GB2278653A - A reverse gear selection inhibitor arrangement and inhibitor therefor comprising pivoting cam plate - Google Patents

Abstract

A reverse gear selection inhibitor arrangement for a motor vehicle gearbox comprises a selector finger and a reverse gear selection inhibitor comprising a cam-plate 41 mounted for example on the base 19 of a gearlever housing for pivotal movement in two opposite directions. The pivotal axis of the cam-plate 41 is off-set from the principal longitudinal axis of the selector finger in the central neutral position by a linear distance. A cam shoulder 46 on the cam-plate 41 is positioned at a distance from the pivotal axis greater than said linear distance. The cam-plate 41 is sprung biassed towards an at-rest position. The selector finger in travelling from a forward gear position v to a reverse gear position contacts one face 47 of the shoulder 46 causing pivotal movement of the cam-plate 41 but such movement is stopped when faces 22 and 21 respectively on the cam-plate 41 and base 19 of the housing 14 abut one another thereby preventing the reverse gear position R being reached directly from the forward v position and stopping the selector portion 8 at the selection neutral position. During pivotal movement, the cam-plate does not cut the selector finger axis. <IMAGE>

Description

A Reverse Gear Selection Inhibitor Arrangement and Inhibitor Therefor This invention relates to a reverse gear selection inhibitor arrangement for use with a motor vehicle gearbox, and to a reverse gear selection inhibitor which may be used in such an arrangement.

The selection of reverse gear on motor vehicles has conventionally required the driver to undertake a deliberate operation with a gearshift lever in order to engage reverse gear. For example, on gearboxes having four forward gears and a reverse gear, the gearshift lever positions for the forward gears in general, have been at the extremities of an H pattern with a central neutral position being at the centre of the H pattern and selection neutral positions being at the lateral ends of the cross member of the H pattern. In order to be able to engage reverse gear, it has been generally necessary for the vehicle driver to overcome spring-applied resistance at one end of the cross member of the H pattern to achieve an enlarged lateral movement of the gear shift lever. Alternatively, or additionally it has sometimes been necessary for the driver to depress the gear shift lever or to operate a button or sub-lever on the lever head in order to be able to engage reverse gear. Such devices have, to a large extent, served to prevent inadvertent engagement of a reverse gear but at least the latterly mentioned alternative or additional devices can be difficult to operate and involve complicated mechanisms.

With the advent of gearboxes having five forward gears and a reverse gear, the separation of the reverse gear position from the forward gear positions of the gearshift lever has been reduced due to an overall limitation on the space available for gearshift lever movement. Thus, the fifth gear position has been situated substantially on the opposite side of a selection neutral position to the reverse gear position, this selection neutral position being on a lateral extension of the cross-member of the above-mentioned H pattern. The central neutral position on such gearboxes generally coincides with the selection neutral position for the third and fourth gear positions. This relative positioning of a forward gear, especially fifth gear, and reverse gear positions has required that greater attention be paid to the prevention of inadvertent engagement of the reverse gear.

A driver wishing to change from fifth gear to fourth gear very often needs to effect the change quickly so as not to lose too much vehicle momentum during the change. In such circumstances the risk of inadvertently engaging reverse gear instead of fourth gear for example, is greatly heightened. The incorporation of the above-mentioned buttons and sub-levers required to be operated before reverse gear can be engaged are unattractive solutions for the reasons given. A requirement that the vehicle driver overcomes a spring-applied resistance to lateral movement of the gearshift lever to a selection neutral position for reverse, alone is also an unattractive solution since the urgency of a change from fifth to fourth gear can cause such resistance to be overcome with dire consequences.

Accordingly, many proposals have been made for mechanisms aimed towards preventing the inadvertent selection of a reverse gear directly from a forward gear. In this connection, reference may be made to the disclosures of GB patent specifications numbered 1418764, 2041119, 2042104, 2067687, 2097493, 2161555 and 2183753 also European patent specifications numbered 247976, 249582 and 486349, USA patent specifications numbered 3933057, 3939724, 4133219, 4228693, 4638678, 4660433 and 4738153 and German patent specification numbered 4110012.

Amongst the proposals disclosed in the above-mentioned patent specifications, is the use of a sprung pawl or cam which interferes with a direct transition from fifth gear to reverse gear but the systems are either complex or rely on reactions between such cams and appendages to a selector shaft or control lever comprising a gearshift lever for example.

