GB2481394A

GB2481394A - Transmission unit for transmitting drive from an engine to an engine ancillary device

Info

Publication number: GB2481394A
Application number: GB1010391.9A
Authority: GB
Inventors: Steven Wynne Hughes
Original assignee: Antonov Automotive Technologies Ltd; Antonov Automotive Europe BV
Current assignee: Antonov Automotive Technologies Ltd; Antonov Automotive Europe BV
Priority date: 2010-06-21
Filing date: 2010-06-21
Publication date: 2011-12-28
Also published as: GB201010391D0; WO2011161407A1

Abstract

A transmission unit 10 for transmitting drive from an engine to an engine ancillary. The transmission unit 10 comprises an input shaft 20 arranged to receive drive from the engine and an output shaft 30 for outputting drive to the engine ancillary. An epicyclic arrangement of gears 40 comprising a sun gear (315, Figure 4), annulus gear (310), planet gear (300)and planet carrier (305) operable to transmit drive for at least two different transmission ratios between the input shaft 20 and the output shaft 30 is also provided. The transmission unit 10 has a one-way clutch (195, Figure 2) acting between the input shaft 20 and the output shaft 30 and arranged to prevent the output shaft 30 from rotating slower than the input shaft 20 and a braking mechanism 50 arranged to selectively brake one of the epicyclic arrangement of gears 40 to change between the at least two different transmission ratios.

Description

A TRANSMISSION UNIT FOR TRANSMITTING DRIVE FROM AN ENGINE TO

AN ENGINE ANCILLARY

The present invention relates to a transmission unit for transmitting drive from an engine to an engine ancillary. The present invention is described herein by way of a practical example as a transmission unit for transmitting drive from an output shaft of an internal combustion engine to an alternator. However, it is readily applicable to other engine ancillaries, for example to transmit drive from an output shaft of an internal combustion engine to a water pump, an oil pump, a power-assisted steering pump, or a supercharger, for example.

Alternators are commonly employed in automotive applications to charge a vehicle's battery and to power the vehicle's electrical system whilst the internal combustion engine of the vehicle is running.

One common type of alternator is the Lundell, or Claw-Pole, alternator which has a rotor comprising a pair of stamped pole pieces fixed around a cylindrical field core and a stator comprising a stator core and stator windings.

A regulator applies a voltage across the field core via two slip rings to cause the two pole pieces to become opposing magnetic poles. The pole pieces have interlocking claws' such that when the rotor spins inside the stator, the alternating claws of the pole pieces induce an alternating current in the stator windings. Traditionally, a diode bridge is used to rectify the AC output of the stator windings into a DC output. The output voltage of the alternator is maintained at a required level, for example 14V, by regulating the field current in the rotor winding using the regulator. The alternator should be matched to the power requirements of the electrical system of the vehicle. More specifically, the power output of the alternator at the required voltage should be at least equal to the minimum power required by the electrical system of the vehicle.

Typically, the alternator is mounted adjacent the internal combustion engine of the vehicle and is connected, via an alternator pulley, to a belt which is driven by a pulley mounted at one end of the driven crankshaft of the vehicle's engine.

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 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.

In the case of an alternator, the power output at the required voltage should be at least equal to the minimum power required by the electrical system of the vehicle at all engine speeds. The worst case scenario should be chosen, which is at low engine speeds, when the alternator rotates slowly. Thus, the alternator should be rated to provide the required power at these low speeds of rotation.

Consequently, at speeds above idle, the alternator is overrated. The alternator is thus oversized and operates below its maximum efficiency at higher operating speeds.

It is an object of the present invention to provide a transmission unit which addresses the above problems.

Accordingly, there is provided a transmission unit which is arranged to transmit drive from an engine-driven input shaft to an engine ancillary at at least two different transmission ratios. The transmission unit includes an epicyclic arrangement of gears, a fluid driven braking mechanism and a linear actuator, wherein the linear actuator is operable to engage the braking mechanism in order to selectively change the transmission ratio of the unit when a different gear ratio for driving the ancillary is required.

