CA1167285A

CA1167285A - Road-speed related shift-lock for gear-trains

Info

Publication number: CA1167285A
Application number: CA000392852A
Authority: CA
Inventors: Otto A. Ebner; Friedrich Schreiner
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1980-12-19
Filing date: 1981-12-21
Publication date: 1984-05-15
Also published as: GB2089912A; IT8125284A0; GB2089912B; IT1139846B; FR2496818A1; DE3048048A1; FR2496818B1; DE3048048C2

Abstract

ABSTRACT

The invention is concerned with a road-speed related shift-lock for gear-trains, for preventing engagement of a reverse gear in a motor-vehicle gearbox when the vehicle is moving at a speed higher than a predetermined speed and in the forward direction, the reverse-gear comprising a coupling element which is secured against rotation relative thereto and has external teeth adapted to engage internal teeth of a sliding sleeve upon the engagement of the reverse-gear. The shift-lock according to the invention is characterized in that a locking ring is arranged between the reverse-gear and the coupling element, the locking ring comprising two half-shells held together by a spring substantially encompassing the half-shells. Each half-shell comprises on a side facing the coupling element a locking lug provided with an annular surface and a chamfer which define a step. The coupling element has in its periphery axial recesses adapted to receive the respective locking lugs of the half shells and the sliding sleeve has an internal bore and a chamfer extending parallel to the chamfer of the locking lug. When the vehicle moves at a speed higher than the predetermined speed, centrifugal forces cause the half-shells to move radially outwardly against the retaining force exerted by the spring such that the internal bore of the sleeve slides over the annular surface of the locking lug until the chamfer of the sleeve abuts against the chamfer of the locking lug, thereby preventing further movement of the sleeve and thus engagement of the internal teeth of the sleeve with the external teeth of the coupling element.

Description

i'7~

The present invention reLates to a road-speed related shift-lock for gear-trains and, more particularly to a lock adapted to prevent the engagement of the reverse-gear in a motor-vehicle gearbox, when the vehicle is moving at a too high speed and in the forward direction.
German Patent ~o. 1,946,496 discloses a road-speed related lock for preventing the reverse-gear from being engaged in motor-vehicle gear boxes. The lock comprises a main drive and a group-drive extending the gear-sequence, the gear-change being locked with the aid of pneumatically operated pressure-cylinders. Control of these cylinders is partly pneumatic and partly hydraulic, and is effected by a series of valves. As a result, this known-locking means is relatively expensive.
Is is an object of the invention to provide a road-speed related shift-lock for gear-trains which is of simple construction and does not require many parts.
It is another object of the invention to provide shift lock of the above-mentioned type which takes up almost no additional space and which can be operated wlthout external actuation (pneumatic/hydraulic/mechanical linkages), and can therefore be maintenance-free and easy to assemble and dismantle.
In accordance with the present invention,there is thus provided a road-speed related shift-lock for gear-trains, for preventing engagement of a reverse-gear in a motor-vehicle gearbox when the vehicle is moving at a ~; speed higher than a predetermined speed and in the forward direction, the reverse-gear comprising a coupling element which i9 secured àgainst rotation relative thereto and has ~ ~ti~

external teeth adapted to engage internal teeth of a sliding sleeve upon the engagement of the reverse-gear, characterized in that a locking ring is arranged between the reverse-gear and the coupling element, the locking ring comprising two half-shells held together by a spring substantially encompassing the half-shells. Each half-shell comprises on a side facing the coupling element a locking lug provided with an annular surface and a chamfer which define a step. The coupling element has in its periphery axial recesses adapted to receive the respective locking lugs of the half-shells and the sliding sleeve has an internal bore and a chamfer extending parallel to the chamfer of the locking lug~ When the vehicle moves at a speed higher than the predetermined speed, centrifugal forces cause the half-shells to move radially outwardly against the retaining force exerted by the spring such that the internal bore of the sleeve slides over the annular surface of the locking lug until the chamfer of the sleeve abuts against the chamfer of the locking lug, thereby preventing further movement of the sleeve and thus engagement of the internal teeth of the sleeve with the external teeth of the coupling elementO
The shift-lock according to the invention thus consists of a locking ring, divided into two half-shells, which is arranged between the reverse gear and the coupling element, the half-shells being held together resiliently :: ~
by a spring substantially encompassing them. A locking lug is provided on the side of each half-shell facing the coupling element, the locking lug having an annular surface and a chamfer which define a step. The coupling element

