EP1792108A1

EP1792108A1 - Damping mass for increased gear shifting comfort

Info

Publication number: EP1792108A1
Application number: EP05776364A
Authority: EP
Inventors: Stig-Erik Johannesson
Original assignee: Volvo Lastvagnar AB
Current assignee: Volvo Truck Corp
Priority date: 2004-09-07
Filing date: 2005-08-30
Publication date: 2007-06-06
Also published as: SE0402150D0; SE0402150L; WO2006041347A1; SE527630C2

Abstract

A damping mass (25) for increased gear shifting comfort, fixedly disposed on a control shaft (24) of a motor vehicle gearbox. The control shaft (24) is coupled to at least one gear shift fork disposed in the gearbox and to a gear shift lever for manual selection of a gear in the gearbox. In the damping mass (25) , a cavity (28) extends substantially along a predetermined radius at a distance from the geometrical center (29) of the control shaft. The cavity is filled with a fluid (30) with predetermined viscosity. A body (23) having a certain predetermined weight is designed to move preferably along said radius in the cavity (28) , with a view to maintaining good gear shifting comfort accompanied by a reduction in torque stress over the control shaft (24).

Description

14906WO, 07-09-2004, DS Damping mass for increased gear shifting comfort

TECHNICAL FIELD OF THE INVENTION The present invention relates to a device for increased gear shifting comfort in a manual gear shift in a gearbox, which device is disposed in a motor vehicle.

PRIOR ART In a motor vehicle with manually operated gearbox, the motions of the gear shift lever are transmitted via a rod or wire system to the control housing of the gearbox. The control housing is usually disposed on the top side of the gearbox. In the control housing there is disposed a control shaft, which is mounted such that it is rotatable and axially displaceable. The rod or wire system of the gear shift lever is usually coupled to one shaft end of the control shaft so as to convert the motions of the lever into rotary motions and into displacing motions of the control shaft in the axial direction thereof. The control shaft is then further coupled to gear shift forks inside the gearbox, which gear shift forks, in a known manner, displace coupling sleeves for the engagement and disengagement of different gears.

In order to provide a better gear shifting comfort, a damping mass is fixedly disposed on the control shaft of the gearbox. Figure 1 shows in diagrammatic representation a side view of a gearbox 5 according to the prior art, having a front part 7 coupled to a vehicle engine (not shown) , a rear part 6 coupled via a transmission (not shown) to the drive wheels (not shown) of the vehicle, a control housing 4 and a damping mass 1 fixedly disposed on a control shaft 2. The weight and radius of the damping mass 1 is tailored such that a predetermined moment of inertia is obtained for increased gear shifting comfort. When a gear is engaged, the control shaft 2 is rotated a bit clockwise or counterclockwise (depending on the selected gear) from a neutral position (see motion arrow 3 in figure 1) . The control shaft 2 can also be displaced a bit along its own geometrical axis (axial direction) and then rotated again for the selection of further gears . A gear shift lever with rod or wire system is not shown in figure 1. The gearbox 5 in figure 1 is in its neutral position and the damping mass 1 is then in its lowermost position. In this context, it may be mentioned that there are arrangements according to the prior art in which the neutral position of the damping mass is obtained by positioning the damping mass straight up in relation to the control shaft. The damping mass does not therefore hang downward from the control shaft. The invention according to the present application produces greatest benefits, however, where a damping mass is used which has its neutral position in a position hanging downward from the control shaft, as shown in figure 1.

Drawbacks with the prior art are that, when driving with an engaged gear, i.e. when the control shaft is rotated clockwise or counterclockwise a bit from its lowermost position, a torque is generated from the damping mass over the control shaft 2, which torque will rotate the control shaft back toward the neutral position and therefore disengage the gear. The lowermost position, in which the damping mass hangs straight down, is shown in figure 1. The torque increases instantaneously, moreover, when driving over bumps in the road or the like, and the torque also varies in dependence on the inclination of the gearbox, i.e. the inclination of the gearbox is dependent on the installation of the gearbox and/or the road gradient. When a gear is engaged, the control shaft is rotated until reaching a stop (not shown) built into the gearbox. The stop also stops the motion of the damping mass, which can produce large and sudden torques over the control shaft. When driving over bumps or the like, the control shaft experiences increased load, since the damping mass 1 is arranged with an overhang. The damping mass 1 can also cause it and the control shaft 2 to start vibrating, which risks fatiguing the control shaft. In the worst case, the various torques which are described above can lead to breakage of the control shaft.

