U.S. patent application number 12/574855 was filed with the patent office on 2010-04-08 for electric power source circuit and abnormality diagnosis system.
This patent application is currently assigned to DENSO CORPORATION. Invention is credited to Kazuhiro Ichikawa, Yutaka Oohashi.
Application Number | 20100085060 12/574855 |
Document ID | / |
Family ID | 42075289 |
Filed Date | 2010-04-08 |
United States Patent
Application |
20100085060 |
Kind Code |
A1 |
Ichikawa; Kazuhiro ; et
al. |
April 8, 2010 |
ELECTRIC POWER SOURCE CIRCUIT AND ABNORMALITY DIAGNOSIS SYSTEM
Abstract
In a power source circuit for supplying electric power of a
battery, a capacitor is charged by the battery when an ignition
switch and a power supply relay are closed. The power supply relay
is opened after the ignition switch is closed. The charge voltage
of the capacitor falls, if the power supply relay has no
fixed-closure abnormality. The charge voltage of the capacitor does
not fall, if the power supply relay has the fixed-closure
abnormality. A microcomputer diagnoses the power supply relay with
respect to its fixed-closure abnormality based on the charge
voltage of the capacitor when the ignition switch and the power
supply relay are operated to open.
Inventors: |
Ichikawa; Kazuhiro;
(Kariya-city, JP) ; Oohashi; Yutaka; (Handa-city,
JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
DENSO CORPORATION
Kariya-city
JP
|
Family ID: |
42075289 |
Appl. No.: |
12/574855 |
Filed: |
October 7, 2009 |
Current U.S.
Class: |
324/503 |
Current CPC
Class: |
G01R 31/3277 20130101;
H01H 47/00 20130101; G01R 31/40 20130101; G01R 31/327 20130101 |
Class at
Publication: |
324/503 |
International
Class: |
G01R 31/02 20060101
G01R031/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 8, 2008 |
JP |
2008-261333 |
Nov 7, 2008 |
JP |
2008-286696 |
Claims
1. An abnormality diagnosis system comprising: a power supply relay
provided to open and close a current path formed between an
electric power source and a power conversion circuit; a capacitor
connected between a reference potential and the current path formed
between the power conversion circuit and the power supply relay; a
pre-charge path formed between the power source and the capacitor
to pre-charge the capacitor by the power source, the pre-charge
path bypassing the power supply relay; a switch provided to open
and close the pre-charge path; and a diagnosis circuit for
diagnosing the power supply relay with respect to fixed-closure of
the power supply relay based on a drop of a charge voltage of the
capacitor produced after both the switch and the power supply relay
are operated to open, the fixed-closure abnormality indicating that
the power supply relay maintains a closed state even if operated to
open.
2. The abnormality diagnosis system according to claim 1, wherein:
the diagnosis circuit is connected to the power source through the
switch and to the capacitor; the diagnosis circuit includes a
memory, which stores data indicating that the diagnosis circuit is
operable after a predetermined time from time both the switch and
the power supply relay are operated to open; the diagnosis circuit
is configured to refer to the memory in diagnosing the power supply
relay when the switch is operated to close.
3. The abnormality diagnosis system according to claim 1, further
comprising: a motor relay provided between the power conversion
circuit and a motor to open and close a current path from the power
conversion circuit to the motor, wherein the diagnosis circuit is
configured to diagnose the power supply relay with respect to
fixed-open abnormality based on the charge voltage of the capacitor
produced when all of the switch, the power supply relay and the
motor relay are operated to close, the fixed-open abnormality
indicating that the power relay maintains an open state even if
operated to close.
4. The abnormality diagnosis system according to claim 3, wherein:
the diagnosis circuit is configured to diagnose the power supply
relay based on a voltage of the power source in addition to the
charge voltage of the capacitor.
5. The abnormality diagnosis system according to claim 3, further
comprising: a switching element provided to open and close a
current path formed of the power conversion circuit and the motor
in parallel to the capacitor, wherein the diagnosis circuit is
configured to diagnose the power supply relay with respect to the
fixed-open abnormality based on the charge voltage of the capacitor
produced when the switching element is operated to open and close
the current path.
7. The abnormality diagnosis system according to claim 1, wherein:
the diagnosis circuit is configured to diagnose the pre-charge path
based on the charge voltage of the capacitor produced when the
switch is in a closed state and the power supply relay is in an
open state.
7. The abnormality diagnosis system according to claim 1, wherein:
the pre-charge path includes a pre-charge resistor connected
between the switch and the capacitor for pre-charging the capacitor
therethrough.
8. The abnormality diagnosis system according to claim 1, further
comprising: a discharge resistor connected to the capacitor in
parallel for discharging the capacitor therethrough.
9. An abnormality diagnosis system comprising: a power supply relay
provided to open and close a current path formed between an
electric power source and a power conversion circuit; a capacitor
connected between a reference potential and the current path formed
between the power conversion circuit and the power supply relay; a
pre-charge path formed between the power source and the capacitor
to pre-charge the capacitor by the power source, the pre-charge
path bypassing the power supply relay; a switch provided to open
and close the pre-charge path; a motor relay provided between the
power conversion circuit and a motor to open and close a current
path from the power conversion circuit to the motor; and a
diagnosis circuit configured to diagnose the power supply relay
with respect to fixed-open abnormality based on a charge voltage of
the capacitor produced when all of the switch, the power supply
relay and the motor relay are operated to close, the fixed-open
abnormality indicating that the power relay maintains an open state
even if operated to close.
10. The abnormality diagnosis system according to claim 9, wherein:
the diagnosis circuit is configured to diagnose the power supply
relay based on a voltage of the power source in addition to the
charge voltage of the capacitor.