- 2 -. ~4~7~ ~

has in its periphery axial recesses adapted to receive the respective locking lugs of the half-shells. At a road-speed of, for example, more than 10 km/h, the half-shells of the locking ring are moved radially outwardly against the retaining force of the spring such that the internal bore of the sleeve will slide over the annular surface of the locking lug. Thereafter, however, the chamfer of the sleeve will bear against the chamfer on the locking lug, thus preventing the gear-shifting movement from continuing.
According to a preferred embodiment of the invention, the locking ring is provided on a side facing the reverse-gear with a flanged part bearing against an end-face of the reverse-gear, and an annular recess is provided between this flanged part and the locking lug for the accommodation of the spring.
In order to limit the movement of the half-shells which tend, under the action of centrifugal forces, to move radially outwardly, preferably three pins are provided in the end-face of the reverse-gear in such a manner that they project partly from the end-face and are each spaced from an outer adjacent surface of the flanged part of the locking ring which moves in response to the centrifugal ~ forces to eventually bear against the pins. In this : embodiment, the distance between each pin and the outer adjacent surface of the flanged part is smaller than, or at most equal to, the distance between the annular surface of the:locking lug and the internal bore surface of the sliding sleeve. This limitation of the radial movement of the half-shells may also be achieved by other means. For example, the end-face of the reverse-gear may be provided

- 3 -, . _, ~, .. ... .. . . ... . . . .... . .. . ....... .... .

~i'7~&~

with an annular recess defining an abutment surface, into which the flanged part of the locking ring projects, in such a manner that the distance between the abutment surface and the outer adjacent of the flanged part is the same as that betweenthe pinand the flanged part of the afore-mentioned embodiment. Furthermore, and again in order to limit the travel of the half-shells, a radial groove may be provided in the end-face of the reverse-gear at a level centrally of each half-shell, at least one axial pin arranged in the flanged part projecting into the groove.
In this embodiment, the travel of the half-shells may also be limited, for example, by means of a grub-screw which also projects into the groove~ In this case, the pin performs the function of a guide-pin.
According to still another preferred embodiment of the invention, each half-shell is provided with a relatively narrow locking lug arranged substantially centrally of the end-face thereo~. This relatively narrow locking lug has the advantage that when, as a result of the centrifugal forces, the half~shells move outwardly as far as the stop, the internal bore of the sliding sleeve can still slide, with relatively great accuracy, over the annular surface. If this narrow locking lug were to be replaced by a locking half-ring, or by a large number of locking lugs essentially constituting a locking half-ring and arranged concentrically with the usual design of coupling ring, then upon engagement of the sliding sleeve, with the half-shells in their released position, the internal bore of the sleeve would no longer slide over the annular surface. Instea~ it would bear against the end-face, more particularly against ~ 7Z ~

the ends, facing the parting surfaces, of the end-faces of the locking ring.
According to still another preferred embodiment of the invention, the spring holding the half-shells of the coupling ring together is an open spring-ring. This open spring-ring may be of various designs. ~ccording to one design, the ends of the ring may be bent radially in such a manner that, when the parting surfaces of the half-shells are placed one upon the other, the bent ends of the spring touch each other or are separated apart only by a very small distance. According to another design, the ends of the spring may be bent radially inwardly, suitable radial groovesbeingprovided in the parting surfaces of the half-shells for enabling the ends of the spring to pass therethrough and into the interior of the locking ring. According to another preferred embodiment, the ends of the spring may be such that one end is in the form of ; an eye and the other end is in the form of a hook. mus, when the haIf-shells are placed one upon the other, the hook is engaged in the eye in such a manner that there is a gap between the inner surface of the hook and the eye, as seen in the tangential direction, the gap corresponding to the maximum expansion of the half-shells when they are in the locking position. In this case, the spring-ring may be of circular, rectangular, or any other suitable cross-section.
The shift-lock according to the invention is of relatively simple construction, since it involves the modiflcation of an element already ~resent in the gear-~30 box, namely the gearwheel with its coupling element, the :

