Viscous fluid shear clutches and control valves therefor

Abstract: In a viscous fluid shear clutch, the value (36) regulating flow from the reservoir (22) to the working chamber is controlled by an actuator (44) responding to a separate thermal sensor (82). (Figs 5a, 5b not shown). The valve (36) may also be influenced by speed, and a spring (42). The pump (25) for feeding the reservoir may comprise a scoop (26) in one housing part (15) indexable relative to another housing part (14) according to the direction of rotation.

Description: This invention relates to viscous fluid shear clutches and control valves for use in such clutches. There are many known forms of viscous fluid clutch for providing drive between an engine and a cooling fan which incorporate arrangements which sense the coolant air temperature and/or the output speed of the clutch and modulate the degree of coupling between the input and output accordingly. However, many systems experience severe hysteresis which means that, in practice, the coolant is either overcooled - representing a needless waste of engine power - or undercooled - leading to possible engine damage. EP-A-274408 discloses a viscous fluid clutch including a casing, an inner rotor, a fluid reservoir, and a scoop pump pumping fluid between the gap and the reservoir. A valve controls the amount of fluid in the clearance gap between the casing and the rotor to modulate the torque transmitted by the coupling. The valve control member is acted upon by a temperature-dependent force and an opposed speed-dependent force derived from the scoop pump, whereby an increase in temperature or a decrease in the speed tends to increase the amount of fluid in the gap and the torque transmitted. A need exists for an arrangement which allows continuous modulation of fan speed versus coolant temperature across substantially the whole operating temperature range. A need exists for a viscous fluid clutch in which the modulation of the drive to the fan is performed with less hysteresis, thus providing improved engine efficiency. Most known forms of viscous fluid shear clutch employ a scoop pump arrangement in which the scoops face an axial end face of the inner clutch member - so called "side scoop" arrangements. Such arrangements require careful and precise alignment of the scoop and the opposing working face of the clutch member and this can be difficult to achieve and time consuming because of- axial float of the shaft. Thus the lowest clearances possible between the scoop and the clutch member still leave significant leakage paths which reduce the efficiency of the scoop pumps. Also, in such arrangements even when the clutch is drained there is still a significant degree of coupling because the scoops are on the side of the clutch member. A need exists for a viscous fluid shear clutch incorporating a pumping arrangement which provides good pumping efficiency, may be assembled easily, and which allows the clearance gap between the drive members to be substantially "dry". A need also exists for a viscous fluid shear clutch which can be assembled for either clockwise or anticlockwise rotation with little or no modification necessary to the component parts. A need also exists for a viscous fluid shear clutch in which the clutch provides full coupling if the temperature signal is lost. Accordingly, this invention provides a viscous fluid shear clutch in accordance with claim 1. Preferably, said thermal sensor means is arranged to provide a temperature dependent force which decreases with an increase in temperature, thereby to provide a failsafe feature. Preferably, said pump means is constituted by a generally plain circumferential wall portion of said inner clutch member and at least one circumferentially extending scoop of limited arcuate extent provided in an opposed cylindrical wall of the casing, each scoop having associated therewith a scoop pump outlet passage arranged adjacent the end region of the scoop which trails in the sense of rotation of the scoop relative to the inner clutch member. To allow assembly for rotation in either sense, said rotary casing preferably includes one part defining at least a major portion of each scoop and another part defining at least a major portion of each scoop pump outlet passage, the two parts being capable of being assembled in either one of two relative angular positions whereby each scoop pump outlet passage can be located at either end region of the associated scoop depending on the intended sense of rotation of the clutch. The thermal sensor means may include: a thermo pressure valve having a valve body defining an inlet for servo fluid, an outlet for connection to said actuator, and a vent, shuttle spool means linearly movable within said body between a first position, which allows communication between said inlet and said outlet, and a second position which allows communication between said outlet and said vent, and a sensor element responsive to the sensed temperature for moving said shuttle spool means. The