GB2286039A - Engine cooling system - Google Patents

Abstract

A cooling system for an internal combustion engine, eg. of a motor vehicle, having a cylinder head (1) attached to a cylinder block (2) optionally with a gasket (3) positioned in between, comprises passages in the cylinder head (1) and block (2) for the flow of coolant therethrough with the passages communicating via at least one connecting duct (4), a pump (13) to circulate the coolant between cylinder head inlet (15) and outlet (5) ducts, mutually independent first (14) and second (10) thermostat valves, a cylinder block bypass duct (11) and metering means, which may comprise a sized aperture and may comprise the at least one connecting duct (4), to control the maximum proportional volume rate of coolant flowing between the cylinder block and the cylinder head. The valves (14, 10) are calibrated respectively to prevent flow of coolant through the cylinder block (2) at a first temperature below, but permit such flow at a second temperature below, the normal operating temperature of the engine and to prevent flow of the coolant through the bypass duct (11) at or above the normal operating temperature of the engine. The metering means is such that at the normal operating temperature of the engine, the volume rate of coolant flowing through the block (2) is less than that through the head (1), eg. 20% to 40%, preferably about 30%, of the total volume rate of coolant flowing through the head (1) and the block (2). <IMAGE>

Description

Engine Cooling System The present invention relates to a cooling system for an internal combustion engine and particularly, but not exclusively, to a cooling system for an internal combustion engine of a motor vehicle.

Internal combustion engines are generally designed to operate efficiently at an elevated temperature, commonly referred to as the normal operating temperature. Because of differences that often occur between the temperatures of various components of an engine, this term, when applied to an engine, is normally understood to convey that the components of the engine are each at their respective normal operating temperature for that engine. However, in order to provide a reference temperature for the purposes of this specification, the normal operating temperature of the engine should be understood to mean the maximum bulk coolant temperature desired when the components of the engine are each at their respective normal operating temperature for that engine.

Operation of an engine which is cold gives rise to uneconomic use of fuel and a high level of unburnt hydrocarbons to be emitted in exhaust gases which is undesirable in view of anti-pollution standards. Lubricants are also less effective below their designed working temperatures and operation of an engine which is cold can give rise to undue wear of moving parts and higher fuel consumption. Thus, it is desirable for an engine to reach its normal operating temperature as rapidly as possible.

On the other hand, overheating of an internal combustion engine under a variety of conditions of load and environment, for example, needs to be prevented. To this end it is desirable for an engine to have a cooling system which, overall, has a high thermal capacity and a high rate of heat dissipation for good thermal stability.

Accordingly, internal combustion engines are generally cooled by the circulation of liquid coolant, water in particular, through passages formed in the cylinder head and the cylinder block components of such engines.

With the need to reconcile the desire for rapid warm-up with that for a high thermal capacity cooling system, much attention has been paid, particularly by the motor vehicle industry, to the design of cooling systems based on the above-mentioned method of circulation of coolant.

Because the heat generated in an internal combustion engine is largely concentrated in the region of the cylinder head, there is a need to cool the cylinder head rapidly after starting the engine. On the other hand, because it is desirable for the cylinder block to reach its operating temperature as quickly as possible, there is a need to strictly control the cooling of this part of the engine during the warm-up period.

To this end, various design proposals have been made in which the flow of coolant through the cylinder head and the cylinder block are respectively controlled during the warmup period to minimize the delay in the engine reaching its normal operating temperature. Systems in which the coolant flow through the cylinder head and block are respectively controlled are sometimes referred to as split cooling systems.

In respect of known proposals, reference may be made to the disclosures of British patent specification number 2034022.

This specification discloses a split cooling system wherein the flow of coolant through the cylinder block is prevented during engine warm-up. Accordingly, as directed by a temperature controlled regulator and thermostat controller, coolant is pumped through the cylinder head and returned to the pump via a by-pass circuit. After warm-up, when the cylinder block has reached its running temperature, flow to the block is permitted by the regulating device, either by redirecting the flow of coolant to the cylinder head via the cylinder block ( which may be termed a series arrangement or by opening a parallel flow duct to the cylinder block which may be termed a parallel arrangement).In this system, after warm-up of the cylinder block, either the coolant flow is sequential through the block and the head, or is parallel through the block and the head, in each case with no preferential flow through the head and in a manner requiring complex external ducting.

