EP0738826A1 - Hydraulic device with differential pistons and its application to a varible thrust drive - Google Patents

Abstract

The piston device comprises two guided pistons (9,11) of different cross sections, In one position, their endfaces (9b,11a) are in contact. A pressure cell (30,15a-c) is filled with hydraulic fluid to transmit force between the pistons. A reservoir (20) and channel (25) enable the amount of fluid in the cell to be altered. This is done by forcing hydraulic fluid through the channel, which is connected to the pressure cell, controlled by one of the pistons, which in a certain position cuts off the inflow of hydraulic fluid. This in turn enables the force transmitted between the pistons to be controlled.

Description

The invention relates to a hydraulic stepped piston arrangement according to the preamble of claim 1, a drive based on the hydraulic stepped piston arrangement, a method for operating the drive, and an application of the drive for actuating valves in internal combustion engines.

Step pistons are known in hydraulic drive technology as pistons or piston systems, in which pistons with different cross-sectional areas are connected to a hydraulic fluid which is under a hydrostatic pressure P. In practical applications, the effect is usually exploited that the hydraulic fluid exerts forces F _i = P * A _i (i: index for distinguishing different pistons) of different strength on pistons with different cross-sectional areas A _i and that the hydraulic fluid essentially exerts itself due to its low compressibility behaves like an incompressible liquid.

A known application of a stepped piston is a hydraulic transmission with two independent pistons, coupled via a hydraulic system, with the cross-sectional areas A _i (i = 1.2). The coupling between the pistons is a force coupling. The force coupling is achieved with the help of a pressure cell filled with a hydraulic fluid, by the pistons acting on the hydraulic fluid in such a way that the movement of each of the pistons perpendicular to the cross-sectional areas displaces them towards the hydraulic fluid. Since all pistons are exposed to the same hydrostatic pressure in the pressure cell, which is mediated by the hydraulic fluid, the pressure cell serves to transmit power between the pistons. In the hydraulic ratio, the forces acting on the piston surfaces are in the same ratio as the piston surfaces, ie F ₁ = F ₂ * A ₁ / A ₂ , while the displacements Δs _{i of} the pistons perpendicular to the piston surfaces are inversely related to the piston surfaces, ie Δs ₁ = Δs ₂ * A ₂ / A ₁ . The hydraulic ratio is used to convert forces while maintaining mechanical energy, with the hydraulics establishing a non-positive connection between the pistons. A typical application of hydraulic translation is the amplification of forces by transferring a force from one piston to another piston with a larger cross-sectional area, e.g. B. in a hydraulic press.

Another known application of stepped pistons is a drive with a variable thrust, a hydraulic fluid which is at a predetermined pressure P being used to generate the thrust. The variable thrust is e.g. B. achieved in that several pistons with different cross-sectional area are rigidly coupled together and successively different piston surfaces are acted upon by the hydraulic fluid or decoupled again from the hydraulic fluid. According to this principle, z. B. the drive for an exhaust valve of an internal combustion engine according to EP-A2-0 075 472: the position of the disclosed exhaust valve is controlled by means of two hydraulically driven pistons rigidly coupled to its movable valve needle, a smaller piston being used to counter the valve against the after the combustion gases have escaped relatively to close the low gas pressure in the combustion chamber of the internal combustion engine, and a larger piston is used to keep the valve closed against the relatively high gas pressure which arises during a combustion cycle.

This use of a stepped piston to generate a variable thrust has the disadvantage that the change in thrust is achieved with a complex hydraulic control. For each individual piston, a separate pressure cell for the hydraulic fluid that causes the force on the piston, and for each pressure cell an active control that suitably adjusts the pressure in the pressure cell, is provided.

The invention seeks to remedy this. The invention, as characterized in the claims, achieves the object of a hydraulic stepped piston arrangement with a simplified control for converting any force into a time-variable force, a drive based on this stepped piston arrangement, a method for operating this drive and a to create the drive actuated valve of an internal combustion engine.

