GEARBOX FOR MOTOR VEHICLES

Abstract: A gearbox for motor vehicles is provided with a device for restraining the reverse gear control fork (9) in its engaged position. The restraining device comprises a locking member (29) mounted slidably in a hole (30) which passes through one wall of the fork (9), and a member (32) for operating the locking member (29), which is operated by the rod that controls the position of the fork (9) and can make the locking member (29) advance through the hole (30) and partially engage a seat (31) formed in the support structure (11) of the gearbox when the fork is put into its engaged position.

Description: The present invention relates to gearboxes for motor vehicles, of the type comprising a support structure, a device for the engagement of reverse, a fork for operating the engagement device articulated to the support structure and movable between a position of engagement of reverse and a position of disengagement, and a control rod for the fork mounted for axial sliding movement relative to the support structure. The object of the present invention is to provide a gearbox of the type specified above with simple and practical means for preventing the accidental disengagement of reverse when the motor vehicle is moving. In order to achieve this object, the invention has as its subject a gearbox for motor vehicles, characterised in that it further comprises a device for restraining the fork in the position of engagement of reverse, including a locking member mounted slidably in a hole which passes through one wall of the fork, and a member for operating the locking member, which is operated by the rod to make the locking member advance through the hole and partially engage a seat formed in the support structure of the gearbox when the fork is put into its position of engagement, so as to lock the fork in the position of engagement. In a preferred embodiment, the operating member comprises a lever articulated on the support structure of the gearbox about the axis of articulation of the fork in juxtaposition to the fork; the fork and the lever have adjacent ends which are disposed between two opposing walls movable by the control rod; and the said ends of the fork and the lever have different dimensions in a direction substantially perpendicular to the opposing walls whereby an axial movement of the control rod between the two positions causes different angular strokes of the fork and the operating lever. In this preferred embodiment, moreover, the operating lever includes a first wall portion in contact with the fork and a second wall portion spaced from the fork, these wall portions being shaped and arranged in such a way that, in the position of disengagement, the hole in the fork has an end facing the second wall portion whereby the fork is free with respect to the support structure of the gearbox, while, when the fork and the operating lever are thrust towards the engaged position, the second wall portion is displaced relative to the fork until it faces the hole, so as to cause the restraining member to partially engage the seat of the support structure, this seat facing the end of the hole opposite the operating lever. Further characteristics and advantages of the invention will become apparent from the description which follows with reference to the appended drawings provided purely by way of non-limiting example, in which: Figure 1 is a partially-sectioned perspective view of a part of a gearbox for motor vehicles according to the present invention, Figures 2 and 3 illustrate in section the part of Figure 1 in two different operating conditions, Figure 4 is a view along the arrow IV of Figure 1, and Figures 5 and 6 are sectional views taken along the lines V-V and VI-VI of Figures 2 and 3. With reference to the drawings, the housing of the gearbox, indicated 1, constitutes the support structure for the internal parts of the gearbox. Figure 1 also illustrates two shafts 3, 4 of the gearbox which are connected together for rotation in order to engage reverse. To this end, the shaft 3 carries a freely rotatable gear 5 which meshes with a gear 6 fixed to the shaft 4 and which can be connected for rotation with the shaft 3 by the axial displacement of a collar 7 forming part of an engagement synchronizing device 8 of known type. The axial position of the collar 7 is controlled by a fork 9 which, by means of a pin 10, is articulated on a wall 11 of a bracket 12 secured to the support structure 1 by screws 13a. The fork 9 has a terminal nose 13 situated between two opposing walls 14 forming part of a single control member 15 which includes two hubs 16, 17 arranged in positions axially spaced from each other and slidably mounted on a control rod 18. The rod 18 is mounted for axial sliding relative to the support structure 1. The axial movements of the rod 18 are controlled, in a manner known in itself, by a sleeve 19 fixed to the rod 18 and provided with an appendage of known type (not illustrated), which is intended to be controlled by an operating member of the gearbox. The rod 18 can adopt a first operative end position in which it controls the engagement of reverse, a central neutral position in which reverse is disengaged, and a second operative end position in which it effects the engagement of a higher