Fluid-pressure and analogous brake systems – Pulsation neutralizers
Reexamination Certificate
2000-04-12
2001-11-27
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Pulsation neutralizers
Reexamination Certificate
active
06322160
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a hydraulic-actuated brake system, especially to a method and an apparatus for damping tactile vibration caused by changes in hydraulic fluid pressure induced in the hydraulic fluid by an operational characteristic of a brake when the brake is being applied to brake a rotating object, such as a wheel of a motor vehicle.
2. Background Information
Hydraulic-actuated brake systems are used extensively as service brakes of motor vehicles. A representative brake system comprises friction brakes at individual wheels. Application of the brakes occurs when the plunger of a brake master cylinder is depressed by a driver of the vehicle pushing on a brake foot pedal. Hydraulic fluid is displaced from the master cylinder to the individual brakes at the individual wheels. The magnitude of hydraulic fluid pressure correlates with the degree to which the brakes are being applied, possibly being amplified by a power brake booster. Generally speaking, the more forcefully the brakes are being applied, the greater the pressure in the hydraulic fluid.
An example of a friction brake mechanism in a motor vehicle is a disc brake where friction pads are pressed against opposite faces of a brake rotor when the brake mechanism is operated by depression of the master cylinder plunger. Because the rotor is turning with the vehicle wheel, the forces applied by the pads to the rotor are effective to brake the rotating wheel, and hence slow the vehicle when the vehicle is moving.
Certain friction brake mechanisms may possess certain operational characteristics that induce pressure changes, or fluctuations, in the hydraulic fluid as they are being operated to apply the brakes. Certain brake-induced pressure changes cause tactile vibration, sometimes referred to as brake roughness or shudder, which may propagate within the vehicle to be sensed by a driver of the vehicle, who may deem the vibration objectionable, even when it has no bearing on the functionality of the brake system or any other vehicle system. For example, vibration may be transmitted to the steering wheel where the driver may feel it through his or her grasp of the steering wheel. Such tactile vibration may manifest itself as torsional vibration. To promote driver satisfaction with a vehicle, it is therefore desirable that a brake system be free of such potential sources of objection, and it is toward that end that the present invention is directed. The invention may also serve to avoid needless warranty and/or repair expenses.
A cause of brake-induced vibration may arise from the nature of the brake mechanism itself. In a motor vehicle that has disc brakes, a cause may be a small divergence of opposite faces of a disc brake rotor from parallelism, even though the respective surfaces of the faces may be perfectly flat. Such divergence creates small differences in the distance between the opposite rotor faces, i.e. rotor thickness, as measured at various locations around the circumference of the rotor. Such differences may replicate a function that is a sinusoidal function of their locations around 360° of the rotor circumference.
When opposing pads of a disc brake are pressed against opposite rotor faces, the small non-parallelism of those faces may induce vibration in the pads that is in turn reflected as pressure fluctuations in the hydraulic fluid. Such fluctuations may be more noticeable when the brakes are being lightly applied, such as to gently slow a moving vehicle, in contrast to more forceful applications, like hard braking for stopping the vehicle. And as observed above, vibration may propagate within the vehicle and be felt by the driver.
As a practical matter, it may not be cost-effective to impose stricter manufacturing tolerances on a disc brake rotor for the purpose of reducing the possible degree of non-parallelism between opposite faces, and consequently it is believed that the present invention may provide a better solution.
A preliminary novelty search developed the following U.S. Pat. Nos.: 3,430,660; 3,757,825; 4,166,655; 5,165,864; 5,410,945; and 5,820,227. Certain of those patents are concerned with avoiding wheel lock-up during hard braking, and none is seen to address the phenomenon with which the present invention is concerned, much less provide a solution for attenuating possibly objectionable brake-induced tactile vibration to levels that are likely not to be deemed objectionable.
SUMMARY OF THE INVENTION
One general aspect of the invention relates to a hydraulic brake system for braking a rotating object. The brake is operated by the displacement of hydraulic fluid from an actuator to the brake, and a damper is associated with a hydraulic line to the brake for damping tactile vibration caused by pressure changes induced in the hydraulic fluid by an operational characteristic of the brake when the brake is braking the rotating object. The damper comprises a housing comprising a bore and a piston that is displaceable within the bore and that divides the bore into a first chamber confronting one axial face of the piston and a second chamber confronting an opposite axial face of the piston. The housing comprises a port that communicates the hydraulic fluid to the first chamber such that increasing hydraulic fluid pressure is effective to displace the piston toward the second chamber. A spring is operated by displacement of the piston within the bore to resist piston displacement toward the second chamber as hydraulic fluid pressure increases and to aid piston displacement toward the first chamber as hydraulic fluid pressure decreases.
Another general aspect of the invention relates to a method for attenuating tactile vibration caused by hydraulic fluid pressure changes induced in a hydraulic brake system by a characteristic of a hydraulic-operated brake when the brake is being actuated to apply brake torque to a rotating object. The method comprises communicating a damper to the hydraulic fluid such that the hydraulic fluid can act on a face of a piston that is displaceable within a bore of the damper, and attenuating the vibration within a frequency range of interest by using a spring to resist piston displacement in one direction within the bore as hydraulic fluid pressure increases and to aid piston displacement in an opposite direction within the bore as hydraulic fluid pressure decreases.
Further aspects will be seen in various features of a presently preferred embodiment of the invention that will be described in detail and in principles of the invention as set forth in various claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawings that will now be briefly described are incorporated herein to illustrate a preferred embodiment of the invention and a best mode presently contemplated for carrying out the invention.
FIG. 1
is a general schematic diagram of a representative motor vehicle hydraulic brake system, including apparatus for practicing principles of the present invention.
FIG. 2
is a longitudinal cross section view through a preferred embodiment of vibration damper associated with the brake system of
FIG. 1
, in accordance with principles of the present invention.
FIG. 3
is a representative graph plot of hydraulic vibration in a brake system that does not practice principles of the present invention.
FIG. 4
is a representative graph plot of hydraulic vibration in the brake system mentioned in
FIG. 3
when principles of the present invention are practiced.
REFERENCES:
patent: 3430660 (1969-03-01), Mitton
patent: 3757825 (1973-09-01), Givens et al.
patent: 4166655 (1979-09-01), Spero
patent: 4203628 (1980-05-01), Ohta et al.
patent: 4998609 (1992-03-01), Nix et al.
patent: 5161864 (1992-11-01), Cardenas et al.
patent: 5320203 (1994-06-01), Wilber et al.
patent: 5390989 (1995-02-01), Kim
patent: 5410945 (1995-05-01), Schops et al.
patent: 5618085 (1997-04-01), Siegel et al.
patent: 5664848 (1997-09-01), Muraski
patent: 5682923 (1997-11-01), Goloff et al.
patent: 5735314 (1998-04-01), Alaze et al.
patent: 5803555 (1998-09-0
Loh Wei-Yi
White Isiah Charles
Zhu Weiping
Brown Gregory P.
Coughlin William J.
Ford Global Technologies Inc.
Nguyen Xuan Lan
Oberleitner Robert J.
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