LOW-VIBRATION GEARBOX

Description

[0001] In the automotive field, the invention falls within the domain of manual gearboxes with a control finger and gear shift fork.

[0002] In these gearboxes, vibrations occur, initiated by the engine and transmitted through the contact between the selector finger and the shift fork used to engage a gear. This results in undesirable movement of the gear selector knob.

[0003] To solve this problem, one can introduce play, or increase existing play, between the shift fork and the shift finger. However, the consequence of such a measure is an increase in the gear shift travel or an increase in the effort required to shift gears.

[0004] Document EP1205692 describes a control finger with an integrated spring system, but this involves a construction complexity that is not compatible with all gearboxes offered at controlled costs.

[0005] To solve this problem, a gear shift control system is proposed for a gearbox. This system includes a gear shift control shaft and a shift fork handle. The shaft includes a grid for rotational mounting relative to a gearbox housing with a stop. The shaft includes a finger arranged radially on the shaft to interact with the shift fork handle to couple the gearbox's power input and output shafts by one or the other of two pairs of gears, each corresponding to a gear ratio, or to decouple said shafts by releasing one of the gears from one of said shafts. The finger presses on the shift fork handle to perform couplings or decouplings, via two opposing convex cylindrical generatrices arranged in planar symmetry.

[0006] According to the invention, the convex generatrix surfaces of the finger have a distal section furthest from the control shaft and a proximal section near the control shaft, this distal section having a constant curvature to press on the fork handle during a rotation of the finger to engage one of the two ratios, and this proximal section having a flatter profile than that of the distal section to clear a space between the corresponding fork bearing surface and the finger after a rotation of the finger to engage the second of the two ratios.

[0007] These principles allow for a reduced shift throw, albeit with increased play in the gear ratio and power transmission. This reduces or eliminates gear knob vibrations caused by the movement of drivetrain components.

[0008] Depending on advantageous and optional features: The proximal section with a flatter profile is a flattening. Or the proximal section with a flatter profile is a section with a constant radius of curvature.

[0009] Also proposed is a gearbox for motor vehicles comprising a gear shift control system according to the principles stated above for gear shifting by a vehicle driver acting directly by hand on the shaft.

[0010] A method for adapting a gearbox to reduce vibrations is also proposed, the gearbox comprising a finger arranged radially on a gear-shifting control shaft, said shaft comprising a grid and being mounted for rotation with a stop relative to a gearbox housing, the gearbox further comprising a shift fork mounted for translation relative to said housing for coupling the gearbox's power input and output shafts by means of one or the other of two pairs of gears, each corresponding to a gear ratio, or for decoupling said shafts by releasing one of the gears from one of said shafts, the shift fork comprising, opposite in planar symmetry, two bearing surfaces on which the finger presses respectively to effect coupling or decoupling, by means of, respectively,of two cylindrical surfaces with convex generatrices opposite each other with the same planar symmetry.

[0011] According to the invention, the convex generatrix surfaces have a distal section of constant curvature to press on the corresponding bearing surface during a rotation of the finger to engage one of the two ratios and the adaptation method is such that material is removed to define a proximal section with a flatter profile than that of the distal section to create a space between the bearing surface of the corresponding fork and the finger after a rotation of the finger to engage a second of the two ratios.

[0012] The invention will be better understood, and other objects, features, details and advantages thereof will become more apparent from the following explanatory description made with reference to the accompanying drawings given solely by way of example illustrating one embodiment of the invention and in which: There figure 1 is a view of an existing system into which the invention is integrated; the figures 2A et 2B are detailed views of this system, in a first position; the figures 3A et 3B are detailed views of this system, in a second position; the figures 4A et 4B are detailed views of this system, in a third position; the figures 5A , 5B And 5C are detailed views of an embodiment, in positions corresponding to the first, second and third positions mentioned above.

[0013] In figure 1 , we have represented the elements, concerned by the invention, of a manual gearbox of a motor vehicle, comprising five forward speed ratios and one reverse speed ratio.

[0014] The system comprises a control shaft 100 operated by means of a shift ball 101 moved by the driver via a gearshift lever. The control shaft 100 is mounted for translation and rotation relative to a gearbox housing (not shown). The control shaft 100 carries a fixed shift finger 103 positioned radially with respect to the shaft. A shaft 200 is arranged perpendicular to the control shaft 100 and carries three shift forks 300, 302, and 303, which are mounted on it for translation.

[0015] Each of these shift forks is designed to select two gear ratios by engaging, as the fork moves in either direction along axis 200, one pair of gears from among two pairs of gears for the rotational coupling of the gearbox's input and output shafts. The selected and engaged pair of gears determines the gear ratio. The shift fork is also capable of disengaging the output shafts from each other by releasing one of the gears from one of the output shafts, thus returning the transmission to neutral.

[0016] Each shift fork has a shift fork arm that interacts with the shift finger 103. The interaction between the finger 103 and the shift fork arm causes the fork to move translationally along the shaft 200, engaging or disengaging a gear ratio. The shift fork to be used is selected by a translational movement of the control shaft 100, which brings the finger 103 to the position of the shift fork arm of the first fork, then the second, and finally the third, depending on the extent of the translation. When a shift fork is selected, the gear ratio of the two gear ratios that the fork controls is selected by the direction of rotation of the control shaft 100 relative to the housing.

