GB2442736A - Cooling internal combustion engines - Google Patents

Abstract

Each cylinder 33 of the i.c. engine 110 is surrounded by an upper water jacket 13 and a lower oil jacket, the latter being formed by a thin walled hollow spacer 20. After start-up from cold, heat is transferred directly from each cylinder 33 to the oil circulating through the thin walled hollow spacer 20 thereby reducing the time taken for the oil to warm up. When the engine 110 is running at a high temperature heat is transferred from the oil to the coolant flowing through the water jacket 13 thereby preventing overheating of the oil. The hollow spacer 20 may be made from copper for good thermal conductivity and may have an inclined upper wall 23. Alternatively, the upper wall of the hollow spacer (220, fig.5) may be at right angles to the cylinder axis. The hollow spacer 20, (220) may be fitted into the water jacket of an existing engine.

Description

An Internal Combustion Engine This invention relates to an interna]

combustion engine and in particular to the cooling of such an engine.

International concern regarding the effect of automotive emissions on global warming has led to strict fuel consumption regulations around the world. Engine manufactures have identified engine friction as a critical factor for improving engine fuel economy and the engine warm-up period is of particular interest because during this operation mode the viscosity of the lubricating oil is high and therefore frictional losses are greatest.

Piston friction accounts for about 30% of the total frictional losses of an engine and in recent years a number of innovative technologies have been developed for reducing piston friction. Two examples of such technologies are split cooling, where cooling of the block is separated from that of the head and the use of a water jacket spacer for open deck engine block designs, where the distribution of cylinder wall temperatures is improved through the insertion of a solid plastic spacer in the water jacket.

In a conventional engine such as that shown in Fig.2, the velocity of the coolant in the water jacket is greatest mid-way along the height of the cylinder (as shown in Fig.2b) where cooling is not critical and the velocity of the coolant is lowest near the top of the cylinder where cooling is most needed. Due to this coolant velocity distribution the temperature decays along the depth of the cylinder, from a maximum at the top to a minimum at the bottom (see Fig. 2a) Lubrication between the cylinder and the piston ring consists of mixed lubrication near the top dead center, and predominantly hydrodynamic lubrication in the lower half of the cylinder. A reduction in friction in the upper section of the cylinder can be achieved through a reduction of the cylinder wall temperature, which increases the viscosity of the oil attached to the wall. To reduce friction in the lower half of the cylinder an increase of the wall temperature is needed, which reduces the viscosity of the oil which also improves the thermodynamic efficiency of combustion. The use of a water jacket spacer concentrates coolant flow in the upper part of the water jacket, thus providing an optimal distribution of coolant velocity and hence cylinder temperature, for improved lubrication and reduced piston friction.

It is further known from US Patent 5,842,447 to provide an engine in which passages are cast into the cylinder block so as to reduce the height of the water jacket and provide an oil jacket surrounding a lower part of each cylinder.

It is an object of this invention to provide an internal combustion engine having improved efficiency particularly after start-up from cold.

According to a first aspect of the invention there is provided an internal combustion engine having a cylinder block, a cylinder defined by a cylinder liner supported by the cylinder block, a reciprocating piston having an upper face moveable within the cylinder along a longitudinal axis of the cylinder between a top dead centre and a bottom dead centre position so as to define a working portion of the cylinder, a coolant jacket surrounding the cylinder liner through which in use coolant is caused to flow so as to cool an upper portion of the working portion of the cylinder wherein an oil jacket formed by a thin walled hollow spacer is interposed between the cylinder block and the cylinder liner, the thin walled hollow spacer surrounds a lower portion of the working portion of the cylinder, has a wall that forms common boundary wall between the oil jacket and the coolant jacket and is arranged, in use, to have oil circulated therethrough.

Advantageously, the boundary wall may be inclined relative to the longitudinal axis of the cylinder so as to increase the surface area of the boundary wall.

An oil pump may he provided to circulate oil from an oil reservoir through the thin walled hollow spacer and through one or more bearings of the engine.

