Fluid-pressure and analogous brake systems – Speed-controlled – Torque sensing
Reexamination Certificate
2000-11-01
2003-08-19
Graham, Matthew C. (Department: 3683)
Fluid-pressure and analogous brake systems
Speed-controlled
Torque sensing
C188S18100R, C188S072100, C303S155000
Reexamination Certificate
active
06607253
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosures of Japanese Patent Application Nos. HEI 11-311010 filed on Nov. 11, 1999 and 2000-259842 filed on Aug. 29, 2000 each including the specification, drawings and abstract are incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to braking torque control apparatus and method for controlling the braking toque of a brake.
2. Description of the Related Art
Japanese Patent Application No.11-43041 describes an electrically driven brake that controls the rotation of a wheel by driving an electric motor to press a friction engagement member against a brake rotor that rotates together with the wheel and thus achieving friction engagement therebetween. The patent application also describes a braking torque control apparatus for controlling the braking torque applied to the wheel by controlling the current supplied to the motor of the electrically driven brake. The braking torque control apparatus determines a target braking torque based on an amount of braking operation provided by a driving person. Based on the thus-determined target braking torque and a pre-stored relationship between the current supplied to the electric motor and the braking torque, the braking torque control apparatus determines a current to be supplied to the motor. Then, the control apparatus supplies the thus-determined current to the motor. As for the relationship between the supplied current and the braking torque, a plurality of relationships in accordance with coefficients &mgr; of friction between the friction engagement member and the brake rotor of the electric brake are pre-stored. A friction coefficient &mgr; is estimated based on an actual current supplied to the motor and the actual braking torque. In accordance with the estimated friction coefficient &mgr;, one of the relationships is determined. In accordance with the thus-determined relationship, a current to be supplied is determined. Thus, this braking torque control apparatus is able to control the actual braking torque to a magnitude corresponding to the brake operation.
SUMMARY OF THE INVENTION
A first object of the invention is to ensure that a braking torque control apparatus will provide braking torque corresponding to brake operation, regardless of the magnitude of the coefficient &mgr; of friction between a brake rotor and a friction engagement member. A second object is to allow good performance of brake control in a braking torque control apparatus that feeds back the actual braking torque in order to provide braking torque corresponding to brake operation, even when the braking torque is undetectable at all or cannot be detected with good precision.
In order to achieve aforementioned and other objects, a braking torque control apparatus in accordance with a first aspect of the invention includes a target braking torque determiner that determines a target braking torque based on an amount of brake operation performed by a driving person, an actual braking torque detector that detects an actual braking torque applied to the wheel, and a braking torque-corresponding brake control portion that controls the brake so that the actual braking torque detected by the actual braking torque detector approaches the target braking torque determined by the target braking torque determiner.
In this braking torque control apparatus, the actual braking torque applied to the wheel is detected, and the brake is controlled so that the actual braking torque approaches the target braking torque. Therefore, braking torque can be provided corresponding to brake operation, regardless of the magnitude of the coefficient &mgr; of friction between the brake rotor and the friction engagement member.
The brake described herein is, for example, an electric brake that includes an electric actuator such as an electric motor or the like. In the electric brake, the brake is actuated by the electric actuator pressing the friction engagement member against the brake rotor. The pressing force is controlled by controlling the electric energy supplied to the electric actuator. The brake may also be a hydraulic brake that includes (1) a wheel cylinder, and (2) an electromagnetic control valve device capable of electrically controlling the hydraulic pressure on the wheel cylinder. In the hydraulic brake, the wheel cylinder hydraulic pressure is controlled by control of the electromagnetic control valve device. The electromagnetic control valve device and the wheel cylinder form an electric control actuator. The brake may be a disc brake, a drum brake, etc.
The brake may be a drum brake. The drum brake may include a brake drum that rotates together with the wheel, a pair of shoes disposed inside the brake drum, the shoes being retained to an unrotatable backing plate by an anchor so that the shoes are prevented from rotating together with the break drum, and an actuator that brings an outer peripheral surface of each shoe into a friction engagement with an inner peripheral surface of the brake drum by moving the shoes away from each other. In the drum brake, the actual braking torque detector detects the actual braking torque applied to the wheel, based on a force acting on the anchor.
When the two shoes of the drum brake are expanded or moved away from each other, the outer peripheral surfaces of the shoes come into friction engagement with the inner peripheral surface of the brake drum, so that friction occurs therebetween. This friction force is the braking force. Due to this braking force, rotation of the brake drum is restrained. Furthermore, a force corresponding to the braking force acts on the anchor. Therefore, by detecting the force acting on the anchor and multiplying the detected value by a dimensional value specific to the brake construction, a braking torque can be determined.
The braking force increases with increases in the coefficient &mgr; of friction between the outer peripheral surfaces of the shoes and the inner peripheral surface of the brake drum if the force expanding the two shoes (which is the actuating force of the drum brake) remains unchanged, that is, if the contact surface pressure between the outer, peripheral surfaces of the shoes and the inner peripheral surface of the brake drum remains unchanged. In the drum brake in particular, the braking force is more likely to be affected by the friction coefficient than in the disc brake, due to the servo effect that the friction force acting on the brake shoes of the drum brake increases the contact surface pressure between the brake shoes and the brake drum. The braking force, that is, the braking torque, varies to a considerably great extent even if it is provided by a fixed amount of brake operation. Therefore, if the braking torque-corresponding brake control is performed on the drum brake, the actual braking torque can be provided in good correspondence to the brake operation (target braking torque), regardless of the magnitude of the friction coefficient.
The brake may also be a duo-servo type drum brake. The duo-servo type drum brake includes a brake drum that rotates together with the wheel, a pair of shoes disposed inside the brake drum, the shoes being retained to a backing plate in such a manner that first end portions of the shoes that face each other are engaged with an anchor and the shoes are prevented from rotating together with the brake drum, a strut provided so that the strut interconnects second end portions of the shoes so as to transmit a force acting on one of the shoes to another one of the shoes, and an actuator that brings an outer peripheral surface of each shoe into a friction engagement with an inner peripheral surface of the brake drum by moving the first end portions of the shoes away from each other. In the duo-servo type drum brake, the actual braking torque detector detects the actual braking torque applied to the wheel, based on a force acting on at least one of the anchor and the strut.
If the first end portions of the shoes are expanded or moved away from
Murashima Keiji
Sawada Naoki
Yamamoto Takayuki
Graham Matthew C.
Kenyon & Kenyon
Toyota Jidosha & Kabushiki Kaisha
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