Further examples of damping mass in a manually operated vehicle gearbox according to the prior art is shown, for example, by US 2003/0131679.

There is therefore a need for a damping mass which helps to maintain good gear shifting comfort, but in which the torques which are detrimental to the control shaft are reduced. This is the principal object of the invention which is described below.

SUMMARY OF THE INVENTION

The inventive solution of the problem with regard to the device according to the invention is described in patent claims 1 and 8. Patent claims 2 to 7 describe preferred embodiments and refinements of the device according to the invention.

The device according to the invention is a damping mass for increased gear shifting comfort, fixedly disposed on a control shaft of a motor vehicle gearbox. The control shaft is coupled to at least one gear shift fork disposed in the gearbox and to a gear shift lever for manual selection of a gear in the gearbox. The invention is characterized in that, in the damping mass, a cavity extends substantially along a predetermined radius at a distance from the geometrical center of the control shaft, and in that a body having a certain predetermined weight is designed to move relative to the damping mass, preferably along said radius in the cavity. The foremost advantage with the device according to the invention is that a short time after a gear has been engaged, i.e. after the control shaft and hence the damping mass has rotated a bit from its lowermost position, the body drops to its lowermost position in the cavity and thus reduces the torque over the control shaft from the damping mass. The torque, which tends to disengage the gear, can be almost totally eliminated.

According to an advantageous first embodiment of the device according to the invention, the cavity around the body is filled with a fluid having a predetermined viscosity. The advantage with this is that when a gear is engaged and the control shaft rotates as far as the stop, the motion of the damping mass is stopped, but since a part of the total weight of the damping mass is present in the body, the torque from the weight of the body in the upward direction is damped by the fluid. As a result of the invention, the large and sudden torque over the control shaft which is generated in connection with the engagement of a gear is therefore reduced.

According to a further advantageous embodiment of the device according to the invention, the cavity is configured as a closed, preferably cylindrical chamber, which chamber extends and is curved along said radius . The body, too, is preferably cylindrical, having the same curvature as the chamber, but with a substantially shorter extent along the radius than the chamber, so that space is obtained for the motion of the body. The body is arranged in the chamber with a predetermined clearance between the shell surface of the body and the walls of the chamber, so that the motion of the body relative to the motion of the damping mass along said radius can be predetermined. The speed of motion of the body relative to the damping mass depends primarily on the viscosity of the fluid, the clearance between the walls of the chamber and the shell surface of the body, as well as the weight of the body.

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

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in greater detail below with reference to the appended figures, which, for illustrative purposes, show further preferred embodiments of the invention and the prior art.

Figure 2 shows in diagrammatic representation a side view of the damping mass according to the invention when the gearbox is in its neutral position.

Figure 3 shows in diagrammatic representation a side view of the damping mass according to the invention when the gearbox is in a position in which a gear is engaged.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Figure 2 shows the damping mass 25 according to the invention when the gearbox (not shown) is in its neutral position, i.e. the damping mass 25 is in its lowermost position. The damping mass 25 is fixed on a control shaft 24, for example, as in the shown illustrative embodiment, by a part 20, formed as a hollow cylinder, which is fixedly disposed on the control shaft 24. The damping mass 25 and the control shaft 24 are rotatable 22 from the shown neutral position into gear positions, situated in the counterclockwise and/or clockwise direction, around the geometrical center 29 of the control shaft. The damping mass 25 extends in the radial direction out from the geometrical center 29 of the control shaft by virtue of the part 21, which connects the hollow cylinder 20 to a part 27 which forms walls and end faces 32 and 33 for a cavity 28 in which a body 23 is movably disposed. The parts 20, 21 and 27 are preferably cast in one piece in a relatively light (low density) material, for example aluminum. According to the shown embodiment, the cavity 28 has the form of a closed cylindrical chamber, which chamber 28 has an extent along a predetermined radius from the geometrical center 29 of the control shaft.

