Patent GB-1501595-A (GB)
Title: Hydrodynamic-mechanical vehicle transmission
IPC: F16H61/62
Filed: 1976-04-22
Abstract: 1501595 Hydromechanical transmissions VOITH GETRIEBE KG 22 April 1976 [24 April 1975] 16397/76 Heading F2D An hydromechanical transmission for a vehicle such as a lift stacker, levelling tractor or wheel loader, comprises, in series, a controllable friction start-clutch 20; an hydrodynamic torque converter 30 of the counter-rotating type, i.e. in which one or more fixed guide rings 34 change the direction of flow so that the turbine 37 and its shaft 39 rotate in a direction opposite to that of the input impeller 31 during normal drive; and an intermeshed planet reverse gear 40, with a forward direct-drive friction clutch 43 and a reverse friction brake 47, together with a forward-neutral-reverse control 58 which, to brake the vehicle during forward motion, is changed from forward to reverse, thereby reversing the turbine shaft 39 and producing hydrodynamic braking, during which the turbine 37 and impeller 31 rotate in the same direction and the torque applied to the start clutch 20 is sustained by reducing engaging pressure on that clutch to permit slip at a reduced torque which can be adjusted to vary the hydrodynamic brake torque. The Specification states that tests have shown that, at the low turbine speeds such as occur during alternate forward inching and the hydrodynamic braking produced by the reverse control, the torque applied to the impeller of the converter during such braking is approximately constant and of a low value which is within the slip torque capacity of the start clutch. Control.-Both clutches 20, 43 and the brake 47 are hydraulically engaged and the pressure in the start-clutch line 61, 62 can be controlled for clutch release or inching, by a pedal 67 acting, through a spring 65, on a clutch pressure regulating valve 64. Starting from the neutral position O, shown, movement of the forwardneutral-reverse valve 58 to forward V supplies line pressure 51 from a single engine-driven pump 50, through lines 55, 57, to the forward clutch 43; and line 53 to the torque converter 30. At the same time pressure building up in the forward clutch line 57 passes through a shuttle valve 80, restrictor 82 and line 83, including an accumulator 84, to shift left a clutch-control valve 63 to cut off exhaust from and supply line pressure 60, through the clutch regulator valve 64, to the start clutch 20, and the regulator valve 64 is loaded by line pressure 51, supplied through a drive-to-brake changeover valve 74, to act through a piston 68 and load spring 66. The vehicle is now set for forward travel and the start clutch 20 can be disengaged, or slipped for inching, by depression of the clutch pedal 67 to oppose the regulator load spring 66. Hydrodynamic braking and reversing.-Movement of the FNR valve 58 to reverse setting R with the vehicle still moving forward changes line pressure from the forward clutch line 57 to that 56 of the reverse brake 47, which causes a temporary loss of pressure in the clutch-brake feed line 55, line pressure 51 being maintained by virtue of a restrictor 55a. The accumulator 84 discharges to the reverse brake 47 through a one-way valve 85, permitting the clutchcontrol valve 63 to exhaust the start clutch 20, and line pressure 60 to pass through a shuttle valve 87 to shift the changeover valve 74 left exhausting the clutch regulator load line 73. Line pressure, through the restrictor 55a, builds up in the reverse brake 47, engaging the latter and thus reversing the rotation of the turbine shaft 39 to initiate hydrodynamic braking. Brake pressure 56, passing through the shuttle valve 80 and restrictor 82, changes the accumulator 84 and shifts the clutch control valve 63 back to the left, to restore line pressure to the start clutch line 61 and exhaust the line 86 to the change-over valve 74. The reversed rotation of the turbine shaft 39 now, by virtue of a non- return valve 76, causes a pump 75 driven thereby to supply pressure through a line 77 and shuttle valve 87 to the change-over valve 74 to maintain its leftward position exhausting the load line 73 of the clutch regulator valve 64, so that the start clutch 20 has slip engagement only, but of sufficient torque capacity to sustain the relatively low and nearly constant torque imposed by the converter turbine 37 on its impeller 31 during the ensuing hydrodynamic braking, with the turbine and impeller now both rotating in the same direction. This torque, and hence the brake torque, can be preset by an adjusting screw 70, and also controlled during drive by depressing the clutch pedal 67, which, by increasing compression of the spring 65, reduces the pressure 62 regulated by the