GB2387882A

GB2387882A - A compact hydraulic actuator for an epicyclic gearbox

Info

Publication number: GB2387882A
Application number: GB0203030A
Authority: GB
Inventors: Timothy Payne
Original assignee: TIM PAYNE OVERDRIVE DESIGNS LT
Current assignee: TIM PAYNE OVERDRIVE DESIGNS LT
Priority date: 2002-02-08
Filing date: 2002-02-08
Publication date: 2003-10-29
Also published as: GB0203030D0

Abstract

A compact hydraulic actuator for an epicyclic gearbox comprises a conical clutch 60 operated by the hydraulic actuator having a piston 45 that is accommodated substantially within a volume defined by the clutch 60 thereby reducing the axial bulk of the hydraulic actuator. The clutch 60 in one position locks for rotation components of the epicyclic, for example, a sun gear (31, fig 2) to a ring gear (27) and in a second position the ring gear (27) or a planet carrier (20) is braked to a housing (10) or otherwise fixed against rotation relative to the housing (10). A reciprocating plunger pump is operated by an eccentric fixed to an input/output shaft and feeds pressurized hydraulic oil to the clutch 60. The gearbox may be retro-fitted in a transfer box for a four wheel drive vehicle and controlled by a control system having a hall effect sensor that enables a push button circuit to be engaged when a preset speed is reached.

Description

Improvements in and relating to epicyclic gearboxes.

This invention relates to epicyclic gearboxes and has particular reference to actuating assemblies for changing the gear ratios between an input shaft and an output shaft.

Epicyclic gearboxes assemblies are well-known in the art and have been used for many years to provide a constant mesh gear train to provide changes between at least two ratios in the manner of an overdrive or under ratio.

Epicyclic gearboxes and gear trains form the basis of the majority of automatic transmission and overdrive systems.

In a typical epicyclic gear change assembly, direct drive is normally obtained by the engagement of a friction clutch to join together to members of the gearing. For overdrive ratio, the clutch is disengaged and the reaction member of the gear train, normally the sun gear, is held stationary by means of a brake. It is usual in such assemblies for the clutch/brake to be biased to one position by means of a series of springs and for the clutch assembly to be moved against the spring pressure by hydraulic means. The hydraulic circuitry and the pump is usually built into the gearbox and is operated by means of the lubricating hydraulic fluid within the box. One of the disadvantages

of this arrangement is that these separate hydraulic pump or actuating mechanism adds significantly to the bulk and size of the gearbox.

There is a considerable market for epicyclic gearboxes to be added as fuel economy devices for motor vehicles. At the present time, medium- sized lorries and 4x4 vehicles particularly diesel-engined vehicles -- are frequently fitted with after-market overdrive assemblies. In modern compact motor vehicle design, the amount of space available to accommodate the gearbox and its actuating accessories is frequently limited and it is necessary and desirable, therefore, to incorporate all the operating components within as small a space as possible. Furthermore, the increasing power of relatively small engines, particularly small diesel engines, means that require torque transmission for such systems is increasing. Accordingly, there is a need for an overdrive assembly that is compacted in design and yet which can handle the increasing torque of modern engines.

While many gearbox/overdrive assemblies have incorporated the hydraulic operating means within the structure of the box itself, all of them incorporate the actuating mechanism

displaced or remote from the clutch/brake assembly. United Kingdom Patent Application No 2,062,140 is typical in this regard in that it describes a gear train in which a hydraulic actuator is coaxial with and rotationally coupled to the sun gear and may be frictionally engaged either to the ring gear or to the transmission casing. The member driven between these two positions by a piston member coaxial with and axially coupled to it, but which is rotationally free with respect to it and which is formed as a disk having a hub projecting from its centre. The hub may be connected to the engagement member so as to be axially fixed thereto, but rotationally free with respect to it. An annular fluid pressure chamber is defined around and coaxial with the hub between the casing and the piston member. The selective supply of fluid pressure to said annular chamber serves to drive the engagement member between its positions whereby the transmission provide either direct coupled stage or estate providing increased rotational speed.

