EP1354128A1

EP1354128A1 - Pressure accumulator for pressurizing a hydraulic device, with which preferably one gas exchange valve of an internal combustion engine is actuated

Info

Publication number: EP1354128A1
Application number: EP02701186A
Authority: EP
Inventors: Hermann Gaessler; Udo Diehl; Karsten Mischker; Rainer Walter; Juergen Schiemann; Christian Grosse; Volker Beuche; Stefan Reimer
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2001-01-16
Filing date: 2002-01-12
Publication date: 2003-10-22
Also published as: JP2004517258A; DE10101584A1; WO2002055847A1; US6779496B2; JP4131668B2; US20030172885A1

Abstract

The invention relates to a pressure accumulator that serves to pressurize a hydraulic device. A gas exchange valve of an internal combustion engine, for example, can be actuated by means of said hydraulic device. The pressure accumulator (62) comprises a housing (64, 68) and a piston (72) that, when operating, is pretensioned by a device (88, 90). The aim of the invention is to be able to construct a pressure accumulator (62) that is as small as possible. To this end, the device (88, 90), which pretensions the piston (72) of the pressure accumulator (62), has, in a motion area of the piston (72), a force-travel characteristic curve with a slope that differs from the slope in another motion area of the piston (72).

Description

Pressure accumulator for pressurizing a hydraulic device, with which a gas exchange valve of an internal combustion engine is preferably actuated

State of the art

The present invention relates to a pressure accumulator for pressurizing a hydraulic device, with which a gas exchange valve of an internal combustion engine is preferably actuated, with a housing and a piston which is biased during operation by a device.

A hydraulic device with such a pressure accumulator is known from DE 198 26 047 AI. Such a hydraulic device is e.g. used to actuate the intake and exhaust valves of an internal combustion engine when it has no camshaft. Such an internal combustion engine has the advantage that the control times of the intake and exhaust valves are independent of the position of the piston of the respective cylinder. Depending on the operating state of the internal combustion engine, e.g. High speed, and depending on the driver's desired torque, valve opening and closing times can be realized, which enable the internal combustion engine to be operated with particularly low emissions and consumption.

The known hydraulic device works with a hydraulic circuit, which consists of a hydraulic reservoir is fed by a high pressure hydraulic pump. An actuating device comprises a piston which can be acted upon hydraulically in both directions of movement and which is connected to the valve stem of a gas exchange valve, for example an inlet valve. One of the two chambers of the hydraulic cylinder can be pressurized with 2/2 directional control valves, which leads to a corresponding movement of the piston and thereby to an opening or closing process of the gas exchange valve on the engine block.

The hydraulic circuit is connected to a hydraulic pressure accumulator, which is designed as a spring-loaded piston accumulator and serves to dampen vibrations in the hydraulic system. Furthermore, a similarly constructed emergency pressure accumulator is connected to one of the two chambers in the hydraulic cylinder, which, when the pressure in the hydraulic line drops, still provides sufficient pressure and fluid volume that the gas exchange valve can be moved into its closed rest position. Both pressure accumulators work with different pressure levels, which are set by different stiffnesses of the corresponding return springs. From DE 198 26 047 AI it is also known to use only a single pressure accumulator, which works as a working pressure accumulator and at the same time as an emergency pressure accumulator.

If only a single pressure accumulator is provided, it must be designed in such a way that sufficient hydraulic medium is stored in the hydraulic system at minimum operating pressure in order to reliably enable the gas exchange valve to move to the closed rest position in an emergency. This requires a relatively soft spring and a large spring travel. In order to be able to ensure at the same time that a there is sufficient damping effect, such a pressure accumulator equipped with a soft spring must build very long depending on the minimum and maximum operating pressure. Such a large pressure accumulator is, however, difficult to accommodate in the space available in an internal combustion engine. In addition, because of the large overall length in such a pressure accumulator, a relatively large fluid volume must be stored in the operating pressure range, which, as a dead volume, has a negative influence on the dynamics of the hydraulic system in addition to the desired damping effect.

The present invention therefore has the task of developing a pressure accumulator of the type mentioned at the outset in such a way that it has a pressure damping function on the one hand and an emergency pressure function on the other hand, and yet it is as small as possible.

