GB972373A - Improvements in and relating to a power transmission mechanism - Google Patents

Abstract

972,373. Clutches. SVENSKA ROTOR MASKINER A.B. Oct. 26, 1960 [Oct. 30, 1959; Oct.11, 1960], No. 36747/60. Headings F2C and F2L. In order to completely stop drive through a transmission including a hydrostatic coupling, an hydraulically engaged friction or positive clutch is provided in series with the hydrostatic coupling. In the embodiment of Figs. 2 and 3 the coupling is of the gear pump type and has intermeshing planet pinions 30, 32 revolubly mounted in a casing 16, 17 driven by an engine, and a sun-wheel 24 connectable by a multi-plate clutch 98 to a driven shaft 26 fast with a fan of an engine coolant system. The clutch is engaged by an annular piston 112 on supplying liquid from the high pressure side 36 of the pump to an annular clutch chamber 108 under the control of a valve 68. The valve 68 is biased to the right by a spring 70 and is moved to the left by a solenoid energized by means responsive to the temperature of the engine coolant. With the engine coolant cold the solenoid is energized, moving valve 68 to the left and the clutch chamber 108 is open to the low pressure side 34 of the pump by way of a bearing 25, passage 66, chamber 62 and passages 78, 80, 82, 86, 110 and the clutch remains disengaged so that the fan is stationary. The sun gear 24 rotates freely at almost the same speed as the casing 16, 17 and the planet gears 32, 30 rotate only slightly so that the pressure in the high-pressure chamber 36 is only slightly greater than that in the low-pressure chamber 34. At the required coolant temperature the solenoid is de-energized and valve 68 moves to the right. The high-pressure side 36 of the pump now communicates with the clutch chamber 108 by way of channels 48, 50, 52, 60, 58, 78, 80, 82, 86, 110. The pressure now supplied is sufficient to engage the clutch, thus connecting the sun 24 to the load, accelerating the fan and de-celerating the sun. The pressure in chamber 38 thus increases, increasing the clutch engagement pressure, until it is sufficient to open a relief valve in a by-pass between the high and low pressure chambers 36, 34. When the fan ceases accelerating it will rotate at almost the engine speed, the pump gears 30, 32 only rotating sufficiently to make up leakage. When the speed of the engine increases the power of the fan increases and also the torque transmitted by the clutch. At a speed determined by the, setting of the relief valve, the valve will open and the pump gears 30, 32 begin to rotate. Further increase in the speed of the engine will have little effect on the speed of the fan as there will be progressively greater slip in the hydrostatic coupling. An alternative use for the transmission is in the drive of a compressor. In this case the solenoid of the valve 68 is controlled by means responsive to the temperature or the pressure at the outlet of the compressor. In a modification the valve 68 is controlled directly by a temperature-responsive element. In another application two clutch devices are provided one in the forward and the other in the reverse drive of a machine tool bed. In this case the clutches are controlled by solenoids controlled by limit switches for the bed. Two clutch devices may also be used in the drive of two pumps, one pump maintaining the circulation in a closed system and its clutch device being controlled in accordance with the system temperature, the other being a make-up pump controlled by the pressure. The clutch devices may be used in the drive to the propellers of a marine vessel. In another embodiment, Fig. 9, the sun 24 is selectively connected to driven shafts 222, 224 by clutches 130, 132 under the control, of the valve 68. On disengaging one clutch and engaging the other there will be a difference of speed between the newly-engaged shaft and the casing, and until synchronization has been attained all the slip will occur in the hydrostatic coupling, thus preventing wear in the friction clutches. A clutch device engageable for either direction of rotation is shown in Figs. 10 and 11. For forward rotation the clutch 98 is engaged as in the previous embodiments by liquid from the high-pressure chamber by way of the channel 50 and the valve 68. Valve 68 has a bore 80 with radial bores 82 at one end which can communicate with the clutch engagement chamber 108 and bores 78 at the other end in permanent connection with the channel 50. A permanently acting pump 158 supplies liquid through a line 136 to a chamber 67 thus acting on the right-hand side of the valve 68. To disengage the clutch device a valve 160 is actuated to open the line 136 to an exhaust line 164 so that the pressure in line 136 and chamber 67 drops to a minimum and valve 68 assumes its extreme right-hand position in which channel 50 communicates via a groove in the valve and a channel 134 with the low pressure side of the gear pump. The clutch is thus disengaged. For forward drive valve 160 is moved to a position closing exhaust line 164 and opening line 136 to an exhaust passage controlled by a relief valve 162 which causes the pressure in line 136 and chamber 67 to rise to a value moving valve 68 leftwards to a position closing channel 134 so that high-pressure liquid from channel 50 engages the clutch. For reverse drive valve 160 is moved to a position shutting off both exhaust line 164 and valve 162. The pressure in line 136 is now determined by a relief valve 174 which is set to a higher value than is valve 162, so that valve 68 is moved fully to the left, cutting off communication between passages 80, 82 and the clutch chamber 108 and opening a path from chamber 67 through passages 148, 150 to the clutch chamber so that the clutch is engaged.