- . . . ......... . .
" ~ ~

i'7~

only additions being the locking ring, the spring, and the stop-pin. The shift-lock according to the invention operates only with the assistance of centrifugal forces, the design of the annular spring being such that it opens only when a specific rotational velocity is exceeded, allowing the locking-ring half-shells to shift outwardly.
Thus no external forces are needed to achieve the desired locking action.
Further characteristics and advantages of the shift-lock according to the invention will become from the following detailed description of a preferred embodiment thereof as illustrated in the accompanying drawings, wherein:
Fig~ 1 is a partial axial section through a shift-lock according to the invention in the assembled condition, Fig. 2 is a front elevation of the shift-lock in partial section, showing the arrangement of the locking lugs:
Fig~ 3 is a radial section through the shift-lock on a level with the annular spring, showing the arrangement ~20 thereof, Fig. 4 is a partial view of the annular spring, the ends of which are in the form of a hook and an eye.
The shift-lock illustrated in Fig. 1 comprises essentially a locking ring 20 arranged in the space between a reverse-gear 22 and a coupling element 23 which is connected to the gear 22 ana secured against rotation relative~ thereto or is integral therewith. The locking ring 20 has on the one hand a flanged part 21 which bears against the end-face of the reverse-gear 22 and, on the ~ 30 other hand, an annular step 17 which projects into an : :::

u~dercut 19 formed in the gear 22. The coupling element 23, in turn, comprises external teeth 4 which co-operate with internal teeth 10 of a sliding sleeve 9. Arranged in the periphery of the locking ring 20 is an annular recess 2 in which is seated a spring 18 in the form of an open annular ring. The locking ring 20 consists of two half-shells 24 and 25, the parting surfaces 26 of which lie one upon the other when the spring 18 is inserted and the gear-box is stationary, or, depending upon the design of the spring, at a road-speed of up to 10 km/h. Each of the half-shells 24 and 25 has a locking lug 15 which is located substantially centrally in the end-face facing the sliding sleeve 9 and which extends in a respective æial recess 16 formed in the coupling element 23. The upper surface of each locking lug 15 has an annular surface 13 and a chamfer 14 which define a step. The sliding sleeve 9, in turn, is provided with an internal bore 7 and a chamfer 6 extending parallel to the chamfer 14. The annular surface 13, chamfer 14, chamfer 6 and internal bore 7 are matched with each other in such a manner that, when the locking ring 20 is in the locking position, the internal bore 7 of the sliding sleeve 9 can slide, in the shifting direction indicated by arrow 8, over the annular surface 13 until the chamfer 6 bears against the chamfer 1~. For the purpose of restricting the travel of the half shells 24 and 25, three stop-pins 1 are provided in the end-face of the gear 22 in such a manner that the half-shells remain relatively concentric as they move radially outwardly under the action of centrifugal forces, Each pin is spaced from the outer surface 3 of the flanged part21 by a distance Sl which is 7~

equal to or smaller that the distance S2 between the internal bore surface of the sleeve 9 and the annular surface 13 of the locking lug 15.
As may be .seen from Fig. 3, the ends 27 of the open spring 18 are inwardly bent and are passed through a groove 28 facing them and provided in the parting surfaces 26 of the half-shells 24 and 25, into the interior of the loc~ing ring 20. The inwardly bent ends 27 of the spring are designed such that, when the parting surfaces-26 lie one upon the other, the ends 27 only just touch or are at a smal.l distance apart. The ends 27 are also bent back to form an angle ~ > 0 with a tangent to the radius of curvature, measured with respect to the longitudinal axis of the groove. The groove 28 is at a level with the annular recess 2 and has substantially the same width as the recess 2.
Fig. 4 shows another possible embodiment for the ends of the spring 18, one end being in the form of an eye 29 while the other is in the form of a hook 30.
The hook and eye engage in each other such that, when the parting surfaces 26 of the half-shells 24 and 25 lie one upon the other, a gap w is defined therebetween which corresponds to the maximum expansion of the half-shells.
The shift-lock according to the invention operates .
as follows.
When the gearbox and the ~ehicle are stationary, and when the vehicle is rolling in the forward direction at a speed of less than 10 km/h, the half-shells 24 and 25 are held together, in their neutral position, by the force of ~he spring 18, i.e. their parting surfaces 26 lie fully ::

.. . . .. ... .. .. . .. . ..

one upon the other. If at this stage, the reverse-gear is engaged, the sliding sleeve 9 is pushed in the direction of the arrow 8 towards the coupling element 23 through which the locking lugs 15 pass. The internal bore 7 of the sleeve 9 will slide over the step of the locking lug 15, whereupon the internal teeth 10 of the sliding sleeve 9 engage with the external teeth 4 of the coupling element 23.
mis engages the reverse-gear 22.
If the vehicle continues to move forward at a speed higher than 10 km/h, the half-shells 24 and 25 of the locking ring 20 will be forced outwardly by the centrifugal force, to such an extent that they overcome the retaining force of the spring 18 and move radially outwardly until they bear, with the outer surface 3 of their flanged parts 21, against the pins 1 and remain in this position. If the driver of the vehicle now attempts to shift into reverse, the sliding sleeve 9 will ~e pushed in the direction of the arrow 8 towards the coupling element 23, but the internal bore 7 of the sleeve will now slide over the annular surface 13 of the locking lug 15 until the chamfer 6 on the sleeve finally bears against the chamfer 14 of the locking lug prevents any continuation of the shift-movement, i.e.
there will be no engagement of the teeth 10 with the teeth

