GB2089912A

GB2089912A - Speed-dependent gearshift prevention arrangement for toothed-wheel gear units

Info

Publication number: GB2089912A
Application number: GB8138253A
Authority: GB
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1980-12-19
Filing date: 1981-12-18
Publication date: 1982-06-30
Also published as: GB2089912B; FR2496818B1; IT8125284A0; CA1167285A; IT1139846B; DE3048048C2; DE3048048A1; FR2496818A1

Abstract

A gearshift prevention arrangement is provided for preventing reverse gear engagement in a motor vehicle when the latter is moving at a speed greater than a predetermined value (e.g. 10 km/h). The arrangement comprises a balking ring (20) located axially between the reverse-gear toothed wheel (22) of the vehicle gear box and a coupling member (23) which is rigid with this wheel and is engaged by a slidable sleeve (9) upon selection of reverse gear. The balking ring (20) comprises two half shells surrounded by a spring ring (18) and provided with shaped balking noses (15) which project through the coupling member (23) towards said sleeve (9). When the toothed wheel (22) rotates above a certain speed, the half shells expand under the action of centrifugal forces, and against the force of the spring (18), to assume a configuration in which the balking noses (15) prevent the sleeve (9) engaging the coupling member (23). <IMAGE>

Description

SPECIFICATION Speed-dependent gearshift prevention arrangement for toothed-wheel gear units The present invention relates to a speeddependent gearshift prevention arrangement for toothed-wheel gear units, and in particular, but not exclusively to such arrangements for preventing the engagement of the reverse gear of a motor vehicle speed-change gear unit when the motor vehicle is moving forwards at speeds greater than a predetermined value.

German patent specification No. DE-PS 1 9 46 496 discloses a speed-dependent gearshift prevention arrangement, for preventing, on a speed-dependent basis, the engagement of the reverse gear of a motor vehicle speed-change gear unit, this unit consisting of a main transmission gear assembly and an auxiliary transmission gear assembly for extending the gear change sequence.

Reverse gear engagement is prevented with the aid of pneumatically-operated pressure cylinders.

These cylinders are controlled partly pneumatically and partly hydraulically by means of a plurality of valves, so that this known gearshift prevention arrangement is relatively costly.

The object of the present invention is to provide a speed-dependent gearshift prevention arrangement for toothed-wheel gear units, which is of simple construction and requires only a few parts so that substantially no additional space is required in the gear unit.

It is a further object of the invention to provide a gearshift prevention arrangement which operates without external activation (pneumatic/hydraulic/mechanical linkage) and can thus be made maintenance-free and easy to assemble and disassemble.

According to the present invention, there is provided a speed-dependent gearshift prevention arrangement for use in a toothed-wheel gear unit in which engagement of a particular gear of the unit is brought about by the coupling together of a toothed wheel associated with that gear and a slidable sleeve, this coupling being secured by the engagement of internal toothing of the sleeve with external toothing of a coupling member coaxial, and fast for rotation, with said toothed wheel; the speed-dependent gearshift prevention arrangement being operative to prevent the engagement of said particular gear at rotational speeds of the associated toothed wheel exceeding a predetermined value, the gearshift prevention arrangement including a balking ring located between said toothed wheel and the coupling member and comprising two part shells held together by means of a spring which substantially surrounds the part shells, said part shells being arranged to expand radially outwardly against the action of said spring at rotational speeds exceeding said predetermined value and each part shell being provided on its side facing the coupling member with at least one balking nose which extends axially through a corresponding recess formed in the coupling member, each said nose being provided at its free end with a step formed by sloping face directed radially inwardly and axially away from the said toothed wheel, and a part-cylindrical surface joining with the sloping face at the radially inner boundary thereof, the dimensioning of said noses being such as to enable the sleeve to be slid over the noses to engage the coupling member when the balking ring is in its unexpanded state, and the surface of the sleeve which faces towards said coupling member being formed, around the mouth to the toothed interior of the sleeve, with a slope corresponding to that of said sloping faces of the balking noses whereby, upon centrifugal expansion of the balking ring, engagement of the sleeve with the coupling member is prevented by the engagement of the sloped surface of the sleeve with said sloping surfaces of the noses.

