GB2099960A

GB2099960A - Viscous fluid couplings

Info

Publication number: GB2099960A
Application number: GB8214367A
Authority: GB
Original assignee: Fichtel and Sachs AG
Current assignee: ZF Sachs AG
Priority date: 1981-06-10
Filing date: 1982-05-18
Publication date: 1982-12-15
Also published as: FR2507721A1; JPS585536A; IT1156358B; GB2099960B; IT8267740A0; DE3122958A1; DE3122958C2

Abstract

In a fan coupling unit, a pumping element (14) pumps shear fluid from the working chamber (7) into the reservoir chamber (6) through a pumping passage (12). The fluid returns through a return passage (19) from the reservoir chamber into the working chamber. First valve means (11) control flow through the return passage. Second non-return valve means (15) prevent the flow of shear fluid from the reservoir chamber to the working chamber through the pumping passage, to avoid undesirable fan speed variations. <IMAGE>

Description

SPECIFICATION Fan coupling unit The present invention is directed to a fan coupling unit comprising a rotor member and a housing. A working chamber is defined within the housing and receives the rotor member. Shear spaces are defined between respective shear faces of the rotor member and the housing. First connecting means are provided for connecting one of said rotor member and said housing to a driving unit. Second connecting means are provided for connecting the other of said rotor member and said housing to a fan unit. The working chamber and a reservoir chamber are at least partially filled with a shear fluid. A pumping passage extends from said working chamber to said reservoir chamber.A pumping unit is associated to the pumping passage and is responsive to relative rotation of the rotor and the housing so as to pump shear fluid from the working chamber into the reservoir chamber. A return passage is provided for admission of shear fluid from the reservoir chamber to the working chamber. First valve means are provided for controlling fluid passage through the return passage. The first valve means are preferably dependent on the temperature of a cooling system associated with an internal combustion engine by which the rotor member is driven. When the first valve means are open in response to a predetermined minimum temperature of the cooling system, the first valve means open the return passage so that shear liquid can enter the working chamber. Under these circumstances, the shear fluid can transmit a considerable torque between the housing and the rotor member.Thereby, the fan unit is driven and effects cooling of the cooling system and the internal combustion engine. When the temperature of the cooling system decreases, the return passage is closed by the first valve means. Thus no further shear fluid is admitted to the working chamber. The transmission oftorque between the rotor member and the housing is reduced. The fan unit rotates with reduced RPM or comes to a standstill. So the cooling action of the fan unit is reduced.

This type of fan coupling unit is known, for exam- ple, from German Auslegeschrift 2,814,608. With the known type of fan coupling unitthe pumping passage is always open. According to the pressure differential between the working chamber and the reservoir chamber shear fluid can flow in different directions. Therefore, even when the return passage is closed, a certain amount of shear fluid is present within the working chamber, the residual shear fluid in the working chamber being in pressure balance with the shear fluid within the reservoir chamber.

Therefore, the fan unit is rotated even when the return passage is closed. Variations and even abrupt variations of the RPM of the fan unit occur. These variations are highly indesirable.

It is a primary object of this invention to eliminate such undesirable variation of the RPM of the fan unit A further object is to reduce the idling RPM of the fan unit, i.e. the RPM which occurs when the first valve means are closed.

A further object is to obtain the desired smooth operation of the fan unit with a minimum of expense.

In view of these objects second valve means are associated to the pumping passage for suppressing flow of shear fluid through the pumping passage from the reservoir chamber to the working chamber.

A further object of this invention is to provide a highly effective pumping unit which is still effective at low relative rotation of the rotor member and the housing.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described preferred embodiments ofthis invention.

Fig. 1 shows a partial longitudinal section through a fan coupling unit of this invention and Fig. 2 shows a section corresponding to line ll-ll of Fig. 1, in an enlarged presentation.