A hydraulic step piston arrangement according to the invention and a drive according to the invention contain two guided pistons of different cross-section, which pistons touch in one position on their end faces, a pressure cell filled with a hydraulic fluid for power transmission between the two pistons and means for changing the amount of hydraulic fluid in the pressure cell. By changing the amount of hydraulic fluid in the pressure cell during the advance of a piston in the direction of the hydraulic fluid, the power transmission to the second piston is modified in a controlled manner.

For example, this arrangement can be operated in such a way that it exerts a predetermined force on one during feed converts the first piston into a force on a second piston, the strength of which is different on two different sections of the movement, the change in the force being achieved by a switchover of the type of coupling between the two pistons controlled by a control device from a positive coupling which the force on the first piston is transmitted essentially completely to the second piston, on a non-positive coupling in the form of a hydraulic transmission, the cross-sectional areas of the two pistons determining the factor by which the force is transferred from the first to the second piston. An advantage of the invention is that the control device can be implemented without elements that have to be activated separately by suitable control commands. Rather, in one embodiment of the control device, the position of a piston alone determines the character of the power transmission between the two pistons. Another advantage of this principle is the possibility of coupling cascades of more than 2 independently movable pistons to one another. In principle, a drive can be created in which a force during the feed is converted into a force with any number of discrete values dependent on the position of a piston without further active control elements.

FIG. 1A-C

Längsschnitt durch einen Antrieb mit hydraulischer Stufenkolbenanordnung während des Vorschubs,

FIG. 1D

Längsschnitt durch einen Antrieb mit hydraulischer Stufenkolbenanordnung während der Rückwärtsbewegung in die Ausgangsposition,

FIG. 2A-C

Längsschnitt durch einen Antrieb mit hydraulischer Stufenkolbenanordnung während des Vorschubs wie in FIG. 1A-C, jedoch mit hydraulischer Kraftübertragung auf den grossen Kolben,

FIG. 2D

Längsschnitt durch einen Antrieb mit hydraulischer Stufenkolbenanordnung während der Rückwärtsbewegung in die Ausgangsposition wie in FIG. 1D, jedoch mit hydraulischer Kraftübertragung auf den grossen Kolben.

In the following, embodiments of the present invention are explained in detail with reference to the following figures. Show it:

FIG. 1A-C

Longitudinal section through a drive with hydraulic stepped piston arrangement during the feed,

FIG. 1D

Longitudinal section through a drive with a hydraulic stepped piston arrangement during the backward movement into the starting position,

FIG. 2A-C

Longitudinal section through a drive with hydraulic stepped piston arrangement during the feed as in FIG. 1A-C, but with hydraulic power transmission to the large pistons,

FIG. 2D

Longitudinal section through a drive with a hydraulic stepped piston arrangement during the backward movement into the starting position as in FIG. 1D, but with hydraulic power transmission to the large pistons.

As examples in FIGS. 1 and 2, drives with the hydraulic stepped piston arrangement according to the invention consisting of a first and a second piston are considered, the first piston 9 (in FIG. 1) and 10 (in FIG. 2) having a larger cross-sectional diameter (A ₁ ) than the second Piston 11 (A ₂ ) and a force F ₁ on the first piston when the first piston is fed in the direction of the force F _{1 is} converted into a force F ₂ . The force F ₂ serves to counteract a force F ₃ (<F ₂ ), which is generated by an unspecified device 40 and which in turn acts on the second piston, in an application not specified here. In the following, indices i = 1 or 2 generally designate physical quantities that relate to the first or second piston.

The two pistons in FIGS. 1 and 2 move essentially in the same direction and the coupling of the two pistons is controlled such that the two pistons touch on their end faces on a first part of the movement. Then F ₁ = F ₂ and for the displacements Δs _{i of} the two pistons, Δs ₁ = Δs ₂ applies. On a second section of the movement, the two pistons act as hydraulic translation together. Then F ₂ = F ₁ * A ₂ / A ₁ and Δs ₂ = Δs ₁ * A ₁ / A ₂ , ie the second piston experiences a reduced force and an increased feed compared to the first piston. Such an arrangement is suitable for ensuring a feed with a counterforce F ₃ (see above), which is reduced in magnitude in the ratio A ₂ / A ₁ during the feed.

