Patent Description:
In vehicles, in particular in commercial vehicles, there are multiple ways of implementing an automatic transmission. Besides automated gearboxes, automated manual transmission (AMT) systems are often used. AMT systems comprise a traditional manual transmission gearbox that is automatically actuated by one or more pneumatic actuators. The pneumatic actuators are connected to functional elements, for example to shifting forks. Upon actuation of the pneumatic actuator, a gear is shifted without a manual actuation of a gearshift lever by a vehicle driver.

<CIT> relates to a pressure medium actuator, the working piston of which is designed as a double-acting piston and can be adjusted to the central position without the use of springs by force-fitting contact with the stop of a parallel auxiliary piston with a different piston surface, whereby the auxiliary piston is designed as a drag piston so that when acted upon by a pressure medium. Generally, pneumatic actuators comprise a pneumatic cylinder and a pneumatic piston. The pneumatic piston is movable relative to the pneumatic cylinder. Up-on movement, the piston actuates the functional element connected to the piston. For initiating such a movement of the piston, a piston head is received in a pneumatic chamber defined by a cylinder body of the pneumatic cylinder. The pneumatic piston is slidably arranged in the pneumatic chamber and movable back and forth along a main axis of the pneumatic chamber. Thereby, the piston is movable between a coupling position, wherein the functional element is engaging with a counter element, and a neutral position, wherein the functional element is not engaging with the counter element. When a pressure p2 in the second chamber is increased, the pneumatic piston is pushed in a positive stroke direction and a volume enclosed by the piston head and the pneumatic chamber is increased. A piston rod connected to the piston head protrudes out of the pneumatic chamber and actuates the functional element. As soon as the piston head approaches the neutral position, it must be decelerated to prevent a hard stop against the pneumatic cylinder. It is known to decelerate the piston head by pressuring the first pressure chamber with a delay to the second pressure chamber. For this purpose, a first pressure valve is used to decelerate the pneumatic piston and a second pressure valve is used to accelerate the pneumatic piston. This causes a high number of switching cycles for the pressure valves. Further, the deceleration results in high deceleration forces acting on the pneumatic cylinder and the pneumatic piston.

Therefore, it is an object of the invention to provide a cost efficient, durable, and reliable pneumatic actuator.

To solve this object, the present invention provides a pneumatic actuator according to independent claim <NUM>.

The bypass allows the pressuring of the first pressure chamber by the second pressure chamber. The outflowing fluid creates a decelerating fluid mass in form of an airbag in front of the piston head next to the bypass. Consequently, a switching cycle of a pressure valve to decelerate the pneumatic piston can be saved.

Preferably, the pneumatic cylinder further comprises a first pressure valve for pressurizing and venting the first pressure chamber and/or a second pressure valve for pressuring and venting the second pressure chamber. In this case, the first pressure valve has a first cross sectional area perpendicular to the main axis and the second pressure valve has a second cross sectional area perpendicular to the main axis. The first cross sectional area and the second cross sectional area may be equal. Further, the bypass may have a third cross sectional area perpendicular to the main axis. The quotient of the first cross sectional area and the third cross sectional area may be less than <NUM>:<NUM> and/or more than <NUM>:<NUM>, in particular less than <NUM>:<NUM> and/or more than <NUM>:<NUM>, preferably less than <NUM>:<NUM> and/or more than <NUM>:<NUM>, and further preferably about <NUM>:<NUM>. The quotient of the second cross sectional area and the third cross sectional area may be less than <NUM>:<NUM> and/or more than <NUM>:<NUM>, in particular less than <NUM>:<NUM> and/or more than <NUM>:<NUM>, preferably less than <NUM>:<NUM> and/or more than <NUM>:<NUM>, and further preferably about <NUM>:<NUM>. An above mentioned quotient facilitates an optimal delay between the pressuring of the pressure chamber facing the active pressure valve and the pressure chamber facing away from the pressure valve. The first pressure valve and/or the second pressure valve may be formed as <NUM>-<NUM> directional control valves, wherein in a first position the pressure chamber is pressured and in a second position the pressure chamber is vented. Hence, the second pressure chamber can be pressurized by the second pressure valve to accelerate the pneumatic piston in positive stroke direction into the neutral position, wherein the first pressure chamber is pressurized by the second pressure valve through the bypass to decelerate the movement of the pneumatic piston in the neutral position with delay. A switching cycle of the first pressure valve is not necessary to decelerate the pneumatic piston in contrast to the state of the art. Further, the constant fluid flow from the second pressure chamber to the first pressure chamber results in a gentle deceleration of the pneumatic piston, which is associated with low deceleration forces acting on the pneumatic cylinder and the pneumatic piston.