The engine may be a multi-cylinder engine and each cylinder of the engine may have an upper working portion surrounded by a coolant jacket and a lower working portion surrounded by an oil jacket formed by a single thin walled hollow spacer.

The thin walled hollow spacer may be made from a material having a high coefficient of thermal conductivity.

The coefficient of thermal conductivity may be higher than that of cast iron.

The invention will now be described by way of example with reference to the accompanying drawing of which:-Fig.l is an exploded pictorial representation of an open deck three cylinder inline engine according to the invention showing a thin walled hollow spacer in a pre-installed position; Fig.2 is a cross-section through one cylinder of a conventional internal combustion engine; Ftg.2a is a graph of cylinder temperature versus cylinder depth for the engine shown in Fig.2; Fig.2b is a graph of coolant flow velocity versus cylinder depth for the engine shown in Fig.2; Fig.3 is a cross-section through one cylinder of the internal combustion engine shown in Fig.l in an assembled condition; Fig.3a is a graph of cylinder temperature versus cylinder depth showing as a dotted line the values for the engine shown in Fig.2 and showing as a solid line the values for the engine shown in Fig.3; Fig.3b is a graph of coolant flow velocity versus cylinder depth showing as a dotted line the values for the engine shown in Fig.2 and showing a as a solid line the values for the engine shown in Fig.3; Fig.4 is an enlarged cross-section through the oil filled spacer shown in Fig.3; Fig.5 is a cross-section through one cylinder of an internal combustion engine according to a second embodiment of the invention; Fig.6 is a line diagram showing conventional water and oil circulation systems used for the engine shown in Fig.2; and Fig.7 is a line diagram showing a water and oil circulation system used for the engines shown in Figs.3 and 5.

With reference to Figs.2, 2a, 2b and 7 there is shown a cross-section through one cylinder of a prior art three cylinder inline open deck internal combustion engine 10 having a cylinder head 11 supporting two camshafts, a cylinder block 12 defining a coolant or water jacket 13, a cylinder liner 32 supported by the cylinder block 12 defining a cylinder 33, a piston 15 slidingly supported in the cylinder, a crankshaft 14 and a connecting rod 16 connecting the piston 15 to the crankshaft 14.

The piston 15 reciprocates in the cylinder 33 between an upper position known as a top dead centre position (shown in Fig.2) and a lower position known as a bottom dead centre position (when the crankshaft is at 180 degrees to the position shown in Fig.2) . This motion causes a top surface of the piston 15 to define a working portion of the cylinder 33 in which the various stages of combustion occur.

As shown in Fig.7, the engine 10 has four intake cam bearings 30, four exhaust cam bearings 31, three connecting rod bearings 34, three crankshaft main bearings 35 and a number of oil supply conduits 45 to supply oil to the various bearings 30, 31, 34, 35. The oil is circulated from an oil reservoir or sump 40 by a pump 42 which collects oil from the sump 40 via a pick-up tube and circulates the oil through an oil filter 43 and an oil to water heat exchanger 44 used to prevent overheating of the oil and then to the oil supply conduits 45 and possibly to other components indicated by hashed box referenced 46. The other components may include a turbocharger, an actuator for a variable valve timing system, piston cooling jets or any other device requiring a source of pressurised oil.

After use the oil is returned to the sump 40 via return conduits (not shown) Coolant is circulated through the water jacket 13 by a pump (not shown) forming part of a general engine cooling system (not shown) which also includes at least one heat exchanger or radiator to reject the heat from the coolant before it is recirculated through the coolant jacket 13.

The coolant is also circulated through the oil heat exchanger 44 to heat the oil upon start-up from cold.

As previously referred to, the velocity of the coolant through the water jacket 13 is not uniform but exhibits the characteristic shown in Fig.2b and this causes the temperature along the cylinder liner 32 to vary as shown in Fig.2a. This variation in cylinder liner temperature is due to the fact that the temperature within the working portion of the cylinder 33 is higher at an upper end of the working portion of the cylinder 33 than it is at a lower end of the working portion of the cylinder 33 and the fact that the velocity of the coolant is not uniform.

