Patent GB-492416-A (GB)
Title: Improvements in or relating to power units
IPC: F16H3/089
Filed: 1937-08-20
Abstract: 492,416. Fluid-pressure servomotorcontrol systems ; variable-speed gearing; hydraulic clutches. SULZER FRERES SOC. ANON. Aug. 20, 1937, No. 22873. Convention date, Aug. 27, 1936. [Classes 69 (ii) and 135] [Also in Group XXIV] A power unit comprises an engine driving through a clutch wherein the torque exerted by the driving member is the same as that exerted on the driven member and in which slip occurs at least temporarily, for instance under starting conditions, a device automatically controlled in accordance with engine speed and controlling the supply of working medium to the engine, and a clutch regulator coupled to the said device so as to be moved thereby to control the engagement of the clutch in accordance with the engine load. In the arrangement shown in Fig. 1, an internalcombustion engine, driving a vehicle through a three-speed gear 5, is provided with a governor 2 which, through a rod 34, controls the delivery of the fuel pumps 3. The various gears are brought in through hydraulically-operated friction clutches 12, 13, 14, the supply of pressure fluid thereto from a pipe 38 being controlled by electromagnetically-operated cocks 15, 16, 17 controlled by a selector switch 19. In the neutral position O of the switch, an electromagnetically-operated cock 23 is moved to the position shown so as to connect the delivery pipe 37 of a pump 17<1> to a pipe 25 which is connected to the pipe 38 through a piston valve 26 actuated by the rod 34. At this time, the engine is running unloaded and the rod 34 occupies its left-hand position, in which the valve 26 permits communication between the pipes 25 and 38. On moving the switch 19 to starting position A, the magnet operating the cock 23 remains energized and the cock 15 is opened. Due to a restriction 27 in the pipe 38, the low gear clutch 12 thus engages gradually, the engine load increases, and the rod 34 moves to the right until, when it reaches the position shown, corresponding to the maximum permissible engine torque, the supply to the pipe 38 is cut off. The clutch 12 may have a slight leak, so that a slight flow through the valve 26 occurs in order to maintain the clutch pressure ; or, as shown, a branch 31 from the pipe 38 may be put into communication with a vent 45 if the rod 34 tends to move to the right beyond the position shown. When clutch slip ceases, the engine load decreases and the rod 34 moves to the left, permitting complete engagement of the clutch. The switch 19 may now be moved to position I, corresponding to normal travel in low gear, causing the cock 23 to cut off communication between the pipes 25 and 37 and to put the latter into direct connection with pipe 38 through a pipe 32. The driver may now increase the engine speed and move the switch 19 successively to positions II and III for normal travel in second and third gears respectively. A pressure accumulator 50 may be provided on pipe 38. The vent 45 may be controlled by a cock coupled to the cock 23 so as to be closed during normal travel ; or a spring-loaded bell-crank lever 52 may coact with a shoulder on the rod 34 so that, during normal travel, the pipe 31 cannot communicate with the vent 45, whereas, during starting, the lever 52 is moved by an electromagnet 51 so as to allow an extended travel of the rod 34. In a modified arrangement, the pump 171 delivers direct into the pipe 38, the delivery pressure being controlled by a relief valve. During starting, air pressure controlled by the valve 26 opposes the spring loading of the relief valve as the engine load increases, so as to maintain a clutch pressure corresponding to the limiting engine load, while during normal travel the opposing air pressure is cut off and air pressure may augment the spring loading. As shown in Fig. 3, a spring-engaged main friction clutch, arranged between the engine and a gear box, is disengaged by supplying compressed air to a servo 75. This is effected by depressing a handle 80, which, through a spring 81, piston 82, piston valve 83, and diaphragm 84, opens a valve 85 to supply compressed air from a source 60 to a pipe 91 leading to the servo. On releasing the handle 80, valve 85 closes and the pressure beneath the diaphragm raises the valve 83 to put the pipe 91 into communication with a vent 92 so as to allow the clutch to engage. During starting, however, a manual switch 77 is closed to open a cock 79. As the engine load increases, the valve 64 operated by the rod 34 allows compressed air to pass from the source 60 to the chamber above the piston 82, causing valve 83 to close when the limiting engine load is reached. When slip ceases, engine load decreases and the pressure above the piston 82 is dissipated through a leak 93, whereby the clutch is completely engaged. The electrodynamic clutch shown in Fig. 4, wherein the field member 96 rotates with the engine and the armature 97 drives the changespeed gear, is disengaged by opening a switch 98 in the field circuit. A cock 99 coupled to the switch is thus turned so that pressure fluid flows from a supply pipe 100 and through a port 107, which at this time is opened by a valve 103 connected to the rod 34, into a servo 105, the piston of which is thus moved against a spring so as to throw the whole of a resistance 106 into the armature circuit. To engage the clutch, switch 98 is closed. The servo is now vented through a passage 104 and the piston moves so as gradually to cut out the resistance 106. As the engine load reaches the limiting value, valve 103 closes the port 107 and the servo piston is arrested. During starting, a cock 108 is opened so that pressure fluid enters the servo if the valve 103 tends to move too far to the right. When slip ceases, the whole of the resistance 106 has been cut out, and cock 108 is now closed. Alternatively, the clutch may be of electromagnetic friction type. In a hydraulic clutch of the pump type, a throttling valve in the pump circuit is operated by a fluid-pressure servo to which fluid is supplied to disengage the clutch, and the venting of which, so as to produce engagement, is controlled by a valve connected to the rod 34. In addition, the throw of the pump plungers may be varied. The Specification as open to inspection under Sect. 91, states also that the clutch may be controlled directly in accordance with the engine load, for instance in accordance with the torsional twist of a shaft through which the power is transmitted. This subjectmatter does not appear in the Specification as accepted.