GB2057986A

GB2057986A - Power transmission gear box to drive plural axles

Info

Publication number: GB2057986A
Application number: GB7914484A
Authority: GB
Original assignee: STONEFIELD VEHICLES
Current assignee: STONEFIELD VEHICLES
Priority date: 1979-04-25
Filing date: 1979-04-25
Publication date: 1981-04-08

Abstract

A power transmission gear box for automatically converting single axle drive into 2-axle drive when needed or preferably 2-axle drive into 3-axle drive from a single power source, comprises in the latter case an input 5, a first output 33 for a first axle of a vehicle, a second output 37 to drive a second axle, means 31 to split the power from the input between the first and second outputs in accordance with a predetermined ratio, and a further output 53 for the third axle, provided with drive means (sprocket wheel 51) rotatable on a shaft 55 for driving the further output 53, a driving connection (sprocket wheel 47 and chain 49) between the said drive means and the output for the first axle of the vehicle, and an automatic clutch 57 for drivingly engaging said drive means and said shaft for the further output when the difference in the speed of rotation of the first and further outputs 33, 53 exceeds a predetermined value. Preferably, there is a manual clutch 27 for engaging the input, and the differential gearing 31 for distributing the power between the first and second outputs comprises an epicyclic gear train to distribute the power in the ratio of 2:1. <IMAGE>

Description

SPECIFICATION Power transmission gear box This invention relates to a power transmission gear box whereby 4 wheel drive can be obtained automatically from 2-wheel drive when needed, and more specifically where 6-wheel drive can be obtained automatically from the gear box when it is needed but whereby at all other times the gear box will provide only 4wheel drive.

In most 6-wheel drive vehicles, the rear bogie axles are both in constant drive with either a common drive to both axles or with separate drives, coupled by a differential which evens the drive when the axles require to revolve at different speeds, i.e. when cornering. In the first construction described above, the wheels have to slip to take up the different speeds and in the second, on poor grip conditions, all the drive can be lost when the wheels on one axle lose their grip with the ground. Another problem with such known constrctions is that complicated, expensive and heavy gearing is needed to drive the third axle and the size of some of the components for driving the axles which would normally be driven if the vehicle was of the 4-wheel drive variety has to be increased, thereby increasing the overall weight of the vehicle.

It is an accepted fact that on good road surfaces, 6-wheel drive is not necessary or advantageous and there is therefore no point in driving the third axle. However, when the vehicle is not on a good road surface, it is advantageous to have the driving going to the axles on which the wheels have the best chance of gripping at any one time and the present invention seeks to provide such an arrangement and an arrangement whereby, if wheels on one of the rear axles begin to slip, then drive will automatically to transmitted to the other rear axle which will, hopefully, mean that the wheels on that axle will grip and maintain traction.

According to the broadest aspect of the present invention, we provide a power transmission gear box for automatically converting single axle drive into 2-axle drive when needed, comprising a first output for a first axle of a vehicle, a further output for a second axle to be driven, drive means rotatable on a shaft for driving the further output, a driving connection between the said drive means and the output for the first axle of the vehicle, and an automatic clutch for drivingly engaging said drive means and said shaft for the further output when the difference in the speed of rotation of the two outputs exceeds a predetermined value.

According to a preferred embodiment of the present invention, we provide a power transmission gear box for automatically converting 2-axle drive into 3-axle drive when required, from a single power source, the gear box comprising an input, a first output to drive a first axle of a 4-wheel drive vehicle, a second output to drive a second axle of a 4-wheel drive vehicle, means to split the power from the input between the first and second outputs in accordance with a predetermined ratio and a further or third output for driving a third axle of the 4-wheel drive vehicle to convert the vehicle into a 6-wheel drive vehicle, there being a driving connection between the first and further outputs, which connection includes an automatic clutch, said further output normally not being driven but being driven when the automatic clutch senses a difference in the rotational speed of the first and further or third outputs, or such difference exceeds a predetermined value.

Preferably, there is a manual clutch for engaging the input, and the differential gearing for distributing the power between the first and second outputs comprises an epicyclic gear to distribute the power in the ratio of 2:1 between the first output which preferably drives the forward one of the two rear axles and the second output which preferably drives the front axle.

Preferably, there is a range change mechanism in the form of an epicyclic gear to vary the drive to the differential gearing. This may, for example, give a 1:1 ratio or a 1:2.7 ratio.

Preferably also, there is an automatic clutch located between the first and second outputs so that if one of these starts rotating faster than the other, for example because of wheel spin on one of the axles, then the clutch will automatically become engaged to ensure the best possible use of all available torque from the input.

