This invention relates to hydrodynamic torque converter-couplings of the kind comprising an impeller member, a turbine member and a reaction member which are mounted for independent rotation about a common axis, together define a toroidal working circuit for a working liquid and each have guide vanes for interacting with the liquid within the working circuit in such a manner that when the turbine member is stationary or rotating at a speed which is low compared with, that of the impeller member, the torque applied to the turbine member by the liquid is greater than the input torque acting on the impeller, the algebraic difference in the two said torques being compensated by a backward reaction torque applied by the liquid to the reaction member which is temporarily held stationary. With increasing turbine member (output) speed , the said torque different:, and thus the reaction torque, decreases until the so-called coupling range is reached (for example with output speed 90% of input speed) at which the reaction torque falls to zero and would there- after become negative. To avoid the resultant further reduction in output torque, the reaction member is allowed to rotate in the direction imposed by such negative reac¬ tion torque and the converter then acts as a fluid coup¬ ling. When the output speed falls below the coupling range, the reaction member is again held stationary and the output torque rises above the input torque.

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Various designs of such converter-couplings are in wide use. Generally, the reaction member is held against rotation in one direction and allowed to rotate in the other direction by means of a free-wheel device either of the roller and inclined surfaces type or the sprag type. For successful operation over a long life, both of these types require high-quality materials and high-precision manufacturing operations on complex shapes to ensure that each of the set of rollers or spags comes into operation at the same time as the others and the working loads are shared between them.

In a torque converter-coupling according to one aspect of the present invention, the reaction member is held against rotation in one direction by engagement of abutment surfaces rotationally connected respectively to a stationary structure and the reaction member, and the conver er-coupling includes means for axially separating the abutment surfaces as the output: speed increases into the coupling range and for engaging the abutment surfaces when the output speed falls below the coupling range.

The relative axial movement between the abutment surfaces into engagement may be effected by a helical constraint of limixed length between a nember carrying one set of the abutment surfaces and the reaction member, relative movement along the constraint being at least initiated by a drag torque exerted by drag means.

The abutment surfaces may conveniently be formed by tooth surfaces of a toothed clutch. Preferably,

the opposite surfaces of the clutch teeth are inclined to the axis to assist axial separation of the toothed clutch when the output speed rises to the coupling range. -

According to another aspect of the invention, there is provided a torque converter-coupling in which the guide vanes of the reaction member are inclined to the axis, wherein the reaction member is mounted for limited movement in the axial direction, and axial move¬ ment of the reaction member in response to the axial component of force exerted by the liquid on the reaction member guide vanes is arranged to engage and disengage a holding clutch for the reaction member.

The converter-coupling may advantageously in¬ clude drag means for exerting drag torque on the reaction member so as to increase the axial force component exerted on it by the flow of liquid interacting with the reaction member guide vanes. Preferably, the drag means are responsive to the speed of rotation of the reaction member in such a manner that the drag torque is reduced or eliminated when the speed is increased. Conveniently, the drag means comprise a drag member mounted for rota¬ tion with the reaction member so as to be subject to a centrifugal separation force opposing a resilient force urging it inwardly into frictional contact with, a fixed external surface of re-volution, increasing centrifugal force tending to reduce such frictional contact.

In one form of embodiment, the drag member comprises a resilient split ring or band mounted in a

cavity in the hub of the reaction member, making fric ^¬ tional contact with a non-rotating surface of revolution and being constrained to rotate with the reaction me ^" mber while being axially movable relatively thereto, the 5 arrangement being such that with increased angular speed of the reaction member, the ring or band expands out of frictional contact with the non-rotating surface.

Preferably the torque converter-coupling embodies both aspects of the invention. 10 If _. desired, a lock-up clutch may be provided for selectively locking the input member to the output member.