In a gearshift mechanism adapted for the alternative engagement of five forward gears and a reverse gear for example by the provision of three fork shafts selectively engageable by a gear shift lever, which is a well known system sometimes referred to as the three rail system, the availability of space in which to accommodate an interference or blocking cam or pawl which is simple and effective while having desirable robustness is very limited.

According to a first aspect of the present invention there is provided a reverse gear selection inhibitor arrangement for a motor vehicle gearbox, which arrangement comprises a selector finger having an end adapted for engagement with a gear selector shaft of the motor vehicle gearbox for gear selection and a reverse gear selection inhibitor comprising a cam-plate mounted for pivotal movement in two opposite directions about a pivotal axis substantially parallel to and off-set from the central neutral position axis (as hereinafter defined) by a linear distance, the cam-plate having a cam shoulder at a distance from the pivotal axis greater than said linear distance, said cam-plate being sprung-biassed against movement in each of the directions towards an at-rest position in which a first face of the shoulder is positioned for contact by a first point on the selector finger in travelling from a forward gear position substantially directly towards a reverse gear position to cause pivotal movement of the plate in one direction and in which a second face is positioned for contact by a second point on the selector finger in travelling from a central neutral position directly towards a selection neutral position for either the selection therefrom of the forward gear position or the reverse gear position to cause pivotal movement of the cam-plate in the other direction, a stop to restrict the pivotal movement of the cam-plate in the one direction and thereby prevent the selector finger reaching the reverse gear position substantially directly from the forward gear position but not so as to prevent sufficient pivotal movement of the plate in the one direction to permit the selector finger to reach the selection neutral position, wherein, during the pivotal movement of the cam-plate in the one or the other direction it does not cut through the central neutral position axis.

It is preferred that the pivotal movement of the cam-plate in the other direction by the contact of the second face of the shoulder by the second point on the selector finger in travelling from the central neutral position directly towards a selection neutral position for either the selection therefrom of the forward gear position or the reverse gear position, is sufficient to permit the selector finger to reach the selection neutral position and that the dimensions of the cam-plate and of the selector finger are such that on moving the selector finger from the selection neutral position to the forward gear position the cam-plate is allowed to resume the at-rest position.

According to a second aspect of the present invention there is provided a reverse gear selection inhibitor as may be used in the reverse gear selection inhibitor according to the first aspect of this invention.

The term central neutral position axis as used in this specification is intended to mean a line corresponding to the position of the principal longitudinal axis of the selector finger when the selector finger is in the central neutral position.

The reverse gear selection inhibitor of this invention permits a simple and effective inhibitor to be constructed which can be both compact and robust. The construction may be such as to permit the installation of the inhibitor into a suitably apertured motor vehicle gearbox in plug-in fashion as an integral unit with a gearshift lever housing for example.

The selector finger is preferably a portion of a gearshift lever comprising integrally connected control and selector finger portions. In such an arrangement, the respective longitudinal axes of the portions may be off-set from one another to accommodate the geometry of the gearbox mechanism with which it is to be employed.

Such a gearshift lever may be mounted in a lever housing for angular movement about a fulcrum point in known manner. The lever housing may comprise a hollow generally cylindrical moulded and/or cast construction of metal, particularly cast iron, and/or plastics material, particularly an engineering plastics material such as polycarbonate. It is preferred that the housing comprises a substantially cylindricallyshaped main body section moulded of plastics material and a metal base ring-like section attached thereto. Attachment of the base may be by moulding the body section against the base section in a mould, the base being provided with suitable angular and/or undercut surfaces to ensure locking of the two sections together. Other possible means of attachment will be evident to the addressee. The housing is preferably of such shape and dimensions as to fit an aperture in a motor vehicle gearbox provided for a gearshift mechanism and is provided with a flange by means of which it may be secured to the gearbox.

The gearshift lever housing is preferably such that the control portion of the gearshift lever extends above the housing for manual manipulation, and the selector finger portion extends below as necessary for extension into the gearbox with which the inhibitor arrangement of this invention is to be used. It will be appreciated that the position of the mounting of the gearshift lever in the housing should be such as to suitably position the end of the selector finger portion for subsequent engagement with gearbox components as necessary, the fulcrum point being positioned appropriately.

In this specification, references to above, below and the vertical all relate to the inhibitor arrangement of this invention being oriented with the selector finger extending downwards. However, other orientations should be correspondingly interpreted.