The gearshift prevention arrangement of the invention finds particular application in motorvehicle speed-change gear units for preventing engagement of the reverse gear of such units above a predetermined vehicle travelling speed.

Thus, advantageously, the balking ring shells are arranged to move radially outwards against the force of the spring at rotational speeds of the said toothed wheel corresponding to a vehicle trayelling speed exceeding 1C km/h.

Preferably the balking ring is constituted by two half shells each provided with a balking nose substantially in the centre of the axial end of the half shells which face the said sleeve.

Furthermore, the balking ring is advantageously formed on its side facing the said toothed wheel with a flange portion which lies against the facing surface of the toothed wheel, an annular recess for receiving the spring being provided in the ring between the flange portion and the balking noses.

In order to avoid the situation in which excessive radially-outward movements of the half shells could prevent movement of the slidable sleeve over the part-cylindrical surfaces of the balking noses at rotational speeds of the toothed wheel greatly in excess of said predetermined value, it is desirable to arrange for the radiallyoutward movement of the half shells to be limited in some manner.In one embodiment of the invention, this is achieved by the provision of stop pins (preferably three in number) projecting from the surface of the toothed wheel which faces the coupling member, the pins being so positioned that they overlie the flange portion of the balking ring in a radially outward direction with the spacing of each pin from the outer diameter of the flange portion being less than, or equal to, the radial distance between the said part-cylindrical surfaces of the balking noses and the inner diameter of the internally-toothed sleeve.

In another embodiment of the invention, the radially-outward movement of the shells is limited by the provision of an annular recess in the surface of the toothed wheel which faces towards the coupling member, this recess serving to accommodate the flange portion of the balking ring and having an outer diameter greater than that of the flange portion when the toothed wheel is at rest. The radial distance between the outer diameter of the flange portion and the outer diameter of the recess is subject to the same restriction as the distance between the pins and flange portion in the embodiment referred to in the preceding paragraph.

Yet another way of limiting the radially-outward movement of the shells is to form the surface of the toothed wheel which faces towards the coupling member with a radial groove in correspondence with each part shell, each said groove being engaged by a respective axial pin provided on the flange portion of the balking ring.

In this case, the limitation on the radial movement of the shell can be made adjustable, for example by providing the flange portion with a setscrew which projects into a corresponding said radial groove, the pin serving as a guide pin and adjustable stop.

Preferably, only a relatively narrow balking nose is centrally provided on each half shell. This relatively narrow balking nose has the advantage that if by virtue of the force of gravity, the half shells move outwards as far as the stop, then the inner bore of the slidable clutch sleeve can always slide over the cylindrical surface of the nose with relatively high accuracy.If instead of each narrow balking nose, there were provided a balking half ring or a large number of balking noses which substantially formed a balking half ring concentric with the remainder of the balking ring structure, then during the engagement of the slidable sleeve with the half shells in their expanded stale, the sleeve would no longer be able to slide by way of its inner bore over the said cylindrical surfaces, but instead, the front end of the sleeve would come to lie against the end face of the balking ring and, in particular, against those ends of the end face of the balking ring which face the separation surfaces.

The spring which holds together the half shells of the balking ring is preferably an open spring ring. This spring ring ma-; be of various dlfferent forms; thus, for example, the ends of the spring can be bent radially outwards such that when the half shells are in their unexpanded state and contact each other along their opposed axiallyextending edge surfaces, the bent spring ends either come into contact with each other or are spaced by only a very small gap. In an alternative form of spring ring, the spring ends are bent radially inwards, and project into an opening defined by complimentary radial recesses provided in the opposed axially-extending edge surfaces of the half shells. In yet anotherform of spring ring, the two spring ends are respectively formed as a hook and as an eye.The hook and eye engage each other such that when the balking ring is in its unexpanded state with the edge surfaces of the half shells lying against each other, an expansion allowance is available, between facing inner surfaces of the hook and eye, which corresponds to the maximum expansion of the half shells when in their expanded gearshift prevention state. The spring ring can have a circular, rectangular or other desirable cross-section.