shuttle spool means preferably isolates both said inlet and said vent from said outlet when it is in an intermediate position. The shuttle spool means is preferably provided at spaced regions with seal surface means engageable in resilient sealing manner with respective valve seats in said valve body and the spacing between said seal surface means may be set as required. Each seal surface means may comprise a resilient 'O' ring. Preferably movement of said shuttle spool means away from said intermediate position causes resilient compression of one of said '0' rings against its valve seat and lifting of the other '0' ring from its valve seat. The invention may be performed in various ways and certain embodiments thereof will now be described by way of example only, reference being made to the accompanying drawings, in which:- Figure 1 is a cranked sectional view through a viscous fluid shear clutch in accordance with this invention; Figures 2a and 2b are transverse sectional views on lines II-II of the clutch of Figure 1, showing the clutch when configured for clockwise rotation of the inner clutch member and anticlockwise rotation thereof, respectively; Figure 3 is an end view on the rear housing of the clutch taken in the direction of arrows III-III of Figure 1; Figure 4 is a detail view of a modified control arrangements for a clutch of the general type illustrated in Figure 1, Figures 5a and 5b are section views of two examples of thermal pressure valve for supplying a temperature dependant pressure signal to the actuator of the clutch of Figure 1, and Figure 6 is a schematic view of a dual temperature thermal pressure valve system for supplying a pressure signal to a viscous fluid shear clutch. Referring to Figures 1 to 3, the invention is applied to a viscous fluid clutch of the general type including an internal clutch member or rotor 10 connected to and driven by a coupling 12 attached to an engine shaft (not shown). The rotor is positioned within a two part casing having a front part 14 and a rear part 15. A bearing 16 supports the rear part of the casing off the coupling 12 or shaft. In this example, the casing includes threaded studs 17 which support the blades of a fan (not shown). The rotor 10 has a series of closely spaced annular rings 18 respectively located in a series of grooves 20 in the front and rear parts 14 and 15 of the casing to define a labyrinthine clearance gap of considerably extended area across which torque may be transmitted by viscous shear forces. The amount of torque transmitted may be increased or decreased by increasing (filling) or decreasing (draining) the amount of viscous hydraulic fluid in the gap. A fluid reservoir 22 is formed between the front casing part 14 and an internal partition wall 24 and fluid is continuously pumped from the clearance gap to the reservoir by diametrically opposed pump arrangements 25. Each pump arrangement 25 comprises an arcuate scoop 25 formed in the rear casing part 15 and spaced closely from the outer circumferential periphery of the internal rotor 10. On rotation of the rotor 10, viscous fluid adjacent each scoop 26 is entrained by the rotor and drawn towards an outlet port 28 in the end of the scoop that trails in the sense of the rotation of the scoop relative to the rotor. Fluid pumped from ports 28 passes to the reservoir 22 via respective radial passages 30. The assembly of the clutch for clockwise and anticlockwise rotation will be discussed below in relation to Figures 2 and 3. Fluid in the reservoir 22 may drain back to the clearance gap via one or more valve openings (one, 32 shown in the drawings) which is opened or closed by a valve blade 34 forming an extension of a control element 36 pivotted at 38 to the partition wall 24. The control element includes an enlarged portion 40 which acts as a bob weight and is disposed relative to the pivot 38 so that the centrifugal force generated on rotation of the casing tends to urge the control element 36 to close the valve opening 32. Closing movement of the control element 36 is resisted by a compression spring 42 located between the control element 36 and the partition wall 24. An actuator in the form of a pressure ram assembly 44 despun from the casing by a bearing 46 includes an axially movable ram 48 provided with a despun button 50 engageable with the control element. The pressure ram assembly 44 is supplied with a pressure signal from a thermal pressure valve of the form illustrated in Figure 5(a) and to be described in detail below. The pressure signal decreases as the sensed temperature increases. In operation, the pump arrangements 25 continually pump fluid from the clearance gap to the reservoir and flow between the reservoir and the gap is controlled dependent on both the engine coolant liquid temperature and the output speed of the clutch - i.e. the rotational speed of the casing 14,15. Both the speed dependent force and the temperature dependent force act in the same sense, tending to move the control element 36 to close