DE102006034920A1 - Reverse spring hydraulic valve clearance compensation unit e.g. roller tappet, for valve drive of internal combustion engine, has valve closure body that fills available space of closure body cap - Google Patents

Abstract

The compensation unit e.g. hydraulic tappet (1), has a valve closure body (7) that is formed as an acicular elongated sealing piston, and a plate-shaped sealing surface provided at a valve seat proximal end of the closure body. The sealing surface cooperates with a correspondingly formed sealing surface (25) of a valve seat (24). A contact surface is provided at a valve seat distal end of the closure body for hydraulic admission flow. The valve closure body fills an available space of a closure body cap (9).

Description

Field of the invention

The The invention relates to a hydraulic valve clearance compensation element for one Valve train of an internal combustion engine, for example for a motor vehicle, with a piston, which is movably guided in a piston housing and supported elastically against this is, in which the piston has a low-pressure space, which has a axial opening in a piston bottom with one of the piston housing and the piston limited High-pressure chamber is connected, and with an effective between the pressure chambers Control valve, comprising a valve closing body, the one on the axial opening a valve seat surrounding the piston bottom underside can be applied in a sealing manner is and in a closing body cap is taken, the cap base as a stroke limiter of the valve closing body effectively is, as well as a valve spring in the opening direction acting on the control valve spring, wherein the valve closing body via a Pressure build-up in the high-pressure chamber during a collapse movement between the piston and the piston housing against a biasing force of the control valve spring in the closing direction hydraulically acted upon.

Background of the invention

hydraulic Valve lash adjusters are used in valve trains of internal combustion engines used in motor vehicles to a valve clearance, which is by thermal expansion, Manufacturing tolerances and wear of the transmission elements in a Cam application to a gas exchange valve results automatically compensate. Usual compensation elements use it in a respective mechanical transmission link that has a cam lobe of the cam on the gas exchange valve transmits a piston in one Housing with guided a sealing game movable is and elastically supported against this by means of a piston spring, so that by a voltage of the piston spring no play on the gas exchange valve arises. The power transmission over the Compensation element on the gas exchange valve is at the Nockenbeaufschlagung controlled by a control valve, which is a flow of hydraulic medium via a axial opening between one as an oil reservoir serving low pressure space of the piston and a high-pressure chamber, the from the hoist and the housing is enclosed controls. The control valve usually includes a closing body with a spherical one or spheroidal Sealing surface usually a control valve ball, which is on a piston underside in the high-pressure chamber is arranged, as well as a control valve spring, which the control valve ball acted upon with a force. In this case, as explained below, basically two Different types of construction.

In a standard construction is the control valve spring as a closing urging member arranged, which the control valve ball with a biasing force against a valve seat of the axial bore formed as a piston bore the piston bottom underside presses. Accordingly, the control valve of the compensation element is when driving over of the associated Valve drive member through the cam of a rotating camshaft, closed in a cam base circle. At a following deflection the piston by a cam lobe is a corresponding travel with a force directly above transferred the compensation element to the gas exchange valve and this actuated directly, ie open. Because the oil is incompressible in the high pressure chamber, the compensation element acts like a "rigid" actuator at the subsequent regression the piston in the housing, when the cam reaches the base circle again and the pressure in the High pressure room sinks, opens that Control valve against the force of the control valve spring and it takes place a pressure equalization between the pressure chambers until the control valve spring the control valve closes again. As it is in this construction, especially during an incipient warm-up hare in still cold engine, to a so-called inflating the compensation element on the Control valve, so can lead to a negative valve clearance, which leads to high engine loads with increased wear is already an alternative design with opening control valve spring been proposed.