The gearshift prevention arrangement of the invention is of relatively simple construction, and only requires the re-design of one of the elements present in a gear unit (namely the toothed wheel with its sliding sleeve) and the provision of the balking ring, spring and stop pins. The gearshift prevention arrangement relies solely on centrifugal force for its operation with the annular spring being so chosen that it only allows the balking ring shells .o expand above a predetermined rotational speed of the toothed wheel. Thus no reliance is placed on externally acting forces or effects to attain the required gearshift prevention action.

A gearshift prevention arrangement embodying the invention will now be particularly described, by way of example, with reference to the accompanying diagrammatic drawing, in which; Figure 1 is an axial part section through the gearshift prevention arrangement in its assembled state; Figure 2 is a part cut-away, front view of the gearshift prevention arrangement showing balking noses thereof; Figure 3 is a radial section through the gearshift prevention arrangement at the location of an annular spring thereof; and Figure 4 shows the end parts of a variant of the annular spring, these end parts being n the form of a hook and eye respectively.

The gearshift prevention arrangement now to be described is arranged to prevent engagement of the reverse gear of a motor-vehicie speedchange gear unit at vehicle speeds in excess of 10 km/h. As can be seen from Figure 1, the gearshift prevention arrangement consists substantially of a balking ring 20 disposed in the interspace between a reverse-gear toothed wheel 22 of the gear unit and a coupling member 23 which is either connected in a rotatably rigid manner to this latter or is integrally formed therewith. The balking ring 20 comprises on the one hand a flange portion 21 by which it lies against the front face of the toothed wheel 22 (that is, the surface of the toothed wheel which faces towards the coupling member 23), and on the other hand an annular step 1 7 which projects into a recess 1 9 provided in the toothed wheel 22.

The coupling member 23 comprises outer toothing 4 arranged to cooperate with inner toothing 10 of a slidable sleeve 9 for the purpose of securing operative coupling together of the toothed wheel 22 and sleeve 9 corresponding to engagement of reverse gear of the gear unit.

A spring 18, in the form of an open annular ring, is disposed in an annular recess 2 provided in the periphery of the balking ring 20.

The balking ring 20 is composed of two halves, namely half shells 24, 25. The opposed axiallyextending edge surfaces 26 of the shells 24 and 25 lie against one another when the spring 1 8 is fitted and the toothed wheel 22 is either at rest or, according to the design of the annular spring, rotating at a speed corresponding to a travelling speed of the motor vehicle of up to 10 km/h. At speeds above this value, the half shells 24, 25 move away from each other as the action of centrifugal forces overcomes the effect of the spring and cause the balking ring to expand.

On their end faces which face towards the sliding sleeve 9, the two half shells 24, 25 are each formed with a balking nose 1 5 arranged substantially in the centre of the corresponding half shell and projecting through recesses 1 6 in the coupling member 23. Each nose 1 5 is provided on its upper (radially outer) side with a step formed by a sloping face 14 directed radially inwardly and axially away from the toothed wheel 22, and a part-cylindrical surface 13 joining with the sloping face at the radially inner boundary thereof. The provision of the surface 1 3 is not essential. The surface 6 of the sliding sleeve 9 which faces towards the coupling member is formed, around the mouth to the inner bore 7 of the sleeve, with a slope parallel to the sloping faces 14.The part-cylindrical surfaces 13, the sloping faces 14, the sloped surface 6 and the inner bore 7 are so matched to each other that when the balking ring 20 is in its expanded state corresponding to its gearshift prevention condition. the sliding sleeve 9, during its gear changing movement in the direction indicated by arrow 8, is able to slide by way of its inner bore 7 over the part-cylindrical surfaces 13 until the sloped surface 6 lies against the sloping faces 14.

In order to limit the radially outward movement of the half shells 24, 25 under the effect of centrifugal forces, three stop pins 1 are provided on the front face of the toothed wheel 22 such that when the half shells 24, 25 move outwards the flange portion 21 of the balking ring engages the stop pins 1. The stop pins are so positioned as to ensure that the half shells remain relatively concentric to each other when against the stop 1.