The temperature of the cylinder liner 32 is so high at the upper end of the cylinder liner 32 that friction is increased due to the very low viscosity of the oil attached to the cylinder wall and so it is advantageous in the upper section of the cylinder to reduce the temperature of the cylinder wall which will increase the viscosity of the oil attached to the wall thereby reducing friction. In the lower half of the cylinder wall the problem is that the temperature of the oil attached to the cylinder wall is too low and so the viscosity of the oil is too high thereby increasing the friction. Therefore, in order to reduce friction in the lower half of the cylinder, an increase in cylinder wall temperature is needed, to reduce the viscosity of the oil.

With reference to Figs.l, 3, 3a, 3b, 4 and 8 there is shown a first embodiment of the invention which in many respects is identical to that previously described.

As before the engine 110 has a cylinder head 11 supporting two camshafts, a cylinder block 12 defining a water jacket 13, a cylinder liner 32 supported by the cylinder block 12 defining a cylinder 33, a piston 15 slidingly supported in the cylinder, a crankshaft 14 and a connecting rod 16 connecting the piston 15 to the crankshaft 14.

As before, the motion of the piston 15 between its top dead centre and bottom dead centre positions causes a top surface of the piston 15 to define a working portion of the cylinder 33 in which the various stages of combustion occur.

However, unlike the engine 10 shown in Fig.2, the engine 110 shown in Figs.l and 3 only has a water jacket 13 surrounding an upper portion of the working portion of the cylinder 33 not the entire working portion. That is to say, at an upper end of the cylinder 33, a water jacket is defined between the cylinder liner 32 and the cylinder block 12 through which coolant is circulated in use to cool the cylinder 33 and at a lower portion of the working portion of the cylinder 33 an oil jacket surrounds the cylinder in the form of a thin walled hollow spacer 20 interposed between the cylinder liner 32 and the cylinder block 12.

As shown in greater detail in Fig.4 the thin walled hollow spacer 20 comprises of a body 21 defining a cavity 22 through which, in use, oil is circulated. The body 21 has an upper wall 23 that is inclined relative to a longitudinal axis of the cylinder 33 around which the thin walled hollow spacer 20 extends. Apertures (not shown) are formed in the wall of the thin walled hollow spacer 20 each of which co-operates with passages (not shown) formed in the cylinder block 12 to provide oil to the hollow spacer 20 and return the oil to the sump 40. The inclined wall 23 forms in use a common boundary wall between the oil jacket and the water jacket 13 and by inclining the upper wall 23 the surface area is increased thereby increasing the heat transfer between the water jacket and the oil jacket. In addition, by using an inclined upper wall 23 the velocity of the coolant in the water jacket 13 can be modified to produce an improved velocity distribution which more closely replicates the temperature variation in the cylinder 33.

The thin walled hollow spacer 20 can be made from a material having a high coefficient of thermal conductivity, such as for example a copper alloy material, thereby improving the transfer of heat from the cylinder liner 32 to the oil and also between the oil and the water in the water jacket 13. Because the inclined wall 23 is very thin this also improves the transfer of heat between the oil and the water. If required it would also be possible to provide small ribs on the inclined wall 23 to further improve heat transfer between the oil and the water. The term high coefficient of thermal conductivity means a material having a higher coefficient of thermal conductivity than cast iron.