Preferably, the bypass is formed by at least a trough hole extending parallel or oblique to the main axis. Through holes are easily manufactured and allow a specific flow of fluid. The at least one through hole may be arranged at a circular ring that is concentrical to the main axis. Such allocation of the at least one trough hole allows a homogenous fluid flow and a homogenous pressure balancing. The bypass may be made of two, three, four, five, six or more through holes, wherein the through holes having an angular distance to each other of <NUM>° divided by the amount of used through holes.

According to the present invention, the pneumatic piston further comprises a piston collar, wherein the piston collar is preferably arranged concentrical to the main axis and partially encircles the piston rod. A first seal, in particular a first ring seal, is provided in the cylindrical body, wherein the piston rod extends through the first seal. In the neutral position the piston collar engages with the first seal and fluidically separates the first pressure chamber into a third pressure chamber and a fourth pressure chamber. Thereby, the piston collar is inserted in the inner diameter of the first seal. The volume of the third pressure chamber is significantly lower than the volume of the first pressure chamber, so after the separation the pressure in the third pressure chamber will increase more strongly than the pressure of the first pressure chamber due to the lower functional volume. This will reliably decelerate and at the end stop the pneumatic piston.

Preferably, the bypass is provided at or in the piston collar. The first pressure valve and/or the second pressure valve may be provided at the outer diameter of the cylindrical body, wherein the piston collar is arranged at the inner diameter. Therefore, the fluid inserted by one pressure valve has a large distance to flow to reach the other pressure valve. This facilitates a delay between the pressure increase in the pressure chamber facing the active pressure valve and the pressure increase in the pressure chamber facing away the active pressure valve.

In a second preferred embodiment, in the coupling position the bypass fluidically connects the first pressure chamber and the second pressure chamber. In the neutral position the bypass fluidically connects the second pressure chamber and the third pressure chamber. In the neutral position, the bypass does not fluidically connect the second pressure chamber and the fourth pressure chamber. The effect of the fluid flowing from the second pressure chamber into the third pressure chamber is much stronger in contrast to the first pressure chamber due to the lower functional volume. The lower functional volume in the third pressure chamber allows a faster pressure balancing between the second pressure chamber and the third pressure chamber due to the bypass. As soon as the piston collar and the first seal engage, thus reducing the functional volume, the pressure in the third pressure chamber increases so rapidly that the deceleration effect increases rapidly as well.

Preferably, the cylinder body comprises a first receiving portion to receive the first seal. The first receiving portion may be formed as a first recess with a first portion diameter, wherein the first seal is arranged inside the first recess. Preferably, the cylinder body comprises a second receiving portion to receive the deformed first seal. As soon as the piston collar and the first seal engage, the first seal will be deformed, in particular a first sealing lip of the first seal is urged in the positive stroke direction. The second receiving portion allows the urging of the first seal by the piston collar with reduced friction and thus provides a durable sealing of the piston collar in the neutral position. The second receiving portion may be formed as a second recess with a second portion diameter, wherein the second portion diameter is lower than the first portion diameter. This leads to an exact radial and axial positioning of the first seal. The cylinder body further comprises a third receiving portion to receive a second seal with a second seal lip. The third receiving portion may be formed as a third recess with a third portion diameter, wherein the third portion diameter is lower than the second portion diameter. The cylinder body may further comprise a fourth receiving portion to receive a third seal lip of the second seal. The fourth receiving portion may be formed as a fourth recess with a fourth portion diameter, wherein the fourth portion diameter is lower than the third portion diameter. The third receiving portion and the fourth receiving portion leads to an exact radial and axial positioning of the second seal. Further, the cylindric body may provide a functional portion that is arranged between the second receiving portion and the third receiving portion. The functional portion may be formed as a functional recess with functional diameter, wherein the functional diameter is lower than the second receiving portion and higher than the third receiving portion. In the neutral position, the third pressure chamber is mainly formed by the functional portion enclosed by the cylindric body, the first seal, the second seal and the piston collar.

