A TRANSMISSION UNIT FOR RELAYING DRIVE FROM A CRANKSHAFT OF

AN INTERNAL COMBUSTION ENGINE TO ENGINE ANCILLARIES WITH

LUBRICATING OIL RETAINED IN A CASING

The present invention relates to a transmission unit for relaying drive from a crankshaft of an internal combustion engine to engine ancillaries

Internal combustion engines typically have a pulley mounted at one end of the driven crankshaft of the engine. The pulley is connected by a belt to front end ancillaries of the engine, e.g. an alternator, a water pump, an oil pump, a power-assisted steering pump, a supercharger. Traditionally, the transmission ratio between the speed of rotation of the crankshaft and the speed of rotation of each ancillary device is fixed for all engine speeds and loads and is a function of the size of the pulley mounted on the front of the crankshaft and the sizes of the pulleys associated with the individual engine ancillaries. This is disadvantageous because each ancillary device typically has to be sized so that it can operate efficiently at low engine speeds and thus each device is effectively oversized for high speed operation. For instance, an alternator has to be rated to give a certain amount of power. The worst case scenario must be chosen, which is at low engine speeds, when the alternator rotates slowly. The alternator must be rated to provide the required power at these low speeds of rotation. Consequently, it is overrated when high engine speeds is considered. Savings can be made both in cost and in weight by reduction in the size of and rating of an alternator.

Solutions to the above problem have been proposed in JP 2001124191, JP 59194152 JP 58207559 and US 4644824, in each of which an epicyclic gear arrangement is used to transmit rotation from an internal combustion engine crankshaft to a pulley engaged by a belt which drives the front end ancillaries. The epicyclic gear arrangement has a flyweight operated brake which enables a transmission ratio change at a selected crankshaft rotational speed. However, the solutions proposed are quite complex and therefore expensive. They also present problems of lubrication. This is recognised in JP 59013164 where an elaborate lubrication system is provided for lubricating the transmission unit with lubricant supplied by a passage extending through the input shaft of the unit.

According to a first aspect of the present invention, there is provided a transmission unit for relaying drive from a crankshaft of an internal combustion engine to an engine ancillary, the transmission unit comprising: a casing which is mountable on an end face of the internal combustion engine; an input shaft rotatable in the casing about an axis of rotation, the input shaft being connectable to or an integral part of the crankshaft of the engine; an output pulley via which drive is output from the transmission unit to a belt for onwards transmission to an engine ancillary; an epicyclic arrangement of sun gear, planet gears, a planet carrier and an annulus gear via which drive can be relayed from the input shaft to the output pulley;

a one-way clutch operable between the output pulley and the input shaft to allow relative rotation therebetween in one sense only; and a flyweight-operated braking mechanism, comprising a ring of flyweights which rotate with rotation of the input shaft, for braking the epicyclic arrangement of gears; wherein: for a first range of lower rotational speeds of the input shaft the transmission unit has a first mode of operation in which drive is transmitted from the input shaft via the epicyclic gear arrangement to the output pulley so that the output pulley rotates at a speed which is higher than the speed of rotation of the input shaft; for a second range of higher rotational speeds of the input shaft the transmission unit has a second mode of operation in which the one-way clutch locks the output pulley to rotate with the input shaft; the flyweight-operated brake mechanism switches the transmission unit between the first and second modes of operation; and the flyweights, the flyweight-operated brake mechanism and the epicyclic gear arrangement of sun gear, planet gears, planet carrier and annular gear are all encased within the casing and any lubricant oil thrown radially outwardly away from the input shaft during rotation of the input shaft and the epicyclic gear arrangement is retained in the transmission unit by the casing.

According to a second aspect of the invention, there is provided an internal combustion engine having a transmission unit for relaying drive from a crankshaft of an internal

combustion engine to an engine ancillary, the transmission unit comprising: a casing which is integral with an end face of the internal combustion engine; an input shaft rotatable in the casing about an axis of rotation, the input shaft being connectable to or an integral part of the crankshaft of the engine; an output pulley via which drive is output from the transmission unit to a belt for onwards transmission to an engine ancillary; an epicyclic arrangement of sun gear, planet gears, a planet carrier and an annulus gear via which drive can be relayed from the input shaft to the output pulley; a one-way clutch operable between the output pulley and the input shaft to allow relative rotation therebetween in one sense only; and a flyweight-operated braking mechanism, comprising a ring of flyweights which rotate with rotation of the input shaft, for braking the epicyclic arrangement of gears; wherein: for a first range of lower rotational speeds of the input shaft the transmission unit has a first mode of operation in which drive is transmitted from the input shaft via the epicyclic gear arrangement to the output pulley so that the output pulley rotates at a speed which is higher than the speed of rotation of the input shaft; for a second range of higher rotational speeds of the input shaft the transmission unit has a second mode of operation in which the one-way clutch locks the output pulley to rotate with the input shaft;

the flyweight-operated brake mechanism switches the transmission unit between the first and second modes of operation; and the flyweights, the flyweight-operated brake mechanism and the epicyclic gear arrangement of sun gear, planet gears, planet carrier and annular gear are all encased within the casing and any lubricant oil thrown radially outwardly away from the input shaft during rotation of the input shaft and the epicyclic gear arrangement is retained in the transmission unit by the casing.