A fan coupling comprises, as it is known in the art, a shaft4 driven by an internal combustion engine (not shown) and connected fast in rotation with a rotor 1. The rotor 1 is surrounded by a housing 2 closed by a partition 5 and defining a working chamber 7. Shear spaces 8a and 8b are defined by shear faces 2a, la and 5b, 1 b, respectively. Furthermore, on the side of the partition 5 remote from the rotor 1 a lid 3 is provided which, with the partition 5, forms a reservoir chamber 6 for shear fluid. The working chamber 7 comprises the shear spaces 8a and 8b between the rotor 1 on the one hand and the housing 2 and partition 5 on the other.In order to render possible the inflow of shear fluid from the reservoir 6 into the working chamber7, an admission bore 10 is arranged in the partition 5 and can be controlled, for example, temperature-dependently by a control member 11. For the connection of the two shear spaces 8a and 8b with one another a passage 19 is provided in the rotor. In the partition 5, in the radially outer region of the rotor 1, a pump device is provided which in case of relative movement between rotor 1 and housing 2 and partition 5 pumps shear fluid out of the working chamber7 into the reservoir 6. This pump device can be seen especially from Figure 2. It comprises a circumferentially extending wedge 14 or a plurality of such wedges 14 which immerge(s) into an annular groove 22 of the rotor 1 so asto define at least one hydrodynamic lubricating wedge.The wedge 14 is here formed such asto approach the opposed face of the annular groove 22 along the direction F of movement of the rotor7. So the passage 12 passing through the wedge 14 between the working chamber7 and the reservoir chamber 6 can pump shear fluid from the working chamber into the reservoir chamber 8 as a result of the hydrodynamic pressure developping on the wedge 14. The opening 20 on the working chamber end of the passage 12 here preferably opens into the region of the pressure maximum of the hydrodynamic lubricating wedge. Considered from the partition 5, when the rotor 1 is rotating with slip, a speed distribution ofthe shear liquid here develops in accordance with the arrows E. The opening 13 on the reservoir side of the passage 12 can be closed by the closure head 16 of a non-return valve 16,13.The valve 16,13 is slightly biased in the closing direction and during operation ofthe pump device strikes with the closure head 16 on a stop 17.

The closure head 16 is defined by the end of a tongue spring, the opposite end of which is secured, for example, by spot welding to a fastening block 18.

This fastening block 18 is situated in front of the closure head 16, when regarded in the direction of rotation ofthe rotor according to the arrow F.

The function of the non-return valve 13, 16 is as follows: When the fan coupling is in the engaged condition, that isto say with the admission bore 10 opened and the shear spaces 8a, 8b filled with shear fluid, the full possible torque is transmitted from the rotor 1 to the housing 2 and thus to the fan blades 9. In this condition the region around the pump device 14,22, 12 is completely filled with shear liquid, so that shear liquid is permanently pumped from the working chamber7 into the reservoir chamber 6 by the hydrodynamic lubricating wedge between wedge 14 and rotor 1. Due to the high pressure in the passage 12the closure head l6ofthevalvel6, 13 is lifted away from the opening 13 on the reservoir side and rests on the stop 17.The pressure generated by the pump device in the passage 12 thus must overcome the biasing action of the non-return valve 16, 13 and the pressure in the reservoir chamber 6 resulting from centrifugal acceleration acting onto the shear fluid situated in the reservoir chamber 6. Under these conditions the fan blades are driven with a precalculated, desired torque, so that the internal combustion engine (not shown) is powerfully cooled. If nowthe temperature established in the cooling system of the internal combustion engine drops below a specific amount, the control member 11 is pressed by a temperature-sensitive element 24 onto the admission bore 10, so that shear fluid can't further enter the working chamber 7.Thus the shear fluid still present in the working chamber7 is entirely pumped out by the pump device 14,22, 12, untii the hydrodynamic lubricating wedge between the wedge 14 and the bottom wall of the groove 22 collapses for lack of shear fluid. At this moment the opening force upon the closure head 16 of the valve 16,13 is eliminated, so that this valve 16, 13, due to the biasing force of the tongue spring 15, goes into the closed position, i.e. the closure head 16 closes the opening 13 on the reservoir side of the passage 12. At this moment the closure pressure acting onto the closure head is additionally increased by the pressure of the shear fluid prevailing in the reservoir chamber 6, which pressure acts upon the closure head 16.The temperature sensitive element 24 is in contact with a cooling liquid contained in a cooling circuit ofthe internal combustion engine, as indicated at 23.

Due to the prevention of a return flow of shear fluid out of the reservoir chamber 6 into the working chamber 7 through the passage 12 closed by the valve 16,13in combination with an effective pump device - residues of shear fluid are prevented from flowing to and fro between working chamber 7 and reservoir chamber 6 when the fan coupling is in the disengaged condition, whereby a very irregular running of the fan blades 9 could occur.

The tongue spring valve 15,16 isofconsiderable advantage because of its simple design and its compactness. A further advantage is that no specific baiasing means are necessary.