Reference may also be made to the disclosures of British patent specification 2193307 wherein a split cooling system is proposed using a double thermostat valve. At partial warm-up, the thermostat valve permits the cylinder head coolant to flow, in limited manner, to the radiator in addition to the block through which a small quantity of coolant flows even at engine start-up. At full warm-up, the valve permits the cylinder head coolant to flow more fully to the cylinder block to the extent that a high proportion of the coolant passing through the head passes through the block.

The disclosures of European patent specification publication 38586 relate to a further proposal employing multiple pumps and valves in a parallel arrangement of a split cooling system and which are electronically controlled.

According to the present invention there is provided an engine cooling system for an internal combustion engine having a cylinder head attached to a cylinder block, said cooling system comprising passages formed in the cylinder head and in the cylinder block for the flow of a coolant therethrough, said passages communicating with one another via at least one connecting duct, a pump to circulate the coolant between inlet and outlet ducts provided on the cylinder head and communicating with the passage therein, mutually independent first and second thermostat valves and a cylinder block by-pass duct, metering means to control the maximum proportional volume flow rate of coolant through the cylinder block and between the cylinder head and the cylinder block, to the total volume rate of coolant flowing through the cylinder head and the cylinder block, wherein the first valve is calibrated to prevent flow of the coolant through the cylinder block passage at a first temperature below the normal operating temperature of the engine as herein before defined but to permit flow of coolant through the cylinder block passage at a second temperature below the normal operating temperature of the engine and the second valve is cal brated to prevent flow of the coolant through the cylinder block by-pass duct at a temperature at or above the normal operating temperature of the engine and wherein the metering means is such that at the normal operating temperature of the engine the volume rate of coolant flowing through the cylinder block passage is less than that through the cylinder head passage.

By means of this invention, a split cooling system may be provided which is simple in construction and effective in operation to provide rapid warm-up and preferential flow of coolant through the cylinder head whereby the high amount of heat which is continued to be generated in the region of the cylinder head after engine warm-up, can be adequately dissipated as may be required for controlling pre-ignition, for example.

It is preferred that the first and second thermostat valves are each of an integrally self operating type such as an expansion capsule type.

It is preferred that the engine cooling system of this invention includes only one pump.

It is preferred that the volume rate of coolant flowing through the cylinder block passage is, at all times during operation of the cooling system, less than that flowing through the cylinder head passage.

It will be appreciated that the cooling system of the present invention only separates the cylinder head and the cylinder block cooling circuits during the initial stage of the engine warm-up period to thereby create a high heat transfer, low thermal inertia circuit in the cylinder head.

For cooling systems employed for motor vehicle engines, a heater circuit attached to the cylinder head circuit will benefit by being capable of rapid heat-up for the added comfort of the vehicle occupants.

Accordingly, it is preferred that in the cooling system of the present invention, a heater circuit is connected between the outlet duct on the cylinder head and an inlet connection to the pump and that the cooling system parameters are such that on starting an engine fitted with such a system from cold, when coolant is circulated only through the cylinder head, heater, cylinder block by-pass duct and the pump, the system will bring the engine to its normal operating temperature in about 60% of the time taken by a system not employing split cooling. The ratio of heat transfer to the coolant during the warm-up period for the cylinder head cylinder block when employing a cooling system of the present invention is preferably in the region of 0.67 : 0.33 and the corresponding ratio of thermal inertia of the cylinder head : cylinder block is preferably in the region of 0.40 : 0.60.

It will be appreciated that in addition to the vehicle heater, preferably included in the cooling system of this invention, rapidly heating up, the fuel inlet ports in the cylinder head also quickly reach their designed normal operating temperature which permits a shorter fuel enrichment period and easier transient fuel control so reducing fuel gas emissions to the exhaust system.

