Shifting device and method for moving shift forks on a shift rod

Abstract

Shifting device consisting of a shift rod (1) on which a plurality of shift forks (2) are arranged, wherein the shift forks (2) each have an opening (3a) in a shift fork carrier (3) of the shift fork (2), in which opening the shift rod (1) is guided, and wherein the shift forks (2) have a shift fork length (L), wherein the shift rod (1) is enclosed by a sleeve (5) which is mounted on the shift rod (1) so as to be movable in the axial direction along the shift rod (1), wherein the openings (3a) of the shift fork carriers (3) are guided axially displaceably on the sleeve (5), which is arranged on the shift rod (1) so as to be freely movable axially and within an opening (3a) of the shift fork carrier (3), characterized in that the sleeve (5) has a Teflon coating on the inside at its end, which serves as a bearing point (5a) for the sleeve (1) on the shift rod (1).

Description

[0001] The invention relates to a shifting device with shift forks and shift rod for a gearshift of a vehicle and a method for moving shift forks on a shift rod. State of the art

[0002] In vehicles, both manual and automated transmissions, shifting devices are widely used. These devices connect the drivetrain components associated with the desired gear by sliding a shift sleeve, transmitting force or torque. A shift fork engages an outer circumferential groove of the axially movable shift sleeve, and a toothing on the inner circumference of the shift sleeve establishes a positive connection between the corresponding idler gear and a transmission shaft when a gear is engaged.

[0003] The entire shifting process typically involves two movements: a selection movement and a shifting movement. The selection movement selects a specific shift fork, which is to be moved to engage the new gear. This process is also known as gate selection. The shifting movement then moves the selected shift fork and, with it, the corresponding shift sleeve. This establishes the power flow with the desired ratio in the drivetrain, and the new gear is engaged.

[0004] There are shifting devices each with a shift rod for each shift fork. In these shifting devices, the shift fork is rigidly connected to the respective shift rod. The selection movement selects a carrier element, which in turn is rigidly connected to the associated shift rod, by moving a shift finger into the carrier position of the desired carrier element. During the subsequent shifting movement, the rigid unit consisting of carrier element, shift rod, shift fork, and shift sleeve is displaced axially. Embodiments of this type of shifting device are known, for example, from DE 10 2005 000 886 A1. These designs require a relatively large installation space and many components because each shift sleeve and shift fork is assigned a separate shift rod, with each shift rod requiring axial movement space.

[0005] Other shifting devices are therefore designed in such a way that all the shift forks of the transmission are arranged so that they can be moved axially on a single shift rod. This results in less installation space and component requirements, and the mass of the entire transmission is reduced. One such solution is known from DE 11 2005 001 381 T5. In this case, the shift fork required for the desired gear is positively connected to the shift rod by a selection movement, while the shaft forks not selected remain axially movable on the shift rod. The subsequent shifting movement is carried out by the axial displacement of one shift rod, whereby the selected shift fork is also moved via the positive connection, while the non-selected shift forks remain in their position. The moved shift fork establishes the torque-transmitting connection in the corresponding ratio via its assigned shift sleeve, i.e.the desired gear is engaged.

[0006] However, in the design according to DE 11 2005 001 381 T5, a large installation space is required for selection and guide elements.

[0007] Shift forks are designed according to the shift force required to move the shift sleeves. The axial extension of the shift fork carrier, which encompasses the shift rod, is large to accommodate greater force and compensate for the reactive torque during shifting. In passenger cars, the shift fork carriers are axially thick because high shift forces are required for the gear synchronization system.

[0008] DE 14 55 674 A1 discloses a shifting device comprising two shift forks. One of the shift forks is mounted on a sleeve that is guided longitudinally along the shift rod. The sleeve is also actuated by a shift finger. The sleeve is thus always moved parallel and does not tilt.

[0009] DE 100 08 872 A1 shows a special rolling bearing that surrounds the shift rod. The bearing is designed so that tilting can never occur. It also does not have a special coating.

[0010] The object of the invention is to create a compact shifting system for multi-stage transmissions with a smaller number of shift rods. Description of the invention

[0011] The object is achieved with a shifting device comprising a shift rod on which a plurality of shift forks are arranged, wherein the shift forks each have an opening in a shift fork carrier in which the shift rod is guided, and wherein the shift forks have a shift fork length, wherein the shift rod is encompassed by a sleeve which is mounted on the shift rod so as to be movable in the axial direction along the shift rod.