There are several mechanical and electronic methods to determine when a gear change is required, such as an electronic engine management system or governor, for

example.

According to a first aspect of the present invention, there is provided a transmission unit for transmitting drive from an engine to an engine ancillary, the transmission unit comprising an input shaft arranged to receive drive from the engine, an output shaft for outputting drive to the engine ancillary, an epicyclic arrangement of gears comprising a sun gear, annulus gear, planet gear and planet carrier operable to transmit drive for at least two different transmission ratios between the input shaft and the output shaft, a one-way clutch acting between the input shaft and the output shaft and arranged to prevent the output shaft from rotating slower than the input shaft, and a braking mechanism comprising an electric actuator arranged to selectively brake one of the epicyclic arrangement of gears to change between the at least two different transmission ratios.

Optionally, the electric actuator is a linear electric actuator.

Optionally, the breaking mechanism further comprises a master cylinder driven by the electric actuator, and a slave cylinder in fluid communication with the master cylinder and arranged to apply a braking force to one of the epicyclic arrangement of gears.

Optionally, the braking mechanism further comprises a first piston slidably located at least partially in the slave cylinder and a second piston slidably located at least partially in the master cylinder.

Optionally, the transmission unit according to any preceding claim, further comprising a casing, which is stationary with respect to the engine.

Optionally, the braking mechanism further comprises at least one rotatable plate fixed to and rotatable with the one of the epicyclic arrangement of gears and at least one non-rotatable plate for selectively braking the one of the epicyclic arrangement of gears.

Optionally, the at least one non-rotatable plate is fixedly mounted to the casing.

Optionally, the first piston is arranged to apply pressure to the at least one non-rotatable plate to engage the at least one non-rotatable plate with the at least one rotatable plate to brake the one of the epicyclic arrangement of gears.

Optionally, the one-way clutch is arranged to allow the output shaft to rotate faster than the input shaft.

Optionally, the slave cylinder and first piston are annular.

Optionally, the planet carrier is fixed to and rotatable with the input shaft and the annulus gear is fixed to and rotatable with the output shaft.

Optionally, the braking mechanism is arranged to selectively brake the sun gear.

Optionally, the braking mechanism is a fluid driven braking mechanism and further wherein the fluid is selected from the groups consisting of liquid, oil, water, air and gas.

Optionally, the braking mechanism further comprises a wet clutch.

Optionally, the braking mechanism further comprises three rotatable plates.

Optionally, the braking mechanism comprises a sealed hydraulic circuit.

Optionally, the master cylinder and slave cylinder are connected by a flexible hose.

Optionally, the two different transmission ratios are 1:1 and 1:1.4 to 1:1.8.

Optionally, the braking mechanism further comprises a resilient means biased against the braking mechanism.

According to a second aspect of the present invention, there is provided a transmission unit for transmitting drive from an engine to an engine ancillary, the unit comprising an input shaft arranged to receive drive from the engine, an output shaft for outputting drive to the engine ancillary, an epicyclic arrangement of gears comprising a sun gear, annulus gear, planet gear and planet carrier operable to transmit drive for at least two different transmission ratios between the input shaft and the output shaft, a one-way clutch acting between the input shaft and the output shaft and arranged to prevent the output shaft from rotating slower than the input shaft, and a braking mechanism comprising a master cylinder and a slave cylinder in fluid communication with the master cylinder, the slave cylinder arranged to a apply a braking force to one of the epicyclic arrangement of gears. Therefore, the brake actuating force can be lower, whilst maintaining a high braking force.

According to a third aspect of the present invention, there is provided a vehicle comprising an engine, an engine ancillary, and a transmission unit as described above.

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 schematic view of a transmission unit having an input shaft, an output shaft, an epicyclic arrangement of gears, a braking mechanism, a master and slave cylinder arrangement and a casing, given by

way of example only;

Figure 2 is an enlarged cross-sectional schematic view showing the input shaft and output shaft of the transmission unit of Figure 1; Figure 3 is an enlarged cross-sectional schematic view showing the casing of the transmission unit of Figure 1; Figure 4 is an enlarged cross-sectional schematic view showing the epicyclic arrangement of gears of the transmission unit of Figure 1; Figure 5 is an enlarged cross-sectional schematic view showing the braking mechanism of the transmission unit of Figure 1; and Figure 6 is an enlarged cross-sectional schematic view showing the master and cylinder arrangement of the transmission unit of Figure 1.