It will be appreciated also that, during the warm-up period and below the second temperature below the normal operating temperature of the engine, the quiescent coolant in the cylinder block effectively acts as a heat insulator enabling the cylinder walls to heat up quickly. At the second temperature below the normal operating temperature when coolant at the second temperature is permitted to flow through the cylinder block, the rate of warm-up of the cylinder block walls to their normal operating temperature may be increased thereby reducing the time of cold operation and the attendant undue friction and wear.

To this end the second temperature is preferably in the region of about 20 to 30at, especially about 25"C, below the normal operating temperature of the engine.

As will be understood; in the engine cooling system of the present invention; between the second temperature below its normal operating temperature and the normal operating temperature itself, coolant will continue to be circulated through the by-pass duct as well as being circulated through the cylinder block.

The at least one connecting duct providing communication between the passages formed in the cylinder head and in the cylinder block for the flow of coolant therethrough, is preferably positioned such as not to prevent a flow of coolant from one end of the cylinder head to the other, but to avoid giving rise to significant localised recirculation of coolant within the cylinder block which might alternatively occur with twin ducts spaced longitudinally of the head and block, for example. Accordingly, it is preferred that the at least one connecting duct is positioned closer to the outlet duct on the cylinder head than to the inlet duct. It is preferred to ensure a high coolant velocity and a high heat transfer coefficient in the cylinder head in order to produce a uniform combustion chamber temperature.

It is preferred that the at least one connecting duct is an internal connecting duct which traverses the jointing interface between the cylinder head and the cylinder block.

Such jointing interface preferably includes a gasket which the connecting duct accordingly also traverses.

The metering means may comprise a sized aperture suitably positioned anywhere such as in the cylinder head, the pump, the first and/or second thermostat valve but preferably comprises the at least one connecting duct.

It is preferred that the metering means has such dimensions that after the normal operating temperature of the engine is reached and the first and second thermostat valves have both been fully activated, the volume rate of coolant flowing through the metering means is in the range of 20% to 40%, and more preferably in the region of 30%, of the total volume rate of coolant flowing through the cylinder head and the cylinder block.

It is preferred that the second valve is calibrated to commence operation at a temperature of about 10 to 20'C, especially about 150 C, below the normal operating temperature of the engine.

It is preferred that the first thermostat valve communicates with the coolant in the cylinder block and so that when it opens it allows the pump to communicate with the cylinder block passages either to: a) draw coolant from the cylinder block passage or b) pump coolant into the cylinder block passage directly via the valve.

In the case of the a) arrangement, the pump is preferably of the dual inlet, mono outlet type, whereas in the case of the b) arrangement, the pump is preferably of the dual outlet, mono inlet type. In both alternatives, one inlet of the pump is connected to the cylinder block by-pass duct and may also be connected to out-put ducts of external heat exchangers such as a heater and/or radiator.

It is preferred that the first thermostat valve is calibrated to open at a temperature lower than the temperature at which the second thermostat valve commences to operate. In this connection, it is preferred that when the first thermostat valve has opened, 25% to 338 of the coolant passing through the pump passes through the cylinder block.

The second thermostat valve preferably communicates with the coolant exiting from the cylinder head via the outlet duct thereon. It is calibrated to be fully operated at a temperature corresponding to the normal operating temperature of the engine. When this second valve is operated, it preferably closes the cylinder block by-pass duct and also opens ducting from the outlet duct on the cylinder head to a radiator, its operation not affecting any communication between the outlet on the cylinder head and any heater connected to the cooling system.

In order to reduce the risk of gas entrapment in the system, the system is preferably provided with a de-gas arrangement, which may be of known type, connected across it. However, because the coolant in the cylinder block is quiescent during at least the first stage of the warm-up period, there is a very significant risk of gas build-up in the cylinder block. It is preferred that gas channels or valves are provided between the cylinder block passage and the cylinder head passage to permit the escape of such gases to such a degassing arrangement. Clearly, such channels or valves should be such as not to significantly interfere with the coolant flow.To this end, it is preferred that the jointing interface of the cylinder head and the cylinder block, and especially a gasket of such a jointing interface when employed, is equipped with one-way de-gas valves situated to permit one-way communication of gas between purpose made channels in the cylinder block and the cylinder head and connected to the passages therein. Such one-way de-gas valves may be valves of a known split elastomer diaphragm or lifting diaphragm type.

