GB2074237A

GB2074237A - Arrangement for scavenging and charging the cylinders of a two- stroke internal combustion engine

Info

Publication number: GB2074237A
Application number: GB8112582A
Authority: GB
Original assignee: Sulzer AG; Gebrueder Sulzer AG
Current assignee: Sulzer AG
Priority date: 1980-04-23
Filing date: 1981-04-23
Publication date: 1981-10-28
Also published as: IT1136824B; DE3016823A1; JPS6246683B2; GB2074237B; JPS56167807A; DE3016823C2; IT8120356A0; DK175781A

Abstract

The cylinder head 3 has inlet ports 7 which extend substantially parallel to the cylinder axis and are closable through the agency of a valve slide member 11 which is arranged to move in oscillation and disposed on a surface of the cylinder head in the combustion chamber 1 of the cylinder, the inlet ports being arranged in a pattern around a fuel injection or ignition device 4 fitted at the centre of the cylinder head. The valve slide member 11 is protected on the combustion chamber side by a water cooled plate 31 which is formed with apertures 32 in register with the inlet ports, the cooled plate bearing axially on the cylinder wall at the periphery and on a flange 35 of a tubular member 34 extending around the device 4 at the centre; and the cooled plate and valve slide member being arranged to move axially as a result of the pressure reversal between the combustion chamber and the air or mixture supply to the inlet ports. The plate 31 is formed of a carbon steel disc 31a and a stainless steel disc 31b providing curvature towards the combustion chamber 1 due to heat expansion. <IMAGE>

Description

SPECIFICATION Arrangement for scavenging and charging the cylinders of a two-stroke internal combustion engine The invention relates to an arrangement for scavenging and charging the cylinders of a twostroke internal combustion engine with air or a fuel-air mixture, the cylinder head having valve ports which extend substantially parallel to the cylinder axis and are closable through the agency of at least one valve slide member which performs a controlled intermittent oscillation and is disposed on the cylinder head surface in the combustion chamber, the valve ports and corresponding apertures in the valve slide member being arranged in at least two rows around a device fitted at the centre of the cylinder head and serving for fuel supply or ignition.

Optimum scavenging and filling of the cylinders of a two-stroke internal combustion engine with air or a fuel-air mixture is of course achieved theoretically when a maximum quantity of scavenging air, in the form of an "air piston" complete as far as possible over the cylinder cross-section, enters the cylinder and expels any combustion gases therein by displacement. For this to occur, the total opening cross-section of all the inlet valve ports must provide a maximum net passage area, i.e., the product of the geometric passage area and the flow coefficient, -- and the displacing "air piston" must remain substantially complete. An arrangement of the kind hereinbefore described has been suggested in German Offenlegungsschrift 2 907 733 to provide a substantially undisturbed air piston.

It has been found difficult to carry this suggestion into practice since the valve slide member, which is in direct contact with the combustion chamber wall, experiences very extreme temperature and pressure conditions, which lead, because of heat expansion effects and/or the high pressure, to distortions and/or irreversible bulging. The reliability of operation and the sealing effect of the valve slide member is at least impaired and the members are liable to excessive wear.

It is the object of the invention so to reduce the stressing of such a valve slide member, that there is no loss of operational reliability and wear is minimised.

Accordingly the present invention provides an arrangement for scavenging and charging a cylinder of a two-stroke internal combustion engine with air or a fuel-air mixture, the cylinder head having inlet ports which extend substantially parallel to the cylinder axis and are closable through the agency of a valve slide member which is arranged to move in a controlled intermittent oscillation and disposed on a surface of the cylinder head in the combustion chamber of the cylinder, the inlet ports being arranged in a pattern around a device for injecting fuel or for ignition fitted at the centre of the cylinder head; in which the valve slide member is protected on the combustion chamber side by means of a fluid cooled plate which is formed with apertures in register with the inlet ports, the cooled plate bearing axially on the cylinder wall at the periphery and on a flange of a tubular member extending around the device at the centre; and the cooled plate and valve slide member being arranged to move axially as a result of the pressure reversal between the combustion chamber and the air or mixture supply to the inlet ports.

The fluid cooled plate protects the valve slide member against overheating and soiling. By its axial movement the cooled plate presses the valve slide member against the surface of the cylinder head when there is excess pressure in the combustion chamber -- i.e. during the compression stroke and at the beginning of the expansion stroke-- and is itself also pressed sealingly on to the valve slide member.

