Technical Field

The present invention relates to a hydro-mechanical device for the transmission of rotary motion or torque. 5 It particularly relates to a device permitting variation of the transmitted rotational speed. Background Art

A conventional variable hydro-mechanical gear system splits drive into two parts. One part of this drive is 0 then transmitted through a hydrostatic device to be recombined with the other part of the drive. Variation in control of the hydrostatic device controls the gear system. This invention simplifies and increases the efficiency of the gear system. 5 Disclosure of the Invention

Broadly, the present invention concerns a transmission device in which an input is arranged to drive a hydrostatic (or hydraulic) unit directly and also to transmit drive mechanically through a housing. The 0 output from the device may be in two parts, one a reaction from the house, the other a reaction from the hydrostatic unit. These two reactions may be combined through one or more planetary gear systems to provide the output drive.

25 In a preferred form, the input directly drives the hydrostatic unit housing. A reaction through a

hydrostatic output drive shaft drives one torque path. The resistance of this torque path turns the hydrostatic unit, so driving the other output and providing a second torque path. It may include a gear pump in this form. The output from the unit is transmitted to a planetary gear system and combined with the output from the ^* irst torque path to provide the output drive from the unit. (Note: the designations "input" and "output" are essentially arbitrary. They relate to the usual mode of use, but the device may be used the other way round. )

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings. Brief Description of Drawings Fig. 1 is a schematic axial section through a transmission device embodying the invention;

Fig. 2 is an alternative arrangement showing reversed drive from the hydrostatic unit;

Fig. 3 shows a third embodiment with drive taken from the outer casing;

Fig. 4 shows an embodiment with power output through a gear;

Fig. 5 shows an alternative way of driving the planetary gear system; Fig. 6 shows an embodiment with a gear pump with different size driving and driven gears, as well as but

not necessarily used with two planetary gears;

Fig. 7 shows a device using a bevel gear arrangement;

Fig. 8 is a cross-section through a hydrostatic unit, in this case a gear pump; and

Fig. 9 is a cross-section through a hydrostatic unit, in this case a double gear pump. Modes for Carrying Out the Invention

In the following description, references to "input" and "output" components and the like refer to a conventional mode of usage of the devices in question.

Unless the context requires otherwise, it will be appreciated that these terms are not absolute, and could be reversed. Fig. 1 shows an embodiment having an outer housing

10 which is generally cylindrical, with a coaxial input shaft 12 and output shaft 14. The input shaft 12 is tubular, and contains a displaceable control rod 13 and a pressure relief valve 16, whose function will be explained later. Inside the main housing 10, there is a hydrostatic unit with a hydrostatic unit housing 18.

This is coupled to the input shaft 12 so as to be rotatable thereby. Off-centre, there is a drive shaft 20 parallel to the input shaft 12. This extends axially beyond the hydrostatic unit housing 18 in both directions. At the input end, it is fast with a gear 21

which engages a gear 22 which turns the outer housing 10. Adjacent the output end, the outer housing 10 has an internal ring gear 24 which turns a planetary gear 26 which, in turn, reacts against a sun gear 28 to turn the output shaft 13. On the end of the drive shaft 20 that projects at the output end, there is a fast-mounted gear 30. Within the hydrostatic unit 18, the drive shaft 20 is fast with an oil pumping gear 32 which meshes with a gear 34 in a pumping arrangement, such that rotation of the drive shaft 20 causes the pumping of oil. In this embodiment, there is no motor to be driven by pumped oil. The oil is returned from an output side of the oil pump to the input side, preferably via a pressure relief valve 16 and/or via a flow control device. As shown, a pressure relief valve 16 is controllable by longitudinal sliding of the rod 14 within the input shaft 12.

When the driveshaft 20 is rotated about the axis of the input shaft 14, thus turning the gear 22 coupled to the outer housing 10, the driveshaft 20 is rotated about its own axis in the hydrostatic unit housing 18. This not only causes the oil pumping gear 32 to turn. It also rotates the gear 30 fast with the outward end of the shaft 20. This meshes with the gear 28 on the output shaft 14 and thus tends to transmit torque to that output shaft.