The FIG. 1A-D illustrate the basic principle of the invention on the basis of four characteristic positions of the two pistons during the advance and during the return movement of the pistons to their starting position. The FIG. 1A-D show the piston arrangement in longitudinal section. The pistons 9, 11 are in the form of a straight cylinder (9) or two cylinders (11) placed one against the other in the direction of the cylinder axes. To guide the pistons 9, 11, a guide member 15 is provided for the two pistons, the guide member having a first and a second sub-segment 15a, 15b, the first sub-segment 15a the direction of movement of the first piston 9 and the second sub-segment 15b the direction of movement of the Defined second piston 11 and the sub-segments are dimensioned and arranged so that the two pistons can touch in a basic position on their end faces 9b and 11a. The sub-segments 15a, 15b have the shape of hollow cylinders, the interior of which is form-fittingly adapted to the jacket 9c or 11c of the pistons 9 or 11, so that the guide member 15 the directions of movement of the pistons parallel to the inner walls of the sub-segments, i. H. in the y direction. In the particular embodiment in FIG. 1, the directions of movement of the two pistons are identical.

FIG. 1A indicates the basic position of the drive. In the basic position, the first piston 9 is at a predetermined distance s = s _max from the point at which the guide member 15 is located on the connecting wall 15c between the Sub-segments 15a and 15b narrowed. The second piston 11 is displaced in the y direction in such a way that it projects into the partial segment 15a over part of its length and its end face 11a touches the end face 9b of the first piston. In the arrangement in FIG. 1, the guide member 15 is designed such that, together with the end faces 11a and 9b, it delimits a cavity 30 between the two pistons. This cavity is filled with a hydraulic fluid. A reservoir 21 is provided for filling the cavity with hydraulic fluid, from which hydraulic fluid can be introduced into the cavity 30 via the channel 26 in the vicinity of the connecting wall 15c. Channel 26 is set up as a one-way line for the hydraulic fluid by conventional means such as a check valve.

A constant force F _{1 is} generated in the negative y direction on the first piston 9 by means of a conventional device 5 for generating a force (e.g. a mechanical lever, a hydraulic press). Without displacement of the hydraulic fluid from the cavity 30, the two pistons 9 and 11 would act as a hydraulic transmission, which would force F ₁ by the factor A ₂ / A ₁ (A ₁ : cross-sectional area of the cavity 30 perpendicular to the y-axis in the area of the partial segment 15a; A ₂ :
The cross-sectional area of the cavity 30 perpendicular to the y-axis in the region of the partial segment 15b) is converted into the force F ₂ on the second piston, the pistons separating in accordance with the above-mentioned law.

The controlled switching according to the invention between a positive coupling between the first piston 9 and the second piston 11, as shown in the basic position according to FIG. 1A is realized, and a non-positive coupling in the form of a hydraulic transmission ratio is achieved by displacing the hydraulic fluid from the cavity 30 on a first section of the movement of the first piston from the basic position in the -y direction is made possible and the displacement of the hydraulic fluid from the cavity 30 is prevented on a second part of the movement. This controlled displacement ensures that on the first part of the movement the two pistons on the end faces 9b and 11a remain in contact and thus the force in the direction of movement is completely transmitted from the first piston 9 to the second piston 11, while the effect of the hydraulic translation only unfolds on the second section of the movement. A control device for realizing this controlled switching shows the arrangement in FIG. 1A-D. The wall of the guide member 15 has an opening through which hydraulic fluid can be displaced into the reservoir 20 via the channel 25, the first piston 9 serving as a flow barrier for the channel 25. The opening in the y direction is arranged between the position s = s _max (FIG. 1A) and a second limit position, which marks the maximum advance of the first piston in the y direction (s = 0). In this construction, the effect of the hydraulic transmission is only put into effect when the outer surface 9c of the first piston 9 closes the inflow to the channel 25 and the reservoir 20. The positioning and dimensioning of the opening to the channel 25 thus determines the above-mentioned parts of the movement on which the two pistons are either in contact at their end faces (FIG. 1A and 1B) or act like a hydraulic transmission (FIG. 1C).

