretofore. In this case, it is assumed that the motor
driving apparatus is adapted for driving an electric motor employed for
generating an assist torque in a motor-driven power steering system of an
automobile or motor vehicle for assisting a driver in manipulating a
steering wheel. A typical example of such motor driving apparatus is
disclosed, for example, in Japanese Unexamined Patent Application
Publication No. 158455/1990 (JP-A-2-158455).
Referring to FIG. 4, an electric motor 2 whose operation is to be
controlled is connected between output terminals 1a and 1b of an H-bridge
circuit 1 which in turn is constituted by a plurality of transistors such
as FETs (field-effect transistor). In the illustrated circuit, there are
employed four transistors or FETs Q1 to Q4, wherein a diode is connected
in parallel to each of the transistors Q1 to Q4 in order to allow a motor
current IM generated upon stopping of the electric motor 2 to flow through
the diodes.
The H-bridge circuit 1 has one end 1c connected to a power supply source 3
which may be constituted, for example, by an onboard battery of a motor
vehicle, wherein a relay 4 is inserted between the one end 1c of the
H-bridge circuit 1 and the power supply source 3 for the purpose of
controlling (i.e., enabling or disabling) the power supply to the electric
motor 2. Further, the H-bridge circuit 1 has the other end 1d connected to
the ground potential GND, wherein a shunt resistor 5 is inserted between
the other end 1d and the ground GND for detecting an electric current I
flowing to or through the H-bridge circuit 1.
There are provided a plurality of driving circuits 6 to 9 in correspondence
to the transistors (FETs) Q1 to Q4, respectively, wherein PWM signals (or
on-signals, i.e., signal for operating the transistor in the constantly or
continuously conducting state which may also be referred to as the on
state) P1 to P4 are selectively applied to the individual transistors Q1
to Q4.
A voltage detecting circuit 11 is provided for detecting a relay contact
voltage VR applied to the one end 1c of the H-bridge circuit 1, while a
current detecting circuit 12 is provided for detecting a current value Id
on the basis of a voltage appearing at one end of the shunt resistor 5.
Further, a torque sensor 30 is provided for detecting a steering torque T
applied to a steering system by a driver through a steering wheel in the
assumed case where the electric motor 2 is employed for generating an
steering assist torque, as mentioned previously.
A control means 20 implemented by using a microcomputer fetches the
detected current value Id, the relay contact voltage VR and the output of
the torque sensor 30 indicative of the applied steering torque T to
thereby output a stop signal S for on/off control of the relay 4 as well
as drive control command signals C1 to C4 for controlling the driving
circuits 6 to 9, respectively.
Next, referring to FIG. 4, description will be made of operation of the
conventional motor driving apparatus on the assumption that the motor
driving apparatus is applied to a motor-driven power steering system of a
motor vehicle for generating an assist torque for assisting a driver in
manipulation of a steering wheel.
For generating a desired assist torque in dependence on the applied
steering torque T as detected, the control means 20 first determines
selectively the transistors (e.g. transistors Q1 and Q4) to be driven
under the PWM control on one hand and to be driven in the on-state on the
other hand and at the same time determines a desired duty ratio value of a
PWM signal (P1) for the transistor selected for the PWM-driving (e.g. Q1).
More specifically, one (e.g. transistor Q2) of the transistors Q1 and Q2
connected to the power supply source 3 and one (e.g. transistor Q3) of the
transistors Q3 and Q4 connected to the ground GND are turned off. In this
state, the other one (e.g. transistor Q1) of the transistors Q1 and Q2
connected to the power supply source 3 is driven under the PWM control
with the other one (e.g. transistor Q4) of the transistors Q3 and Q4
connected to the ground GND is driven continuously in the on-state.
Thus, the electric motor 2 connected between the output terminals 1a and 1b
of the H-bridge circuit 1 is driven for an angular distance in a direction
under supply of a motor current IM as commanded by the control means 20.
In that case, in order to enhance the controllability of the duty ratio of
each of transistors Q1 to Q4 while suppressing generation of heat and
noise upon turning on/off of the transistors, only the transistor Q1
connected to the power supply source 3 is driven under the PWM control
with the transistor Q4 connected to the ground GND being maintained
steadily in the conducting state (i.e., on state).
Parenthetically, when the electric motor 2 is to be driven in the reverse
direction, then the operating states of the transistors are so reversed
that the transistors Q2 and Q3 are driven with only the transistor Q2
being driven under the PWM control while the transistors Q1 and Q4 are
both turned off.
