GB2307964A

GB2307964A - A fixed ratio balanced gearbox for a wankel engine

Info

Publication number: GB2307964A
Application number: GB9522947A
Authority: GB
Inventors: Bryan Nigel Victor Parsons
Original assignee: Birmingham Research & Dev Ltd
Current assignee: Birmingham Research & Dev Ltd
Priority date: 1995-11-09
Filing date: 1995-11-09
Publication date: 1997-06-11
Anticipated expiration: 2015-11-09
Also published as: GB9522947D0; GB2307964B

Abstract

A fixed ratio gearbox 40 for a Wankel engine 10 comprises an internal gear 44 and an external gear 48 arranged to be maintained in meshing engagement, one of the gears, for example the internal gear 44, is mounted to be driven eccentrically (see fig 4) in an orbital path by a crankshaft 14 of the engine. The external gear 48 is mounted on an output shaft 50 and the internal gear 44 is further connected, via elastomeric blocks (64, fig 5), to a plate 53 which acts as a vibration coupling reacting to rotation vibrations in the output so that out of balance forces of the engine rotor are balanced by being matched to that of an out of balanced flywheel (18, fig 1).

Description

FIXED RATIO GEARBOX FOR WANKEL ENGINE The present invention relates to a fixed ratio gearbox for a Wankel Engine.

The rotors of a Wankel Engine move eccentrically generating out of balance forces, which must be balanced. Balancing is achieved by the use of an out of balance flywheel mounted on the crankshaft of the engine on one side of the rotor and an out of balance weight mounted on the crankshaft on the other side of the rotor.

When a fixed ratio gearbox is used with a Wankel Engine, for example to power a light aircraft, external gears are conventionally used. Torsional vibration damping means is also required in the output train, which complicates the design of the fixed ratio gearbox.

The present invention provides a fixed ratio gearbox for a Wankel Engine in which the components of the gearbox are used to counterbalance the engine avoiding the need for a separate balance weight.

In accordance with one aspect of the present invention, a fixed ratio gearbox for a Wankel Engine comprises; an internal gear and an external gear arranged to be maintained in meshing engagement with the internal gear, one of said gears being mounted to be driven eccentrically in an orbital path by an input shaft, said input shaft being driven by the engine; means to prevent rotation of said one gear; said other gear being drivingly mounted on an output shaft; the motion of said one gear being matched to that of an out of balance flywheel, to balance the out of balance forces of the engine rotor.

With the fixed ratio gearbox of this invention, the eccentrically driven gear avoids the need for a separate balance weight with consequent weight saving which is important, particularly in aircraft applications. Furthermore, the input and output shafts may be coaxial, so that the gearbox may be located coaxially of the Wankel Engine thus minimising the front elevation and thus drag.

According to a preferred embodiment of the invention, said one gear is constrained to move in an orbital path by means of a series of pins which engage in circular apertures in a plate or by means of a series of cranks rotationally mounted on a plate. The plate is preferably mounted with respect to the gearbox housing, by means of resilient elements which will provide torsional vibration damping of the output train.

According to a further preferred embodiment of the invention, the input shaft is the crankshaft of the Wankel Engine.

An embodiment of the invention is now described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic cross-sectional side elevation of a conventional fixed ratio gearbox and Wankel Engine; Figure 2 is a diagrammatic cross-sectional side elevation of a fixed ratio gearbox in accordance with the present invention; Figure 3 is a diagrammatic cross-sectional plan view of the gearbox illustrated in Figure 2; Figure 4 is a section along the line IV-IV of Figure 2; and Figure 5 is a section along the line V-V of Figure 2.

Figure 1 illustrates a single rotor Wankel Engine of known design, suitable for use in aircraft. The engine 10 has a triangular rotor 12 which rotates eccentrically about a crankshaft 14 within an epitrochoidal casing 16. An out of balance flywheel 18 is mounted on the crankshaft 14 at the rear of the engine 10 and a balance weight 20 is mounted on the crankshaft 14 at the front of the engine, rotation of the flywheel 18 and balance weight 20 with the crankshaft 14 being arranged to balance the forces created by the eccentric movement of the rotor 12.

A fixed ratio gearbox 22 is mounted at the front end of the engine 10.

The gearbox 22 has an inner input shaft 24 which is splined onto the crankshaft 14 of the engine 10. The inner input shaft 24 is connected to a coaxially mounted outer input shaft 28 by means of a vibration coupling 26. The vibration coupling 26 may be in the form of a rubber doughnut, alternating segments of the doughnut being connected to the inner and outer shafts 24 and 28. The vibration coupling 26 isolates torsional vibrations in the output train.

The outer input shaft 26 has an input gear 30 formed thereon. The input gear 30 meshes with an output gear 32 mounted on an output shaft 34 which is parallel to the axis of the input shafts 24 and 26 but spaced radially thereof. A propeller boss 36 is provided at the outer end of output shaft 34.

The fixed ratio gear box 40 illustrated in Figures 2 to 5, comprises a gear box casing 42 adapted to be secured to the casing 16 of a single rotor Wankel Engine 10, as illustrated in Figure 1.

An internal gear 44 is rotatably mounted on a crank 46, formed on the end of the crankshaft 14 of the Wankel Engine 10, so that rotation of the crankshaft 14 will drive the internal gear 44 about an orbital path.

An external gear 48 is mounted on an output shaft 50, the output shaft 50 being rotatably mounted with respect to the gearbox casing 42, so that it is coaxial with the crankshaft 14 of the engine 10. External gear 48 meshes with the internal gear 44 and remains in mesh, as the internal gear 44 is driven about its orbital path by crank 46.