The end of the selector finger should be adapted for engagement with and axially moving a gear selector shaft of the gearbox with which the inhibitor arrangement of this invention is to be used. Thus, for example, when the gearbox is of the three rail kind having three selector shafts having so-called forks for engagement by the selector finger end, clearly, adaptation should preferably shape and dimension the selector finger end to ensure positive engagement with respective forks and their smooth sliding operation in gear selection.

It will be appreciated that the inhibitor arrangement of this invention may be used with gearboxes wherein the selector finger is not required to engage a three rail system. Thus, the selector finger end may engage with a single rail for example in a remote selection system which may include a three rail system positioned remotely from the selector finger.

While the cam-plate may be mounted directly onto the gearbox with which the inhibitor arrangement of this invention is to be used, it is preferably mounted on the base of a gearlever housing. The cam-plate may be of generally arcuate-, sickle-, C- or J-shape for example, but preferably comprises a substantially ring-like shape or disc-like shape having a central aperture and more preferably with a peripheral portion of generally sickle-or J-shape. The ring-like shape or disc-like shape having a closed loop form is preferred for strength and stability of the cam-plate. However, the shape should be such that in use, the cam-plate itself does not cut the central neutral position axis during its pivotal movement in either direction.

The cam-plate is preferably mounted on a pin, preferably located in a peripheral wall of a gearshift lever housing, so that the cam-plate can pivot in its own plane. When the cam-plate includes an arcuate-, sickle-, C- or J-shape, the pivotal axis of the cam-plate is preferably arranged near one end of such shape.

The cam-plate has a cam-shoulder and, when the cam-plate includes a preferred arcuate-, sickle-, C- or J-shape, the pivotal axis of the cam-plate is preferably arranged at an end remote from the shoulder.

The cam-plate is sprung-biassed against movement in each of the pivotal directions towards an at-rest position. While this may be achieved by a combination of springs or other resilient devices, it is preferably achieved with a single torsion spring. It is preferred that the single torsion spring is a spring having legs against which a surface or pin on the cam-plate can act to increase the tension in the spring in moving in either the one pivotal direction or the other. To this end it is preferred that the legged spring is mounted on a bush, stub or boss around the pivotal axis of the cam-plate. It is preferred also that a pin on the cam-plate extends between the crossed-over legs of the spring which are otherwise maintained in that position by a stop device in the form of a lug for example which may be on the end of a gearshift lever housing, or on a gearbox, on which the cam-plate is mounted for example.

The cam-plate is provided with a stop face which cooperates with a stop face on the gearshift lever housing for example and such stop faces are kept spaced apart when the cam-plate is in the at-rest position.

The shoulder of the cam-plate has two faces. These faces are preferably substantially planar and substantially at right angles to one another, their planes being substantially parallel to the pivotal axis of the cam-plate.

However, it will be appreciated that the shapes and relative positions of the faces may be varied to suit particular requirements.

For example, the first face may be angled to the second face and/or shaped such that if a movement of the selector finger directly from the forward gear position to the reverse gear position is attempted, as soon as the selection neutral position is reached, the selector finger will be directed into the next lower forward gear position for example.

It is preferred that the cam-plate may be steadied at a position remote from the pivotal axis in particular on the side opposite to the pivotal axis, for example by sliding contact with the mounting surface such as an end face of a gearshift lever housing.

The mounting surface for the cam-plate, such as the base end face of a lever housing, is preferably profiled to accommodate stops nd stop faces, pivotal mounting of the cam-plate and sliding support for the cam-plate as desired.

The first and second points on the selector finger for contacting the shoulder are preferably points on the selector finger itself and may be points within areas for contacting the shoulder. It is preferred that the first and second points are on substantially flat surfaces of the body of the selector finger and especially surfaces angled so that initial contact with the faces of the shoulder respectively in operation of the mechanism, is area contact.

To this end the cross-sectional shape of the body of the selector finger at least in the region of cam-plate contact, is preferably rectangular but may be for example trapezoidal.

The forward gear position may be the position of the selector finger for any forward gear which is substantially on the opposite side of the selection neutral position for the reverse gear.

It will be appreciated that in the present context, a selection neutral position is a position to which the selector finger may be moved from a central neutral position, which itself may dominate a coincident selection neutral position, and is a neutral position from which a gear position may be reached directly.