FIG. 1D shows how the drive returns to its basic position according to FIG. 1A is returned. It is assumed that the counterforce F ₃ generated by the device 40 is always large enough to move the pistons back into their basic position after a corresponding reduction in the force F ₁ (for example F ₁ = F ₂ = 0). During this return movement, the two pistons initially act as a hydraulic transmission for the force F ₃ , F ₃ acting more intensely on the first piston 9 in the ratio A ₁ / A ₂ . At the same time, the distance decreases between the end faces 11a and 9b of the two pistons until the two pistons touch. Up to this point the two pistons move in such a way that the volume of the cavity 30 remains constant corresponding to the volume of the enclosed quantity of hydraulic fluid. With a further movement of the pistons in the direction of their starting position, the volume of the cavity increases and the enclosed quantity of hydraulic fluid is no longer sufficient to fill the cavity 30. In order to fill the cavity 30 again, the amount of hydraulic fluid which has been displaced during the feed or has escaped through small leaks is replenished. For this purpose, hydraulic fluid flows from the reservoirs 21 and / or 20 into the cavity 30. The inflow from the reservoir 20 is only possible when the opening to the channel 25 is no longer covered by the lateral surface 9c of the first piston. The inflow of hydraulic fluid from the reservoir 20 or 21 can be realized particularly simply in that the reservoir and cavity are designed as a communicating system for the hydraulic fluid. B. due to a pressure gradient or gravity hydraulic fluid flows into the cavity until it is filled.

In the arrangement in FIG. 1 is the position s of the first piston 9, at which the displacement of hydraulic fluid from the cavity 30 is prevented and the hydraulic transmission is activated, determined by the arrangement of the opening in the guide element which forms the access to the channel 25. The arrangement in FIG. 1 can easily be modified so that the hydraulic ratio can be activated at any position s in the range 0 <s <s _max . This goal is achieved in that instead of channel 25 in FIG. 1, a connecting channel is created between the cavity 30 and the reservoir 20, which channel is accessible regardless of the position s for the hydraulic fluid in the cavity 30, but which can be operated with a controllable valve depending on the Position s can either be opened or locked. In this way, the position s at which the hydraulic transmission is activated can be regulated. A channel opening, which enables a connection to the cavity 30 regardless of the position s, z. B. be installed at the transition between the connecting wall 15c and the sub-segment 15b.

FIG. 2 shows a special embodiment of the drive according to the invention in FIG. 1. In connection with the explanation of the functioning of the arrangement in FIG. 1, it was not relevant to specify the device 5 for generating the force F _{1 in} more detail. The arrangement in FIG. 2 is a special embodiment of the drive in FIG. 1 such that the device 5 is designed as a hydraulic system.

The special design of the device 5 as a hydraulic system necessitates the installation of additional elements on the guide member 15. Furthermore, the first piston 9 is replaced by a modified piston 10 in order to enable the power to be transmitted to the first piston and to control the sequence of movements of the pistons 10, 11 to realize. In particular, the arrangement in FIG. 2 shows a hydraulic braking device which ensures that the speed of the pistons is throttled when the position s of the first piston falls below a lower limit or exceeds an upper limit; In this way, the impact of the pistons on fixed limiting elements is dampened and low-wear operation of the drive is ensured.

In the arrangement in FIG. 2, the force F _{1 is} transmitted hydraulically as a compressive force to the end face 10a of the piston 10 facing away from the second piston 11. A pressure chamber 80 is set up as a device for generating the compressive force, which is formed by the end face 10a of the first piston, the wall of the partial segment 15a and of the Boundary wall 16 is formed and serves to hold a hydraulic fluid. The hydraulic fluid is supplied under pressure P ₁ by means of a supply system, which includes the reservoir 60 for hydraulic fluid and the connecting channels 53 and 51, under the control of the control unit 70 through the opening 51a. For the pressure chamber 80, the first piston 10 forms a movable wall, on which the force F ₁ = P ₁ * A ₁ acts in the -y direction. A controlled drain is provided for draining the hydraulic fluid from the pressure chamber 80: likewise under the control of the control unit 70, the hydraulic fluid can flow via the connecting channels 52 and 54 into a reservoir 61 which is under the internal pressure P ₂ <P ₁ . The inflow or outflow of hydraulic fluid is controlled with the aid of a control valve 50, which is controlled by the control unit 70 by means of the communication interface 71. The control valve is designed as a slide valve, which either enables the inflow of hydraulic fluid from the reservoir 60 into the pressure chamber and at the same time prevents the outflow into the reservoir 61 or vice versa: for this purpose, connecting members 50a and 50b are synchronously used as controllable connections between the connecting channels 53 and 51 or the connecting channels 52 and 54 are pushed, the connecting element 50a isolating the connected connecting channels from one another and the connecting element 50b realizing an open connection between the connected connecting channels, which the flow of hydraulic fluid in the in FIG. 2 permitted by an arrow.