This object is achieved in a pressure accumulator of the type mentioned at the outset in that the device which prestresses the piston of the pressure accumulator has a force-path characteristic curve with an incline in a range of motion of the piston which differs from the incline in another range of motion of the Kolbens differs.

According to the invention, a prestressing device with a non-linear characteristic is therefore used in the pressure accumulator. It goes without saying that when the piston is acted upon from its non-pressurized rest position, a rather soft characteristic of the pretensioning device is desired, that is to say a change in pressure entails a relatively large movement path of the piston. In contrast, in a range of motion of the piston which is distant from the rest position of the piston, there is one. stiff characteristic of the pretensioner of the Piston desired, a change in pressure should only cause a relatively small movement of the piston.

In this way, both desired functions, namely the emergency pressure function and thus the vibration damping function, can be implemented in a single pressure accumulator: the emergency pressure function is present in the range of movement of the piston of the pressure accumulator in which the pretensioning device has a relatively soft characteristic. In this range of movement of the piston, the pressure accumulator can thus release a sufficiently large fluid volume into the hydraulic circuit even with a small pressure drop, as is necessary for the safe operation of, for example, a gas exchange valve in the event of a pressure loss. The

Vibration damping function is present in the range of movement of the piston in which the force-displacement characteristic is comparatively steep. In this range of movement of the piston, even larger pressure fluctuations only lead to a small piston movement. Correspondingly, only a small movement path of the pretensioning device can also be provided in this movement range of the piston, which in turn benefits from a short overall length of the pressure accumulator.

The pressure accumulator according to the invention can therefore be used on the one hand to store a fluid volume for emergency operation and on the other hand in normal operation to dampen vibrations and at the same time is very small. It can therefore be easily and easily integrated into the available space. In addition, due to the low stored fluid volume and the high rigidity of the pretensioning device, optimal vibration damping can be achieved in normal operation without impairing the system dynamics. Advantageous developments of the invention are specified in the subclaims.

In a first further development it is mentioned that the device which prestresses the piston of the pressure accumulator has at least two devices arranged in series with force-displacement characteristics of different gradients which prestress the piston during operation. The desired properties of such a pressure accumulator are particularly easy to achieve, since the different functions are also physically separate.

It is particularly preferred that the devices for pretensioning the piston comprise at least two springs arranged in series, the rigidity of one spring being different from that of the other spring. An accumulator with such a two-stage spring assembly can be easily built and very inexpensive be ^'and is also robust.

In a particularly preferred embodiment of the pressure accumulator according to the invention, it has an elongated part with two end sections and a support section arranged between the end sections, which has a larger outer dimension than the end sections and on which two adjacent springs are supported, the one spring being in operation between the one side of the support section and the piston and the other spring between the other side of the support section and the housing is tensioned. Such an elongated part enables reliable guidance of the piston on the one hand and the corresponding springs on the other.

It is also provided that at least two stops are provided, which prevent the springs in the Operation to be clamped on block. The tensioning of springs on block ^' has two main disadvantages: On the one hand, most springs show a clearly non-linear and, above all, often not reproducible characteristic behavior in the range of motion that lies just before a tension on block. This is also undesirable in the present case. In addition, when the springs are tensioned on the block, there can be signs of wear on the contacting surfaces of the springs, which can impair the life of the springs. This is prevented by the stops according to the invention.

Such stops are particularly simple to implement in connection with the elongated part described above: In this case, the length of the elongated part can be adjusted such that one axial end of the elongated part strikes a stop with the housing of the pressure accumulator and the other axial end of the elongated part Partly forms a stop with the piston.

Basically, all types of springs are suitable for the pressure accumulator according to the invention. Examples are coil springs, air springs and also magnetic springs. However, it is particularly preferred that at least one of the springs is a plate spring. The use of disc springs results in a further reduction in the length of the pressure accumulator due to the better relationship between the spring work and the installation space. In addition, the damping effect of the accumulator is increased due to the strong friction damping in a plate package.