The stop to restrict pivotal movement of the cam-plate in the direction responsive to the selector finger travelling from a forward gear position directly towards a reverse gear position, but not so as to prevent the selector finger reaching the selection neutral position, can be any combination of abutting surfaces, one of which is on the cam-plate and the other on for example a gearshift lever housing, which is preferred, or alternatively on the gearbox with which the inhibitor arrangement is to be used. The positions of the abutting surfaces are such that they are brought into full abutting relationship when the selector finger reaches the selection neutral position in travelling from the forward gear substantially directly towards the reverse gear position, but are spaced apart when the camplate is in the at-rest position. It will be appreciated that when the stop includes an abutting surface on the gearbox the stop may only be effective when the inhibitor arrangement is in use with the gearbox.

The dimensions of the cam-plate and of the selector finger are preferably such that on moving the selector finger from the selection neutral position to the forward gear position the cam-plate is allowed to resume the at-rest position.

Accordingly, the cam-plate is then in place to prevent selection of the reverse gear position directly from the forward gear position.

It will be appreciated that on moving the selector finger from the central neutral position towards the selection neutral position for the forward gear or for the reverse gear, contact between the selector finger and the shoulder effects pivotal movement of the cam-plate against the sprung biassing to permit the selector finger to reach the selection neutral position while maintaining the freedom to select therefrom appropriately either the forward gear or the reverse gear position substantially directly.

If desired, the selection neutral position for the selection of the reverse gear position may be displaced slightly from that for the selection of the forward gear. If this is a feature of the gear-box with which the inhibitor arrangement of this invention is to be used, further resistance to the travel of the selector finger from the selection neutral position for the forward gear position to the selection neutral position for the reverse gear position may be introduced by an additional spring for example. Such further resistance may be introduced by way of further resistance to the pivotal movement of the cam-plate by an additional spring for example. Alternatively or in addition, such further resistance may be provided in the gearbox and, in particular, between the selector finger and the gearbox casing or the selector shaft with which the end of the selector finger is adapted to engage for example.

The dimensions of the cam-plate and of the selector finger are preferably such that the pivotal movement of the camplate in each of the one direction or the other direction caused by the selector finger is within the dimensions of the mounting surface, preferably the base of a gearshift lever housing, on which the cam-plate is mounted, measured perpendicular to the pivotal axis of the cam-plate.

The present invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a semi-schematic sketch showing parts of three selector shafts of a so-called three-rail gearbox with which the reverse gear selection inhibitor arrangement of the present invention may be used.

Figure 2 illustrates schematically the gear selection positions of a gear selector finger in sliding the selector shafts of Figure 1 from their respective neutral positions as shown in Figure 1.

Figure 3 is a sketch of a perspective view of a gearshift lever mechanism including a gearshift lever housing on the base of which is mounted a reverse gear selection inhibitor to form an inhibitor arrangement according to the present invention.

Figure 4 is a sketch representing a vertical crosssection taken through the gearshift lever mechanism and inhibitor illustrated in Figure 3.

Figure 5 is a sketch of a perspective underneath plan view of part of the gearshift lever mechanism and inhibitor shown in Figure 3 with the selector finger in the central neutral position.

Figure 6 is a sketch similar to Figure 5 but showing the selector finger in a specific selection neutral position and prevented from reaching the reverse gear position.

Figure 7 is a sketch similar to Figure 5 but showing the selector finger in the reverse gear position.

Figures 8 is a schematic representation corresponding generally to Figure 5 and showing the forward and reverse gear positions in approximate relation to one another.

Figure 9 is a schematic representation showing the movement of the selector finger from the central neutral position to the fifth gear position.

Figures 10 and 11 are schematic representations generally corresponding respectively to Figures 6 and 7.

In the drawings in which like numbers correspond, 1, 2 and 3 are parts respectively of three selector shafts of a socalled three-rail gear-box in which the shafts are each slidable axially in both directions. The respective upstanding fork configurations indicated generally 4, 5 and 6 which are shaded, are selectively engageable by the end 7 of the selector finger 8 of the gearshift lever indicated generally by 9, which also has the control portion 10 and which is a component of the gearshift lever mechanism indicated generally by 11. Figure 2 shows the relative positions to which the end 7 of the selector finger portion 8 moves to engage the upstanding fork configurations 4, 5, 6 and slide the selector shafts 1, 2, 3 respectively in the selective engagement of the five forward gears indicated by Roman numerals I to v and of the reverse gear R. For the sake of clarity, the positions of the end 7 of the selector finger portion 8 which correspond to the respective positions of the selector finger portion 8 are herein numbered the same. The central neutral position of the selector finger is indicated by 12. The selection neutral positions for selection of the forward gear position v and for the reverse gear position R are indicated by 13 and 13' respectively.