Preferably, the driving connection between the first and further outputs comprises a sprocket rotatable with the first output, a sprocket rotatable on a drive shaft for the further output and an endless drive member entrained around the two sprockets and the automatic clutch has one set of clutch plates rotatable with the sprocket rotatable on the drive shaft for the further output and a second set of clutch plates rotatable with the said shaft, the clutch being engaged only when the two sets of plates begin to rotate at different speeds, or the relative rotational speed of the two sets of plates exceeds a predetermined value.

The automatic clutch described above is now commercially available in the U.K. and is known as a viscostatic clutch. Such clutches incorporate two sets of clutch plates or discs rotatable relative to each other, the plates of one set being alternately arranged with those of the other set, and the plates are immersed in a liquid which, unless violently agitated, acts as a lubricant. However, when the liquid is agitated, it undergoes a molecular change and becomes more viscous. This viscosity increases as the agitation of the liquid increases. Hence, limited slipping between the clutch plates may occur, but as soon as this moves above a certain predetermined value, the liquid turns into a pasty viscous mass which tends to lock the two plates together.It will be appreciated, however, that different types of automatic clutch could be used instead of a viscostatic clutch.

From the foregoing, it will be understood that the clutches can act as a differential gear to permit minor discrepances in axle speeds on good road surfaces, but will act as a nonslip differential to lock axles together when one axle connected to another by the clutch starts rotating at considerbly higher speed than the other.

Also according to the present invention, we provide a method of imparting drive to a further output from a previously driven output comprising driving a drive member which is rotatable on a shaft rotatable with the further output from the previously driven output, providing an automatic clutch between the said shaft and said drive member, and arranging for said automatic clutch to engage and impart drive from the drive member to the shaft whenever the shaft is rotating at a slower speed than that of the previously driven output, or the difference in said speeds exceeds a predetermined limit.

The present invention is now described by way of example with reference to the accompanying drawings, in which: Figure 1 is a partly schematic perspective view showing a power transmission gear box for an automatically engageable 6-wheel drive for a vehicle driven by an input shaft from a standard gear box; Figure 2 is a schematic representation of a 2-speed transposing gear box for a 4-wheel drive vehicle, and Figure 3 is a partly schematic side elevation showing the modification which has to be made to the 2-speed transposing box of Fig. 2 to convert it into an automatically engaging 6wheel drive mechanism.

Referring to the drawings, Fig. 1 shows a main gear box 1, a main chain drive 3 driven from an input shaft 5 from the gear box 1 and a 2-speed transposing gear box 7 driven from the main chain drive 3, which transposing box is converted into a 6-wheel drive power transmission gear box by the addition of a further drive arrangement 9.

Mounted on the end of the input shaft 5 remote from the gear box 1 is a gear sprocket 11 around which is engaged a drive chain 1 3. The chain 1 3 also engages an input sprocket 1 5 of the 2-speed transposing box 7 and a further gear wheel 1 7 for operating a power take off shaft 1 9 having front and rear outputs engageable by a suitable clutch 21.

The main chain drive and its associated sprockets is the subject of U.K. Patent Application No. 15952/76.

The input sprocket 1 5 is rotatably mounted on a shaft 23 and is connected to an eipcyclic range change mechanism 25 by a manual clutch 27. The range change mechanism 25 includes an epicyclic gear 29 which can be arranged to give a 1:1 drive ratio from the sprocket 15 by locking an annulus and a sun gear together in known manner (see Fig. 2) or a higher range can be obtained by locking the annulus to "earth", i.e. the casing, so that the carrier will rotate at a higher output speed, e.g. at 2.7 times the speed of rotation of the sprocket 1 5. The eipcyciic range change mechanism is of known construction.

The output from the range change mechanism, i.e. the carrier thereof, has further planetary gear wheels mounted thereon which form part of an epicyclic differential gear mechanism 31 distributing power to the front and rear axles of a vehicle by means of a first or rear output 33, the shaft 35 of which is driven by means of the annulus of the differential 31 and a second or front output 37 driven from the sun gear of the differential gear mechanism 31, the arrangement being such that one-third of the total power is transmitted to the front output 37 and twothirds to the rear output 33.It will of course be appreciated that different power sharing ratios could be achieved but it is preferred that the major proportion be available for the rear wheels especially when a second rear axle is provided which is also to be driven from one of the rear axles, as is the case with the present invention.

A first set of clutch plates 41 is keyed to a shaft 39 driving the front output 37, which plates are alternately arranged between the plates 43 of a second set of clutch plates rotatable with the shaft 35. Under normal driving conditions wherein front and rear outputs 33 and 37 are rotating at the same speed, the two sets of clutch plates 41 and 43 will rotate at the same speed. The clutch plates 41, 43 form part of a self-energising or automatic, viscostatic clutch 45, the clutch plates rotating in a housing filled with a liquid which, under normal circumstances, is a liquid but which, when agitated, undergoes a molecular change and becomes more viscous.

