This invention relates to mechanical torque converters and more especially to a stepless variable ratio mechanical torque converter in which the input to output speed ratio and, therefore, torque multiplication is infinitely variable within predetermined limits.

Conventionally, continuously variable ratio mechanical transmission systems rely on the frictional forces generated between rotating components to transmit torque. To effect a ratio change, a control system is required to adjust the relative positions of these components.

Torque converters in accordance with this invention are load sensitive and the input to output speed ratio adjusts automatically in response to a variation in the relative values of input torque and output load. No control system is necessary and torque is transmitted only via toothed gearing.

According to the present invention there is provided a torque converter comprising a fixed structure which supports within coaxial bearings a rotatable housing, the housing in turn supporting within coaxial bearings carrier shafts of input and output gear wheels whose axes are coincident with the axis of rotation of the housing, the housing also carrying bearings about which rotates a first intermediate gear wheel which is adapted to mesh with the input gear wheel, a second intermediate gear wheel which is adapted to mesh with the said first intermediate gear wheel and a third intermediate gear wheel which is adapted to mesh with the output gear wheel, the intermediate gear wheels rotating about axes which intersect the axis about which the housing rotates.

The three intermediate gear wheels may rotate about bearings located on a cross member of the housing. Preferably, the second and third gear wheels define an integral unit.

A free wheel mechanism is preferably positioned between the fixed structure and the housing. More than one such free wheel mechanism may be provided.

The invention will now be described by way of example only with reference to the accompanying diagrammatic drawings in which:-

Figure 1 is a side view in section of a torque converter in accordance with the present invention; and

Figure 2 is a side view in section of the torque converter shown in Figure 1 on which the forces acting during maximum torque multiplication are indicated.

Reference will firstly be made to Figure 1 of the drawings.

The torque converter illustrated comprises a rotatable gear housing 1 mounted within coaxial bearings 2 of a fixed structure 3. A cross member of the housing 1 comprises two sections 9a and 9b set at different angles to the axis of rotation of the housing 1, section 9a including a bearing 8 and section 9b including a bearing 10. The gear housing 1 supports a carrier shaft 4 of an input bevel pinion 5 within a bearing 6 and a carrier shaft 14 of an output crown wheel 13 within a bearing 15. The teeth of the input bevel pinion 5 mesh with complementary teeth of an intermediate crown wheel 7 which is supported by the bearing 8. The teeth of the intermediate crown wheel 7 also mesh with complementary teeth of an intermediate bevel pinion 11 which is formed entegral with an output bevel pinion 12. Both the intermediate bevel pinion 11 and the output bevel pinion 12 are supported by the bearing 10, and the teeth of

output bevel pinion 12 mesh with complementary teeth of the output crown wheel 13. A free wheel mechanism 16 is located between the gear housing 1 and the fixed structure 3.

In one example of the embodiment illustrated in Figures 1 and 2 the input bevel pinion 5, crown wheel 7 and intermediate bevel pinion 11 have respectively 27 , 40 and 27 teeth. Output bevel pinion 12 and output crown wheel 13 have respectively 37 and 52 teeth.

For the purpose of explanation, it is assumed that the forces acting between meshing gear teeth act midway along the length of the teeth as indicated in Figure 2. Thus , the input torque acting on the input bevel pinion 5 can be represented as a force "F" acting at 30 units distance from axis "aa"; that is to say, 30F units of torque about axis "aa".

During maximum torque multiplication, the rotatable housing 1 will remain stationary about axis "aa" and the gears will rotate about their respective axes. Intermediate bevel pinion 11 has the same dimensions as input bevel pinion 5 and force "F" acting on intermediate crown wheel 7 about axis "bb" will therefore produce 30F units torque in intermediate bevel pinion 11 about axis "cc", and a reactive force "F" which will act through the axis "cc" at 33 units distance from axis "aa". Output bevel pinion 12 has a pitch radius of 41 units distance and therefore a force of 0.73F will act between the teeth

of the output bevel pinion 12 and the output crown wheel 13. Also, a reactive force of 0.73F will act through axis "cc" at 62 units distance from axis "aa". The force 0.73F acting on the teeth of the output crown wheel 13 at 58 units distance from axis "aa" will produce 42.3F units torque about axis "aa", that is to say 141% of the input torque.

The reactive force "F" acting through the axis "cc" at 33 units distance from the axis "aa", will produce 33F units torque on the gear housing about axis "aa" , and will act in the same direction as the input torque. The reactive force 0.73F acting through the axis "cc" at 62 units distance from axis "aa" will produce 45.3F units torque on the gear housing about axis "aa" , this torque acting in the reverse direction to the input torque. Rotation of the gear housing in a direction opposite to the direction of rotation of the input shaft is prevented by the free wheel mechanism 16. Thus, the resultant 12.3F units of torque, that is to say 41% of the input torque, will have no effect.

The load acting on the transmission system will resist the rotation of the gears which occurs during torque multiplication, and in consequence the 30F units of torque acting on the input bevel gear 5 through gear 7 will attempt to turn the gear housing 1 and gears as a unit about axis "aa". This will oppose the nett 12.3F units of torque established through axis "cc", and produce

a resultant 17.7F units of torque or 59% input torque on the gear housing about the axis "aa".

A decrease in the transmission load will reduce the output torque requirement and the 17.7F units torque acting on the gear housing will start to turn the housing thereby reducing the relative rotation between the gears and, therefore, the input to output speed ratio. Any further reduction in the transmission load will produce a further increase in the rotational speed of the gear housing, and a corresponding reduction in the input to output speed ratio. If reduction in transmission load is sufficient, the gear housing will reach the input shaft speed and the whole assembly will rotate as a unit to produce direct drive.

An increase in the transmission load during direct drive will reverse the sequence explained above and increase torque multiplication. Also, the rotational speed of the gear housing will be directly influenced by any variation in the magnitude of the input torque. Thus, the mechanism will respond to any change in the relative values of the input torque and the transmission load continuously to produce optimum torque output.

It is to be understood that the foregoing is merely exemplary of one embodiment of a torque converter in accordance with the invention and that modifications can readily be made thereto without departing from the true scope of the invention as set out in the appended claims.

Thus, the relative sizes of the gears and the angular relationship of their axes may be changed to provide an alternative ratio range. In a practical application the plain bearings indicated could be replaced by ball on roller type bearings, and to provide a greater ratio range for vehicle application two or more units could be connected in series.