The invention also relates to a hydraulic device for actuating a gas exchange valve

Internal combustion engine, in particular of a motor vehicle, with a fluid reservoir, a fluid pump, a fluid line, a pressure accumulator connected to the fluid line a housing and a piston biased during operation by a device, and with an actuating device which is connected to the fluid line via a valve device and actuates the gas exchange valve.

In order to reduce the overall dimensions of the hydraulic device, it is proposed that the pressure accumulator be designed in the manner described above.

Exemplary embodiments of the invention are explained in detail below with reference to the accompanying drawing. The drawing shows:

Figure 1 is a schematic diagram of a

Hydraulic device for actuating a gas exchange valve of an internal combustion engine;

Figure 2 shows a section through a first

Embodiment of a pressure accumulator of the hydraulic device of Figure 1;

FIG. 3 shows a pressure-displacement diagram to explain the function of the pressure accumulator from FIG. 2;

Figure 4 shows a schematic section through a second embodiment of a pressure accumulator;

Figure 5 shows a schematic section through a third embodiment of a pressure accumulator;

Figure 6 shows a schematic section through a fourth embodiment of a pressure accumulator; and

Figure 7 is a schematic section through a fifth embodiment of a pressure accumulator. In FIG. 1, a hydraulic device bears the reference number 10 overall. It serves to actuate a gas exchange valve, which in the present case is designed as an inlet valve of an internal combustion engine 14.

The inlet valve 12 is actuated by a hydraulic cylinder 16. This comprises a housing 18 in which a piston 20 with a piston rod 22 is slidably guided. The piston rod 22 is passed through the housing 18 and connected to a valve stem 24, which in turn is molded onto a plate-shaped valve element 26. In the closed state of the inlet valve 12, the valve element 26 lies tightly against a valve seat 28 in the upper region of a combustion chamber 30 of the internal combustion engine 14. If no hydraulic pressure is available, the piston 20 is pressed upwards by a spring 32 and the inlet valve 12 is thereby closed.

The hydraulic device 10 further comprises a reservoir 34, from which hydraulic fluid is conveyed by a high-pressure pump 36 into a high-pressure hydraulic line 38. After a check valve 40, the high-pressure hydraulic line 38 branches into a branch 42, which opens directly into a lower working space 44 of the hydraulic cylinder 16. Another branch 46 of the high-pressure hydraulic line 38 leads to a 2/2-way switching valve 48 which is pressed into its closed position by a spring 50 in the de-energized state. The branch 46 of the high-pressure hydraulic line 38 leads after the 2/2 switching valve 48 to an upper working ^chamber 52 of the hydraulic cylinder 16. From there, a high-pressure hydraulic line 54 leads via a further 2/2 switching valve 56 and a check valve 58 back to Reservoir 34. The 2/2-way valve 56 is opened by a spring 57 in the de-energized state. At the point where the high-pressure hydraulic line 38 branches into the branch 42 and the branch 46, a branch line 60 opens, which is connected to a pressure accumulator 62. Its structure is shown in detail in Figure 2.

The pressure accumulator 62 comprises a housing 64, which overall has an approximately cylindrical shape and in which a cylindrical cavity 66 is formed. On the right-hand side in FIG. 2, the cavity 66 is closed by a cover 68, whereas on the left-hand side in FIG. 2 it is connected to the spur line 60 via a connecting channel 70. In the present exemplary embodiment, the cover 68 has a ventilation opening lying outside the cutting plane and therefore not visible.

A piston 72 is slidably held in the cavity 66. The radial outer surface of the piston 72 is sealed off from the inner wall of the cavity 66 by a sealing ring 74 which is inserted into an annular groove 76 in the outer outer surface of the piston 72. A piston rod 78 is formed on the piston 72. This extends from the piston 72 in the direction of the cover 68. The piston 72 and the piston rod 78 are coaxial with the cavity 66 of the housing 64 of the pressure accumulator 62.

Coaxial with the piston 72 and the piston rod 78 there is an elongated, tubular part 80 in the cavity 66 of the pressure accumulator 62. The elongated, tubular part 80 is slid onto the piston rod 78 in a sliding connection. The elongate, tubular part 80 comprises a cylindrical end section 82 lying on its left side in FIG. 2 and a cylindrical end section 84 lying on its right side in FIG. 2. Between the two end sections 82 and 84 there is a support section 86, the outside diameter of which is larger is as the outer diameter of the left end portion 82 and the right end portion 84. The support portion 86 thus has the shape of an annular collar.