It will thus be appreciated that it there is substantial relative movement between the sets of clutch plates 41 and 43 for example when the wheels on the axle associated with one of the outputs 33, 37 begin to slip, then the liquid will become agitated and will, due to its increased viscosity (lt becomes almost like a tacky gum), cause the sets of clutch plates to become locked together.

In accordance with the present invention, a drive sprocket 47 is rotatable with the set of clutch plates 43 and is connected by means of an endless drive chain 49 to an input sprocket 51 of a further or third output 53 for driving the second rear axle of the vehicle.

The sprocket 51 is rotatable on a drive shaft 55 of the third output 53 and is connected to the drive shaft 55 by an automatic clutch similar to the clutch 57 described in detail with reference to Fig. 2. The automatic clutch together with the sprockets 47 and 51 form part of the drive arrangement 9 and comprises a first set of clutch plates rotatable with the sprocket 51 and a second set of clutch plates rotatable with the shaft 55, the two sets of plates being located in a suitable housing and being rotatable within a normally liquid material which, when agitated, becomes extremely viscous.

Under normal operating conditions, the power transmission gear box described above will operate as a 4-wheel drive gear box driving the first and second outputs 33 and 37, with the clutch 45, when not engaged, acting as a differential. Under these circumstances, the road wheels associated with the axle driven by the third output 53 will be rotating at the same speed as the wheels on the other two axles and hence, the speed of rotation of the shaft 55 will be the same as that of the shaft 35.The two sprockets 47 and 51 are identical and hence, due to chain 49, the sprocket 51 will rotate at the same rotational speed as that of the shaft 35 which means that the two sets of plates in the clutch 57 will be rotating at the same speed. How- ever, should the wheels associated with the first output 33 begin to spin, the sprocket 47 will begin to rotate at a speed faster than the shaft 55 and as a result the sprocket 51's speed of rotation will increase relative to that of shaft 55.This means that the two sets of plates of the clutch 57 will begin to move relative to each other at a faster and faster rate and as a result the viscostatic material around the plates will be agitated and become very viscous or tacky, thus tending to lock or engage the clutch which will automatically begin to drive the output 53 and hence the wheels of the third axle at the same speed as those associated with the output 33. Of course, any increase in speed of the output 33 will also have an affect on the output 37 because of the automatic clutch 45.

It will of course be appreciated that under normal operating conditions, the clutch 57 will act as a differential allowing the wheels associated with the third axle to rotate at slightly different speeds from the other wheels of the vehicle, e.g. when cornering.

The advantage of arranging for two-thirds of the power from the input sprocket 1 5 to be transmitted to the first rear output 33 is that this higher proportion of power is readily available when required to drive the third axle of the vehicle.

It will be appreciated that by taking a drive direct from the first output 33 and causing it automatically to drive a third output 53 when required through an automatic clutch, a very simple mechanism is provided which only gives a modest increase in weight to the vehicle. Of course, a drive mechanism from the output 33 to sprocket 51 other than that specifically described with reference to the drawings is possible, e.g. a belt/pulley drive or even interengaging gear pinions.

It should also be appreciated that the invention as defined in the appended claims can also be used for purposes other than converting 2-wheel drive to 4-wheel drive or 4-wheel drive to 6-wheel drive. Also, of course, automatic clutches other than the viscostatic one described can be used.

Although this invention has been specifically described with reference to the driving of a further axle on a vehicle, it should be realised that the invention could also be used to drive a live axle on a further vehicle, e.g. a trailer.

Claims

1. A power transmission gear box for au tomatically converting single axle drive into 2axle drive when needed, comprising a first output for a first axle of a vehicle, a further output for a second axle to be driven, drive means rotatable on a shaft for driving the further output, a driving connection between the said drive means and the output for the first axle of the vehicle, and an automatic clutch for drivingly engaging said drive means and said shaft for the further output when the difference in the speed of rotation of the two outputs exceeds a predetermined value.

2. A power transmission gear box for automatically converting 2-axle drive into 3-axle drive when required, from a single power source, the gear box comprising an input, a first output to drive a first axle of a 4-wheel drive vehicle, a second output to drive a second axle of a 4-wheel drive vehicle, means to split the power from the input between the first and second outputs in accordance with a predetermined ratio and a further or third output for driving a third axle of the 4-wheel drive vehicle to convert the vehicle into a 6wheel drive vehicle, there being a driving connection between the first and further outputs, which connection includes an automatic clutch, said further output normally not being driven but being driven when the automatic clutch senses a difference in the rotation speed of the second and third outputs or such difference exceeds a predetermined value.