Such an assembly is unnecessarily bulky due to the presence of the actuating mechanism and spring gear axially displaced from the clutch/brake member itself. The clutch/brake member in such gear trains is typically a

frustoconical element in which the conical surfaces define the brake/clutch surfaces in the manner described in the above UK Patent Application No. 2,062,140.

We have found, surprisingly, that we can produce a compact design whereby the hydraulic actuating mechanism is accommodated substantially within the volume defined by the clutch/brake member itself. Surprisingly, this leads to an extremely compact design and also permits the design of a clutch/brake member having a greater diameter for a given size of gearbox. This in turn results in a potentially greater clutch/brake contact area for any given axial dimension of the member, thus allowing for greater torque transmission. In one aspect of the present invention, there is provided an actuating assemblies for an epicyclic gearbox having a sun gear, ring gear and planet gears and carriers therefor, which assembly comprises: -

an operating member incorporating engaging means movable between a position in which said member locks for rotational one with the other, two of said sun gear, said ring gear and said planet gear carrier, and a second position in which one of said sun gear, said ring gear or

said planet carrier is a braked to a housing or otherwise fixed against rotation relative to said housing, hydraulic means for the supply of fluid under pressure to move said member between said positions characterized in that the hydraulic means acting on the operating member to move it from said one position to the other is accommodated substantially within the volume defined by the operating member itself.

The operating member may be in the form of a frustocone, the inner and outer conical surfaces of which constitute I the clutch/brake surfaces. Each surface may be provided with a suitable friction coating to aid engagement and release. The member may be biased to one of said positions by means of suitable biasing means which may typically be one or more springs.

In a further aspect of the present invention, the operating member is amounted coaxially with said sun gear, ring gear and planet carrier. The operating member may be capable of adopting a third position intermediate these said two positions referred to above whereby the said sun gear, ring gear and carrier are all free of contact with the operating member and the gearbox is effectively in a neutral or

l freewheel configuration.

The hydraulic means may include a pump operated by means of an eccentric driven by the output shaft to the gearbox. In one aspect of the invention, the eccentric may act on a rocking dolly to impart reciprocating motion to a pump piston, said dolly having a surface adapted to lie contiguous the surface of the eccentric to overlay an area thereof and a contoured head or dolly portion adapted to abut an upper part of said piston with the axis of the body of said dolly being dispose substantially radially with respect to the centre of the eccentric. The pump piston may be biased towards the eccentric and the eccentric and the dolly may be operated against the bias.

The operating member may be acted upon by a piston mounted coaxially with it comprising an annular cavity constituting a hydraulic volume and at least one feed conduit whereby the application of fluid under pressure to a volume causes or allows the volume to expand to move said operating member from a first position to a second position. The piston may be biased to said first position and the expansion of the fluid volume acts against the biasing means to move the member. In one aspect of the invention,

the hydraulic volume may be defined by the piston and another component, wherein the piston moves axially of the axis of rotation with respect to said component in response to an increase in the hydraulic pressure within the said volume and moves the operating or clutch/brake member with it. In one embodiment of the overdrive may be fitted to the transfer box of a 4x4 vehicle and is sufficiently compacted as to be installed in one piece. This compacted unit enables easier maintenance by making it much easier to remove the component in one piece for servicing purposes.

Following is a description by way of example only and with

reference to the accompanying informal drawings of methods of carrying the invention into the effect.

In the drawings: Figure 1 is a section through the input assembly for an epicyclic gearbox in accordance with the present invention.

Figure 2 it is a detailed section through the gearbox of Figure 1.

Figure 3 is a perspective view of the clutch assembly for selectively engaging the sun wheel with the ring gear and the gearbox housing.

Figure 9 is a section of Figure 3 showing the hydraulic area. Figure 5a is a diagrammatic section of the pressure pump in accordance with the present invention.

Figure 5b is a diagrammatic section showing the "dolly" or "bomb" at the extent of maximum travel.

Figure 6 is a circuit diagram of a control circuit for use in the present invention.