valve 64, which, in turn, reduces the slip torque of the start clutch 20 and hence the hydrodynamic brake torque. Hydrodynamic braking persists until the vehicle stops, whereupon the turbine shaft 39 ceases to drive the pump 75, permitting the change-over valve 74 to be returned to the right, restoring line-pressure loading to the clutch regulator valve 64, to produce non-slip full engagement of the start clutch 20 resulting in reverse drive of the vehicle. In Fig. 5 (not shown) a torque-splitting sunring-planet train (26) is arranged between the start clutch 20 and the torque converter 30 to provide a mechanical path from its planet carrier to the input carrier 42 of the reverse gear 40 and a fluid path, also to the carrier 42, through the torque converter 30 and a one-way clutch 28, which latter is overrun when, for a wholly mechanical high speed mode, the input impeller 31 of the converter is locked to the stationary guide wheel 34 by an internal brake (35) to overdrive the reverse gear input 42. The brake (35) is arranged in the core of the converter, and is applied by fluid pressure (91) supplied through a valve (92) fed through the valve 74 and actuated by a centrifugal device (93) driven by the reverse gear input 42. A pressure limiting valve (48) maintains torque converter pressure at a constant value below that (91) of the mechanical brake (35), and the mechanical brake (35) is automatically released by the change-over valve 74 during hydrodynamic braking. To assist in maintaining hydrodynamic brake torque at the constant desired value, the sliptorque pressure 62 supplied to the start clutch 20 is further controlled by a pressure comparison valve (94), see also the valve 94, Fig. 6, loaded in one direction by torque-converter pressure 95, supplied, in the braking mode, through a valve 98 which constitutes the clutch regulator loading piston 68 of Fig. 1. The torque-converter pressure 95 is maintained constant by the limit valve (48) and serves as a measure of hydrodynamic brake torque. The comparison valve 94 is loaded in the opposite direction by pressure 97 set by the clutch pressure regulator valve 64, whereby, during hydrodynamic braking, any deviation from the desired brake torque, as set by depression of the clutch pedal 67, or by the screw adjuster 70, is sensed by the comparison valve 94 and applied to the clutch line 62 to set the slip torque to the value for the desired brake torque. In Fig. 6, the pressure control arrangement of Fig. 5 (not shown), is modified to provide more precise positioning of the vehicle by using clutch pedal depression to reduce clutch slip torque and accelerator pedal depression to increase it, both during forward inching and hydrodynamic braking. The comparison valve 94 is loaded in one direction through a shuttle valve 103, alternatively through either of two lines, one, 100, by-passing the clutch regulator loading valve 98, the other, 95a, passing through that valve in its relaxed, braking, position, shown, both lines being fed with torqueconverter pressure 95 through a regulator valve 105 loaded by the accelerator pedal in the sense of decreasing regulated pressure 95a with increase in accelerator depression. During forward drive, line pressure 73 from the changeover valve 74, Fig. 1, shifts the valve-piston 98 left to cut off the shuttle-valve line 96a and load the main clutch regulator valve spring 66 for full non-slip clutch engagement. Depression of the clutch pedal 67 completes the by-pass line 100 whereby further clutch pedal depression reduces clutch pressure and accelerator depression increases it to control inching slip. During hydrodynamic braking the change-over valve 74, Fig. 1, exhausts the line 73 allowing the valve-piston 98 to relax the regulator loading spring 66, producing slip in the clutch 20 which is reduced by further depression of the clutch pedal and increased by accelerator depression, for corresponding reduction and increase of brake torque. In Fig. 9 (not shown), the clutch pedal 67 of Fig. 1 is replaced by a brake pedal (110) initial depression of which, through a valve (111) supplies pressure (113) to shift the forwardneutral-reverse valve 58 to the reverse position for hydrodynamic braking, and also to shift a change-over valve (117) which transfers line pressure from a small area (115) of the clutch regulator valve (64a) for use during non-slip forward drive, to a larger area (116) to reduce clutch pressure to the slip range for hydrodynamic braking, and the magnitude of the slip pressure is reduced by further depression of the brake pedal. This embodiment may provide for hydrodynamic braking in both directions of travel by means not further described. The control may alternatively be electro-hydraulic.