speed ratio of the gearbox. The constructional details of the means for engaging this higher speed ratio are not illustrated in the drawings, since they are of a type known per se and do not fall within the scope of the present invention. Moreover, the omission of these details from the drawings make for more immediate comprehension of the latter. In any case, a gearbox having a structure of the type discussed above has been described and illustrated in the prior Italian Utility Model Application No. 53633-B/84 filed by the same Applicant on 11.7.1984. The snap-locking of the control rod 18 in each of its three operative positions is effected by the engagement of a ball locking member 20a, biassed by a spring (not illustrated), in a corresponding seat 20 formed in the control rod 18. Figures 1 and 2 illustrate the rod 18 in its central neutral position in which both reverse and the higher speed ratio are disengaged. With reference to Figure 2, the position of the control rod 18 corresponding to the engagement of reverse is displaced towards the right with respect to the position illustrated in Figure 2, while the position corresponding to the engagement of the higher speed ratio is displaced towards the left. In accordance with what is described and illustrated in the utility model application mentioned above, when the control rod 18 is not in the position corresponding to the engagement of the higher speed ratio, the hub 16 is connected to the rod 18 through the engagement of a locking pin 21 in a radial hole 22 in the hub 16 and in a locating notch 23 formed in the rod 18. The pin 21 has a greater length than the axial length of the hole 22 and is kept in partial engagement with the notch 23 because of the engagement of the end of the pin 21 opposite the notch 23 against the outer surface of a further control rod 24 forming part of the gearbox. Still in accordance with what is illustrated in the aforesaid utility model application, the further control rod 24 has a transverse hole 25 in which is inserted a thrust member 26 loaded by a spring 27. When the control rod l8 is in its central neutral position illustrated in Figure 2, the notch 23 and the locking pin 21 are located in correspondence with the thrust member 26. If the control rod 18 is thrust towards the left (with reference to Figure 2) so as to effect the engagement of the higher speed ratio, the hub 16 (and as a result the whole member 15) cannot follow the movement of the rod 18 because of its engagement against an abutment surface 28 defined by the wall of the support structure 1. The axial movement of the rod 18 towards the left with respect to the hub 16 (with reference to Figure 2) causes the locking pin 21 to leave the locating notch 23 and become engaged in the hole 25 against the action of the thrust member 26. Consequently, the member 15 controlling the engagement of reverse remains locked in a fixed position in which reverse is disengaged, when the control rod 18 effects the engagement of the higher speed ratio (as long as the rod 18 is displaced, the rod 24 is held in position by conventional means, not illustrated, of the type described, for example, in the aforesaid utility model application). According to the present invention, provision is made for a restraining device to lock the fork 9 in position when the latter is in the position of engagement of reverse. This restraining device includes a locking member 29 mounted slidably in a hole 30 which passes through the wall of the fork 9. The locking member 29 has a dimension in a direction parallel to the axis of the hole 30 greater than the length of this hole. When the fork 9 is in the position of engagement of reverse, the locking member 29 is partially inserted in a flared seat 31 formed in the wall 11 of the bracket 12, whereby the fork 9 is held in a fixed position. The engagement of the locking member 29 in the seat 31 upon the engagement of reverse is achieved by means of an operating member 32 comprising a lever which is articulated on the wall 11 about the same axis of articulation as the fork 9 and has a terminal nose 32a juxtaposed to the terminal nose 13 of the fork 9 and arranged with the latter between the two walls 14 forming part of the control member 15. The width of the terminal nose 32a of the lever 32 in a direction substantially perpendicular to the walls 14 corresponds substantially to the distance between these walls, while the terminal nose 13 of the lever 9 has a slightly smaller width. Consequently, movements of the control member 15 in an axial direction, effected by the movement of the control rod 18 between its central neutral position and the operative end position corresponding to the engagement of reverse, cause slightly different angular strokes of the lever 9 and the operating member 32. This occurrence can be confirmed by an examination of Figures 2 and 3 which illustrate how, in the condition of disengagement of reverse, the nose 32a protrudes slightly to the left of the nose 13 (see Figure 2), while, in the condition of engagement of reverse, the nose 32a protrudes slightly to the right of the nose 13 (see Figure 3). With reference to Figures 5 and 6, the wall of the operating lever 32 has, adjacent the hole 30, a first wall portion 33 in contact with the fork 9 and a second