WO1995008057A1

WO1995008057A1 - Internal combustion engine

Info

Publication number: WO1995008057A1
Application number: PCT/SE1993/000750
Authority: WO
Inventors: Jan Dellrud; Mark James
Original assignee: Saab Automobile Aktiebolag
Priority date: 1993-09-16
Filing date: 1993-09-16
Publication date: 1995-03-23
Also published as: SE9501818L; GB9508380D0; GB2286429A; SE503465C2; SE9501818D0; DE4397580T1

Abstract

An internal combustion engine (1) having a cylinder block (2) with cylinders (40) with valves (5a, 5b, 6a, 6b) arranged in the roof of the combustion chamber, and piston (4) reciprocable within a liner (19) in the cylinder. The cylinder has a smaller diameter upper portion (20) and a larger diameter lower portion (40B) with a shoulder (34) therebetween. The upper end (44) of the liner (19) abuts the shoulder (34) in the cylinder located substantially level with the upper piston ring (32). The valve seats (17) of corresponding valves (5a, 5b, 6a, 6b) protrude radially of the valve seats into the wall of the upper portion (20) of the cylinder.

Description

Internal Combustion Engine

This invention relates to internal combustion engines and in particular to spark ignition engines.

Internal combustion engines basically have two types of construction, these being the traditional cylinder block having a separate cylinder head with the combustion chamber valves therein, and the so called monoblock construction in which the cylinder head is formed integrally with the cylinder block. Typically the cylinders in the engine are each lined with a cylinder liner which in a traditional engine may have its upper end abutting the cylinder head, and which in a monoblock construction may abut a shoulder in the top of the cylinder.

In particular the monoblock construction provides difficulties in the machining of valve seats in the cylinder head. Further the areas adjacent the combustion chamber at the top of the cylinder liner are subject to conditions of extreme heat and pressure. The extreme heat and pressure conditions that occur in the combustion chamber adjacent to the top of the liner cause particular problems of high stress in the interbore regions of siamesed cylinder bore engine designs.

The present invention provides an engine having a valve with a larger than usual diameter for a given cylinder diameter, while at the same time minimizing the annular gap between the uppermost part of the radial piston surfaces,the so called top land, and the cylinder wall. The reduction of the annular gap is sought for because excessive gaps cause excessive generation of NOx, since incomplete combustion takes place in such an annular gap. The present invention also provides for a reduction of heat and pressure load which the joint between the top end surface of the cylinder liner and the cylinder head is subjected to. Conventionally said joint is exposed directly by the squish effect. Such a joint area usually is very difficult to cool sufficiently by using close lying cooling channels due to physical restrictions from the liner. The present invention also aims to provide a better cooling of this heat and pressure exposed area. The cylinder liner is also exposed to forces, if the combustion pressure penetrates the joint, that tend to push the liner downwards unless the cylinder is form-locked in position. The present invention also reduces this risk. One other significant advantage of the lower liner surface is that if the liner is made in cast iron or a material which has a lower thermal conductivity than that of the cylinder block parent material, preferrably aluminum alloy, it may help to reduce localised hot areas in the combustion chamber, thereby allowing an improvement in performance by raising the detonation limit of the engine. If the liner is further away from the heat source and is somewhat shielded by the piston top land it potentially operates at a lower temperature than that of a conventional liner design. Aluminium in place of the cast iron at the very top of the cylinder bore also permits more heat to be dissipated from the combustion chamber to engine coolant.

Accordingly there is provided an internal combustion engine having a cylinder block with at least one cylinder with a combustion chamber having at least one pair of valves arranged in the roof of the cylinder and a piston reciprocable therein, the cylinder having a liner arranged within the cylinder such that the top end surface of the liner is substantially coincident with the upper piston ring when the piston is at T.D.C. characterised in that the cylinder has a smaller diameter upper portion and a larger diameter lower portion with an annular shoulder therebetween and the top end surface of the cylinder liner abuts the shoulder formed on the lower end of the upper cylinder portion, the upper portion of the cylinder having a minimum diameter at least equal to the inner diameter of the liner and at least one of the valve seats of corresponding valves protrudes radially of the valve seats into the wall of the upper portion of the cylinder. T.D.C. is the top dead centre position of the piston as it reciprocates in the cylinder.

Preferably the upper portion of the cylinder has a diameter which is slightly greater than the internal diameter of the cylinder liner. This preferred embodiment enables the cylinder liners to be fully honed insitu in the monoblock type engine construction.The slightly greater diameter of the upper portion of the cylinder enables reversal of the honing stroke without affecting the honing stones or the resulting honing pattern on the cylinder wall. This is particularly important during engine reconditioning or rebuilding.

Another advantage that can be derived from the preferred construction is to prevent the piston from abutting the upper cylinder wall portion if said portion 'is slightly out of alignment with the lower cylinder caused by any radial displacement of the upper cylinder wall portion or the liner seats during machining thereof.