Upon pressure reversal -- i.e., when the pressure of the air in the inlet ports exceeds the pressure in the combustion chamber-the cooled plate moves down and disengages from the valve slide member which also separates from the surface of the cylinder head, its axial movement preferably being limited to just half the "axial stroke" of the cooled plate. In this state, in which its intermittent oscillatory movements to open and close the inlet ports occur, the valve slide floats self-supportingly between the cylinder head and the cooled plate and so is not subjected to wear.

The opening and more particularly, the closing movements of the valve slide and cooled plate can be considerably facilitated if the cylinder head is formed adjacent the inlet ports with additional orifices communicating with the apertures of the valve slide when it is in its closed position. The additional bores act during closing as vents for the air trapped in the orifices in the valve slide and in the gaps between the same and the valve plate or cylinder head.

The cooled plate can be adjusted relative to the cylinder head and guided in its movement to ensure that the cylinder head ports and the registering apertures in the plate are always correctly positioned relatively to one another in the axial movements of the plate. The adjustment and guiding of the plate can take place e.g. at the connection of coolant lines from the cylinder head to the cooled plate; the connection can also have sealing elements providing for the axial movement of the cooled plate.

Advantageously, the cooled plate is embodied by two rigidly interconnected discs made of materials having different heat expansion coefficients. If the two materials are selected appropriately, positive curvature of the valve plate towards the combustion chamber -- i.e., convex curvature, can be limited, and in the extreme case it can be zero, but it can be arranged so that it never becomes negative at any of the temperatures occurring, so that the alternate bending stresses occurring in operation can be maintained at an appropriately low level. Also, various steps can be taken to prevent particles of dirt and products of combustion sticking to and being caked on the cooled plate bearing surfaces near the combustion chamber, an event which reduces the valve stroke in the course of time.

Conveniently in this case, the cooled plate bears in the cylinder wall by way of its outer edge, the support surface being preceded by a horizontal gap, and/or the plate has near the cylinder wall, a skirt which extends into the combustion chamber and which is at a small distance from the cylinder wall associated with the horizontal gap, the penetration of particles of dirt therefore being prevented because of the compression of the gap volume. For the same reason, the valve plate can bear by way of its inner periphery on the flange of the tubular member by way of tips or teeth which effectively limit the support surface to a minimum, thus ensuring that the dirt built up at each stroke is effectively pushed through.

A drive of simple construction for the valve slide member can be provided if the slide member is connected to a sleeve which extends coaxially around the tubular member through the cylinder head and terminates at the top in a flange from which at least one arm extends radially outwards to a drive, or each arm extending through a respective aperture, extending over the range of arm pivoting, in an intermediate ring via which the injection or ignition device is mounted on the cylinder head. In this event a deformable ring diaphragm can be introduced as sealing element between, on the one hand, the cooled plate and the valve slide or its sleeve and, on the other hand the tubular member; and in the event of overpressure in the combustion chamber, the diaphragm is pressed by the valve plate against a sealing edge of the- axial slide.

In order to promote a fuller understanding of the above and other aspects of the invention, an embodiment will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a longitudinal section through the left half of a cylinder head of an internal combustion engine on the line I-I of Figure 2; Figure 2 is a section on the line Il-Il of Figure 1; Figures 3a and 3b show the detail A of Figure 1,and Figure 4 is a section on the line IV--IV of Figure 3a.

A combustion chamber 1 of a cylinder 2 of a diesel engine, not shown in any greater detail, is closed at the top by a cylinder head 3 having at its centre a fuel injection or ignition device 4. The cylinder 1 receives a piston 6.

The cylinder head 3 has inlet ports 7 for the supply of air in the case of diesel engines and a fuel-air mixture in the case of Otto engines. The ports 7 are arranged in three circular rows, 9, 9a, 10 concentric with the cylinder axis and are in the form of longitudinal bores in the cylinder head 3; the bores in the rows 9, 9a, 10 have different diameters. The cylinder 1 communicates by way of the rows 9. 9a, 10 of ports with an air chamber 8 indicated in diagrammatic form. A controlled opening and closing of the ports 7 is provided by a valve slide member 11 in which through orifices 12 corresponding in arrangement, shape and size to the ports 7 are disposed.

A cooled plate 31 is interposed between the combustion chamber 1 and the valve slide 11 and is formed with orifices 32 corresponding to and registering with the ports 7. In the example shown the plate 31 is embodied by two rigidly interconnected discs 31 a, 31 b, having disposed therebetween, flow ducts 33 for a coolant, e.g.

water. As already stated, the discs 31 3 lib are with advantage made of different materials; for instance, the disc 31a near the combustion chamber 1 can be made of carbon steel and thus have a lower coefficient of heat expansion than the disc 31b which is made e.g. of stainless steel.