Embodiments of the invention will now be de¬ scribed by way of example with reference to the accompany- 15 ing drawings , in which:-

Figure 1 is an axial sectional view of the major part of a torque converter-coupling in accordance with the present invention, with the reaction member free to rotate in one direction; 20 Figure 2 shows a portion of Figure 1 on an enlarged scale, with the reaction member held stationary,

Figure 3 is a fragmentary view oh an enlarged scale in the direction of the line III-III of Figure 2;

Figure 4 is a view in the direction of the 25 arrow IV of Figure 3 ;

Figure 5 is an axial sectional view of a hub portion of a modified torque converter-coupling in accordance with the invention; - MPI

Figure 6 is a plan view of the friction band of

Figure ^' 5; and

Figure 7 is a cross-sectional view through the friction band and co-operating sleeve of Figure 5. The torque converter-coupling shown in Figure 1 is of generally conventional construction in that it includes an impeller member 1, a turbine member 2 and a reaction member 3 which together define a toroidal working circuit - . Each of the three elements 1, 2, 3 is formed with a set of guide vanes la, 2a, 3a, each set of guide vanes terminating in an annular core portion lb, 2b, 3b, which together form a toroidal core for the working circuit 4.

In accordance with usual practice, the guide vanes- are angled and/or curved to obtain the required performance of the converter-coupling and in particular, the guide vanes 3a of the reaction member 3 , whether curved or not, are inclined to the axis of the coupling. The impeller 1, which in this embodiment is assembled from several components including an outer rotating casing 6 defining the radially outermost portion of the working circuit, is bolted to a driving flange 7 of an input member 8 haying a spigo- portion 9 to engage in a recess in the output member of an internal com- bustion engine (not shown) which is connected to the driving flange 7 through a diaphragm member (not shown) .

The turbine member 2 is bolted to a flange 11 which is connec-e≤ by splines 13 to an output shaft 12.

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The inner (left-hand) end 1-4 of the shaft 12 is jour- nalled by means of a ball-bearing 15 in the input member 8 and a radial-roller thrust bearing IS is mounted between the flange 11 and the input member 8_ The other end of the shaft 12 ^* is journailed or otherwise supported in a stationary casing 17 having a sleeve portion 18 sur¬ rounding the shaft 12 with clearance. A sleeve member 19 is mounted on the sleeve portion 18 by means of straight, axial splines 20 in one half of the sleeve member 19, the other half being journalled on a hub portion 21 of the flange 11 by means of a suitable bearing 22. The sleeve member 19 is axially located relative to the impeller assembly 1 and the turbine assembly 2, 11 by radial roller thrust bearings 23 and 2^ . A reaction member hub 25 is rotatably mounted on the sleeve member 19 by means of a pair of plain bushes 26 which also allow the hub to move axially on the sleeve 19. The radially outer surface of the hub 25 is splined to engage in corresponding splines 27 in a central bore in the reaction member 3. A pair of spring rings 28 engaged in the bore in the reaction member 3 engage the end surfaces of the hub 25 to locate the latter relative to the reaction member.

The range of axial movement of the hub 25 and thus of the reaction member assembly, is limited by end rings 29 and 30 welded or otherwise secured to τhe sleeve member 19 and forming each a race of the respective bearing 2*-v _t 23. The end ring 30 and the adjacent end of

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the hub 25 are formed with complementary sets of shallow clutch teeth 31, 32. As can be..seen in Figures 3 and 4, the clutch teeth each have a substantially radial and axial abutment face 33 on one flank, the other flank 34 of each tooth being relatively long and gently sloping. The tips 35 of the teeth are narrow and flat and corre¬ spondingly flat and narrow lands 36 are formed at the roots of the flanks 33, 34.

In operation, when the converter-coupling is acting as a torque converter, the direction of liquid flo through the reaction member blade 3a is at: an angle to these blades such as to exert an axial force on the reaction member assembly 3 which moves the latter (to the right in Figures 1 and 2) to being the two sets of clutch teeth 31- and 32 into full engagement. The reaction member 3 will then be prevented from rotating as a result of mutual engagement of the abutment surfaces 33 on the two s-ets of clutch teeth.

When the speed of the output shaft 12 reaches the coupling range and/or when a lock-up clutch (not shown) is engaged to transmit the drive directly between the input member 8 and the shaft 12, the direction of the force exerted by the liquid on the guide vanes 3a will be changed in such a manner that its circumferential component will be reversed so as to unload the abutment surfaces 33 and the sloping surfaces 3-- will ride over each other- to assist movement of the reaction member 3 to the left in Figures 1 and 2, thus disengaging the

teeth 31, 32 and allowing the reaction member to rotate in the same direction as the input member.

