Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
2001-01-23
2003-02-18
Lerner, Avraham (Department: 3618)
Motor vehicles
Steering gear
With electric power assist
C361S161000
Reexamination Certificate
active
06520279
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a current-carrying control device which controls a switching condition (conductible condition or cutoff condition) of a current-carrying line by a relay such as electromagnetic relay or semiconductor relay, or to an electric power steering apparatus including such the current-carrying control device. More particularly, the present invention relates to a device capable of preventing an overheat of the relay practically.
2. Description of the Related Art
In the electric power steering apparatus used for a small vehicle such as light car, a steering torque generated at a steering shaft by steering a handle of the vehicle is sensed by a torque sensor. Corresponding on the steering torque, a steering-assistance torque is generated by flowing a current to an auxiliary motor (hereafter simply called motor) attached at the steering shaft from a battery of the vehicle. In current control of the motor for the torque generation, an H-bridge circuit including usually four FETs (Field Effect Transistor) is used, the motor is driven by a control portion including a microcomputer with PWM (Pulse Width Modulation) system through a driving circuit including the H-bridge circuit.
In the current-carrying line of the driving circuit (if circumstances require, current-carrying line between the driving circuit and a power source, and current-carrying line between the driving circuit and the motor), a relay such as electromagnetic relay is provided as similarly as a general motor control device so as to control the switching condition of the current-carrying line by the control portion. That is, in the case of the electronic power steering apparatus, at a non-operation condition of the apparatus, the current-carrying line is made the cutoff condition by keeping the relay an open state so as to avoid generation of a large current (over-current) by a reverse connection of the battery (to connect the battery of the vehicle with a reverse polarity). In case of a short fault in the FET at an operation of the apparatus, the relay is switched to the open state so as to cut the current-carrying line in order to avoid generation of the large current, malfunction of the motor, or regenerative lock caused by the fault.
The regenerative lock means here phenomena that both terminals of a motor coil are connected by the short fault of the FET, and the handle of the vehicle connected to the motor becomes hard or impossible in rotary operation because so called regenerative break at the motor is generated. In order to solve the problem of such regenerative lock, a relay such as electromagnetic relay is necessary to provide even at the current-carrying line between the driving circuit (exactly, the H-bridge circuit) and the motor.
In such electric power steering apparatus, although measures have carried out to protect the FET from heating by controlling the carrying current to the FET (that is, carrying current to the motor.) so that a temperature of the FET is not more than a designated temperature in related art, measures have not carried out to positively protect the relay from heating. This is because of the following. In related art, such electric power steering apparatus has used only for a small vehicle such as light car as above-mentioned because it is difficult to generate a large steering-assistance torque comparing with a hydrolic device. The current flowing through the motor is low level, maximum about 40 A, at a full operating condition of the apparatus such as operation of the quick turn of the wheel. Because of that, a calorific value of the relay or parts generating heat arranged at periphery thereof (the above FET, for example) is not so large, and the overheat of the relay is prevented practically without problem by means of measures that a suitable radiator is provided.
However the above electric power steering apparatus is easy in electric control. There are various merits that a hydraulic pump and an oil piping are not need and the structure is simple. Accordingly, an application for a normal passenger car is investigated nowadays, and it is possible to apply for a large vehicle in future.
When the apparatus is mounted in such comparatively large vehicle, the current of the motor is needed maximum 60 to 80 A for example in order to drive the motor and then generate the designated steering-assistance torque in the full operating condition of the apparatus such as quick return of the wheel. At such condition, the calorific value (in proportion to a square of the current) from the relay itself or parts generating heat at periphery thereof increases substantially, and it is impossible to protect the relay from the overheat with only the operation of the radiator.
A design so that the relay does not become an overheat state under the condition of the above-mentioned current-increase is possible in principle by providing a radiator corresponding to a maximum calorific value at the control unit of the apparatus where the driving circuit, the microcomputer, and the relay are stored or by selecting a capacity of the relay itself for the maximum current. However practically it is impossible. In this case, the radiator becomes large extremely, and the relay becomes large particularly. Because of that, the ontrol unit is not stored at the narrow limit of space for arranging the unit of this kind in the vehicle.
When the relay becomes the overheat condition for example, there is the possibility that the relay coil thereof deteriorates (decrease of life), burns, or a solder connecting the terminal thereof melts. Such overheat condition must be avoided positively and certainly at a viewpoint to make sure of a high reliability of the steering system in the vehicle.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to provide a current-carrying control device which controls a switching condition of a current-carrying line by a relay such as an electromagnetic relay or a semiconductor relay and an electric power steering apparatus including such current-carrying control device, more particularly, a device for avoiding an overheat of the relay positively and certainly with a small construction.
A current-carrying control device according to the invention has a relay provided at a current-carrying line of a load and controlling the current-carrying line to a conductible condition or cutoff condition by a switching operation of the relay. The current-carrying control device also has a temperature sensor detecting a temperature at a designated portion where a temperature of the relay can be detected or calculated, and a current control unit carrying out a current correction control for correcting down a current flowing through there lay according to necessity based on a detection temperature detected by the temperature sensor in order to keep the temperature of the relay less than an allowable temperature.
Here in “load”, various kinds of electric loads are included such as a motor, a solenoid, and a lamp. “Current-carrying line of load” means a series of current path (comprising circuit conductor or cable) between the load and a power source (positive pole and negative pole). In case of that there is a driving circuit as a load, a current path between the driving circuit and the power source and a current path between the driving circuit and the load are included.
In “relay”, a usual electromagnetic rely, a semiconductor relay, and a switching element such as FET are included. “Temperature of relay” is a temperature of place where it is judged whether by the overheat, a function or a reliability of the relay deteriorates, or is lost or not (that is, whether less than the allowable temperature or not). According to circumstances, is an average temperature of all of relays, or a temperature of a specific place having heat problem of the relay (for example, temperature of the contact of the electromagnetic relay, terminal, or coil).
In “designated portion where the temperature of the relay can be detected or calcul
Fukumoto Tetsuya
Higashihara Yoshiteru
Sawano Takamoto
Lerner Avraham
Omron Corporation
LandOfFree
Current-carrying control device and electric power steering... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Current-carrying control device and electric power steering..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Current-carrying control device and electric power steering... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3137534