An operating linkage for the gearbox of a commercial vehicle with a safety system for preventing the gears from becoming disengaged

Abstract: An operating linkage (10) for the gearbox (C) of a commercial vehicle includes a transmission connecting rod (16) articulated at one end to the structure of the vehicle and at the other end to a joint (13) connecting two transmission rods (11, 12). A spring pawl is associated with the connecting rod (16) and, in cooperation with a cam positioning device (18) fixed to the mounting of the linkage, intervenes when the gears are disengaged to prevent them from slipping out of engagement because of sudden and violent jolting of the vehicle.

Description: The present invention relates to an operating linkage for the gearboxes of commercial vehicles comprising the features as outlined in the preamble of claim 1. Such an operating linkage is known from DE-C 35 19 749. Conventional linkages have a problem in that the gears slip out of engagement as a result of vibrations and jolting of the vehicle. In fact, if the considerable mass of the whole linkage system is taken into account, it is clear that the inertia of the masses which come into play as a result of excessive jolting and vibration of the power unit and the cab may accidentally cause the aforementioned disengagement. Current solutions use springs which are interposed externally between the support structure and the transmission levers, or between the support structure and the connecting rods for the articulation of the joints between the transmission levers, and urge the parts of the linkage into the configuration in which a gear is engaged, increasing the force necessary for the driver to engage the opposite gear. The object of the present invention is to further develop a generic linkage of the type specified at the beginning of the description which is simply and cheaply without increasing the loads applied to the gear lever by the user. According to the invention, this object is achieved by the features as defined in claim 1. The linkage preferably includes a push rod supported slidably by the connecting rod and parallel thereto, a cam element fixed to the support structure and having a profiled edge parallel to the plane of articulation of the connecting rod, the edge having a first portion whose average radial distance from the pivot axis of the connecting rod is greater than the average radial distance therefrom of two adjacent second portions of the edge connected to the first portion, and a spring interposed between the push rod and the connecting rod and adapted to urge the push rod against the edge of the cam element, the pivoting of the connecting rod compressing the spring when the push rod slides from one of the two second edge portions of the cam element towards the first portion. By virtue of these characteristics, the safety system operates only during the stage of disengagement of the gears, whilst the loads on the gear lever remain unchanged during the engagement stage. Further characteristics and advantages of the linkage according to the invention will become clear from the detailed description which follows with reference to the appended drawings, provided by way of non-limiting example, in which: Figure 1 is a side view of a gearbox operating linkage according to the invention, Figure 2 is a detail of Figure 1 on an enlarged scale, Figure 3 is a section taken on the line III-III of Figure 2, Figure 4 is a view similar to Figure 2 and shows a variant of the linkage, and Figure 5 is a section taken on the line V-V of Figure 4. With reference to the drawings, a linkage, generally indicated 10, for operating the gearbox C of a commercial vehicle comprises first and second transmission levers 11 and 12 interposed between the selector of the gearbox C and the manual gear lever, indicated L in the drawings, situated in the driver's cab of the vehicle. A linkage of this type, which includes a joint 13 between the levers 11 and 12 comprising a spherical support element rotatable within a tubular body which forms part of the cross member of the joint, is described and illustrated in European Patent Application EP-A-0 376 902 filed by the Applicant and to which reference is made (published on 04/07/90). The joint 13 between the transmission levers 11 and 12 is formed in correspondence with a connecting rod 16 interposed between a mounting 17 fixed to the structure A of the vehicle, in this case, the engine block, and the articulation joint between the transmission levers. When the gears are engaged/disengaged, therefore, the connecting rod 16 pivots about the horizontal axis X-X of the connecting rod, its pivoting movement being indicated by the arrow R in Figure 1. With reference to Figures 1-3, an elongate plate-like arm 18 is also fixed to the mounting 17 and has a first end 18a keyed rigidly to the mounting 17 in correspondence with the lower end of the connecting rod 16 (with reference to the installed configuration of the linkage) and a second end 18b with a substantially V-shaped cam profile 19 defining a central portion 19a and two side portions 19b. The average radial distance of the central portion 19a of the cam 19 from the axis of rotation X-X of the connecting rod 16 is greater than the average distance therefrom of the adjacent portions 19b connected thereto. At its end which is articulated to the joint 13, the connecting rod 16 has a tubular seat 21 which has an axis Y-Y substantially parallel to the connecting rod itself and in which is slidable a push rod 22 with a sperhical end 22a in frontal contact with the cam profile 19 at the end 18b of the arm 18. A helical spring 24 is interposed between the push rod 22 and a screw adjustment device 23 for urging the end 22a of the push rod 22 against the cam 19 with a predetermined force. In the configuration of Figures 1-3, the gearbox is in neutral, which is the condition of maximum compression of the spring 24 by the cam profile 19. Clearly, when a gear is engaged, the connecting rod 16 pivots clockwise or anticlockwise (with reference to Figures 1 and 2) so that the push rod 22a slides over the cam profile 19 towards the portion 19b of that profile and progressively "unloads" the spring 24. The force required for the push rod 22 to compress the spring 24 again by sliding along on the cam profile 19 prevents any accidental disengagement of the gears. In the variant shown in Figures 4 and 5, in which similar elements have been indicated by the same reference numerals, instead of the cam profile 19, the arm 18 has two holes 26 with axes parallel to the axis of articulation X-X of the connecting rod 16, arranged at equal radial distances from that axis and interconnected by inclined planes perpendicular to the connecting rod 16. Adjacent the joint 13 between the transmission levers 11 and 12, the connecting rod 16 has a tubular seat 27 which has an axis Z-Z parallel to the axis of articulation X-X of the connecting rod 16 and in which a metal ball 28 can slide. The ball is urged towards a face 18c of the arm 18 by a helical spring 30 which is housed in the tubular seat 27 and reacts against a resilient split ring 31 provided at one end of the tubular seat 27. In the configuration shown in Figures 4 and 5, which corresponds to the condition in which the gears are not engaged, the ball 28 is in contact with the face 18c of the arm 18. When the gears are engaged, the ball is resiliently snap-engaged in the holes 26 under the action of the spring 30 resiliently to lock the connecting rod 16 and thus prevent the accidental disengagement of the gear in a similar manner to that described above.

