GB2244113A

GB2244113A - A piston of changeable compression height

Info

Publication number: GB2244113A
Application number: GB9109381A
Authority: GB
Inventors: Dieter Schmidt; Friedrich Wirbeleit; Martin Bechtold; Klaus Binder; Dr Peter Konhauser
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1990-05-12
Filing date: 1991-05-01
Publication date: 1991-11-20
Anticipated expiration: 2011-05-01
Also published as: DE4015267C1; GB9109381D0; FR2661949B1; FR2661949A1; GB2244113B

Abstract

A piston of changeable compression height has an arrangement for controlling the oil flow between two control chambers 7, 8 of the piston. In order to achieve a simple and insensitive construction of the control devices for this oil flow between the control chambers, it is proposed to employ a valve chamber which comprises a hollow space 10 and has in each case at least one oil bore 19, 20 leading to the first and second control chamber 7, 8 respectively, the bars 19, 20 being restrictive and lying at right angles such that flow from the second to the first chamber is restricted while flow from the first to the second is relatively unrestricted. <IMAGE>

Description

1 A 1Diston of changeable compression height The invention relates to a

piston of changeable compression height having two control chambers and means f or controlling the oil f low between the chambers, with an outer piston part and an inner piston part guided in axially displaceable f ashion relative to said outer piston part and articulated on a connecting rod, between which, situated axially opposite and separated by the inner piston part, are f ormed the two control chambers, the volumes of which can be altered in mutually reciprocal fashion, the first control chamber being arranged between a f irst surf ace of the inner piston part and a surface of the outer piston part which faces the piston top, and the second control chamber being arranged between a second surf ace of the inner piston part and a surface facing the skirt of the outer piston part, with a f irst oil bore in the inner piston part, which connects the first control chamber to an oil feed and contains a nonreturn valve which opens towards the first control chamber, and with a second oil bore in the inner piston part, which connects the first control chamber to the crankcase and contains a pressure relief valve opening towards the crankcase, and with a device in the inner piston part for controlling the oil flow between the two control chambers, which is provided with a third restriction bore.

Pistons of changeable compression height are known and described, for example, in German Patent 3,807,244. Pistons of this kind have an inner piston part positively connected to the crankshaft and an outer piston part nonpositively connected to said inner piston part via a hydraulic system and arranged displaceably on the inner piston part. Arranged between inner piston part and outer piston part are two control chambers, which are connected by oil bores and the volumes of which can be altered in a mutually reciprocal fashion.

During the exhaust and refill phase, the inertia force pulls on the outer piston part, thereby causing a pressure rise in the lower control chamber. As a result, oil f lows via a restrictor from the lower control chamber into the upper 2 control chamber. In addition, the increase in the volume of the upper control chamber brings about an oil flow into this control chamber from the gudgeon pin via a nonreturn valve. This results in an increase in the compression height of the piston.

Following the ignition of the mixture in the combustion chamber and the consequent rise in the gas pressure, this gas pressure is transmitted to the upper control chamber and discharges oil into the crankcase in a controlled fashion via a pressure relief valve. At the same time, oil flows from the upper control chamber into the lower control chamber via a restrictor and via a nonreturn valve. In this way, the volume of the upper control chamber and hence the compression height is reduced.

Thus, to reduce the compression height the oil flow must be able to pass as far as possible unhindered f rom the upper control chamber into the lower control chamber, i. e. a large inflow cross-section must be available, whereas to increase the compression height the nonreturn valve closes and the oil can now only flow off out of the lower control chamber into the upper control chamber via the restrictor. To achieve this flow behaviour, however, two different control devices are necessary according to German Patent 3,807,244, namely a restrictor on the one hand and a nonreturn valve on the other hand, the expense involved in the construction of the piston thereby being considerably increased and malfunctions due to dirt accumulation at and damage to the sensitive components, such as the nonreturn valve, having to be accepted.

The present invention seeks to improve a piston of the type referred to in such a way that, for the same flow behaviour of the oil f low between the control chambers, a simple and insensitive construction of the control device for this oil flow is made possible. The intention is, in particular, to attempt to reduce the number of moving elements of the control devices, or to avoid these altogether.

