Brakes – Wheel – Axially movable brake element or housing therefor
Reexamination Certificate
1999-04-02
2001-10-23
Oberleitner, Robert J. (Department: 3613)
Brakes
Wheel
Axially movable brake element or housing therefor
C188S072300, C188S07000R, C188S136000, C188S024140, C188S024150
Reexamination Certificate
active
06305506
ABSTRACT:
TECHNICAL FIELD
The present invention relates in general to an electrically operated braking system having a motor-driven disc brake activated by an electric motor for braking a wheel of an automotive vehicle. More particularly, this invention is concerned with improvements in techniques for enabling the motor-driven disc brake to produce an increased wheel braking force, without increasing a drive force or torque to be generated by the electric motor.
BACKGROUND ART
In such an electrically operated braking system, there has been a need or desire to increase the wheel braking force for a given drive force or torque generated by an electric motor used for the disc brake. JP-U-5-22234 proposes a conventional braking system, which is arranged in an attempt to meet the above-indicated need. In this conventional braking system, a boosting mechanism is provided between an electric motor and friction pads of a disc brake, so that the drive force generated by the motor is boosted by the boosting mechanism before it is transmitted to the friction pads. For producing a relatively large wheel braking force, however, the motor and the boosting mechanism in this conventional braking system are subject to a comparatively large load, and therefore tend to have relatively large sizes, leading to an accordingly increased size of the motor-driven disc brake.
DISCLOSURE OF INVENTION
It is therefore an object of the present invention to provide an electrically operated braking system wherein a motor-driven disc brake for braking a vehicle wheel is capable of producing a sufficiently large wheel braking force without increasing a nominal capacity of an electric motor, by effectively utilizing a friction force generated by a friction pad and a disc rotor upon braking of the wheel, while avoiding an increase in size of the disc brake.
The above object may be achieved by any one of the following features of the present invention, which are numbered like the appended claims, so as to show possible combinations of the features:
(1) An electrically operated braking system comprising a motor-driven disc brake including an electric motor as a drive source for braking a wheel of an automotive vehicle, and a motor control device for controlling the electric motor, the motor-driven disc brake further including: (a) a disc rotor having a friction surface and rotating with the wheel; (b) a friction pad movable for contact with the friction surface to restrict rotation of the disc rotor; (c) a pad support mechanism for supporting the friction pad such that the friction pad is movable in a direction intersecting the friction surface; (d) a pad pressing mechanism comprising the electric motor and a pressing member, the electric motor producing a drive force for moving the pressing member to force the friction pad against the friction surface of the disc rotor; and (e) a self-servo mechanism for providing a self-servo effect of boosting a friction force generated between the friction surface and the friction pad, on the basis of the friction force.
In the braking system of the present invention, the self-servo mechanism is adapted to boost the friction force and apply the boosted friction force to the friction pad. The friction force thus boosted by the self-servo mechanism with a given drive force of the electric motor is larger than the friction force which is generated with the same drive force of the electric motor when the self-servo mechanism is not provided. In this braking system, therefore, the load acting on the electric motor is reduced, and the size and capacity of the motor are accordingly reduced, as compared with those of the motor in the conventional braking system wherein only the drive force of the motor is used to press the friction pad against the disc rotor, without utilizing a self-servo effect of the friction pad based on the friction force generated by the motor. Accordingly, the motor-drive disc brake can be made small-sized and comparatively easily installed on the vehicle body.
The present electrically operated braking system can be used as an ordinary brake for braking a running vehicle. In this case, the braking system may be adapted to effect automatic control of braking forces to be applied to vehicle wheels, such as anti-lock and traction controls.
The electric motor used in the present braking system may be a wound-rotor type motor, or an ultrasonic motor. The holding torque produced by the ultrasonic motor in its non-energized off state is larger than that produced by the wound-rotor type motor. In this respect, the braking system using the ultrasonic motor can be suitably used as a parking brake. In this case, the braking force required for holding the parked vehicle stationary can be obtained with a comparatively small amount of electric power consumption.
The motor-driven disc brake may use a pair of friction pads which are disposed on the opposite sides of the disc rotor and which are forced against the opposite friction surfaces of the disc rotor. In this case, the self-servo mechanism may be adapted to use the friction force between the disc rotor and one of the two friction pads, for providing the self-servo effect with respect to either the above-indicated one friction pad or the other friction pad.
(2) An electrically operated braking system according to the feature (1), wherein said pad pressing mechanism includes a first pressing device for generating a first pressing force for pressing the friction pad against the disc rotor based on the drive force of the electric motor, and the self-servo mechanism includes a second pressing device for generating a second pressing force for pressing the friction pad against the disc rotor based on the friction force which is generated between the friction pad and the disc rotor based on the first pressing force.
In the above braking system, the first and second pressing forces may be transmitted to the friction pad through respective different paths or a single path.
(3) An electrically operated braking system according to the feature (1) or (2), wherein the motor-driven disc brake includes a pair of friction pads disposed on the opposite sides of the disc rotor, respectively, and the pad pressing mechanism and the self-servo mechanism include a lever corresponding to each of at least one of the friction pads, the lever including (a) a first connecting portion at which the lever is connected to a stationary member such that the lever is pivotable about a first axis perpendicular to an axis of rotation of the disc rotor, (b) a first bearing portion which receives the friction force generated between the corresponding one of the friction pads and the disc rotor when the vehicle is running in a predetermined first direction which is one of a forward and a reverse running direction of the vehicle, (c) an engaging portion which is engageable with a back surface of the above-indicated corresponding friction pad, and wherein the first connecting portion, the first bearing portion and the engaging portion are positioned relative to each other such that the friction force received by the first bearing portion from the above-indicated corresponding friction pad causes a moment to act on the lever in a direction that causes the engaging portion to approach the disc rotor.
In the above braking system, the lever constitutes a major part of the self-servo mechanism.
In one form of this braking system, the first bearing portion (effort point), the relative position (lever ratio) of the first connecting portion (fulcrum) and the engaging portion (load point) is determined so that the friction force generated between the friction pad and the disc rotor is boosted and transmitted to the friction pad. According to this arrangement, the self-servo mechanism achieves an effective self-servo function to boost the friction force. In another form, the level has an input portion at which the drive force of the electric motor is received. In this case, the single lever permits the first and second pressing forces to be transmitted to the friction pad, and th
Imai Kazuhiko
Kurasako Ryoichi
Shirai Kenji
Yoshino Yasunori
Kenyon & Kenyon
Oberleitner Robert J.
Pezzlo Ben
Toyota Jidosha & Kabushiki Kaisha
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