The present invention will now be illustrated, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic drawing of one engine cooling system according to this invention.

Figure 2 is a schematic drawing of an engine cooling system according to this invention and is an alternative to that shown in Figure 1.

Figure 3 is a sketch of the gasket employed in the cooling systems shown in Figure 1 and Figure 2.

Figure 4 is a sketch showing details of one of the one-way de-gas valves employed with the gasket as shown in Figure 3.

Figure 5 is a sketch showing by way of enlargement, details of the thermostat 10 shown in Figures 1 and 2.

In the drawings in which like numbers correspond; the cylinder head 1, of an internal combustion engine, is bolted in known manner ( not shown ) to the cylinder block 2 with the gasket 3 positioned in between. The gasket 3 has two connecting ducts 4 ( only one is shown in Figures 1 and 2 situated close to the outlet duct 5 on the cylinder head 1.

The connecting ducts 4 serve also as metering means. The cylinder head 1 and the cylinder block 2 are provided with internal passages ( not shown in detail ) for the flow of coolant therethrough, and which passages communicate through the connecting ducts 4. To the outlet duct 5, is attached a manifold 6 to which is connected conduits to a motor vehicle heater 7, a radiator 8 and a de-gas valve arrangement 9. Within the manifold 6 is situated a by-pass thermostat valve 10 ( see Figure 5 for detail ).Also connected to the outlet duct 5 is one end of the cylinder block by-pass duct 11, the other end of which is connected to the outlet conduits from the heater 7 and the radiator 8 ( to which is connected the return conduit from the de-gas valve arrangement 9 ) and to the inlet 12 of the pump 13 in Figure 1 ( 13' in Figure 2 ). 14 is a cylinder block thermostat valve with which the pump 13 ( 13' communicates. Pump 13 of Figure 1 is a dual inlet, single outlet pump, whereas pump 13' of Figure 2 is a dual outlet, single inlet pump.

The arrows shown in Figure 1 and Figure 2 indicate the direction of coolant flow when the engine in each case is fully warm and therefore reached its normal operating temperature.

With reference to Figure 1; with the engine started from cold, and under which condition the thermostat valve 14, which is of the expansion capsule type, is in the closed state and the by-pass thermostat valve 10, which is also of the expansion capsule type, is in a state closing off the conduit to the radiator 8 but leaving conduit to the heater 7 and the by-pass duct 11 open, the pump 13 pumps coolant into the cylinder head 1 via the cylinder head inlet duct 15 and through the cylinder head 1 to the manifold 6 from which the coolant travels then down the by-pass duct 11 and through the conduit of the heater 7 and back to the inlet 12 of the pump 13.While the thermostat valve 14 is closed, the coolant in the cylinder block 2 remains substantially static, allowing the cylinder block 2 to warm-up; at the same time, recirculation of the coolant passing through the cylinder head 1 allows the cylinder head 1 to heat up quickly but with rapid distribution of the heat to facilitate a uniform temperature rise. As indicated above, the position of the by-pass thermostat valve 10 in the manifold 6 is such as to permit coolant to pass through the conduit of the heater 7 and back to the pump 13.When partial warm-up has been achieved, as detected by the thermostat valve 14, the temperature of the coolant passing in the vicinity of the thermostat valve 14 and which is a temperature below, particularly a second temperature below, the normal operating temperature of the engine, causes it to open thereby allowing the pump 13 to draw coolant from the passages of the cylinder block 2 and through the metering connecting ducts 4 from the cylinder head 1. In this way, some of the heated coolant from the cylinder head 1 is employed to assist in warming-up the cylinder block 2 during this stage. The full out-put of the pump 13 is still discharged through the cylinder head 1 first, flowing from end to end, to produce a high coolant velocity and a high heat transfer coefficient in the cylinder head 1 to achieve an even combustion chamber temperature and thereby control of pre-ignition.The metered circulation through the cylinder block 2 reduces the coolant velocity and heat transfer coefficient in the cylinder block 2 thereby permitting elevation of the cylinder temperatures, even though there is only a small difference in the bulk coolant temperature between the cylinder head 1 and the cylinder block 2. The proportion of coolant drawn through the cylinder block 2 is about 25 to 33% and in the region of 30% of the coolant pumped into the cylinder head 1 via the inlet duct 15.