The optimised flow velocity distribution is shown on Fig.3b as a solid line and the velocity distribution with no spacer is shown as a dotted line. It can be seen that with the thin walled hollow spacer 20 in position the velocity of the coolant increases towards the top of the cylinder 33 so as to mimic the temperature distribution within the cylinder 33. The effect of this change in flow velocity distribution can be seen in Fig.3a where the solid line shows the cylinder liner temperature distribution with the thin walled hollow spacer 20 in place and the dotted line shows the temperature distribution with no spacer. It can be seen that with the thin walled hollow spacer 20 in place the temperature of the cylinder liner 32 falls towards the upper end of the cylinder 33 and is lower than that present when the thin walled hollow spacer 20 is not in place. This will increase the viscosity of the oil at the upper end of the cylinder 33 thereby reducing friction at the upper end of the cylinder 33. At the lower end of the cylinder 33 the temperature of the cylinder liner 32 is increased compared to the situation where no thin walled hollow spacer 20 is used, this will reduce the viscosity of the oil at the lower end of the cylInder 33 thereby further reducing friction.

As shown in Fig.8, the engine 110 has four intake cam s bearings 30, four exhaust cam bearings 31, four connecting rod bearings 34, four crankshaft main bearings 35 and a number of oil supply conduits 45 to supply oil to the various bearings 30, 31, 34, 35. The oil is circulated from an oil reservoir or sump 40 by a pump 42 which collects oil from the sump 40 via a pick-up tube and circulates the oil through an oil filter 43 to the thin walled hollow spacer 20 which is connected to the oil supply conduits 45 and possibly to other components indicated by hashed box referenced 46. After use the oil is returned to the sump 40 via return conduits (not shown) . Coolant is circulated through the water jacket 13 by a pump (not shown) forming part of a general engine cooling system (not shown) which also includes at least one heat exchanger or radiator to reject the heat from the coolant before it is recirculated through the coolant jacket 13.

One significant difference between this arrangement and that shown in Fig.7 is that no coolant to oil heat exchanger is required because the thin walled hollow spacer 20 is in intimate contact with the coolant jacket 13 through the inclined common wall 23. As mentioned above the very thin nature of the common wall 23 enables good conduction of heat away from the oil into the water flowing through the water jacket 13 when the engine is running normally with a radiator bypass (not shown) closed so that the water passing through the water jacket 13 also passes through a radiator (not shown) . One of the disadvantages of the construction shown in US Patent 5,842,447 is that it is extremely difficult to produce a very thin section wall between the oil and water both from a physical casting viewpoint and also from the aspect of porosity which is always an issue with thin walled castings. Therefore it is not possible to -10 -achieve the same level of conduction from the oil to the water through a cast wall as it is with the thin inclined wall 23 of the thin walled hollow spacer 20. This would be even more so if the thin walled hollow spacer 20 is made from a highly conductive material such as a copper alloy and the cylinder block were made from cast iron.

In addition, the use of thin walled hollow spacer 20 to form the oil jacket significantly reduces warm-up friction throughout the engine 110 because the wall between the oil flowing through the thin walled hollow spacer 20 and the cylinder liner 32 is very thin and so has a minimal restriction on conduction of heat from the cylinder 33 SO that heat can be transferred quickly from the cylinder 33 to the oil which improves oil warm-up and increases the bulk oil temperature faster from a cold-start than is possible

with any of the prior art designs. It will also be

appreciated that during start-up from cold the radiator bypass will be open so that water is not circulated through the radiator, the interface between the water jacket and the oil will not therefore have a great effect on the time taken to heat the oil.

It will be appreciated that it is advantageous to rapidly increase the temperature of the oil because this will reduce its viscosity thereby reducing parasitic losses such as pumping losses and reduce friction in any bearing to which the oil is supplied.

It will also be appreciated that because of the very good conduction through the thin inclined wall 23 it is not necessary in most cases to use an oil/ water heat exchanger to cool the oil when the engine is running hot. The temperature of the oil can be maintained at a sufficiently low temperature by conduction through the thin inclined wall 23 into the water passing through the water jacket 13. This means that the total volume of oil required can be reduced -11 -because a significant volume of oil is normally contained within the oil to water heat exchanger and within the pipes connecting the oil to water heat exchanger to the engine.

It will be appreciated that if the volume of oil is reduced s then the time taken to heat the bulk oil will also be reduced thereby further increasing warm-up of the oil.

