GB2330885A

GB2330885A - Gear change mechanism

Info

Publication number: GB2330885A
Application number: GB9722992A
Authority: GB
Inventors: David Benjamin Hirons; Michael Leslie Walters
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-11-01
Filing date: 1997-11-01
Publication date: 1999-05-05
Also published as: GB9722992D0

Abstract

A gear change mechanism for use with a gearbox input shaft, the gear change mechanism comprising cam means 1 having a radial track 3 and a peripheral track (5, fig 2), with a first cam follower 17 adapted to interconnect the radial track 3 and the gearbox input shaft 11 to transmit one of the required rotational or translational movement in response to the rotation of the cam means 1, and a second cam follower 27 adapted to interconnect the peripheral track (5, fig 2) and the gearbox input shaft 11 to transmit the other of the required rotational or translational movement in response to the rotation of the cam means 1. The gear change mechanism is capable of providing a sequential or semi-automatic change mechanism for a conventional gearbox.

Description

GEAR CHANGE MECHANISM The present invention relates to a gear change mechanism for use with a gearbox input shaft requiring translational and rotational motion and more particularly is concerned with a sequential gear change mechanism or a semi-automatic gear change mechanism such as may be used in motor vehicles.

Gear change mechanisms for manual transmissions are generally operated by moving a gear shift lever into one of a number of slots arranged in the configuration of the letter H, although additional slots may be provided to allow the use of further gears. Thus a gear is selected with a combination of longitudinal (translational) and, if necessary, lateral movements. The longitudinal and lateral movements are translated into translational and rotational movements of an input shaft of a gearbox.

It is desirable in a number of applications, for example in motor sport and for disabled drivers, to simplify the manner in which the gear change lever operates such that the selected gear can be changed by movements of the gear lever in one of two directions. However, it is also desirable for a number of reasons to retain the conventional type of gearbox and to avoid the need to use a specially adapted gearbox or an automatic gearbox.

It is therefore an object of the present invention to provide a gear change mechanism which is capable of providing a sequential or semi-automatic change mechanism for a conventional gearbox.

According to the present invention there is provided a gear change mechanism for use with a gearbox input shaft requiring translational and rotational motion, the gear change mechanism comprising cam means having a radial surface and a peripheral surface, a first cam track being provided in the radial surface and a second cam track being provided in the peripheral surface, a first cam follower adapted to interconnect the first cam track and the gearbox input shaft to impart one of the required translational and rotational motions to the shaft in response to rotation of the cam means, and a second cam follower adapted to interconnect the second cam track and the gearbox input shaft to impart the other of the required translational and rotational motions to the shaft in response to rotation of the cam means.

Thus, variation of the radial distance of the first cam track from the axis of the cam means may be used to impart the one of the required translational and rotational motions to the gearbox input shaft and variation in the position of the second cam track along the axis of the cam means may be used to impart the other of the required translational and rotational motions to the shaft. The first cam track may be used to impart translational motion and the second cam track may be used to impart rotational motion.

Detents may be provided around the periphery of the cam means and co-operable with stop means to provide a number of stop positions corresponding to the various intended configurations of the gears. At least one of the detents may be deeper that the remainder such that the stop means requires to be withdrawn at least partially from the detent in order to be able to rotate the cam means past the deeper detent.

One of the cam tracks may be connected to the gearbox input shaft for imparting translational motion by way of a rocker link which incorporates a peg engaging in a slot provided in the input shaft. The other of the cam tracks may be connected to the gearbox input shaft for imparting rotational motion by way of a rocker link which engages with an axially extending shaft mounted on the input shaft.

The cam means may be axially adjustable. For example biasing means may be provided in the region of one end of the cam means and threaded adjusting means may be provided in the region of the other end of the cam means. The biasing means may comprise a coil spring or Belleville washers.

Means may be provided for temporarily releasing at least one of the cam followers from its associated cam track.

The cam means may be rotated by a ratchet mechanism, the ratchet mechanism comprising a ratchet gear rotatable with the cam means, a pawl biased into engagement with the ratchet gear on opposite sides of a tooth thereof, the pawl being mounted on actuator means which is rotatable in opposite directions by a user such that rotation of the actuator means in one direction by the user causes the pawl to be released from the ratchet gear and to re-engage therewith and subsequent rotation of the actuator means in the other direction causes consequent rotation of the ratchet gear and the cam means. The actuator may be biased to a predetermined position.

For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is a side elevational view of a circular cam drum for use in a gear change mechanism according to the present invention; Figure 2 is a single-plane view of the entire periphery of the cam drum shown in Figure 1; Figure 3 is a side elevational view, partly in section, of the cam drum of Figures 1 and 2 incorporated in part of a gear change mechanism; Figure 4 is an end elevational view, partly in section, corresponding to Figure 3; and Figure 5 is an elevational view of one embodiment of a mechanical link for rotating the cam drum.

The gear change mechanism shown in the drawings converts translational movement of a gear shift lever (not shown) into translational and rotational movement of an input shaft of a conventional gearbox.

The gear change mechanism incorporates a rotary circular cam drum 1 which has a first cam track 3 formed in a side face thereof as shown in Figure 1 and a second cam track 5 formed around the periphery thereof as shown in Figure 2.

In the present embodiment, the first cam track 3 formed in the face of the cam plate controls translational movement of a gearbox input shaft and the second cam track 5 controls rotational movement of the input shaft, although it is clear that the functions of the two cam tracks could be interchanged. A number of detents 7a, 7b, 7c, 7d, 7e, 7f, 7g, 7h (eight as illustrated) are also provided around the periphery of the cam drum to provide a number of stop positions for the various intended configurations of the gears (not shown), with position 7a corresponding to the angular rotation of the cam drum when in sixth gear, 7b corresponding to fifth gear, 7c corresponding to fourth gear, 7d corresponding to third gear, 7e corresponding to second gear, 7f corresponding to first gear, 7g corresponding to neutral and 7h corresponding to reverse.

Detents 7a and 7f are deeper that the other detents in order to prevent a stop pin (not shown in Figures 1 and 2) moving between detents 7a and 7h (i.e. from 6th to reverse) and in order to prevent the stop pin moving between detents 7f and 7g (first and neutral) unless the pin is released, for example by way of a lever (not shown) connected by way of a Bowden cable, or by electromechanical or hydraulic means.

In use of the cam tracks shown in Figures 1 and 2, the position corresponding to sixth gear is shown at the lefthand side of the track 101 in Figure 1 and the upper part of the track 201 in Figure 2, with the stop pin engaging in the detent 7h. To move from sixth gear to fifth gear the cam drum 1 is rotated anticlockwise with the cam pegs following the cam tracks. The first cam track 3 moves radially outwardly to position 103 which causes translational movement of a gearbox input shaft as will be explained in more detail hereinafter, while the second cam track 5 causes no change in moving to position 203.

To move from fifth gear to fourth gear the cam drum is again rotated anticlockwise. The first cam track 3 moves radially inwardly by way of a dwell point 105 to a position 107, while the second cam track 5 is initially straight, but then at position 205 (corresponding to the dwell point 105) moves axially to cause a rotational movement of the gearbox input shaft as will be explained in more detail hereinafter before moving in a straight line to position 207.

When moving from fourth gear to third gear the first cam track moves radially outwardly to position 109, while the second cam track moves in a straight line to position 209.

When moving from third gear to second gear the first cam track moves radially inwardly, by way of a dwell point 111, to position 113, while the second cam track is initially straight, but then at position 211 (corresponding to the dwell point 111) moves axially to cause a rotational movement of the gearbox input shaft before moving in a straight line to position 213.

When moving from second gear to first gear the first cam track moves radially outwardly to position 115, while the second cam track moves in a straight line to position 215.

Before moving from first gear to neutral, it is first necessary to retract the stop pin and then the cam plate can be rotated anticlockwise. In moving to neutral, the first cam track moves a short distance radially inwardly, by way of a dwell point 117, to position 119, while the second cam track is initially straight, but then at position 217 (corresponding to the dwell point 117) moves axially to position 219 to cause a rotational movement of the gearbox input shaft.

When moving from neutral to reverse, the first cam track moves a short distance radially inwardly to position 121, while the second cam track moves in a straight line to position 221.

Movement in the clockwise direction is essentially the reverse of clockwise movement except that it is not necessary to retract the stop pin when moving between neutral and first.

The cam drum 1 is shown mounted in part of a gear change mechanism in Figures 3 and 4 which are considerably simplified in order clearly to show important aspects of the gear change mechanism. Figure 3 shows a stop pin 9 mounted at the periphery of the cam drum to provide positive location at each gear engagement location.

Translational movement of a gearbox input shaft 11 is controlled by the first cam track 3 by way of a rocker link 13. The rocker link is pivotable about a pivot pin 15 and is provided at one end thereof with a cam peg 17 engaging with the first cam track 3 and at the other end with a peg 19 engaging in a slot 21 provided in the input shaft 11 so as to allow rotational movement of the shaft. The cam peg 17 may be biased into the cam track 3 if desired. Thus, radial deflection of the first cam track 3 as the cam drum is rotated causes the rocker link to pivot and to generate corresponding translational movement of the input shaft 11.

Rotational movement of a gearbox input shaft 11 is controlled by the second cam track 5 by way of a rocker link 23. The rocker link 23 is pivotable about a pivot pin 25 and is provided at one end thereof with a cam peg 27 engaging with the second cam track 5 and at the other end with an aperture 29 engaged by an axially extending pin 31 secured in a slot 33 provided in the input shaft 11 so as to allow translational movement of the shaft. The cam peg 27 may be biased into the second cam track 5 if desired.

Thus, axial deflection of the second cam track 5 as the cam drum is rotated causes the rocker link 23 to pivot and to generate corresponding rotational movement of the input shaft 11.

Thus the two cam tracks 3 and 5 co-operate to allow the gearbox input shaft 11 to replicate the translational and rotational movements characteristic of a manual gearbox.

In the illustrated embodiment, the axial position of the cam drum 1 can be adjusted to allow for wear and/or manufacturing tolerances and/or for phasing the gearbox inpout shaft 11 relative to the selectors within the gearbox. Adjustment is effected by providing biasing means 35 at one end of a mounting shaft 37 of the cam drum and by providing an adjustable screw 39 at the other end of the mounting shaft 37 which acts on the end of the mounting shaft by way of a thrust plate 41. The biasing means 35 may be in the form of a coil spring or, as illustrated, in the form of a plurality of Belleville washers.

Means (not shown), such as an electromagnetic sensor, may be provided for sensing the rotational position of the cam drum 1 in order to be able to determine which gear is engaged by the mechanism. Information from the sensor may be used to provide a dashboard display, for example a digital indication, of the selected gear.

A problem that arises from time to time in motorsport is that when a driver is involved in an incident and the vehicle's engine is stalled with a gear engaged, current sequential and semi-automatic gearboxes often cannot be returned to neutral with the result that the vehicle cannot be re-started and may be forced to retire when the nature of the incident would not otherwise require this. The gear change mechanism according to the present invention may be provided with means for avoiding this problem. Means (not shown) may be provided for freeing the cam peg 27 from the second cam track 5, for example by providing means for effecting limited movement of the rocker link 23 away from the cam drum 1, against a biasing force, sufficient to release temporarily the cam peg 27 from the second cam track 5. The cam drum can then be rotated more easily, either by way of the gear lever or the like or by means of biasing means, such as a torsion spring, in order to rotate the cam drum to a predetermined location, for example corresponding to the "neutral" position, at one of the ends of the first cam track 3. Alternatively, the cam peg 17 may be freed from the first cam track 3. Means may be provided for moving the gearbox input shaft 11 to a position corresponding to neutral in the transmission in order to facilitate re-engagement of the peg with the cam track.

Thus the gear change mechanism according to the present invention can be used as a replacement for a conventional gear change mechanism without the need for an entirely new gearbox: that is, without the need to change the main gearbox casing or the existing selector mechanism.

However, once realised, the gear change mechanism can be used in ways not previously contemplated. For example, gearbox layouts are constrained by the need to allow the driver to use an H-pattern shift with the result that, for example, fourth gear is generally direct drive and fifth gear is an overdrive ratio. With the gear change mechanism according to the invention the gears can be selected in any order as determined by the cam tracks without the need to re-manufacture the gear selector mechanism of the transmission. For example, it is possible to select fifth gear between third gear and fourth gear without the driver knowing and the gear ratios can be adjusted accordingly to secure optimum performance from the gearbox.

The cam drum 1 can be rotated by any convenient means. For example, the cam drum can be rotated by a mechanical link to a gear lever which is movable in opposite directions to change up or to change down. Alternatively, the cam drum can be rotated by a stepper motor (not shown) which causes the cam drum to rotate through a predetermined angle in either a clockwise direction or an anti-clockwise direction, e.g. as a result of the driver moving a lever or depressing a selected one of two levers which may be positioned, for example, on the steering wheel of a vehicle. In a semi-automatic gear change mechanism incorporating a stepper motor, movement of the lever may send a signal to a vehicle management unit which can control engine speed and clutch actuation to supplement gear selection. Such an embodiment is suited to use with disabled drivers rather than in motorsport applications.

The use of a stepper motor is not the only manner in which sequential or semi-automatic gear changes can be accomplished, and other electro-mechanical, pneumatic or hydraulic means may be provided if desired.

A mechanical link for rotating the cam drum is shown in Figure 5. As can be seen from Figures 4 and 5, a ratchet gear 43 is mounted on the shaft 37 carrying the cam drum (not shown). The ratchet gear 43 is engaged by a pawl 47 which is biased into engagement with the ratchet gear by a biasing spring 49, the pawl engaging with opposite sides of a tooth on the ratchet gear. The pawl 47 is pivotably mounted on an actuator plate 51 which is mounted on a shaft 53 to which a gear lever (not shown) is splined. The actuator plate is therefore pivotable clockwise or anticlockwise depending upon the direction in which the gear lever is moved. Actuator plate 51 is formed with an aperture 55 through which the shaft of the cam drum extends for limiting movement of the actuator plate. A pivotably mounted retaining lever 57 is urged against the actuator plate 51 by biasing means 59, the retaining lever and the actuator plate being configured such that the retaining lever 57 returns the actuator plate to a predetermined intermediate position irrespective of which direction the actuator plate is pivoted.

In use, pivoting of the actuator plate 51 in a clockwise direction causes the upper edge 61 of the pawl to engage with the adjacent ratchet tooth 63, the upper edge being configured such that movement relative to the ratchet tooth 63 causes the pawl to be released from the ratchet wheel and to move so as to engage the adjacent ratchet tooth 63.

When the gear lever is released, the retaining lever 57, urged by the biasing means 59, causes the actuator plate to move anticlockwise so as to rotate the cam drum in an anticlockwise direction and to return the actuator plate to the configuration shown in Figure 5.

Pivoting of the actuator plate 51 in an anticlockwise direction causes the reverse effect to pivoting in the clockwise direction.

Claims

CLAIMS 1. A gear change mechanism for use with a gearbox input shaft requiring translational and rotational motion, the gear change mechanism comprising cam means having a radial surface and a peripheral surface, a first cam track being provided in the radial surface and a second cam track being provided in the peripheral surface, a first cam follower adapted to interconnect the first cam track and the gearbox input shaft to impart one of the required translational and rotational motions to the shaft in response to rotation of the cam means, and a second cam follower adapted to interconnect the second cam track and the gearbox input shaft to impart the other of the required translational and rotational motions to the shaft in response to rotation of the cam means.
2. A gear change mechanism as claimed in claim 1, wherein the first cam track is used to impart translational motion and the second cam track is used to impart rotational motion.
3. A gear change mechanism as claimed in claim 1 or 2, wherein detents are provided around the periphery of the cam means and co-operable with stop means to provide a number of stop positions corresponding to the various intended configurations of the gears.
4. A gear change mechanism as claimed in claim 3, wherein at least one of the detents is deeper that the remainder such that the stop means requires to be withdrawn at least partially from the detent in order to be able to rotate the cam means past the deeper detent.
5. A gear change mechanism as claimed in any preceding claim, wherein one of the cam tracks is connected to the gearbox input shaft for imparting translational motion by way of a rocker link which incorporates a peg engaging in a slot provided in the input shaft.
6. A gear change mechanism as claimed in any preceding claim, wherein the other of the cam tracks is connected to the gearbox input shaft for imparting rotational motion by way of a rocker link which engages with an axially extending shaft mounted on the input shaft.
7. A gear change mechanism as claimed in any preceding claim, wherein the cam means is axially adjustable.
8. A gear change mechanism as claimed in claim 7, wherein biasing means is provided in the region of one end of the cam means and threaded adjusting means is provided in the region of the other end of the cam means.
9. A gear change mechanism as claimed in claim 8, wherein the biasing means comprises a coil spring.
10. A gear change mechanism as claimed in claim 8, wherein the biasing means comprises Belleville washers.
11. A gear change mechanism as claimed in any preceding claim, wherein means is provided for temporarily releasing at least one of the cam followers from its associated cam track.
12. A gear change mechanism as claimed in any preceding claim, wherein the cam means is rotated by a ratchet mechanism, the ratchet mechanism comprising a ratchet gear rotatable with the cam means, a pawl biased into engagement with the ratchet gear on opposite sides of a tooth thereof, the pawl being mounted on actuator means which is rotatable in opposite directions by a user such that rotation of the actuator means in one direction by the user causes the pawl to be released from the ratchet gear and to re-engage therewith and subsequent rotation of the actuator means in the other direction causes consequent rotation of the ratchet gear and the cam means.
13. A gear change mechanism as claimed in claim 12, wherein the actuator means is biased to a predetermined position.
14. A gear change mechanism substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.