11. The abnormality diagnosis system according to claim 9, further
comprising: a switching element provided to open and close a
current path formed of the power conversion circuit and the motor
in parallel to the capacitor, wherein the diagnosis circuit is
configured to diagnose the power supply relay with respect to the
fixed-open abnormality based on the charge voltage of the capacitor
produced when the switching element is operated to open and close
the current path.
12. The abnormality diagnosis system according to claim 9, wherein:
the diagnosis circuit is configured to diagnose the pre-charge path
based on the charge voltage of the capacitor produced when the
switch is in a closed state and the power supply relay is in the
open state.
13. The abnormality diagnosis system according to claim 9, wherein:
the pre-charge path includes a pre-charge resistor connected
between the switch and the capacitor for pre-charging the capacitor
therethrough.
14. The abnormality diagnosis system according to claim 9, further
comprising: a discharge resistor connected to the capacitor in
parallel for discharging the capacitor therethrough.
15. A power source circuit for a power conversion circuit
comprising: an electric power source; a power supply relay provided
to connect and disconnect the power source and the power conversion
circuit; a capacitor connected between a reference potential and a
current path formed between the power conversion circuit and the
power supply relay; a switch provided to connect and disconnect the
power source and the capacitor, the switch bypassing the power
supply relay; and a Zener diode having a cathode connected to the
switch and an anode connected to the capacitor.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This patent application is based on and incorporates herein
by reference Japanese Patent Applications No. 2008-261333 filed on
Oct. 8, 2008 and No. 2008-286696 filed on Nov. 7, 2008.
FIELD OF THE INVENTION
[0002] The present invention relates to an electric power source
circuit and an abnormality diagnosis system for the electric power
source circuit. The electric power source circuit includes an power
supply relay for opening and closing an electric power conversion
circuit and an power supply part, a capacitor connected between an
electric current path, which is formed between the power conversion
circuit and the power supply relay, and a reference potential
source, a pre-charge path bypassing the power supply relay for
pre-charging the capacitor, and an on/off switch for connecting and
disconnecting the pre-charge path and the power supply part.
BACKGROUND OF THE INVENTION
[0003] In a conventional electric power source circuit, an power
supply relay is provided in an electric current path between an
electric power conversion circuit and a battery to turn on and off
the electric current path. In a case that the length of the current
path between the power conversion circuit and the battery is long,
a capacitor is conventionally provided near the power conversion
circuit so that the capacitor is pre-charged by the battery to
stably supply the power conversion circuit with electric power.
[0004] If the power supply relay is used, it is desired to diagnose
whether the power supply relay normally operates. The power supply
relay is diagnosed with respect to its abnormality (malfunction) of
fixed-closure, in which the power supply relay is persistently
closed due to fixation of a movable contact. This fixed-closure can
be determined by detecting a charge voltage of the capacitor in
response to a trigger that is caused when an on/off switch part
(ignition switch) for connecting and disconnecting the battery and
a part operating the power conversion circuit is closed. At the
time immediately after the ignition switch is turned on, the
capacitor is supposed to have not been charged yet because the
power supply relay has been turned off. If the capacitor has been
charged, the power supply relay is diagnosed as being in the
abnormal condition of fixed-closure.
[0005] Fusion abnormality is considered as one of the causes of the
fixed-closure of the power supply relay. This abnormality arises,
when a large electric current flows from the battery to the
capacitor at the time of turning on the power supply relay to the
closed state and melts the movable contact to a fixed contact
during closure of the power supply relay. It is therefore desired
to avoid the fusion abnormality. A power supply relay, which can
supply a large electric current, may be used to avoid the fusion
abnormality. This power supply relay however is large in size and
costly.
[0006] JP 11-245829 proposes to connect a capacitor connected
between a H-bridge circuit of an electric motor and a power supply
relay to a battery through an on/off switch part (ignition switch)
and a pre-charge resistor. When the ignition switch is turned on,
the charge of the battery is supplied to charge the capacitor
through the ignition switch and the resistor. As a result, even
when the power supply relay is turned on subsequently, a large
current is restricted from flowing from the battery to the
capacitor through the power supply relay.
[0007] The fixed-closure of the power supply relay may arise for
causes other than the large current, which flows to the capacitor.
It is therefore also desired in the proposed power source circuit
to diagnose whether the power supply relay is in the fixed-closure
state. In the case of an arrangement, in which the capacitor is
charged by turning on the ignition switch, the capacitor may not
produce a large voltage difference, by which the fixed-closure of
the power supply relay is detectable, between the capacitor
voltages at the time of turning on the ignition switch. It is
therefore difficult to diagnose the power supply relay with respect
to the fixed-closure abnormality.
[0008] It is also possibly difficult to diagnose fixed-open
abnormality, in which the power supply relay is persistently held
in the fixed-open state, because the capacitor is charged by
turning on the ignition switch.
SUMMARY OF THE INVENTION
[0009] It is therefore an object of the present invention to
improve an electric power source circuit and an abnormality
diagnosis system, so that an abnormality of an power supply relay
may be diagnosed even in an arrangement that the power source
circuit has a pre-charge path for pre-charging a capacitor
connected between a current path of an electric power conversion
circuit and the power supply relay and the ground.
[0010] According to the present invention, an abnormality diagnosis
system is provided for a power source circuit, which includes an
electric power source, a power supply relay, a capacitor, a
pre-charge path and a switch. The power supply relay is provided to
open and close a current path formed between the electric power
source and a power conversion circuit. The capacitor is connected
between a reference potential and the current path formed between
the power conversion circuit and the power supply relay. The
pre-charge path is formed between the power source and the
capacitor to pre-charge the capacitor by the power source. The
pre-charge path bypasses the power supply relay. The switch is
provided to open and close the pre-charge path.