The gearbox in accordance with the present invention comprises a generally cylindrical housing 10 having in a forward face 11 a bearing assembly 12 adapted to accommodate input and output shaft assembly indicated generally at 13. Shaft assembly 13 comprises an input shaft 15 and an output shaft 16 mounted coaxially one with respect to the other and each capable of rotating one with

respect to the other, the output shaft 16 being journalled for rotation in bearing assembly 12.

Turning now to the detail of Figure 2, the input shaft 15 extends inwardly of housing 10 and carries intermediate its length, a planet carrier assembly 20 for rotation there with. The planet carrier 20 has a plurality (typically three) rearwardly extending axles (not shown) symmetrically spaced about the axis of rotation of input shaft 15, each of which axles carries a planet gear 21.

The output shaft 16 is journalled for rotation with respect to the input shaft 15 and has a rearwardly extending portion defined by a first annulus 22 having an outstanding flange 23 the outer extremity of which carries a further rearwardly extending cylindrical annulus 25 having on its inner surface a plurality of gear teeth 26 adapted to engage with the teeth of the planet gears 21. The cylindrical annulus 25 and its associated gear teeth 26 serve to define the ring gear 27 of the epicyclic gear assembly. The forward end 18 of input shaft 15 carriers a sun wheel assembly indicated generally at 30. Assembly 30 includes a sun gear wheel 31 which is adapted to engage with the gears of each of planet gears 21, the arrangement

being such that the planet gears 21, the ring gear 27 and the sun gear wheel 31 between them defined an epicyclic gear assembly. Sun gear 31 is adapted to be controlled by either being clutched for rotation with the ring gear 27 or clutched for engagement with housing 10 so that the sun gear 31 is maintained substantially stationary with respect to the housing.

As is common with epicyclic gear systems, when sun gear 31 is clutched for rotation with the ring gear 27, there is no relative movement between the components within the epicyclic gear train and the output shaft is effectively locked for rotation with the input shaft. On operating the clutch mechanism to release the sun gear 31 from the ring gear 27 and lock it in a stationary engagement with housing 10, the rotation of the input shaft causes the planet gears 21 to react against the stationary sun gear 31 so to cause rotation of the ring gear 27. In the example illustrated, there will be an increase in the rate of rotation of the output shaft as defined by the ratio of the number of teeth on the ring gear against the number of teeth on the sun gear. The operation of the clutch mechanism is more easily

understood from Figure 3 of the accompanying drawings.

Back plate 41 to gearbox housing 10 is provided with a central bearing block 42 which accommodates the rearward end of the input shaft 15 (not shown). The back plate 41 carries an annular brake plate 43 having a frustoconical surface 44 constituting a brake engaging surface. Brake plate 43 is fixedly secured to back plate 41. Spaced about bearing block 42 are a plurality of return springs 44 each of which is adapted to act against a hydraulic piston 45 which is carried by the input shaft and is free for rotation there on. Each spring 44 is located in recessed pockets on each of said back plate 41 and piston 45 which serves to constrain piston 45 against rotation. The cylindrical outer surface 46 is machined as a close fit for the inwardly directed extremity 47 of brake plate 43 and the portion of hydraulic piston 45 juxtaposed back plate 41 provided with a generally U-shaped section 48 adapted to accommodate a seal. Likewise inward extremity 47 of brake plate 43 accommodates seal 49 and is further cut away at 51 to define a hydraulic cavity. Back plate 41 and break plate 43 is further provided with a conduit 51 to provide a hydraulic feed to cavity 50. The hydraulic piston 45 is capable of limited axial movement with respect to the axis of the input shaft 15 the extent of which is defined by

thrust rings 53. In the datum position, the returns springs 44 bias hydraulic piston 45 forwardly to engagement with cone clutch and sun gear 60. In this datum position, the sun gear 31 and the ring gear 27 are locked for rotation and one with the other) the planet gears remains stationary and the speed of the output shaft is identical with the speed of the input shaft.