The operation of the drive in FIG. 2 described in detail. The FIG. 2A-C denotes the position of the elements of the drive during the movement of the pistons 10, 11 from a basic position in which the distance s assumes a maximum value given by the position of the boundary wall 16 (FIG. 2A) and the two pistons 10 and 11 touch on the end faces 10b and 11a, in a End position (FIG. 2C), in which the distance s assumes a minimum value. FIG. 2D describes the drive during the return movement of the pistons from the end position into the basic position according to FIG. 2A. FIG. 2C marks an intermediate position of the drive, in which the pistons 10 and 11 begin to separate from one another at the end faces 10b and 11a by activating the hydraulic transmission. The FIG. 1X and 2X (X = A, B, C, D) thus show equivalent states of motion.

During the movement of the pistons from the basic position into the end position, hydraulic fluid flows from the reservoir 60 into the pressure chamber 80. The control valve at this stage connects the connection channels 51 and 53 and prevents the outflow of hydraulic fluid by isolating the connection channels 52 and 54 from one another.

In order to control the movement of the two pistons, the inflow of hydraulic fluid into the pressure chamber 80 is regulated by the first piston itself. In order to achieve this regulation, the connecting channel 51 conducts hydraulic fluid through an opening 51a through the wall of the partial segment 15a. This opening 51a is positioned with respect to the y direction so that in the basic position according to FIG. 2A would be blocked by the lateral surface 10c of the first piston 10, there would not be at least one special passage channel which would lead hydraulic fluid from the opening 51a to the pressure chamber 80. The drive in FIG. 2 has two such through channels 12, 13, which are accommodated in the first piston 10 and are thus moved with the piston relative to the opening 51a. The two through-channels each establish a connection between an opening on that part of the lateral surface 10c of the piston 10 which faces the opening 51a and an opening in the end face 10a. The two through channels have different cross-sectional areas and thus offer different Flow resistances for the hydraulic fluid. They are arranged in such a way that at the beginning of the movement of the first piston only the through-channel 12 with the larger cross-sectional area establishes a connection between the opening 51a and the pressure chamber 80 (see FIG. 2C-D). This connection only remains as long as the inlet opening 12a overlaps the opening 51a during the advance of the first piston 10. The second through-channel 13 is set up so that when the first piston is advanced from the moment from which the inlet opening 12a no longer overlaps the opening 51a, it establishes the connection between the connecting channel 51 and the pressure chamber 80 (FIG. 2B, C). . Since the second through-channel 13 has a smaller cross-sectional area than the first through-channel, it reduces the inflow of hydraulic fluid to the pressure chamber 80 per unit of time in comparison to the basic position according to FIG. 2A. Since the speed of the first piston during the advance is greater, the greater the amount of hydraulic fluid flowing into the pressure chamber 80 per unit of time, the above-mentioned braking effect is achieved in this way when the distance s is reduced to less than a certain one Positioning and dimensioning of the through channels and the opening 51a certain distance.

The inflow of hydraulic fluid into the cavity 30 through the channels 25 and 26 and the displacement of hydraulic fluid from the cavity 30 through the channel 25 functions when the drive in FIG. 2 according to the same principles as in the case of the drive in FIG. 1 apart from a design simplification for the drive in FIG. 2: With the drive in FIG. 2, channels 25 and 26 are not routed to different reservoirs, as shown in FIG. 1 (reservoirs 20, 21), they rather have a connection to a common reservoir 29 for the hydraulic fluid via the channel 28. Since channel 26 in FIG. 1 and FIG. 2 serves exclusively to fill the cavity 30 with hydraulic fluid and to displace Hydraulic fluid through the channel 26 is incompatible with the function of the drive is shown in FIG. 2 installed a check valve 27 between channel 26 and channel 28. In this way, channel 26 is both in FIG. 1 as well as in FIG. 2 designed as a one-way line for hydraulic fluid. A free bidirectional exchange of hydraulic fluid between the reservoir 29 and the cavity 30 is only possible via the channel 25. The direction of flow of hydraulic fluid in the channels 25 and 26 is for the different positions of the drive in FIG. 2 marked by arrows.

