Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
2000-04-19
2002-06-04
Swann, J. J. (Department: 3611)
Motor vehicles
Steering gear
With electric power assist
C180S446000
Reexamination Certificate
active
06397971
ABSTRACT:
The present invention relates to an electrically powered steering for automobiles and the like, in particular to the improvement in steering feeling in case of failure.
In
FIG. 10
shows a typical electrically powered steering system. In
FIG. 10
, reference numeral
100
designates an electric motor, which generates a steering assisting force, which connected between the output terminals of a motor driving circuit
110
comprising a bridge circuit of four FETs
110
a
to
110
d
, and which is controllably driven when a drive unit
120
turns on one of the opposed pairs of FETs in the motor driving circuit
110
. In such a typical electrically powered steering system, when the FET
110
c
, for instance, causes a short circuit, a closed circuit is formed between the FET
110
c
, the motor, a parasitic diode in the FET
110
d
and the FET
110
c
. When a drive operates the steering wheel, the motor
100
is rotated by a steering shaft through a speed reducer to induce an electromotive force in the motor
100
. Since a large current flows in the closed circuit, the closed circuit works as a braking circuit to require the driver to apply an excessive steering force, which deteriorates the driving operation.
When the motor is reversely rotated in such a state that the FET
110
c
has caused short circuit as stated earlier, no braking action is provided since no current flows because of the absence of the closed circuit. This means that the braking force, or the required steering force, becomes different, depending on the steering directions. Since the steering force in the right direction and that in the left direction become unbalanced, the steering feeling extremely deteriorates.
In order to cope with this problem, there has been provided a proposal as disclosed in JP-B-796387. Now, a conventional electrically powered steering system will be explained, referring to FIG.
11
. In this Figure, parts identical to those shown in
FIG. 10
are designated by the same reference numerals, and explanation of these parts will be omitted.
As shown in
FIG. 11
, the motor
100
is connected to the output terminals of the motor driving circuit
110
through a relay
130
.
When the FET
110
c
causes a short circuit as stated earlier, this conventional powered steering system opens the relay
130
to prevent a closed circuit or braking circuit from being provided, preventing the steering feeling from being deteriorated.
Although this conventional electrically powered steering system can open the relay
130
in case of failure to prevent the braking circuit from being provided, the electrically powered steering system has created a problem in that the behavior of the vehicle becomes unstable under the influence of the moment of inertia of the motor
100
since the motor
100
is coupled to the steering shaft through the speed reducer.
It is an object of the present invention to solve this problem, and to provide an electrically powered steering system capable of making the behavior of a vehicle stable to provide good steering feeling even in case of failure.
According to a first aspect of the present invention, there is provided an electrically powered steering system comprising an electric motor for assisting a steering force based on a steering torque, and an electric motor driving circuit for driving the electric motor based on an inertia compensation current in case of failure, wherein the inertia compensation current becomes greater as the electric motor has an angular acceleration increased and provides the electric motor with a torque in a direction identical to the electric motor angular acceleration.
According to a second aspect of the present invention, there is provided an electrically powered steering system comprising an electric motor for assisting a steering force based on a steering torque, and an electric motor driving circuit for driving the electric motor based on a viscosity compensation current in case of failure, wherein the viscosity compensation current becomes greater as the electric motor has an angular speed increased and provides the electric motor with a torque in a direction opposite to the electric motor angular speed.
According to a third aspect of the present invention, there is provided an electrically powered steering system comprising an electric motor for assisting a steering force based on a steering torque, and an electric motor driving circuit for driving the electric motor based on an inertia compensation current and a viscosity compensation current in case of failure, wherein the inertia compensation current becomes greater as the electric motor has an angular acceleration increased and provides the electric motor with a torque in a direction identical to the electric motor angular acceleration, and wherein the viscosity compensation current becomes greater as the electric motor has an angular speed increased and provides the electric motor with a torque in a direction opposite to the electric motor angular speed.
According to a fourth aspect of the present invention, the electric motor is prohibited from operating when failure occurs at the electric motor or the circuit.
According to a fifth aspect of the present invention, the system further comprises a vehicle speed sensor for detecting a vehicle speed, wherein the compensation current is modified in response to the detected vehicle speed.
According to a sixth aspect of the present invention, the compensation current becomes greater as the vehicle speed increases.
According to a seventh aspect of the present invention, the compensation current is determined based on a preset vehicle speed in case of failure at the vehicle speed sensor.
According to an eighth aspect of the present invention, there is provided an electrically powered steering system comprising an electric motor for assisting a steering force based on a steering torque, an electric motor driving circuit for driving the electric motor, the circuit comprising a bridge circuit including four switching devices, and the circuit having the motor connected between output terminals thereof through a resistor, and a switch for short-circuiting both ends of the resistor in normal operation.
According to a ninth aspect of the present invention, the system further comprises a vehicle speed sensor for detecting a vehicle speed, wherein the resistor has a value of resistivity modified in response to the detected vehicle speed.
According to a tenth aspect of the present invention, the value of resistivity becomes smaller as the vehicle speed increases.
According to an eleventh aspect of the present invention, the value of resistivity is determined based on a preset vehicle speed in case of failure at the vehicle speed sensor.
According to a twelfth aspect of the present invention, there is provided an electrically powered steering system comprising an electric motor for assisting a steering force based on a steering torque, and a switch for short-circuiting both terminals of the electric motor, wherein the switch is driven by a duty signal in case of failure.
According to a thirteenth aspect of the present invention, the system further comprises a vehicle speed sensor for detecting a vehicle speed, wherein the duty signal for driving the switch has a duty ratio modified in response to the detected vehicle speed.
According to a fourteenth aspect of the present invention, the duty ratio becomes greater as the vehicle speed increases.
According to a fifth aspect of the present invention, the duty ratio is determined based on a preset vehicle speed in case of failure at the vehicle speed sensor.
According to a sixteenth aspect of the present invention, the system further comprises an alarm for warning that failure occurs in case of failure.
In accordance with the first aspect, an adverse effect by the moment of inertia of the motor can be compensated even in the case of failure to make the behavior of the vehicle stable and improve steering feeling.
In accordance with the second aspect, an adverse effect on steering feeling by the viscosity of the motor
Bottorff Christopher
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
Swann J. J.
LandOfFree
Electrically powered steering system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrically powered steering system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrically powered steering system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2927524