It should be noted that the figures are illustrated for simplicity and are not necessarily drawn to scale.

Figure 1 shows a transmission unit 10 of the present invention illustrating the main components of the transmission unit. The transmission unit 10 has an input shaft 20 which may be driven by an external power source, for example an internal combustion engine, and an output shaft 30 for driving an ancillary device, for example an alternator (not shown). The input shaft 20 is coupled to the output shaft 30 by an epicyclic arrangement of gears 40.

The transmission unit 10 also has a braking mechanism 50 for selectively braking one of the gears of the epicyclic arrangement of gears 40, in order to change the transmission ratio of the transmission unit 10, and a master and slave cylinder arrangement 60 for engaging the braking mechanism 50. Figure 1 also shows a static casing, or enclosure, 70 inside which the epicyclic arrangement of gears 40 and the braking mechanism 50 may be housed.

As shown in Figure 2, the transmission unit 10 comprises a pulley 100 driven by a belt (not shown). The belt may be driven by a crankshaft pulley (not shown) which is rotated either directly or indirectly by the crankshaft of the internal combustion engine (not shown) . The diameter of the pulley 100 is chosen to give a required transmission ratio between the pulley 100 and the engine crankshaft pulley. The pulley 100 may be fixedly connected to the input shaft 20 and rotatable therewith about a main axis 110.

The pulley 100 comprises an annular belt engaging section, or grooves, 120 which takes the axis of rotation of input shaft 20, i.e. main axis 110, as its axis of rotation.

Extending inwardly from the annular outer section 120 of the pulley 100 is a web 130, which extends perpendicularly to the annular section 120. The web 130 connects the annular portion 120 with the input shaft 20.

The input shaft 20 is journalled for rotation in the transmission unit 10 by bearings 140, for example, roller or ball type bearings, which act between a sleeve portion 150 of the input shaft 20 and the static casing 70.

The output shaft 30 of the transmission unit 10 is rotatable about the main axis 110 and comprises a first shaft portion 160 and a second shaft portion 170. The first and second shaft portions 160, 170 are connected by an annular flange 180 extending radially therebetween. The output shaft 30 is journalled for rotation in the unit 10 by bearings 190 which act between the second shaft portion 170 and the epicyclic arrangement of gears 40.

A one-way clutch 195, for example a sprag clutch, acts between the sleeve portion 150 of the input shaft 20 and the first shaft portion 160 of the output shaft 30 allowing relative rotation between the input shaft 20 and the output shaft 30 in one direction of rotation only. The clutch 195 is arranged to allow the output shaft 30 to rotate faster than the input shaft 20, but prevents the output shaft 30 from rotating slower than the input shaft 20. Thus, when the braking mechanism 50 is disengaged, the clutch 195 causes the output shaft 30 to rotate at the same speed as the input shaft 20.

As shown in Figure 3, the static casing 70 of the unit comprises a back plate 200 and a cover 205.

-10 -The back plate 200 includes an outer section 210 extending annularly about the main axis 110. The outer section 210 includes a first annular recess 215 disposed toward the radially outermost edge of the outer section 210, a second annular recess 220 disposed toward the radially innermost edge of the outer section 210, and a third recess 225 located therebetween. The second annular recess 220 defines an axis longitudinally through the centre of its circular cross-section. In this embodiment, the axis of the second annular recess 220 corresponds to the main axis 110, about which the input shaft 20 rotates. The back plate 200 further comprises a boss 230 towards the radially innermost edge of the back plate 200 and a web 235 extending in a radial direction between the outer section 210 and the boss 230. The radially innermost face of the boss 230 defines an opening 235 through which the output shaft 30 may extend. A seal 240 may be provided in the opening 235, between the boss 230 and the output shaft 30 to prevent the escape of lubricant from the unit 10.