Such hydraulic valve lash adjusters with opening control valve spring are known as Reverse Spring Hydraulic lash adjusters (RSHVA) or Normally Open Lash Adjuster (NOLA), for example from the EP 1 298 287 A2 and the WO 2006 010 413 A1 , known. In this case, the control valve spring is reversely arranged, usually within the piston bore between reservoir and high pressure chamber, so that the control valve ball or the closing body is acted upon in the opening direction with a spring force and consequently the control valve is open in the cam base circle. In this arrangement, the control valve ball is usually accommodated in a closing body cap which is held on the bottom of the piston bottom and has opening slots as an oil passage for the control oil and a bottom for limiting the stroke of the control valve ball.

In the case of an RSHVA, with the cam deflection, a control oil flow from the high-pressure chamber to the low-pressure chamber in the closing direction first sets in, with the compensating element collapsing, that is, the piston and the housing being pushed together. In this case, the control valve ball of the STEU flows around it, whereby it is applied both hydrostatically and hydrodynamically against the action of the control valve spring with a force until a resulting axial force presses the control valve ball against the valve seat and the control valve closes. The collapsing movement of the RSHVA manifests itself in a characteristic idle stroke before the actual operation of the gas exchange valve takes place. RSHVAs therefore act as "soft" control elements, which rule out a negative valve clearance.

Of the Leerhub the RSHVAs affects the valve lift of the gas exchange valves as well as the valve timing in the internal combustion engine. A corresponding speed-dependent Leerhub characteristic can specifically in a valve or camshaft control to improve the thermodynamic efficiency, to reduce exploited the pollutant emissions and to improve the idle quality become.

• – von der Strömungsgeometrie, die durch die Steuerventilbauteile, insbesondere durch die Ventilkörpergeometrie und die Ventilsitzgeometrie bestimmt ist, sowie von Strömungshindernissen und Strömungsumlenkungen im Strömungsweg zwischen den Druckräumen,
• – von eingeschwemmten Kontaminationen (Abrieb, Verunreinigungen, Fremdkörper) im Steueröl beziehungsweise Motoröl,
• – von dem Volumenverhältnis von Hochdruckraum zu Ölreservoir,
• – von der konstruktionsbedingten so genannten hydraulischen Steifigkeit des Ausgleichselementes,
• – von räumlichen Verlagerungen des Schließkörpers und/oder der Steuerventilfeder innerhalb der Aufnahmen dieser Bauteile des Ausgleichselementes im Betrieb, und
• – von Fertigungs- und Materialtoleranzen.

The advantages of the RSHVA design are contrasted with its relative temperature and production tolerance-sensitive operating behavior. In particular, the hydrodynamics of such a compensation element is difficult to determine by a relatively complex geometry of the control valve components, which influences the oil transfer between the pressure chambers. Studies have shown that over the entire engine oil temperature range of -25 ° C to + 160 ° C, a significant oil viscosity dependence of the closing behavior of the control valve occurs. The function of an RSHVA is therefore dependent on the individual

• The flow geometry, which is determined by the control valve components, in particular by the valve body geometry and the valve seat geometry, as well as flow obstacles and flow deflections in the flow path between the pressure chambers,
• - of contaminated contaminants (abrasion, impurities, foreign bodies) in the control oil or motor oil,
• From the volume ratio of high-pressure chamber to oil reservoir,
• - of the design-related so-called hydraulic rigidity of the compensating element,
• - Of spatial displacements of the closing body and / or the control valve spring within the recordings of these components of the compensation element in operation, and
• - of manufacturing and material tolerances.

Thereby conditionally, can in this clearance compensation element type comparatively large fluctuations in performance occur during operation, resulting in Leerhub- and closing time fluctuations and in an undesirable temperature-dependent Express closing behavior, and Thus, the actual benefits of RSHVAs can limit or make them at least more difficult to use. An essential goal The advancement of RSHVAs is therefore such disturbing or to minimize difficult-to-control parameters.