According to the present invention, the above stated object is solved by a method according to independent claim <NUM>.

The method is defined by the following steps:.

Preferred embodiments of the present invention are laid down in the dependent claims.

Preferably, the pneumatic piston comprises a bypass, wherein in the second phase the third pressure chamber is pressurized trough the bypass by the second pressure chamber to decelerate the movement of the piston head. This ensures a rapid deceleration as soon as the second phase begins.

In further preferred embodiment, a second pressure valve is arranged at the second pressure chamber to pressurize the second pressure chamber and to move the piston head in the positive stroke direction from the coupling position into the neutral position. Thereby, the first pressure chamber is pressurized simultaneously by the second pressure valve through the bypass, wherein the bypass causes a delay between the pressuring of the second pressure chamber and the first pressure chamber. Therefore, one pressure valve can be used to, first, accelerate the piston head and then, decelerate the piston head in the desired position.

Preferably, the second pressure chamber is pressurized to a pressure p2 to accelerate the piston head in the positive stroke direction from the coupling position into the neutral position. The third pressure chamber is pressurized to a pressure p3 to decelerate the movement of the piston head in the second phase and stop the movement of the piston in the neutral position. Preferably, the second pressure p2 is lower than the third pressure p3.

Preferably, in the second phase a pressure balancing between the second pressure chamber and the third pressure chamber is provided through the bypass.

According to the present invention, the above stated object is solved by a gearbox, in particular a gearbox for a commercial vehicle, according to claim <NUM>.

According to the present invention, the above stated object is solved by a commercial vehicle according to claim <NUM>.

For a more complete understanding of the invention, the invention will now be described in detail with reference to the accompanying drawings. The detailed description will illustrate and describe what is considered as preferred embodiments of the invention, which is defined by the appended claims.

In particular, any reference signs in the claims shall not be construed as limiting the scope of the invention. The wording "comprising" or "including" does not exclude other elements or steps. The word "a" or "an" does not exclude the plurality. The wording "at least a" items comprising also the number <NUM>, i.e. a single item, and further numbers like <NUM>, <NUM>, <NUM> and so forth. The word "about" includes a deviation of ± <NUM>% of the total.

<FIG> shows a commercial vehicle <NUM> having a motor <NUM>, a gearbox <NUM>, a clutch <NUM> and a drive shaft <NUM> connecting the motor <NUM> to the clutch <NUM> and the gearbox <NUM>. The gearbox <NUM> comprises a shifting fork <NUM>. Using the shifting fork <NUM>, first gear wheels <NUM> of the gearbox <NUM> can be actuated and moved in a positive stroke direction R1 or in a negative stroke direction R2. In <FIG>, a larger first gear wheel <NUM> engages a smaller second gear wheel <NUM> of a driven shaft <NUM>. Shifting fork <NUM> can be moved in negative stroke direction R2. Shifting fork <NUM> slides first gear wheels <NUM> along shaft <NUM> and thereby the larger first gear wheel <NUM> is disengaged from smaller second gear wheel <NUM> and a smaller first gear wheel <NUM> is brought into contact with a larger second gear wheel <NUM>. Thereby a gear of the gearbox <NUM> is changed.

The gear of gearbox <NUM> may be changed of a known pneumatic actuator <NUM> shown in <FIG> or a pneumatic actuator <NUM> shown in <FIG>. Pneumatic actuator <NUM>, <NUM> may actuate a functional element <NUM> by a piston element <NUM>, wherein functional element <NUM> is shifting shifting fork <NUM> of gearbox <NUM>. Pneumatic actuator <NUM>, <NUM> comprises a pneumatic cylinder <NUM> and a pneumatic piston <NUM>. A cylinder body <NUM> of pneumatic cylinder <NUM> defines a pneumatic chamber <NUM>, having a main axis A. On a first side <NUM>, the pneumatic chamber <NUM> is closed by a cylinder head <NUM> of the pneumatic cylinder <NUM>. Pneumatic cylinder <NUM> is integrally formed with a housing <NUM> of gearbox <NUM>. In <FIG>, pneumatic actuator <NUM>, <NUM> is received inside the gearbox <NUM> in an interior <NUM>.