At this juncture, it is noted that when a short-circuit fault occurs in any
one of the transistors Q1 and Q4 or Q2 and Q3 during operation of the
electric motor 2, the electric current I flowing through the H-bridge
circuit 1 or the motor current IM becomes excessively large. To say in
another way, an overcurrent flows through the H-bridge circuit 1 and hence
through the electric motor 2.
Such overcurrent is then detected by the current detecting circuit 12, and
the detected current value Id indicating the overcurrent is supplied to
the control means 20 from the current detecting circuit 12. In response,
the control means 20 generates immediately a stop signal S for
interrupting application of the PWM signal to the H-bridge circuit 1 to
thereby stop operation of the electric motor 2 in order to protect the
H-bridge circuit 1, the electric motor 2, the power supply source 3, the
relay 4, a fuse (not shown) and so forth from injury or damage due to the
overcurrent.
However, when the motor driving apparatus is employed in association with
the motor-driven power steering system of a motor vehicle with the
electric motor 2 generating an assist torque for the motor-driven power
steering system, the stop processing executed by the control means 20 as
mentioned above means that the assist torque applied to the steering wheel
of the motor vehicle is abruptly reduced to zero during operation of the
motor vehicle, which will give rise to not a little shock and uneasiness
to the driver or operator. For this reason, the processing for generating
the stop signal S immediately in response to occurrence of the
short-circuit fault is not preferred.
As is apparent from the above description, the motor driving apparatus
known heretofore suffers a problem that because the electric motor 2 is
stopped abruptly by interrupting immediately the power supply to the
electric motor 2 when the detected current value Id indicates abnormality
during operation of the electric motor 2, inconveniences such as mentioned
above may arise, although it depends on the applications for which the
electric motor 2 is employed.
SUMMARY OF THE INVENTION
In the light of the state of the art described above, it is an object of
the present invention to provide a motor driving apparatus which makes it
possible to continue a controlled or suppressed power supply to an
electric motor which is subjected to the control of the motor driving
apparatus, even when the detected current value indicates abnormality, to
thereby prevent occurrence of shock due to abrupt stoppage of operation of
the motor in a system in which the motor is employed.
In view of the above and other objects which will become apparent as the
description proceeds, there is provided according to an aspect of the
present invention a motor driving apparatus which includes a plurality of
transistors connected in the form of an H-bridge circuit, a power supply
source connected to one end of the H-bridge circuit, a relay inserted
between the one end of the H-bridge circuit and the power supply source, a
ground potential connected to the other end of the H-bridge circuit, a
plurality of driving circuits for applying a pulse-width modulated signal
or a turn-on signal selectively to the individual transistors, and a
control means which is in charge of controlling on/off operation of the
relay and the driving circuits. The control means turns off one of the
transistors inserted at the side of the power supply source and one of the
transistors inserted at the side of the ground, while driving the other
one of the transistors inserted at the side of the power supply source and
the other one of the transistors inserted at the side of the ground under
PWM control (pulse-width modulation control) and in a conducting or on
state, respectively, for thereby driving an electric motor connected
between output terminals of the H-bridge circuit. The motor driving
apparatus further includes a current detecting circuit for detecting an
electric current flowing to or through the H-bridge circuit and hence
through the electric motor. On the other hand, the control means is
comprised of an abnormality decision means for determining abnormality of
a detected current value outputted from the current detecting circuit.
When it is determined by the abnormality decision means that the detected
current value indicates abnormality, both of the other ones of the
transistors inserted at the sides of the power supply source and the
ground, respectively, are driven under the PWM control (pulse-width
modulation control).
By virtue of the arrangement stated above, there can be realized a motor
driving apparatus which is capable of continuing a power supply in a
suppressed state so that no shock can take place even when abnormality is
detected on the basis of the current value detected by the current
detecting circuit.
In a preferred mode for carrying out the invention, the abnormality
decision means may further include an abnormality decision range setting
means for setting an abnormality decision range on the basis of a relation
between a duty ratio value of the pulse-width modulated signal applied to
the transistors driven under the pulse-width modulation control and the
current value detected by the current detecting circuit, wherein
abnormality of the detected current value is determined when the duty
ratio value and the detected current value fall within the abnormality
decision range.
