Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
2000-06-05
2002-01-01
DePumpo, Daniel G. (Department: 3611)
Motor vehicles
Steering gear
With electric power assist
C180S443000, C318S434000
Reexamination Certificate
active
06334503
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrically operated power steering apparatus in which a drive force of a motor assists a required value of steering torque applied to a steering wheel operated by an operator of an automotive vehicle.
2. Discussion of the Related Art
An electrically operated power steering apparatus for an automotive vehicle is generally constructed to include (a) a torque transmitting system transmitting steering torque which is applied to a steering wheel by a vehicle operator, to a steerable wheel of the vehicle laying on a road surface, so as to assist the steering torque, (b) a motor applying a drive force thereof to the torque transmitting system, and (c) a controlling device controlling an electric power supply to the motor.
Japanese Patent Publication No. 10-100913 discloses an example of a conventional type of the electrically operated power steering apparatus identified above. In this example, the temperature of a winding of a motor is estimated on the basis of a voltage and a current value of the motor, without the provision of a temperature sensor detecting a temperature of the motor. The estimated temperature results in preventing overheat of the motor.
However, in general, what can be accurately estimated in relation to the temperature of a winding of a motor by the use of a voltage and a current value of the motor is an increase of temperature of the motor winding at each one of a plurality of discrete points of time after a reference point of time. The increase is calculated from the temperature of the heated portion obtained at the reference point of time. The increase is a relative value, not an absolute value of temperature of the motor winding. In addition, the example explained above is not designed to detect or estimate an absolute value of temperature of the motor winding at the reference point of time. Consequently, this example fails to obtain the temperature of the motor with an adequately high precision.
In the case where a temperature sensor is arranged sufficiently near a winding of a motor, the temperature of the motor can be sequentially detected at a high precision. However, in this case, since such a temperature senor is generally expensive, there arises a problem that the substantial increase in the cost of an electrically operated power steering apparatus is unavoidable.
In addition, a problem of generation of heat as a result of a supply of an electric power to a motor arises about the motor in an electrically operated power steering apparatus, but the same problem can also arise about other electrical parts of the apparatus.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electrically operated power steering apparatus in which the temperature of a heated portion of the apparatus which emits heat as a result of a supply of electric power to a motor can be more precisely obtained in lower cost.
The object may be achieved according to any one of the following modes of this invention. Each of these modes of the invention is numbered like the appended claims, and depends from the other mode or modes, where appropriate. This type of explanation about the present invention is for better understanding of some ones of a plurality of technical features and a plurality of combinations thereof disclosed in this specification, and does not mean that the plurality of technical feature and the plurality of combinations in this specification are interpreted to encompass only the following modes of this invention:
(1) An electrically operated power steering apparatus for an automotive vehicle having a steering wheel to be operated by an operator of the vehicle and a steerable wheel thereof laying on a road surface, comprising:
a torque transmitting system transmitting a steering torque which is applied to the steering wheel by the operator, to the steerable wheels;
a motor applying a drive force thereof to the torque transmitting system so as to assist the steering torque;
a controlling device controlling an electric power supply to the motor, thereby permitting reduction in a required value of the steering torque with the assist of the drive force of the motor; and
a power supply restricting device utilizing a temperature of a heated portion of the electrically operated power steering apparatus which emits heat as a result of the electric power supply to the motor, at a reference point of time, as an initial temperature of the heated portion, utilizing a plurality of electric power-related values each of which is related to at least one of a current and a voltage value of the motor, as a plurality of physical quantities related to temperature increases of the heated portion each of which is an increase of the temperature of the heated portion from that at the reference point of time, and restricting the electric power supply to the motor such that an actual value of the temperature of the heated portion does not exceed a predetermined upper limit thereof.
In general, the temperature of the heated portion, if not changed or gently changed, forms a constant relationship thereof with an ambient temperature of the heated portion. In addition, the ambient temperature of the heated portion can be detected without using a temperature sensor exclusively used for detection of the temperature of the heated portion. Accordingly, the temperature of the heated portion, if not changed or gently changed, can be easily detected or estimated.
The use of at least one of a current and a voltage value of the motor permits estimation of an increase of the temperature of the heated portion from that at a reference point of time. In addition, control of the motor is usually effected with feedback of at least one of a current and a voltage value of the motor. Therefore, a sensor detecting at least one of a current and a voltage value of the motor is usually provided with the electrically operated power steering apparatus. Consequently, in many cases, at least one of a current and a voltage value of the motor can be easily detected.
There exists a technology of using the temperature of the heated portion detected or estimated in the manner mentioned above, as an initial temperature of the heated portion. There also exists a technology of using at least one of a current and a voltage value of the motor as a physical quantity related to an increase of the temperature of the heated portion from that at a time when the initial temperature of the heated portion has been obtained. These two technologies can cooperate with each other to estimate the temperature of the heated portion at each one of a plurality of discrete points of time after the initial temperature of the heated portion has been obtained.
Based on the above findings, the apparatus according to this mode (
1
) utilizes the temperature of the heated portion at a reference point of time as an initial temperature of the heated portion, and utilizes at least one of a current and a voltage value of the motor as a physical quantity related to an increase of the temperature of the heated portion from that at the reference point of time. Further, the apparatus according to this mode (
1
) restricts an electric power supply to the motor so as to prevent an actual value of the temperature of the heated portion from exceeding a predetermined upper limit of the temperature of the heated portion.
Consequently, in the apparatus according to this mode (
1
), it is not indispensable to employ a temperature sensor which exclusively detects the temperature of the heated portion with a high precision and which is expensive. Therefore, a substantial increase in the cost of the apparatus resulting from the addition of a function of obtaining the temperature of the heated portion to an electrically operated power steering apparatus can be easily avoided.
Further, in the apparatus according to this mode (
1
), a determination as to whether the restriction on the electric power supply to the motor is necessary or not is per
Fukumura Kenichi
Kamimae Hajime
DePumpo Daniel G.
Toyoda Koki Kabushiki Kaisha
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