[0011] In one aspect, a diagnosis circuit is provided for
diagnosing the power supply relay with respect to fixed-closure of
the power supply relay based on a drop of a charge voltage of the
capacitor produced after both the switch and the power supply relay
are operated to open. The fixed-closure abnormality indicates that
the power supply relay maintains a closed state even if operated to
open.
[0012] In another aspect, a motor relay is provided between the
power conversion circuit and a motor to open and close a current
path from the power conversion circuit to the motor. A diagnosis
circuit is provided to diagnose the power supply relay with respect
to fixed-open abnormality based on a charge voltage of the
capacitor produced when all of the switch, the power supply relay
and the motor relay are operated to close, the fixed-open
abnormality indicating that the power relay maintains an open state
even if operated to close.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The above and other objects, features and advantages of the
present invention will become more apparent from the following
detailed description made with reference to the accompanying
drawings. In the drawings:
[0014] FIG. 1 is a circuit diagram showing an abnormality diagnosis
system according to a first embodiment of the present
invention;
[0015] FIG. 2 is a flowchart showing processing of diagnosing
fixed-closure abnormality of a power supply relay in the first
embodiment;
[0016] FIG. 3 is a time chart showing an example of the processing
of diagnosing fixed-closure abnormality in the first
embodiment;
[0017] FIGS. 4A and 4B are time charts showing a principle of
processing of diagnosing fixed-open abnormality of a power supply
relay in a second embodiment of the present invention;
[0018] FIG. 5 is a flowchart showing the processing of diagnosing
the fixed-open abnormality of the power supply relay in the second
embodiment;
[0019] FIG. 6 is a flowchart showing processing of diagnosing
fixed-open abnormality of a power supply relay in a third
embodiment of the present invention;
[0020] FIG. 7 is a circuit diagram showing an abnormality diagnosis
system according a fourth embodiment of the present invention;
and
[0021] FIG. 8 is a flowchart showing processing of diagnosing
fixed-open abnormality of a power supply relay in a fifth
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
First Embodiment
[0022] According to a first embodiment, an abnormality diagnosis
system for an electric power source circuit of the present
invention is applied to an abnormality diagnosis system for a power
source circuit of an electric power steering apparatus mounted on a
vehicle.
[0023] Referring to FIG. 1, an electric motor 10 is a DC motor with
brushes. The motor 10 is an actuator provided in a steering
apparatus, which power-assists steering operation of a driver. The
motor 10 is supplied with electric power of a battery 12 through a
H-bridge circuit 20.
[0024] The H-bridge circuit 20 is an electric power conversion
circuit for supplying the electric power of the battery 12 to the
motor 10. Specifically, the H-bridge circuit 20 has
parallel-connected series arms. In one series arm, switching
elements 21 and 22 are connected in series. In the other series
arm, switching elements 23 and 24 are connected in series. The
switching elements 21 to 24 may be transistors. A pair of terminals
of the motor 10 is connected to junctions of two switching elements
of each arm, respectively. Resistors 25 and 26 are connected to the
switching elements 21 and 24 for fail-safe operation,
respectively.
[0025] A microcomputer 30 is provided to control a drive amount
(torque, etc.) of the motor 10 as a subject of control by
controlling the H-bridge circuit 20. The microcomputer 30 includes
a CPU, a ROM, a RAM, etc. in the known manner. The microcomputer 30
further includes a non-volatile memory 32. The memory 32 may be an
EEPROM, etc., which maintains its storage even when the power
supply is interrupted.
[0026] As an electric power source circuit for supplying the
electric power of the battery 12 to the motor 10 through the
H-bridge circuit 20, a power supply relay 40 is connected to
connect and disconnect the battery 12 and the H-bridge circuit 20,
that is, to open and close a current path between the battery 12
and the H-bridge circuit 20. The power supply relay 40 is an analog
normally-open type relay, which is an electromagnetic relay such as
a movable core-type relay. The power supply relay 40 closes a
current path when excited to turn on. The power source circuit
further includes a capacitor 42 and a discharge resistor 44, which
connects a current path between the power supply relay 40 and the
H-bridge circuit 20 and the reference potential source (for
example, ground). The capacitor 42 is connected at a position
closest to the H-bridge circuit 20 so that the length of a wire
(current path) between the capacitor 42 and the H-bridge circuit 20
may be shortened to a minimum. The capacitor 42 has a large
capacitance so that the electric power is supplied to the H-bridge
circuit 20 stably. The discharge resistor 44 is provided to
discharge the capacitor 42.
[0027] The power source circuit further includes an electric motor
relay (motor relay) 46, which connects and disconnects the
terminals of the motor 10 and the H-bridge circuit 20. The motor
relay 46 also may be an analog normally-open type relay, which is
an electromagnetic relay such as a movable core-type relay. The
motor relay 46 closes a current path when excited to turn on.
[0028] The power source circuit further includes an on/off
activation switch (ignition switch 50) operable for activating a
vehicle-mounted control system by a user, and a diode 52 for
allowing supply of the electric power of the battery 12 to the
microcomputer 30 through the ignition switch 50. A diode 54 is
connected between a junction of the power supply relay 40 and the
H-bridge circuit 20 and a junction of the cathode of the diode 52
and the microcomputer 30. The diode is forward-biased in a
direction from the junction between the junction of the power
supply relay 40 to the microcomputer 30. A resistor 56 is connected
in parallel to the diode 54 between the junction of the power
supply relay 40 and the H-bridge circuit 20 and the junction
between the cathode of the diode 52 and the microcomputer 30.