The selector shaft pairs (1 and 2), (2 and 3), are linked in known manner by movable pins (not shown) which prevent adjacent shafts moving together whereby it is not possible for the selector finger portion end 7 to slide more than one shaft at a time.

The selector finger portion 8 is biassed towards the central neutral position by opposing transverse sprung pistons (not shown) mounted in the gearbox aperture (not shown) into which the selector finger portion 8 projects. In known manner also, a sprung ball running in a short groove in the wall of the piston depressed when the end 7 of selector finger portion 8 is moved towards the selection neutral position for reverse gear, provides additional resistance to the movement of the finger portion 8, and therefore of the end 7, from the selection neutral position 13 for the forward fifth gear to the selection neutral position 13' for reverse gear. It will be seen from Figure 1 that in order for the end 7 to slide shaft 1 to engage reverse gear, lateral movement of the end 7, additional to that to engage the fifth gear is necessary.

The gearshift lever 9 is mounted in the lever housing 14 comprising a substantially cylindrical body section 15 injection moulded from polycarbonate plastics material with an upper flange 16, a lower internal shoulder 17 and the spigots 18 having rectangular location pads 29 for the steel base 19. The cylindrical body section 15 is provided with vertical slots 31 and 32 arranged diametrically opposite one another, each extending through the thickness of the body section 15. The housing further comprises a similarly moulded closure portion comprising the flange 33 surrounding a cylindrical portion, terminating above the flange 33 in lipped part 34 for engagement by the rubber sealing boot 35, and terminating below the flange 33 in the plug part 36.

The steel base 19 of the housing 14 comprises a steel ring of diameter substantially equal to the diameter of the cylindrical section 15. The upper side of base 19 is provided with slots (not shown) into which the rectangular location pads 29 fit, holes being provided in the base 19 into which spigots 18 fit, with the base 19 in axial alignment with the section 15. Firm attachment of the steel base 19 to the section 15 is achieved by heat moulding/welding the spigot ends over the base 19. The lower side of base 19 is provided with a radial slot 30 into which can be located a selector finger position sensing probe for example. Opposite the radial slot 30, the lower side of base 19 is provided with the depending stepped peripheral portion 20 terminating at one end in vertical planar surface 21 for abutting with surface 22 on the camplate, the abutting surfaces in combination forming a stop.

The peripheral portion 20 terminates at its other end in the lug 23 having lands 24 and 25 against which the ends of the legs 26 and 27 respectively, of legged spring 28, can rest.

The gearshift lever 9 is shown in Figure 4 to be in the central neutral position and the central neutral position axis of the selector finger portion 8 is indicated by y.

The gearshift lever 9 has fulcrum point 37 located at the centre of relative movement of the ball 38 within the socket 39. The ball 38 comprises a suitably bored steel sphere heat shrunk onto the gearshift lever 9. The ball 38 is drilled transversely right through to take pin 40 which is held firmly in the ball 38. The socket 39 comprises a cagelike cylindrical polycarbonate injection moulding having slots (not shown) extending 75% of its height alternately from its upper and lower edges subject to two diametrically positioned slots being enlarged and deepened to 90% of its height to accommodate the ends of pin 40. The socket 39 has an internal concave spherical shape to substantially match the external shape and dimensions of the ball 38. The nature of the socket 39 allows it to be sprung onto the ball 38 and to accommodate pin 40 passing there-through in the enlarged and deepened slots provided.

The manner of assembly of the ball 38, socket 39 and pin 40 will be evident from the foregoing. The assembly thus produced is inserted into the body section 15 of the housing from above with the ends of the pin 40 aligned with the slots 31 and 32 respectively and the assembly lowered into the housing until the socket 39 reaches internal shoulder 17. The plug part 36 of the closure portion of the housing is then inserted to hold the socket 39 axially in position and at the same time bring flanges 33 and 16 into contact for securing together. The flanges are provided with holes 51 for this purpose and for securing the housing to the gearbox with which the gearshift lever mechanism is to be used and which gearbox is provided with a suitable aperture to accept the mechanism.

