Controller for automobile

Details Controller for automobile Controller for automobile

1999-06-03

2001-02-27

Jackson, Stephen W. (Department: 2836)

Electrical transmission or interconnection systems

Vehicle mounted systems

Automobile

C307S009100, C307S109000

Reexamination Certificate

active

06194792

ABSTRACT:

TECHNICAL FIELD
The present invention reduces a rush current to a capacitor, that is, a rush current flowing through a relay contact by charging a smoothing capacitor for reducing ripple components in an operating current and thereafter, supplying the operating current to a load from a DC power unit by closing the relay contact when supplying the operating current to the load through the relay contact from the DC power unit.
BACKGROUND ART
An electric-power-steering controller is described below as a conventional vehicle controller.
FIG. 4
is a circuit diagram showing the conventional electric-power-steering controller disclosed in, for example, Japanese Patent Application No. 5-64268, in which the controller is locally shown by a block diagram. In
FIG. 4
, symbol
40
denotes a motor for outputting an auxiliary torque to the steering wheel (not illustrated) of a vehicle and
41
denotes a battery for supplying a motor current IM for driving the motor
41
.
Symbol
42
denotes a large-capacity (1,000 to 3,600 &mgr;F.) for absorbing the ripple component of the motor current IM,
43
denotes a shunt resistor for detecting the motor current IM, and
44
denotes a bridge circuit comprising a plurality of semiconductor switching devices (e.g. FETs) Q
1
to Q
4
for switching the motor current IM in accordance with the magnitude and direction of the auxiliary torque. Symbol
46
denotes a normally-open relay for supplying or cutting off the motor current IM according to necessity.
Symbol
47
denotes a driving circuit for driving the motor
40
through the bridge circuit
44
and moreover driving the relay
46
and
48
denotes motor-current detection means for detecting the motor current IM through an end of the shunt resistor
43
. The driving circuit
47
and motor-current detection means
48
constitute the peripheral circuit element of a microcomputer to be described later.
Symbol
50
denotes a torque sensor for detecting the steering torque T of a steering wheel and
51
denotes a speed sensor for detecting the speed V of a vehicle.
Symbol
55
denotes a microcomputer (ECU) for computing the auxiliary torque in accordance with the steering torque T and vehicle speed V and moreover, generating a driving signal corresponding to the auxiliary torque by returning the motor current IM, which inputs a rotational direction command Do and current controlled variable I
o
for controlling the bridge circuit
44
to the driving circuit
47
as driving signals.
The microcomputer
55
is provided with motor current decision means
56
for generating the rotational direction command D
o
of the motor
40
and the motor current command Im corresponding to the auxiliary torque, subtraction means
57
for computing the current deviation &Dgr;I between a motor current command Im and the motor current IM, and PID operation means
58
for computing correction values of P (proportion) term, I (integration) term, and D (differentiation) term from the current deviation &Dgr;I and generating the current controlled variable I
o
corresponding to a PWM duty ratio.
Moreover, though not illustrated, the microcomputer
55
includes a publicly-known self-diagnostic function in addition to an A-D converter and PWM timer circuit, detects a trouble in the relay
46
or troubleshoots a system at the start of the system, and unless any trouble is detected, turns on the relay
46
to supply power to the bridge circuit. Furthermore, while the system operates, the microcomputer
55
always self-diagnoses whether the system normally operates. If a trouble occurs, the microcomputer
55
releases the relay
46
through the driving circuit
47
to cut off the motor current IM.
Then, operations of an electric-power-steering controller are described by referring to FIG.
4
. The microcomputer
55
captures the steering torque T and vehicle speed V from the torque sensor
50
and speed sensor
51
, feedback-inputs the motor current IM from the shunt resistor
43
, and generates the rotational direction command D
o
of a power steering and the current controlled variable I
o
corresponding to the auxiliary torque value to output them to the driving circuit
47
.
The driving circuit
47
closes the normally-open relay
46
under a steady driving state. However, when the rotational direction command D
o
and current controlled variable I
o
are input, the circuit
47
generates a PWM driving signal to apply the signal to the semiconductor switching devices Q
1
to Q
4
of the bridge circuit
44
.
Thereby, the motor current IM is supplied to the motor
40
from the battery
41
through the relay
46
, shunt resistor
43
, and bridge circuit
44
. The motor
40
is driven by the motor current IM to output a required amount of auxiliary torque in a required direction.
In this case, the motor current IM is detected through the shunt resistor
43
and motor-current detection means
48
and returned to the subtraction means
57
in the microcomputer
55
and thereby, controlled so as to coincide with the motor current command Im. Moreover, the motor current IM includes ripple components due to the switching operation of the bridge circuit
44
under PWM driving but it is smoothed and controlled by the large-capacity capacitor
42
.
When this type of electric-power-steering controller is started, it performs troubleshooting and thereafter, turns on the relay
46
to supply a control current corresponding to the desired steering torque T to the motor as described above, and operates so as to output a required amount of auxiliary torque. However, because the capacitor
42
has a large capacity, an excessive rush current flows through the relay contact when the relay
46
is turned on. As a result, when the controller is repeatedly started, the contact is welded due to transition and the current supplied to the motor
40
cannot be cut off when a system trouble occurs.
In the case of the relay
46
, however, the durability of the contact against the rush current becomes important when the controller is repeatedly started in addition to the fact of satisfying a desired maximum supply current. Thus, a relay having a higher current-supply performance is used as a countermeasure and thus, part costs increase and resultingly, the product cost increases.
In the case of a system requiring a large auxiliary torque, the control current further increases and the impedance must be reduced in order to reduce the heat produced by the capacitor
42
due to increase of a ripple current and thereby, the capacity increases. Therefore, the rush current further increases, and not only the cost increases but also a problem occurs that the reliability of the controller is deteriorated.
The present invention is made to improve the reliability of the controller and reduce the product cost and makes it possible to select a relay in accordance with a maximum control current value by reducing a rush current. Therefore, it is possible to use a relay having a cost lower than a conventional one, reduce the product cost, and improve the reliability.
DISCLOSURE OF THE INVENTION
The present invention is directed to a vehicle controller that includes a relay contact for outputting a driving current to a large current load by a DC power supply and controlling the current, a smoothing capacitor connected between the large-current load of the relay contact and the earth, and spare charging control means for charging the capacitor for a predetermined time before closing the relay contact.
The spare charging control means sets a spare charging voltage level for a capacitor to an optional and cuts off charging after charging a capacitor for a predetermined time.
The spare charging control means is constituted so as to not influence the charged voltage of a capacitor for deciding an abnormal state such as welding of a relay.
The spare charging control means starts the controller and simultaneously starts the operation of an internal constant-voltage circuit and then immediately starts capacitor charging.


REFERENCES:
patent: 4875539 (1989-10-01), Abukawa et al.
paten

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