GB2151725A

GB2151725A - A hydraulically controlled friction clutch and motor vehicle power unit utilising this clutch

Info

Publication number: GB2151725A
Application number: GB08424590A
Authority: GB
Inventors: Giorgio Lupo
Original assignee: Fiat Auto SpA
Current assignee: Fiat Auto SpA
Priority date: 1983-12-23
Filing date: 1984-09-28
Publication date: 1985-07-24
Also published as: ES536611A0; DE8429140U1; IT1160246B; GB2151725B; GB8424590D0; IT8368354A0; FR2557236A3; ES8600660A1; FR2557236B3

Abstract

An hydraulically controlled friction clutch constituted by an actuator cylinder (26) rotatable with the input member (18) of the clutch (20) and the thrust chamber (36) of which is connected to a circuit for supplying a liquid under pressure and to a discharge circuit. The discharge circuit includes a normally-open interception valve (76) rotatable with the actuator (26) and closed by centrifugal action. Valve closure commences at a clutch input member rotary speed of approximately 1000 r.p.m. and is complete when the speed is approximately 2500 r.p.m. The clutch is interposed between the vehicle gearbox (16) and differential (22) but may instead be between the engine (10) and gearbox. The movable member (82) of the valve may be spherical instead of the shape shown. <IMAGE>

Description

SPECIFICATION A hydraulically controlled friction clutch and motor vehicle power unit utilising this clutch The present invention relates to hydraulically controlled friction clutches for coupling a rotating input member and a rotating output member coaxial therewith for rotation with one another.

In particular, the invention relates to a friction clutch of the type in which the input member and the output member are provided with respective alternate coaxial friction discs which can be pressed together axially be means of the hydraulic control, and in which this hydraulic control includes an actuator constituted by a cylinder body connected for rotation with the input member and in which a piston facing the said discs is slidable, the piston defining with the cylinder a thrust chamber, and in which there is provided an hydraulic control circuit including a source of liquid under pressure, supply means for supplying the liquid under pressure to the said thrust chamber and discharge means for discharging the liquid from the thrust chamber and including a normally-open interception valve rotatable with the hydraulic actuator and activated centrifugally to close.

The object of the invention is to provide a friction clutch of the type defined above of simple and sturdy construction and of reliable operation in an entirely automatic manner in dependence on the speed rotation of the input member This object is achieved by means of the features set forth in the characterising portion of Claim 1, and in the dependent Claims 2 to 7.

The friction clutch according to the invention finds particularly advangeous application in power units for motor vehicles including an engine, a stepwise or stepless change-speed gearbox and a differential.

In this application, the clutch according to the invention can be utilised for the connection between the output of the gearbox and the input of the differential, or else for connection between the engine shaft and the input shaft of the gearbox.

The second arrangement is preferred, particularly in the case in which a stepless change-speed gearbox is used, because with this arrangement engagement of the friction clutch is obtained as a function of the speed of rotation of the engine with the selector in low ratio and disengagement takes place on the basis of the speed of the vehicle or else the speed of rotation of the input member of the differential. Therefore, as the vehicle slows, the friction clutch according to the invention behaves similar to a "lock-up" independently of the ratio of the gearbox and the speed of revolution of the engine. Upon rapid braking of the vehicle, locking of the stepless variator in a ratio other than the lowest is prevented, thus avoiding the risk of damage to the variator itself and difficulty in restarting the vehicle.

The invention will now be described in detail with reference to the attached drawings provided purely by way of non-limitative example, in which: Figure 1 is a schematic and partially sectioned view of a power unit for a motor vehicle, including a friction clutch according to the invention; Figure 2 illustrates on an enlarged scale a first variant of a detail of the clutch; Figure 3 illustrates on an enlarged scale a second variant; Figure 4 illustrates on an enlarged scale a third variant; and Figure 5 is a graph which illustrates the operating characteristics of the friction clutch.

