EP3071805A1

EP3071805A1 - Hydraulic valve drive of an internal combustion engine

Info

Publication number: EP3071805A1
Application number: EP14793777.5A
Authority: EP
Inventors: Steve Beier; Arno BÄCHSTÄDT; Hendrik THOMANN
Original assignee: Schaeffler Technologies AG and Co KG
Current assignee: Schaeffler Technologies AG and Co KG
Priority date: 2013-11-22
Filing date: 2014-10-08
Publication date: 2016-09-28
Anticipated expiration: 2034-10-08
Also published as: US20180230868A1; US9957856B2; EP3071805B1; US20160273420A1; US10247061B2; CN105765181A; DE102013223926A1; CN105765181B; WO2015074652A1; DE102013223926B4

Abstract

The invention proposes a hydraulic valve brake (14) for a hydraulic valve drive of an internal combustion engine. The valve brake comprises a housing (19) with a housing wall (17) and with a housing base (20), and comprises a piston (6) which moves axially in the housing and one end side of which, together with the housing wall and the housing base, delimits a hydraulic pressure chamber (21) and the other end side of which actuates a gas exchange valve (2). The housing wall is extended through in the region of the pressure chamber (21) by one or more flow transfer openings (24, 25), the opening cross sections of which are controlled by a control edge (25), which delimits the end side at the pressure chamber side, of the piston. In this case, it is the intention for the axial distance (h) between the control edge of the piston, when the latter is fully retracted into the housing, and the housing base to be set by means of a spacer (26) of predetermined thickness (d).

Description

Hydraulic valve train of an internal combustion engine

The invention relates to a hydraulic valve brake for a hydraulically variable valve train of an internal combustion engine. The hydraulic valve brake comprises a housing having a housing wall and a housing bottom, a piston extending axially in the housing, whose one end side bounds a hydraulic pressure chamber with the housing wall and the housing bottom and whose other end actuates a gas exchange valve, wherein the housing wall in the region of the pressure chamber of a or several overflow openings is interspersed, the opening cross-sections are controlled by a pressure chamber side end limiting the control edge of the piston.

The invention also relates to an internal combustion engine with a hydraulic valve train having such a hydraulic valve brake.

Background of the invention

An integral part of hydraulically variable valve trains, which operate according to the lost-motion principle and in which between the drive side, usually the cam of a camshaft, and the output side, ie the gas exchange valve, a so-called hydraulic linkage with variable Absteuerbarem hydraulic volume, is a hydraulic valve brake that controls the touchdown speed of the closing gas exchange valve independently of the cam position and limits it to preset values that are acoustically and mechanically acceptable. Hydraulic valve trains, each with a generic hydraulic valve brake, are known, for example, from US Pat. No. 6,550,433 B2 and from EP 0 507 521 A1. In such a valve brake, the pressure chamber, which decreases with closing gas exchange valve, is relieved of pressure via one or more overflow openings which run laterally in the housing wall and increasingly reduce their opening cross-sections from a pressure chamber-side control edge of the piston entering the housing become. Since the components of the hydraulic valve brake can not be economically produced with arbitrarily high precision, component tolerances remain, which result in different brake characteristics even within a single production lot. The change of charge with gas exchange valves, which close at the same operating point with mutually different Hubverläufen to different crank angles with respect to the Kolbentotpunkte, but affects the performance and emissions behavior of the internal combustion engine.

Object of the invention

The present invention has for its object to provide with simple structural means Vorraussetzungen for an improved performance of an internal combustion engine with hydraulic valve train and a hydraulic valve brake of the type mentioned.

Summary of the invention

This object is achieved in that the axial distance of the control edge of the retracted completely in the housing piston is adjusted to the housing bottom by means of a spacer of predetermined thickness. This setting significantly reduces and ideally eliminates the effects of component tolerances that significantly affect the brake characteristics of the valve brake. Because shortly before the placing of the gas exchange valve whose delay curve at constant hydraulic fluid viscosity is highly dependent on the course of coverage of the controlled by the piston control edge opening cross-sections in the housing wall. The axial distance between the piston control edge and the housing bottom (or a housing part which is fixed relative to the housing bottom) in a reference point, ie, when the piston is fully retracted, now effects a displacement of the overlap characteristic that corresponds to the predetermined thickness of the spacer in such a way that the hydraulic valve brakes all or in Batches have the same or a sufficiently similar delay curve. Valve brakes set in accordance with the invention are suitable not only for valve trains with (automatic) hydraulic valve clearance compensation, but also for valve drives with (manual) mechanical valve clearance compensation, in which case large motors with hydraulically variable valve train are in focus in the latter case. In the case of the mechanical valve clearance adjustment, the overlap profile of the piston control edge and opening cross-section (s) merely has an offset around the (uniformly set) valve clearance. Because in this case, the piston and the decisive for the axial distance housing bottom are spaced around the valve clearance when the gas exchange valve closes.