Preferably the axial length of the upper portion of the cylinder is such that it extends axially just beyond the end surface of the piston when at T.D.C.

Also according to the invention there is provided a monoblock construction having an integral cylinder head and cylinder block construction.

Conveniently the invention is particularly useful for petrol engines.

The invention will be described by way of example and with reference to the accompanying drawings in which:

Fig 1. is a cross section of a spark ignition engine according to the invention showing on left hand side of the vertical centre line a cylinder, and on the right hand side the piston occupying the top dead centre position (T.D.C). Fig 1 is taken on the line A - A of Fig 2,

Fig 2. is a view of the cylinder roof and cylinder liner seen from below in Fig 1., and

Fig 3. is an enlarged sector of Fig 2. showing a portion of an inlet valve.

With reference to Fig 1 - 3, there is illustrated an overhead cam operated valve internal combustion engine 1, which is a spark ignition four-stroke Otto engine of monoblock construction in which the cylinder head 3 is formed integrally with the cylinder block 2. The explanatory embodiment shows an Otto engine, but the invention could also be applied to Diesel engines.

The engine may have a plurality of cylinders 40, preferably four or six cylinders, which are each lined by cylinder liners 19 in which a respective piston 4 is reciprocable, and is connected to a crank shaft (not shown) via a connecting rod (not shown) . Each cylinder 40 has a concave combustion chamber roof 41 in which are located four valves 5a, 5b and 6a,6b for operation of the engine. The valves 5a, 5b are inlet valves which have a larger diameter than the other valves 6a, 6b which are outlet valves. The valves 5a, 5b and 6a,6b are slidable mounted in valve guides 16 and are biased by valve springs 15 to a closed condition against valve seats 17a,17b located in the roof 41 of the chamber. The upper end portions of the valve stems 42 are received in slack adjusters/cam followers 14 which are in abutment with cams 43 mounted on cam shafts 7 and 8. the operational valve gear 7, 8, 14, etc. is located within a cam cover 9 which fed with lubricating oil through oil channels 13.

The valve seats 17a for inlet valves 5a,5b are each connected to a inlet channel 11 which joins a common inlet port 10. The valve seats 17B for the exhaust valves 6 are connected to an exhaust system (not shown) by a respective exhaust channel 12.

Each cylinder 40 has a larger diameter lower portion 40A which accommodates the cylinder liner 19 and a smaller diameter upper wall portion 20 adjacent the roof 41. Each cylinder liner 19 is arranged within the respective cylinder 40 so that upper end surface 44 of the liner 19 abuts an annular shoulder 34 formed between the upper and lower portions 40 and 20 respectively of the cylinder. The shoulder 34 is located such that the top end surface 44 of the liner is located slightly above or substantially coincident with the upper piston ring 32 when the piston 4 is at top dead centre (T.D.C.) on its stroke. Preferably the cylinder liner end 44 is located 2mm above the top piston ring 32 at T.D.C. The upper cylinder wall portion 20 is of a slightly larger diameter than the internal diameter of the cylinder liner (19). For example in a cylinder with a cylinder liner 19 having a diameter of 60mm, the diameter of the wall portion 20 will be larger by approx. 0.2mm. The upper wall portion 20 extends axially upwardly to meet the roof 41 and circumferentially define the squish plane 45 about 1mm above the piston end face 46 at T.D.C. The imaginary squish plane is caught between the piston end face 46 and annularly located squish generating areas 25,26 arranged in the roof 41 of the cylinder. The air-fuel mixture caught between these areas 25,26 and the piston end face are squished and hereby given a high velocity and mixing effect directed towards the spark plug, thus creating a homogenous charge for a promotion of a complete combustion.

The piston 4 has a top land 18 extending between its end face 46 and the top piston ring 32, and which is about 6mm in axial length, just smaller than the axial length 7mm of the upper portion 20 of the cylinder.

The upper part of upper portion 20 has a notch 21 cut out in the cylinder wall in order to accommodate respective valve seats 17B when mounting the valve seats in position. The notch 22, shown in dotted outline, represents the maximum notch size due to production tolerances, but still located by margin to the upper end 44 of the liner.

The layout of the combustion chamber roof 41 is best seen in Fig 2. The four valves 5a,5b, 6a,6b are substantially equiangularly spaced around a threaded plug hole 31 which in use receives a sparking plug. The liner 19 has an outer circumference 23 and an inner circumference 24. The roof 41 has adjacent its outer periphery in the squish plane 45 two flat squish areas, a circumferential area 26 and two diametrically opposed larger areas 25.