The cover 205 comprises a rim 245 extending annularly about the main axis 110. When the cover 205 is assembled on to the back plate 200, the rim 245 is located in the first annular recess 215 of the back plate 200 to seal the outer portion of the static casing 70 and prevent the escape of lubricant from the unit 10. The cover 205 further comprises a front face 250 extending annularly about, and in a substantially perpendicular direction from, the main axis 110. Extending axially, in a rearward direction, from the rear surface of the front face 250 are inner and outer annular lips 255, 260. The radially innermost face of the -11 -inner annular lip 255 defines an opening 265 through which the input shaft 20 may extend. A seal 270 may be provided in the opening 265, between the inner annular lip 255 and the input shaft 20 to prevent the escape of lubricant from the unit 10.

As depicted in Figure 4, the epicyclic arrangement of gears 40 comprises planet gears 300, rotatably mounted on a planet carrier 305, an annulus gear 310 and a sun gear 315.

The planet carrier 305 is fixed to the input shaft 20 for rotation therewith. The planet carrier 305 comprises a first flange 320 extending from the sleeve portion 150 of the input shaft 20, a second flange 325, on which the planet gears 300 are rotatably mounted, and an annular lip 330 extending axially between the first and second flanges 320, 325.

The annulus gear 310 may be fixed to the second shaft portion 170 of the output shaft 30 for rotation therewith.

The sun gear 315 is integrally formed with an annular flange 335. The planet gears 300 mesh with both the radially inward facing teeth of the annulus gear 310 and radially outward facing teeth of the sun gear 315 to transmit torque from the input shaft 20 to the output shaft when the braking mechanism 50 is engaged (as discussed below) If the teeth of the annulus gear 310, the planet gears 300 and the sun gear 315 are helical then an axial force will arise from the transmission of torque from the planet -12 -carrier 305 to the sun gear 315. The applied torque gives rise to an axial force on the sun gear 315 and hence the annular flange 335. The axial force on the annular flange 335 generated by a transmission of torque through the planet gears 300 is resisted by a thrust bearing 340. The thrust bearing 340 is mounted on the rear surface of the front face 250. Helical gears tend to be less efficient than spur gears, but quieter. If spur gears are used for the annulus gear 310, the planet gears 300 and the sun gear 315 then the transmission unit will be more efficient and simpler and the thrust bearing 340 may be replaced by a reduced friction surface, since no gear-generated axial forces would require reaction.

Figure 5 shows the braking mechanism 50 in further detail. The annular flange 335 of the sun gear 315 has, on its radially outermost surface, a friction disc carrier section 400 with external grooves 410. Friction discs 420 are mounted in the grooves 410 such that the friction discs 420 rotate with the sun gear 315. Three non-rotatable brake discs 430 are mounted in grooves 440 provided on the radially inward-facing surface of the outer annular lip 260 of the cover 205. The brake discs 430 are slidable axially along the grooves 440 of the outer lip 260 but cannot rotate relative to the outer lip 260. Each friction disc 420 can engage at least one of the non-rotatable brake discs 430.

The braking mechanism 50 may also have a fixed end stop 450 secured to the rear side of the front face 250 of the cover 205. The braking mechanism 50 may be lubricated such that it forms a wet clutch arrangement.

-13 -Preferably, the friction discs 420 and brake discs 430 are arranged alternately in the axial direction, with a non-rotating brake disc 430 at either end of the arrangement.

Figure 6 shows the master and slave cylinder arrangement 60 of the unit 10 in further detail. The master and slave cylinder arrangement 60 serves to selectively engage or disengage the braking mechanism 50 such that rotation of the sun gear 315 relative to the casing 70 is prevented or enabled, respectively. Through preventing the rotation of the sun gear, the transmission ratio of the unit can be altered. The master and slave cylinder arrangement 60 comprises a slave cylinder assembly 500 in fluid communication with a master cylinder assembly 505 via a conduit 510 such as a flexible hose, for example.