The adjustment of the axial distance between the piston control edge and the housing bottom can be done in various ways. In particular, an adjustment is provided in discrete thickness graduations of the spacer, wherein the respective thickness is predetermined as a result of a previous test or measurement of the delay course of the unadjusted valve brake and accordingly removed the spacer of a group sorting and paired with the valve brake. The spacer can then be joined either firmly to the housing or fixed to the piston. The spacer causes in the path-time course of the retracting into the valve brake piston, that the cross sections of the overflow openings are covered only at a larger piston travel of the piston control edge. The term "spacer" is not necessarily limited to a single part, but may also include a group of two or more parts, which are then summed up as stacks of the predetermined thickness. Due to the variety of possible combinations, the group sorting can be limited to a few individual thicknesses and, in the limiting case, to a single thickness in this case.

In an alternative embodiment, the spacer may be integrally formed as a non-separate part as a projection of the piston on the pressure chamber side end face or as a projection of the housing on the housing bottom. The axial distance can then be adjusted by machining the projection thickness. Compared to the aforementioned embodiment with joined Dis- Dancing piece causes a shortening of the projection by the predetermined thickness, that in the path-time course, the opening cross-sections are already covered by the piston control edge at a smaller piston stroke and that, accordingly, the valve brake is, so to speak, "slower".

Brief description of the drawings

Further features of the invention will become apparent from the following description and from the drawings, in which the invention is explained in principle and with reference to an exemplary designed valve brake. Unless otherwise stated, the same or functionally identical features or components are provided with the same reference numbers. Show it:

Figure 1 is a schematic representation of a hydraulically variable valve drive according to the prior art;

Figure 2 is a schematic representation of a hydraulic valve train with mechanical valve clearance compensation and inventive valve brake;

Figures 3, the un-adjusted valve brake according to Figure 2 in different

Piston positions in the basic measurement of the braking characteristic;

Figure 4 is a schematic diagram for the dimensional predetermination and assignment of a spacer;

Figure 5 shows the valve brake according to Figures 2 and 3 in an enlarged view; FIG. 6 shows a simplified diagram for the check of the set valve brake;

FIG. 7 is a longitudinal sectional view of the assembled valve brake in a constructive embodiment; tion;

Figure 8 shows the housing according to Figure 7 as a single part in longitudinal section; 9 shows the detail Z according to FIG. 7

Detailed description of the drawings

Figure 1 shows the basic structure of a known hydraulic valve drive for variable-stroke actuation of a valve spring 1 in the closing direction kraftbeaufschlagten gas exchange valve 2 in the cylinder head 3 of an internal combustion engine. The following components are shown:

a master piston 5 driven by the cam 4 of a camshaft,

a slave piston 6 'actuating the gas exchange valve,

a 2-2-way electromagnetic hydraulic valve 7,

a high-pressure space 8 delimited by the master piston and the slave piston, from which hydraulic fluid can flow out into a medium-pressure space 9 when the hydraulic valve is open,

a piston pressure accumulator 10 connected to the medium pressure space,

a non-return valve 1 1 opening in the direction of the medium-pressure space, via which the medium-pressure space is connected to the lubricant circuit of the internal combustion engine,

- And serving as a hydraulic fluid reservoir low-pressure chamber 12 which is connected via a throttle 13 to the medium-pressure space and the contents of which is immediately available during the starting process of the internal combustion engine.

The variability of the valve lift is generated by the fact that the high-pressure space 8 between the master piston 5 and the slave piston 6 'acts as a so-called hydraulic linkage, the hydraulic volume displaced by the master piston proportional to the stroke of the cam 4, neglecting leaks, depending on the Opening time and the opening duration of the hydraulic valve 7 in a first, the slave piston acting on sub-volume and in a second, in the medium-pressure chamber 9 including piston accumulator 10 and in the low-pressure chamber 12 outflowing partial volume is split. As a result of the thus decoupled movement of the gas exchange valve 2 from the movement of the cam, the stroke transmission of the master piston to the slave piston and thus not only the control times, but also the lift height of the gas exchange valve can be fully variably adjusted within the elevation of the cam.