the aperture 32 in the partition wall 24, and these forces are opposed by the spring 42. An increase in the sensed temperature reduces the pressure signal applied to the ram assembly, so the control element 36 tends to open the aperture 32, thus increasing fluid in the clearance gap. Likewise, a reduction in the rotation speed of the casing and thus the fan - reduces the centrifugal force opposing the spring 42, so again tending to open the aperture and increase fluid in the gap. An important feature of this arrangement is that if the pressure supply to the pressure ram assembly fails for any reason, the control element 36 will tend to open the aperture thus flooding the clearance gap with fluid to ensure that drive between the fan and the engine is preserved. A further advantage is that the balance of a temperature dependent force against a centrifugally generated speed dependent force provides reduced hysteresis when the sensed temperature falls, because the speed force varies as the square of the speed. Also, the fan speed versus coolant temperature characteristics can be predicted reasonably accurately because the temperature/force characteristic of the thermal pressure valve and the speed/force characteristic of the speed sensor can be predicted mathematically. This leads to a significant improvement of the efficiency of the cooling system because it allows the fan speed to be tied more closely with the coolant temperature (i.e. the cooling requirement) so that the problems of wasting engine energy by overcooling or risking engine damage by overheating are avoided. Referring now to Figures 2a,2b and 3, the casing parts 14,15 of the clutch of Figure 1 are configured so that they can be assembled for engine rotation in either the clockwise sense (Figure 2a) or anticlockwise sense (Figure 2b). For proper operation of the scoop pumps, the pump outlet passages or ports 28 must be in the trailing end of the scoops 26, as mentioned above, and so the layout of the scoops 26 and ports 28 must be changed for rotation in the opposite sense. This is achieved in the present arrangement by providing the scoops 26 in the rear casing part 15 and the outlet port and passages in the front casing part and designing the arcuate extent of the scoops and the gaps therebetween in relation to the pitch of the bolts 43 which secure the casing together so that the "handedness" of the clutch can be switched simply by indexing the front and rear casing parts by one bolt spacing. For ease of assembly during manufacture, the front casing part includes a notch mark 47 and the rear casing part includes the letters 'A' and 'C' which should be lined up with the mark to denote anticlockwise or clockwise rotation respectively. Figure 4 shows an arrangement similar in some aspects to that of Figure 1, and so common reference numerals have been used where appropriate. Figure 4 shows a "closed loop" arrangement in which a thermal pressure valve of the form illustrated in Figure 5b below provides a temperature dependent force which increases with an increase in temperature. The pressure from the assembly is applied via a common yoke assembly 52, to the ends of two rocking control members 54,56, one of which, the master control member 54 has a valve blade 34 cooperating with the aperture 32. Each of the control members has a bob weight portion 52 which centrifugally generates a force which opposes the temperature dependent force applied by the assembly 44. An increase in sensed temperature or a decrease in the speed of the casing tends to adjust the master control member 49 to increase the fluid in the clearance gap. Referring now to Figures 5(a) and 5(b), two forms of thermo pressure valve are illustrated, one (Figure 5a) providing a pressure signal which decreases with an increase in temperature and the other (Figure 5b) providing a pressure signal which increases therewith. The valve of Figure 5(a) comprises a valve body 66 which defines an inlet 68, an outlet 70, and a vent 72. A shuttle spool 74 is mounted in the body and includes at each end region an 'O' ring 75,76 which engages a respective chamfered valve seat 77,78 provided within the valve body. The shuttle spool 74 is made of two parts 71,73 threaded together which allow the spacing between the '0' rings to be adjusted. In use, the valve is adjusted so that, when in the equilibrium or intermediate position of the shuttle spool 74, both '0' rings seal against their valve seats so that there is no communication between any of the inlet 68, outlet 70 and vent 72. Shifting of the shuttle spool 74 to the left, as viewed in Figure 5a,will compress the '0' ring seal 76 against the valve seat 78, thus maintaining the seal between the inlet 68 and the outlet 70, whilst at the same time lifting the '0' ring 75 off the valve gear 77 so allowing flow between the outlet 70 and the vent 72. Likewise, rightward shifting of the shuttle spool 74 allows flow between the inlet 68 and the outlet 70, whilst preventing flow between the outlet 70 and the vent 