When the pistons move back into the basic position (FIG. 2C), the connection of the pressure chamber 80 to the reservoir 60 is interrupted by the slide valve 50, while the connection to the reservoir 61 is open in order to enable displacement of hydraulic fluid from the pressure chamber 80 and the To reduce forces F ₁ and F _{2 in} such a way that force F ₃ can cause the return movement. The first piston 10 in FIG. 2 has a braking device which determines the speed of the pistons during the return movement from the end position according to FIG. 2C in the basic position according to FIG. 2A is slowed down shortly before reaching the end position and is organized according to a similar principle as the braking during feed already dealt with: As shown in FIG. 2D compared to FIG. 2A can be seen, the braking takes place during the return movement by reducing the hydraulic fluid displaced per unit of time from the pressure chamber 80 via the connecting channel 52, the opened control valve 50, the connecting channel 54 into the reservoir 61. At the beginning of the return movement, the displacement of hydraulic fluid from the pressure chamber 80 is limited by the part of the area of the passage opening in the partial segment 15a between the pressure chamber 80 and the connecting channel 52 which is not covered by the lateral surface 10c of the first piston. The flow of hydraulic fluid is in for this situation FIG. 2D represented by arrows in the connecting channel 52. As the return movement progresses, this current is reduced and finally prevented when the lateral surface 10c covers the opening to the channel 52. In order not to abruptly suppress the displacement of hydraulic fluid from the pressure chamber 80 and thus abruptly brake the first piston 10 and instead always ensure a minimal, well-defined displacement, a through-channel 14 is installed in the first piston 10, which has the end face 10a and the outer surface 10c of the first piston 10 connects in such a way that hydraulic fluid always passes from the pressure chamber 80 into the connection channel 52 via the passage channel 14 when the volume of the pressure chamber falls below a predetermined limit and without such a passage channel 14 the piston itself provides access to the connection channel 52 would be blocked. By suitably dimensioning the cross section of the through-channel, the amount of hydraulic fluid displaced per unit of time from the pressure chamber 80 and thus the speed of the pistons 10 and 11 on the last piece of the return movement into the basic position of the drive can be determined.

An obvious application of a drive according to FIG. 2 is the actuation of a valve of an internal combustion engine (e.g. a cylinder intake or exhaust valve) with a counterforce that changes over time. An example is an exhaust valve on the cylinder of an internal combustion engine, in which the valve needle has to be displaced when the valve is opened against the force due to the gas pressure prevailing in the combustion chamber of the internal combustion engine and the force of a resetting device which counteracts a displacement of the valve needle with a suitable counterforce. When the exhaust valve is opened, high-pressure combustion gases escape from the combustion chamber. The gas pressure usually decreases so quickly that the total force F ₄ that the opening of the Valve opposes, namely the force due to the gas pressure and the force of the reset device, during the opening of the valve decreases sharply. A drive that has to move the valve needle by a predetermined distance when opening the valve and thereby reduces the thrust adapted to the total force F ₄ has a more favorable energy balance than a drive without a corresponding adjustment of the thrust.