The slave piston 6 'is equipped with a hydraulic valve brake 14', which reduces the contact speed of the closing gas exchange valve 2 decoupled from the movement of the cam 4 to a mechanically and acoustically acceptable level. In the illustrated embodiment of principle, the valve brake is a throttle gap, which is formed during the final closing phase of the gas exchange valve by the overlap of a cylindrical projection 15 on the pressure chamber side end face of the slave piston with an overflow 16 which extends concentrically to the slave piston housing wall 17 ' ,

Figure 2 shows the slave side of a hydraulically variable valve train of a large engine, the gas exchange valves 2 are actuated via rocker arm 18 with mechanical valve clearance compensation. The highly schematic representation is with respect to the valve train on the hydraulic valve brake 14 with housing 19 and slave piston, hereinafter referred to as piston 6, reduced. The hollow-cylindrical housing with a housing wall 17 and a housing bottom 20 serves to guide the piston traveling axially therein, one end of which with the housing wall and the housing bottom defining a hydraulic pressure chamber 21. The other end of the piston actuates the gas exchange valve 2 by means of the mechanical valve clearance compensation device in the form of a valve clearance adjustment screw 22 in the rocker arm.

In the housing wall 17, overflow openings 23 and 24, via which the pressure chamber 21 communicates with the sensor-side hydraulic system (not shown here) run (see FIG. 1). The overflow opening 23 serves with a relatively large opening cross-section as the main flow opening, via which, when the piston 6 moves in and out, the lowest possible volume flow reaches and leaves the pressure chamber. The overflow opening 24 forms with a relatively small opening A cross section of the flow restrictor, over which the pressure chamber in the final closing phase of the gas exchange valve 2 can relieve only under significant delay of the retracting piston. The control of the opening cross-sections via a control edge 25 of the piston, which is formed in the simplified representation by the peripheral edge between the outer surface of the piston and the pressure chamber side end face.

The illustration shows the piston 6 in fully retracted in the housing 19 position in which the piston during the valve clearance adjustment on the between see the adjusting screw 22 and the valve-side end face of the piston measured valve clearance L is. In the operating state of the internal combustion engine, however, the valve clearance is largely or completely shifted to the pressure chamber side end side. The axial distance between the piston control edge 25 and the housing bottom 20 is adjusted according to the invention by means of a spacer 26, which influences the deceleration curve of the retracting into the housing piston so that all valve brakes of the internal combustion engine have substantially the same braking characteristics and that accordingly all gas exchange valves 2 of the internal combustion engine close with about the same stroke course.

The determination of the spacer thickness d required for the axial distance h to be set takes place as explained below with reference to the schematic figures 3 to 6. FIGS. 3a-c show the (still) unadjusted hydraulic valve brake 14 with three different retraction positions of the piston 6 during the basic measurement of the course of movement s (t). In this measurement taking place under oil, the temporal stroke course of the piston acted upon by a defined force is detected until it reaches the housing bottom 20. The measurement starts at the stroke s = m and ends at s = 0 when the piston touches down on the case back.

The measurement result is shown very simplified in Figure 4 based on the curve with thick line width. The upper branch of the curve with a large gradient, ie with a comparatively high closing speed of the gas exchange valve 2 3a corresponds to the piston position in Figure 3a until the pressure chamber 21 can still largely unrestricted over the main flow opening 23 relieve. The subsequent branch of the curve with medium gradient, ie with a comparatively average closing speed corresponds to the piston position in Figure 3b, wherein the piston control edge 25, the main flow opening already completely covered and the pressure relief mainly only via the throttle flow opening 24 takes place. The lower curve branch with a small gradient, ie with low closing speed corresponds to the piston position in Figure 3c, wherein the piston control edge completely covers both the main flow opening and the throttle flow opening and the pressure relief only via leakage gaps and ggfls. Further, not shown here Drosselstromöffnun- conditions in the housing bottom 20 is carried out.

