GB1185354A - Fluid Pressure Brake Systems - Google Patents

Abstract

1,185,354. Fluid pressure brakes; valves. NORTH AMERICAN ROCKWELL CORP. 4 May, 1967 [15 June, 1966], No. 20757/67. Headings F2F and F2V. [Also in Division G3] In a vehicle brake system having selectively operable fluid pressure actuated front and rear brakes 22, 24 and 36,38, signal generating means in the form of transducers 44, 46, 48, 50 produce separate signals indicative of the rotational speeds of the front and rear wheel sets of the vehicle, discriminator means 56 for comparing the signals and detecting a difference therebetween, and control means in the form of a pulser responsive to a detected difference between the signals for maintaining the brakes associated with the front wheel set actuated but with reduced fluid pressure independently of the fluid pressure applied to the brakes of the rear wheel set when the brakes are operated. As shown in Fig. 1, the brakes are hydraulically applied by means of a master cylinder 10 which supplies fluid via conduits 12 and 16 to the front wheel brake cylinders 18 and 20 and to the rear wheel brake cylinders 32, 34 via conduit 26, pulser unit 64 and conduits 27 and 30. The pulser unit includes a valve to control fluid communication between the source and the rear brakes. The transducers 44 and 46 are respectively connected to rectifiers or detectors 52 and 54 to supply at their outputs two continuous direct-current voltage levels which are proportional to the tangential or rotational velocities of the front wheels 22 and 24. The output signals of the detectors 52 and 54 are fed to the input of an adder circuit 55 and fed to the discriminator 56. The alternating current voltage signals generated by the transducers are rectified by the detectors 52 and 54. The transducers 48 and 50 associated with the rear wheels are connected to detectors 58 and 60, the output signals of which are fed to the input of an adder circuit 61 and fed to the discriminator 56. The arrangement is such that the discriminator 56 produces an output signal only if the input voltage signals are of unequal value, such as occurs when rear wheel locking takes place. The output signal of the discriminator 56 is fed through an amplifier 62 to a pilot relay 210 which controls a pulser relay 63 to activate the pulser 64 to periodically and repeatedly interrupt fluid communication between the conduits 26 and 27 leading to the rear wheel brakes so that these brakes will be repeatedly released and reapplied by the activating pulser 64 so that the wheels tend to resume their normal rotational speed. When this occurs the negative levels of signals fed to the discriminator 56 by detectors 58 and 60 will become substantially equal to the positive voltage levels of the signals fed into the discriminator from detectors 52 and 54. The output signal of the discriminator 56 will thus be reduced to zero and de-energize the relay 63 to consequently deactivate the pulser 64 and permit the cylinders 32 and 34 to operate the rear wheel brakes 36 and 38 in the normal manner. Fig. 6 shows the circuitry associated with the transducers 44, 46, 48 and 50, the signals produced therein being fed through the detector circuits 52, 54, 58, 60, to supply opposed voltage signals to terminals 175a and 175b of the discriminator 56. The voltage signal on the slider 208 will be zero whenever the sum of the voltage signals on the sliders 164 and 164a is equal and opposite in sign to the sum of the voltage signals on the sliders 164b and 164c. This condition will exist when the rear wheels 36 and 38 have the same tangential rotational velocity as the front wheels 22 and 24. As soon as one or both of the rear wheels 36 and 28 begins to rotate slower with a corresponding decrease in the rotational velocity of either or both of the front wheels 22 and 24, the positive voltage signal applied at the terminal 175b will be correspondingly greater in absolute magnitude than the voltage applied to terminal 175a. The resulting voltage signal will be impressed on the slider 208 and fed to the amplifier 62 and thence through a branch circuit containing a forwardly directed diode 209 and an operating winding 211 of the pilot relay 210 to cause energization of the pulser relay 63 which activates the pulser 64 in the manner described above. A Zener diode 216 is shunted across the winding 211 to prevent damage in case of high-voltage generation. Pulser unit construction.-Fig. 9 shows the construction of the pulser unit 64 which consists of a reciprocating plunger 316 in a bore 318 provided in the pulser 64, the reciprocal movement of the plunger 316 being achieved by rotation of a cam 312 driven by gearing 308, 306 from an electric motor 302. When the pilot relay 210 is energized a switch 212 is closed to allow current to flow from a battery 214 and energize the winding 384 of the pulser relay 63 to close a switch 386 for energizing the motor 302. Simultaneously a circuit is completed through a second terminal 390 to energize a coil 356. As the cam 312 rotates it bears down upon a plate 314 to urge it and the plunger 316 in a downward direction against the bias exerted by a spring 320. This relieves a latch member 364 and a spring 363 is compressed as a plunger 358 is displaced to the left by energization of the coil 356 to swing the latch member 364 to the left to allow reciprocal operation of the plunger 316. Downward movement of the plunger 316 opens a valve member 328 to place a chamber 336 in communication with a chamber 334 thus allowing communication between the conduits 26 and 27. As the plunger 316 rises the valve is closed closing communication between the conduits 26 and 27. In this way the fluid pressure in the conduit 27 is pulsated to reduce the effective braking torque applied to the rear wheels to allow the latter to regain speed until the summation of their rotational speeds equals the summation of the rotational speeds of the front wheels. Fig. 2 shows an alternative arrangement for a tractor trailer vehicle supplied with a conventional compressed-air braking system. A separate pulser circuit being provided in the trailer braking system to control the supply of compressed air to the trailer brakes to avoid locking of the trailer brakes and locking of the rear wheel brakes of the tractor. The pulser units 64a and 114 in the tractor-trailer braking system shown in Fig. 2 takes the form of a solenoid operated three-way air valve which normally supplies fluid communication between the conduits 26 and 27 or 86 and 87 but opens the valve to exhaust when wheel locking occurs.