GB1600001A

GB1600001A - Power transmission systems

Info

Publication number: GB1600001A
Application number: GB507477A
Authority: GB
Original assignee: VAUGHAN SPRUCE P
Current assignee: VAUGHAN SPRUCE P
Priority date: 1978-02-02
Filing date: 1978-02-02
Publication date: 1981-10-14

Description

(54) IMPROVEMENTS IN OR RELATING TO POWER TRANSMISSION SYSTEMS (71) I, PAUL VAUGHAN-SPRUCE, a British Subject, of "Parc Garland", The Lizard, Near Helston, Cornwall, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to automatic power transmission systems which operate to provide a variable speed ratio between power input and output shafts in accordance with input and output power/rotational speed conditions.

The invention is of broad, but by no means exclusive, application to automatic transmission gearboxes for motor vehicles.

A prime mover, such as a vehicle engine, normally operates most efficiently over a predetermined speed range and thus it is commonly coupled to the load through a gearbox which appropriately matches the prime mover to the load. When the operating speed range of the load is greater than the preferential speed range of the prime mover, as occurs for example with a motor vehicle, the traditional approach is to provide a variable ratio gearbox with a stepped series of fixed gear ratios which are selectable to provide an approximate balance between the prime mover and the load at all speeds of the latter. Such an arrangement has the disadvantage that the nature of a fixed ratio gearbox provides restricted flexibility for matching the power/speed characteristics of the engine output and the load, and optimum matching can only be achieved at a number of fixed points, corresponding to the individual gear ratios, between which points the matching is more or less approximate. The matching characteristics of such a gearbox arrangement can only be improved by increasing the number of fixed ratios available, thereby materially increasing both the cost and the complexity of the gearbox, and also the control system with an automatic transmission.

The object of the invention is to provide a power transmission system which overcomes the foregoing disadvantage by providing an input/output speed ratio which is infinitely variable in accordance with the input and output power/rotational speed conditions. A further object is to provide such a transmission system which can be designed in the form of an automatic self-regulating variable ratio gearbox constructed of gear wheels and pinions of tradi tional design and function, arranged on shafts or axles which can be mounted in standard bearings.

According to the invention an automatic power transmission system of infinitely-variabl ratio has dual power transmission paths b etweer input and output shafts which are interconnected through first and second stage gear mechanisms, the first stage comprising an epicyclic-type or differential gear mechanism providing said two transmission paths which ar of different effective gear ratio and which are combined in the second stage which comprises a differential gear mechanism with reaction gea means including a cage which is able to rotate freely in either direction and which carries a planet gear of the second stage, the reaction torque tending to rotate the cage being the resultant of three torque applied thereto, namely two torques which are applied from th input through said dual transmission paths respectively and a third torque which is provided by the resistance to rotation of a load coupled to the output shaft.

Thus the direction of speed of rotation of the cage of the reaction gear means of the second stage is governed by the torque differed tial between the input and output shafts. The arrangement enables a predetermined torque te be transmitted between the input and output shafts, while allowing for the speed of a prime mover coupled to the input shaft to increase should said pressure differential become too great.

A power transmission system in accordance with the invention can be designed to provide an infinitely variable ratio over a wide range such as is required in automotive applications.

Thus the system may, for example, operate over a range of gear ratios from 10:1 to 1:1.

Preferably the ratio of the effective overall gear ratios of the two transmission paths through the complete system is unity when the speed ratio of the input and output shafts is unity. Thus in this condition the power transmitted is split equally between the two paths.

The term "gear" is used herein in a broad generic sense and is not to be constructed narrowly as restricted to gear arrangements with meshing teeth. Although the latter will in most instances be employed a system in accordance with the invention may provide a friction drive, for example in whole or in part utilising an arrangement of belts and pulleys, between the shafts.

Two embodiments of the invention are illustrated diagrammatically, by way of example, in the accompanying drawings and will now be described with reference thereto. In the drawings: Figure 1 is a side view of one embodiment in the form of a system designed for automotive use and with a second stage differential gear mechanism of sun and planet type; Figure 2 is a sectional view on the line II - II in Figure 1; Figure 3 is a view corresponding to that of Figure 1 illustrating the second embodiment also designed for automotive use and utilising a second stage differential gear mechanism of crown wheel and differential pinion type; and Figure 4 is a view on the line IV - IV of Figure 3.