According to the present invention there is provided a piston of changeable compression height having two control chambers and means f or controlling the oil f low between the 1 Q K j I- 3 chambers, with an outer piston part and an inner piston part guided in axially displaceable fashion relative to said outer piston part and articulated on a connecting rod, between which, situated axially opposite and separated by the inner piston part, are formed the two control chambers, the volumes of which can be altered in mutually reciprocal fashion, the first control chamber being arranged between a first surface of the inner piston part and a surface of the outer piston part which faces the piston top, and the second control chamber being arranged between a second surface of the inner piston part and a surface facing the skirt of the outer piston part, with a first oil bore in the inner piston part, which connects the first control chamber to an oil feed and contains a nonreturn valve which opens towards the first control chamber, and with a second oil bore in the inner piston part, which connects the first control chamber to the crankcase and contains a pressure relief valve opening towards the crankcase, and with a device in the inner piston part for controlling the oil flow between the two control chambers, which is provided with a third restriction bore, wherein the device comprises an element which forms a hollow valve chamber and is connected to the first and second control chamber, in each case by a first or second restriction bore respectively, the restriction bores being aligned at right angles to one another and the mouth of the restriction bore which connects the valve chamber to the second control chamber entering the valve chamber tangentially.

Preferably, the oil bore connecting the valve chamber to the first control chamber is arranged approximately centrally in the valve chamber. A plurality of restriction bores may be provided in each case, at least one of which opens tangentially into the valve chamber. Preferably, the inlet of the second restriction bore into the second control chamber is sharp-edged and the inlet of the first restriction bore towards the first control chamber is such as to favour flow.

In the inner piston part of a piston of the type described above, a chamber-shaped control device is inserted in the course of the oil bore between upper and lower control chamber. The control device, which is designed as a hollow 4 valve chamber, has one oil bore leading to the upper control chamber and one oil bore leading to the lower control chamber. The oil flow through these bores is here influenced by the position and design of the bores in such a way that a high pressure loss occurs during the flow of oil from the lower control chamber into the upper control chamber, corresponding to a severe restriction, but a small pressure loss occurs during the flow of oil in the opposite direction.

Embodiments of the invention is described below by way of example with reference to the drawing, in which:

Figure 1 shows a piston according to the invention with valve chamber, in longitudinal section, Figure 2 a, b shows a valve chamber with the oil flows, on an enlarged scale, Figure 3 a-d shows another embodiment of the valve chamber with the oil flows, Figure 4 shows a further development of the valve chamber.

A piston, denoted by refernce 1 in Figure 1, of changeable compression height comprises an outer piston part 2 and an inner piston part 3. The outer piston part 2 comprises the piston skirt and the piston top 4 and is held displaceably on the inner piston part 3 in the axial direction of the piston 1. Inserted in the inner piston part 3 is a hollow gudgeon pin 6 on which a connecting rod (not shown in this f igure) is articulated in customary f ashion with its small-end boss. A valve plate 9 is firmly attached to the inner piston. A seal 5 serving as a stop ring and sliding on the inner piston is firmly connected to the outer piston.

Enclosed between the outer piston part 2 and the inner piston part 3 is a f irst, upper control chamber 7, which is connected to a second, lower control chamber 8 via an oil bore, which is arranged in the valve support plate 9 and into which a valve chamber 10 is inserted.

Both control chambers 7 and 8 are filled with oil from the lubricatingoil circuit of the internal combustion engine. The change in the compression height is caused by the f orce acting on the outer piston part 2 resulting from gas force, inertia f orc? and friction f orces oil being displaced f rom -w 1 one control chamber to the other. During the reduction of the compression height, oil is discharged in a controlled fashion from the upper control chamber 7, via an oil bore 11 (represented in dashes) and a pressure relief valve 12, into the crankcase of the internal combustion engine. The volume of the lower control chamber 8, which increases during this process, is at the same time replenished largely unhindered with oil from the upper control chamber 7, via the valve chamber 10 inserted in the valve support plate 9.

During the increase in the compression height, oil from the lower control chamber 8 is likewise forced into the upper control chamber 7 via the valve chamber 10, which in this case acts as a restrictor. For the purpose of supplying oil to this upper control chamber 7, there is a feed bore 13 in the inner piston part 3 and in the valve support plate 9, which bore is represented here in dashes and in the course of which is inserted a non-return valve 14 blocking the outflow of oil from the upper control chamber 7. The inflow of oil from the lubricating-oil circuit of the internal combustion engine can here be accomplished via the hollow gudgeon in a manner not shown here. From here, the oil passes via a bore 15 into the interior space 16 of the hollowed-out gudgeon pin 6, said interior space serving as a reservoir, from which oil can be fed continuously to the upper control chamber in the upwardadjustment phase via a further bore 1 in the gudgeon pin 6 and an annular groove (not visible) and via the feed bore 13 and the valve 14.