4 of the coupling element 23. If the driver now slows the vehicle down by applying the brakes, the centrifugal force acting upon the half-shells will also be reduc~d accordingly, thus allowing the spring 18 to return the two half-shells 24 and 25 to their neutral position with the parting surfaces 26 thereof lying one upon the other. The driver can now complete the gear-shift without difficulty.

_ g _

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A road-speed related shift-lock for gear-trains, for preventing engagement of a reverse-gear in a motor-vehicle gearbox when said vehicle is moving at a speed higher than a predetermined speed and in the forward direction, said reverse-gear comprising a coupling element which is secured against rotation relative thereto and has external teeth adapted to engage internal teeth of a sliding sleeve upon the engagement of said reverse-gear, characterized in that a locking ring is arranged between said reverse-gear and said coupling element, said locking ring comprising two half-shells held together by a spring substantially encompassing said half-shells, each said half-shell comprising on a side facing said coupling element a locking lug provided with an annular surface and a chamfer which define a step, said coupling element having in its periphery axial recesses adapted to receive the respective locking lugs of said half-shells and said sliding sleeve having an internal bore and a chamfer extending parallel to the chamfer of said locking lug, whereby when said vehicle moves at a speed higher than said predetermined speed, centrifugal forces cause said half-shells to move radially outwardly against the retaining force exerted by said spring such that the internal bore of said sleeve slides over the annular surface of said locking lug until the chamfer of said sleeve abuts against the chamfer of said locking lug, thereby preventing further movement of said sleeve and thus engagement of the internal teeth of said sleeve with the external teeth of said coupling element.

2. A shift-lock according to claim l, characterized in that said locking ring comprises on a side facing said reverse-gear a flanged part bearing against an end-face of said reverse-gear, and in that an annular recess is provided between said flanged part and said locking lug for the accommodation of said spring.

3. A shift-lock according to claim 2, characterized in that in order to limit the radial outward movement of said half-shells, pins are secured to said end-face of said reverse-gear in such a manner that said pins project partly from said end-face of said reverse-gear and are each spaced from an outer adjacent surface of said flanged part by a distance equal to or smaller than the distance between the annular surface of said locking lug and the internal bore surface of said sliding sleeve.

4. A shift-lock according to claim 2, charac-terized in that in order to limit the radial outward movement of said half-shells, said end-face of said reverse-gear is provided with an annular recess defining an abutment surface, into which said flanged part projects, said abutment surface being spaced from an outer adjacent surface of said flanged part by a distance equal to or smaller than the distance between the annular surface of said locking lug and the internal bore surface of said sliding sleeve.

5. A shift-lock according to claim 2, charac-terized in that in order to limit the radial outward movement of said half-shells, said end-face of said reverse-gear is provided with a radial groove at a level centrally of each half-shell, a corresponding axial pin arranged in said flanged part projecting into said groove.

6. A shift-lock according to claim 1, characterized in that each said locking lugs are arranged substantially centrally on end-faces of said half-shells.

7. A shift-lock according to claim 1, characterized in that said spring is an open spring-ring.

8. A shift-lock according to claim 7, characterized in that said spring has inwardly bent ends and in that a groove is provided in parting surfaces of said half-shells, said bent ends of said spring passing through said grove and into the interior of said locking ring.

9. A shift-lock according to claim 2, characterized in that said spring is an open spring-ring having inwardly bent ends and in that a groove is provided in parting surfaces of said half-shells at a level with said annular recess, said groove having substantially the same width as said annular recess, said bent ends of said spring passing through said groove and into the interior of said locking ring.

10. A shift-lock according to claim 7, characterized in that said spring has bent ends, one end defining an eye and the other end defining a hook, said hook and eye being engaged with each other such that, when parting surfaces of said half-shells lie one upon the other, a gap is defined therebetween.

11. A shift-lock according to claim 7, charac-terized in that said spring has ends which are substantially radially inwardly bent such that they are in tangential contact with each other when parting surfaces of said half-shells lie one upon the other.

12. A shift-lock according to claims 1 or 7, characterized in that said spring has a circular cross-section.

13. A shift-lock according to claims 1 or 7, characterized in that said spring has a rectangular cross-section.