Producing the plate 31 in the form of two discs 31 a, 31 b simplifies production of the coolant ducts 33 in one of the discs and also makes it possible, by appropriate choice of the materials used for the discs, to ensure that heat expansion of the plate 31 takes the form of a limited positive curvature towards the combustion chamber 1.

The plate 31 rests by way of its outer edge, in a recess 43 in cylinder head 3, on the cylinder side wall; the axial depth of recess 43 is so adpated to the thickness of the plate 31 that the effect of the reversal of the pressure gradient between the air chamber 8 and the combustion chamber 1 during a cycle causes the plate 31 to make an axial movement just sufficient to ensure sufficient clearance for the valve slide 11. The plate 31 bears by way of its inner periphery on a tubular member 34 which extends around the injection nozzle 4 and which has a flange ring 35 at its bottom end. The injection nozzle 4 is also carried, with the interposition of a seal 1 5, by the inner port flange ring 35 on member 34.

The plate disc 31 a is extended prolonged at a short distance to form a peripheral skirt 37 spaced from the cylinder wall by a gap 36 which ends at the top in a second horizontal gap 38 preceded by the plate outer edge serving as bearing and sealing surface. The function of the two gaps 36, 38 is to inhibit deposition and jamming of dirt and combustion products from the gas volume in the combustion chamber 1, such volume decreasing during compression by approximately 1/6. Dirt can enter the gaps 36,38 during compression but is ejected in the subsequent scavenging and charging of the combustion chamber 1. To prevent accumulations of impurities, the support means by which the plate 31 bears on the flange ring 35 can take the form of tips or teeth 39 in the ring 35 (Figure 4) which offer no surface for the deposition of particles of dirt.

The coolant feed between the discs 31a and 31 b is by way of bore 40 which extends in the cylinder head 3 and terminates in a tubular member 41 extending into the disc 31 b. Extending around the outside of member 41 is an O-ring 42 serving to seal the coolant entry into the plate 31 across the gaps, necessary for the axial movement of the plate 31, between the axial depth of the recess 43 in the cylinder head 3 and the thickness of the plate 31. The member 41, which extends into the disc 31 b with relatively reduced clearance, also serves to prevent accidental rotation of the plate 31 to guide the axial movement of the plate 31, whose orifices 32 are in alignment with the ports 7.

To facilitate the axial movement of the valve plate 31 ,to reduce resistance to movement arising because of venting of the voids and gaps during closing and because of the additional force during opening, the cylinder head 3 is formed with additional orifices 5 connecting the air chamber 8 to the orifices 12 when the valve. slide 11 is in the closed position. The bores 5 need not necessarily be longitudinal bores through the cylinder head 3, their only function being to connect the orifices 12 to the air space of the air chamber 8 when the valve slide 11 is in the closed state.

The valve slide member is also arranged for axial movement, but only by approximately half the travel of the cooled plate 31, and for oscillatory rotation in a second recess 44 which is formed in the surface of the cylinder head 3 and which is of smaller diameter than the recess 43.

The valve slide member 11 is carried by a sleeve 14 which is integral with the valve slide 11, extends coaxially around the tubular member 34 and through the top of the cylinder head 3. The outside surface of sleeve 14 is mounted for rotation in two radial bearings 1 7 separated from one another by a spacer 1 6.

At the top end the sleeve 14 is provided with a flange 1 8 which to facilitate assembly is engaged on the sleeve 14 releasably by way of serrations 21 and is retained on the sleeve 14 by bolts 22.

As can be seen in Figure 2, three arms 19 which extend radially outwards connect flange 1 8 to a toothed ring 20 which meshes with a gear 24 on a drive shaft 23.

The axial bearing 25 for the unit comprising the elements 1 8, and 11 is disposed at the top end of the cylinder head 3; it bears on a shoulder in the inner edge of the head and its axial dimension is such that the valve slide 11 can carry out only half the axial stroke of the cooled plate 31 when the same descends.

A tubular spacer 45 is secured externally to the member 34 whose flange ring 35 serves as a support for the injection nozzle 4 and as a support for the inner edge of the valve plate 31. At its top end the spacer 45 abuts a main flange 45 which bears on a shoulder of member 34 and is secured bya nut47.