Figure 1 schematically illustrates a power unit for motor vehicles, including an internal combustion engine 10 the shaft 12 of which is connected to the input shaft 14 of a gearbox 16 having an output shaft 18 coupled, via a friction clutch 20, to a differential 22 which drives the half-starts 24 of the drive wheels of the vehicles.

The gearbox 16 can be of the step-wise type or else of the stepless speed-change type. In the second case it can be constituted by ab expansible pulley-type variator or by an epicyclic variator with conic planetary gears.

The friction clutch 20 includes a fly-wheel or cylindrical body 26 formed by an annular element 28 coupled for rotation with the output shaft 18 of the gearbox 16 and having a radially inner axial portion 30 and a radial outer axial portion 32 between which is movable a sealed annular piston 34. The inner face of the annular piston 34 defines, with the cylindrical body 28, a thrust chamber 36 and is subjected on its opposite face to the action of resilient means, in the illustrated example constituted by a cup spring 38, tending to press this piston 34 against the cylindrical body 28.

The outer axial part 32 of the cylindrical body 28 carries an annular skirt 40 within which are inserted, in an axially slidable manner, a plurality of axially slidable annular friction driving discs 42.

The reference numeral 44 indicates a toothed wheel supported coaxially in a rotatable manner on the output shaft 18 of the gearbox 16 and meshing with a toothed ring 46 formed on the casing of the differential 22. The toothed wheel 44 has an axial tubular projection 48 extending in the direction of the cylindrical body 28 and carrying a series of axially slidable annular driven friction discs 50 intercalated with the driving discs 42.

The thrust chamber 36 is connected to an hydraulic supply circuit including one or more passages 52 formed in the axial part 30 of the cylindrical body 28 and communicating, through radial passages 54 and an axial passage 56 formed in the shaft 18, with a supply and control unit 58.

The unit 58 includes a two-position control valve 60 of the "on-off" type known per se, normally of the type having proportional electrical control, which allows oil to be supplied selectively from a collection reservoir 62 to the duct 56 through an hydraulic pump 64 or else cuts off this supply by connecting the duct 56 to discharge to the reservoir 62.

In the cylindrical body 26 there is formed a discharge passage including a radially outer axial section 66 formed in the part 28 close to the part 32, a radially inner axial section 68 formed in the axial part 30, and a radial section 70 which interconnects the axial sections 66 and 68.

The end of the axial section 68 opposite the radial section 70 opens into an annular chamber 72 defined between the axial part 48 of the toothed wheel 44 and the axial part 30 of the cylindrical body 26 and communicating with the zone containing the friction discs 42 and 50 through radial lubrification passages 74 formed in the projection 48.

In the radial section 70 there is fitted an interception valve generally indicated 76 and comprising a valve seat 70 with which cooperates a valve shutter 80 carried by a centrifugal mass 82 freely slidable within the radial section 70 between the seat 78 and the axial portion 30 of the cylinder body 28.

In the illustrated example, the valve shutter 80 is of conical form and the centrifugal mass 82 has a series of peripheral axial grooves 84 for the passage of oil.

The centrifugal mass 82 is arranged and dimensioned in such a way as to obtain gradual closure of the valve seat 78 by the valve shutter 80, thereby obstructing the communication between the thrust chamber 36 and the chamber 72 when the speed of rotation of the shaft 18 and thus of the cylinder body 26 exceeds a predetermined threshold value.

The operation of the friction clutch 20 will now be described below.

Activation of the friction clutch 20 is controlled, during operation of the engine 10, through the "on-off" valve which is controlled by means of a conventional selection lever operated by the driver.