Figure 2 shows on an enlarged scale the valve chamber 10 shown in Figure 1 and partially also the elements surrounding the latter, which are known from Figure 1. In the figure, the oil flow through the valve chamber 10 between the two control chambers 7 and 8 has additionally been drawn in, in Figure 2a the oil flow from the upper control chamber 7 into the lower control chamber 8 and in Figure 2b the oil flow in the opposite direction. The valve chamber 10 is inserted into the valve support plate 9 secured on the inner piston part 3. The interior space 18 of said valve support plate is in each case connected via at least one restriction bore 19 or 20 to 1 6 the f irst control chamber 7 or the second control chamber 8, respectively in order to permit the controlled passage of oil between these two control chambers.

In Figure 2a, the arrow 21 indicates the oil flow from the upper control chamber 7 into the lower control chamber 8. The oil passes from the upper control chamber 7, via the restriction bore 19, into the interior space 18 of the valve chamber 10 and from there, via the restriction bore 20, into the lower control chamber 8. In this direction, the oil flows essentially unhindered and without especial losses, with the result that rapid filling of the lower control chamber 8 is made possible.

Figure 2b, in which identical parts are provided with identical reference numerals, indicate by means of the arrow 22 the oil flow in the opposite direction, i.e. from the lower control chamber 8 into the upper control chamber 7. AS explained above, the oil flow in this direction is to take place in a restricted fashion. As can be seen from the figure, the introduction of the oil flow into the interior space 18 through the restriction bore 20 results in a hinderance to the oil flowing off through the restriction bore 19 into the upper control chamber 7. The tangential introduction of the oil flow 22 through the restriction bore 20 into the interior space 18 of the chamber produces a vortex there which firstly, due to the viscosity of the oil, dissipates a considerable part of the energy of flow and secondly results in a constriction of the cross-section for the flow of oil flowing out through the bore 19. The desired restricting ef fect f or the f low of oil from the lower (8) into the upper control chamber 7 is thereby achieved.

It is a prerequisite for the control illustrated in Figure 2 of the oil flow between the two control chambers 7 and 8 that the restriction bores 19 and 20 extend approximately at right angles to one another, that the restriction bore 19 leading to the upper control chamber 7 is arranged approximately centrally in the wall closing off the interior space 18 in relation to the upper control chamber 7 and that the restriction bore 20 opens tangentially into the periphery of the interior space, the provision of a plurality of 1 7 restriction bores 20 also being possible, although it is then necessary for these to be arranged in such a way that they produce a vortex revolving in the same direction. The inflow of oil into the interior space 18 of the valve chamber 10 from the lower control chamber 8 via the restriction bore 20 is particularly advantageous if the oil flow flowing out into the upper control chamber 7 is constricted in the immediate vicinity of that opening 23 of the restriction bore 19 which faces the interior space 18 of the valve chamber 10. This can be achieved by arranging the restriction bore 20 in such a way that it lies in a plane which is at a tangent to the opening 23 of the restriction bore 19, i.e. if the restriction bore 20 is as close as possible to the wall closing off the interior space 18 in relation to the upper control chamber 7, as shown in Figure 2.

Figure 3 shows another embodiment of the valve chamber 10. The construction of the chamber is in principle the same as that described above, except that the interior space 18 is designed as a swirl chamber here assumed to be disc-shaped. Identical parts are again provided with identical reference numerals. In Figures 3a and 3b, a valve chamber 10 is shown in longitudinal section and cross-section respectively, with the oil (21) flowing unhindered out of the upper control chamber 7 into the lower control chamber 8. The oil flow 21 passes through the restriction bore 19, arranged centrally in the wall of the swirl chamber 18, and the swirl chamber 18 itself into the restriction bore 20 and, from there, into the lower control chamber 8. As can be seen from the figure, no great vortex is built up during this process, allowing the oil to flow rapidly.without especial losses.