[0017] The movement of the drive shaft is limited by an internal grid 102 which has raised patterns that interact with a stop mounted on the housing. The interaction of the grid pattern and the stop on the housing assists (guides) the driver in shifting gears.

[0018] In the figure, only the handle of fork 300, referenced as 301, is visible. It hides the handles of forks 302 and 303. Also in the figure, finger 103 is slightly set back from handle 301 and is aligned with one of the other two handles.

[0019] In figure 2A The system is represented according to the prior art at the neutral position. The figure is a cross-section perpendicular to the drive shaft 100, at the level of the finger 103. The drive shaft 100 is moved forward (or backward) in translation to interact with the fork arm 302. The drive shaft 100 is positioned at an angle, relative to the housing, which corresponds to the neutral position: neither of the two gear ratios controlled by this fork is engaged. The finger 103 and the fork arm 302 each have a cylindrical shape with the axis of the drive shaft 100 as their directrix and the shapes visible in the figure as their generatrix.

[0020] Finger 103 is positioned within the fork's handle 302, which is shaped like a small U (i.e., slightly flattened) surrounding finger 103. The handle 301 of the fork 300 is visible in the background, and the shaft 200 is also visible in cross-section. This overall figure shows that if the shaft 100 rotates in one direction, the fork 302 will slide in translation in a direction parallel to the shaft 200, thus engaging a gear ratio. If the shaft 100 rotates in the opposite direction, the fork 302 will slide in translation in the opposite direction, again parallel to the shaft 200, thus engaging another gear ratio. It is specified that the amplitude of the rotation of the control shaft 100 is determined by the interaction of a grid stop attached to the housing and the grid 102 carried by the control shaft 100.

[0021] In figure 2B Finger 103 was shown within the fork's handle 302, in a closer view, the view being a section along the same plane as the cross-sectional view of the figure 2a We observe that the handle defines a space shaped like the interior of a lowercase u, and that the finger comprises a proximal section (near the control shaft 100) referenced 103, which is thinner (essentially a concave rod widening as it moves away from the shaft 100) than an intermediate convex section 103b, itself wider than a distal section (the furthest from the control shaft 100), referenced 103c (this is a termination). The finger 103, in its neutral position, has the same planar symmetry as the interior space of the u in the handle of the fork 302. The section 103b has, on each of its faces derived from one another by this planar symmetry, a constant curvature with radius of curvature R.

[0022] The dimensions of the finger 103 and those of the fork 302 are such that a set of values ​​a is present in the direction of translation of the fork 302, that is to say parallel to the axis 200. Whatever the vibrations of the system, when the surface of the finger 102 comes into contact with the surface of the fork 302, it is on one of the surfaces of the convex section 103b of constant curvature, to the left, or to the right of the finger 103.

[0023] In figure 3A The preceding elements are shown, according to the prior art, after rotation of the drive shaft 100 to engage a gear ratio, with movement of the shift fork 302 to the right of the figure. The stop fixed to the housing, via the grid 102, prevents further rotation of the drive shaft 100.

[0024] We see in figure 3B that the constant curvature surface of section 103b pressed against the fork 302 in the right-hand direction. The constant curvature surface is in contact with the fork surface on the right, on the side in which the fork was pushed, and rather on the distal side of the finger (away from the control shaft 100). The clearance remains at value a, despite the rotation of the finger, due to the constant curvature of the surfaces of the convex section 103b.

[0025] In figures 4A et 4B The preceding elements were represented, according to the prior art, after the arrival of the fork 302 on the pinion stop, by the action of the so-called "anti-release" retention systems. Thus, the fork continued slightly the translation it had followed between the figures 2A et 2B on the one hand, and 3A and 3B on the other. The constant curvature surface is in contact with the fork surface on the left, on the side opposite to the direction in which the fork was pushed, and rather on the proximal side of the finger (near the control shaft 100). The clearance remains at value a, despite the change of side, due to the constant curvature of the surfaces of the convex section 103b.

[0026] Due to vibrations, the system can move between the extreme positions of the figure 2B and the extreme position of the figure 3B The play, always measured along the direction parallel to the axis 200, is always of the value a.

[0027] In figures 5A à 5C The invention was presented. figure 5A corresponds to the position of the control shaft 100 represented in figure 2A et 2B , there figure 5B corresponds to the position of the control shaft 100 represented in figure 3A et 3B , and the figure 5C corresponds to the position of the control shaft 100 represented in figure 4A et 4B .

[0028] There figure 5A This represents the elements of the invention, which are similar to the previous ones (the reference numerals for the finger are incremented by 1000), except that the convex section 103b of surfaces with a constant radius of curvature has been modified and replaced by a proximal convex portion 1103e and a distal convex portion 1103d (always defined with respect to the drive shaft). The finger 1103 has a cylindrical shape with its direction along the axis of the drive shaft 100 and its generatrix being the shapes visible in the figure.