[0012] The addition of a sleeve results in an improvement over the current system and saves enormous space.

[0013] The sleeve has a coating on the inside, e.g. Teflon, which serves as a bearing for the sleeve on the shift rod.

[0014] The advantage is that the shift fork carriers have an axial width, whereby the total width of all shift fork carriers is less than half the length of the sleeve.

[0015] The problem is also solved by a method for moving shift forks on a shift rod, wherein the bearing forces between the shift fork carrier and the sleeve and bearing forces between the sleeve and the shift rod determine the reduction of the actuating force of the shift fork. Description of the characters Fig. 1 shows a section through a shift rod with shift forks in the prior art, Fig.2 shows a device according to the invention with shift rod and shift forks, Fig. 3 shows the solution according to the invention, Fig. 4 shows a section with force distribution, Fig. 5 shows a force curve.

[0016] Fig.1 shows a shift rod 1 positioned in front of a transmission with gears 4. The shift rod 1 carries, for example, three shift forks 2, which are movably connected to the shift rod 1. The shift forks 2 have shift fork supports 3, which are thickened portions for dissipating forces from the shift fork to the shift rod. The shift fork supports 3 thus extend axially along the shift rod 1 to a length that far exceeds the thickness d of the actual shift fork 2. The middle shift fork 2 has a shift fork support 3', which encompasses the shift fork support 3 of the left shift fork 2 and is axially supported on the shift rod 1 over a very wide area.

[0017] A shift drum with grooves, which is not shown in this figure, as well as cams on the shift fork carrier, which engage the grooves of the shift drum, lead to an axial movement of the shift forks 2.

[0018] Fig. 2 and Fig.3 show the solution according to the invention with a sleeve 5, which extends along the longitudinal axis of the shift rod 1 as an additional displaceably mounted component. In the top illustration of the Fig. 2 contains the shift rod with the sleeve 5 and the shift forks 2, all of which are in a non-activated state. The sleeve 5 is arranged centrally on the shift rod 1. In this unloaded state, the sleeve 5 moves freely axially on the shift rod 1 and within an opening 3a of the shift fork carrier 3.

[0019] The sleeve 5 has a Teflon coating at both ends in the area of ​​bearing points 5a, so that the sleeve 5 can move over the shift rod 1 with minimal friction and is only supported at the ends. The Teflon coating is applied in a ring shape to the inner wall of the sleeve.

[0020] In the middle drawing of the Fig.2 shows how the middle shift fork 2 is moved axially to the right over a displacement path 8 by actuation via the shift drum.

[0021] This sleeve 5 is manufactured in such a way that it can slide freely in all shift forks 2 in the unloaded state, but when a shift fork 2 is axially displaced due to the profile in the shift drum, the shift fork 2 clamps the sleeve 5 due to the balance of force and reaction.

[0022] Due to this clamping effect, the shift fork 2 and the sleeve 5 move together in the axial direction, in the example to the right.

[0023] The non-actuated shift forks are not carried by the sleeve and remain stationary in their initial position. This eliminates the need to move these masses.

[0024] In Fig.4 shows the forces that occur and are used to calculate the forces on the shift fork 2 and on the sleeve 5.

[0025] The following equations show the relationships between the forces: Forces on the shift fork Forces on the sleeve ΣF x = 0 = -F + Fa - (µ * Ag) - (µ * Bg) ΣF x = 0 = -(µ * Ah) - (µ * Bh) + Fa - F ΣF y = 0 = Ag - Bg ΣF y = 0 = Ah - Bh ΣM z = 0 = -(Bg * 2 * L1) + (F * L) ΣM z = 0 = (F * L) - (Bh * L0) Operating force on the shift fork Actuating force on the sleeve Fa = F + (µ * F * L) / (L1) Fa = F * (1 + 2µ * L / L0)

[0026] If we first consider the situation in the section shown on the shift fork in the coordinate system X' and Y': The actuating force F a the shift drum rests on the shift fork carrier 3. The actuating force F a The displacement force F on the fork is directed in the opposite direction and also causes a moment over the length L of the shift fork 2.

[0027] The bearing forces A g and B g at the respective ends of the shift fork carrier 3 act as forces against the actuating force F a .