With the preferred arrangement mentioned above, it is possible to detect
the short-circuit fault of the transistor with high reliability regardless
of variation of the duty ratio value of the PWM driving signal and the
motor current value detected by the current detecting circuit. Thus, the
motor driving apparatus capable of making decision as to occurrence of
abnormality with high reliability can be implemented in a simple and
inexpensive circuit configuration.
In another preferred mode for carrying out the invention, the control means
may further include a stop condition setting means for setting stop
condition for deenergizing or turning off the relay, and a stop condition
decision means for deciding whether the stop condition is met or not when
abnormality of the detected value of the motor current is determined. When
the stop condition is met, a stop signal is outputted to the relay to
thereby interrupt electric power supply to the H-bridge circuit and hence
to the electric motor.
Owing to the arrangement mentioned above, there can be obtained a motor
driving apparatus which is capable of stopping the power supply in
dependence on the abnormality status determined after the motor driving
mode is changed over to the PWM driving mode.
In yet another preferred mode for carrying out the invention, the stop
condition decision means may be so implemented as to output the stop
signal so long as the detected value of the motor current and the duty
ratio value remain within the abnormality decision range, even when both
of the other transistors mentioned previously are driven under the
pulse-width modulation control upon determination of abnormality of the
detected motor current value.
By virtue of the arrangement mentioned above, there can be implemented a
motor driving apparatus capable of interrupting immediately the abnormal
current which makes appearance upon occurrence of a short-circuit fault in
the transistor which is controlled to be in the nonconducting or off
state.
In still another preferred mode for carrying out the invention, the stop
condition decision means may be so realized as to decrease gradually a
motor current supplied to the electric motor so far as the motor current
as detected by the current detecting circuit lies outside of the
abnormality decision range when both of the other transistors mentioned
previously are driven under the pulse-width modulation control upon
determination of abnormality based on the detected current value, while
outputting the stop signal when the detected motor current value becomes
lower than a predetermined current value inclusive thereof.
With the arrangement mentioned above, there can be provided a motor driving
apparatus which is capable of maintaining the supply of the motor current
while decreasing gradually the power supply to the motor until the motor
is stopped completely.
In a further preferred mode for carrying out the invention, the electric
motor may be employed as a drive source in a motor-driven power steering
system of a motor vehicle for generating an assist steering torque for
assisting a driver in his or her manipulation of a steering wheel. In that
case, the control means may include a drive control signal generating
means for determining a motor current supplied to the electric motor in
dependence on a steering torque applied by the driver.
By virtue of the arrangement mentioned above, there can be realized a motor
driving apparatus which is capable of controlling the motor current even
when a short-circuit fault occurs in the PWM-driven transistor during the
assist torque generating operation of the motor-driven power steering
system to thereby secure safety by suppressing occurrence of shock which
will otherwise be given to the steering system and hence to the driver.
In a yet further preferred mode for carrying out the invention, the
electric motor may be employed in a motor-driven power steering system of
a motor vehicle, wherein the stop condition can be so determined that
safety of a driver of the motor vehicle is ensured even when the motor is
stopped.
With the arrangement mentioned above, there is realized a motor driving
apparatus which can ensure safety of the steering system as well as that
of the driver even when the motor is stopped in the course of operation of
the motor-driven power steering system.
In the motor driving apparatus associated with the motor-driven power
steering system, the stop condition decision means may preferably be so
implemented as to output the stop signal when the steering torque applied
by the driver is smaller than a predetermined value.
With the above arrangement, there is implemented a motor driving apparatus
which is capable of securing the safety of the driver in the course of
operation of the motor-driven power steering system by stopping the power
supply to the motor when the steering wheel has attained a neutral
position after the control of the motor current which is effected by
suppressing a steep change in the steering torque.
In this conjunction, the stop condition decision means may be so
implemented as to output the stop signal when the motor current supplied
to the electric motor becomes smaller than a predetermined value.
With this arrangement, there can be obtained a motor driving apparatus
which can ensure safety during the motor-driven power steering control
operation.
Furthermore, in the case in which the motor is employed for generating an
assist steering force for a motor-driven power steering system of a motor
vehicle, the control means should preferably include a drive control
signal generating means for determining the motor current in dependence on
a steering torque applied by a driver.
