Expansible chamber devices – Piston
Reexamination Certificate
2002-04-08
2003-03-04
Look, Edward K. (Department: 3745)
Expansible chamber devices
Piston
C060S533000
Reexamination Certificate
active
06526868
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to pumps in general, and more particularly to improvements in hydraulic pumps of the type known as master cylinders. Such master cylinders are utilized in many types of motor vehicles to actuate clutches and/or brakes.
A master cylinder normally comprises a cylindrical housing, a piston which is reciprocable in and defines with the housing a plenum chamber for a supply of hydraulic fluid, a piston rod or push rod which can receive motion from a pedal or from an actuator to shift the piston from a retracted position to an extended position and to thus pressurize and expel pressurized fluid into the cylinders of the brake system or into the cylinder of the clutch actuating mechanism, and at least one spring serving to cause the piston to reassume its retracted position when the operator of the motor vehicle ceases to depress the brake pedal or the clutch pedal or when the operation of the brake or clutch is interrupted by the actuator which receives signals from the control unit for the power train of the motor vehicle.
Published German patent application Serial No. 197 55 548 discloses a master cylinder wherein the piston is movable axially relative to two spaced-apart sealing rings which are sealingly installed in the housing and sealingly engage the piston. A drawback of such master cylinders is that each actuation can involve, or is likely to involve, the generation of often highly pronounced and highly unpleasant screeching, creaking or squealing noises attributable to the absence of any or adequate films of lubricant between the parts (such as the piston and the sealing rings) which must move relative to each other in response to depression of the brake pedal or clutch pedal. Thus, the adhesion between the surface of the piston and the surface(s) of one or more sealing elements is likely to be sufficiently pronounced to cause the generation of readily detectable noise whenever the operator of the motor vehicle decides to move the piston relative to the housing of the master cylinder or when such decision is rendered by the electronic control unit and effected by the actuator of the prime mover in the motor vehicle.
The generation of the just discussed noise can be avoided, or the intensity of such noise can be reduced, by adequate lubrication, i.e., by the establishment of a satisfactory hydrodynamic film of lubricant between the surface or surfaces of the moving part(s) (such as the piston) and the stationary part(s), such as the housing and/or the sealing element(s) of the master cylinder. It has been ascertained that a master cylinder is likely to generate noise regardless of whether its piston is made of steel, aluminum or a plastic material with or without a metallic or plastic jacket. The generation of noise is attributable to the development of oscillations which can or are likely to be sufficiently pronounced to constitute a cause of discomfort to the operator and other occupant(s) of the motor vehicle.
Attempts to overcome such drawbacks of presently known master cylinders by utilizing special lubricants have met with limited success, partly or mainly because it is difficult or impossible to ensure adequate lubrication during the entire useful life of the master cylinder and/or of the arrangement (such as the brake system or the clutch) which is connected with and is actuated by the master cylinder.
Another drawback of many presently known master cylinders is that they are likely to be vibrated by the parts which receive pressurized fluid from the plenum chamber of the housing. For example, if the master cylinder is installed to actuate the disengaging unit (such as a slave cylinder) for a friction clutch in the power train of a motor vehicle, vibrations of the slave cylinder (such vibrations are normally attributable to vibrations of the internal combustion engine in the power train) are a cause of pulsating changes of fluid pressure in the conduit connecting the slave cylinder with the chamber in the housing of the master cylinder. The fluid (such as oil) in the chamber of the housing causes the piston of the master cylinder to vibrate and to transmit such undesirable movements to the piston rod and thence to the clutch pedal or to the actuator, depending upon the nature of the clutch (i.e., whether the clutch is disengaged in response to actuation of a pedal or in response to signals furnished to the actuator by an electronic control circuit). The just discussed oscillations of the piston rod are a cause of discomfort and/or uncertainty to the operator of the motor vehicle and/or a cause of undesirable stressing of the actuator for the clutch.
A power train wherein the clutch is actuated by a master cylinder by way of a slave cylinder is disclosed, for example, in commonly owned U.S. Pat. No. 5,632,706 granted May 27, 1997 to Kremmling et al. for “MOTOR VEHICLE WITH ELECTRONIC CLUTCH MANAGEMENT SYSTEM”.
OBJECTS OF THE INVENTION
An object of the invention is to provide a single or dual master cylinder which is constructed and assembled in such a way that movements of its piston(s) relative to the housing(s) are less likely to generate pronounced noise (or any noise) than the movements of the piston(s) in conventional master cylinders for use in the power trains of motor vehicles.
Another object of the invention is to provide a master cylinder the operation of which is satisfactory (such as without the generation of any noise or any appreciable noise) during the entire useful life of the master cylinder and/or of the power train in which the master cylinder is put to use.
A further object of the invention is to provide a master cylinder which is constructed and assembled in such a way that it prevents the transmission of undesirable stray movements from one or more controlled parts (such as a slave cylinder) to the part or parts (such as a pedal or an actuator) serving to actuate the master cylinder.
An additional object of the invention is to provide a simple, inexpensive and reliable solution of the afore-discussed problems associated with the utilization of conventional single or dual master cylinders.
Still another object of the invention is to provide a novel housing-piston combination for use in the above outlined master cylinder.
A further object of the invention is to provide a novel and improved housing-seal-piston combination for use in the improved master cylinder.
Another object of the invention is to provide a novel and improved piston-piston rod combination for use in the above outlined master cylinder.
An additional object of the invention is to provide a novel and improved piston for use in the master cylinder.
Still another object of the invention is to provide a novel and improved method of preventing the generation of noise (or pronounced noise) during actuation of a master cylinder in the power train of a motor vehicle.
A further object of the instant invention is to provide a novel and improved method of preventing the transmission of stray movements from a slave cylinder or from a combustion engine to the piston rod or to the actuator which is utilized to initiate the operation of the improved master cylinder.
Another object of the invention is to provide a motor vehicle wherein the power train employs one or more novel and improved master cylinders.
An additional object of the invention is to provide a novel and improved brake system for use in a motor vehicle.
Still another object of the invention is to provide a novel and improved friction clutch assembly for use in a motor vehicle.
A further object of the present invention is to provide novel and improved methods of making pistons for use in master cylinders for the brakes or clutches of motor vehicles.
Another object of the invention is to provide a novel and improved conduit for use in or in conjunction with the above outlined master cylinder.
SUMMARY OF THE INVENTION
One feature of the present invention resides in the provision of a master cylinder which can be utilized in a motor vehicle and comprises a housing, a piston member whic
Adler Dieter
Bertelshofer Thomas
Grell Karl-Ludwig
Helfmeier Ulrich
Peschke Harald
Darby & Darby
Lazo Thomas E.
Look Edward K.
Luk Lamellen und Kupplungsbau Beteiligungs KG
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