Arranged between the support section 86 and the piston 72, coaxially to the piston 72, to the piston rod 78 and to the elongate, tubular part 80, is a package 87 comprising a total of 12 plate springs 88 (for reasons of clarity, not all plate springs 88 have reference numbers). The package 87 is divided into four individual assemblies (without reference numerals) each consisting of three parallel plate springs 88. Arranged between the support section 86 and the cover 68 of the housing 64 is a package 89 composed of three parallel plate springs 90.

In the pressure-free idle state of the pressure accumulator 62 shown in FIG. 2, the plate springs 88 and 90 are relaxed. In this state, there is a free space between the left axial end of the elongated tubular part 80 in FIG. 2 and the piston 72. There is also a free space between the axial end of the elongated tubular part 80 on the right in FIG. 1 and the bottom of a recess 92 in the cover 68 of the housing 64. The plate springs 88 are generally softer than the plate springs 90. The spring travel of the package formed from the plate springs 88 is overall greater than the spring travel of the composite formed from the plate springs 90.

The hydraulic device 10 shown in FIG. 1 with the pressure accumulator 62 shown in FIG. 2 operates as follows:

The high-pressure pump 36 pumps hydraulic fluid from the reservoir 34 into the hydraulic line 38 and from there via the branch line 42 into the lower working space 44 of the hydraulic cylinder 16. When the switching valve 48 opens and the switching valve 56 is closed, the upper working chamber 52 of the hydraulic cylinder 60 is also pressurized by hydraulic fluid. In this case, since the engagement surface in the axial direction on the upper side of the piston 20 of the hydraulic cylinder 16 is larger than on its underside, the piston 20 is pressed down and the inlet valve 12 is opened.

If the switching valve 48 is closed and the switching valve 56 is opened, the upper working chamber 52 is connected to the ambient pressure via the branch line 54, as a result of which the piston 20 moves up again and the inlet valve 12 is closed. In this way, very fast opening and closing times of the intake valve 12 can be achieved without the intake valve 12 having to be mechanically actuated, for example by a camshaft of the internal combustion engine 14.

If the high-pressure pump 36 does not deliver, ie the hydraulic line 38 and the branch line 60 are depressurized, the piston 72 of the pressure accumulator 62 is in the rest position shown in FIG. In the diagram in FIG. 3, in which the path s of the piston 72 of the pressure accumulator 62 is plotted against the hydraulic pressure p, this corresponds to a position which is identified by the reference symbol 94.

If the high-pressure pump 36 is switched on, the pressure in the hydraulic line 38 and the branch line 60 rises. Since the plate springs 88 have a lower rigidity than the plate springs 90, the elongate, tubular part 80 initially remains stationary during this pressure increase, whereas the piston 72 moves in the direction of the cover 68 of the housing 64 and thereby compresses the plate springs 88. The distance between the left axial end in FIG. 2 of the elongated tubular part 80 and the piston 72 is selected such that the piston 72 then comes into contact with the elongated tubular part 80 when the minimum operating pressure PBMIN is reached. The corresponding path covered by piston 72 is SPBMIN in FIG. 3. The geometry within the pressure accumulator 62, in particular the length of the left end section 82 of the elongated, tubular part 80, is selected such that when the piston 72 comes into contact with the elongated, tubular part 80, the plate springs 88 do not yet block went.

If the pressure is increased further, the elongated tubular part 80 is moved by the piston 72 in the direction of the bottom of the recess 92 in the cover 68 of the housing 64. As a result, the plate springs 90 are deformed. Since the plate springs 90 are considerably stiffer than the plate springs 88, there is a significantly higher slope in the curve shown in FIG. 3 in this area. The distance between the right axial end in FIG. 2 of the elongated tubular part 80 and the bottom of the recess 92 in the cover 68 is selected such that when the hydraulic pressure reaches the maximum operating pressure PBMAX, the elongated tubular part 80 abuts reaches the bottom of the recess 92 in the cover 68. The length of the right end section 84 of the elongated tubular part 80 is in turn chosen such that when the elongated tubular part 80 contacts the cover 68, the springs 90 of the composite 89 are not yet completely deformed. In this case, the piston 62 has covered the maximum possible distance SPBMAX.