[0028] The bearing forces A g and B gThey cancel each other out in the Y direction. Their frictional force acts only in the X direction.

[0029] The moment on the shift fork carrier 3 is twice the length L1, i.e. the total extension of the shift fork carrier 3 multiplied by the bearing force B g . The actuating force F a is therefore composed of the displacement force F on the shift fork 2 and a factor of displacement force F, friction coefficient µ, length of the shift fork L divided by half the width L1 of the shift fork carrier 3.

[0030] For the forces on the sleeve 5, the bearing forces B h and A h on the sleeve 5, more precisely acting on the bearing points 5a of the ends of the sleeve 5.

[0031] The forces in the X-direction of the sleeve's coordinate system consist of the actuating force F a and the displacement force F, where factors of the bearing forces A h and B hinteract with the friction coefficient µ.

[0032] The resulting actuating force on the sleeve relativizes the displacement force F with a factor that includes the length L of the shift fork and the length of the sleeve L0 between the bearing points 5a.

[0033] Therefore, the width of the shift fork support 3 can be reduced. This additional sleeve helps reduce the thickness of the shift fork while maintaining the clamping required for shifting.

[0034] In Fig. 5 are a diagram showing force on the shift fork, plotted against the width of the shift fork carrier 3, and force on the sleeve 5 plotted against the length of the sleeve 5.

[0035] It can be seen that the width of the shift fork carrier 3 determines the actuating force F a reduced. Regardless of this, it can be seen that the moderate length L0 of the sleeve 5 already reduces the actuating force F a significantly reduced.

[0036] The arrow indicates a possible length of sleeve 5, which is 150 mm. The actuating force F a For a single solution with only the shift fork carrier 3, this corresponds to a width of 60 mm. Using three shift forks 2 would require a shift rod 1 length of approximately 200 mm.

[0037] The movement of an actuated shift rod begins with a very brief sliding of the shift fork carrier 3 until the friction of the opening 3a causes the shift fork carrier to tilt relative to the sleeve. This causes the sleeve 5 to be driven along in the movement. Reference symbol: 1 shift rod 2 shift forks 3, 3' shift fork carrier 3a Opening 4 gears 5 sleeve 5a Storage locations 8 Displacement path X and Y global coordinate system for the sleeve X' and Y' Local coordinate system for the fork L0 Length of the sleeve from end to end 2*L1 Width of the shift fork carrier F Displacement force on the fork L Distance of the displacement force from the center of the sleeve B h & A h Bearing forces on the sleeve A g & B g Bearing forces on the fork F a Operating force of the shift fork R Radial distance, point of action F a α Angle of the point of action µ friction coefficient

Claims

[1] Shifting device consisting of a shift rod (1) on which a plurality of shift forks (2) are arranged, wherein the shift forks (2) each have an opening (3a) in a shift fork carrier (3) of the shift fork (2), in which opening the shift rod (1) is guided, and wherein the shift forks (2) have a shift fork length (L), wherein the shift rod (1) is enclosed by a sleeve (5) which is mounted on the shift rod (1) so as to be movable in the axial direction along the shift rod (1), wherein the openings (3a) of the shift fork carriers (3) are guided axially displaceably on the sleeve (5), which is arranged so as to be freely movable axially on the shift rod (1) and within an opening (3a) of the shift fork carrier (3), characterized by that the sleeve (5) has a Teflon coating on the inside at its end, which serves as a bearing point (5a) of the sleeve (1) on the shift rod (1). [2] Switching device according to claim 1, characterized bythat the coating is applied in a ring shape on the inside of the sleeve. [3] Switching device according to one of the preceding claims, characterized by that the shift fork carriers (3) have an axial width (2*L1), wherein the total widths (2*L1) of all shift fork carriers (3) are less than half the length (L0) of the sleeve (5). [4] Method for displacing shift forks on a shift rod (1) of a shifting device according to claim 1, wherein the bearing forces (B g , A g ) between the shift fork carrier (3) and the sleeve and bearing forces (B h , A h ) between the sleeve and the shift rod (1) the reduction of the actuating force (F a) of the shift fork (1), wherein the sequence of a movement of the shift rod (1) with a sliding of the shift fork carrier (3) until the friction of an opening (3a) leads to a tilting of the shift fork carrier (3) relative to the sleeve in order to take the sleeve (5) along in the movement.

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