When this lever is disposed in the neutral position, the valve 60 is arranged in a closed position so that communication between the pump 64 and the duct 56 is interrupted, whereas the communication between this duct 56 and the discharge 62 is opened. In this condition, any oil which may be present in the thrust chamber 36 is free from static pressure and flows out to the exterior, through an automatic ball valve 86 of conventional type fitted in the piston 34, collecting in the reservoir 62. The friction discs 42 and 50 are therefore completely free so that the output shaft 18 of the gearbox 16 is disengaged from the differential 22.

When the selector lever is disposed in the forward or reverse operating position, the valve 60 is arranged in the open position, thereby opening communication between the pump 64 and the passage 56. The oil under pressure is then sent through the radial passages 54 and the passages 52 into the thrust chamber 36.

In conditions with the engine 10 idling, or when the output shaft 18 of the gearbox 16 rotates at a speed beneath the calibration valve of the valve 76, oil sent into the chamber 36 discharges through the passages 66, 70 and 78 into the chamber 72 in such a way as to lubricate the friction discs 42 and 50 in the phase in which they slide with respect to one another.

Upon an increase in the speed of rotation of the engine 10, and therefore of the output shaft 18 of the gearbox 16, the centrifugal mass 82 tends to displace radially outwardly thereby progressively closing the valve shutter 80 against the valve seat 78. Consequently, the oil pressure in the thrust chamber 36 gradually increases causing approach of the piston 34 against the friction discs 42 and 50 until they are completely pressed together.

When the valve 76 closes completely, the pressure necessary for complete engagement of the clutch 20 is established in the thrust chamber 36, whilst the lubrication of the discs 42 and 48 is obviously interrupted which results in them being clamped together.

When the speed of the cylinder unit 26 decreases again beneath the threshoid value, the valve 76 gradually opens again causing disengagement of the clutch 20.

In the case of the friction clutch 20 illustrated in the example of Figure 1, in which the gearbox 16 is of the stepless type, the friction clutch 20 has a "lock-up" tupe of behaviour independently of the ratio of the variator 16 and the speed of rotation of the engine 10. In fact, whilst engagement of the clutch 20 takes place in dependence on the speed of rotation of the engine 10, with the variator 16 in low ratio, disengagement occurs on the basis of the speed of rotation of the vehicle and always at the same speed for any ratio of the variator 16. It is clear, in fact that this speed corresponds to a definite angular velocity of the casing of the differential 22 and therefore of the output member 44 of the clutch 20.

The operation of the friction clutch 20 in these conditions is represented in the graph of Figure 5, in which plotted along the abscissa are, respectively, the speed of rotation of the engine 10 in the low ratio of the variator 16 and the speed of the vehicle, and plotted along the ordinate is the couple transmitted by the clutch 20. As can be seen, the commencement of engagement of the clutch 20 takes place, by way of example, at a speed of rotation of the engine 10 about equal to 1000rpm, and the complete engagement takes place at approximately 2500rpm, whilst the disengagement commences at a speed of the vehicle about 16 to 17 km/h and is completed at about 7 to 8 km/h. As can be seen, then, the take-up characteristic of the clutch 10 is extremely gradual and progressive, and is similar to that of conventional centrifugal clutches of mechanical type.

It is clear, naturally, that the friction clutch 20 could be applied in a different manner from that illustrated and described above, and for example could be inserted between the engine 10 and the gearbox 16. In this case, however, the clutch wouid obviously be sensitive to the speed of rotation of the engine 10 and therefore unwanted disengagement of the clutch could take place at low speeds of rotation of the engine 10 with the gearbox 16 in high ratio.

Further, it is necessary to note that the interception valve 76 could have different configurations from that illustrated in Figure 1, and for example could be of the type illustrated in the variants of Figures 2 to 4.

In the case of Figure 2 the axial passage 68 is not present and the passage 66 is connected to a lateral discharge outlet 87 adjacent to the valve seat 78. The valve shutter 80 and the centrifugal mass 82 have, in this case, a conformation similar to that of Figure 1.