In the normal operating state of the hydraulic device 10, the hydraulic pressure in the hydraulic lines 38, 42, 46 and 60 is in the range between the minimum operating pressure PBMIN and the maximum operating pressure PBMAX. In this case, the pressure accumulator 62 works as a vibration damper for pressure vibrations occurring in the hydraulic fluid of the hydraulic device 10. Due to the great stiffness of the disc springs 90, even larger amplitudes of the pressure vibrations result in only a small movement of the piston 72. Therefore, the length of the package 89 of the disc springs 90 can be small, which in turn reduces the overall length of the pressure accumulator 62.

The high stiffness of the disc springs 90 also enables a reduction in the fluid volume stored in the pressure accumulator 62. This enables the desired vibration damping in the operating pressure range without impairing the system dynamics of the hydraulic device 10. By using the plate springs 90, the damping effect of the pressure accumulator 62 is also improved, since a strong friction damping occurs between the individual plate springs 90.

Compared to a conventional pressure accumulator, the pressure accumulator 62 shown in FIG. 2 is very small. In order to be able to provide vibration damping in the same operating pressure range in the case of a conventional pressure accumulator, this would have to have a significantly longer spring travel and thus a significantly greater overall length. This is shown in dashed lines in FIG. 3. The spring travel required in a conventional pressure accumulator for the same operating pressure range and the same emergency pressure properties is identified in FIG. 3 by SPBMAX '. The gain in overall length in the pressure accumulator 62 compared to a conventional pressure accumulator is the difference between SPBMAX 'and SPBMAX.

In the event of a pressure drop within the hydraulic device 10, for example due to a failure of the high pressure pump 36, iX d ω P ⁾ to <P.> - <! H m N φ α 3 co ω ^ K d = W TJ Ö P- H P <Cd ω ö? m CQ

PJ-- a rr d φ d ⁾ Φ 0 P ^ d p- Φ ti 0 = P- ^ τj Φ ^> <; tr 0 aa Φ p- t p- P ⁾ P- a P. J Ml P- Mi ü P- P Cb 3 a M d CQ cr txi P. Φ P. ω d CQ 3 a Φ Φ a P. Ω Q rr CQ P p, Φ Mi Ω d S ii HH p- Ω tr Φ P- ¹ P CD a ii tr φ D rr φ p. CD φ φ σ Φ P ⁾ ro 3 d = P- JP) Φ) pι rr? R Φ P- ^ P ⁾ a - P ⁾ Φ o P P- CD P- CQ - ii ad p- CQ Q Ω rr ^ H. d P. d P- CD CQ a 0 CQ H. P- d ii φ Φ P 3 Φ rd Ω α d 5 P p- Mi P ^J P- P- ¹ O Ό 0 Φ CQ P ⁾ CD P. CQ

P- d CD Φ P, Ω * τ- P- P ^* ca Φ 0 P Φ p- φ P- P Φ a 3 tr <! d et J P- φ aa cn H- Ξ h-> φ? P-? d CQ P- P- a Φ P. W • P- P. 3 CQ WQ ω rr Φ SD: P P- ii CD CQ N ii Ω - »Ω CQ CD Φ N ISi Mi Ω Φ ω a P ω N rr rr Φ aa li rr ro T3 d ^ φ? rt rr φ H; s: td tr p> 0 rr ÜJ ii ^■ ! Φ d = ii Q ^ P Φ a φ HP ^J a PJ ≤ p-! ^ A Φ da φ Φ - - H- o Hl P.