wall portion 34 spaced from the fork, these wall portions 33, 34 being joined by an inclined wall portion 35. When the fork 9 is in the position of disengagement of reverse (see Figure 5), the wall portion 34 of the operating lever 32 faces the hole 30 and the locking member 29 is disengaged from the seat 31, so that the fork 9 is free with respect to the support structure 1 of the gearbox. If the control rod 18 is brought from the position illustrated in Figure 2 to the position illustrated in Figure 3 so as to effect the engagement of reverse, the different angular stroke of the operating lever 32 with respect to the fork 9 causes an engagement firstly of the wall portion 35 and secondly of the wall portion 33 on the locking member 29. In this way, the latter is forced through the hole 30 by the operating lever 32 until it partially engages the seat 31, so as to lock the fork 9 to the support structure 1. In the condition of engagement of reverse, the wall portion 33 faces the end of the hole 30 opposite the seat 31, so that it prevents the accidental disengagement of the fork 9 from the position of engagement of reverse. When the control rod 18 is moved again from the position illustrated in Figure 3 towards the position illustrated in Figure 2, the operating lever 32 is brought into the position illustrated in Figure 5, whereby further movement of the fork 9 causes the locking member 29 to leave the seat 31 as a result of the engagement of the locking member with the flared side wall of the seat 31. Naturally, the principle of the invention remaining the same, the details of construction and forms of embodiment may be varied widely from that described and illustrated purely by way of example, without thereby departing from the scope of the present invention.

Claims: 1. Gearbox for motor vehicles, comprising: a support structure (1), a device for the engagement (8) of reverse, a fork (9) for operating the engagement device (8), articulated on the support structure (1) and movable between a position of engagement of reverse and a position of disengagement, a control rod (18) for the fork(9) mounted for axial sliding relative to the support structure (1), characterised in that the gearbox further comprises a device for restraining the fork (9) in the position of engagement of reverse, including: a locking member (29) mounted slidably in a hole (30) which passes through one wall of the fork (9), and a member (32) for operating the locking member (29), which is operated by the rod (18) to make the locking member (29) advance through the hole (30) and partially engage a seat (31) formed in the support structure (1, 12) of the gearbox when the fork (9) is put into its position of engagement, so as to lock the fork (9) in the position of engagement. 2. Gearbox according to Claim 1, characterised in that the operating member (32) comprises a lever articulated on the support structure (1) of the gearbox about the axis of articulation of the fork (9) in juxtaposition to the fork (9), in that the fork (9) and the operating lever (32) have adjacent ends (13, 32a) which are disposed between two opposing walls (14) movable by the control rod (18), and in that the dimensions of the said ends (13, 32a) of the fork (9) and the operating lever (32) in a direction substantially perpendicular to the opposing walls (14) are different from each other, whereby an axial movement of the control rod (18) between the two positions causes different angular strokes of the fork (9) and the operating lever (32). 3. Gearbox according to Claim 2, characterised in that the operating lever (32) includes a first wall portion (33) in contact with the fork (9) and a second wall portion (34) spaced from the fork (9), these wall portions (33, 34) being shaped and arranged in such a way that, in the position of disengagement, the hole (30) in the fork (9) has one end facing the second wall portion (34) whereby the fork (9) is free with respect to the support structure (l) of the gearbox, while, when the fork (9) and the operating lever (32) are thrust towards the position of engagement of reverse, the first wall portion (33) is displaced relative to the fork (9) until it faces the hole (30), so as to cause the locking member (29) to partially engage the seat (31) formed in the support structure (1, 11), this seat (31) facing the end of the hole (30) opposite the operating lever (32). 4. Gearbox according to Claim 3, characterised in that the two opposing walls (14) form part of an auxiliary control member (15) slidably mounted on the control rod (18), and that means are provided for holding the auxiliary control member (15) in a fixed position on the control rod (18) when the control rod (18) is moved between the position of engagement of reverse and the position of disengagement, and for locking the auxiliary control member (15) relative to the support structure (1) of the gearbox when the control rod (18) is moved between the position of engagement and a further operative position opposite the operative position of engagement of reverse, in which the control rod (18) effects the engagement of the higher speed ratio of the gearbox.

Inventors: FALZONI, GIANLUIGI, MARAN, LUCIANO
Applicants: FIAT AUTO S.P.A.
Application year: 1986
Main classification: G05G5
IPC codes: F16H63