BACKGROUND TO THE INVENTION One particular example of a continuously variable transmission uses the conversion of pure rotational motion to reciprocating rotational motion to drive an output shaft. A device is used to convert the rotational input motion to reciprocating output motion.

Continuous output motion is achieved by sequentially transferring reciprocating rotational motion to the output shaft through a series of devices. Each of the devices rotates the output shaft for a portion of a cycle of rotation of the device.

The devices are arranged such that each device in turn grips the output shaft, rotates it as a result of the reciprocating motion and releases it in time for the next device to take over. The first device is then returned to its original position by the return portion of the reciprocating motion to be ready for its next turn to grip and rotate the output shaft.

A typical problem with this arrangement is pulsing in the output motion. The pulsing is a result of the sine wave nature of the reciprocating motion. The motion imparted to the output shaft by each device includes a portion where the shaft is accelerated until a maximum rotational speed is reached, after which the output shaft is decelerated. The gripping of the output shaft is coordinated with the sine wave profile of the output motion to only use a small portion of the motion before and after the maximum speed, i. e. a small portion surrounding the peak of the sine wave profile. Even so, the portion that is used still has sine wave characteristics and the take over from one device to the following one includes a instantaneous change in speed, which produces the pulsing.

One solution to pulsing is to use a greater number of devices to transfer the reciprocating rotational motion to the output shaft. This reduces pulsing since a smaller portion of the reciprocating cycle of each device needs to be used to rotate the output shaft, i. e. a smaller portion of the cycle before and after the sine wave peak is used. However, even with a large number of devices there is still a degree of pulsing and practical considerations demand that as few devices as possible are used.

In this specification the term"flatline output motion"means reciprocating rotational output motion which includes a portion of motion with substantially constant speed.

OBJECT OF THE INVENTION It is an object of this invention to provide a continuously variable transmission with flatline output motion.

SUMMARY OF THE INVENTION In accordance with this invention there is provided a continuously variable transmission including a transfer member being rotatably connected to a crankshaft lobe and being constrained to sliding movement in first and second directions, the first and second directions being at a right angle to each other; the transmission also including at least one output arm sliding connected to the transfer member proximate a first end of the arm and having a second end of the arm extending from the transfer member, the arm having a pivot point intermediate the first and second ends thereof, the output arm including a slider located at a point along the length of the output arm; the transmission also including at least one connecting arm being rotatably connected at a first end thereof about the crankshaft axis of rotation and rotatably connected proximate a second end thereof to the output arm slider, the connecting arm also including a connector at its second end, and the connector being configured to be selectively connected and disconnected to a connecting member secured to an output shaft; whereby the rotational motion from the crankshaft is transmitted as flatline reciprocating output motion to the output shaft by means of the arrangement of the transfer member, output arm and connecting arm.

There is also provided for the transfer member to be slidingly movable in the first direction in a first slider secured to a frame, and for the frame to be sliding moveable in the second direction in a second slider secured to a support structure, preferably a casing of the transmission.

There is further provided for the sliding connection between the transfer member and the output arm to comprise a radially extending slot formed in the transfer member, within which an output arm slider is located, the output arm slider being sliding movable within the slot and rotatably connected to the output arm.

There is also provided for the transfer member to comprise a plate, preferably a circular plate, alternatively a spoked plate frame, and for a plurality of output arms to be sliding connected to the plate by means of rotational connections to output arm sliders located within radially extending slots in the plate.

There is further provided for the connecting member to comprise a disc, alternatively a drum.

There is still further provided for the connector to include a gripping surface configured to be locatable over a complimentarily shaped disc gripping surface, and means for the connector gripping surface to selectively grip and release the disc gripping surface.

There is still further provided for a distance from the crankshaft axis of rotation to the output arm pivot point to be termed distance"A", for the distance from the crankshaft axis of rotation to the connecting arm rotatable connection to the output arm slider to be termed distance"B", and for the ratio of A/B to be adjustable by changing distance"A"through adjustment of the output arm pivot point along a line extending radially from the axis of rotation of the crankshaft.

There is still further provided for the ratio of A/B to be adjustable within a range of values from a ratio of A/B<1 to a ratio of A/B>1.

There is still further provided for the pivot point location to be adjustable by means of a screw jack or wedging arrangement, alternatively a screw jack and wedging arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention are described below by way of example only and with reference to the: Figure 1 which is a diagrammatical representation of a preferred embodiment of the invention; and Figure 2 is a side view of a portion of the embodiment of Figure 1.

DETAILED DESCRIPTION OF THE INVENTION The preferred embodiment of a continuously variable transmission (1) according to the invention shown in Figure 1 and Figure 2 includes a transfer member (2) that is rotatably connected to a crankshaft lobe (3). The transfer member (2) is constrained by means of two sets of sliders (4,5) to sliding movement in two directions only, which are at right angles to each other.

The first set of sliders (4) is located in a frame (6) and pins (6a) on the transfer member (2) extend (s) from the transfer member (2) into the first set of sliders (4). This allows sliding movement of the transfer member in the first direction.

The second set of sliders is located in the casing of the transmission (1), and pins (7) on the frame (6) extend into the second set of sliders (5). This allows sliding movement of the frame in the second direction.

The first direction is at a right angle to the second direction. This arrangement of the sliders (4,5) forces the transfer member (2) to describe a circular path when the crankshaft (8) is rotated.