In an elegant simple package, embodiments of the present invention provide a well lubricated engine ancillary drive mechanism mountable in an engine between the engine crankshaft and the pulley from which drive is transmitted to the engine ancillary devices. The device does not require an elaborate lubrication system, separate oil pump or complex lubricant supply passages. The device provides a transmission ratio switch at a chosen speed without the need for the electrical componentry associated with the device and without need for the supply of high pressure hydraulic fluid to the device. Thus the device can be used with existing engines with minimal redesign.

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which:

Figure 1 is a cross-sectional view in perspective of an engine ancillary drive mechanism according to the present invention; and

Figure 2 is a cross-section through the mechanism of Figure 1 taken in a plane parallel to and intersecting with the rotational axis of the crankshaft of the engine.

Figure 1 shows an engine ancillary drive mechanism 10 which comprises a pulley 11 which is capable of driving a belt (not shown) which relays drive to ancillary devices of an engine, such as an alternator, water pump, oil pump, power-assisted steering pump, an air-conditioning pump and supercharger. Also shown in the figure is an input shaft

12. This shaft will either be an end part of a crankshaft of an internal combustion engine, or will be a separate shaft connectable to a crankshaft of an internal combustion engine to rotate with the engine crankshaft.

A static casing 13 is illustrated in the Figures. It comprises a planar flange portion 13a which extends as an annulus around the transmission unit 10. From the inner edge of the flange 13a there extends a boss 13b having an annular section 13c extending perpendicular to the flange

13a, a front face 13d, extending radially inwardly from the annular section 13c in parallel with the flange 13a and spaced from the flange 13a by the annular section 13c, and a lip 13e extending away from the radially innermost edge of the front face 13d back towards the flange 13a, in parallel with the annular section 13c. The lip 13e provides an annular surface which defines an aperture through the front face 13d. The annular lip 13e and the annular section 13c both have a common central axis which is coincident with the rotational axis of the input shaft 12.

The pulley 11 comprises an annular belt engaging section 11a which takes the axis of rotation of input shaft 12 as its axis of rotation. This annular section 11a overlies the annular section 13c of boss 13b. Extending inwardly from the annular outer section 11a is a web lib, which extends perpendicularly to the annular section 11a. The web lib connects the annular portion 11a with a sleeve portion lie of the output pulley, the sleeve portion lie extending in parallel with the annular outer portion 11a and within the radially outer portion 11a. A sun gear 40 of an epicyclic arrangement of gears of the unit is integrally formed with the sleeve portion lie at an end of the sleeve portion lie.

The input shaft 12 is fixed to an annulus gear 14. The annulus gear 14 rotates with the input shaft 12. The input shaft 12 is journalled for rotation in the unit by bearings 15 which act between a hub 16 and a forwardly extending lip portion Hd of the pulley 11. The hub 16 is mounted on the shaft 12 for rotation therewith. Seals 17 and 18 are provided respectively between the hub 16 and input shaft 12 and the hub 16 and the pulley 11. The seals 17, 18 prevent escape of lubricant from the unit 10.

Also shown in the Figures are planet gears 19 which are rotatably mounted on a planet carrier 20. The planet carrier 20 is an annular member extending around the input shaft 12, the inner sleeve portion 14a of annulus 14 and the sun 40. The planets 19 mesh with both radially inward facing teeth of the annulus 14 and radially outward facing teeth of the sun 40.

The planet carrier 20 has a radially outward annular friction disc carrier section 20a, with external grooves. Friction discs 21 are mounted in the groovesso that the friction discs 21 rotate with the planet carrier 19 while being slidable axially along the grooves. Each friction disc 21 can engage at least one non-rotatable brake disc 22. The plurality of non-rotating brake discs 22 are mounted in grooves provided on the interior of the annular section 13c of the boss 13b. They are slidable axially along the boss 13b but cannot rotate relative to the boss. Biasing springs 23 apply a force on the assembly of friction discs 21 and brake discs 22, the biasing springs 23 acting via a pusher plate 24. The pusher plate 24 is attached to the planet carrier 20 to move with the planet carrier 20. The assembly of rotatable friction discs 21 and non-rotating brake discs 22 is sandwiched between the pusher plate 24 and a fixed end stop 45 secured to the casing 13.

A plurality of flyweights 44 are arranged in an annular ring to act between the annulus 14 and the planet carrier 20. The planet carrier 20 has an annular flange 25 which provides a reaction surface engaged by the ring of flyweights 44. Each of the flyweights 44 is L-shaped and on rotation of the ring of flyweights 44 about the input shaft axis each flyweight 44 rotates about its elbow.