[0029] The distal convex part 1103d has surfaces that are identical to the distal part of the convex part 103b of the prior art, i.e. having a constant radius of curvature.

[0030] The proximal convex portion 1103e has a radius of curvature greater than that of the distal intermediate portion 1103d, even infinite. In the embodiment presented, it is infinite, meaning that the proximal convex portion 1103e has a flat surface, obtained by removing material compared to the previous geometry of the prior art. This is therefore an adaptation of the gearbox to reduce vibrations.

[0031] It follows from this feature of the invention that when the finger is in the neutral position as in figure 5A , the game is of the value a. This comes from the fact that the limit between the proximal and distal convex parts 1103e and 1103d is such that in this position of the finger, the maximum width of the latter, measured parallel to the axis 200, is unchanged, despite the modification compared to the anterior art.

[0032] In figure 5B The system according to the invention was represented in the same situation as that of the prior art in figures 3B Thus, after rotation of the drive shaft 100 to engage a gear, the shift fork 302 moves to the right of the figure. The stop fixed to the housing, via the grid 102, prevents further rotation of the drive shaft 100. It can be seen that the constant curvature surface of the distal convex section 1103d has pressed against the shift fork 302 in the right-hand direction. The constant curvature surface (distal section 1103d) is in contact with the surface of the shift fork 302 on the right, the side in which the fork was pushed. The clearance is a + x, due to the rotation of the finger, caused by the flat surface of the proximal convex section 1103e on the left side.

[0033] In figures 5C The system according to the invention was represented in the same situation as that of the prior art in figures 4B , after the fork 302 reached the pinion stop, due to the action of the so-called "anti-release" retention systems. Thus, the fork 302 continued slightly the translation it had followed between the figures 5A And 5B The flat surface (proximal section 1103e) is in contact with the fork surface on the left, on the side opposite to the direction in which the fork was pushed. The clearance is always of the value a + x.

[0034] Due to vibrations, the system can move between the extreme positions of the figure 5B and the extreme position of the figure 5C The play, always measured along the direction parallel to the 200 axis, is always of the value a + x.

[0035] Instead of a flat surface, the proximal convex part 1103e may have a variable curvature from one end to the other, in any case greater than that of the distal convex part 1103d, or fixed, again with a value greater than that of the distal convex part 1103d.

Claims

1. A gear shift control system, for a gearbox, said system comprising a gear shift control shaft (100) and a fork bracket (302), said shaft (100) comprising a grid to be mounted for rotation with respect to a gearbox housing with stopper, the shaft comprising a finger (1103) disposed radially on the shaft (100) for interacting with the fork bracket (302) for coupling shafts of power input and output of the box by one or the other of two pairs of pinions each corresponding to a gear ratio, or decouple said shafts by releasing one of the pinions vis-à-vis one of said shafts , the finger (1103) pressing on the fork holder to perform couplings or decouplings, characterized in that the finger presses on the fork grip via two cylindrical surfaces of convex generatrix (1103d, 1103e) opposite in planar symmetry, the convex generatrix surfaces (1103d, 1103e) of the finger (1103) having a distal section (1103d) furthest from the drive shaft (100) and a proximal section (1103e) near the drive shaft (100), said distal section (1103d) having a constant curvature to press the fork grip upon rotation of the finger (1103) to engage a first of the two gears, and said proximal section (1103e) having a profile flatter than that of the distal section to provide a space between the bearing surface of the corresponding fork (302) and the finger (1103) after a rotation of the finger (1103) to engage the second of the two reports.

2. System according to claim 1, characterized in that the proximal section (1103e) of flatter profile is a flat.

3. System according to claim 1, characterized in that the proximal section (1103e) of flatter profile is a section of constant radius of curvature.

4. Gearbox for a motor vehicle comprising a gear shift control system according to one of claims 1 to 3 for the gear changing by a driver of the vehicle.

5. A method of adapting a gearbox to reduce vibrations, the gearbox comprising a finger (1103) disposed radially on a shaft (100) for controlling the shifting of gear ratios, said shaft (100) comprising a grid and being mounted in rotation with a stop relative to a gearbox housing, the box also comprising a fork bracket (302) mounted in translation with respect to said housing to couple input and output power shafts of the box by one or the other of the two pairs of pinions each corresponding to a gear ratio, or decouple said shafts by releasing one of the pinions vis-à-vis one of said shafts, the fork bracket (302) comprising, opposite in planar symmetry, two bearing surfaces on which the finger presses respectively to proceed with the coupling or the uncoupling, characterized in that the finger presses on the two bearing surfaces of the fork holder through the intermediary area, respectively, of two convex generatrix cylindrical surfaces (1103d, 1103e) opposite in the same planar symmetry, the convex generatrix surfaces (1103d, 1103e) having a distal section of constant curvature (1103d) to press on the surface of corresponding support during a rotation of the finger (1103) to engage a first of the two reports and the method is such that material is removed to define a proximal section (1103e) of profile flatter than that of the distal section of constant curvature (1103d) to release a space between the bearing surface of the corresponding fork (302) and the finger (1103) after a rotation of the finger (1103) to engage a second of the two reports.