72. At one end, the shuttle spool 74 is connected via a spring to the actuator rod 80 of a thermal sensor 82 such as a wax capsule, which senses the temperature of the engine coolant. The temperature/pressure characteristics of the thermo valve can be biassed by turning an adjustable cap 34 which applies an adjustable biass force via a spring 86 to the left hand end of the shuttle spool 74. The valve of Figure 5(b) operates in the reverse sense, i.e. the output pressure increases with sensed temperature, but the components are similar in form and have been given common reference numbers. In this arrangement biass adjustment may be effected by turning the thermal sensor housing 88. Apart from at lower temperatures of the operating range, both valves modulate the pressure substantially linearly with sensed temperature. Figure 6 shows schematically a dual temperature thermal pressure valve system which responds to two different temperatures. In the example shown, the valve responds both to the intercooler temperature and to the engine coolant temperature. Both temperatures are sensed by thermopressure valves 90,92 respectively of the form shown in Figure 5(b) - i.e. which provide an increase in the output pressure as the sensed temperature increases. The temperature modulated pressure signals are supplied to a combiner valve 94 which comprises a body 96 defining left-hand, central and right hand chambers 97,98,99, respectively. The central chamber 98 includes a shuttle spool 100 with the two 'O' rings 101,102 which seal against valve seats 103,104 in the valve body when the shuttle spool is in an intermediate position. Each of the other chambers includes a piston 106 having a push rod for engaging the shuttle valve 100. The output pressure signal is taken from the central chamber, between the two valve seats 103,104. The engine coolant modulated pressure signal is supplied to the right hand chamber 99 and the left hand end of the central chamber. The intercooler moderated temperature is supplied to the left hand chamber 97, and the right hand end of the central chamber. In use the combiner valve 94 provides a combined pressure signal to the clutch which is modulated in accordance with both the intercooler temperature and the engine temperature. In practice, the system could be set up so that the fan runs at an idle speed of 150 rpm when there is no cooling demand from either the intercooler or the engine coolant. When the intercooler signals a demand the system may supply a control pressure which causes the fan to run at, say, 800 rpm. This may be a simple on-off control or there may be continuous modulation up to 800 rpm. When the engine coolant signals a demand the system may supply a pressure signal which modulates the fan output speed in accordance with temperature from 800 rpm to just below the engine speed.The above forms of clutch automatically vary the output speed of the casing 14/15 in accordance with the sensed temperature. The clutch may be modified to adjust the output speed as required by a user, i.e. by providing some form of pressure control for controlling the pressure supplied to the ram. In the above examples of viscous clutch the force applied via assembly 44 is hydraulically generated; it could of course be generated in other ways, for example by an electrical force transducer. Likewise, in the above examples of thermo-pressure valve, the force signal applied by the wax capsule could be applied by a force transducer and could represent a variable other than sensed temperature.

Claims: A viscous fluid shear clutch comprising:- a rotary casing (14,15), an inner clutch member (10) within the casing (14,15) and spaced therefrom by a clearance gap, a fluid reservoir (22) communicating with said clearance gap, pump means (25) arranged to pump fluid from the clearance gap to the reservoir (22) in response to relative rotation between the casing (14,15) and the inner clutch member (10), valve means (32,34,36) arranged to control the flow of fluid between the pump means (25) and the clearance gap and including a movable control element (36), thermal sensor means including a remote sensor (66 et sec) for sensing the temperature of a coolant fluid and a separate actuator (44) for applying to said movable control element (36) a temperature dependent force which acts upon said movable control element (36) and which is substantially invariant for a given temperature, and speed sensor means (40) for generating a speed dependent force which acts upon said movable control element (36), whereby an increase in the sensed temperature or a decrease in the sensed speed tends to cause the movable control member to be moved to adjust the valve means to increase the fluid in the clearance gap, characterised in that said speed sensor means including a mass means (40) pivotally mounted within the rotary casing (14,15) for centrifugally generating a speed dependent force, and applying it to said control element (34), whereby said cluth provides substantially continuous modulation