Claims: An operating linkage for a gearbox of a commercial vehicle, including at least one pair of transmission levers (11, 12) interconnected with the interposition of a joint (13) and articulated to the structure of the vehicle by means of a connecting rod, including resilient engagement means (22, 24 or 28, 30) supported by the connecting rod (16) and adapted to cooperate with abutment means (18, 19, 26) fixed to the structure (A) of the vehicle in order to prevent an accidental disengagement of the gears; characterised in that said connecting rod is articulated at one end to the structure of the vehicle and at the other end to said joint (13) connecting said two transmission levers (11, 12), and in that a cam element (19) or a detent in the form of two recesses (26) is provided on said abutment means to cooperate with said resilient engagement means. A linkage according to Claim 1, wherein a push rod (22, 22a) is supported slidably by the connecting rod (16) and parallel thereto, said cam element (18, 19) has a profiled edge (19) parallel to the plane of articulation of the connecting rod (16), said edge (19) has a first portion (19a) whose average radial distance from the pivot axis (X-X) of the connecting rod (16) is greater than the average radial distance therefrom of two second portions (19b) of said edge (19) adjacent and connected to the first portion (19a), and a spring (24) is interposed between said push rod (22) and said connecting rod (21, 16) to urge the push rod (22, 22a) against said edge (19), whereby pivoting of said connecting rod (16) compresses said spring (24) when said push rod (22) slides from one of the two second portions (19b) of the edge (19) towards the first portion (19a). A linkage according to Claim 1, wherein a slider (28) is slidable supported by and substantially parallel to the pivot axis (X-X) of said connecting rod (16); said two recesses (26) are provided at equal radial distances from the pivot axis (X-X) of the connecting rod (16) and interconnected by inclined planes on a plate-like element (18) being said abutment means which is perpendicular to the pivot axis (X-X) of said connecting rod (16); and a spring (30) is interposed between said slider (28) and said connecting rod to urge the slider (28) towards said plate-like element (18), whereby pivoting of said connecting rod (16) due to the engagement of the gears causes the resilient snap-engagement of the slider (28) with one of said recesses (26). A linkage according to Claim 2, wherein said cam element is constituted by an elongate metal plate (18) substantially parallel to said connecting rod (16) and having a first end (18a) which is fixed to said support structure (17, A) in correspondence with the pivot axis (X-X) of said connecting rod (16) and a second convex end (18b) which is substantially V-shaped with a flattened vertex and defines said profiled edge (19). A linkage according to Claim 3, wherein said slider is constituted by a metal ball (28) slidable in a tubular seat (27) of the connecting rod (16), and wherein said recesses are defined by two holes (26) with axes (Z-Z) substantially parallel to the pivot axis (X-X) of said connecting rod (16).

Inventors: BRUNO MARCO, BRUNO, MARCO
Applicants: IVECO FIAT, IVECO FIAT S.P.A.
Application year: 1990
Main classification: F16H59
IPC codes: F16H61, F16H59