3. A power transmission gear box as claimed in claim 2 wherein a manual clutch is provided for engaging the input.

4. A power transmission gear box as claimed in claim 2 or 3 wherein the differential gearing for distributing the power between the first and second outputs comprises an epicyclic gear to distribute the power in the ratio of 2:1 between the first output and the second output.

5. A power transmission gear box as claimed in claim 4 wherein the first output drives the forward one of the two rear axles and the second output drives the front axle.

6. A power transmission gear box as claimed in any one of claims 2-5 wherein there is a range change mechanism in the form of an eipcyclic gear to vary the drive to the differential gearing.

7. A power transmission gear box as claimed in any one of claims 2-6 wherein there is an automatic clutch located between the first and second outputs so that if one of these starts rotating faster than the other then the clutch will automatically become engaged to ensure the best possible use of all available torque from the input.

8. A power transmission gear box as claimed in any one of claims 1-7 wherein the driving connection between the first and further outputs comprises a sprocket rotatable with the first output, a sprocket rotatable on a drive shaft for the further output and an endless drive member entrained around the two sprockets.

9. A power transmission gear box as claimed in claim 8 wherein the automatic clutch has one set of clutch plates rotatable with the spocket rotatable on the drive shaft for the further output and a second set of clutch plates rotatable with the said shaft, the clutch being engaged only when the two sets of plates begin to rotate at different speeds, or the relative rotational speed of the two sets of plates exceeds a predetermined value.

1 0. A method of imparting drive to a further output from a previously driven output comprising driving a drive member which is rotatable on a shaft rotatable with the further output from the previously driven output, providing an automatic clutch between the said shaft and said drive member, and arranging for said automatic clutch to engage and impart drive from the drive member to the shaft whenever the shaft is rotating at a slower speed than that of the previously driven output, or the difference in said speeds exceeds a predetermined limit.

11. A method of imparting drive to a further output from the second of two previously driven outputs, said method being substantially as hereinbefore described with reference to the accompanying drawings.

11. A power transmission gear box substantially as hereinbefore described with reference to the accompanying drawings.

12. A method of imparting drive to a further output from a previously driven output, said method being substantially as here it before described with reference to the accompanying drawings.

CLAIMS (17 Apr 1980)

1. A power transmission gear box for automatically converting 2-axle drive into 3-axle drive when required, from a single power source, the gear box comprising an input, a first output to drive a first axle of a 4-wheel drive vehicle, means to split the power from the input between the first and second outputs in accordance with a predetermined ratio and a third output for driving a third axle of the 4-wheel drive vehicle to convert the vehicle into a 6-wheel drive vehicle, there being a driving connection between the first and third outputs, which connection includes an automatic clutch, said further output normally not being driven but being driven when the automatic clutch senses a difference in the rotational speed of the irst and third outputs, or such difference exceeds a predetermined value.

2. A power transmission gear box as claimed in claim 1 wherein a manual clutch is provided for engaging the input.

3. A power transmission gear box as claimed in claim 1 or 2 wherein the differential gearing for distributing the power between the first and second outputs comprises an epicyclic gear to distribute the power in the ratio of 2:1 between the first output and the second output.

4. A power transmission gear box as claimed in claim 3 wherein the first output drives the forward one of the two rear axles and the second output drives the front axle.

5. A power transmission gear box as claimed in any one of claims 1 to 4 wherein there is a range change mechanism in the form of an epicyclic gear to vary the drive to the differential gearing.

6. A power transmission gear box as claimed in any one of claims 1 to 5 wherein there is an automatic clutch located between the first and second outputs so that if one of these starts rotating faster than the other then the clutch will automatically become engaged to ensure the best possible use of all available torque from the input.

7. A power transmission gear box as claimed in any one of claims 1 to 6 wherein the driving connection between the first and third outputs comrpises a sprocket rotatable with with the first output, a sprocket rotatable on a drive shaft for the third output and an endless drive member entrained around the two sprockets.

8. A power transmission gear box as claimed in claim 7 wherein the automatic clutch has one set of clutch plates rotatable with the sprocket rotatable on the drive shaft for the third output and a second set of clutch plates rotatable with the said shaft, the clutch being engaged only when the two sets of plates begin to rotate at different speeds, or the relative rotational speed of the two sets of plates exceeds a predetermined value.

9. A method of imparting drive to a third output from the second of two previously driven outputs comprising driving a drive member which is rotatable on a shaft rotatable with the third output from the previously driven second output, providing an automatic clutch between the said shaft and said drive member, and arranging for said automatic clutch to engage and impart drive from the drive member to the shaft whenever the shaft is rotating at a slower speed than that of the previously driven second output, or the difference in said speeds exceeds a predetermined limit.

1 0. A power transmission gear box substantially as hereinbefore described with reference to the accompanying drawings.