The slave cylinder assembly 500 comprises an annular slave piston 515, for engaging the braking mechanism 50, slidably located at least partially in the second annular recess 220. A crown 520 of the piston 515 and the second annular recess 220 together define a chamber 525 in which hydraulic fluid may be held. Preferably, the piston 515 and the second annular recess 220 are accurately machined for a close fit. 0-rings 530 are located in a groove 535 on the outer surface of the piston 515 to prevent the escape of hydraulic fluid from the chamber 525 around the sides of the piston 515.

A passage 540 is formed in the back plate 200 to enable the transfer of hydraulic fluid into and out of the chamber 525 in order to axially displace the slave piston 515. The passage 540 extends in an axial direction from the rear side -14 -of the back plate 200 to the second annular recess 220 to connect the chamber 525 with a port 545 formed on the rear side of the back plate 200.

The master cylinder assembly 505 comprises a master cylinder housing 550, having a circular cross-section, and an actuator 555. In this example, the actuator 555 is a linear electric actuator. A master piston 560 is located at least partially within the master cylinder housing 550 such that a crown 565 of the piston 560 and the inner surfaces of the master cylinder housing 550 define a master cylinder chamber 570 in which hydraulic fluid may be held.

Preferably, the piston 560 and the master cylinder housing 550 are accurately machined for a close fit. 0-rings 575 are located in a groove 580 on the outer surface of the piston 560 to prevent the escape of hydraulic fluid from the master chamber 570 around the sides of the piston 560.

A passage 585 is formed in a wall of the master cylinder housing 550 such that the master chamber 570 is in fluid communication with a port 590 formed on the outer surface of the master cylinder housing 550. In this example, the passage 585 extends radially through the master cylinder housing 550 from the alternator side of the housing 550 to the master chamber 570. The port 590 of the annular housing 550 is connected to the port 545 of the back plate via the conduit 510 such that the master chamber 570 is in fluid communication with the chamber 525. The conduit 510 may be a flexible hose to allow positional flexibility of the master cylinder assembly 505. The actuator 555 is operable to apply a force to the piston 560, via a rod, in the axial direction of the master cylinder housing 550 such -15 -that the piston 560 may be displaced in an axial direction.

The displacement of the master piston 560 by the actuator 555 in an axial direction away from the actuator 555 reduces the volume of the master chamber 570, causing the transfer of hydraulic fluid from the master chamber 570 to the chamber 525, via the conduit 510. The hydraulic fluid transferred to the chamber 525 exerts an axial force on the slave piston 515, causing the piston 515 to slide axially away from the back plate 200 to engage the braking mechanism 50. The surface area of the master piston crown 565 may be greater than the surface area of the slave piston crown 520 such that the force exerted on the slave piston 515 by the hydraulic fluid is greater than the force exerted on the master piston 560 by the actuator 555, thereby achieving a mechanical advantage.

The braking mechanism 50 is sandwiched between the annular slave piston 515 and the fixed end stop 450. The application of an axial force to the annular slave piston 515 by the hydraulic fluid causes the piston 515 to apply an axial force to the assembly of rotatable friction discs 420 and non-rotating brake discs 430, pressing the friction discs 420 and brake discs 430 together, to thereby prevent relative rotation therebetween. The axial force exerted by the piston 515 is resisted by the end stop 450. Thus, the axial displacement of the master piston 560 by the actuator 555 can prevent rotation of the sun gear 315 relative to the casing 70.

In preferred embodiments, the annular piston 515 may comprise a pusher 595 for transferring the force applied by the piston 515 to the assembly of rotatable friction discs -16 - 420 and non-rotating brake discs 430. However, in other embodiments, the piston 515 may simply be extended to directly apply a force to the assembly.

For example, the linear actuator may be controlled electronically by an engine management system monitoring engine speed or required electrical load.

In a first mode of operation of the transmission unit 10, the actuator 555 is operated to displace the master piston 560 in an axial direction away from the actuator 555 such that the volume of the master chamber 570 is reduced.