Each of the embodiments illustrated is constructed from generally standard components, using conventional technology for assembly and lubrication. A power input shaft I is coupled to a power output shaft 0' via two power transmission paths, between which the transmitted power is split and which are provided by a first stage gear mechanism A of sun and planet type or similar mechanism and recombined by a second stage modified differential mechanism B the reaction gear means of which is coupled to the output shaft 0'. The two power transmission paths of gear mechanism A are of different effective gear ratio and the input and output shafts are aligned on a common central axis C - C of the two stages.

Referring now specifically to the embodiment of Figures 1 and 2, the gear mechanisms A and B illustrated therein are basically similar to those found in the gear-change clusters of an automotive "automatic" gearbox. In this case, however, a central through shaft 0 passing through the output shaft O' is used as a power transmission path between the mechanisms A and B and in addition as a "carrier" shaft on which sun and planet assemblies of gear mechanisms A and B can freely and independently rotate. Two shafts D and E, on which planet pinions 1 and 2 of the stages A and B are respectively mounted, revolve in parallel motion around the axis C - C.

The sun and planet differential gear mechanism A further comprises a sun pinion 3 fixed on the hollow input shaft I which can rotate freely on the through shaft 0. The sun pinion 3 is in mesh with the planet pinion 1 on the shaft D which is carried by a cage assembly 4. At the input side this cage is mounted on the shaft 0 through a journal bearing 5, and the other side of the cage is fixed to a hollow shaft 6 also journalled on the through shaft 0. The planet pinion 1 is mounted outside the cage 4 and a secondary planet pinion 7 is also mounted on the shaft D within the cage. The pinion 7 meshes with a secondary sun gear 8 fixed on the shaft 0. Thus the power input to shaft I is split along two power transmission paths, a primary path through pinions 3, 1, 7 and 8 to the shaft 0 and a secondary by-pass power transmission path through the cage 4 and shaft 6 to which the reaction gear torque of the first stage gear mechanism is applied.

In operation the input torque is applied to the sun pinion 3, which causes the pinion 1 to rotate about its own axis on the shaft D and to orbit with the cage 4 around the central axis C - C. The proportioning of the power transmitted between the two transmission paths is determined by the relationship between these two induced rotations of the pinion 1 and depends on the resistance to rotation of the workload coupled to the output shaft 0' as expressed via the gear mechanism B which is sensed via the reaction of a sun pinion 9 of the mechanism B which is mounted on the hollow shaft 6 which carries the output of the secondary power transmission path of gear mechanism A.

By virtue of the principle of sun and planet type gear mechanisms a heavy bias, or line of least resistance, is incorporated in one of the transmission paths of the first stage.

Bearing the foregoing in mind, the second gear mechanism B is subject to two different power inputs, firstly from the sun pinion 8 fixed on the shaft 0 and secondly through the pinion 9 which is driven by the cage 4. The mechanism B has a second sun gear 10 fixed on the shaft 0 within a cage assembly 11 freely rotatable around the axis C - C and mounted on the shaft 0 through journal bearings 12. The sun gear 9 is in mesh with the planet pinion 2 mounted on the shaft E which is journalled in the cage 11. A second planet pinion 13 also mounted on the shaft E is coupled to the sun pinion 10 through ajockey pulley 14 which meshes with both pinions 10 and 13 and is mounted on a parallel shaft F within the cage 11. A third planet pinion 15 also fixed on the shaft E is in mesh with an output sun pinion 16 fixed to the output shaft O' which rotates on the through shaft 0.

In operation the two power inputs respective.

ly applied to the second stage gear mechanism B at the sun pinions 9 and 10 are not only of different magnitude but also their transmitted effects on the planet pinion shaft E are in opposition. As the output shaft O' is directly meshed via the pinions 15 and 16 to the shaft E its resistance to motion provides a reaction torque. The sun pinions provide an altemative or dual motion "potential" in the shaft E, either to revolve about its own axis or with the cage 11 around the central axis C - C, and hence it is possible to create a positive reaction pressure which is resolved by allowing the cage 11 to be completely unrestrained. Thus the action of the two input transmission paths and the output resistance path as combined by the described mechanism B is expressed in the motion of the cage 11 around the axis C - C.

