In anti-lock brake systems, the state of rotation of a vehicle wheel is typically monitored by a sensor. When the sensor detects a tendency of the wheel to be retarded beyond some established limit, i.e., to "lock", the accumulation of hydraulic pressure in the affected wheel brake cylinder is stopped. The pressure is reduced by partial evacuation of the wheel brake cylinder. Once the wheel speed has been reestablished above that for a "locked" wheel, the hydraulic pressure can be reestablished. In order to provide a modulation of hydraulic pressure, a hydraulic fluid pump having pistons or plungers is typically included, with the piston oscillated by means of an eccentric driven, for example, by an electric motor. In the anti-lock brake system art and related bearing art, various arrangements have been provided to create a rotating eccentricity to provide a periodic reciprocating actuation to a hydraulic pump plunger through contact with a bearing surface. However, in order to provide a designed eccentricity, a rotating imbalance occurs. The elimination of the rotating imbalance, while maintaining the eccentric contacting surface, is not addressed in the prior anti-lock brake art, as indicated in the following patents:
U.S. Pat. No. 4,166,657, issued to Blomberg et al., is directed to an anti-lock brake system which generates a relieving force to counter the braking force and shows in FIG. 1 an eccentric 40 driving a plunger 14. However, no mention is made of counterweighting.
U.S. Pat. No. 4,892,363, issued to Burgdorf shows an anti-lock brake system having a double plunger in a hydraulic pump, but no disclosure is made of eccentric modulation or counterweights. Rather, a fail safe system is disclosed in which a return line is connected from the wheel brakes to the suction chamber of a hydraulic pump, with the chamber terminating in a suction line extending from the chamber to a hydraulic fluid reservoir, with a valve or restrictor positioned in the return line upstream of a junction point between the return line and the suction line.
U.S. Pat. No. 4,568,131, issued to Blomberg et al. is directed to a hydraulic brake modulator, but shows in FIG. 2 an eccentric 13 which through a needle bearing 14, eccentric strap 15 and balls 16, 17 causes pistons 11, 12 to oscillate (col. 4, lines 15-21). No mention is made of counterweighting.
U.S. Pat. No. 4,657,120, issued to Farr shows an anti-lock braking system flywheel mechanism which includes an eccentric 40 which drives a plunger 41. No provision for counterweighting is discussed, however.
The use of counterweights to balance designed eccentricities is shown in the following patents:
U.S. Pat. No. 3,946,706, issued to Pailler and directed to two sets of head-to-tail pistons mounted in a star, shows two eccentric equilibrating counterweights 29 and 30 being in one piece with eccentric discs 16 and 17 so as to compensate for the vibratory forces exerted by the discs and their attached devices on a journal 18. Also shown are two eccentric counterweights 31 and 32 which are solid with a shaft 3 to compensate for the vibratory forces exerted on the shaft as a result of the eccentricity of the journal 18 and of the assembly coupled with the journal 18.
U.S. Pat. No. 4,550,571, issued to Bertsch shows a counterweight mounted to the drive shaft of an eccentrically driven piston in a Stirling cryogenic refrigerator.
U.S. Pat. No. 4,524,644, issued to Pierrot and directed to a counterweight for an orbital drive mechanism, shows a counterweight rotatably mounted by means of a bearing on an extension or crank arm formed integrally with an eccentric.
U.S. Pat. No. 4,545,123, issued to Hartmann and directed to a jigsaw adjusting mechanism shows a counterweight adapted to receive an eccentric integrally formed with a drive gear. The counterweight reciprocates in opposition to a plunger assembly.
In order to overcome the difficulties caused by vibrations due to the rotating imbalance of the eccentricity, counterweights which are provided increase the mass and the physical dimensions of the system. To address these shortcomings, the present invention provides counterweight embodiments which reduce system mass and axial dimension and provide more exact location of the counterweight to counter the eccentricity.