In the case of Figure 3, the valve shutter 76 is constituted by a ball 88 engaged against the centrifugal mass 82, whilst in the case of Figure 4 the centrifugal mass is constituted by a ball 90 adapted to serve also as a valve shutter.

Naturally the details of construction and the embodiments can be widely varied with respect to what has been described and illustrated, without by this departing from the scope of the present invention.

Claims

1. A hydraulically controlled friction clutch for rotatably coupling a rotatably input member with a coaxial rotatable output member, particularly for motor vehicle power units, in which the input member and the output member are provided with respective alternate coaxial friction discs which can be pressed together axially by means of the hydraulic control, and in which the said hydraulic control includes an actuator constituted by a cylinder body rigidly connected for rotation with the input member of the clutch and in which a piston facing the said discs is slidable, the said piston defining with the cylinder a thrust chamber, and an hydraulic control circuit including a source of liquid under pressure, supply means for supplying liquid under pressure to the said thrust chamber, and discharge means for discharging the liquid from the thrust chamber, said discharge means including a normally-open interception valve rotatable with the hydraulic actuator and activated centrifugally to close, characterised by the fact that in the cylinder body (28) of the hydraulic actuator (26) there is formed a discharge passage (66, 70, 68) having a radially directed portion (70), and by the fact that the interception valve (76) includes a valve seat (78) formed in the said radial portion (70) of the discharge passage and a centrifugal mass (82, 90) slidable in the said radial portion (70) between the valve seat (78) and the axis of the hydraulic actuator (26), carrying a valve shutter (80, 88, 90) cooperating with the said valve seat (78); the said centrifugal mass (82, 90) being dimensioned and positioned in such a way that the closure displacement of the valve shutter (80, 88, 90) of the interception valve (76) starts when the speed of rotation of the input member (18) is of the order of 1000 rpm and is complete when the speed of rotation of this input member (18) is of the order of 2500 rpm.

2. A clutch according to Claim 1, characterised by the fact that the discharge passage (66, 70, 68) communicates, downstream of the interception valve (76), with a lubrication chamber (72) for the friction discs (42, 50).

3. A clutch according to Claim 1, characterised by the fact that the valve shutter (80) is conical.

4. A clutch according to Claim 1, characterised by the fact that the valve shutter (88, 90) is spherical.

5. A clutch according to Claim 1, characterised by the fact that the centrifugal mass (88) is spheri cai and itself constitutes the valve shutter.

6. A clutch according to Claim 1, characterised by the fact that it is fitted to a power unit for a motor vehicle including an engine (10), a gearbox (16) and a differential (22), and is disposed between the gearbox (16) and the differential (22) with its input member (26) coupled to the output shaft (18) of the gearbox (16) and its output member (48, 44) connected to the differential (22).

7. A friction clutch according to Claim 1, characterised by the fact that it is fitted in a power unit for a motor vehicle including an engine (10), a gearbox (16) and a differential (22) and is disposed between the engine (10) and the gearbox (16).

8. A power unit for a motor vehicle, including an engine, a gearbox connected to the engine shaft and having an output shaft, a differential connected to the gearbox, and an hydraulically controlled friction clutch according to one or more of Claims 1 to 8 interposed between the engine and the differential, wherein characterised by the fact that the friction clutch (20) is associated with a control unit (58) including a valve (60) displaceable between an activation position in which it allows supply of liquid under pressure to the friction clutch (20) and a closer position in which this supply is prevented.

9. A power unit according to Claim 8, characterised by the fact that the friction clutch (20) is fitted between the gearbox (16) and the differential (22).

10. A power unit according to Claim 8, characterised by the fact that the friction clutch (20) is interposed between the engine (10) and the gearbox (16).

11. A power unit according to Claim 9 or Claim 10, characterised by the fact that the gearbox (16) is constituted by a stepless speed variator.

12. A clutch substantially as herein described and shown in the accompanying drawings.

13. A power unit substantially as herein described and shown in the accompanying drawings.