The DE 10 2004 018 457 A1 shows a RSHVA with different closing body geometries and guide aids for guiding the respective closing body in a respective closing body cap. Accordingly, the valve closing body may be formed, inter alia, as a so-called needle, which is formed by a prolonged with a circular cylindrical spacer ball. Furthermore, the valve closing body may have a spherical cap as a sealing surface and / or a flattened cap bottom side end. As guide means may be provided, inter alia, step-shaped recesses, cylindrical guide surfaces, centric guide lugs or Führungsseindenkungen and circular cylindrical pins on the mutually corresponding Schließkörper- and valve cap designs. By the guide means in particular unfavorable twists and lateral displacements of the valve closing body are prevented. In this case, the valve closing body is enclosed with guide play by a parallel to the axis of the RSHVA extending cylindrical guide surface. This also causes the acting oil flow predominantly hydrostatic acts, so that the valve closing body is moved linearly like a piston.

Of the The focus of this document is to create an RSHVA, in which by a guided hydrostatic axial loading of the valve closing body undesirable eccentric Displacements and rotational movements, in particular caused by unguided hydrodynamic flow charges, be prevented. The well-known RSHVA indicates accordingly improved, less fluctuation-prone operating behavior. It However, there are no indications for further optimization the initially explained Influencing factors.

Object of the invention

Of the Invention has for its object to provide a RSHVA, in the disadvantages described above are largely avoided, in particular undesirable Fluctuations in operation are further reduced, and at the same time constructively simple and inexpensive is and a reliable one Operation guaranteed.

Summary of the invention

The invention is based on the finding that in a hydraulic valve clearance compensation element in the reverse-spring construction, with the help of a Ventilschließköpers, the free volumes in the high-pressure chamber and difficult to determine hydrodynamic flow effects and reduces which has a simple valve seat geometry, a more stable, especially temperature-resistant operating behavior can be achieved.

The The invention is therefore based on a hydraulic valve clearance compensation element for a valve train an internal combustion engine, in particular for a motor vehicle, with a Piston in a piston housing movably guided and is elastically supported against this, wherein the piston having a low pressure space, which via an axial opening in a piston bottom with one of the piston housing and the piston limited High-pressure chamber is connected, and with an effective between the pressure chambers Control valve, comprising a valve closing body, the one on the axial opening a valve seat surrounding the piston bottom underside can be applied in a sealing manner is and in a closing body cap is taken, the cap base as a stroke limiter of the valve closing body effectively is, as well as a valve spring in the opening direction acting on the control valve spring, wherein the valve closing body via a Pressure build-up in the high-pressure chamber during a collapse movement between the piston and the piston housing against a biasing force of the control valve spring in the closing direction hydraulically acted upon.

moreover is according to the invention provided that the valve closing body as a needle-shaped elongated Sealing piston is formed, the valve seat near the end of a plate-shaped, substantially flat sealing surface having, with a correspondingly formed sealing surface of the Valve seat cooperates, and its valve seat remote end an attack surface for having hydraulic loading, wherein the valve closing body a Volume of the surrounding him closing body cap largely fills.

By this structure with a high pressure space-reducing valve closing body is advantageous a simpler hydraulics and a less sensitive closing behavior of the compensation element achieved. With a valve closing body, the is designed as a sealing piston, with a body shape comparable to one so-called valve needle, but functionally with a plate-shaped sealing element acting, will for the control valve the simple valve seat geometry of a valve plate - instead as usual a valve ball or a valve cone - with a simultaneous, extensive reduction of a free dead space volume of the closing body cap connected.

The Reduction of the dead space of the closing body cap improves the so said hydraulic rigidity of the clearance compensation element. This is an important design feature of a power transmission device with hydraulic components, especially in power transmission a cam follower on a gas exchange valve, in the previous Reverse spring control valve designs tend to go unnoticed is. For the hydraulic stiffness prevail is the relationship a pressure space volume to a pressure transmitting surface. These relationship is achieved by reducing the dead space volume of the closing body cap through the needle-shaped Closing member in operative connection with its comparatively large plate-shaped sealing surface significantly improved in favor of hydraulic rigidity, so that total the hydraulic rigidity of the RSHVA of advantageous rigidity a purely mechanical transmission element approaches.