With the arrangement mentioned above, a motor driving apparatus which can
ensure safety by obviating shock taking place upon steep change in the
steering torque is realized because even when a short-circuit fault occurs
in the transistor driven under the PWM control during the assist torque
control operation of the motor-driven power steering system, the control
of the motor current can be continued while decreasing gradually the motor
current substantially to zero, wherein operation of the apparatus is
stopped after the necessity for generation of the assist torque has
disappeared.
The above and other objects, features and attendant advantages of the
present invention will more easily be understood by reading the following
description of the preferred embodiments thereof taken, only by way of
example, in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the course of the description which follows, reference is made to the
drawings, in which:
FIG. 1 is a block diagram showing generally a circuit configuration of a
motor driving apparatus according to a first embodiment of the present
invention;
FIG. 2 is a view illustrating operation of motor current detection upon
occurrence of abnormality in the motor driving apparatus according to the
first embodiment of the invention;
FIG. 3 is a view for illustrating an abnormality decision range employed in
the first embodiment of the invention; and
FIG. 4 is a block diagram showing a configuration of a conventional motor
driving apparatus known heretofore.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now, the present invention will be described in detail in conjunction with
what is presently considered as preferred or typical embodiments thereof
by reference to the drawings. In the following description, like reference
characters designate like or corresponding parts throughout the several
views.
Embodiment 1
A first embodiment of the invention (i.e., exemplary mode for carrying out
the invention) will be described by reference to FIG. 1 which is a block
diagram showing generally a circuit configuration of a motor driving
apparatus according to the first embodiment of the present invention. As
can readily be understood from FIG. 1, the motor driving apparatus
according to the instant embodiment of the invention differs from the
conventional apparatus described hereinbefore by reference to FIG. 4 only
in that some of the functions incorporated in the control means 20 are so
modified as to implement the teachings of the present invention.
Accordingly, like reference characters as those shown in FIG. 4 are used
in FIG. 1 for designating the components similar or equivalent to those
mentioned previously by reference to FIG. 4 and repeated description
thereof will be omitted.
Now referring to FIG. 1, the control means 20 is provided with an A/D
(analogue/digital) converter 21 for converting the detection signals,
i.e., the steering torque T, the relay contact voltage VR and the detected
current value Id, into corresponding digital signals, respectively, which
are suited for processing executed by a microcomputer constituting the
control means 20 and a drive control signal generating means 22 which
serves to generate drive control signals C1 to C4 for the driving circuits
6 to 9, respectively, on the basis of the steering torque T, the relay
contact voltage VR and the detected current value Id which are indicated
by the digital signals obtained as the outputs of the A/D converter 21, as
mentioned above. So long as the arrangement mentioned above is concerned,
the function and configuration of the motor driving apparatus according to
the instant embodiment of the invention is substantially same as those of
the conventional motor driving apparatus described hereinbefore by
reference to FIG. 4.
According to the present invention incarnated in the first embodiment, the
control means 20 is further provided with an abnormality decision range
setting means 23 for setting an abnormality decision range FR (see FIG. 3)
on the basis of a relation between the duty ratio values of the PWM
signals for those of the transistors Q1 to Q4 which are operated under the
PWM control and the detected current value Id, i.e., the detected value of
the current flowing through the H-bridge circuit to the motor 2 and an
abnormality decision means 24 for deciding abnormality of the detected
current value Id when both the motor-applied voltage and the detected
current value Id fall within the abnormality decision range FR, to thereby
output an abnormality decision signal E to the drive control signal
generating means 22.
On the other hand, the drive control signal generating means 22 is so
arranged as to respond to the abnormality decision signal E when the
detected current value Id indicates abnormality, to thereby drive both the
other resistors (e.g. transistors Q1 and Q4) connected to the power supply
source 3 and the ground GND, respectively, (i.e., inserted at the sides of
the power supply source 3 and the ground potential GND, respectively,
under the PWM control.
Besides, the control means 20 includes a stop condition setting means 25
for setting the stop condition for deenergizing or turning off the relay 4
and a stop condition decision means 26 which responds to the abnormality
decision signal E to thereby decide whether the stop condition is
satisfied or not, when abnormality of the detected current value Id is
determined.
When the stop condition is met, the stop condition decision means 26
outputs the stop signal S to the relay 4 to thereby make the relay 4 stop
the power supply to the H-bridge circuit 1.
By way of example, the stop condition decision means 26 may be so arranged
that in response to the abnormality decision signal E indicating
abnormality of the detected current value Id, the stop condition decision
means 26 outputs the stop signal S so long as the abnormality decision
range FR is validated even in the state where both the transistors Q1 and
Q4 are driven under the PWM control.