A piston head <NUM> of pneumatic piston <NUM> is received in pneumatic chamber <NUM> of pneumatic cylinder <NUM>. The piston head <NUM> is connected to a piston rod <NUM> of pneumatic piston <NUM> that extends through a cylinder orifice <NUM> of pneumatic cylinder <NUM> on a second side <NUM> opposite the first side <NUM>. Piston rod <NUM> is sealed in cylinder body <NUM> by a second ring seal <NUM>. The cylinder orifice <NUM> is formed in a bottom <NUM> of cylinder body <NUM>. A first diameter D1 of piston head <NUM> is larger than a corresponding second diameter D2 of cylinder orifice <NUM>. During assembly of pneumatic actuator <NUM> pneumatic piston <NUM> is inserted from first side <NUM> through a head opening <NUM>. After insertion of pneumatic piston <NUM> head opening <NUM> of pneumatic chamber <NUM> is closed by cylinder head <NUM>. However, the inner diameter D2 may also correspond to the maximum outer diameter D2 such that pneumatic piston <NUM> can be inserted into pneumatic chamber <NUM> from second side <NUM> through cylinder orifice <NUM>.

Piston head <NUM>, piston rod <NUM>, an inner wall <NUM> of cylinder body <NUM> and second ring seal <NUM> enclose a first pressure chamber <NUM> with a first volume V1. For moving pneumatic piston <NUM> in negative stroke direction R2, a first pressure p1 is applied to the first volume V1. Opposite the first volume V1, a second pressure chamber <NUM> with a second volume V2 is enclosed by piston head <NUM>, inner wall <NUM> of cylinder body <NUM> and cylinder head <NUM>. For moving pneumatic piston <NUM> in positive stroke direction R1, a second pressure p2 is applied to the second volume V2.

If first pressure p1 exceeds an ambient pressure pa, that also applies to the second volume V2, the first volume V1 is increased and pneumatic piston <NUM> performs a negative stroke in negative stroke direction R2. If second pressure p2 exceeds ambient pressure pa, that also applies to first volume V1, second volume V2 is increased and pneumatic piston <NUM> performs a positive stroke in positive stroke direction R1. A bearing guides pneumatic piston <NUM> such that positive stroke direction R1 and negative stroke direction R2 is parallel to main axis A.

By applying varying pressures p1, p2 to first volume V1 and second Volume V2 pneumatic piston <NUM> is movable back and forth with regard to pneumatic cylinder <NUM>. In a neutral position opposite the piston head <NUM>, piston rod <NUM> is not engaged with the functional element <NUM>. In a coupling position opposite the neutral position near piston head <NUM>, piston rod <NUM> is engaged with functional element <NUM>. Piston rod <NUM> transmits the movement of piston head <NUM> to functional element <NUM>. When pneumatic piston <NUM> performs a positive stroke in positive stroke direction R1 functional element <NUM> engaging the piston rod <NUM> is actuated and moved in positive stroke direction R1 as well. During a negative stroke of pneumatic piston <NUM> in negative stroke direction R2, functional element <NUM> is also moved in negative stroke direction R2.

For engaging functional element <NUM>, piston rod <NUM> comprises a groove <NUM>. Preferably groove <NUM> is a substantially U-shaped groove <NUM>. Additionally or alternatively, piston rod <NUM> may also comprise a radial projection (not shown) for engaging functional element <NUM>. Groove <NUM> extends along the entire circumference of piston rod <NUM>. However, groove <NUM> may also extend only partially around the circumference of the piston rod <NUM>.

Pneumatic piston <NUM> is a two-part construction. Piston head <NUM> and piston rod <NUM> are manufactured independently and attached to each other up-on assembly of pneumatic piston <NUM>. A connection member <NUM> attaches piston head <NUM> to piston rod <NUM>, wherein connection member <NUM> may be a screw <NUM>. Pneumatic piston <NUM> may also be one part.