• Vorgegeben ist ein konstanter Druck P₁ im Reservoir 60 für die Hydraulikflüssigkeit. Um einen Vorschub der Ventilnadel zu gewährleisten, muss auf dem ersten Teilstück der Bewegung vor Aktivierung der hydraulischen Übersetzung F₄<F₁=F₂=P₁*A₁ sein.
• Auf dem zweiten Teilstück der Bewegung nach Aktivierung der hydraulischen Übersetzung muss F₄<F₂=F₁*A₂/A₁=P₁*A₂ sein.
• Um den Energieverbrauch des Antriebs zu optimieren, soll die Strecke, um die der erste Kolben 10 bewegt werden muss, um den Vorschub der Ventilnadel um die Distanz S_N zu realisieren, minimal sein. Dadurch wird die Menge Hydraulikflüssigkeit, die in die Druckkammer 80 befördert werden muss, minimiert.
• Um das Ventil zu schliessen, wird das Steuerventil 50 gemäss FIG. 2D geschaltet. F₄ muss gross genug sein, um die Kolben wieder in ihre Grundstellung zu befördern. Sollte der Gasdruck dazu nicht ausreichen, dann lässt sich die fehlende Kraft immer aufbringen durch eine geeignete Gestaltung der genannten Rückstellvorrichtung mit konventionellen Mitteln, z. B. durch Installation einer geeignet vorgespannten Luftfeder.

A drive of the type shown in FIG. 2 shown type can be used as follows. The valve needle corresponds to the device 40 with F ₃ = F ₄ , it being irrelevant how the force of the second piston 11 is transmitted to the valve needle, e.g. B. by a rigid connection or by a non-positive connection via a hydraulic system. In order to move the valve needle by a predetermined distance S _N when the valve opens, the drive according to FIG. 2 set up according to the following criteria, the distance S _N corresponding to a displacement s _{2 of} the second piston 11:

• A constant pressure P ₁ in the reservoir 60 for the hydraulic fluid is specified. In order to ensure that the valve needle is advanced, the first section of the movement before activation of the hydraulic transmission must be F ₄ <F ₁ = F ₂ = P ₁ * A ₁ .
• On the second part of the movement after activation of the hydraulic transmission, F ₄ <F ₂ = F ₁ * A ₂ / A ₁ = P ₁ * A _{2 must} be.
• In order to optimize the energy consumption of the drive, the distance by which the first piston 10 must be moved in order to feed the valve needle by the distance S _N should be minimal. This will make the crowd Hydraulic fluid that must be pumped into the pressure chamber 80 is minimized.
• In order to close the valve, the control valve 50 according to FIG. 2D switched. F ₄ must be large enough to return the pistons to their home position. If the gas pressure is not sufficient for this, then the missing force can always be exerted by a suitable design of the reset device mentioned using conventional means, eg. B. by installing a suitably preloaded air spring.

Because of the third criterion, the first part of the movement should be as short as possible and the ratio A ₂ / A ₁ should be as small as possible, provided that the relationships for the forces F ₄ and F ₂ mentioned in the first two criteria are met. The fulfillment of this secondary condition is obvious if specific information for F _{4 is given} as a function of the time and the position of the valve needle.

The specified special embodiments of the drive according to the invention can be modified in various ways. In the case of the drive according to FIG. 2, the hydraulic fluid for generating the force F ₁ by any pressure-transmitting medium, for. B. a gas to be replaced. Furthermore, the pistons do not necessarily have to have the same directions of movement. However, with regard to the force transmission between the pistons during the part of the movement in which the pistons touch at their end faces 10b and 11a, it should then be taken into account that a component of the force acting on the second piston is absorbed by the sub-segment 15b. The relationships mentioned for F ₁ and F ₂ would have to be modified accordingly. Furthermore, the drives in FIG. 1 and FIG. 2 can also be operated inversely, namely in such a way that the force F ₃ on the smaller piston is converted into a force on the larger piston (where F ₂ = 0), the pistons in turn act like a hydraulic transmission over part of the movement and touch each other on their end faces 9b or 10b and 11a over another part of the movement, whereby the hydraulic transmission is deactivated. In this case, in contrast to the arrangement in FIG. 1 and 2 do not touch the pistons on their end faces in an initial position and during the first part of the movement the amount of hydraulic fluid in the cavity 30 would be constant. Furthermore, you can build a cascade of three or more pistons by expanding the drives discussed, by using two pistons with the above-mentioned design means such. B. according to FIG. 1 or 2 coupled together.