On the lower side of base 19 of the housing 14, the camplate 41 is mounted for pivotal movement about pin 42 on which it is held by circlip 43. A spacer boss (not shown) on the cam-plate is positioned and bored so that the pin 42 passes therethrough. The eye of legged spring 28 is fitted over the spacer boss before securing the cam-plate 41 to the pin 42, the spring being pre-tensioned and the ends of legs 26 and 27 positioned on the lands 24 and 25 respectively.

The cam-plate 41 is provided with pin 44 which extends towards the base 19 to locate between the legs 26 and 27 against which it can act respectively on pivotal movement of the cam-plate 41 in one direction or the other. However, cam-plate 41 has an upstanding integral peripheral part 45 dimensioned to be in slidable contact with the base 19 and to terminate at one end at surface 22 which in combination with surface 21 forms the stop as described above.

The cam-plate 41 is provided with the shoulder 46 having a first face 47 and a second face 48 for contact respectively by a first point 49 and a second point 50 on the selector finger portion 8 of the gearshift lever 9.

Operation of the illustrated reverse gear selection inhibitor arrangement and inhibitor of this invention will now be described.

The mounting of the gearshift lever 9 in the housing 14 by way of ball 38, socket 39, pin 40 and slots 31 and 32 permits angular movement of the selector finger portion 8 of the lever 9 in all pivotal directions and particularly backwards, forwards and sideways about the fulcrum point 37.

The pin 40, located in slots 31 and 32 prevents rotation of the lever 9 about its own axis and thereby maintains the selector finger portion 8 and particularly the end 7 in correct orientation for engagement in use with the forks 4, 5, 6 of the selector shafts 1, 2, 3 of the gearbox with which it is to be used.

Figures 5 and 8 show the position of the cam-plate 41 with the selector finger portion 8 of the gearshift lever 9 in the central neutral position indicated by shaded area 12 in Figure 8. The cam-plate 41 is shown to be in the at-rest position. In order to select forward gear position v from the position 12 and having regard to the geometry and arrangement of the forks configurations 4, 5, 6, the selector finger portion 8 must first be moved transversely from right to left in Figure 8 and correspondingly in Figure 5. In so moving, the selector finger portion 8 contacts the face 48 of the cam shoulder 46 and pivotal movement of the cam-plate 41 about pin 42 (Figure 6) is resisted by the reaction of leg 26 of spring 28 on pin 44. However, in overcoming this resistance the selector finger portion 8 can reach position 13 as shown in Figure 9 and marked more clearly in Figure 10, that is to say t position for selection of the forward gear v position. If the selector finger portion 8 is moved in the upward direction in Figure 9 from position 13 as reached directly from position 12, it will be seen that contact between the selector finger portion 8 and face 48 (see Figure 5) of shoulder 46 will be broken and the cam-plate 41 will be restored to its at-rest position, with the selector finger portion 8 in the forward v position, by the action of spring 28 through leg 26 on pin 44. In Figure 9, two positions of the cam-plate are shown, one to which it is pivotally moved by the selector finger portion 8 moving from the position 12 to the position 13 and the second which is the at-rest position.

With the selector finger portion 8 being in the forward gear position and the cam-plate 41 in the at-rest position, movement then of the selector finger portion 8 downwards back towards the position 13 as shaded in Figure 10 causes the selector finger portion 8 to contact face 47 (see Figure 6) of shoulder 46 to cause pivotal movement of cam-plate 41 about pin 42 against the resistance applied by spring 28 through contact between pin 44 and leg 27 of the spring 28.

However, surface 22 on the cam-plate 41 coming into abutting contact with surface 21 on the base 19 acts as a stop preventing further pivotal movement of the cam-plate 41 in the anticlock-wise direction in Figure 6 and Figure 10 allowing the selector finger portion 8 to reach only the selection neutral position 13 and thus preventing movement of the selector finger portion 8 any further in the downward direction.