The reduction in volume of the master chamber 570 causes the transfer of hydraulic fluid from the master chamber 570 to the chamber 525, via the passage 585, port 590, conduit 510, port 545 and passage 540. The hydraulic fluid exerts an axial force on the piston 515 so that the piston 515 is displaced axially away from the back plate 200 and exerts an axial force on the friction discs 420 and brake discs 430 such that they are pressed together, thereby preventing rotation of the sun gear 315.

In this mode, the input shaft 20 and the planet carrier 305, fixed thereto, rotate relative to the static sun gear 315. Accordingly, the planet gears 300, which mesh with the sun gear 315, rotate about the static sun gear 315. The planet gears 300 mesh with and transfer torque to the annulus gear 310 such that the annulus gear 310 and the output shaft 30, to which the annulus gear 310 is fixed, rotate about the main axis 110 at an angular velocity greater than that of the planet carrier 305. Thus, in the first mode of operation, the output shaft 30 rotates faster -17 -than the input shaft 20. The transmission ratio, i.e. the multiple of the angular velocity of the input shaft 20 at which the output shaft 30 rotates, is a function of the number of teeth on the annulus gear 310 and the sun gear 315. For example, the transmission ratio could be 1.4:1 or 1.7:1 such that the output shaft 30 completes 1.4 or 1.7 revolutions for every revolution of the input shaft 20.

In a second mode of operation of the transmission unit 10, the actuator 555 is operated to displace the master piston 560 in an axial direction toward the actuator 555 such that the volume of the master chamber 570 is increased.

The increase in volume of the master chamber 570 causes the transfer of hydraulic fluid from the chamber 525 to the master chamber 570, via the passage 540, port 545, conduit 510, port 590 and passage 585. The transfer of hydraulic fluid away from the chamber 525 draws the slave piston 515 toward the back plate 200 so that the slave piston 515 no longer applies a force sufficient to press together the friction discs 420 and brake discs 430, thereby allowing rotation of the sun gear 315. It may be desired to incorporate one or more resilient members, such as return springs, in the unit 10 acting on the piston 515 to bias the piston 515 to disengage the braking mechanism.

In this second mode, the free rotation of the sun gear 315 means that torque ceases to be transmitted from the planet gears 300 to the annulus gear 310 and instead the one-way clutch 195 locks the output shaft 30 to rotate with the input shaft 20 at the same rotational speed. Thus, in the second mode of operation, the transmission ratio of the unit 10 is 1:1.

-18 -The unit 10 operates such that when the braking mechanism 50 is engaged the alternator is driven by the output shaft 30 at a rotational speed which is a first multiple of crankshaft speed and when the braking mechanism is disengaged the alternator is driven by the output shaft at a rotational speed which is a second, lesser, multiple of crankshaft speed. By using the unit 10, the alternator may be driven at a higher multiple of crankshaft speed to increase power output at low engine speeds. Thus, the alternator can be designed such that it is smaller and lighter and rated to operate more efficiently at higher speeds.

The use of helical threads in the epicyclic arrangement of gears is optional and spur gears could equally well be used.

The operation of the unit 10 may be controlled so that the braking mechanism is engaged for selected engine operating conditions in which it is desired to "speed up" the alternator. For instance when the engine is idling and the alternator needs to be rotated at a higher multiple of crankshaft speed in order to generate sufficient power to run the vehicle's electrical system. The operation of the unit 10 may be controlled by an electronic engine management system (not shown) which may control the operation of the actuator 555, thus controlling the movement of the master piston 560.

It is envisaged that the unit 10 could be attached to a front cover of an alternator via lugs affixed to the -19 -alternator housing and secured thereto with fastening means, for example bolts. Alternatively, the back plate 200 could be formed as an integral part of the alternator cover.

The master and slave cylinder arrangement60 defines a sealed hydraulic circuit. Since the master cylinder assembly 505 and slave cylinder assembly 500 are linked via the conduit 510, the master cylinder assembly 505 can be remote from the remainder of the unit 10. Thus, the position of the master cylinder assembly 505 may be varied depending on the space constraints of a given engine and the size of the remainder of the unit 10 may be greatly reduced.