[0029] The microcomputer 30 is activated when the electric power of
the battery 12 is supplied through at least one of the diode 52 and
the diode 54. The microcomputer 30 controls the drive amount of the
motor 10. The microcomputer 30 drives the motor 10 in the forward
rotation direction or in the reverse rotation direction by
selectively turning on and off the switching elements 21 and 24
periodically or turning on and off the switching elements 22 and 23
periodically. The amount of current supplied to the motor 10 is
controlled based on a duty ratio of an on-time of the switching
elements relative to one cycle time (on-and-off time) of the same
in the periodic on-off control.
[0030] The microcomputer 30 executes processing to turn on (close)
the power supply relay 40 and the motor relay 46 in advance of
controlling the drive amount of the motor 10.
[0031] One terminal of an excitation coil of the power relay 40 is
connected to one terminal (cathode of the diode 52) of the ignition
switch 50, which is not connected to the positive-side of the
battery 12. The other terminal of the excitation coil is grounded
through the switching element 60. When the microcomputer 30 turns
on the switching element 60 under a condition that the ignition
switch 50 is in the closed state, a current flows from the battery
12 to the ground through the excitation coil of the power supply
relay 40 from the battery 12. The excitation coil of the power
supply relay 40 responsively generates magnetic force thereby to
move a movable contact of the power supply relay 40. As a result,
an input terminal, which is connected to the battery 12, and an
output terminal, which is connected the H-bridge circuit 20, are
connected (turned on to closed state).
[0032] The motor relay 46 has an excitation coil, one terminal of
which is connected to the capacitor 42 and the H-bridge circuit 20
and the other terminal of which is grounded through a switching
element 62. When the microcomputer 30 turns on the switching
element 62 to the closed state, a current flows to the ground from
the battery 12 through the excitation coil of the motor relay 46.
The excitation coil of the motor relay 46 responsively generates
magnetic force thereby to move a movable contact of the motor relay
46. As a result, an input terminal, which is connected to the
H-bridge circuit 20, and an output terminal, which is connected to
the motor 10, are connected (turned on to closed state).
[0033] When the ignition switch 50 is turned on, the microcomputer
turns on the switching element 60 to turn on the power supply relay
40 to the closed state, and then turns on the switching element 62
to turn on the motor relay 46 to the closed state. With the relays
40 and 46 being thus set to the closed state, the drive amount of
the motor 10 is controlled by controlling the H-bridge circuit 20
so that the motor 10 assists the steering operation of a
driver.
[0034] When the ignition switch 60 is turned on, the capacitor 42
is pre-charged by the current supplied from the battery 12 through
the pre-charge resistor 56, before the power supply relay 40 is
turned on to the closed state by the microcomputer 40. As a result,
the capacitor 42 is charged to the charge voltage, which
corresponds to the voltage of the battery 12, before a time point
the power supply relay 40 is turned on to close. Specifically, the
charge voltage of the capacitor 42 is a voltage VPC, which
corresponds to a resistance division ratio R44/(R44+R56) of the
voltage VIG of the battery 12 (specifically less a voltage V52 of
the diode 52). The resistance R56 of the pre-charge resistor 56 is
set to be far smaller than the resistance R44 of the discharge
resistor 44. Therefore, at the time point the power supply relay 40
is turned on, the charging of the capacitor 42 to be close to the
voltage of the battery 12 is completed readily. The current, which
flows from the battery 12 to the capacitor 42 at the time of
turning on the power supply relay 40, is reduced to be sufficiently
small.
[0035] Since the capacitor 42 is pre-charged by the turn-on of the
ignition switch 50, it is difficult to diagnose whether the power
supply relay 40 has fixed-closure abnormality with respect to some
charge voltages of the capacitor 42 produced before the power
supply relay 40 is turned on. Therefore, the fixed-closure
abnormality of the power supply relay 40 is detected by monitoring
or checking whether the charge voltage of the capacitor 42 drops by
turning off the power supply relay 40 to the open state after the
ignition switch 50 is turned off to the open state by a driver.
[0036] This fixed-closure malfunction diagnosis processing is
executed by the microcomputer 30 as shown in FIG. 2 in response to
the turn-on of the ignition switch 50 as a trigger. The
microcomputer 30 thus operates as a diagnosis circuit as well as a
motor control circuit.
[0037] First at step S10, a keyword stored in a predetermined
address of the non-volatile memory 32 is read out. The keyword is
provided to indicate a result of diagnosis (presence or absence) of
the fixed-closure abnormality. The keyword is initially set to "A,"
which is predetermined to indicate "normal (no abnormality)." At
step S12, it is checked whether the keyword is "A" indicating no
abnormality. If the keyword is "A," the switching elements 60 and
62 are turned on at step S14 to thereby turn on the power supply
relay 40 and the motor relay 46 to the closed state. The drive
amount of the motor 10 is also controlled so that the steering
operation by a driver is assisted by the motor 10.
[0038] This step S14 is repeated until it is determined at step S16
that the ignition switch 50 is turned off to the open state. After
the ignition switch 50 is turned off (S16: YES), the keyword "A" is
written in the predetermined address of the memory 32. At step S20,
the power supply relay 40 is turned off to the open state.
Specifically, by turning off the switching element 60, the current
flowing in the excitation coil of the power supply relay 40 is
interrupted. Since the magnetic flux generated by the current
flowing in the excitation coil is reduce to zero, the power supply
relay 40 is turned off to the open state, in which the movable
contact is disconnected from the fixed contact in the power relay
40.