The case shown in Figures 3c and 3d with an oil f low 22 in the opposite direction, f rom the lower control chamber 8 into the upper control chamber 7, dif f ers f rom that shown in Figures 3a and 3b by the fact that the oil flow 22 passing through the restriction bore 20 opening tangentially into the swirl chamber 18 is swirled in the chamber in the manner shown before it can pass into the upper control chamber 7 through the central restriction bore 19. The structure of this vortex 8 results in a pressure loss which brings about the desired restriction effect.

It is also conceivable here for a plurality of restriction bores 20 of the type described opening into the swirl chamber 18 to be provided. However, the important point here is that all these restriction bores should open tangentially into the swirl chamber 18, more specifically in such a way that they produce a vortex rotating in the same direction.

Figure 4 shows a further possible embodiment for the valve chamber 10 of particularly simple construction. The valve chamber arranged between the upper (7) and the lower (8) control chamber has a restriction bore 19 and a restriction bore 20 which merge into one another. The possibility of unhindered f low of the oil f low 21 f rom the upper into the lower control chamber is achieved by the shaping of the opening 24 of the restriction bore 19 towards the upper control chamber 7 in a manner which is particularly favourable for flow, while the 'desired restriction effect for the oil flow 22 in the opposite direction is achieved by the sharp-edged design of the opening 25 of the restriction bore 20 towards the lower control chamber 8 and the pressure loss caused thereby as the oil flows into the bore 20.

This flow-influencing design of the openings 24 and 25 can of course also additionally be employed in conjunction with the above-described designs of the valve chamber 10 in accordance with Figures 2 and 3 in order to improve the restriction effect.

By virtue of the design according to the invention of the valve chamber of a piston of changeable compression height, it is possible to achieve the requisite hydraulic characteristics of the valve device using simple means without moving parts and hence cheaply and in a manner not susceptible to disturbances.

In the case of slow-running internal combustion engines, it has been found that it is possible to dispense with a special design of the openings 24 and 25 and nevertheless achieve the desired restriction effect solely by means of the A a 1 1 9 restriction bores 19 and 20. This effect is achieved by virtue of the fact that the valve chamber 10 coincides with the first restriction bore 19 and the second restriction bore 20 to form a single restriction bore.

claims 1. A piston of changeable compression height having two control chambers and means for controlling the oil flow between the chambers, with an outer piston part and an inner piston part guided in axially displaceable fashion relative to said outer piston part and articulated on a connecting rod, between which, situated axially opposite and separated by the inner piston part, are formed the two control chambers, the volumes of which can be altered in mutually reciprocal fashion, the first control chamber being arranged between a first surface of the inner piston part and a surface of the outer piston part which faces the piston top, and the second control chamber being arranged between a second surface of the inner piston part and a surface facing the skirt of the outer piston part, with a first oil bore in the inner piston part, which connects the - first control chamber to an oil feed and contains a nonreturn valve which opens towards the first control chamber, and with a second oil bore in the inner piston part, which connects the first control chamber to the crankcase and contains a pressure relief valve opening towards the crankcase, and with a device in the inner piston part for controlling the oil flow between the two control chambers, which is provided with a third restriction bore, wherein the device comprises an element which forms a hollow valve chamber and is connected to the first and second control chamber, in each case by a first or second restriction bore respectively, the restriction bores being aligned at right angles to one another and the mouth of the restriction bore which connects the valve chamber to the second control chamber entering the valve chamber tangentially.

Claims

2. A piston according to Claim 1, wherein the oil bore connecting the

valve chamber to the first control chamber is arranged approximately centrally in the valve chamber.

3.

A I A piston according to Claim 1 or 2, wherein a plurality 1 1 11 of restriction bores are provided in each case, at least one of which opens tangentially into the valve chamber.

4. A piston according to any one of Claims 1 to 3, wherein the inlet of the second restriction bore into the second control chamber is sharpedged and the inlet of the first restriction bore towards the first control chamber is such as to favour flow.

5. A piston of changeable compression height, substantially as described herein, with reference to, and as illustrated in, the accompanying drawings.

Published 1991 at The Patent Office. Concept House, Cardiff Road, Newport. Gwent NP9 1RH. Further copies may be obtained from Sales Branch. Unit 6, Nine Mile Point Cwrafelinfach, Cross lkys, Newpoit, NPI 7HZ Printed by Multiplex techniques lid, St MarY Cray. Kent.