Four pins 52 are provided on the face of the internal gear 44, the pins 52 engaging the peripheries of circular apertures 54 in a plate 53. The apertures 54 are of the same radius as the throw of the crank 46, so that as the internal gear 44 is driven around its orbital path by rotation of crankshaft 14, the pins 52 will remain in engagement with the peripheries of apertures 54, preventing rotation of the internal gear 44 relative to the casing 42. Meshing of the gears 44 and 48 thus causes external gear 48 to rotate, driving the output shaft 50. The ratios of the gears 44 and 48 are chosen to provide the required step down ratio of the gearbox.

The plate 53 is centred with respect to the gearbox casing 42, by means of a bearing 56 which it is rotatively mounted on the crankshaft 14. Four rectangular windows 58 are provided in the plate 53 intermediate of the apertures 54. A rear plate 60 is secured at its outer periphery to the gearbox casing 42 and is located in juxtaposed relationship to the plate 53. The rear plate 60 has four vanes 62 which extend axially of the gearbox 40, the vanes extending through the windows 58 in plate 53.

Elastomeric blocks 64 are located on either side of the vanes 62 and engage the opposed edges of the windows 60, to resiliently resist rotation of the plate 53 in both directions. The elastomeric blocks 64 which locate the plate 53 rotationally, act as a vibration coupling, reacting torsional vibrations in the output train.

The crank 46 is formed on the crankshaft 14 of the Wankel Engine 10, so that it is 1800 out of phase with the rotor 16 of the engine 10. The internal gear 44 is weighted so that its eccentric movements, in combination with the movement of an out of balanced flywheel 18 of conventional design, will balance the out of balance forces of the rotor 16.

Internal gear 44 of the gearbox 40 will consequently replace the separate balance weight 20 used hitherto, thereby saving at least some of the weight of this component.

Furthermore, the crankshaft 14 and output shaft 50 of the gearbox 40 are coaxial so that the gearbox 40 may be made of similar dimensions to the Wankel Engine 10. This is in contrast to the conventional gearbox 22 as illustrated in Figure 1, in which the offset between the input and output shafts increases the height of the gearbox significantly.

Further modifications may be made without departing from the invention.

For example, the pins 52 and apertures 54 may be replaced by cranks acting between the internal gear 44 and plate 53. Furthermore the plate 53 may be resiliently mounted rotationally in any suitable manner to provide the torsional vibrational coupling. In place of the elastomeric blocks 64 any suitable resilient means may be used to resiliently mount the plate 53.

While in the above embodiment the internal gear is driven eccentrically by the input shaft, the external gear may alternatively be mounted on the input shaft and driven eccentrically, the internal gear being drivingly mounted on the output shaft.

While in the above embodiment the input and output shafts are coaxial, the output shaft may be offset from the input shaft, if required.

Claims

1. A fixed ratio gearbox for a Wankel Engine comprising an internal gear and an external gear arranged to be maintained in meshing engagement with the internal gear, one of said gears being mounted to be driven eccentrically in an orbital path by an input shaft, said input shaft being driven by the engine; means to prevent rotation of said one gear; said other gear being drivingly mounted on an output shaft; the motion of said one gear being matched to that of an out of balance flywheel, to balance the out of balance forces of the engine rotor.

2. A fixed ratio gearbox according to claim 1 in which the internal gear is mounted on the input shaft and is driven eccentrically thereby.

3. A fixed ratio gearbox according to claim 1 or 2 in which said one gear is mounted on a crank on the input shaft.

4. A fixed ratio gearbox according to any one of the preceding claims in which the means to prevent rotation of the internal gear comprises at least three pins, the pins extending from the rear face of the internal gear, each pin engaging the periphery of a circular aperture in a plate which is disposed parallel to the internal gear, the radius of the apertures being equal to the eccentricity of movement of the internal gear so that the pins remain in engagement with the peripheries of the circular apertures as the internal gear is driven around its orbital path, the plate being constrained from rotation.

5. A fixed ratio gearbox according to any one of claims 1 to 3 in which the means to prevent rotation of the internal gear comprises a plurality of cranks, the cranks being rotationally mounted between a rear face of the internal gear and a plate disposed parallel to the internal gear, the plate being constrained from rotation.

6. A fixed ratio gearbox according to claim 4 or 5 in which four pins or cranks are provided at angularly spaced locations about the internal gear.

7. A fixed ratio gearbox according to any one of claims 4 to 6 in which the input and output shafts are coaxial.

8. A fixed ratio gearbox according to claim 7 in which the plate is resiliently constrained from rotation.

9. A fixed ratio gearbox according to claim 8 in which a rear plate is secured to the gearbox housing in juxtaposed relationship to the plate, the rear plate having a series of angularly spaced vanes, the vanes extending axially of the gearbox through windows in the plate, resilient means acting between either side of the vanes and opposed edges of the windows, so as to resiliently resist rotation of the plate in both directions.

10. A fixed ratio gearbox according to claim 9 in which the resilient means comprises elastomeric blocks.

11. A fixed ratio gearbox according to any one of claims 7 to 10 in which the plate is rotationally mounted about the input shaft.

12. A fixed ratio gearbox according to any one of claims 1 to 11 in which said one internal gear is mounted on a crank on the input shaft.

1 3. A fixed ratio gearbox according to any one of claims 1 to 12 in which the input shaft is the crank shaft of the engine.

14. A fixed ratio gearbox substantially as described herein with reference to and as shown in Figures 2 to 5 of the accompanying drawings.

reference to and as shown in Figures 2 to 5 of the accompanying drawings.