Afurtheradvantage of this invention isthatthe closing operation ofthe valve head 16 is supported by the pressure in the reservoir chamber 6, so that a perfect function is warranted even when the pressure in the reservoir chamber is small. The provision of the abutment member 17 for the valve head 16 avoids dependency of the operation of the head 16 on the flow of shear fluid within the reservoir chamber. The type of pumping unit according to this invention makes sure that shear fluid is driven out from the working chamber into the reservoir chamber even if the relative rotation between the rotor member and the housing is slow, e.g. when the internal combustion engine driving the rotor member is idling.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

Claims

1. A fan coupling unit comprising a rotor member having an axis; a housing defining a working chamber, said working chamber receiving said rotor member, shear spaces being defined between respective shear faces of said rotor member and said housing; first connecting means for connecting one of said rotor member and said housing with a driving unit; second connecting means for connecting the other of said rotor member and said housing to a fan unit; a reservoir chamber; a shear fluid at least partially filling said working chamber and said reservoir chamber; a pumping passage from said working chamber to said reservoir chamber; a pumping unit associated with said pumping passage and responsive to relative rotation of said rotor member and said housing for pumping shear fluid from said working chamber into said reservoir chamber;; a return passage for admission of shear fluid from said reservoir chamber to said working chamber; first valve means for controlling fluid flow through said return passage; and second valve means associated with said pumping passage for suppressing flow of shear fluid through said pumping passage from said reservoir chamber to said working chamber.

2. Afan coupling unit as set forth in claim 1, wherein said return passage is nearer two said axis than said pumping passage.

3. Afan coupling unit as set forth in claim 1, wherein said second valve means comprise a nonreturn valve.

4. A fan coupling unit as set forth in claim 3, wherein said non-return valve is biased towards a closing position in which said pumping passage is closed.

5. Afan coupling unit as set forth in claim 4, wherein said non-return valve is subjected to the delivery pressure of said pumping unit such asto be opened when said delivery pressure exeeds a predetermined minimum valve.

6. Afan coupling unit as set forth in claim 3, wherein said non-return valve comprises a closure head supported by a tongue spring.

7. A fan coupling unit as set forth in claim 3, wherein said non-return valve is located within said reservoir chamber and co-operates with a mouth of said pumping passage opening into said reservoir chamber.

8. A fan coupling unit as set forth in claim 1, wherein said reservoir chamber is provided on said housing for common rotation therewith.

9. A fan coupling unit as set forth in claim 8, wherein said reservoir chamber is defined by a lid fastened to said housing and by a partition seperating said reservoir chamber from said working chamber.

10. A fan coupling unit as set forth in claim 9, wherein said pumping passage extends through said partition.

11. A fan coupling unit as set forth in claim 9, wherein said return passage extends through said partition.

12. Afan coupling unit as set forth in claim 11, wherein said second valve means comprise a closure head supported by atongue spring, said closure head being located adjacent one end of said tongue spring and co-operating with a mouth of said pumping passage adjacent a reservoir chamber side of said partition, the other end of said tongue spring being fixed to said partition, said other end of said tongue spring being in a leading location with respect to the location of said closure head when regarded in the direction of rotation of said one of said rotor member and said housing.

13. Afan coupling unit as set forth in claim 6, abutment means being provided for limiting the opening movement of said closure head.

14. Afan coupling unit as set forth in claim 1, said pumping unit comprising awedge member fixed to a first one of said rotor member and said housing, said wedge member comprising a wedge surface, said wedge surface co-operating with an opposite surface of a second one of said rotor member and said housing so as to define a hydrodynamic wedge of said shear fluid within said working chamber, said hydrodynamic wedge decreasing in height along the direction of rotation of the one of said rotor member and said housing connected to said driving unit, said pumping passage opening into said working chamber at a location of reduced height of said hydrodynamic wedge.

15. Afan coupling unit as set forth in claim 14, wherein said hydrodynamic wedge is defined between a wedge surface rising with respect to a plane perpendicular to said axis along a circular path about said axis and an opposite surface substantially parallel to said plane.

16. Afan coupling unit as set forth in claim 1, wherein said rotor member is connected to said driving unit.

17. Afan coupling unit as set forth in claim 1, wherein said first valve means are temperature controlled valve means.

18. Afan coupling unit as set forth in claim 17, wherein said first valve means are controlled in dependency of the temperature of a cooling circuit associated with an internal combustion engine driving said fan coupling unit.

19. A fan coupling unit substantially as described with reference to the accompanying drawing.