The predetermination of the spacer thickness d, which in the schematic representation according to FIG. 5 is identical to the axial distance h, now takes place by means of the reference curves drawn in FIG. 4 with thin line thickness. These represent different "fast" valve brakes, which in the figure from left to right increasingly require more time for the measuring path s = m and consequently become "slower" in this direction. Each reference curve is associated with a spacer 26 of individual thickness d, the reference curves corresponding to increasing thicknesses from left to right. The reference curve with the greatest agreement with the previously measured course of movement of the valve brake 14 (curve with thick line width) determines the individual thickness of this valve brake and thus the selection of a spacer to be paired with this thickness from a group sorting. In this case, the measured curve of a relatively "slow" valve brake is more in line with one of the right reference curves, so that this valve brake is assigned a spacer with a greater thickness than a relatively "fast" valve brake, which more closely matches one of the left reference curves and their course of motion already closer to the default setting.

Figure 5 shows the valve brake 14 with the thus sorted and mounted spacer 26, by means of which the axial distance h between the piston control edge 25 and the housing bottom 20 is set offset by the predetermined thickness d with respect to the unconfined valve brake. In a new path-time measurement, it is possible, with an unchanged measuring path s = m, to check whether, according to FIG. 6, the setting of the braking characteristic (curve with thick line width) lies within a desired course of motion, as represented by a "slow" limit curve (FIG. Curve with thin line width right) and a "fast" limit curve (curve with thin line width left) is given.

FIGS. 7 to 9 show various views of an engineered example of a hydraulic valve brake 14 according to the invention, which actuates a gas exchange valve 2 of a large engine with a mechanical valve clearance adjustment by means of a rocker arm 18 in accordance with FIG. The screwed by means of an external thread 27 in the cylinder head 3 of the engine housing 19 of the valve brake comprises a tubular housing wall 17 and a side of the pressure chamber 21 joined housing bottom 20 which is formed by a valve seat 28 with a check valve 29 inserted therein. The axially displaced in the housing and secured for transport purposes by means of a snap ring 30 against complete extension piston 6 is hollow cylindrical with a gas exchange valve side end face forming piston crown 31. The pressure chamber-side end face of the piston is provided with a recess 32 in the form of a countersink, in which a serving as a spacer 26 shim with a predetermined thickness d is fixed by means of a longitudinal compression bandage. A bore 33 passing through the piston crown serves as a vent and - in the case of a leak-prone longitudinal compression bandage - as pressure relief of the piston interior.

The housing wall 17 is penetrated in each case by four main flow openings 23 and throttle flow openings 24 in the form of bores via which the pressure space 21 communicates with the sensor-side hydraulic system (not illustrated here), as explained above. The main flow openings extend in a first transverse plane and the significantly smaller flow restrictor openings extend in a second transverse plane, which is offset from the first transverse plane in the retraction direction of the piston 6. The valve receptacle 28 comprises an outer annular collar 34 which is inserted in a pressure-reducing means 35 of the housing wall 17 and clamped by means of the screw 27 against a shoulder 36 in the cylinder head 3, and a relative to the annular collar in the direction of the recess 32 projecting hollow cylinder portion 37. The non-return valve 29 comprises a valve carrier 38 likewise inserted in the valve receptacle 28 and having a valve ball 40 spring-loaded therein against a valve seat 39. This opens in the direction of the pressure chamber 21 and controls a further overflow opening 41, via which the pressure chamber also communicates the encoder-side hydraulic system communicates to initialize the extension of the piston 6 when opening the gas exchange valve 2. When completely resting on the valve seat shim 26 of the hydraulic medium is transferred into the pressure chamber initially via beads 42 on the annular end face 43 of the hollow cylinder portion.

The opening cross-sections of the main and throttle flow openings 23 and 24 are controlled by the control edge 25 of the piston 6 passing over it and are all in the illustrated, completely retracted piston position as well as in the piston position extended by the set valve clearance L according to FIG locked. In order not to delay the final retraction movement of the piston too strong, the annular collar 34 is penetrated by a permanently open, further throttle flow opening 44 whose hydraulic resistance ultimately determines the touchdown speed of the gas exchange valve 2. Since with completely retracted in the housing 19 piston 6, the shim 26 rests on the annular end face 43, in this case the relevant for the set axial distance h between the control edge 25 of the fully retracted in the housing 19 piston 6 and the housing bottom 20 reference is not the annular collar 34th but the annular end face, which is like the annular collar fixed part of the valve seat 28. Accordingly, the unadjusted valve brake 14 is provided with a dummy shim (not shown) of known thickness, so that in the above-described basic measurement (see Figures 3a-c) of the piston with the dummy shim on the ring front side and not on the Ring collar of the valve seat touches down. The dummy shim to be disassembled according to the basic measurement may, if necessary, be provided with a circumferential O-ring which, on the one hand, holds the dummy shim easily removable in the recess 32 and, on the other hand, seals the pressure chamber 21 with respect to the bleed bore 33.