By the correct overall design of the gearbox it is possible to prevent rotation of the cage 11, by providing that the three torques applied thereto by each of the two inputs to the second stage and by the output cancel one another out.

However, as the power inputs from the first stage are not stable an increase in the power applied to the input shaft I will disrupt the stability of the gear mechanism B and thus cause the unrestrained cage 11 to rotate. In practice the rotational speed of the cage does not affect the torque that can be applied at the output, it merely means that the input shaft I can revolve at increased velocity.

Thus the described stepless automatic gear-b box relies for operation on the ability to transmit overall a designed torque between the input shaft I and the output shaft regardless of speed differential. When the design torque applied through the gearbox is higher than the resistance to motion of the load, the vehicle to which the gearbox is fitted will accelerate. The converse also applies, namely that when the torque applied from the load through the gearbox is greater than the input torque supplied by the engine the vehicle will decelerate.

The embodiment of Figures 3 and 4 operates in an analogous manner to the first embodiment and the first gear stage A is identical therewith apart from the.use of different gear ratios between the meshing pinions. The same reference numerals are accordingly used for like components of the first stage A in both embodiments. However, in the second embodiment the second stage B utilises a bevel pinion differen tial gear arrangement basically similar to the differential gear arrangements used in the final drives of automotive vehicles but modified as will now be described. In this case the central shaft of mechanism B also forms the output shaft 0 but does not extend through to 0' the input side of the gearbox and the second stage has a separate input shaft G to which the crown pinion 8 of the first stage is fixed and which provides the carrier shaft for the first stage reaction gear assembly and the input shaft I.

At the inner end the output shaft 0 terminates in a bevel pinion 20. A bevel pinion 22 corresponding to and facing the pinion 20 is fixed to the shaft G and two diametrically opposed bevelled differential pinions 23 and 24, respectively mounted on two aligned stub shafts H and J mesh with and form a bridge between the pinions 20 and 22. The stub shafts H and J are rotatable in a cage assembly including a cage 25, and they rotate in a plane at right angles to the central axis C - C. This cage assembly is rotatably mounted on the output shaft 0 and, as usual with such differential gear mechanisms, the differential pinions 22, 23 revolve not only around their common axis but also around the axis C - C. An additional differential pinion 26 mounted on the stub shaft H has bevel teeth in mesh with a bevel gear 21 rotatably mounted on the output shaft O. The described bevel gear arrangement transmits one of the input torques to the second stage from the first stage to the cage 25.

The second input reaction torque to the cage 25 of the second stage B is applied via a shaft K rotatably mounted parallel to the central axis C - C. A pinion 27 mounted at the input end of this shaft meshes with the output pinion 9 of the second transmission path through the first stage, and a second pinion 28 fixed adjacent the output end of the shaft K meshes with a pinion 29 fixed tothe pinion 21 through a hollow shaft L mounted on the shaft O and on which the cage 25 ss rotatably mountea whereby to apply the second input torque thereto. The resistance torque from the output shaft 0 is applied to the cage 25 via the bevel pinion 20, and thus as before the reaction tor que applied to the tending to rotate the second stage differential gear assembly, including the cage 25, is the resultant of three torques, and the dual power transmission paths provided by the sun and planet gear mechanism of the first stage are combined in the second stage in a manner analogous to that described with reference to the first embodiment.

The provision of a reverse gear drive can be achieved in either embodiment in two ways.

Firstly, by incorporating a separate reverse pinion, which is manually selected, as in the traditional type of gearbox. Alternatively, re verse drive can be achieved by applying a braking action to one of the reaction gear com ponents described. The first of these methods - has the advantage of providing a full variable ratio range in both forward and reverse gear, whilst the second method does not involve the meshing engagement or disengagement of gear wheels, thereby reducing wear.