The benefits of the invention also include those present with the use of a conventional water jacket spacer namely, improved cylinder temperature distribution resulting in reduced piston friction, increased thermodynamic efficiency of combustion, reduced bore distortion and reduced block coolant volume.

is With reference to Fig.5 there is shown a second embodiment of the invention which is identical to that previously described with reference to Figs.3, 3a, 3b and 8 with the exception that the thin walled hollow spacer 220 used in the engine 210 does not have an inclined upper boundary wall. In this embodiment the boundary wall 223 is arranged to be at approximately 90 degrees to the longitudinal axis of the cylinder 33 it surrounds. Although this has a negative effect on the temperature transfer from the water jacket 13 due to the reduction in surface area and more importantly does not provide such an optimised flow through the water jacket 13 such an arrangement still provides an improved performance compared to an engine with no spacer and because of the direct heat transfer from the cylinder 33 to the oil greatly reduces the time taken to warm up the oil after a cold start thereby reducing parasitic losses such as pumping losses and reduces friction in any bearing to which the oil is supplied.

The oil and coolant flows shown in Fig.8 apply to this embodiment exactly as they do to Fig.3 with the exception that instead of there being an oil supply to the thin walled -12 -hollow spacer 20 the oil supply would be to the thin walled hollow spacer 220.

A significant advantage in using a thin walled hollow spacer to provide the oil jacket is that it is potentially possible to provide the advantages of the invention to a conventional open deck engine having a water jacket by fitting a thin walled hollow spacer in accordance with the invention into Lhe water jacket. Only minimal modifications may be required comprising primarily of the need to supply the oil to the thin walled hollow spacer and return the oil from the thin walled hollow spacer. Further advantages include the ease of manufacture compared to casting in such an oil jacket, the ability to use a material for the hollow spacer having a high coefficient of thermal conductivity and the ease in which a thin boundary wall between the oil and the water can be produced.

It will be appreciated by those skilled in the art that although the invention has been described by way of example with reference to one or more embodiments it is not limited to the disclosed embodiments and that one or more modifications to the disclosed embodiments or alternative embodiments could be constructed without departing from the scope of the invention.

Claims (7)

1. -13 -Claims 1. An internal combustion engine having a cylinder block, a

   cylinder defined by a cylinder liner supported by the cylinder block, a reciprocating piston having an upper face moveable within the cylinder along a longitudinal axis of the cylinder between a top dead centre and a bottom dead centre position so as to define a working portion of the cylinder, a coolant jacket surrounding the cylinder liner through which in use coolant is caused to flow so as to cool an upper portion of the working portion of the cylinder wherein an oil jacket formed by a thin walled hollow spacer is interposed between the cylinder block and the cylinder liner, the thin walled hollow spacer surrounds a lower portion of the working portion of the cylinder, has a wall that forms common boundary wall between the oil jacket and the coolant jacket and is arranged, in use, to have oil circulated therethrough.
2. 2. An engine as claimed in claim 1 wherein the boundary wall is inclined relative to the longitudinal axis of the cylinder so as to increase the surface area of the boundary wall.
3. 3. An engine as claimed in claim 1 or in claim 2 wherein an oil pump is provided to circulate oil from an oil reservoir through the thin walled hollow spacer and through one or more bearings of the engine.
4. 4. An engine as claimed in any of claims 1 to 3 wherein the engine is a multi-cylinder engine and each cylinder of the engine has an upper working portion surrounded by a coolant jacket and a lower working portion surrounded by an oil jacket formed by a single thin walled hollow spacer.

   -14 -
5. 5. An engine as claimed in any of claims J to 4 wherein the thin walled hollow spacer is made from a material having a high coefficient of thermal conductivity.
6. 6. An engine as claimed in claim 5 in which the coefficient of thermal conductivity is higher than that of cast iron.
7. 7. An internal combustion engine substantially as described herein with reference to the accompanying drawing.