With the arrangement of selector shaft fork configurations 4 and 5 together with the means preventing simultaneous movement of selector shafts 1 and 2 as described earlier above, movement of the selector finger portion 8 directly from position 13 to the reverse gear position is in any event prevented. However, it will be seen that even if lateral movement of the selector finger portion 8 is made to overcome the additional resistance to movement of the selector finger portion 8 from position 13 to position 13', in the process of moving in the downward direction from the forward gear y position, reached as described above, the surface 22 on the cam-plate 41 coming into abutting contact with surface 21 on the base 19 will still act as a stop preventing a movement of the selector finger portion 8 substantially directly from the forward v gear position to the reverse gear R position (shown in Figure 8 (dotted) and in Figure 11). In Figure 10, two positions of the cam-plate 41 are shown, one in which it is in its at-rest position and the second in which it has been rotated anti-clockwise by the face 47 of shoulder 46 being contacted by point 49 on the selector finger portion 8 in moving the latter from the forward gear v position substantially directly to the position 13 and position 13'.

It will be seen that if the selector finger portion 8 is moved from left to right in Figure 6 and in Figure 10 to the central neutral position 12, the contact between the selector finger portion 8 and the face 47 of the cam shoulder will be broken to allow the cam-plate to resume its at-rest position under the action of spring 28 through leg 27 on pin 44.

With the cam-plate in its at-rest position and the selector finger portion 8 in the central neutral position, movement of the selector finger portion 8 from right to left in Figure 11 through the selector neutral position 13 to selection neutral po tion 13' overcoming the additional resistance referred to above, the cam-plate is pivotally moved clockwise by contact between the point 50 on the selector finger portion 8 with face 48 of the shoulder 46 as shown. Such rotation removes any blocking action of the cam-plate 41 to the movement of the selector finger portion 8 to the reverse gear position R as shown in Figure 11. In Figure 11 two positions of the cam-plate 41 are shown, one in which it is in the at-rest position and the second in which it has been pivotally moved by movement of the selector finger portion 8 from position 12 to position 13'.

It will be appreciated that movement of the selector finger portion 8 from the position R to position 12 via positions 13 and 13 will permit the cam-plate 41 to resume its atrest position.

It will be seen that in the pivotal movement of the camplate in either direction in operation as described, the central neutral position axis is not cut through by the camplate. Further, the pivotal movement of the cam-plate in each direction is within the circumference of the base 19.

The reverse gear selection inhibitor arrangement comprising a reverse gear selection inhibitor mounted on a gearshift lever housing and as specifically described with reference to the accompanying drawings is clearly adapted for installation into a suitably apertured motor vehicle gearbox in plug-in fashion as an integral unit.

Claims (20)

Claims

1. A reverse gear selection inhibitor arrangement for a motor vehicle gearbox, which arrangement comprises a selector finger having an end adapted for engagement with a gear selector shaft of the motor vehicle gearbox for gear selection and a reverse gear selection inhibitor comprising a cam-plate mounted for pivotal movement in two opposite directions about a pivotal axis substantially parallel to and off-set from the central neutral position axis as hereinbefore defined by a linear distance, the cam-plate having a cam shoulder at a distance from the pivotal axis greater than said linear distance, said cam-plate being sprung-biassed against movement in each of the directions towards an at-rest position in which a first face of the shoulder is positioned for contact by a first point on the selector finger in travelling from a forward gear position substantially directly towards a reverse gear position to cause pivotal movement of the plate in one direction and in which a second face is positioned for contact by a second point on the selector finger in travelling from a central neutral position directly towards a selection neutral position for either the selection therefrom of the forward gear position or the reverse gear position to cause pivotal movement of the plate in the other direction, a stop to restrict the pivotal movement of the plate in the one direction and thereby prevent the selector finger reaching the reverse gear position substantially directly from the forward gear position but not so as to prevent sufficient pivotal movement of the cam-plate in the one direction to permit the selector finger to reach the selection neutral position, wherein during the pivotal movement of the camplate in the one or the other direction it does not cut through the central neutral position axis.

2. A reverse gear selection inhibitor arrangement as claimed in Claim 1 wherein the pivotal movement of the camplate in the other direction by the contact of the second face of the shoulder by the second point on the selector finger in travelling from the central neutral position directly towards a selection neutral position for either the selection therefrom of the forward gear position or the reverse gear position, is sufficient to permit the selector finger to reach the selection neutral position and the dimensions of the cam-plate and of the selector finger are such that on moving the selector finger from the selection neutral position to the forward gear position, the cam-plate is allowed to resume the at-rest position.

3. A reverse gear selection inhibitor arrangement as claimed in either of Claim 1 or Claim 2 wherein the inhibitor is mounted on the base of a gearshift lever housing.