Further, the stop condition decision means 26 may be so implemented as to
decrease gradually the duty ratio value of the PWM signals P1 and P4 and
hence the motor current IM when the abnormality decision range FR is
invalidated as a result of driving of both the transistors Q1 and Q4 under
the PWM control upon occurrence of abnormality in the detected current
value Id and issue the stop signal S only when the detected current value
Id is decreased to a predetermined current value (e.g. when the detected
current value Id becomes approximately zero).
On the other hand, the stop condition for generating the stop signal S is
so established that a system such as a motor-driven power steering system
of a motor vehicle which employs the electric motor 2 can be protected
against degradation of safety even when the electric motor 2 is stopped.
By way of example, assuming that the electric motor 2 of the motor driving
apparatus according to the invention is employed in a power steering
system of a motor vehicle, the condition for generating the stop signal S
may be so established that stoppage of the electric motor 2 does not
impair safety of a driver of the motor vehicle even when operation of the
electric motor 2 is stopped. In that case, the stop condition decision
means 26 may be so arranged as to allow the stop signal S to be outputted
when the steering torque T applied by the driver assumes a value smaller
than a predetermined magnitude.
Furthermore, the stop condition decision means 26 may be so implemented as
to allow the stop signal S to be outputted when the electric motor 2 is
not positively driven or when the motor current IM is smaller than a
predetermined value.
Next, referring to FIGS. 2 and 3, description will be directed to operation
of the motor driving apparatus according to the first embodiment of the
invention shown in FIG. 1.
It is now assumed that the transistors Q2 and Q3 are constantly turned off
with the transistor Q4 being constantly turned on whereas the transistor
Q1 is driven under the PWM control (i.e., driven by using a pulse width
modulated signal whose duty ratio can be controlled), to thereby control
the motor current IM, as illustrated in FIG. 2.
In the state where the motor current IM is controlled in this manner, it is
again assumed that abnormality (1), (2) or (3) mentioned below take place.
On the basis of such assumption, description will be made in what manner
these abnormalities can be coped with according to the invention
incarnated in the first embodiment thereof.
At this juncture, it should be mentioned that the abnormality decision
range FR shown in FIG. 3 is set by the abnormality decision range setting
means 23. More specifically, the voltage applied to the motor 2, i.e.,
motor-applied voltage VM (=VR.times.D) is determined on the basis of the
duty ratio value D of the PWM signal P1 and the relay contact voltage VR,
whereon the abnormality decision range FR is set on the basis of a
relation between the motor-applied voltage VM and the detected current
value Id.
(1) Short-Circuit Fault of Transistor Q1
In this case, the transistor Q1 assumes constantly conducting state (i.e.,
on state) with the PWM signal P1 being rendered invalid or ineffective,
which results in increasing of the motor current IM. Consequently, the
relation between the motor-applied voltage VM (determined on the basis of
the relay contact voltage VR and the duty ratio value D of the PWM signal
P1) and the detected current value Id may fall within the abnormality
decision range FR.
Consequently, the abnormality decision means 24 decides abnormality of the
detected current value Id (and hence the motor driving current) to thereby
output an abnormality decision signal E.
In this conjunction, it should be noted that because the abnormality
decision is made by checking whether or not the relation mentioned above
falls within the abnormality decision range FR, the decision can be
conducted with high reliability regardless of variations of the duty ratio
value D and/or the detected current value Id.
In response to the abnormality decision signal E, the drive control signal
generating means 22 outputs to the driving circuit 9 the drive control
signal C4 for applying the PWM signal P4 to the transistor Q4 to thereby
drive both the transistors Q1 to Q4 concurrently under the PWM control.
In that case, it will however be appreciated that the transistor Q1
continues to remain in the conducting or on state because of the
short-circuit fault.
The state mentioned above is substantially equivalent to the state in which
the transistor Q1 is continuously turned on with the transistor Q4 being
driven under the PWM control.
As a result of this, the detected current value Id tends to assume a value
close to that of the normal characteristic (see FIG. 3), which in turn
means that operation of the motor driving apparatus can be continued for
the time being. Besides, because of restoration to the state approximating
the normal one, it can be identified or decided that the abnormality now
of concern is ascribable to the short-circuit fault of the transistor Q1.