To ensure that the sleeve 9 can always slide over the part-cylindrical surfaces of the noses 1 3, the spacing S1 (reference 3) of each pin from the outer diameter of the ring flange portion 21 is made less than, or equal to, the radial distance S2 (reference 12) between the said part cylindrical surfaces 13 of the balking noses 1 5 and the inner bore of the sleeve 9.

As can be seen from Figure 3, the ends 27 of the open spring 18 are bent radially inwards such as to pass into the interior of the balking ring 20 through an opening 28 formed in the radially inner wall of the annular recess 2 in a zone of meeting of the half shells 24, 25 along their opposed axially-extending edge surfaces 26. The opening 28 has substantially the same width as the annular recess 2 and is made up of two recesses formed as the specular image of each other in respective ones of said shell edge surfaces 26.The spring ends 27 are so formed that they only just make contact with each other, or are spaced by a small gap, when the shell edge surfaces 26 lie on each other in the unexpanded state of the balking ring, the ends 27 being bent sufficiently far back that a tangent thereto forms an angle , which is greater than 00, with a radial line passing through the balking ring axis.

Figure 4 shows a variant of the spring 1 8 in which the ends of the spring are respectively formed as an eye 29 and a hook 30. The hook 30 and eye 29 engage each other such that when the balking ring is in its unexpanded state with the edge surfaces 26 of the half shells 24, 25 lying against each other, an expansion allowance W (reference 31) is available for expansion of the half shells 24, 25.

The gearshift prevention arrangement operates substantially in the following manner.

When the vehicle provided with the speedchange gear unit incorporating the gearshift prevention arrangement, is at rest or is coasting forwards at a speed of less than 10 km/h, the half shells 24, 25 are held together in their unexpanded state by the force of the spring 1 8, i.e.

their axially-extending edge surfaces 26 lie fully against each other. If under these conditions, an attempt is made to engage reverse gear by sliding the sleeve 9 in the direction of arrow 8 towards the coupling member 23, the sleeve 9 will pass over the steps on the balking noses 1 5, without obstruction, so that the internal toothing 10 of the sleeve 9 comes into engagement with the external toothing 4 of the coupling member 23. The reverse gear is thus engaged.

When the vehicle is cruising forwards at a speed greater than 10 km/h, then the action of centrifugal forces on the half shells 24, 25 of the balking ring 20 is sufficient to overcome the force of the spring 1 8 holding the shells together; as a result, the half shells 24, 25 move radially outwards into a position in which the outer surface of their flange portion 21 lies against the pins 1 (the shells remaining in this position until the vehicle speed drops to below 10 km/h).If the vehicle driver now attempts to engage reverse gear, the sieeve 9 will initially slide towards the coupling member 23 in the direction of arrow 8 with the surface of its inner bore 7 passing over the part-cylindrical surfaces 1 3 of the balking noses 1 5. This sliding movement only continues until the sloped surface 6 of the sleeve 9 comes up against the sloping faces 14 of the balking noses 1 5. By this means, any continuation of the gear changing movement, i.e. engagement of the coupling toothing, is prevented. Only when the vehicle driver has braked to a sufficient extent, does the centrifugal force acting on the half shells become correspondingly reduced to enable the spring 1 8 to return the two half shells into their unexpanded state in which the axially-extending edge surfaces 36 of the shells lie against each other. The driver can now complete the gear changing movement without difficulty.