4. A reverse gear selection inhibitor arrangement as claimed in Claim 3 wherein the housing comprises a main body section moulded of plastics material and a metal base ringlike section attached thereto.

5. A reverse gear selection inhibitor arrangement as claimed in any one of the preceding claims wherein the camplate comprises a substantially ring-like shape or disc-like shape having a central aperture.

6. A reverse gear selection inhibitor arrangement as claimed in Claim 5 wherein the cam-plate has a peripheral portion of generally sickle-shape or J-shape.

7. A reverse gear selection inhibitor arrangement as claimed in Claim 6 wherein the pivotal axis of the cam-plate is at one end of such sickle-shape or J-shape.

8. A reverse gear selection inhibitor arrangement as claimed in any one of the preceding claims wherein the camplate is sprung-biassed towards an at-rest position by a single torsion spring.

9. A reverse gear selection inhibitor arrangement as claimed in Claim 8 wherein the spring is a legged spring and a pin on the cam-plate extends between the crossed over legs of the spring.

10. A reverse gear selection inhibitor arrangement as claimed in any one of the preceding claims wherein the first face and the second face on the cam shoulder are substantially at right angles to one another.

11. A reverse gear selection inhibitor arrangement as claimed in any one of Claims 3 to 10 wherein the base end face of the housing is profiled to accommodate stops, stop faces and pivotal mounting of the cam-plate.

12. A reverse gear selection inhibitor arrangement as claimed in any one of the preceding claims wherein the first and second points on the selector finger are points within areas for contacting the shoulder.

13. A reverse gear selection inhibitor arrangement as claimed in any one of the preceding claim wherein the forward gear position is the fifth forward gear position.

14. A reverse gear selection inhibitor arrangement as claimed in any one of Claims 3 to 13 wherein the dimensions of the cam-plate and of the selector finger are such that pivotal movement of the cam-plate in each of the one direction and the other direction caused by the selector portion is within the dimensions of the base of the housing measured perpendicular to the axis of the housing.

15. A reverse gear selection inhibitor arrangement as claimed in any one of the preceding claims wherein the inhibitor is mounted on a gearshift lever housing for installation into a suitably apertured motor vehicle gearbox in plug-in fashion as an integral unit.

16. A reverse gear selection inhibitor arrangement substantially as herein described with reference to the accompanying drawings.

17. A reverse gear selection inhibitor arrangement as claimed in any one of the preceding claims when used with a gearbox of the three rail type.

18. A reverse gear selection inhibitor for a motor vehicle gearbox in which gear selection is achieved by movement of a selector finger having an end adapted for engagement with a gear selector shaft of the gearbox which inhibitor comprises a cam-plate mounted for pivotal movement in two opposite directions about a pivotal axis substantially parallel to and off-set from the central neutral position axis as hereinbefore defined by a linear distance, the camplate having a cam shoulder at a distance from the pivotal axis greater than said linear distance, said cam-plate being sprung-biassed against movement in each of the directions towards an at-rest position in which a first face of the shoulder is positioned for contact by a first point on the selector finger in travelling from a forward gear position substantially directly towards a reverse gear position to cause pivotal movement of the plate in one direction and in which a second face is positioned for contact by a second point on the selector finger in travelling from a central neutral position directly towards a selection neutral position for either the selection therefrom of the forward gear position or the reverse gear position to cause pivotal movement of the plate in the other direction, a stop to restrict the pivotal movement of the plate in the one direction and thereby prevent the selector finger reaching the reverse gear position substantially directly from the forward gear position but not so as to prevent sufficient pivotal movement of the cam-plate in the one direction to permit the selector finger to reach the selection neutral position, wherein during the pivotal movement of the camplate in the one or the other direction it does not cut through the central neutral position axis.

19. A reverse gear selection inhibitor as claimed in Claim 18 wherein the pivotal movement of the cam-plate in the other direction by the contact of the second face of the shoulder by the second point on the selector finger in travelling from the central neutral position directly towards a selection neutral position for either the selection therefrom of the forward gear position or the reverse gear position, is sufficient to permit the selector finger to reach the selection neutral position and the dimensions of the cam-plate and of the selector finger are such that on moving the selector finger from the selection neutral position to the forward gear position, the cam-plate is allowed to resume the at-rest position.

20. A reverse gear. selection inhibitor substantially as described herein with reference to the accompanying drawings.