Farther reduces advantageously by replacing the conventional Ball valve seat geometry through the particularly simple, manufacturing tolerance insensitive and robust plate valve seat geometry the viscosity dependence the closing behavior of the control valve.

Of the Sealing piston does not work during closing by flowing around with control oil by a hydrodynamic admission as in the conventional Valve ball lifted off the cap bottom of the closure cap, but predominantly by a hydrostatic pressure on an attack surface on the cap bottom side End, the necessary axial closing force the control valve generates. The closing body is therefore essentially by the hydrostatic pressure and less by the acceleration of the oil flow at the flow in driven the high-pressure chamber.

The attack surface may be advantageous as a circumferential chamfer at the valve seat remote end formed of the valve closing body be over an oil passage in the closing body cap hydraulically can be acted upon. The sealing piston can be inexpensive in a conventionally trained and Be arranged on the piston crown fastener cap.

in the The result is the flat sealing geometry of the valve seat and the predominantly hydrostatic actuation of the closing body cap largely filling Closing body resulting more stable closing and idle stroke behavior of the RSHVA across from Temperature and oil viscosity changes as well as opposite Manufacturing tolerances achieved.

In addition, it can be provided that the Valve-closing body is guided with a guide clearance in the closing body cap. Since the sealing piston according to the invention in any case largely fills the cap, whereby its circumference preferably extends adjacent to the inner wall of the closing body cap, an automatic centering is advantageously achieved by the guide with a guide play and ensures a high tilting stability of the closing body.

Next this simplest leadership opportunity, can on the valve closing body and / or on the closing body cap Of course also more expensive guide means with a higher one guidance accuracy or extended leadership functions arranged as an anti-tip device and / or as a centering device and / or as an anti-rotation of the valve closing body are effective. In particular, an additional Anti-rotation of the closing body can be beneficial to unwanted Rotational movements of the closing body in Safe operation.

The tilting stability can be advantageously increased by the fact that the valve seat remote, cap bottom end of the valve closing body at least in a central region form-fitting adapted to the cap floor. There will be no unnecessary dead space released. In addition, thereby in the open valve state of the closing body the control valve spring is laid flat on the cap floor, which as a stroke limit of the control valve is used. This results a uniform opening gap at the valve seat, through which a perfect opening and closing function or a uniform oil transfer the control valve is supported.

Farther it can be provided that in the valve closing body a contamination collecting device is trained. about the oil supply of the oil reservoir (Low pressure space) can finest impurities, for example by abrasion, manufacturing residues and unclean oil, into the RSHVA, which lead to functional fluctuations or malfunctions or reinforce them. By a contamination catcher can be so conditional undesirable influences largely exclude.

A advantageous contaminant catcher may be considered a coaxial to the axial opening arranged, open at the valve seat near the end of the valve closing body Recess formed in the valve closing body be. Particularly simple and effective is a hole as in the closing body introduced, comparatively deep cylindrical collecting bag, the purged particles receives. In a bottom-side depression of the recess can be Collect these particles particularly safely, so they barely recycle get into the oil circuit can. On more expensive, upstream in low-pressure chamber, or filter As a rule, particle separators can be dispensed with. additionally The catch function of contaminants is through the recess reduces the weight of the valve closing body.

Brief description of the drawings

The Invention will be described below with reference to the accompanying drawings on some embodiment explained in more detail. In this shows

1 a section of a RSHVA with a control valve according to the invention in a longitudinal section in the open position, and

2 a longitudinal section of a valve closing body of the RSHVA according to 1 on a larger scale.

Detailed description the drawings

This in 1 RSHVA shown is advantageous as a hydraulic ram 1 , For example, a bucket tappet or a roller tappet, a valve train of an internal combustion engine formed in a motor vehicle.