A linear electric actuator 555 may be used to operate the hydraulic circuit. Alternatively, a continuously driven pump may be used. However, the hydraulic circuit only draws power at the moment when the master piston 560 is displaced and so is preferable.

During rotation of the epicyclic arrangement of gears 40, the gears thereof tend to throw lubricating oil radially. This radially outwardly expelled oil is then caught by the inner surfaces of the cover 205 and the outer section 210 of the back plate 200 and is kept within the static casing 70. It is not lost outside the mechanism.

The bearings 140, 190, the seals 240, 270 and the close fit of the rim 245 of the cover 205 in the first recess 215 of the back plate 200 prevent the escape of lubricant from outside the static casing 70. Thus, having the epicyclic arrangement of gears encased within the static casing 70 enables the creation of an elegant, simple design which -20 -requires a minimum of parts and does not require special provision for lubrication.

It will be appreciated that the foregoing is only one specific example and a number of variations and modifications are possible.

For example, the transmission unit 1 could be used with other types of engine such as a gas turbine or a non-vehicular engine.

Although in the above disclosed embodiment the input shaft 20 drives the planet carrier 305, the output shaft 30 is driven by the annulus gear 310 and the sun gear 315 is controlled by the braking mechanism, other arrangements of gears can be used. For example, the input shaft 20 could drive the planet carrier 305, the annulus gear 310 could be controlled by the braking mechanism 50, and the output shaft could be driven by the sun gear 315. This gives a different gear ratio.

Any number of planet gears 300, including a single planet gear 300, may be rotatable mounted on the planet carrier 305.

Although the above disclosed embodiments have been described as having an annular shaped piston in an annular recess, the hydraulic brake could be effected by one or more separate cylindrical cavities, each having a piston, spaced around the static casing 7.

-21 -Although the master and slave cylinder arrangement has been described as a hydraulic circuit, other fluids may be used. For example, a pneumatic system could be employed.

The braking mechanism could have any number of friction discs or brake discs.

Any other gear ratios may be selected.

Although the actuator has been described as a linear electric actuator, other electric or electronic actuators may be used.

The present invention neatly solves the problem of providing a transmission unit which can provide a step-up gear ratio between the alternator and the internal combustion engine at low engine speeds and permitting a different or 1:1 drive at higher engine speeds.

Claims

-22 -CLAIMS: 1. A transmission unit for transmitting drive from an engine to an engine ancillary, the transmission unit comprising: an input shaft arranged to receive drive from the engine; an output shaft for outputting drive to the engine ancillary; an epicyclic arrangement of gears comprising a sun gear, annulus gear, planet gear and planet carrier operable to transmit drive for at least two different transmission ratios between the input shaft and the output shaft; a one-way clutch acting between the input shaft and the output shaft and arranged to prevent the output shaft from rotating slower than the input shaft; and a braking mechanism comprising an electric actuator arranged to selectively brake one of the epicyclic arrangement of gears to change between the at least two different transmission ratios.
2. The transmission unit of claim 1, wherein the electric actuator is a linear electric actuator.
3. The transmission unit of claim 1, wherein the breaking mechanism further comprises: a master cylinder driven by the electric linear actuator; and a slave cylinder in fluid communication with the master cylinder and arranged to apply a braking force to one of the epicyclic arrangement of gears.

-23 -
4. A transmission unit according to claim 3, wherein the braking mechanism further comprises a first piston slidably located at least partially in the slave cylinder and a second piston slidably located at least partially in the master cylinder.
5. A transmission unit according to any preceding claim, further comprising a casing, which is stationary with respect to the engine.
6. A transmission unit according to any preceding claim, wherein the braking mechanism further comprises at least one rotatable plate fixed to and rotatable with the one of the epicyclic arrangement of gears and at least one non-rotatable plate for selectively braking the one of the epicyclic arrangement of gears.
7. A transmission unit according to claims 5 and 6, wherein the at least one non-rotatable plate is fixedly mounted to the casing.
8. A transmission unit according to claim 6, wherein the first piston is arranged to apply pressure to the at least one non-rotatable plate to engage the at least one non-rotatable plate with the at least one rotatable plate to brake the one of the epicyclic arrangement of gears.
9. A transmission unit according to any previous claim, wherein the one-way clutch is arranged to allow the output shaft to rotate faster than the input shaft.