In operation, hydraulic fluid is introduced into the hydraulic cavity 50 via hydraulic feed 51 until the pressure with in the cavity is sufficient to overcome the bias of the return springs 44. Continued application of hydraulic pressure will result in the bias of the return springs 44 being overcome so that the hydraulic piston 45 is urged rearwardly (towards back plate 41) to disengage the sun gear 31 from the ring gear 27. While hydraulic pressure is maintained the piston is urged rearwardly to withdraw the cone clutch onto the brake surface 43 thus locking sun gear 31 to back plate 41 and hence housing 10.

In this way the piston of the cone clutch assembly associated with the sun gear is disposed substantially within the volume of the cone clutch 60 itself. This has the effect of reducing, significantly, the axial bulk of

the system where, hitherto, it has been necessary to employ actuating means externally of the cone clutch thus adding significantly to the bulk of the device.

The hydraulic supply may be fed from the general oil supply for the gearbox. In this embodiment, he first annulus 22 of the output shaft 16 is provided on its external surface with an eccentric 70. The eccentric 70 drives a plunger pump 71 having a piston 72 and a return spring 73 which serves to maintain the piston in operating contact with eccentric 70. In order to maintain a close fit between the eccentric 70 and the upper extremity of the piston 72, the eccentric operates on a piston 72 via a dolly 74 the arrangement being such that the dolly 74 "rocks" to accommodate the varying attitude of the cylindrical surface of eccentric 70 with respect to the upper extremity of piston 72 as the eccentric 17 rotates about the axis of annulus 22. This reduces wear at the tope of piston 72.

The pump assembly described above is capable of providing hydraulic actuation of the clutch/brake assembly and for lubrication of the operating components of the gearbox.

The gearbox of the invention may be provided with a separate sump which avoids the need for some components to

operate in an oil bath. This reduces oil shear within the box and permits satisfactory operation of the box for extended period at significant angles of inclination away from the nominal horizontal.

: will be apparent, therefore, that to a large extent the device itself correcting. When the gearbox is stationary, the plunger pump is inoperative and no fluid will be supplied. On rotation of the input shaft 15 there will be some motion of the output shaft 16 and initially this will be at the same speed as the input shaft since the clutch assembly will be located in its forward position under the influence of returns springs 44 to maintain the sun gear 31 for rotation with ring gear 27. As the gearbox commences to function and the speed of the input/output shaft 15/16 increases, the piston 72 of pump 71 will reciprocate at an increasing rate to provide a positive hydraulic pressure within the hydraulic system. Above a certain threshold, therefore, the hydraulic pressure in the gearbox will be sufficient to drive the clutch assembly 40 rearwardly against the bias of returns brings 44 to disengage the sun gear from the ring gear and to brake the sun gear to break the housing. This will then produce a reaction between the the planet gears and the ring gear with a result that the

speed of rotation of the output shaft will be increased with respect to the speed of rotation of the input shaft and depending upon the teeth ratio of the sun gears, the planet gears and the ring gear.

The invention envisages a speed control unit which is mounted near the drive shaft. The drive or input shaft 15 incorporates a magnet and the housing juxtaposed input shaft 15 includes a hall effect sensor (not shown) which detects the pulsating field of the magnet on the shaft.

This will enable the push button circuit to be engaged when a preset speed is reached. Figure 6 is a circuit diagram of a control system for use in conjunction with the epicyclic gearbox of the present invention.

Referring to Figure 6, the Hall effect sensor output signal is differentiated by a 3.9nF. capacitor and 100 K-Ohm resistor to produce a thin pulse which is then buffered by IC 1 a.

This pulse fed via the 68nF. capacitor is rectified by a lN4148AN5819 diodes and integrated by the 6.81.E'uC which charges to a voltage dependent upon the revolutions per second at which the drive shaft rotates.

! The voltage across the 6.81,uF is compared by a hysteresis comparator ICIb with the voltage from the slider of the lOKQ potentiometer RV1 which is set to correspond to the desired revolutions. The comparator has a hysteresis dead band of 0.2 volts to prevent the circuit hunting and switching on and off erratically.

When the revolutions are such that the 6.8,uF is charged to a higher voltage than the potentiometer setting plus roughly half the dead band, the comparator output goes low and the inverter IClc output goes high and enables the power to the Flip Flop switch unit via emitter follower Q1.