The pestle 1 has a cylindrical piston 2 on that in a piston housing 4 is guided axially movable with a sealing play. Inside the piston 2 a cylindrical recess forms a low-pressure space or an oil reservoir 3 , which is supplied via an unillustrated feed with control oil. In an end-side piston bottom 19 of the piston 2 is a centric piston bore 26 arranged, which is the low pressure room 3 with one through the piston crown 19 and the case 4 limited high pressure room 5 combines. The axial opening 26 is through a control valve 6 beauschlagbar that a control oil exchange between the two pressure chambers 3 and 5 controls.

The control valve 6 comprises a valve closing body designed according to the invention 7 a control valve spring formed as a helical compression spring 8th and a closing body cap 9 , The control valve spring 8th supports the low pressure room 3 towards a support surface 27 the piston bore 26 from and acts in the opening direction, ie the high-pressure chamber 5 towards the valve closing body 7 with a spring force.

The valve closing body 7 is enlarged for clarity in the 2 shown. It is designed as a cylindrical sealing piston, the valve seat-side end of a plate-shaped sealing surface 10 having. At its valve far end is the closing body 7 in a middle area 11 plan educated. The middle area 11 is surrounded by a circumferential chamfer, which is an attack surface 12 for the tax oil forms. Furthermore, a contamination catcher 13 provided, which is advantageous as a cylindrical, valve seat-side, central bore in the valve closing body 7 , with a bottom-sided depression 14 is formed and optionally via the oil reservoir 3 collects and stores contaminated impurities.

The closing body cap 9 has a collar-shaped cap flange 15 on, with which they are at the bottom 28 of the piston crown 19 in a to the front end of the piston crown 19 towards slightly tapered circular recess 16 , is advantageously held by a clamp connection. Between the cap flange 15 the closing body cap 9 and a caseback 18 of the housing 4 is supported by a trained as a helical compression spring piston spring 20 from.

The valve closing body 7 is in the closing body cap 9 guided with a radial guide play, which except for one by the bevel 12 subject area 17 for oil intake and a small remaining free volume in the area of the cap flange 15 from the closing body 7 is filled. Accordingly, a free space volume of the high-pressure chamber 5 around that of the closing body 7 reduced volume of space. The oil intake area 17 is over a cap oil passage 23 , For example, one or more slot-shaped openings in the side wall region of the closing body cap 9 , over the outer part of the high-pressure chamber 5 , with control oil, essentially for hydrostatic loading of the attack surface 12 , feedable.

In the in the 1 shown open valve state is the valve closing body 7 through the preloaded control valve spring 8th against a cap ground 21 the closing body cap 9 pressed, causing its center area 11 positive fit plan to the cap bottom 21 is applied. The cap ground 21 acts as a stroke limiter for the closing body 7 in the opening direction of the control valve 6 , This will be the width of an opening gap 22 or a Schließkörperhub the control valve 6 certainly. This position corresponds to a camshaft position in the cam base circle.

When acted upon by a cam lobe of a cam of the rotating camshaft of the internal combustion engine, the piston 2 and the case 4 pushed together, causing the RSHVA ram 1 initially generates a free-stroke. In doing so, oil flows over the opening gap 22 and the piston bore 26 in the low pressure room 3 , At the same time it builds in the high pressure room 5 an increasing hydraulic pressure on the valve closing body 7 or its attack surface 12 essentially hydrostatically charged and against the action of the control valve spring 8th to one with the plate-shaped sealing surface 10 of the closing body 7 corresponding plane sealing surface 25 a valve seat 24 applies, so that the control valve 6 closes. As a result, the further mechanical loading by the cam on the now incompressible high-pressure chamber 5 transferred to the gas exchange valve to be operated and this opened.

With the further rotation of the camshaft, the cam returns with respect to the plunger 1 back into the cam base circle, so that the gas exchange valve closes. The piston spring 20 pushes the piston 2 and the case 4 so far apart, until no more play between the plunger 1 and the camshaft or the cam is present. The pressure in the high-pressure chamber drops 5 and the control valve 6 opens, leaving control oil in the high pressure room 5 can flow in.