In analogy to FIGS. 3 to 6, the axial distance h is then adjusted by the thickness d of the adjusting disk 26 such that all hydraulic valve brakes 14 of the internal combustion engine have substantially the same braking characteristics and accordingly all the gas exchange valves 2 are largely uniform within a very small one Close the crank angle range. Unlike in Figure 4 with eight reference curves shims 26 are provided with five different thicknesses in each case 0.1 mm gradation in the embodiment shown here.

In FIGS. 7 and 9, the spacer 26 is pressed against its outer casing 45 in the inner casing 46 of the recess 32 of the piston 6. In order to avoid the risk of an associated impermissible expansion of the piston 6, which is tightly guided in the housing wall 17, alternative fasteners (not shown) may be provided. For example, the spacer may be provided with a central bore, which is pressed on the one hand on a pin-like projection of the then solid piston or through the other a pin or screw is guided, which adds the spacer with the piston.

List of reference numbers

1 valve spring

2 gas exchange valve

3 cylinder head

4 cams

5 master piston

6 slave pistons / pistons 7 hydraulic valve

8 high pressure room

9 medium-pressure room

10 piston pressure accumulator

1 1 check valve

12 low pressure room

13 throttle

14 hydraulic valve brake

15 cylindrical projection

16 overflow opening

17 housing wall

18 rocker arms

19 housing

20 caseback

21 pressure chamber

22 Valve clearance adjustment screw / mechanical valve clearance adjustment device

23 overflow opening / main flow opening

24 overflow opening / throttle flow opening

25 piston control edge

26 spacer / shim

27 external thread / screw connection

28 valve seat

29 check valve

30 snap ring

31 piston bottom

32 recess in the piston

33 breather hole

34 ring collars

35 Countersink in the housing wall

36 shoulder in the cylinder head

37 hollow cylinder section

38 valve carrier

39 valve seat valve ball

further overflow opening

Beading on valve seat

Ring face of the valve seat further throttle flow opening Outer jacket of the spacer Inner jacket of the recess

Claims

claims

Hydraulic valve brake (14) for a hydraulically variable valve train of an internal combustion engine, comprising a housing (19) with a housing wall (17) and a housing bottom (20), an axially in the housing (19) traversing piston (6), whose one end face with the Housing wall (17) and the housing bottom (20) defines a hydraulic pressure chamber (21) and the other end of a gas exchange valve (2) is actuated, wherein the housing wall (17) in the region of the pressure chamber (21) of one or more overflow openings (23, 24 ) whose opening cross-sections are controlled by a control edge (25) of the piston (6) delimiting the pressure chamber-side end face, characterized in that the axial distance (h) of the control edge (25) of the piston (6) completely retracted in the housing (19) to the housing bottom (20) by means of a spacer (26) of predetermined thickness (d) is set.

Hydraulic valve brake according to claim 1, characterized in that the piston (6) is provided on the pressure chamber-side end face with a hollow cylindrical recess (32) and that the spacer (26) is a shim fixed therein, by means of the disc thickness (d) of the axial distance ( h) is set.

Hydraulic valve brake according to claim 2, characterized in that the adjusting disc (26) in the recess (32) of the piston (6) is pressed.

Hydraulic valve brake according to one of the preceding claims, characterized in that the housing bottom (20) by a valve in the housing wall (17) pressure-tight inserted valve receptacle (28) with a further overflow opening (41) and by a pressure chamber (21) opening towards non-return valve ( 29) is formed, which controls the further overflow opening (41). Hydraulic valve brake according to claim 4, as far as dependent on claim 2, characterized in that the valve receptacle (28) with an annular collar (34) in a countersink (35) of the housing wall (17) is inserted and opposite the annular collar (34) in the direction the recess (32) of the piston (6) projecting hollow cylinder portion (37), wherein the axial distance (h) of the piston control edge (25) to the annular end face (43) of the hollow cylinder portion (37) is set.

Internal combustion engine comprising a hydraulic valve drive, characterized in that the valve drive with a hydraulic valve brake (14) according to one of the preceding claims and with a mechanical adjusting device (22) of the valve clearance (L) between the valve-side end face of the piston (6) and the gas exchange valve ( 2) is provided.