As described each of the embodiments utilises, for the first stage A, a differential gear mechanism of sun and planet type. It will be appreciated that any similar gear mechanism providing the two power transmission paths through the first stage A and providing the necessary mutually "biased" torques for the second stage B reaction gear means could in stead be employed in the first stage. For exam ple, the sun and planet first stage gear mechan isms of the embodiments could be replaced by a mechanism basically similar to the modified differential mechanism as used in the second stage B of the embodiment of Figures 3 and 4.

An epicyclonic gear ring assembly would pro vide another functionally similar mechanism which could alternatively be employed in the first stage A instead of the described sun and planet mechanisms.

An automotive transmission system employ ing the invention may advantageously employ a fluid coupling torque converter between the engine and the gearbox, as an alternative to the more usual friction plate clutch. The system may embody a ratchet device to restrain the freely rotatable cage of the second stage B, thereby providing a fixed bottom gear especially useful when the workload becomes abnormally large, for example when starting a vehicle on a steep hill.

Claims

WHAT I CLAIM IS:

1. An automatic power transmission system of infinitely variable ratio with dual power transmission paths between input and output shafts which are interconnected through first and second stage gear mechanisms, the first stage comprising an epicyclic-type gear mechanism providing said two transmission paths which are of different effective gear ratio and which are combined in the second stage which comprises a differential gear mechanism with reaction gear means including a cage which is able to rotate freely in either direction and which carries a planet gear of the second stage, the reaction torque tending to rotate the cage being the resultant of three torques applied thereto, namely two torques which are applied from the input through said dual transmission paths respectively and a third torque which is provided by the resistance to rotation of a load coupled to the output shaft.

2. A power transmission system according to Claim I, wherein the second stage mechanism is of sun and planet type with three sun gears in mesh with said reaction gear means, two of these sun gears respectively being driven by the two transmission paths from the first stage gear mechanism and the third connected to the output shaft.

3 A power transmission system according to Claim 2, wherein a shaft through which sun gears of the two gear stages are coupled also provides a carrier shaft on which the reaction gear assembly cages of both stages revolve.

4. A power transmission system according to Claim 1, wherein the second stage gear mechanism is of bevel pinion type with two opposed bevel pinions one of which is driven by one of the transmission paths of the first stage and the other of which is fixed to the output shaft, these bevel pinions mutually meshing with at least one differential bevel pinion of said gear assembly which is rotatably mounted on a shaft to which a further bevel pinion is fixed, said further bevel pinion meshing with a bevel pinion fixed to the cage of the reaction gear means.

5. A power transmission system according to Claim 4, wherein the second input torque applied to the cage of the second stage mechanism from the other transmission path of the first stage is applied through a shaft rotatable about a fixed axis parallel to the output shaft axis and on which is fixed a pinion meshing with a pinion fixed to said shaft on which the cage is mounted.

6. A power transmission system according to any one of the preceding Claims, wherein the first stage gear mechanism comprises two sun pinions one of which is fixed to the input shaft and the other of which is fixed to a shaft providing an output to the second stage and acting as a carrier shaft for the reaction gear cage of the first stage, these two sun pinions respectively meshing with two pinions fixed to a common shaft of the first stage reaction gear assembly the cage of which transmits the other output torque to the second stage.

7. A power transmission system according to any one of the preceding Claims, wherein the input and output shaft axes are aligned aad the input shaft is a hollow shaft rotatably mounted on the carrier shaft on which a cage assembly of the first stage is rotatably mounted.

8. A power transmission system according to any one of the preceding Claims, wherein the ratio of the overall gear ratios of the two transmission paths through the complete system is unity when the speed ratio of the input and output shafts is unity.

9. A power transmission system according to any one of the preceding Claims, wherein a ratchet device is incorporated and is engageable to restrain the cage of the second stage for rotation in one direction only and thereby provide a fixed bottom gear.

10. An automotive power transmission system according to any one of the preceding Claims, wherein a fluid coupling torque converter is provided to couple said input shaft to a vehicle engine.

11. An automatic power transmission system constructed and arranged substantially as herein particularly described with reference to Figures 1 and 2 or Figures 3 and 4 of the accompanying drawings.