In order to increase the forces exerted on' the reaction member 3 by the liquid when the reaction member is required to move axially, a drag torque opposing rotation of the reaction member 3 is exerted on the latter by a resilient band 41 which is cut at one position on its circumference at 42 and is lines with a suitable frictional material 43 which makes frictional contact with the outer surface of the sleeve member 19. The band 41 is located in an annular recess 44 in the hub 25 and is prevented from rotating relative to the hub 25 by engagement of a peg 45 in a slot 46 in the hub, the slot 46 being of sufficient axial length to permit t.he necessary axial movement of the reaction member 3 relative to the peg 45. The friction material 43 and the resilient force with which it is applied to the outer surface of the sleeve member 19 can be chosen to provide the required drag torque opposing rotation of the re- action member 3 and thus to determine the axial force exerted on the reaction member 3 during transitions between the locked and unlocked states and vice versa of the reaction member. When the rotational speed of the reacτ:ion member rises , centrifugal force will cause the band 41 to expand against its internal.resilience until the drag torque is eliminated, or reduced to an acceptable value.

When the clutch teeth 31 and 32 are disengaged toleave the reaction member free to rotate, their tip surfaces 35 need only to be separated by a small dis-tance sufficient to prevent contact, cut in certain transitional conditions the tip surfaces 35 of the teeth 32 may rotate in contact ^" with those of the teeth 31 without being damaged. ■In the modification shown in Figures 5 to 7, the reaction member 3 is splined onto a sleeve 51 (with straight splines 52). The hub 25' carrying the clutch teeth 32 is formed on its outer surface with two sets of helical teeth 5 ^J J and 55 which are engaged with helical splines 53, formed on the internal surface of the sleeve 51- Engage ent and disengagement of the clutch teeth 31 and 32 is effected by helical movement of the hub 2 ' within the sleeve 51. Accordingly, there is no requirement for the reaction member 3 to be allowed specific axial freedom. Accordingly, the reaction member 3 is axially located by engagement of its spring rings 23 with radially outward extensions 5β of the axially inner races of the thrust bearings 23 and 24, the extensions 56 bearing against the ends, of the sleeve 51.

In order to initiate engagement of the clutch teeth 31 and 32 when the reaction member 3 attempts to reverse its direction of rotation as the output speed moves through the coupling range, the hub 25 accommodates in its internal annular recess k ¹ a resilient friction band 57 which is divided at one point of its circumference by a gap 58 and frictionally engages the sleeve member 19. A

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peg 59 is screwed into the hub 25' andhas a reduced diameter portion 60 engaged in a slot βl _. formed near one end of the friction band 57- This end of the friction band is -thus anchored to the hub against rotational movement while 5 permitting axial movement of the hub despite frictional engagement between the band 57 and the sleeve member 19-

Re erring to Pig. 7, it will be appreciated that clockwise rotation of the peg 59 (and hub 25') will increase the frictional engagement of the band 57 with the sleeve

10 member 19 and will thus increase the drag torque exerted by the band 57 on the hub 25' whereas anticlockwise movement of the hub 25' and peg 59 will reduce the frictional engagement of the friction band 57 and will thus reduce the frictional drag exerted on the hub 25'- Accordingly, the

15 anchored end of the band 57 is chosen such that the greater drag occurs in the direction in which the reaction member would rotate backwards relative to input rotation. The handing of the splines 53 and teeth 5 ,55 is furthermore chosen such that the transfer of this drag torque through

20 the teeth -4 and 55 and the helical splines 53 to the reaction member 3 results in an axial force on the hub 25* to the right in Figure 5 to engage the clutch teeth 32 with the teeth 31-

When the output speed rises through the coupling .25 range, the torque exerted by the liquid on the reaction member 3 will now be in the forward direction and the resulting forward rotation of the reaction member 3 will draw the hub 25' to the left in Figure 5 to separate the

clutch teeth 31 and 32, this being effected by the reversed and reduced but still effective drag torque, assisted by the inclined faces of the teeth 31_ and 32 ^" . With increasing rotational speed of the reaction member 3 in the forward direction, the band 57 will expand radially to reduce or eliminate the frictional drag.

As in the embodiment of Figures 1. to 4, the connection between the band 57 and the hub 25' may by made by fixing a peg, such as the peg 5 of Figure 2, to the band 57 near the appropriate end of the latter, the hub 25' then being formed with a slot to accommodate this peg, the slot being of sufficient length axially of the hub to permit the necessary axial movement of the hub.

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