To apply varying pressures to first pressure chamber <NUM> a first pressure valve <NUM> and to second pressure chamber <NUM> a second pressure valve <NUM> is provided. First pressure valve <NUM> and/or second pressure valve <NUM> may be formed as a <NUM>-<NUM> directional control valve. For accelerating and decelerating pneumatic piston <NUM> first pressure chamber <NUM> and second pressure chamber <NUM> must be pressurized or vented. If the piston head <NUM> is in the coupling position, near cylinder head <NUM>, second pressure valve <NUM> is in a first position that second pressure chamber <NUM> get pressurized, while first pressure valve <NUM> is in a second position that first pressure chamber <NUM> gets vented. Due to the pressure difference between first volume V1 and second volume V2 pneumatic piston <NUM> gets accelerated in positive stroke direction R1. As soon as piston head <NUM> approaches the neutral position, piston head <NUM> must be decelerated. For this purpose, first pressure valve <NUM> is switched, so first pressure chamber <NUM> gets pressurized as well. As soon as a pressure balancing has been achieved, pneumatic piston <NUM> comes to a stop. Accordingly, in the state of the art the movement of pneumatic piston <NUM> requires both a switching of second pressure valve <NUM> for acceleration and a switching of first pressure valve <NUM> for deceleration. Due to the high number of switching operations, pressure <NUM>, <NUM> valves are subjected to a high load.

To counteract the high load, the switching cycles of the pressure valves <NUM>, <NUM> should be reduced. One embodiment of the invention is shown in <FIG>, where identical elements in the prior art and in the invention have the same reference signs. <FIG> shows a detail of pneumatic actuator <NUM> according to the invention, wherein especially piston rod <NUM> and first pressure chamber <NUM> are equally designed to the known pneumatic actuator <NUM> from <FIG>.

Pneumatic piston <NUM> further comprises a piston collar <NUM> with a diameter D3, wherein piston collar <NUM> is arranged concentrically to main axis A and partially encircles piston rod <NUM>. Piston collar <NUM> comprises a bypass <NUM>, wherein bypass <NUM> is made of six through holes <NUM>. Through holes <NUM> are extending parallel to main axis A and are arranged at a circular ring that is concentrically to main axis A and having an angular distance of <NUM>°. Using bypass <NUM>, fluid can flow from first pressure chamber <NUM> to second pressure chamber <NUM> and the other way around. First pressure valve <NUM> has a first cross sectional area <NUM> perpendicular to main axis A and second pressure valve <NUM> has a second cross sectional area <NUM> perpendicular to main axis A, wherein first cross sectional area <NUM> and second cross sectional area <NUM> are equal. Bypass <NUM> has a third cross sectional area <NUM> perpendicular to main axis A that is built by the sum of each cross sectional area of the at least a through hole <NUM>. The quotient of first cross sectional area <NUM> and third cross sectional area <NUM> is less than <NUM>:<NUM> and/or more than <NUM>:<NUM>, in particular less than <NUM>:<NUM> and/or more than <NUM>:<NUM>, preferably less than <NUM>:<NUM> and/or more than <NUM>:<NUM>, and further preferably about <NUM>:<NUM>. The quotient of second cross sectional area <NUM> and third cross sectional area <NUM> is less than <NUM>:<NUM> and/or more than <NUM>:<NUM>, in particular less than <NUM>:<NUM> and/or more than <NUM>:<NUM>, preferably less than <NUM>:<NUM> and/or more than <NUM>:<NUM>, and further preferably about <NUM>:<NUM>. An above mentioned quotient facilitates a delay between the pressuring of the pressure chamber facing the active pressure valve and the pressure chamber facing away from the pressure valve. As a result, piston head <NUM> is, first, accelerated in positive stroke direction R1 by the pressurized fluid provided by second pressure valve <NUM>. Second, the fluid flows with a delay through the bypass <NUM> into first pressure chamber <NUM> and promotes the deceleration of piston head <NUM>.

