Electricity: motive power systems – Periodic – repetitious or successive operations control of...
Reexamination Certificate
2001-07-24
2003-01-21
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Periodic, repetitious or successive operations control of...
C318S375000, C318S434000
Reexamination Certificate
active
06509706
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wiper control apparatus using a semiconductor switching element such as a MOSFET.
2. Description of the Prior Art
One of previously known wiper control apparatus is disclosed in JP-A-9-193748. In this wiper control apparatus, as seen from
FIG. 13
, when a combination switch
17
is set at an intermittent mode (INT), a driving circuit
20
turns on an interruption switch MOSFET
19
to start a motor
15
so that a wiper reciprocates once. Then, the terminals P and Q of a wiper switch
16
are connected to each other. Then, the driving circuit
20
turns off the interruption switch
19
to interrupt the power supply to the motor
15
. When the terminals P and Q of the wiper switch
16
are connected, a battery-voltage side terminal K and a ground side terminal J are connected to each other through a contact terminal T
1
and braking resistor
18
so that the motor
15
is braked. Thus, the wiper stops quickly.
However, the wiper control apparatus presents the following problems.
(1) When the wiper motor
15
generates an abnormal current as if it is locked, a large current continues to flow through a MOSFET
19
or resistor
18
. Therefore, the resistor
18
or MOSFET
19
may be excessively heated and burned. In order to avoid the burning, a countermeasure for setting a large current rating for the resistor
18
and MOSFET
19
and providing a radiator is required. This upsizes the apparatus and makes it expensive.
(2) When the plus terminal and minus terminal of a battery
11
are erroneously connected inversely, a large current continues to flow through the parasitic diode of the MOSFET
19
and the resistor
18
. Therefore, the resistor
18
and the MOSFET may be burned.
(3) For some time after the MOSFET
19
turns on, since the terminals P and Q of the wiper switch
16
remain connected, a tunneling current will flow through a passage of wiper switch
16
→resistor
18
→MOSFET
19
from the battery
11
. This leads to unnecessary dissipation of heat and noise.
(4) Setting the intermittent time and the after-wash wiping operation time after the washer has been operated is carried out in an analog manner using the charging/discharging theory of a capacitor. This leads to a large change in these times.
In order to solve the problems (1) to (4) of the above wiper control apparatus, JP-A-2000-335374 proposed a wiper control apparatus which is compact, reliable and surely operable using a semiconductor switch and a digital controller.
In the proposed wiper control apparatus, also when the abnormality of the wiring downstream of the wiper motor
15
being short-circuited to a chassis (ground) occurs, a large current continues to flow through the resistor
18
so that the resistor may be excessively heated and burned.
Now it is assumed that short-circuiting of the wiring to the chassis (ground) has occurred between the ground side terminal J and the combination switch
17
. In this case, a current flows via the battery-voltage side terminal K of ground side terminal J of the wiper motor
15
and the short-circuited point so that the wiper motor
15
rotates.
On the other hand, the contact P of the wiper switch
16
is periodically changed between the contact points Q and R. While the contact P is being in contact with the contact Q (about 0.1 sec), a large current flows via the contact P, resistor
18
, combination switch
17
and short-circuited point. This also occurs between the combination switch
17
and the switch device and between the combination switch
17
and the resistor
18
.
At this time, since the current is limited by the resistor
18
having a resistance of 2-4 &OHgr; (if the voltage of the battery
11
is 12 V, the current is 5 V at the maximum), the fuse will not be broken. As a result, the current continues to flow through the resistor
18
so that it may be excessively heated and burned. In order to avoid the burning, the countermeasure of providing a radiator with the current rating of the resistor
18
being increased is required. This increases the scale of the apparatus and the production cost thereof.
FIG. 14
shows timing charts of signals in an ignition switch (IG) of a wiper control apparatus
12
, a motor AS switch
16
, wiper motor
16
and brake resistor
18
. As seen from
FIG. 14
, when abnormality of short-circuiting occurs downstream of the wiper motor
15
, a current continues to flow through the wiper motor
15
so that the contact point of the motor AS switch
16
is periodically changed between the high side and low side. Correspondingly, the current continues to flow through the braking resistor
18
.
SUMMARY OF THE INVENTION
An object of the present invention is to improve the wiper control apparatus proposed in JP-A-2000-335374 and to solve the problem when abnormality of the wiring downstream of a wiper motor being short-circuited occurs in the conventional wiper control apparatus to provide a wiper control apparatus which is compact, reliable and surely operable using a semiconductor switch and a digital controller.
In order to attain the above object, in accordance with the first aspect of the present invention, there is provided a wiper control apparatus comprising:
a combination switch for setting an operation mode of a wiper;
a wiper motor which is driven according to the operation mode set by the combination switch;
an autostop (AS) switch for producing a signal having a level varying according to a park position and other positions as the wiper motor rotates;
a first semiconductor switch element for on/off controlling energization of the wiper motor;
a second semiconductor switch element for turning on a closed circuit for braking the wiper motor by passing a reverse current through the wiper motor while energization for the wiper motor is off;
a controller for supplying a first ON/OFF control signal to the first semiconductor switch element and a second ON/OFF control signal to the second semiconductor switch element;
current detecting means for detecting a current flowing through the second semiconductor switch; and
current limiting means for limiting a current flowing through the second semiconductor switch element if the current detected by the current detecting means exceeds a prescribed threshold value.
In this configuration, since an abnormal current is limited when abnormality of short-circuiting occurs downstream of the wiper motor, the safety of the wiper control apparatus can be improved. Since heat generation can be reduced when the apparatus is in a normal operation and abnormality of short-circuiting occurs, the wiper control apparatus can be downsized.
Preferably, the current limiting means interrupts the second ON/OFF control signal the current limiting means interrupts the second ON/OFF control signal when the number of limiting the current reaches a prescribed number of times.
In this configuration, when the number of limiting the current reaches a prescribed number of times, the closed circuit for braking can be surely interrupted so that the safety of the wiper control apparatus can be improved.
Preferably, the first semiconductor switch element is an N-channel MOSFET, and the second semiconductor switch element is a P-channel MOSFET.
In this configuration, the wiper control apparatus can be downsized and manufactured at low cost.
Preferably, a Zener diode is connected to the semiconductor switch element.
In this configuration, inverted electromotive force when the first semiconductor switch is excessively heated and cut off and interrupted is dissipated. The first semiconductor switch can be protected when a battery is erroneously connected in a reverse direction. The second semiconductor switch element can be surely turned off in a manner of shifting the electric potential of its gate electrode.
Preferably, the first semiconductor switch element is located downstream or upstream of the wiper motor.
Where the first semiconductor switch element is arranged upstream, it is protected from malfunction such as short-
Harris Connie
Nappi Robert E.
Yazaki -Corporation
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