of the rotary speed of the casing in accordance with said sensed temperature. A viscous fluid shear clutch according to Claim 1, wherein said thermal sensor means is arranged to provide a temperature dependent force which decreases with an increase in temperature, whereby accidental removal of said force tends to adjust the valve means (32,34,36) to increase the fluid in the clearance gap. A viscous fluid shear clutch according to Claim 2, wherein said temperature dependent force and said speed dependent force act on the movable control element (36) in the same sense. A viscous fluid shear clutch according to any preceding Claim, wherein said pump means (25) is constituted by a circumferential wall portion of said inner clutch member (10) and at least one circumferentially extending scoop (26) of limited arcuate extent provided in an opposed cylindrical wall of the casing (15), each scoop (26) having associated therewith a scoop pump outlet passage (28) arranged adjacent the end region of the scoop (26) which trails in the sense of rotation of the scoop (26) relative to the inner clutch member (10). A viscous fluid shear clutch according to Claim 4, wherein said rotary casing includes one part (15) defining at least a major portion of each scoop (26) and another part (14) defining at least a major portion of each scoop pump outlet passage (28), the two parts being capable of being assembled in either one of two relative angular positions whereby each scoop pump outlet passage (28) can be located at either end region of the associated scoop (26) depending on the intended sense of rotation of the clutch. A viscous fluid shear clutch according to Claim 5, wherein said two parts (14,15) are connected together by means of a series of connecting elements (43) equiangularly spaced about an axis at a pitch whereby assembly for reverse rotation may be achieved by indexing one part relative to the other about said axis by an amount equal to the angular pitch of the connecting elements (43). A viscous fluid shear clutch according to any preceeding Claim, wherein said thermal sensor means includes: a thermo pressure valve having a valve body (66) defining an inlet (68) for servo fluid, an outlet (70) for connection to said actuator (44), and a vent (72), shuttle spool means (74) linearly movable within said body (66) between a first position, which allows communication between said inlet (68) and said outlet (70), and a second position which allows communication between said outlet (70) and said vent (72), and a sensor element (82) responsive to the sensed temperature for moving said shuttle spool means (74). A viscous fluid shear clutch according to Claim 7, wherein said shuttle spool means (74) prevents flow between said outlet (70) and said inlet (68) or said vent (72) means when in an intermediate position. A viscous fluid shear clutch according to Claim 7 or Claim 8, wherein said shuttle spool means (74) is provided at spaced regions with seal surface means (75,76) engageable in resilient sealing manner with respective valve seats (77,78) in said valve body (66). A viscous fluid shear clutch according to Claim 9, wherein said seal surface means comprise annular seal elements of resilient material. A viscous fluid shear clutch according to Claim 9, wherein said shuttle spool (74) means is adjustable to allow the spacing between said seal surface means (75,76) to be set as required. A viscous fluid shear clutch according to any one of Claims 7 to 11, including bias means (84,86) for applying an adjustable bias force to said shuttle spool means (74). A viscous fluid shear clutch according to Claim 8 or any claim dependent thereon, wherein movement of said shuttle spool means (74) away from said intermediate position causes resilient compression of one of said seal surface means (75,76) against its valve seat (77,76) and lifting of the other seal surface means from its valve seat (78,77). A viscous fluid shear clutch according to any of Claims 7 to 13, wherein said sensor element (82) is a force transducer. A viscous fluid shear clutch according to any preceding Claim in combination with a valve arrangement (94) for receiving two pressure demands and supplying one thereof to said actuator (44), said valve arrangement (94) including a valve body (96) defining an outlet port and at least two inlet ports each for receiving respective pressure demands, a shuttle spool means (100) controlling the flow between said inlet and outlet ports and movable between one position in which one of said inlet ports communicates with said outlet port and another position in which the other of said ports communicates with said outlet port, wherein means (97,106;99,106) are provided for moving said shuttle spool between said aforementioned positions dependent on at least one of said demand pressures.

Inventors: ELMER ARTHUR ERNEST HENRY, ELMER, ARTHUR ERNEST HENRY
Applicants: KYSOR INDUSTRIAL CORP, KYSOR INDUSTRIAL CORPORATION
Application year: 1990
Main classification: F16D35
IPC codes: F16D35