-24 -
10. A transmission unit according to any of claims 2 to 9, wherein the slave cylinder and first piston are annular.
11. A transmission unit according to any preceding claim, wherein the planet carrier is fixed to and rotatable with the input shaft and the annulus gear is fixed to and rotatable with the output shaft.
12. A transmission unit according to claim 11, wherein the braking mechanism is arranged to selectively brake the sun gear.
13. A transmission unit according to any preceding claim, wherein the braking mechanism is a fluid driven braking mechanism and further wherein the fluid is selected from the groups consisting of liquid, oil, water, air and gas.
14. A transmission unit according to any preceding claim, wherein the braking mechanism further comprises a wet clutch.
15. A transmission unit according to any previous claim, wherein the braking mechanism further comprises threerotatable plates.
16. A transmission unit according to any preceding claim, wherein the braking mechanism comprises a sealed hydraulic circuit.
17. A transmission unit according claim 3, wherein the master cylinder and slave cylinder are connected by a flexible hose. -25
18. A transmission unit according to any preceding claim, wherein the two different transmission ratios are 1:1 and 1:1.4 to 1:1.8.
19. A transmission unit according to any preceding claim, wherein the braking mechanism further comprises a resilient means biased against the braking mechanism.
20. A transmission unit for transmitting drive from an engine to an engine ancillary, the unit comprising: an input shaft arranged to receive drive from the engine; an output shaft for outputting drive to the engine ancillary; an epicyclic arrangement of gears comprising a sun gear, annulus gear, planet gear and planet carrier operable to transmit drive for at least two different transmission ratios between the input shaft and the output shaft; a one-way clutch acting between the input shaft and the output shaft and arranged to prevent the output shaft from rotating slower than the input shaft; and a braking mechanism comprising a master cylinder and a slave cylinder in fluid communication with the master cylinder, the slave cylinder arranged to a apply a braking force to one of the epicyclic arrangement of gears.
21. A transmission unit substantially as hereinbefore described with reference to and as shown in the accompanying figures.-26 -
22. A vehicle comprising: an engine; an engine ancillary; and a transmission unit according to any previous claim.*.:r: INTELLECTUAL . ... PROPERTY OFFICE Application No: GB 1010391.9 Examiner: Mr Patrick Phillips Claims searched: 1 -20, 22 Date of search: 20 October 2010 Patents Act 1977: Search Report under Section 17 Documents considered to be relevant: Category Relevant Identity of document and passage or figure of particular relevance to claims X 1 -10, 13 US 2002/049 112 Al -19, 22 (MITSUBISHI) Whole document.X 2 -4, 6 -GB2455097 A 8, 10 -19 (ANTONOV AUTOMOTIVE) Figures and Page 8; Line 20 to Page 9; Line 22.X 2 -4, 6 -US 6066065 A 8, 10, 13-(NEW VENTURE GEAR) Whole document.X 2-4,6-U55842944A 8, 10, 13 -(MITSUBISHI) Whole document.X 20,22 GB2091357A (BORG) Figure 1 and Page 1; Lines 58 to 66.Categories: X Document indicating lack of novelty or inventive A Document indicating technological background and/or state step of the art.Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of before the filing date of this invention.same category.& Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:Search of GB, EP, WO & US patent documents classified in the following areas of the UJKCX Worldwide search of patent documents classified in the following areas of the IPC FO2B; F16H The following online and other databases have been used in the preparation of this search report WPI, EPODOC Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk *.:r: INTELLECTUAL . ... PROPERTY OFFICE International Classification: Subclass Subgroup Valid From F16H 0003/52 01/01/2006 F16H 0003/44 01/01/2006 F16H 0029/12 01/01/2006 F16H 0031/00 01/01/2006 Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk