GB2159217A - Gear selection indicator in a multi-ratio transmission - Google Patents

Abstract

The invention is concerned with an actuator position sensing system for use in a multi-ratio transmission comprising two actuators each movable between discrete positions to selectively engage one or more gear sets. Two selector rails 51 and 52 are each moved longitudinally of their own axes by means not shown to operate gear actuators (not shown) and thereby engage a corresponding gear set (not shown). Each selector rail is shown in a neutral condition. The diagram to the right of Fig. 2 indicates axial movement necessary to engage second or fourth gear for rail 51 and third and first for rail 52. Lever arm 53 couples movement of the selector rails to a position indicator 59. An operating arm of the position indicator takes up a unique position for any combination of the discrete positions of the selector rails 51 and 52 thereby providing an indication of which gear set or combination of gear sets is engaged. <IMAGE>

Description

SPECIFICATION Multi-ratio power transmission The invention relates to multi-ratio power transmissions. The invention is concerned particularly with such transmissions which comprise at least two actuators, each movable between discrete positions to selectively engage one or more gear sets of the transmission.

In an automatically controlled transmission of this kind, in which for ratio changes, a series of functions such as enegagement and disengagement of clutches and engagement and disengagement of gear sets is required for each ratio change, it is desirable to ensure that each step in the series has been completed successsfully before the next step is initiated. It is undesirable to rely on a command having been given for each step and then to allow a time delay for implementation.

This is partly because the time delay must allow for the longest probable time to effect the step and partly because if there is any delay in effecting the step, damage could be caused by implementing a subsequent step prior to completion of the previous step. One kind of step for which it is required to produce a signal to the effect that the step has been completed is the engagement or disengagement of a gear set. To this end, it is known to provide position sensors, coupled to movement of gear actuators in order to provide signals to indicate that a desired discrete position has been reached by the actuator. In a gear box with four forward speed ratios and a reverse ratio, it is known to provide one double actuator for first and third ratios with a discrete central position in which neither first nor third gear set is engaged.A similar actuator is provided for second and fourth ratios with a neutral position in which neither gear set is engaged. Similarly there is provided a reverse gear actuator with discrete positions for reverse and neutral.

Position sensors are costly items and cost is of particular importance in automotive transmissions intended for mass production.

An object of the present invention is to provide a multi-ratio power transmission in which one position sensor is effective to sense the position of more than one actuator.

In accordance with the present invention there is provided a multi-ratio power transmission comprising two actuators each movable between discrete positions to selectively engage one or more gear sets and an actuator position sensing system comprising a lever arm coupled at a first point to movement of a first actuator, at a second point to movement of a second acuator and at a third point to a position indicator such that the third point takes up a unique position for each combination of discrete positions of the actuators.

The first acuator may be capable of selectively engaging either one of two gear sets or of engaging neither of them and the second actuator may be capable of selectively engaging either one of two further gear sets or of engaging neither of them. The third point on the lever arm may lie outside the first and second points by a distance equal to half the distance between the first and second points.

In an alternative arrangement, the first actuator is capable of selectively engaging either one of two gear sets or neither of them and the second actuator is capable of selectively engaging one further gear set or of disengaging it. The third point may lie outside the first and second points and be spaced from the second point by a distance equal to the spacing between the first and second points.

The position sensor may be a rotary position sensor coupled to the lever arm by crank mechanism.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a diagrammatic layout of a transmission to which the present invention can be applied; Figure 2 shows an arrangement for a common position sensor for a first-third gear selector and a second-fourth gear selector; and Figure 3 corresponds to Fig. 2 but shows an arrangement for a common position sensor for a second-fourth gear selector and a reverse gear selector.

Referring first to Fig. 1, an input shaft 11 is connected permanently to a first clutch 1 2 and a second clutch 1 3. The first clutch 1 2 is mounted on a flywheel 14 and when engaged drives a hollow input shaft 1 5. A shaft 1 6 passes through the hollow shaft 1 5 to drive clutch 13, which is a wet clutch running in oil. When clutch 1 3 is engaged. it drives a sleeve 1 7 mounted freely rotatably on an extension of shaft 1 5. Shaft 1 5 carries integral input gears 18, 1 9 and 21 for first, third and reverse gears respectively.Sleeve 1 7 carries integral input gears 22 and 23 for second and fourth gears respectively.

A lay shaft 24 carries output gears 25, 26, 27 and 28 respectively for first, third, second and fourth gear ratios. These output gears mesh respectively with input gears 18, 19, 22 and 23 to form four gear sets. All of these output gears are in themselves freely rotatable on shaft 24. A reverse output gear 29 is carried on a gear selector ring 31 which is splined to a shoulder 32 on lay shaft 24 for rotation therewith. Reverse output gear 29 can mesh with reverse input gear 21 through an idler gear, not in the plane of shafts 1 6 and 24 and thus not shown. A second selector ring 33 is splined to and slideable on a shoulder 34 of lay shaft 24 and is thus rotatable therewith. In neutral, the idler reverse gear is kept out of mesh with either input gear 21 or output gear 29 and all forward output gears 25 to 28 are rotatable freely on the lay shaft 24.To engage first gear, a first gear actuator GA1 moves selector ring 31 so that it engages teeth 30 of a synchromesh mechanism associated with first output gear and thus locks the first output gear 25 against rotation with respect to lay shaft 24. A similar actuator GA3 can move the same selector ring 31 to engage output gear 26 with the lay shaft and thus establish third gear. Selector ring 33 can similarly be moved by actuator GA2 or GA4 to engage second or fourth gear. A fifth gear actuator GAR (not shown in Fig. 1) is provided to interengage the idler gear with both reverse gears 21 and 29 to establish reverse gear ratio. Output drive from the transmission is taken from an output drive gear 35.

First and third input gears and reverse input gear are, as previously explained, mounted on hollow input shaft 1 5. Input drive to this shaft is by way of the dry clutch 1 2 so this clutch has to be disengaged while first, third or reverse is selected and then engaged to establish drive. Similarly, second and fourth input gears 22 and 23 are driven by the sleeve 1 7 which in turn can be driven by the wet clutch 1 3. Thus, to engage second or fourth gear, clutch 1 3 must be disengaged and when the gear has been selected the clutch is re-engaged to establish drive through the transmission in second or fourth gear.

In order to change between one forward ratio and the next higher or next lower ratio, the new ratio is selected while the old ratio is still driving. The clutch associated with the driving gear is then disengaged simultaneously with engagement of the clutch associated with the new ratio. This arrangement allows drive through the transmission to be continuous even during ratio changes.

All the elements of the transmission described so far are mounted within a housing 36. The housing carries a hydraulic cylinder 37 which is arranged to operate a release mechanism 38 for the dry clutch. Release and engagement of the wet clutch 1 3 is by way of hydraulic fluid supplied to an inlet 39. The housing also carries a pump and control valve assembly 41 which is driven continuously with the transmission input through a drive gear 42 at the input to the wet clutch and a further gear 43 mounted on the pump input shaft 44.

Fig. 2 shows a longitudinally movable selector rail 51 for selective engagement of second and fourth gear sets or for engagement of neither of them in a central position. Selector rail 51 is coupled to move with selector sleeve of Fig. 1. In practice the gear actuators GA2, GA4 shown in Fig. 1 may be a common double-acting actuator remote from the sleeve 33 and coupled to it through the selector rail 51. A second selector rail 52 lies parallel to the selector rail 51 and is coupled to the selector sleeve 31 of Fig. 1. In other respects, second selector rail 52 and its association with a double acting gear actuator may correspond to details of the selector rail 51 and its double-acting gear actuator.

A lever arm 53 is connected by a ball joint 54 to selector rail 51 and by a ball joint 55 to selector rail 52. The ball joints provide first and second points on the lever arm 53 which are coupled to movement of the actuators.

There is provision for sliding movement of the ball joints to cater for a change in the distance between the connections of the lever arm to the selector rails when one selector rail is moved with respect to the other.

The lever arm 53 also extends to a third point 56 at which it is pivoted to link 57 which is in turn coupled to a crank arm 58 of a rotary position sensor 59. The distance between points 55 and 56 is half the distance between points 54 and 55 as indicated by the dimensions X and X/2 shown in Fig. 2.

The selector rails are shown in neutral positions in which points 54 and 55 are at discrete central positions represented by the letter N to the right of the drawing. Movement available to selector rail 51 when either second or fourth gear set is engaged by the corresponding gear actuator is represented by the positions 2 and 4 to the right of the drawing. Engagement of the second gear set is represented by movement to the right from the position shown of the selector rail by a distance equal to the distance between points N and 2 at the right hand side of the drawing.

Engagement of fourth gear set is represented by corresponding movement in the opposite direction. The movement available to selector rail 52 for engagement of first or third gear set is depicted in a similar manner.

As each of points 54 and 55 associated with selector rails 51 and 52 respectively are moved to each of their three possible discrete positions, lever arm 53 causes point 56 to take up associated discrete positions. These positions are depicted to the right of Fig. 2.

There are four discrete positions for point 56, each corresponding to engagement of a single gear set. There is a further, central position representing neutral, that is engagement of no gear sets. Three further positions represent simultaneous engagement of gear sets one and two together, two and three together and three and four together. Clearly it is impossible for gear sets two and four to be engaged simultaneously or for gear sets one and three to be engaged simultaneously. There is no practical possibility in the transmission under consideration of simultaneous engagement of first and fourth gear sets but a further unique position corresponding to this state could be indicated on Fig. 2.

The position indicator 59 is coupled to point 56 in such a way as to provide an indication in the form of an electrical signal as to which discrete position is occupied by point 56 and thus which discrete gear set or combination of gear sets is engaged. In this way, a single position indicator can provide signals indicative of the state of engagement of four gear sets.

Fig. 3 shows an arrangement corresponding in principle to that shown in Fig. 2 but in this case, one of the selector rails is associated with second gear, fourth gear and neutral and the other selector rail is concerned with neutral and reverse. It should be observed that in this arrangement, the third point 61 on lever arm 62 is spaced from a second point 63 on a selector rail 64 by a distance equal to the distance between point 63 and a point 65 on selector rail 66.

It should be explained that in the case of Fig. 2, it is desirable to engage two numerically adjacent gear sets simultaneously during a transmission associated with engagement and disengagement of clutches between drive in the two associated gear ratios. In the case of Fig. 3, the control system may be such that for normal operation the transmission, second gear set is engaged simultaneously with the reverse gear set and the distinction between driving in second or reverse gear is established by engagement of one or the other of the clutches.

Typically a four speed and reverse transmission will have three selector rails, one for reverse gear, a second for first and third ratios and a third for second and fourth ratios. The present invention may be employed to provide a single position indicator for two of the selector rails while a further position indicator is provided for the third selector rail.

Claims (7)

1. A multi-ratio transmission comprising two actuators each movable between discrete positions to selectively engage one or more gear sets and an actuator position sensing system comprising a lever arm coupled at a first point to movement of a first actuator, at a second point to movement of a second actuator and at a third point to a position indicator such that the third point takes up a unique position for each combination of discrete positions of the actuators.

2. A transmission as claimed in claim 1 wherein the first actuator is capable of selectively engaging either one of the two gear sets or of engaging neither of them and the second actuator is capable of selectively engaging either one of two further gear sets or of engaging neither of them.

3. A transmission as claimed in claim 2 wherein the third point on the lever arm lies outside the first and second points by a distance equal to half the distance between the first and second points.

4. A transmission as claimed in claim 1 wherein the first actuator is capable of selectively engaging either one of two gear sets or neither of them and the second actuator is capable of selectively engaging one further gear set or of disengaging it.

5. A transmission as claimed in claim 4 wherein the third point lies outside the first and second points and is spaced from the second point by a distance equal to the spacing between the first and second points.

6. A transmission as claimed in any one of the preceding claims wherein the position sensor is a rotary position sensor coupled to the lever arm by a crank mechanism.

7. A multi-ratio power transmission substantially as described with reference to and as illustrated by the accompanying drawings.