The transfer member (2) in this embodiment comprises a circular plate in which seven slots (9) are formed. Within each slot (9) a slider (10) is connected to an output arm (11) at a first end (12) thereof. For the sake of clarity only one of the seven output arm arrangements is shown. The output arm (11) extends from the transfer member (2) and has a pivot point (13) along the length of the arm (11). The pivot point is adjustable along a line (13a) extending radially from the axis of rotation (14) of the crankshaft (8).

The output arm (11) also has a slider (15) incorporated along its length. The output arm slider (15) is located proximate the second end (16) of the output arm (11).

The transmission (1) also includes a connecting arm (17) which is rotatably connected about the crank shaft (8) axis of rotation (14) at a first end (18) thereof. The connecting arm (17) has a disc gripping device (19) at its second end (20), which is configured to selectively grip and release a disc (21) secured to an output shaft (23). The connecting arm is pivotally connected (22) to the output arm slider (15) The arrangement of the output arm (11) and connecting arm (17) causes the gripping device (19) to undergo reciprocating output motion, of which a portion is flatline output motion. Since the connecting arm (17) is rotatably connected

about the crankshaft (8) axis of rotation (14), the reciprocating motion is in the form of an arc of which the centre is the crankshaft (8) axis of rotation (14).

The gripping device (19) is operated to grip disc (21) when the reciprocating output motion of the gripping device reaches its portion of flatline motion, and to release the disc at the end of the portion of flatline output motion. The disc is therefore gripped and moved through the arc of the reciprocating motion, which rotates the disc (21) and the output shaft (23) to which the disc (21) is connected.

As stated before, the transmission (1) has a plurality of these output arm (11) and connecting arm (17) arrangements, spaced around and connected in exactly the same way to the transfer member (2).

Each gripping device (19) is arranged to selectively grip and release the disc (21). The seven gripping devices (19) are operated sequentially, each one in turn gripping the disc (21) when the output motion of that particular gripping device (19) is in its flatline portion, and releasing the disc when the end of the flatline portion is reached. The disc (21) is therefore rotated by means of the gripping devices (19), causing the output shaft to be rotated.

The gripping devices (19) are sequentially operated such that at some suitable crankshaft related timing prior to one gripping device releasing the disc, the next one grips it, there being a period when both gripping devices are gripping simultaneously prior to the first releasing thereby not allowing the disc to slow down. Since the gripping devices (19) only grip the disc (21) when it reaches its flatline portion of output motion and since all of the gripping devices (19) are operated at the same reciprocating speed, there is no difference in speed between one gripping device (19) when it is about to release the disc and the gripping device (19) next in sequence to grip the disc (21). This removes

pulsing from the reciprocating motion imparted to the disc (21) and the output shaft.

The manner in which the rotational motion from the crankshaft is flatlined, is by suitable arrangement of the geometry of the linkage comprising the transfer plate (2) the output arm (11) and the connecting arm (17).

As stated above, the pivot point (13) is adjustable along a radial line extending from the crankshaft (8) axis of rotation (14). The distance between the crankshaft axis of rotation (14) and pivot point (13) is indicated as"A"in Figure 1. The distance between the crankshaft axis of rotation (14) and the pivotal connection (22) between the output arm slider (15) and the connecting arm (17) is indicated as"B"in Figure 1.

By changing the position of pivot point (13), by means of a screw jack and wedging arrangement (not shown), the ratio of A/B is changed. If pivot point (13) is moved to coincide with pivotal connection (22), A/B =1, and no reciprocating motion is generated at the gripping device (19). This means the disc (21) and output shaft (not shown) will not be rotated, even though the crankshaft (8) may still be rotating and moving the transfer member (2).

By moving pivot point (13) closer towards the crankshaft axis of rotation (14), the ratio of A/B become less than 1, which means that reciprocating motion is imparted to the gripping device (19), and the disc (21) and output shaft (not shown) is rotated.

If pivot point (13) is moved past pivotal connection (22), the ratio of A/B becomes larger than 1. The reciprocating motion imparted to the gripping device is now the reverse to motion described above for the scenario where A/B is smaller than 1. This means that the disc (21) and output shaft (not shown) is

rotated in the reverse direction, all still with the same rotational motion from the crankshaft (8).

It is therefore possible to change the speed with which the output shaft is rotated from some predetermined maximum speed to zero and to some predetermined maximum reverse speed, all with a constant rotational speed of the crankshaft (8) and with a fixed throw crankshaft (8) in which dimension"C" is not adjustable. This means that changing distance"A"allows the effective gear ratio of the transmission to be changed.

It is further possible to change the speed of rotation of the crankshaft (8).

The transmission therefore provides for continuously variable transmission of input motion to an output shaft with reduced pulsing in the output motion.

It will be appreciated that there are other embodiments of a continuously variable transmissions that fall within the scope of this invention.

It is for instance possible to use various numbers of output arms and to change shape of the transfer member accordingly. In one embodiment the transfer member is triangular, with three output arms leading from it.

It is also possible for eccentric input motion to be generated by means other than a crankshaft.

It is also possible to use a crankshaft which has a crankshaft throw lobe (3).

This means dimension"C"in Figure 1 may be changed. Changing distance"C" also allows the effective gear ratio of the transmission to be changed, just as changing dimension"A"changes the gear ratio.