1

hydraulic tappet

2

piston

3

Low pressure room, oil reservoir

4

piston housing

5

High-pressure chamber

6

control valve

7

Valve closing body

8th

Control valve spring

9

Closing body cap

10

Closing body sealing surface

11

mid-range

12

attack surface

13

Contamination catcher

14

depression

15

cap flange

16

Kolbenbodenausnehmung

17

Oil pickup area

18

caseback

19

piston crown

20

piston spring

21

cap base

22

Opening gap, Schließkörperhub

23

Cap passage

24

valve seat

25

Valve seat sealing surface

26

axial opening piston bore

27

support surface

28

Piston crown underside

Claims (10)

Hydraulic valve clearance compensation element for a valve train of an internal combustion engine, for example for a motor vehicle, with a piston ( 2 ) housed in a piston housing ( 4 ) is movably guided and elastically supported against this, in which the piston ( 2 ) a low-pressure space ( 3 ), which via an axial opening ( 26 ) in a piston bottom ( 19 ) with one of the piston housing ( 4 ) and the piston ( 2 ) limited high-pressure space ( 5 ) and with one between the pressure chambers ( 3 . 5 ) effective control valve ( 6 ), comprising a valve closing body ( 7 ), which at one the axial opening ( 26 ) on a piston bottom ( 28 ) surrounding valve seat ( 24 ) is sealingly applied and in a closing body cap ( 9 ) whose cap bottom ( 21 ) as a stroke limiter of the valve closing body ( 7 ) is effective, as well as a valve closing body ( 7 ) acting in the opening direction control valve spring ( 8th ), wherein the valve closing body ( 7 ) via a pressure build-up in the high-pressure chamber ( 5 ) during a collapse movement between the piston ( 2 ) and the piston housing ( 4 ) against a biasing force of the control valve spring ( 8th ) is hydraulically acted upon in the closing direction, characterized in that the valve closing body ( 7 ) is formed as a needle-shaped elongated sealing piston whose valve seat near the end of a plate-shaped sealing surface ( 10 ), which with a correspondingly formed sealing surface ( 25 ) of the valve seat ( 24 ) and whose valve seat remote end has an attack surface ( 12 ) for hydraulic actuation, wherein the valve closing body ( 7 ) a volume of space surrounding the closing body cap ( 9 ) largely fills. Hydraulic valve clearance compensation element according to claim 1, characterized in that the valve closing body ( 7 ) with a guide play in the closing body cap ( 9 ) is guided. Hydraulic valve clearance compensation element according to claim 1 or 2, characterized in that on the valve closing body ( 7 ) and / or on the closing body cap ( 9 ) Guide means are arranged or formed. Hydraulic valve clearance compensation element according to claim 3, characterized in that the guide means as a tilt protection and / or as a centering means and / or as a rotation of the valve closing body ( 7 ) are effective. Hydraulic valve clearance compensation element according to at least one of claims 1 to 4, characterized in that the valve seat remote, cap bottom end of the valve closing body ( 7 ) at least in a central area ( 11 ) positively to the cap bottom ( 21 ) is adjusted. Hydraulic valve clearance compensation element according to at least one of claims 1 to 5, characterized in that the attack surface ( 12 ) as a circumferential chamfer at the valve seat remote end of the valve closing body ( 7 ) is formed, which via an oil passage ( 23 ) in the closing body cap ( 9 ) is hydraulically acted upon. Hydraulic valve clearance compensation element according to at least one of claims 1 to 6, characterized in that in the valve closing body ( 7 ) a contaminant catcher ( 13 ) is trained. Hydraulic valve clearance compensation element according to claim 7, characterized in that the contamination collecting device ( 13 ) as one coaxial with the axial opening ( 26 ) arranged on the valve seat near the end of the valve closing body ( 7 ) open, recess in the valve closing body ( 7 ) is trained. Hydraulic valve clearance compensation element according to claim 8, characterized in that the recess as a cylindrical Collection bag is formed. Hydraulic valve clearance compensation element according to claim 8 or 9, characterized in that the recess has a bottom-side depression ( 14 ) having.