Gear shift mechanism for preventing unintentional gear disengagement in a vehicle gearbox

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a gear shift mechanism for a vehicle gearbox, comprising a gear lever, which is mounted for pivoting in a first plane between two end positions, and spring means, which in one lever position on one side of a predetermined neutral position between said end positions, loads the lever towards one end position, and on the other side of said neutral position loads the lever towards the other end position. The purpose is to decrease the risk of unintentional gear disengagement (gear jump out) .

PRIOR ART

In modern motor vehicles, especially trucks with a cab spring-mounted relative to the chassis and consequently also relative to the engine and the gearbox, problems arise at times with gear disengagement when driving on uneven surfaces and during rapid retardation, i.e. the gear shift lever moves unintentionally from the selected (engaged) gear position to the neutral position. This can be caused by mass forces in the shift mechanism or a large relative movement between the vehicle cab and the engine/gearbox. This causes the gear shift lever to be affected by disengaging forces from its sealing bellows fixed to the cab.

By providing the inner controls of the gearbox with blocking balls, unintentional gear disengagement can be counteracted to some extent, but this solution is in many cases insufficient since it provides too low blocking torque.

In a known shifting mechanism of the type descnjjeα. ay way of introduction, an outer blocking mechanism in the form of three tensile springs, so-called "kick-over springs", which spring-load a shift bar joined to the gear shift lever towards one of the other end positions on either side of the gear shift lever neutral position, is disclosed in figure 1 in EP1101051. This solution is space-consuming, firstly, due to the fact that it requires as many as three springs and, secondly, due to the fact that the springs must be relatively long, i.e. longer than the radius of the arc along which the shift bar moves when the shift lever is moved between its end positions in the longitudinal direction of the vehicle, since the torque lever and thus the blocking torque is directed proportionally to the difference between the length of the springs and the radius of movement. For these reasons, the moment arm will be in many cases too short to provide a torque sufficient to prevent unintentional gear disengagement.

In figure 2 to 4 in EP1101051 another known shifting mechanism of the type described by way of introduction is shown. Here a pivot element 22 is arranged around a shift lever 7. The pivot centre c of said pivot element is positioned, compared to a pivot centre a of said shift lever, in such a way so that springs 29 can be more loaded when the gear shift lever is in a neutral position compared to when the gear shift lever is in an engaged gear position. The configuration in figures 2 to 4 gives a compact fairly complicated solution.

DE10358510 discloses a gear change arrangement 1 for a gearbox of a vehicle, where a gear shift lever 2 cooperates with a sliding selector shaft 4 (arranged inside of a gearbox housing) and a compression spring

5, and where said gear shift lever 2 from a neutrax position can be positioned in engaged gear positions. The compression spring 6 is arranged between a pivot element 9 of the gear shift lever 2 and the gearbox lever 2. The compression spring shows a higher preload in a neutral position (Schn) compared to said engaged gear positions (Ese and Esz) . The design of the arrangement in DE10358510 makes it harder to increase the spring force when the gear shift lever is positioned in one of the engaged gear positions. An increased spring force, when in an engaged gear position, gives a better performance when considering counteracting unintentional gear disengagement. Another disadvantage is that the lever 2 transfers forces from the spring 5 to the sliding selector shaft 4, and as a consequence the design will probably have to be adapted by way of, for example special sealings and bearings for the gearbox.

Another disadvantage with all the above mentioned known art is that said arrangements are not so flexible, and thus, cannot in an easy way be adapted and installed in vehicles with different models of gearboxes .

The purpose of the present invention is to achieve a shifting mechanism of the type described by way of introduction, which has a compact design, decreased complexity and increased spring force when the gear shift lever is in engaged gear position, and at the same time easy to adapt to different gearbox models.

SUMMARY OF THE INVENTION

The device according to the invention is a gear shift mechanism for preventing unintentional gear disengagement in a vehicle gearbox, comprising a

gearbox lever, which is mounted for pivoting around a first pivot point in a first plane between two end positions, and spring means, which in one gearbox lever position on one side of a predetermined neutral position between said end positions, loads said gearbox lever towards one end position, and on the other side of said neutral position loads the gearbox lever towards the other end position. The invention is characterized in that a first end of a bar is rotatably fixed to the gearbox lever at a first distance from said first pivot point of the gearbox lever, and that a second end of said bar is rotatably fixed to a main lever at a second distance away from a main lever pivot point, and that a first end of said spring means is rotatably fixed to the main lever in a pivot point at a third distance away from said main lever pivot point and that a second end of said spring means is rotatably fixed to a second pivot point at a fixed position relative to said first pivot point and said main lever pivot point.

The device according to the invention shows several advantages compared to prior art. One advantage of the invention is that a transfer of forces to the gearbox lever from the spring means are minimized, and as a consequence there is no need to have special sealings and bearings for the different levers and shafts. Further, the design of the device according to the invention is fairly simple and compact, which gives space saving possibilities and increased cost effectivness . The device according to the invention also gives the possibility to easily adapt a gear jump out hindering device to different gearbox models, due to its simple design and possibility to arrange the

spring means and main lever parts external of the gearbox and at a distance away from the gearbox lever.

According to an embodiment of the device according to the invention when said gearbox lever is in the neutral position, the main lever pivot point, the first end and the second pivot point of said spring means are arranged in line with each other, with the main lever pivot point arranged between the first end and the second pivot point of said spring means. This gives zero torque acting on the main lever pivot point and/or the first pivot point of the gearbox lever when the gearbox lever is positioned in neutral, and consequently there will arise a torque with a certain quantity, which counteracts unintentional gear disengagement when the gearbox lever is positioned in one of said end positions of said gearbox lever.