The body 23, too, is in the form of a cylinder, but which, according to the illustrated embodiment, has only around 2/3 of the extent along the predetermined radius which the chamber 28 has. The body 23 is preferably homogenous and made in a relatively heavy material (high density) , for example steel/cast iron. By virtue of the gravitational force and the configuration of the body 23 and of the chamber 28, the body 23 slides down into its lowermost position, as is shown by figure 2.

Provided in the chamber 28 and around the body 23 is a fluid 30, having a predetermined viscosity. The fluid 30 is preferably a liquid with low temperature sensitivity, for example a silicone oil.

The body 23 is disposed in the chamber 28 with a certain predetermined clearance 26, which, together with the viscosity of the fluid 30, substantially determines how easily and at what speed the body 23 can move along the predetermined radius and relative to the part 27.

Figure 3 shows the same embodiment according to the invention as in figure 2, but in a situation in which the gearbox (not shown) has a gear engaged, i.e. the damping mass 25 has in figure 3 rotated a bit counterclockwise 31 from its lowermost position (the neutral position) . Figure 3 shows what happens a short while after the gear position has been adopted. As shown in figure 3, the body 23 slides down into its lowermost position, which means that the torque over the control shaft 24, which tends to disengage the gear, is heavily reduced. The viscosity of the fluid 30 and the clearance 26 are tailored such that sufficient inertia for the ease at which the body 23 can move relative to the part 27 is obtained, in connection with the rotation of the damping mass 25 from the neutral position into a gear position (or vice versa) . According to the invention, the torque effect from the total weight of the damping mass 25, i.e. inclusive of the weight of the body 23 and of the fluid 30, can thereby be maintained at the point of gear shift, for good gear shifting comfort, whereas the torque effect from the body 23 is heavily reduced directly after the damping mass 25 has changed position (been rotated) and the body 23 has managed to slide down into its lowermost position according to figure 3.

In an alternative embodiment (not shown) , the end faces 32, 33 of the chamber 28 can be mutually connected by a duct with predetermined flow area, which flow area largely determines the motion and speed of the body 23 relative to the damping mass 25.

The device according to the invention is not limited to the abovementioned embodiments. Within the scope of the following patent claims, the chamber 28 and the body 23 can have a form other than cylindrical, for example spherical, of square cross section or of oval cross section. The body might also be imagined to consist of a plurality of bodies, for example two balls. Another possibility is that the chamber and the body do not need to be curved exactly along a certain radius, but that a certain deviation from the radius is possible. However, the invention works best if a certain radius is utilized for the curvature of the chamber and the body around the geometrical center of the control shaft. The fluid may also be constituted by a gas, for example air.

Claims

1. A damping mass (25) for increased gear shifting comfort, fixedly disposed on a control shaft (24) of a motor vehicle gearbox, the control shaft (24) being coupled to at least one gear shift fork disposed in the gearbox and to a gear shift lever for manual selection of a gear in the gearbox, characterized in that, in the damping mass (25), a cavity (28) extends substantially along a predetermined radius at a distance from the geometrical center (29) of the control shaft, and in that a body (23) having a certain predetermined weight is designed to move relative to the damping mass, preferably along said radius in the cavity (28) .

2. The damping mass as claimed in claim 1, characterized in that the cavity (28) around the body (23) is filled with a fluid (30) having a predetermined viscosity.

3. The damping mass as claimed in claim 1, characterized in that the cavity (28) is configured as a closed, cylindrical chamber, which chamber extends and is curved along said radius .

4. The damping mass as claimed in the preceding claim, characterized in that the body (23) is cylindrical, having the same curvature as the chamber (28) and a substantially shorter extent along the radius than the chamber.

5. The damping mass as claimed in claims 2 to 4, characterized in that the body (23) is arranged in the chamber (28) with a predetermined clearance (26) between the shell surface of the body and the walls of the chamber, with a view to predetermining the motion and speed of the body relative to the motion of the residual damping mass (20, 21, 27) along said radius.

6. The damping mass as claimed in any one of the preceding claims, characterized in that the body (23) has a predetermined weight with a view to predetermining the motion and speed of the body relative to the motion of the residual damping mass (20, 21, 27) along said radius.

7. The damping mass as claimed in any one of the preceding claims, characterized in that the body (23) is preferably homogenous and made in a material with preferably a higher weight than the weight of the residual damping mass (20, 21, 27) .

8. A gearbox for a motor vehicle, characterized by a damping mass (25) as claimed in claim 1.