When the coolant passing over the by-pass thermostat valve 10 reaches the temperature consistent with the engine having attained a temperature of about 15 C below its normal operating temperature, the valve 10 is caused to begin to operate and, at a temperature consistent with the engine having attained its normal operating temperature fully operates to close the cylinder block by-pass duct 11 and to open the manifold 6 to the conduit to the radiator 8. Under these conditions, the pump 13 is able to draw coolant from the cylinder block 2, the heater 7 and the radiator 8 and pump that coolant into the cylinder head 1 via the inlet duct 15.The proportion of coolant drawn through the metering connecting ducts 4 and through the cylinder block 2 at the normal operating temperature of the engine remains in the region of about 30%, of the coolant pumped into the cylinder head 1 via the inlet duct 15.

Figure 3 is a plan view of the gasket 3 shown in Figure 1.

The two metering connecting ducts 4 are located at the rear end of the engine. The holes 16 are holes corresponding to the engine cylinder bores and the remaining holes are bolt holes and holes to accommodate mechanical components of the engine. Attached to the gasket 3 are one-way de-gas valves 17, of which there are fifteen, positioned to permit the one-way passage of gas from the cylinder block 2 to the cylinder head 1 from which it can be transmitted to the manifold 6 and thereby to the de-gas valve arrangement 9.

Figure 4 shows details of one of the one-way valves 17 employed with the gasket shown in Figure 3 which valve is of the split elastomer diaphragm type. The skilled addressee will be aware of alternative valves which may be employed.

Figure 2 illustrates an alternative cooling system to that shown in Figure 1 and is likewise in accordance with the present invention. The principal difference between the cooling systems shown in Figure 1 and Figure 2 is that in the system of Figure 2, the pump 13' is such that when the cylinder block thermostat valve 14 opens, the pump pumps coolant into and through the passages of the cylinder block 2 and out through the metering connecting ducts 4 into the cylinder head 1. In this alternative system, the flow of coolant, at the partial and fully warmed-up stages, in the cylinder head 1 and in the cylinder block 2 is very largely a parallel arrangement with the proportion of coolant passing through the cylinder block being about 30%, of that passing through the manifold 6, and the balance of about 70% being pumped directly into the cylinder head 1 by the pump via the inlet duct 15.At the fully warmed-up stage, the full flow from the pump 13' may be drawn from the radiator 8 so fully utilizing, and not compromising, the heat dissipation capability of the system. Other details of the alternative system shown in Figure 2 are as described with reference to Figure 1 and also with reference to Figure 3, Figure 4 and Figure 5.

The cooling systems illustrated with reference to the accompanying drawings are of simple construction and are effective in achieving rapid warm-up of the engine to its normal operating temperature while maintaining a relatively high coolant velocity and a relatively high heat transfer coefficient in the cylinder head and a lower coolant velocity and a lower heat transfer coefficient in the cylinder block. Thus, even combustion chamber temperatures with attendant control of pre-ignition and quickly elevated cylinder temperatures with attendant increase in lub-icGnt efficiency and associated reduced friction and wear, are achieved.