The Flip Flop circuit incorporates a 5 volt regulator (781L05) and three TTL logic ICs.

IC3 (7479) is a toggling "T" connected D type flip flop which drives the solenoid output transistor Q2 (TIP132) via R 12 (2.2k). At power up the flip flop starts in the "off' state. By pressing a push button connected to ICE (MAX 6816), the state of the flip flop is toggled to "on" IC 4 removes the effects of any contact bounce from the push button to prevent erroneous setting of the flip flop. IC2 (7900) is an inverter used to obtain the correct positive

going pulse to trigger the flip flop state.

It is a safety requirement that the electronics and solenoid +12 volts are taken directly to the ignition switched supply. Loss of power to the unit or solenoid will cause the overdrive to drop out.

The overdrive will drop out when the chosen road speed is not exceeded. The overdrive will also drop out when the pressure of the hydraulic fluid falls below the threshold required to overcome the bias of return springs 44.

Claims

1. An actuating assembly for an epicyclic gearbox having a sun gear, ring gear and planet gears and carriers therefor, which assembly comprises: -

an operating member incorporating engaging means moveable between a position in which said member locks for rotation, one with the other, two of said sun gear, said ring gear and said planet gear carrier, and a second position in which one of said sun gear, said ring gear or said planet carrier is braked to a housing or otherwise fixed against rotation relative to said housing, and hydraulic means for the supply of fluid under pressure to move said member between said positions, wherein the hydraulic means acting on the operating member to move it from said one position to the other is accommodated substantially within the volume defined by the operating member itself.

2. An assembly according to claim l, wherein the operating member is in the form of a frustocone, the inner and outer conical surfaces of which constitute the clutch/brake surfaces.

3. An assembly according to claim 2, wherein each of the inner and outer conical surfaces is provided with a suitable friction coating to aid engagement and release.

4. An assembly according to any preceding claim, wherein the member is biased to one of said positions by means of suitable biasing means.

5. An assembly according to claim 4, wherein the biasing means includes one or more springs.

6. An assembly according to any preceding claim, wherein the operating member is mounted coaxially with said sun gear, ring gear and planet carrier.

7. An assembly according to any preceding claim wherein the operating member is capable of adopting a third position intermediate these said two positions whereby the said sun gear, ring gear and carrier are all free of contact with the operating member and the gearbox is effectively in a neutral or freewheel configuration.

8. An assembly according to any preceding claim, wherein the hydraulic means includes a pump operated by means of an eccentric driven by the output shaft to the gearbox.

9. An assembly according to claim 8, wherein the eccentric acts on a rocking dolly to impart reciprocating motion to a pump piston, said dolly having a surface adapted to lie contiguous the surface of the eccentric to overlay an area thereof and a contoured head or dolly portion adapted to

abut an upper part of said piston with the axis of the body of said dolly being disposed substantially radially with respect to the centre of the eccentric.

10. An assembly according to claim 9, wherein the pump piston is biased towards the eccentric and the eccentric and the dolly are operated against the bias.

11. An assembly according to any preceding claim, wherein the operating member is acted upon by a piston mounted coaxially with it comprising an annular cavity constituting a hydraulic volume and at least one feed conduit whereby the application of fluid under pressure to a volume causes or allows the volume to expand to move said operating member from a first position to a second position.

12. An assembly according to claim 11, wherein the piston is biased to said first position and the expansion of the fluid volume acts against the biasing means to move the member.

13. An assembly according to claim 11 or claim 12, wherein the hydraulic volume is defined by the piston and another component, wherein the piston moves axially of the axis of rotation with respect to said component in response to an increase in the hydraulic pressure within the said volume and moves the operating or clutch/brake member with it.

14. An assembly according to any preceding claim further arranged to be fitted to the transfer box of a 4x4 vehicle and sufficiently compacted as to be installed in one piece.

15. A transfer box of a 4 x 4 vehicle having fitted thereto an assembly as defined in any preceding claim.

16. An assembly substantially as described hereinbefore with reference to the accompanying drawings and/or as shown in one or more of those drawings.