The bottom end of spacer 45 serves as a gastight bearing surface for one side of a resiliently deformable ring diaphragm 48 serving to seal the gap between the spacer 45 and the sleeve 14 and/or valve slide 11 such gap otherwise providing a flow connection to the combustion chamber 1. The other end of diaphragm 48 is received in an annular groove 49, visible in Figures 3a and 3b, in the inner edge of disc 31b when the plate 31 is in its bottom position, i.e. the position it takes when there is a pressure drop from the air chamber 8 to the combustion chamber 1.After the valve plate 31 has moved axially into its top position in which it forces the valve slide 11 against the surface of the cylinder head 3, the diaphragm 48 distorts, as shown in Figure 3b, and becomes clamped between the plate 31 and the valve slide 11, bearing on a sealing edge 50 in the form of a shoulder on the inside edge of the valve slide 11. By becoming thus clamped, the diaphragm 48 cannot react to excess pressure in the combustion chamber 1 by disengaging from its bearing surface and from the annular groove 49, and ensures reliable sealing tightness even in the event of a pressure drop directed outwardly from the combustion chamber 1.

The tubular member 34 bears on the top of the cylinder head 3 by way of the circular flange 46 and an intermediate ring 29, bolts 28 (Figure 2) tightening the ring 29 and flange 46 on to the cylinder head 3. The ring 29 has apertures 30 whose opening angle spans at least the pivoting region of a respective one of the radially outwardly extending arms 1 9. The apertures 30 enable the injection nozzle 4 at the centre of cylinder head 3 to be supported without such support hampering the oscillatory opening and closing movement of the valve slide 11.

Claims

1. An arrangement for scavenging and charging a cylinder of a two-stroke internal combustion engine with air or a fuel-air mixture, the cylinder head having inlet ports which extend substantially parallel to the cylinder axis and are closable through the agency of a valve slide member which is arranged to move in oscillation and disposed on a surface of the cylinder head in the combustion chamber of the cylinder, the inlet ports being arranged in a pattern around a device for injecting fuel or for ignition fitted at the centre of the cylinder head; in which the valve slide member is protected on the combustion chamber side by means of a fluid cooled plate which is formed with apertures in register with the inlet ports, the cooled plate bearing axially on the cylinder wall at the periphery and on a flange of a tubular member extending around the device at the centre; and the cooled plate and valve slide member being arranged to move axially as a result of the pressure reversal between the combustion chamber and the air or mixture supply to the inlet ports.

2. An arrangement as claimed in Claim 1, in which the cylinder head is formed with additional orifices adjacent the inlet ports, which orifices communicate with the apertures of the valve slide member when it is in its closed position.

3. An arrangement as claimed in Claim 1 or 2, in which the cooled plate is movable relative to the cylinder head and is guided in its axial movement.

4. An arrangement as claimed in Claim 1 ,2, or 3, in which the cooled plate comprises two rigidly interconnected discs made of materials having different thermal expansion coefficients.

5. An arrangement as claimed in any preceding Claim, in which the connection of the coolant lines from the cylinder head to the cooled plate have sealing elements which provide sealing-tight connection while allowing axial movement of the plate.

6. An arrangement as claimed in any preceding Claim, in which the cooled plate bears in the cylinder wall by way of its outer edge, the support surface being preceded by a horizontal gap open to the combustion chamber.

7. An arrangement as claimed in Claim 6, in which the cooled plate has a skirt which extends into the combustion chamber and which is at a small distance from the cylinder wall to leave an annular gap associated with the horizontal gap.

8. An arrangement as claimed in any preceding Claim, in which the cooled plate bears on a flange on the tubular member by way of teeth or edges which limit the support surface area.

9. An arrangement as claimed in any preceding Claim, in which the valve slide member is connected to a sleeve which extends coaxially around the tubular member through the cylinder head and which terminates at the top in a flange from which at least one arm extends radially outwards to drive means, the or each arm extending through a respective aperture extending over the range of movement of the arm in an intermediate ring via which the said device is mounted in the cylinder head.

10. An arrangement as claimed in Claim 9, in which a deformable ring diaphragm seal is provided between, on the one hand, the cooled plate and the valve slide member or its sleeve and, on the. other hand the tubular member, the arrangement being such that in the event of over pressure in the combustion chamber the diaphragm is pressed by the cooled plate against a sealing edge of the valve slide member.

11. An arrangement for scavenging and charging a cylinder of a two-stroke internal combustion engine substantially as herein described with reference to the accompanying drawings.