According to another embodiment of the device according to the invention the spring means is a tension type spring. The spring means being of the tension type together with the design of the device according to the invention gives the possibility to increase the force from the spring means with marginal or no increase in space consumption.

According to another embodiment of the device according to the invention the length of said bar is adjustable. This gives the possibility to decrease the influence from variations in dimensions and tolerances of the parts involved, and thus it will be easier to adjust the position of the main lever relative to the gear lever. A further embodiment and another way to adjust said positions is via an extended hole on the main lever and/or the gear lever, so that positions of pivot

points of said first and second ends of saiα oar are movable relative each of the levers .

Further advantageous embodiments of the invention emerge from the dependent patent claims following patent claim 1.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be described in greater detail below with reference to accompanying drawing which, for the purpose of exemplification, shows a preferred embodiment of the invention and also the technical background.

Figure 1 shows diagrammatically one embodiment of a shifting device according to the invention when in an engaged gear position.

DETAILED DESCRIPTION OF THE INVENTION The invention will be described in more detail below with reference to an example shown in the accompanying drawing .

Figure 1 discloses a gear shift mechanism according to the invention for preventing unintentional gear disengagement in a vehicle gearbox, comprising a gearbox lever (7) , which is mounted for pivoting around a first pivot point 9 in a first plane and between two end positions. The end positions are preferably positions for an engaged gear condition of the gearbox. Said gearbox lever 7 can be non-rotationally joined to a gearbox shaft in said pivot point 9. The gearbox shaft, which is not disclosed, rotates together with the gearbox lever and the gearbox shaft can also be displaceable in an axial direction.

A first end 10 of a bar 4 is rotatably fixed to the gearbox lever 7 at a first distance from said first pivot point 9. A second end 11 of the same bar 4 is rotatably fixed to a main lever 1 at a second distance away from a main lever pivot point 3. The pivot point 3 can, for example, be pivoted with a bearing 2. A first end 12 of a spring means 5 is rotatably fixed to the main lever 1 in a pivot point 14 at a third distance away from said main lever pivot point 3. A second end 13 of said spring means 5 is rotatably fixed to a second pivot point 6 at a fixed position relative to said first pivot point 9 and said main lever pivot point 3.

When one gear is to be engaged the gearbox lever 7 is moved forward or backwards , thus changing the angular position of the main lever 1. With the angular displacement on _. one side of a predetermined neutral position between said end positions (gear engaged positions) a moment arm X is obtained, providing a torque M, which strives to keep the main lever 1 in an engaged gear position. The spring means 5 loads said gearbox lever 7 towards one of the end positions. Torque M is the result of spring means force Fm multiplied by the moment arm X. The torque M is transferred to the gearbox lever 7 via the bar 4 creating the force F2 that multiplied by moment arm Y provides a torque Mi _θV er at the gearbox lever 7 thereby striving to hold the gearbox lever 7 in the engaged gear position, and thus decreasing the risk of unintentional gear disengagement.

The device according to the invention was designed so that when the gearbox is in a neutral position there is

no force or torque acting on the gearbox lever 7. This neutral position configuration is obtained when aligning the tension spring 5 and the main lever 1, thus resulting in the moment arm X becoming zero . When the gearbox lever 7 is in the neutral position, the main lever pivot point 3, the first end 12 of said spring means 5 and the second pivot point 6 of said spring means 5 are arranged in line with each other, with the main lever pivot point 3 arranged between the first end 12 and the second pivot point 6 of said spring means 5. If the value of moment arm X is zero there is no torque M acting on the levers 1 and 7.

The device according to the invention is also designed to provide an increasing torque M or Mi _eV er during the movement towards gear engaged position of the gear shift lever . The whole torque M or Mieve _r is obtained when the levers are in the gear engaged position, so that, no comfort impairment is noticed. Thus, the spring means force Fm is lower when in engaged gear position compared to neutral position.

In one further preferred embodiment of the invention the bar 4 can be adjustable via for example a thread and nut design as disclosed in figure 1. The possibility to adjust the length of the bar 4 makes it easier to synchronize the positions of the gearbox lever 7 and the main lever 1, especially when it comes to find the right neutral position of the gearbox lever 7 and the main lever 1. Another possible embodiment of the invention regarding adjustment of the positions of the gear lever 7 and the main lever 1 relative each other is to have an extended hole on the main lever 1 and/or the gear lever 7. In this way the pivoting points of the bar ends 10 and/or 11 can be locked in

the right position in the extended hole/-s relative each of the levers. The locking can be done, for example, with a screw and nut design, where the screw is threaded through a hole of said first and second ends of the bar 4 and through said extended hole.

In one preferred embodiment of the invention the gearbox lever 7 is connected to a gear shift lever (not disclosed) , via at least a shift bar, in a third pivot point 15 positioned at a fourth distance from said first pivot point 9 of said gearbox lever 7.

In another embodiment of the invention the pivot points 10 and 15 can be one pivot point common for connecting both the shift bar and said bar 4. In a corresponding way said pivot points 14 and 11 can be common for connecting both the end 12 of the spring means 5 and said bar 4.

In another preferred embodiment of the invention the gearbox lever 7 can be prolonged in the upper end and used as a gear shift lever. Thus, the upper end of the gear shift lever is controlled by the driver of the vehicle for gear selection.

The invention should not be deemed to be limited to the embodiments described above, but rather a number of further variants and modifications are conceivable within the scope of the following patent claims .