[0039] After the power supply relay 40 is turned off to the open
state, a charge path from the battery 12 to the capacitor 42 is
interrupted, the charge voltage of the capacitor 42 decreases by
discharging through the discharge resistor 44 and power consumption
of the microcomputer 30. It is noted that the microcomputer 30 is
maintained operative with the charged power of the capacitor 42
even after the ignition switch 50 and the power supply relay 40 are
turned off. The capacitor 42 is discharged to a lowest limit
voltage (for example, 5V) required for the microcomputer 30 to
operate in about a certain time after the power supply relay 40 is
turned off. At step S22, it is checked whether a predetermined time
T1 has elapsed after the power supply relay 40 is turned off. This
time T1 is set to correspond to a possible minimum of the certain
time or more to check whether the charge voltage of the capacitor
42 drops in the predetermined time T1. If the time T1 has elapsed
(S22: YES), the keyword is changed at 524 to "B" thereby indicating
that the power supply relay 40 has fixed-closure abnormality, in
which the movable contact is continuously connected to and not
disconnected from the fixed contact in the power supply relay 40.
In the case that the power supply relay 40 has no fixed-closure
abnormality, the microcomputer 30 becomes inoperative before step
S24 is executed, that is, before the elapse of time T1, and the
keyword is not changed to "B."
[0040] If it is determined that the keyword is not "A" (S12: NO),
it indicates that step S24 has been executed and the keyword has
changed to "B," which indicates that the power supply relay 40 has
the fixed-closure abnormality. At step S26, the fixed-closure
abnormality is indicated to an outside. For example, this
abnormality is indicated by turning on a malfunction indicator
light (MIL) 34. In addition, the assist control is prohibited. As a
result, the motor relay 46 is not turned on to the closed state and
hence the motor 10 is not driven because of no supply of power from
the battery 46.
[0041] After step S26, it is checked at step S28 whether the
ignition switch 50 is turned off by a driver. If the ignition
switch 50 is turned off (S28: YES), the keyword "A" is written in
the non-volatile memory 32 in place of the keyword "B" at step S30.
Steps S22 and S24 follow step S30.
[0042] After step S24, the sequence of processing is ended.
[0043] The operation of diagnosing the fixed-closure is shown in
FIG. 3. In FIG. 3, (a) indicates a change of the ignition switch
50, (b) indicates a change of the output voltage VIG corresponding
to the battery voltage (anode-side voltage of the diode 52) of the
ignition switch, (c) indicates a change of the charge voltage VPC
of the capacitor 42, (d) indicates change of the keyword, (e)
indicates a change of the power supply relay 40, (f) indicates a
change of a check result of the fixed-closure abnormality, and (g)
indicates a change of the malfunction indicator light 34.
[0044] As shown in FIG. 3, when the ignition switch 50 is turned on
by a user at time t1, the output voltage VIG of the ignition switch
50 and the capacitor 42 starts to be charged to provide the voltage
VPC. Then, when the keyword is referred to and confirmed to be "A,"
the microcomputer 30 turns on the switching element 60 and
maintains the turn-on of the power supply relay 40 at time t2. As a
result, the current path between the battery 12 and the capacitor
42 is closed. Even after the ignition switch 50 is turned off at
time t3, the microcomputer 30 maintains the switching element 60 in
the turned-on condition to maintain the power supply relay 40 in
the turned-on condition, so that the capacitor 42 maintains its
charge voltage VPC. The microcomputer maintains this condition
until it completes the required various post-processing, for
example, writing the keyword "A." At time t4, at which the
post-processing is completed, the microcomputer 30 turns off the
switching element 60. As long as the power supply relay 40 has no
abnormality, it is turned off to open the current path between the
battery and the capacitor 42.
[0045] However, if the power supply relay 40 has the fixed-closure
abnormality, the power supply relay 40 cannot turn off to open the
current path. As a result, the capacitor 42 is persistently
connected to the battery 12. The charge voltage VPC therefore does
not drop after time t4. If this condition continues to be more than
the predetermined time T1, the microcomputer 30 changes the keyword
and writes "B" in place of "A" at time t5.
[0046] When the ignition switch 50 is turned on again at time t6,
the microcomputer 30 refers to the keyword stored in the
non-volatile memory 32. Since the stored keyword is "B," the
microcomputer 30 determines that the power supply relay 40 has the
fixed-closure abnormality and turns on the malfunction indicator
light 54 at time t7. When the ignition switch 50 is turned off at
time t8 again, the microcomputer 30 changes the keyword to "A." If
the power supply relay 40 does not have the fixed-closure
abnormality any more, the capacitor 42 is allowed to discharge
through the resistor 44. The charge voltage VPC falls and becomes
less than the predetermined threshold level Vth. As a result, when
the ignition switch 50 is turned on next time, the power supply
relay 40 is determined to be normal and the assist control is
performed.
[0047] The first embodiment provides the following advantages.
[0048] (1) The power supply relay 40 is diagnosed whether it has
the fixed-closure abnormality, based on the charge voltage of the
capacitor 42 after both of the ignition switch 50 and the power
supply relay 50 are turned off to the open state. Thus, the
fixed-closure abnormality can be detected.
[0049] (2) The operability of the microcomputer 30 is stored as
data of the keyword, if the microcomputer 30 remains operable after
the elapse of the predetermined time T1 from the turn-off of both
of the ignition switch 50 and the power supply relay 40 to the open
state. By referring to the value of the keyword when the ignition
switch 50 is turned on, the power supply relay 40 is diagnosed
whether it has the fixed-closure abnormality. If the fixed-closure
abnormality of the power supply relay 40 is confirmed when the
ignition switch 50 is turned on, a driver can be notified of the
abnormality appropriately.
[0050] (3) The capacitor 42 is charged by the battery 12 through
the pre-charge resistor 56, the resistance of which is smaller than
that of the discharge resistor 44. The capacitor 42 can therefore
be charged to increase its charge voltage closely to the voltage of
the battery 12 before the power supply relay 40 is turned on to
connect the capacitor 42 and the battery 12 therethrough.