The valves 5a,5b, 6a, 6b, are located so that the radially outer sector (radially with respect to cylinder liner) of each valve protrudes radially passing the circumferential squish area 26 and into the upper portion 20 of the cylinder wall. The outer circumference 28 of each inlet valve 5a or 5b intersects the annular upper portion 20 of the cylinder wall bounded by the inner and outer peripheries 23,24 of the liner 19, as does the outer circumference 27 of each exhaust valves 6a,6b. This is best seen in Fig 3. where outer circumference 27 of the inlet valve 5a has a periphery 37 that extends some 50% across the annular continuum of the liner 19 as defined by the upper portion 20 of the cylinder wall. Said annular continuum being limited by the circumferences of the upper and lower cylinder portions, which are substantially the same as the inner and outer peripheries 23,24 of the liner 19.

The upper cylinder wall portion 20 will have shaped concave cavities formed therein to accommodate a part of the valve seats. This will enable the usage of larger inlet and outlet valves for a given cylinder diameter.The cavities also have radially successively decreasing depth to the top end of the cylinder liner 19, due to the inclination of the valves and corresponding valve seats. The cavities thus formed will be equiangularly spaced in the annular continuation of the cylinder wall formed by the upper portion 20 of the cylinder wall. The other annular sectors of the upper portion 20 of the cylinder wall, between the cavities, maintain a narrow gap between the top land of the piston and the surrounding cylinder wall, thus limiting any NOx-creating pockets around the top land area.

The top end surface 44 of the liner 19 being lowered to a position in level with the upper piston ring when the piston is at TDC, gives a further advantage since the joint between the annular shoulder 34 and the top end surface of the liner is not directly exposed to the heat and pressure due to the squish effect. Conventional designs where the joint is situated in the squish plane, causes bad cooling of this particularly hot spot of the combustion chamber and the risk increases for the combustion gases to penetrate the joint and even push the liner downwards.

The cylinder block and head are formed with a plurality of cooling channels 30 therein for the passage of cooling water.

Claims

1. An internal combustion engine (1) having a cylinder block (2) with at least one cylinder (40) with a combustion chamber having at least one pair of valves (5a, 6a) arranged in the roof of the cylinder and a piston (4) reciprocable therein, the cylinder (40) having a liner (19) arranged within the cylinder such that the top end surface(44) of the liner (19) is substantially coincident with the upper piston ring (32) when the piston is at T.D.C. c h a r a c t e r i s e d i n that the cylinder (40) has a smaller diameter upper portion and a larger diameter lower portion (40B) with an annular shoulder (34) therebetween and the top end surface (44) of the cylinder liner (19) abuts the shoulder (34) formed on the lower end of the upper cylinder portion , the upper portion (20) of the cylinder (40) having a minimum diameter at least equal to the inner diameter of the liner (19) and at least one of the valve seats 17a,17b of corresponding valves (5a,6a) protrudes radially of the valve seats into the wall of the upper portion(20) of the cylinder.

2. An engine as claimed in Claim 1 c h a r a c t e r i s e d i n that the upper portion (20) of the cylinder (40) has a diameter which is greater than the internal diameter of the cylindrical liner (19) .

3. An engine as claimed in Claim 2 c h a r a c t e r i s e d i n that the cylinder liner (19) has a diameter of 60mm and the upper cylinder wall (20) has a diameter of 60.2mm.

4. An engine as claimed in Claim 2 or Claim 3 c h a r a c t e r i s e d i n that the axial length of the upper portion (20) of the cylinder (40) is such that it extends axially just beyond the end surface (46) of the piston (4) when at T.D.C.

5. An engine as claimed in any one of Claims 1 to 4 c h a r a c t e r i s e d i n that the axial length of the upper portion (20) of the cylinder (40) is substantially equal to the length of the top land (18) of the piston.

6. An engine as claimed in any one of claims 1 to 5 c h a r a c t e r i s e d i n that said one pair of valves (5a, 6a) constitute an inlet valve (5a) and an outlet valve (6a), and both said valves (5a, 6a) have valve seats (17) that protrudes radially of the valve seats into the wall of the upper portion (20) of the cylinder.

7. An engine as claimed in Claim 6 c h a r a c t e r i s e d i n that the combustion chamber has two pairs of valves (5a,6a and 5b,6b), and each of said valves has a valve seat (17) that protrudes radially of the valve seats into the wall of the upper portion (20) of the cylinder.

8. An engine as claimed in claim 7 or Claim 8 c h a r a c t e r i s e d i n that the valve seats protrudes radially of the valve seats into the wall of the upper portion (20) of the cylinder for a distance up to 50% of the radial width of the annular continuum of the liner (19) formed by the upper portion (20) of the cylinder wall.

9. An engine as claimed in any one of Claims 1 to 8 c h a r a c t e r i s e d i _n that the valve also protrudes into an annular squish plane (26) located where said upper cylinder portions (20) intersect the roof (41) of the combustion chamber.

10. An engine as claimed in any one of Claims 1 to 9 c h a r a c t e r i s e d i n that the engine is formed of the monoblock construction having an integral cylinder head (3) and cylinder block (2) construction.