Patent GB-1328722-A (GB)
Title: Hydrodynamic converter coupling or brake
IPC: F16H41/04
Filed: 1971-04-30
Abstract: 1328722 Change-speed gear; hydrodynamic torque converters and couplings; hydrodynamic brakes; cooling VOITH GETRIEBE KG 30 April 1971 [2 May 1970] 12468/71 Headings F2C F2D and F2E On a motor-vehicle, an hydrodynamic powertransmitting torque-converter 3, or coupling, or power-absorbing brake, Fig. 3, comprises first and second bladed wheels one of which may rotate, or in a brake only, may be stationary, whilst the other, for hydrodynamic braking of an output shaft 6 can be optionally coupled to that shaft by fluid-pressure-engaged means comprising a stepped piston 36, a smaller step 38 of which receives pressure from an auxiliary pump 25, to produce immediate moderate brake response, whilst a larger step 37 receives pressure which builds up from an initial low or negative value at the highest pressure discharge zone 21 of the toroidal working circuit, such discharge pressure being itself a measure of the hydrodynamic brake torque, whereby the piston load automatically adjusts to brake torque and is independent of speed. Fig. 1 shows a split-torque torque-converter drive between an engine 1 and road-wheels 6a, combined with a forward-reverse planet gear 4, 5 in the fluid path only, the reverse train providing the coupling between the torque-converter turbine 10 and output 6 for hydrodynamic braking as above referred to. The engine drives a ring gear 2a of the torque-split train, the carrier of which is fast on the final output shaft 6 for the mechanical path, whilst the sun 2c drives through the converter impeller 10, turbine 16 and forward-reverse gear 4, 5, as the fluid path to the torque-combining point 22 on the output shaft 6. The reactor vanes 15 are in the permanently fixed casing to which the impeller 10 can be braked at 11, 12 by fluid pressure applied through an output-speed-responsive solenoid valve 40 to a piston 13 for cutting out the fluid path and providing reaction for a fixed reduction ratio wholly mechanical drive for normal travel at the higher speeds. At this time also a valve 29 is operated to supply converter discharge pressure to a regulator valve 28 (see below) which produces minimum pressure in the toroidal circuit of the converter. The torque converter is of the type in which an axial flow turbine 16 rotates at very high speed and normally reversely of the impeller 10. The turbine 16 drives the sun 4c of the trains 4, 5, the carriers of which are fast to output 6, the first ring 4a being fast to the second sun 5c. Braking the first ring 4a at 23 provides reduced forward drive in the train 4 alone, whilst braking the second ring 5a at 32 provides a compounded reduced reverse. Hydrodynamic braking is normally initiated whilst travelling in the upper speed range with fixed ratio wholly mechanical drive, fixed impeller and minimum torque converter pressure at 21. For such braking the reverse brake 32 is applied by the stepped piston 36 to couple the turbine at a negative step-down ratio to output 6, by movement of a manual switch 44 to a position I for first stage braking, which energizes two solenoid valves 30, 31. The latter 31 directs pump pressure 25 to the smaller piston step 38 for immediate moderate braking response. The valve 30 feeds converter discharge pressure 21 to the larger piston step 37, the pressure level being at a first stage, as determined by the regulator valve 28, loaded by an initially lightly compressed spring 41 opposing delivery pressure supplied through the valve 29, this pressure building up to a high value as brake torque increases, so that loading on the piston 36 automatically increases with brake torque. For a second stage, more powerful braking, the brake switch is moved to setting II, where it additionally feeds a switch 46 which is opened in response to converter pressure 21 to control energization of a solenoid valve 43, applying pump pressure 25 to a piston 42, compressing the regulator-valve loading-spring 41, the action being a pulsing one as follows. With the switch 46 closed the rapid-response solenoid valve 43 is open, to apply pump pressure to the piston 42, thus increasing converter discharge pressure 21, which opens the switch 46, to close the solenoid valve 43 reducing converter pressure 21. This cycle repeats at a frequency of 10 to 30 Hz to establish a mean converter pressure 21 determined by the setting of the pressure switch 46. A third stage III of the brake switch 44 acts similarly on a second pressure switch 47, whilst a fourth stage IV opens the solenoid valve 43 fully. A limit valve 27 limits system pressure, and to avoid the consequent negative pressure that would otherwise be produced at the inlet 20 of the converter during braking, air is allowed to be drawn into the toroidal circuit either by a oneway flap valve 35 or by seals 18, 19 closing the feed circuit. By these means brake torque is maintained constant independent of speed. In Fig. 2, not shown, the pulse loading of the regulator valve spring 41 is replaced by steplessly-variable electromagnetic direct-loading of a regulator valve (53) replacing 43. In Fig. 3 a two element fluid coupling 57 is used as a brake only, one bladed element 58 being permanently fixed, whilst the other 59 is clutched to the vehicle output shaft 56, to be braked, by applying a brake 70, to station a ring gear 63 of a planet train of which the carrier 62 is the output shaft 56 and the sun 61 is fast to the bladed wheel 57. The brake 70, which is applied to produce hydrodynamic braking, is actuated, as above described by a stepped piston 66, the smaller step 68 of which receives pumped pressure to initiate braking, whilst the larger step 67 receives pressure from the hydrodynamic working circuit 57 at 83, through a solenoid valve 90 to provide torque-responsive loading of the piston. An auxiliary pump 75, driven by the output shaft 56, feeds the small piston step 68 through a solenoid valve 91, and also the working fluid circuit 57, the latter through a pressure-limit valve 78, non-return valve 79 cooler 76 and on-off solenoid valve 81. A controllable pressure regulating valve 88 is provided between the working circuit 57 and the large piston step 67 for adjusting brake torque, and a second discharge outlet 84 from the working circuit feeds through a non-return valve 86 and cooler 76 back to the working circuit at 82 for a closed cooling circuit. Initially the coupling 57 is empty and braking is initiated by energizing the solenoid valves 81, 90, 91, filling the working fluid circuit 57, and applying pumped pressure to the small piston step 68 of the clutch 70. Pressure building up in the working circuit 57 is subsequently applied to the large piston step 67 at a value set for the required brake torque by applying variable magnetic loading, manually controllable at 54, to the pressure-regulating valve 88. The coupling-fill valve 81 could be dispensed with, if emptying the working circuit 57 during non-operation is not required.