<FIG> shows piston head <NUM> in the coupling position and the first phase. During the movement of piston head <NUM> in positive stroke direction R1, first pressure valve <NUM> is venting first pressure chamber <NUM>. A controller <NUM> is provided to control at least first pressure valve <NUM> and second pressure valve <NUM>. Pneumatic piston <NUM> moves in positive stroke direction R1 from the coupling position into the neutral position. As long as bypass <NUM> is fluidically connected to first pressure valve <NUM>, pneumatic piston <NUM> is in the first phase. To enter the second phase, first pressure chamber <NUM> must be separated into a third pressure chamber <NUM> with a third volume V3 and a fourth pressure chamber <NUM> with a fourth volume V4. <FIG> shows piston head <NUM> between the coupling position and the neutral position in the second phase.

For this purpose, cylinder body <NUM> provides a first ring seal <NUM>, which engages with piston collar <NUM>. As soon as piston head <NUM> has sufficiently moved in positive stroke direction R1, piston collar <NUM> engages in first ring seal <NUM>. First ring seal <NUM> seals piston collar <NUM> in such a way that first pressure chamber <NUM> is separated into third pressure chamber <NUM> and fourth pressure chamber <NUM>. Bypass <NUM> is arranged on piston collar <NUM> in such a way that it leads from second pressure chamber <NUM> into third pressure chamber <NUM>. Accordingly, bypass <NUM> is no longer fluidically connected to first pressure valve <NUM>. The fluid continues to flow from second pressure chamber <NUM> through bypass <NUM> into third pressure chamber <NUM>. Due to the smaller volume of third volume V3 in contrast to first volume V1, the pressure balancing takes place much faster than with the larger first volume V1. The further deceleration begins with the second phase. The pressure p3 increases until piston head <NUM> comes to a stop, as shown in <FIG>. In contrast to the state of the art, first pressure valve <NUM> does not have to be switched from venting to pressuring for deceleration of pneumatic piston <NUM>, but the pressure balancing is achieved by bypass <NUM> in piston collar <NUM>. Consequently, one switching operation is saved.

<FIG> and <FIG> show pneumatic piston <NUM> in the second phase, third pressure chamber <NUM> is enclosed by cylinder body <NUM>, first ring seal <NUM>, second ring seal <NUM> and piston collar <NUM>.

Claim 1:
A pneumatic actuator (<NUM>) for actuating a shifting fork (<NUM>) of a gearbox (<NUM>) of a commercial vehicle (<NUM>), comprising:
a pneumatic cylinder (<NUM>), the pneumatic cylinder (<NUM>) comprising:
a cylinder body (<NUM>) defining a pneumatic chamber (<NUM>) having a main axis (A),
a cylinder head (<NUM>) closing the pneumatic chamber (<NUM>), and
a pneumatic piston (<NUM>) for actuating the shifting fork, the pneumatic piston (<NUM>) comprising:
a piston head (<NUM>),
a piston rod (<NUM>) for connecting the piston head (<NUM>) to the shifting fork (<NUM>),
wherein the piston head (<NUM>) is received in the pneumatic chamber (<NUM>) slidable along the main axis (A) between a coupling position and a neutral position,
wherein the neutral position refers to a position in which the piston rod (<NUM>) is configured such that it is not engaged with the shift fork (<NUM>) and wherein the coupling position refers to a position in which the piston rod (<NUM>) is configured such that it is engaged with the shift fork (<NUM>),
wherein the piston head (<NUM>) is configured such that it separates the pneumatic chamber (<NUM>) into a first pressure chamber (<NUM>) and a second pressure chamber (<NUM>), and
a bypass (<NUM>) fluidically connecting the first pressure chamber (<NUM>) and the second pressure chamber (<NUM>), wherein the pneumatic piston (<NUM>) further comprises a piston collar (<NUM>),
wherein the cylinder body (<NUM>) comprises a first seal (<NUM>),
wherein the piston rod (<NUM>) extends through said first seal (<NUM>), and
wherein in the neutral position the piston collar (<NUM>) is configured such that it engages with the first seal (<NUM>) to separate the first pressure chamber (<NUM>) into a third pressure chamber (<NUM>) and a fourth pressure chamber (<NUM>).