Claims

1. A speed-dependent gearshift prevention arrangement for use in a toothed-wheel gear unit in which engagement of a particular gear of the unit is brought about by the coupling together of a toothed wheel associated with that gear and a slidable sleeve, this coupling being secured by the engagement of internal toothing of the sleeve with external toothing of a coupling member coaxial, and fast for rotation, with said toothed wheel; the speed-dependent gearshift prevention arrangement being operative to prevent the engagement of said particular gear at rotational speeds of the associated toothed wheel exceeding a predetermined value, the gearshift prevention arrangement including a balking ring located between said toothed wheel and the coupling member and comprising two part shells held together by means of a spring which substantially surrounds the part shells, said part shells being arranged to expand radially outwardly against the action of said spring at rotational speeds exceeding said predetermined value and each part shell being provided on its side facing the coupling member with at least one balking nose which extends axially through a corresponding recess formed in the coupling member, each said nose being provided at its free end with a step formed by a sloping face directed radially inwardly and axially away from the said toothed wheel, and a part-cylindrical surface joining with the sloping face at the radially inner boundary thereof, the dimensioning of said noses being such as to enable the sleeve to be slid over the noses to engaged the coupling member when the balking ring is in its unexpanded state, and the surface of the sleeve which faces towards said coupling member being formed, around the mouth to the toothed interior of the sleeve, with a slope corresponding to that of said sloping faces of the balking noses whereby, upon centrifugal expansion of the balking ring, engagement of the sleeve with the coupling member is prevented by the engagement of the sloped surface of the sleeve with said sloping surfaces of the noses.

2. An arrangement according to Claim 1, wherein the balking ring is formed on its side facing the said toothed whael with a flange portion which lies against the facing surface of the toothed wheel, an annular recess for receiving the spring being provided in the ring between the flange portion and the balking noses.

3. An arrangement according to Claim 2, wherein in order to limit radially-outward movement of the part shells, stop pins are provided projecting from the surface of the toothed wheel which faces the coupling member, the pins being so positioned that they overlie the flange portion of the balking ring in a radially outward direction with the spacing of each pin from the outer diameter of the flange portion being less than, or equal to, the radial distance between the said part-cylindrical surfaces of the balking noses and the inner diameter of the internally-toothed sleeve.

4. An arrangement according to Claim 3, wherein three said stop pins are provided.

5. An arrangement according to Claim 2, wherein in order to limit the radially-outward movement of the part shells, an annular recess is provided in the surface of the toothed wheel which faces towards the coupling member, this recess serving to accommodate the flange portion of the balking ring and having an outer diameter greater than that of the flange portion when the toothed wheel is at rest.

6. An arrangement according to Claim 2, wherein in order to limit the radially-outward movement of the part shells, the surface of the toothed wheel which faces towards the coupling member is formed with a radial groove in correspondence with the centre of each part shell, each said groove being engaged by a respective axial pin provided on the flange portion of the balking ring.

7. An arrangement according to any one of the preceding claims, wherein each said part shell is provided with a said balking nose disposed substantially in the centre of the axial end of the shell which faces the said sleeve.

8. An arrangement according to any one of the preceding claims, wherein said spring is an open spring ring.

9. An arrangement according to Claim 8, wherein in one of the zones of meeting of the part shells along opposed axially-extending edge surfaces, an opening is formed in the radially inner wail of the said spring-receiving annular recess of the ring, said opening having substantially the same width as the spring-receiving annular recess and being made up of two recesses formed as the specular image of each other in respective ones of said edge surfaces, and the ends of the spring being bent inwards to project through said opening into the interior of the balking ring.

10. An arrangement according to Claim 8, wherein one end of the spring is bent in the form of a hook whereas the other end is fashioned as an eye and is engaged by said hook, the form of the eye being such as to enable expansion of the spring ring upon expansion of the balking ring.

11. An arrangement according to any one of Claims 8 to 10, wherein said spring has a circular cross-section.

12. An arrangement according to any one of Claims 8 to 10, wherein said spring has a rectangular cross-section.

1 3. An arrangement according to Claims 8 or Claim 9, wherein the ends of said spring are bent substantially radially inwards, so that they make tangential contact with each other when the balking ring is in its unexpanded state with the opposing axialiy-extending edge surfaces of the part shells juxtaposed each other.

14. A toothed-wheel gear unit incorporating a gearshift prevention arrangement according to any one of the preceding claims, said unit being a motor-vehicle speed-change gear unit and said particular gear being the reverse gear of the unit.

1 5. A speed-dependent gearshift prevention arrangement substantially as hereinbefore described with reference to Figures 1 to 3 or Figures 1, 2 and 4 of the accompanying drawings.