Ω CQ CD P- a P- φ P- tr 0 M a 0 P- P- P- rr M Ω. a 0 PJ P-

? r Ω P- P- CQ a ^ Ω aa ω Hl P ^J ω CD a CQ, ω P ^ tr P- D tr CD P rr

P- tr a Ω d P- Cd c P ^J P. Ω PJ P- cn 0 CD tr 00 P- <i Ό cn P- Φ Ω P- P P. Q P- p. tr Ω a φ> t. Φ - P ^J P .o 3 P- Φ Φ Φ 0 ii K3 φ at P ¹ a φ ts φ ^

Φ Φ P ^J Φ rX M ii CQ P- Ω P d M P- Φ rf co φ ü P- M Φ

3 P. - CD rr 3 er P tr p- Φ 3 rr t CD a Q rr d Ω s, Ml> 1 P- a CD p,

P- l- ¹ P- - Φ P- P- P ¹ Φ Φ CQ P- Φ Pα d 3 tr P- Φ P ⁾ P. 3 a P- H- ¹ P- rr P- Φ P- aa 0 σi ω CT \ CΛ P- Φ rr CD ü -0 H a Φ φ φ P "P ⁾ p- Ω P ⁾ H φ

Φ Ω ii PJ 0 rr a tSJ Φ a P rr Φ M P, cπ CQ a P P, M rr PJ tr CQ σi

P- a

Pf a O Ω Φ -α tr P O φ CD Φ Ω. Φ Φ CQ Q CQ -

3 φ d P "CQ t a 0). CD Φ J P <13 tr P- μ. CQ ^ P- M M P, Φ S" Φ <P

0) ü H p> Φ 3 - Λ Ω CD ii - d Φ rr rr ω CD Φ to P s- Mi ii CQ PP d Φ 0 P. a Mi CD J d tr P- Φ Φ CD M P- Ω rr D P. P- P- Φ d = rr PP 3 a Ω PJ ω ω 0 = rr H "rr P- Φ a P- ω 3 P- P ⁴ P- M P- α M a P. Ω Φ Φ φ rr tr w

Φ er * H φ ω ii 3 P- rr Φ CQ J 3 P, od = a P- P. Φ? H p. N P- CQ i Φ 3 3 P ⁾ P> PJ CQ H P- P- J a ⁴ Ω Φ m M Φ P- ¹ Φ <d H CD

P- tr P- p- CQ rr Ξ rr p- Ω φ Φ a Φ tr> P. P ⁾ φ aa rt P φ 0 P.

<l- 0 CQ er 3 Φ φ P- φ Φ P P- a 0 & Ö Φ tr rf Φ ß d P- - - a P ¹ ro P ¹

Φ P- H Φ Φ aa CQ P- Φ Ω i Φ P- P- a rr CQ a co P- <rr φ t s- H i ih p- CQ a ü rr Ω rr p ⁾ aa 'α 3 P φ P- Φ ∞ P- p- Φ P- p, φ tr Λ ^" CD φ P. tr φ r. CQ P. Φ P ⁾ = PJ ω MO d Ω P. Φ 3 a tr CQ P- ^ d Φ Ω ι-3 rr P- P- ii • CQ Φ 3 P. OP ⁾ Φ a "φ P- P- rr Φ P- φ rr 0 a P- tr Φ d ⁾ φ CQ P. φ CD Ü TJ Φ φ d ii rr 3 a Φ M Cd P- P- * PD

P rr P- ω P- rr J Φ M Hi a CD CQ CD Φ Φ a φ ^' Φ p. Ω P tr fO P- Mi (QHPK dd φ rrj ⁾ i P- ö ^ h- ¹ Φ Φ a 3 Φ tr PJ Φ d tu d = N CQ d cr ^ Ω a ω MS φ Φ Φ rr P- «a H "φ ii Ω aa p. 00 ^" Φ Φ d Φ ω p- P-? R CQ Φ P- PJ = ii C add CQ o φ a Φ a P 0 P ⁴

0- Q O ii P- P- CQ Mi H D CQ rr P tr CQ Φ P Ω d H H P, 3 rr CQ t \ J

Φ da Ω p. rr d = ω ⁾ Ό φ M φ P> CQ ^ ii tr Mi P ⁾ Φ CQ 0 od CD a CQ tr φ Φ a 'd Φ P- P- P ⁾ rr tr ≤ M ω Φ Φ P ta P Φ tr et Φ Q Φ Φ P h- ¹ ii HP ¹ P- CQ φ CD ^ φ Φ tr 01 O co a P. 3 rr cn JP Φ P. rf φ ü ω CQ adc P- Ω (ϋ tr CD a CQ Φ o Φ φ Φ CD P Φ φ P ¹ N tr J Prr

