Method of and circuit for testing an electrical actuator...

Details Method of and circuit for testing an electrical actuator... Method of and circuit for testing an electrical actuator...

1999-05-11

2001-12-11

Huynh, Kim (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

With specific quantity comparison means

C361S093100, C324S527000

Reexamination Certificate

active

06330140

ABSTRACT:

FILED OF THE INVENTION
The present invention relates to a method of and circuit for testing an electrical actuator power electronic drive stage. Such a circuit may be used for testing a drive stage of a vehicle, for instance for driving an electric motor of an electric power assisted steering (EPAS) system.
BACKGROUND OF THE INVENTION
DE 2 751 116 discloses a testing arrangement for testing vehicle lighting circuits. Constant current sources are switched so as to supply currents depending on the expected load to different lighting circuits. The voltages across the lighting circuits are measured and a fault is indicated if the voltage is higher than a preset expected value. This arrangement therefore detects bulb failure in such lighting circuits.
DE 3 842 921 discloses an arrangement for monitoring the currents drawn by electrical loads. The load current is measured by switching a current sensing resistor into the load circuit and measuring the voltage across the resistor. This voltage is compared with a threshold which indicates whether the load current is acceptable.
DE 4 338 462 discloses a control system for electrical consumers in a motor vehicle. Power is applied to the electrical consumers via a constant current source while switching off the battery voltage for a short time. The voltage across the consumer is monitored and a fault is indicated if it has an unacceptable value during the short time when the constant current source is connected in place of the battery voltage.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, there is provided a circuit for testing an actuator drive stage, comprising a power supply circuit for supplying reduced current to the drive stage before supplying normal current thereto, a measuring circuit for measuring an electrical parameter within the drive stage, and a comparator for comparing the measured parameter with an acceptable value to signal a fault condition when the measured parameter corresponds to a current through the drive stage which is different from an expected value.
Preferably the power supply circuit comprises a contact for supplying the normal current and at least one resistor connected in parallel with the contact for supplying the reduced current before the contact is closed. The resistor may be constructed from two or more discrete components connected in series. A switch may be provided for disconnecting the at least one resistor from the contact.
A controller, such as a microcontroller, may be provided for closing the contact in the absence of a signalled fault condition. The controller may be arranged to switch on at least one active device of the drive stage while the reduced current is supplied to the drive stage.
The controller may be arranged, during supply of the reduced current, to switch on at least part of the drive stage, to switch off the drive stage, and to signal a fault in the actuator if a drive stage output voltage falls below a threshold value in less than a predetermined time period.
The measuring circuit may comprise a circuit for measuring the supply voltage to the drive stage. The measuring circuit may comprise a circuit for measuring an output voltage of the drive stage. The measuring circuit may comprise a potential divider whose output is connected to an analogue-to-digital converter, which may be provided within the controller.
According to a second aspect of the invention, there is provided a method of testing an actuator drive stage, comprising supplying reduced current to the drive stage before supplying normal current thereto, measuring an electrical parameter within the drive stage, signalling a fault condition if the measured parameter corresponds to a current through the drive stage which is different from an expected value, and supplying normal current to the drive stage in the absence of signalling of a fault condition.
It is thus possible to provide an arrangement which signals a fault in an actuator drive stage or in an actuator connected thereto before normal or full power is supplied to the drive stage. It is therefore unnecessary for excessive current, arising for instance from a short circuit in the drive stage or the actuator, to have to be broken, for instance by a contact of an electromagnetic relay, if a fault exists within the drive stage of the actuator. It is further unnecessary to rely on storage of a fault indication detected during previous operation of the actuator.
The invention will be further described, by way of example, with reference to the accompanying drawings, in which:


REFERENCES:
patent: 3112435 (1963-11-01), Barney
patent: 4523563 (1985-06-01), Moore et al.
patent: 5448492 (1995-09-01), Kolomyski et al.
patent: 5574632 (1996-11-01), Pansier
patent: 5712550 (1998-01-01), Boll et al.
patent: 4443351C (1996-06-01), None
patent: 2680007A (1993-02-01), None

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