[0051] (4) The discharge resistor 44 is connected in parallel to
the capacitor 42. The speed of drop of the charge voltage of the
capacitor 42 caused when the ignition switch 50 and the power
supply relay 40 are turned off can be increased. As a result, the
predetermined time T1 can be set to be short. Even if the ignition
switch 50 is turned on again in a short time, the fixed-closure of
the power supply relay 40 can be diagnosed readily.
Second Embodiment
[0052] A second embodiment is described next with respect to parts
different from the first embodiment.
[0053] In the second embodiment, the power supply relay 40 is
further diagnosed with respect to its fixed-open abnormality, in
which the movable contact cannot be moved to close the input
terminal and the output terminal in the power supply relay 40.
[0054] The principle of diagnosing the power supply relay 40 with
respect to the fixed-open abnormality is shown in FIGS. 4A and 4B,
in which the power supply relay 40 is assumed to be normal and
abnormal, respectively. In FIGS. 4A and 4B, (a1) and (a2) indicate
changes of the ignition switch 50, (b1) and (b2) indicate changes
of the power supply relay 40, (c1) and (c2) indicate changes of the
motor relay 46, (d1) and (d2) indicate changes of the output
voltage VIG of the ignition switch 50, and (e1) and (e2) indicate
changes of the charge voltage VPC of the capacitor 42.
[0055] If the power supply relay 40 is normal, as shown in FIG. 4A,
when the ignition switch 50 is turned on, the output voltage VIG of
the ignition switch 50 rises and the capacitor 42 starts to be
charged. The capacitor 42 is charged to the voltage VPC, which is
close to the output voltage VIG. This charge voltage VPC
corresponds to a division of the voltage VIG of the battery 12 by
the pre-charge resistor 56 and the discharge register 44. When the
power supply relay 40 is turned on to the closed state by turning
on the switching element 60, the charge voltage VPC of the
capacitor 42 further rises to the output voltage of the power
supply relay 40, which is substantially the same as the battery
voltage. Even if the motor relay 46 is turned on to the closed
state by turning on the switching element 62, the charge voltage
VPC of the capacitor 42 does not change.
[0056] If the power supply relay 40 has the fixed-open abnormality,
the power supply relay 40 is not turned on to the closed state
because of its abnormality even when the switching element 60 is
turned on. That is, the current path between the capacitor 42 and
the battery 12 through the power supply relay 40 remains
disconnected. The charge voltage VPC of the capacitor 42 remains to
be slightly lower than the ignition output voltage VIG. Since this
voltage difference is small, it is not easy to detect the
fixed-open abnormality of the power supply relay 40 accurately
based on this small difference. If the motor relay 46 is turned on
to the closed state by turning on the switching element 62 under
this condition, the charge voltage VPC of the capacitor 42 falls.
This is because the resistance of the discharge path of the
capacitor 42 is decreased. Specifically, the capacitor 42 is
connected in parallel to not only the discharge resistor 44 but
also the excitation coil of the motor relay 46 as well as the
resistors 25, 26 and the motor 10. Thus the resistance of the
discharge path of the capacitor 42 is reduced to be less than the
resistance of the discharge resistor 44 itself. The ratio of
division of the voltage VIG by the pre-charge resistor 56 and the
discharge path parallel to the capacitor 42 becomes smaller than
that provided by the pre-charge resistor 56 and the discharge
resistor 44. Thus, the charge voltage VPC of the capacitor 42 is
decreased considerably from the ignition output voltage VIG. Based
on this large charge voltage drop, the fixed-open abnormality is
detected.
[0057] The fixed-open abnormality diagnosis processing is executed
in the second embodiment as shown in FIG. 5. This processing is
executed by the microcomputer 30 in response to the turn-on of the
ignition switch 50 as a trigger.
[0058] First, at step S40, the fixed-closure abnormality of the
power supply relay 40 is diagnosed by referring to the keyword
stored in the non-volatile memory 32. At step S42, it is checked
whether the keyword is "B," indicating the fixed-closure
abnormality. If the keyword is "B" (S42: YES), the abnormality is
indicated by the malfunction indicator light 34 and the assist
control is prohibited.
[0059] If the keyword is not "B" (S42: NO), the motor relay 46 is
turned on to the closed state by turning on the switching element
62. It is checked at step S48 whether a predetermined time T2 has
elapsed after the turn-on of the motor relay 46. The predetermined
time T2 is set to a shortest possible time, in which the charge
voltage VPC of the capacitor 42 is supposed to fall by the amount
a. After an elapse of the predetermined time T2 (S48: YES), it is
checked at step S50 whether the charge voltage VPC of the capacitor
42 is less than a predetermined threshold voltage, which is less
than the ignition output voltage VIG by the amount a. This step is
for diagnosing the power supply relay 40 with respect to the
fixed-open abnormality. The amount of drop a of the capacitor
voltage is determined in accordance with the voltage VIG of the
battery 12, the resistance of the pre-charge resistor 56 and the
resistance of the discharge path, which includes the discharge
resistor 44 and is connected in parallel to the capacitor 42. If
the charge voltage VPC is less than the predetermined threshold
voltage (550: YES), it is determined at step S52 that the power
supply relay 40 has the fixed-open abnormality. At step S54, the
fixed-open abnormality is indicated by the malfunction indicator
light 34 and the assist control is prohibited.
[0060] This processing is terminated when steps S44 or S54 has been
completed or when it is determined at step S50 that the charge
voltage VPC remain higher than the predetermined threshold
voltage.
[0061] The second embodiment provides the following advantages in
addition to the foregoing advantages of the first embodiment.