The essence of the invention can be summarized as follows:

The hydraulic stepped piston arrangement according to the invention has two guided pistons (9, 10, 11) with different cross sections, the pistons touching one another on their end faces (9b, 10b, 11a), a pressure cell (30, 15a-c) filled with hydraulic fluid. for power transmission between the two pistons, and means (25, 20) for changing the amount of hydraulic fluid in the pressure cell. The amount of hydraulic fluid is changed in that hydraulic fluid can be displaced through a channel (25) connected to the pressure cell and the flow of hydraulic fluid through the channel is controlled by one of the pistons (9, 10) being displaced by a predetermined distance Hydraulic fluid access to the channel (25) blocked only on part of the route. By controlling the amount of hydraulic fluid during the movement of the pistons, the force transmission mediated by the pressure cell between the two pistons can be controlled and a constant force on one of the pistons can be converted into a variable force on the second piston, the pistons touch one another on their end faces (9b, 10b, 11a) during part of the movement and act like a hydraulic transmission for the forces acting on the piston during another part.

Claims (13)

Hydraulic stepped piston arrangement with two guided pistons (9, 10, 11) of different cross-section, which pistons touch in one position on their end faces (9b, 10b, 11a), and with a pressure cell (30, 15a-c) filled with hydraulic fluid Power transmission between the two pistons, characterized by means (25, 20) for changing the amount of hydraulic fluid in the pressure cell. Step piston arrangement according to claim 1, characterized in that the means contain a passage (25) for the hydraulic fluid, connected to the pressure cell, and a device (9, 10) for controlling the flow of the hydraulic fluid through the passage. Step piston arrangement according to claim 2, characterized in that one of the pistons (9, 10) is part of the device and, when displaced by a predetermined distance, blocks the access of hydraulic fluid to the channel (25) only on part of the distance. Step piston arrangement according to one of claims 2-3, characterized in that the channel (25) is connected to a reservoir (20) for the hydraulic fluid. Drive with a stepped piston arrangement according to one of claims 1-4 and a device (5) for generating a force on one of the pistons (9, 10) in the direction of the other piston (11). Drive according to claim 5, characterized in that for the device (5) for generating a force on the one of the pistons a device for transmission a pressure force on an end face (10a) of one of the pistons with a pressure medium, which device includes a pressure chamber (80) and a supply system (50, 51, 53) for introducing the pressure medium from a reservoir (60) into the pressure chamber (80) contains, one of the pistons (10) forming a movable wall of the pressure chamber. Drive according to claim 6, characterized in that the supply system includes a plurality of through channels (12, 13) for the hydraulic fluid in one of the pistons (10), which through channels are connected (12b) to the pressure chamber (80) and an opening ( 12a) on the outer surface (10c) of one of the pistons (10), the openings being connected to the reservoir (60) in different areas for different through channels (12, 13) for the position of the one of the pistons (10). Drive according to claim 7, characterized in that the through-channels are designed in such a way that the flow resistances of the through-channels (12, 13) increase in the order in which the through-channels move when one of the pistons (10) is displaced due to the action of the force ( 5) successively connected to the reservoir (60). Drive according to one of claims 6-8, characterized in that means (61, 54, 52, 50) for receiving hydraulic fluid, which displaces from the pressure chamber (80) when its volume is reduced by displacement of one of the pistons (10) is present, the displaced hydraulic fluid flowing through a channel (14) in one of the pistons (10) when the volume falls below a predetermined lower limit. Method for operating a drive according to one of claims 5-9, characterized in that The two pistons (9, 10, 11) touch in an initial position on their end faces (9b, 10b, 11a), • the piston with the larger cross-sectional area is moved by means of the device (5) for generating a force, and • During its movement, the amount of hydraulic fluid in the pressure cell (30, 15a-c) is first reduced and then kept constant. Method for operating a drive according to one of claims 5-9, characterized in that The two pistons (9, 10, 11) do not touch each other on their end faces (9b, 10b, 11a) in an initial position, • the piston with the smaller cross-sectional area is moved by means of the device (5) for generating a force, and • during its movement, the amount of hydraulic fluid in the pressure cell (30, 15a-c) is initially constant and, after touching the two pistons (9, 10, 11), is increased on their end faces (9b, 10b, 11a). Valve of an internal combustion engine, with a drive according to one of claims 5-9. Internal combustion engine with a valve, in particular cylinder inlet valve or cylinder outlet valve, according to claim 12.

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