P- Φ a? t a CD <P. P- P- fU: ι H J P P CD s; CQ ii P Cd P • CQ d = Mi Φ CQ tr Φ J Φ rr d Ω d to

CD tr a o Φ Φ tr

CD rr Ω P- CQ Φ M Ω Φ P CD Φ ω P tr & t) O CQ P- Φ

Ω φ P- co Φ N r ω tr Φ d tr ii rr CD tö H ii φ φ P- UD? P ⁾ P. ra 3 t P rr 3 d P- 0 Φ p. P- σi J φ p- Φ P ⁾ P, H 3 O 0 Φ CD Φ Φ

P- Φ P- Q cQ P ¹ P- P f Mi P- P- s: d ω P CQ φ T) rr Φ CD d Ω CD P- <! rr Ω CD P Φ 3 o cn er d P- rr

P. φ • N M P 'T3 Φ O tr Φ P "i P DO Φ a P- CQ P?

P <Φ Φ P- a φ a H _l. d ^ P, α- J ⁾ S

P- Φ s: P- to Φ d P- Φ t φ a (> P Φ P ¹ P- ii P. a Φ

Ω 4 P- Ω 3 N P-, CQ 0 P- p- φ φ ra H t P li a ^* Φ Φ da φ CD P- taa M 3 a P φ P. Φ a H Φ rr? R rr P- Φ

H 03 Φ CQ φ * rr P CD a

CQ

H cπ

Claims

Expectations

1. Pressure accumulator (62) for pressurizing a hydraulic device (10), with which a gas exchange valve (12) of an internal combustion engine (14) is preferably actuated, with a housing (64, 68) and one in operation by a device (88, 90) preloaded piston (72), characterized in that the device (88, 90), which prestresses the piston (72) of the pressure accumulator (62), has a force-displacement characteristic curve with a gradient in a range of motion of the piston (72), which differs from the slope in another range of movement of the piston (72).

2. Pressure accumulator (62) according to claim 1, characterized in that the device which prestresses the piston (72) of the pressure accumulator (62), at least two in

Row arranged devices (88, 90) with force-displacement characteristics of different slope, which bias the piston (72) during operation.

3. Pressure accumulator according to claim 2, characterized in that the devices for biasing the piston (72) comprise at least two springs (88, 90) arranged in series, the stiffness of one spring (88) being different from that of the other spring (90 ) differs.

4. Pressure accumulator (62) according to claim 3, characterized characterized in that the pressure accumulator (62) has an elongated part (80) with two end sections (82, 84) and a support section (86) arranged between the end sections (82, 84), which has a larger outer dimension than the end sections (82, 84) and on which two adjacent springs (88, 90) are supported, the one spring (88) in operation between one side of the support section (86) and the piston (72) and the other spring (88, 90) between the other side of the support section (86) and a housing section (68) is tensioned.

5. Pressure accumulator (62) according to one of claims 3 or 4, characterized in that at least two stops are provided which prevent the springs (88, 90) from being tensioned on a block during operation.

6. Pressure accumulator according to claims 4 and 5, characterized in that the length of the elongated part (80) is matched such that the one axial end of the elongated part (80) has a stop with a housing section (68) of the pressure accumulator (62) and the other axial end of the elongate member (80) abuts the piston (72).

7. Pressure accumulator according to one of claims 3 to 6, characterized in that at least one of the springs

(88, 90) is a disc spring.

8. hydraulic device (10) for actuating a gas exchange valve (12) of an internal combustion engine (14), in particular a motor vehicle, with a fluid reservoir (34), a fluid pump (36), a fluid line (38, 42, 44, 54, 60), a pressure accumulator (62) connected to the fluid line (38, 42, 44, 54, 60) with a housing (64, 68) and one in operation by a device (88, 90) biased piston (72), and with an actuating device (16) which is connected to the fluid line (38, 42, 44, 54, 60) via a valve device (48, 56) and actuates the gas exchange valve (12), characterized in that that the pressure accumulator (62) is designed according to one of the preceding claims.