Electricity: motive power systems – Constant motor current – load and/or torque control
Reexamination Certificate
2000-03-10
2001-08-14
Ro, Bentsu (Department: 2834)
Electricity: motive power systems
Constant motor current, load and/or torque control
C318S626000, C318S599000, C123S361000, C123S376000
Reexamination Certificate
active
06274993
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application relates to and incorporates herein by reference Japanese Patent Applications No. 11-73659 filed on Mar. 18, 1999 and No. 11-321478 filed on Nov. 11, 1999.
BACKGROUND OF THE INVENTION
The present invention relates to a motor drive control. The present invention is suitable for application to an electronic throttle control apparatus for vehicles, specifically for driving a throttle valve disposed in an engine intake pipe by a direct current motor in accordance with a pedal stroke of an accelerator pedal and the like.
U.S. Pat. No. 5,712,550 (Japanese PCT Laid-open Publication JP-A-9-501817) teaches an electronic throttle control apparatus which drives a motor by an H-bridge drive circuit and executes a current limitation while ensuring responsiveness of a valve to be driven. This kind of throttle control apparatus is described with reference to
FIGS. 22-26
.
As shown in
FIG. 22
, the electronic throttle control apparatus is for opening and closing a throttle valve
100
by a motor
101
. An accelerator sensor
102
detects a pedal stroke of an accelerator
103
. A control circuit
104
controls a current supply to the motor
101
through a drive circuit
105
so that the throttle angle is controlled in accordance with the pedal stroke. The drive circuit
105
has four switching devices Q
1
-Q
4
in a H-bridge configuration and connected to the motor
101
. A drive logic circuit
106
receives drive command signals A
1
-A
4
from the control circuit (microcomputer and the like)
104
and supplies the current to the motor
101
. The current supplied to the motor is monitored by a current detection circuit
107
. As shown in
FIG. 24
, the drive logic circuit
106
has a comparator
108
, latches
109
and
110
, D flip-flop (DFF)
111
, and timers
112
,
113
and
114
. A high level value Vref(H) and a low level value Vref(L) are provided to be used selectively as a comparison reference for the comparator
108
.
As shown in
FIG. 25
, the motor is supplied with a current of 100% duty ratio to speed up the valve operation during the drive start period (Tst). When the valve is driven to approach a target valve position (Tbr), the motor is supplied with the current in the reverse direction to brake the valve operation. Further, the drive start and braking current is limited to a high current value Ilimit(H). The current limitation is effected by detecting the motor current IM by the current detection circuit
107
and temporarily interrupting the current supply each time the current IM reaches the current limitation value. With this current limitation, the output loss of the drive devices such as power MOSFETs and the like in the Hbridge can be reduced.
On the other hand, a certain limited current is continued to be supplied for a fixed time period even under a lock condition, so that the operation restores from a light lock condition where the valve cannot be controlled to the target position and stays at substantially the same position. This light lock condition may occur from freezing (icing) of water remaining on the valve. Specifically, as shown in
FIG. 26
, the limit of the current supplied to the motor is switched to a low value Ilimit(L) (<Ilimit(H)), when a motor lock occurs during a period of limiting a motor current IM to the current limitation value Ilimit(H) at the time of motor drive start time (Tst) or braking time (Tbr). The motor lock is detected when the current limitation continues for a predetermined time period (T
300
).
More specifically, the latch
109
in
FIG. 24
stores a history that the current reaches the current limitation value at every predetermined time period To. It is determined that the current limitation is being effected with the current limitation value Ilimit(H) by monitoring the latch
109
. The predetermined time period To for this determination is set longer than the switching operation period T
1
under the current limitation operation condition.
Thus, the lock condition is determined when the current continues to reach the current limitation value for the predetermined time period, and the current limitation operation is switched to Ilimit(L) thereby to reduce the motor current. As a result, the drive device can be sized smaller for a low cost.
During the current limitation mode by Ilimit(L), the current supply is continued when the motor current IM decreases within the predetermined time period and it is determined that the lock condition has been released. Further, the motor current supply is interrupted when the motor current IM does not decrease during the predetermined time period.
However, as shown in
FIG. 26
, if the switching time period T
2
between the drive start current supply to the braking current supply, it is erroneously determined that the current limitation operation is continuing due to the sum of a limitation period T
3
in the drive start current supply period Tst and a limitation period T
4
in the braking current supply period Tbr (T
3
+T
4
>T
300
). It is assumed that the history of whether the current has reached the current limitation value within the period longer than the switching period T
1
under the current limitation operation is stored to check the lock condition.
The count value which is the sum of the count value T
3
in the drive start current supply period Tst and the count value T
4
in the braking current supply period Tbr comes to exceed the predetermined value t
300
, if the current supply condition in which the current does not reach the current limitation value during the predetermined time period in the course from the drive start current supply to the braking current supply is not ensured. As a result, the lock condition is erroneously determined. This erroneous determination causes the current limitation by Ilimit(L) and reduces the output torque at the time of braking current supply. The valve position will undergoes an overshoot as shown in FIG.
26
.
According to the conventional apparatus shown in
FIG. 25
, the current supply is switched to the braking current supply (at timing t
200
) after the braking current supply at the current value less than the current limitation value is effected for more than the predetermined period To which is for checking the continuation of the current limitation, so that the above erroneous determination may be avoided. That is, the control circuit (microcomputer)
104
produces the drive command signal at the time of switching from the drive start current supply to the braking current supply to ensure the current supply condition of less than the current limitation value for a period (period Tre in
FIG. 25
) longer than the period To.
Specifically, the control circuit (microcomputer)
104
temporarily produces the command drive signal of 0% duty ratio (current circulation) in the period Tre between the drive start current supply and the braking current supply. The output terminal Q of the D flip-flop
111
in
FIG. 24
changes to a L-level and reset the count of the timer
113
once, thereby preventing the erroneous determination.
According to this method, however, the control response characteristics is lowered and the overshoot is caused due to insufficient braking force resulting from the delay of braking current supply after the drive start current supply. Further, the program of the control circuit (microcomputer)
104
which produces the drive command signal becomes complicated.
It is also considered for avoiding other erroneous determination to shorten the drive start current supply time period to slow down the motor operation speed at the time of drive start so that the motor operation speed may be sufficiently reduced even with the braking operation delayed as above. However, the program of the control circuit (microcomputer)
104
becomes very complicated, and the lowering of the original motor operation response characteristics causes lessening of control performance.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a motor drive contr
Itabashi Toru
Shirai Kazunari
Denso Corporation
Nixon & Vanderhye P.C.
Ro Bentsu
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