Claims (23)

Claims:

1. An engine cooling system for an internal combustion engine having a cylinder head attached to a cylinder block said cooling system comprising passages formed in the cylinder head and in the cylinder block for the flow of a coolant therethrough, said passages communicating with one another via at least one connecting duct, a pump to circulate the coolant between inlet and outlet ducts provided on the cylinder head and communicating with the passage therein, mutually independent first and second thermostat valves and a cylinder block by-pass duct, metering means to control the maximum proportional volume flow rate of coolant through the cylinder block and between the cylinder head and the cylinder block, to the total volume rate of coolant flowing through the cylinder head and the cylinder block, wherein the first valve is calibrated to prevent flow of the coolant through the cylinder block passage at a first temperature below the normal operating temperature of the engine, as herein before defined, but to permit flow of coolant through the cylinder block passage at a second temperature below the normal operating temperature and the second valve is calibrated to prevent flow of the coolant through the cylinder block by-pass duct at a temperature at or above the normal operating temperature of the engine and wherein the metering means is such that at the normal operating temperature of the engine the volume rate of coolant flowing through the cylinder block passage is less than that through the cylinder head passage.

2. An engine cooling system as claimed in Claim 1 wherein the first and second thermostat valves are each of an integrally self operating type.

3. An engine cooling system as claimed in Claim 1 or Claim 2 wherein the volume flow rate of coolant flowing through the cylinder block passage is at all times during operation of the cooling system less than that flowing through the cylinder head passage.

4. An engine cooling system as claimed in any one of the preceding claims wherein the system includes only one pump.

5. An engine cooling system as claimed in any one of the preceding claims wherein a heater circuit is connected between the outlet duct on the cylinder head and an inlet connection to the pump.

6. A cooling system as claimed in any one of the preceding claims wherein below the normal operating temperature of the engine the ratio of heat transfer to the coolant for the cylinder head : cylinder block is 0.67 : 0.33 and the ratio of thermal inertia for the cylinder head : cylinder block is 0.4 : 0.6.

?. A cooling system as claimed in any one of the preceding claims wherein the second temperature below the normal operating temperature of the engine is in the region of 20 to 30 e C below the normal operating temperature of the engine.

8. A cooling system as claimed in any one of the preceding claims wherein the at least one connecting duct is positioned closer to the outlet duct on the cylinder head than to the inlet duct.

9. A cooling system as claimed in any one of the preceding claims wherein the at least one connecting duct is an internal connecting duct which traverses the jointing interface between the cylinder head and the cylinder block.

10. A cooling system as claimed in Claim 10 wherein the jointing interface includes a gasket.

11 A cooling system as claimed in any one of the preceding claims wherein the metering means comprises the at least one connecting duct.

12. A cooling system as claimed in any one of the preceding claims wherein the metering means are such that after the normal operating temperature of the engine has been reached the volume rate of coolant flowing through the metering means is in the range of 20% to 40%, preferably in the region of 30t of the total volume rate of coolant flowing through the cylinder head and the cylinder block.

13. A cooling system as claimed in any one of the preceding claims wherein the second valve is calibrated to commence operation at a temperature of about 10 to 20 e below the normal operating temperature of the engine.

14. A cooling system as claimed in any one of the preceding claims wherein the first thermostat valve is such that when it opens it allows the pump either to draw coolant from or alternatively pump coolant into the cylinder block passage directly via the valve.

15. A cooling system as claimed in any one of the preceding claims wherein the first thermostat valve is calibrated to open at a temperature lower than the temperature at which the second thermostat valve commences to operate.

16. A cooling system as claimed in Claim 15 wherein when the first thermostat valve has opened 25% to 33% of the coolant passing through the pump passes through the cylinder block.

17. A cooling system as claimed in any one of the preceding claims wherein the second thermostat valve communicates with the coolant exiting from the cylinder head and is calibrated to be fully operated at a temperature corresponding to the normal operating temperature of the engine.

18. A cooling system as claimed in Claim 17 wherein the second thermostat valve when fully operated closes the cylinder block by-pass duct.

19. A cooling system as claimed in Claim 18 wherein the second thermostat valve when operated opens ducting from the outlet duct on the cylinder head to a radiator.

20. A cooling system as claimed in any one of the preceding claims wherein the system is provided with a de-gas arrangement.

21. A cooling system as claimed in Claim 20 wherein the degas arrangement includes one-way de-gas valves.

22. A cooling system as claimed in Claim 21 wherein the degas-valves are incorporated in a gasket of the jointing interface of the cylinder head and the cylinder block.

23. A cooling system substantially as described herein with reference to the accompanying drawings.