[0062] (5) The power supply relay 40 is diagnosed with respect to
the fixed-open abnormality based on the charge voltage VPC of the
capacitor 42 present when the ignition switch 50, the power supply
relay 40 and the motor relay 46 are turned on. Even if the
capacitor 42 is pre-charged, the power supply relay 40 can be
diagnosed accurately with respect to the fixed-open
abnormality.
[0063] (6) The power supply relay 40 is diagnosed with respect to
the fixed-open abnormality based on the charge voltage VPC of the
capacitor 42 and the voltage of the battery 12 (ignition output
voltage VIG), when the ignition switch 50, the power supply relay
40 and the motor relay 46 are turned on. Thus, the predetermined
threshold voltage for checking the fixed-open abnormality of the
power supply relay 40 by comparison with the charge voltage VPC can
be set by using the ignition output voltage VIG.
Third Embodiment
[0064] A third embodiment is described next with respect to parts
different from the second embodiment.
[0065] In the third embodiment, the abnormality diagnosis
processing is executed as shown in FIG. 6 in response to the
turn-on of the ignition switch 50 as a trigger. In FIG. 6, steps
S60, S62, S64 and S66 are executed in addition to the steps
executed in the second embodiment (FIG. 5).
[0066] If it is determined at step S42 that the fixed-closure
abnormality is not present (NO), it is then checked at step S60
whether a predetermined time 13 has elapsed. The predetermined time
13 is set to correspond to a period required to charge the
capacitor 42 to a predetermined voltage .beta. by the ignition
voltage VIG through the pre-charge resistor 56. If the
predetermined time elapses (S62: YES), it is checked at step S62
whether the charge voltage VPC is greater than the predetermined
voltage .beta.. This step S62 is for checking whether the
pre-charge path including the pre-charge resistor 56 has any
abnormality. Specifically, the pre-charge path is determined to be
abnormal, if the charge voltage VPC does not rise sufficiently even
after an elapse of time, in which the capacitor 42 is supposed to
have been pre-charged sufficiently. The predetermined voltage
.beta. is therefore set to correspond to the charge voltage, which
the capacitor 42 normally attains in the predetermined time T3. If
the charge voltage VPC is less than the predetermined voltage 13
(S62: NO), this abnormality of low pre-charge voltage is indicated
by the malfunction indicator light 34 at step S64 and the motor
relay 46 is turned on to the closed state at step S66.
[0067] If the charge voltage VPC is greater than the predetermined
voltage .beta. (S62: YES), steps S46 to S54 are executed to
diagnose the power supply relay 40 with respect to the fixed-open
abnormality in the similar manner as in the second embodiment.
[0068] The third embodiment provides the following advantage in
addition to the advantages of the first embodiment and the
advantages of the second embodiment.
[0069] (7) The pre-charge path is diagnosed with respect to its
abnormality based on the charge voltage VPC of the capacitor 42
produced after the ignition switch 50 is turned on. It can be
therefore detected in advance, by turning on the power supply relay
40 to the closed state, that a large current will flow in the motor
relay 46.
Fourth Embodiment
[0070] A fourth embodiment is described next with reference to
parts different from the first embodiment.
[0071] In the fourth embodiment, as shown in FIG. 7, a Zener diode
80 is connected to the pre-charge resistor 56 between two current
paths, one of which is between the diode 52 and the microcomputer
30 and the other of which is between the power supply relay 40 and
the H-bridge circuit 20. The breakdown voltage Vz of the Zener
diode 80 is set such that the current, which flows in the power
supply relay 40 when the power supply relay is turned on, does not
exceed an upper limit value of an allowable current. The breakdown
voltage Vz is also set such that the charge voltage VPC produced by
the capacitor 42 before and after the turn-on of the power supply
relay 40 may be distinguished accurately. The charge voltage VPC of
the capacitor 42 is preferably greater than one half (1/2) of the
voltage of the battery 12 and less than nine-tenth ( 9/10) of the
same.
[0072] According to the fourth embodiment, the power supply relay
can be diagnosed with respect to its fixed-closure abnormality
based on the charge voltage VPC of the capacitor 42 after the
ignition switch 50 is turned on and before the power supply relay
40 is turned on to the closed state.
[0073] It is possible to perform this operation by increasing the
resistance of the pre-charge resistor 56 without the Zener diode
80. The increase of the resistance of the pre-charge resistor 56
will necessarily reduce the current, which flows from the battery
12 to the capacitor 42. As a result, time required to pre-charge
the capacitor 42 becomes long and the start of control of the motor
10 is delayed more.
[0074] The fourth embodiment provides the following additional
advantage.
[0075] (8) Since the Zener diode 80 is connected in series to the
pre-charge resistor 56, the capacitor 42 can be quickly charge to a
voltage, which is sufficiently lower than the charge voltage VPC
attained when the power supply relay 40 is turned on to the closed
state. As a result, the pre-charge can be completed quickly and the
fixed-closure abnormality of the power supply relay 40 can be
detected in advance of the turn-on of the power supply relay
40.
Fifth Embodiment
[0076] A fifth embodiment is described next with reference to parts
different from the second embodiment (FIG. 5).
[0077] In this embodiment, abnormality diagnosis processing is
executed as shown in FIG. 8 by the microcomputer 30 in response to
the turn-on of the ignition switch 50 as a trigger. In the fifth
embodiment shown in FIG. 8, steps S46a and S70 are additionally
executed relative to the processing of the second embodiment shown
in FIG. 5. Step S46a is a replacement of step S46.