Subsequently, the duty ratio value D is progressively diminished to thereby
reduce gradually the motor current IM. At the time point when the detected
current value Id of the motor current IM becomes substantially equal to
zero, the stop signal S is outputted to thereby stop or interrupt the
power supply to the H-bridge circuit 1 and hence to the electric motor 2.
Thus, when a short-circuit fault occurs in the transistor Q1, operation of
the electric motor 2 can be stopped smoothly while ensuring safety for a
system associated with the motor 2.
Thereafter, the H-bridge circuit 1 is repaired by exchanging the transistor
Q1 with a sound one to restore the normal state of the H-bridge circuit 1,
whereupon the drive control for the H-bridge circuit 1 can be performed in
the ordinary manner.
(2) Short-Circuit Fault of Transistor Q2
Because the short-circuit fault occurs in the transistor Q2 connected in
series to the transistor Q4 which is held constantly in the conducting or
on state, the motor current IM flowing to the electric motor 2 is
interrupted, whereas a large current I2 flows to the ground GND from the
power supply source 3, as can be seen in FIG. 2.
As a consequence, the detected current value Id increases within the
abnormality decision range FR as shown in FIG. 3, substantially in the
manner described previously, whereupon both the transistors Q1 and Q4 are
concurrently driven under the PWM control.
In that case, the duty ratio value of the PWM signals P1 and P4 applied
concurrently to the transistors Q1 and Q4, respectively, are significantly
decreased through feedback control performed by the control means 20 on
the basis of the detected current value Id, the current I flowing to the
H-bridge circuit 1 can be effectively suppressed.
In this conjunction, it should however be noted that because no large
current I2 can flow through the electric motor 2, the detected current
value Id continues to remain within the abnormality decision range FR.
Furthermore, on the basis of the status mentioned above, it can be
discriminatively identified that the short-circuit fault now of concern
does not take place in the transistor Q1.
(3) Short-Circuit Fault of Transistor Q3
Because the motor current IM can scarcely flow through the electric motor 2
when the short-circuit fault occurs in the transistor Q3 connected in
series to the transistor Q1 driven under the PWM control, a large current
I3 flows from the power supply source 3 to the ground GND, as can be seen
in FIG. 2.
Consequently, the detected current value Id increases up to a level which
falls within the abnormality decision range FR, as in the case of the
short-circuit fault of the transistor Q2, whereby the transistors Q1 and
Q4 are simultaneously put into PWM operation.
In this case, the PWM duty ratio value for the transistors Q1 and Q4 are
reduced under the effect of the feedback control of the detected current
value Id through the control means 20, involving effective reduction of
the detected current value Id.
In this case, because the large current I3 can not flow through the
electric motor 2, as in the case of the short-circuit fault of the
transistor Q2, the detected current value Id is prevented from going out
of the abnormality decision range FR. Thus, it can be identified that the
abnormal state now of concern is not due to the short-circuit fault of the
transistor Q1.
More specifically, in the case of the short-circuit fault of the transistor
Q1 mentioned above, the detected current value Id assumes a value
corresponding to the motor current IM. Thus, the motor current IM can be
controlled. However, in the case of the short-circuit fault of the
transistors Q1 or Q3, the detected current value Id does not represents
the motor current IM, rendering it impossible to control the motor current
IM.
Thus, when the detected current value Id does not go out of the abnormality
decision range FR notwithstanding of the PWM-driving of the transistor Q1
and Q4 upon decision of abnormality, as in the case of the short-circuit
faults (2) and (3) mentioned above, continuation of the power supply to
the H-bridge circuit 1 is of no use. Accordingly, the stop condition
decision means 26 outputs immediately the stop signal S with preference
being put on the protection of the power supply source 3, to thereby
deenergize the relay 4 for interrupting the power supply to the H-bridge
circuit 1.
In other words, only when the abnormality which permits the control of the
motor current IM takes place, as in the case of the short-circuit fault
(1) mentioned previously, the control of the electric motor 2 is continued
to reduce gradually the power supply to a level at which the motor
operation can be smoothly stopped, from the standpoint of safety. On the
other hand, when such abnormality takes place which makes it impossible to
control the motor current IM, as in the case of the short-circuit faults
(2) and (3) mentioned previously, the power supply is instantaneously
interrupted in order to protect the power supply source 3, the relay 4, a
fuse (not shown) and others by obviating load imposed to these elements.
Embodiment 2
In the case of the first embodiment of the motor driving apparatus
according | | |
