Patent GB-1426182-A (GB)
Title: Control system for hydrodynamic torque converter transmission
IPC: F16H47/08
Filed: 1972-02-07
Abstract: 1426182 Change speed control S R M HYDROMEKANIK AB 7 Feb 1973 [7 Feb 1972] 5486/72 Heading F2D The mode of operation of an hydrodynamic torque converter transmission on a motor vehicle (e.g. by lock-up and reactor brake control) is controlled by means comprising an input-driven pump delivering to an outputdriven pump through a passage in which the pressure is dependent on the relative flow and hence speeds of the pumps, and produces a shift signal operating shift means to change the said mode. In the arrangement shown, the torque converter C drives through a threeelement planet gear, and there are two shift points, each controlled by separate input and output pumps 8, 10 and 12, 14 respectively, connected through separate lines 16, 18 producing the respective shift signals when the pressure in them zeroises. Converter and gear system.-The control may be applied to that of a simple converter lock-up clutch, but as shown, it controls what is known as the SRM type DS transmission, which is one in which, in a first speed range, the reactor of a three-element hydrodynamic torque converter C rotates reversely in a " double rotation " phase to drive a sun gear of a three-element planet train, the carrier of which is held by a brake 6, whilst the output ring gear, permanently connected to the main turbine, receives the additional torque of the reversely rotating reactor. In a second speed range the carrier brake 6 is released and a brake 4 applied to the reactor so that the overall transmission now acts in a " single rotation " phase as a simple three-element torque converter. In third range both brakes are released and a converter lock-up clutch is engaged for one-to-one mechanical drive. The signal pumps 8, 12, above referred to, determine the first shift point, and 10, 14 the second. Pressure supply.-An input driven low pressure pump E co-operates with an input driven high pressure pump F to supply liquid pressure to a servo-feed line 34 and to the shift signal pumps 8, 10 which are driven by the pump E. A compressed air system supplies a manual FNR valve A and a valve B linked to the engine throttle, for air pressure control of valves 60, 72, 74, 78, controlling start, kickdown, and vehicle braking as described below. Control operation. Start.-Initially, with the engine idling and the output stationary, movement of the driver's valve A into a F or R drive setting, and opening the engine throttle causes air operation of valves 72, 74 respectively, providing a series path for line pressure 34 through a line 70 to act at 68 leftwards on a 2-3 shift valve 2 which then directs line pressure to act on one side of the converter impeller to clutch it to its driving housing ready to drive the vehicle. Initially the output driven shift signal pumps 12, 14 cannot accept the delivery of their corresponding input pump 8, 10, so that pressure builds up in the respective communicating lines 16. 18, to cause depression of spring loaded pilot valves 26, 24 respectively, exhausting line 38, 52 and permitting springs to centralize a 1-2 shift valve 42, in which position the latter pressurizes a line 46 applying the carrier brake 6 for first speed range, in which the vehicle now accelerates. 1-2 Upshift.-At an output-input speed ratio of 0À22 the capacities of the input and output signal pumps 10, 14 equalize, zeroizing pressure in the line 18, which permits a spring to raise the pilot valve 24 to supply line pressure 34 through line 38 to shift the 1-2 valve 42 left through a first step, which exhausts the carrier brake 6 and pressurizes the reactor brake 4, producing upshift to second range. 2-3 Upshift.-At a higher speed ratio, corresponding to that in which the tractive effort in hydraulic drive is the same as that what it would be in mechanical drive, the capacities of signal pumps 8, 12 equalize, zeroizing line 16, to permit spring return of the pilot valve 26, which pressurizes a line 62 acting at 67 to move the 2-3 valve 2 right, pressurizing a line 96 which acts on the right face of the impeller to disconnect it from its driving housing and engage the lock-up clutch for direct oneto-one mechanical drive in third stage. The same pressure 62, 62A also shifts the 1-2 valve 42 a second step leftwards to exhaust the reactor brake 4. The 2-3 shift pressure is supplied to the line 62 from the pilot valve 26 under the following supervisory control. Shift pressure 52 from the pilot valve 26 has access to a line 58 through an output driven two-stage centrifugal valve 54 (which also drives the signal pumps 12, 14) which opens the communication only above a predetermined vehicle speed, reached at a first step below which lock-up is inhibited by the valve 54. Pressure from the line 58 is supplied to the final shift valve line 62 through a kick-down valve 60 which is closed, to prevent upshift, by air pressure from the throttle actuated valve B in kick-down position. At a higher speed the centrifugal valve 54 reaches a second step, whereupon it communicates the line 52 with the kickdown valve 60 through a second line, so that direct-drive is maintained independently of the position of the kick-down valve 60. In addition the throttle-actuated valve B supplies a variable air pressure to control the load on a piston at the top of the valve 54 opposing the centrifugal load on that valve. The speeds at which the first and second steps of the valve are reacted are thus raised by increasing the engine throttle opening. Downshifts.-Although the 2-1 downshift can be controlled by the shift signal pumps 10,14, since drive is hydraulic in both first and second stages, the 3-2 downshift cannot be so controlled since the relative speed of the signal pump 8, 12 is invariable in direct mechanical drive. A 3-2 downshift is achieved by the centrifugal valve returning to its first step to blank the shift line 58 or, between the first and second steps by kick-down causing the valve 60 to break the shift line 58 to 62. Downshift lysteresis is provided by release valves 28, 30 in the signal pressure lines 16, 18, which valves are loaded closed at higher pressures but open at lower pressures. Also shown, but not described, are a valve 78 actuated by the vehicle hydraulic braking system to apply the planet gear reaction brake 6 during direct drive, for braking the vehicle; a blocking device for the FNR control A; a heat exchanger D; and pressure-limit valves 80, 82, controlling converter working pressure. In Fig. 2, not shown, the torque converter is of the single rotation type, and a one-way planet-carrier brake replaces the brake 6 of Fig. 1. Only one servo feed pump is used and the brake valve 78 is eliminated.