[0078] Specifically, if the power supply relay 40 has no
fixed-closure abnormality (542: NO), the motor relay 46 is turned
on to the dosed state and the duty ratio Duty of the H-bridge
circuit 20 is controlled to be less than a minimum duty ratio Dmin
at step S46a. The minimum duty ratio Dmin is a minimum value of the
duty control for the motor 10 by the H-bridge circuit 20 at the
time the motor 10 is driven. When the switching elements 21 and 24
are turned on, the current path formed of the switching elements
21, 24 and the motor 10 is added in parallel to the discharge
resistor 44. When the switching elements 22 and 23 are turned on,
two current paths are connected in parallel to the discharge
resistor 44. One current path is formed of the switching elements
22, 23 and the motor 10, and the other current path is formed of
the resistors 25, 26 and the motor 10. As a result, the resistance
of the discharge paths including the discharge resistor 44 and
connected in parallel to the capacitor 42 is decreased, and the
charge voltage VPC of the capacitor 42 is decreased more quickly.
Thus, the fixed-open abnormality can be detected at step S50 more
accurately. The duty ratio is controlled within a range, in which
the rotor of the motor 10 is not displaced. Thus, it is prevented
that the steering wheel is moved by the motor unintentionally.
[0079] In the duty ratio control, the switching elements 21 and 24
may be turned on and off periodically at the same time, or the
switching elements 22 and 23 may be turned on and off periodically
at the same time. The switching elements 21, 24 and the switching
elements 22, 23 may be turned on alternately. In either of the
cases, the period in which the switching elements 21, 24 are turned
on continuously and the period in which the switching elements 22,
23 are turned on continuously should be limited to a period not to
move the rotor of the motor 10.
[0080] The duty ratio control is stopped at S70, if the main relay
40 has no fixed-open abnormality (S50: NO) or the assist control is
prohibited (S54).
[0081] The fifth embodiment provides the following advantage in
addition to the advantages of the second embodiment.
[0082] (9) Since the H-bridge circuit 20 is duty-controlled in
diagnosing the power supply relay 40 with respect to the fixed-open
abnormality, the diagnosis operation can be performed more
accurately.
Other Embodiments
[0083] The foregoing embodiments may be modified as follows.
[0084] The fourth embodiment may be modified similarly as the
second embodiment is modified by the third embodiment.
[0085] The third embodiment may be modified similarly as the second
embodiment is modified by the fifth embodiment.
[0086] The fixed-closure diagnosis performed in the first
embodiment need not be based on the drop of the charge voltage VPC
produced after both of the ignition switch 50 and the power supply
relay 40 are turned on to the closed state. For example, this
diagnosis may be performed based on the drop condition of the
voltage during a period in which a voltage greater than the low
limit value of the operation voltage of the microcomputer 30 after
both of the ignition switch 50 and the power supply relay 40 are
turned on to the closed state.
[0087] In the second and the third embodiments, the microcomputer
need not have input terminals provided exclusively to monitor the
ignition output voltage VIG and the charge voltage VPC to detect
the fixed-open abnormality. The fixed-open abnormality may be
detected based on only the charge voltage VPC. In this case, when
the motor relay 46 is turned on after the ignition switch 50 and
the power supply relay 40 are turned on, the charge voltage VPC
does not fall if the power supply relay 40 has no fixed-open
abnormality. However, the charge voltage falls if the power supply
relay 40 has the fixed-open abnormality. Therefore it is possible
to diagnose the power supply relay 40 with respect to the
fixed-open abnormality based on whether the charge voltage VPC
falls more than a predetermined amount after the motor relay 46 is
turned on to the closed state.
[0088] In each embodiment, the keyword need not be written and
stored in the non-volatile memory 32 for the fixed-closure
diagnosis. For example, the keyword may be written and stored in a
back-up RAM, which is maintained operable irrespective of a
condition of the ignition switch 50, that is, a condition of
connection between the microcomputer 30 and the battery 12. The
keyword may be written and stored in a volatile memory. Even in
this case, the keyword "B" indicating the fixed-closure abnormality
can be maintained, because the power supply to the microcomputer 30
is maintained by the power supply relay 40. It is thus possible to
perform the fixed-closure abnormality based on checking whether the
keyword B is stored in the volatile memory, when the ignition
switch 50 is turned on next time. The processing of writing the
keyword "A" at the time the ignition switch 50 is turned off may be
obviated.
[0089] In the foregoing embodiments, the power supply relay 40 may
be diagnosed with respect to the fixed-closure abnormality in the
conventional manner by setting the resistances of the pre-charge
resistor 56 and the discharge resistor 44.
[0090] In the fourth embodiment, the abnormality diagnosis
performed in the other embodiments may be performed.
[0091] In the foregoing embodiments, the discharge resistor 44 may
be obviated. Even in this case, the current path for charging the
capacitor 42 is interrupted by turning off the power supply relay
40 to the open state under the condition that the ignition switch
50 is in the turned-off condition. The voltage of the capacitor 42
thus falls as the power of the capacitor 42 is consumed by the
microcomputer 30. As a result, the power supply relay 40 is
diagnosed with respect to the fixed-closure abnormality based on
the charge voltage VPC of the capacitor 42 in the similar manner as
in the foregoing embodiments.
[0092] The motor 10 is not limited to the brush-type DC motor but
may be a brushless-type DC motor. In this case, a three-phase
inverter may be used as the power conversion circuit.
[0093] The motor 10 is not limited to be used in the electric
power-assisting apparatus but may be used in a gear ratio varying
apparatus, which is provided between an input shaft mechanically
coupled to a steering wheel and an output shaft driven to rotate by
an electric motor and varies a ratio of rotation amount of the
output shaft relative to a rotation amount of the input shaft. The
motor 10 may be used in a steering system of a steer-by-wire
system. In these cases, it becomes possible in the fifth embodiment
that the duty ratio may be set to a value, which will cause a small
amount of movement of the rotor of the motor 10 without any turning
the steering wheel. The motor 10 may also be used to drive an air
compressor or a motive power generator mounted in a vehicle.
* * * * *