In use, the output shaft 14 may be held fast, and

drive taken from the outer housing 10.

The gear 22 linking the drive shaft 20 to the outer casing 10 may be an internal gear on the casing 10 or it could be an external gear on the axis of the input shaft 12.

Fig. 2 shows an embodiment similar to that of Fig. 1, with corresponding opponents correspondingly numbered. However, the hydrostatic unit now includes a motor comprising gears 50 and 52. This acts to turn an internal output shaft 54, which acts to drive the gear 28 on the main output shaft 14. Shafts 56 and 58 in the pump and in the motor respectively are idler shafts not connected to the drive shaft 20' and the internal output shaft 54. It can, of course, be arranged that the motor gears 50,52 should rotate at the same speed as, or a selected different speed from, the pump gears 32,34.

Fig. 3 shows another embodiment which is quite similar to that shown in Fig. 2. It should be appreciated that the embodiments described so far show the hydrostatic unit coupled directly to the outer housing 10. Alternatively, the coupling could be via an idler gear system.

Considering, for example, the operation of the embodiment shown in Fig. 3, the operation of the pump and motor can be controlled by control means which are not shown ( such as a flow control device or a pressure relief

valve as shown within the input shaft 12 in Figs. 1 and 2). If both the pump and motor are stopped, then there is direct transmission of torque from the input shaft 12 via the drive shaft 20' and gear 22 to the outer housing 10. Thus the housing rotates at the same speed as the input shaft 12. An output can be derived from the outer housing 10.

However, rotation of the components as described tends to cause rotation of the drive shaft 20' . If such rotation is allowed, it creates pressure in the pump 32,34. Oil tends to be pumped to the motor 50,52, which acts to turn the output shaft 14. Thus two outputs are available, from the outer housing 10 and from the output shaft 14. By reducing the force from the housing 10, the oil pressure is reduced, thus affecting the transmission of torque. If the hydrostatic unit has a pressure relief control, this can be used to set torque. If there is a flow control, this can be used to set the speed. (The controls will generally act on the fluid passing between the pump and the motor. )

Fig. 4 shows an embodiment substantially as in Fig. 3 but with the output shaft 14 integral with a gear assembly for output drive.

Fig. 5 shows another variant in which the outer housing 10' has a reduced-diameter output shaf portion 70 at the output end, coupled to planet gears 72 of a

gear train 74 to which the output shaft is also coupled. Thus output can be derived through the shaft or the gear train 74.

Fig. 6 shows a further variant having a hydrostatic unit whose drive is arranged through two planetary gear systems. This is exemplified in an embodiment similar to that of Fig. 1, having a pump but no motor.

Fig. 7 shows another variant of a device, very schematically. A hydrostatic unit 80 includes a motor 82 and a pump 84. They are coupled to respective axial shafts 86,88 (that of the motor passing through that of the pump). Each of the drives 86,88 is fast with a respective one of an opposed pair of frustoconical bevel gears 90,92 (which may have the same or different numbers of teeth. These are engaged by complementary portions of a surrounding annular bevel gear 94. This is coupled to a housing 96, from which an output is derived. Input is fed to a housing 98 of the hydrostatic unit.

The use of bevel gears instead of planetary gears can be applied to other embodiments too. Also generally applicable is the coaxial arrangement of the input and output of the pump (and motor).

Figs. 8 and 9 are sectional views through pumps.

(Motors are similar. ) Fig. 8 illustrates a pump of any of the previously-described embodiments showing a pair of gears 100,102 which might be, for example, the gears

32,34 of the pump shown in Fig. 1 or .Fig 2. There are input and output conduits 104. The oil flow impelled by the gears may be as shown by the arrows. Fig. 9 shows a variant in which the gears are doubled-up, to produce a mechanically balanced assembly.

The invention is not limited to the use of gear pumps. Any type of fluid pump and/or motor may be used, or even other types of hydrostatic coupling device e.g. a torque converter.