As shown in the Figure, the transmission unit 10 is at rest. In this condition the flyweights 44 are not spinning and therefore apply no force. The biasing springs 23 via the pusher plate 24 apply pressure on the stack of friction discs 21 and brake discs 22 in order to brake the planet carrier 20 and to hold it stationary.

A sprag clutch 30 acts between the inner sleeve 14a of the annulus 14 and the sleeve portion lie of pulley 11 and functions as a one-way clutch allowing relative rotation between the annulus 14 and the pulley 11 only in one direction of rotation. The clutch 30 allows the pulley 11 to rotate faster than the annulus 14, but prevents the pulley 11 from rotating slower than the annulus 14.

The teeth of the annulus 14, the planets 19 and the sun 4 are all helical and so an axial force arises from the transmission of torque from the annulus 14 via the planet gears 19 to the sun gear 40. The applied torque gives rise to an axial force on the planet gears 19 and hence the planet carrier 20. The axial force on the planet carrier 20 generated by a transmission of torque through the planet gears 19 acts in the same direction as the force applied by the biasing spring 23 and acts to force the pusher plate 24 to push the friction discs 21 into engagement with the brake discs 22 and therefore to hold the planet carrier 20 stationary.

Once drive is relayed via the input shaft 12 to the annulus 14, the flyweights 44 start to spin. The force applied by the ring of flyweights 44 acts on the planet carrier 20 to move the planet carrier 20 to the right of the position shown in Figure 2. The L-shaped flyweights 44 rotate about their elbows and apply a force on the planet carrier 20 in opposition to the force applied by the biasing springs 22 and the force resulting from the relayed torque. At low speeds the flyweight force is less than the sum of the other two forces and so the planet carrier 20 is held

still and rotation is transmitted from the input shaft 12 via the annulus 14, the planet gears 19 to the sun gear 40 and thereby to the pulley 11 and onwards to the belt engaged by the pulley. This achieves a transmission ratio whereby the speed of rotation of the pulley 11 is a multiple of the speed of rotation of the input shaft 12 and the pulley 11 rotates faster than the input shaft 12.

As the speed of rotation increases the force applied by the flyweights 44 increases and eventually overcomes the force applied by the biasing springs 23 and the axial force arising from the torque transmitted via the planet gears 19. When this happens the planet carrier 20 and the pusher plate 24 are slid to the right of their positions shown in Figure 2 and the brake assembly is released to allow rotation of the planet carrier 20. The rotation of the planet carrier 20 and the planet gears 19 means that torque ceases to be transmitted from the annulus 14 via the planet gears 19 to the sun gear 40 and instead the one-way clutch 30 locks the pulley 11 to rotate with the annulus 14 at the same rotational speed.

The fact that the force balance comprises partly the axial force resulting from torque transmitted via the planet gears 19 is helpful to the change process. As the speed of rotation of the annulus increases and the flyweights 44 start to release the brake, then the torque transmitted via the planet gears 19 will reduce and therefore the axial force resulting therefrom will also reduce, meaning that the force applied by the flyweights 44 can further act to disengage the brakes. This allows for a quick changeover. In reverse fashion, when the speed of rotation of the input

shaft 12 is slowing then the brake assembly starts to be applied and the more the brakes are applied then the more torque is transmitted via the planet gears 19 and the greater is the resultant axial force so that the brakes become applied even more.

It is envisaged that the flange 13a will be attached to a front cover of an internal combustion engine. Alternatively, the flange 13a and the boss 13b extending therefrom could be formed as an integral part of the engine front cover. In either event, an aperture defined by the flange 13a will expose the epicyclic gear arrangement of the invention to lubricating oil of the crank case of the internal combustion engine so that lubricating oil can flow directly into and out of the epicyclic gear arrangement from the crank case. Thus, is no need for the engine to be provided with specific oil flow passages, nor is there any need for the epicyclic gear box to be provided with specific lubricant flow passages. This is made possible by having the casing 13 surround and encase the brake assembly of brake discs 22, friction discs 21 and flyweights 44 and also surround the epicyclic arrangement of planet carrier 20, annulus 14, planets 19 and sun lie.

During rotation of the epicyclic arrangement the gears thereof tend to throw lubricating oil radially outwardly away from the input shaft 12. This radially outwardly expelled oil is then caught by the inner surface of the boss 13b of the casing 13 and is kept within the mechanism and/or returned to the engine crank. It is not lost outside the mechanism. The bearings 15 and 31 and the seals 17 and 18 prevent escape of lubricant from outside the cover 13.

Thus, having the epicyclic gear components encased radially within the boss 136 of the casing 13 enables the creation of an elegant simple design which requires a minimum of parts and does not require special provision for lubrication.