WO1994007009A1

WO1994007009A1 - Engine cooling system

Info

Publication number: WO1994007009A1
Application number: PCT/GB1993/001934
Authority: WO
Inventors: Thomas Tsoi Hei Ma
Original assignee: Ford Motor Company Limited; Ford Werke A.G.; Ford France S.A.; Ford Motor Company
Priority date: 1992-09-12
Filing date: 1993-09-13
Publication date: 1994-03-31
Also published as: GB2270560A; GB9219362D0

Abstract

An internal combustion engine has a cooling system with a closed coolant circuit which comprises coolant passages in the cylinder head (22), the block (20) of the engine, a radiator (26) connected in parallel with the engine, a circulation pump (10) for circulating the coolant around the engine and the radiator, and a reservoir (30) connected in parallel with the engine and disposed below the level of the cylinder head (22). The coolant is transferred between the reservoir (30) and the engine by gravity and by the pressure head of the circulation pump (10). The cooling system is only partially filled with coolant so that the coolant from the cylinder head (22) is drained to the reservoir (30) by the action of gravity when the engine is at a standstill while leaving coolant in the cylinder block (20) and the circulation pump (10). The cylinder head (22) is gradually refilled with coolant from the reservoir (30) after engine startup as a pressure head is built up by the circulation pump (10).

Description

Title

Engine Cooling System

Field of the invention

The present invention relates to an internal combustion engine and is particularly concerned with the design of the cooling system to reduce the warm up time of the engine.

Background of the invention

It is desirable to reduce the effectiveness of the engine cooling system when the engine is cold in order to achieve more rapid warm up. This is a requirement not only to reduce exhaust emissions but also to improve passenger comfort.

The thermostatic valve which is to be found in all engines acts to prevent circulation of the coolant through the radiator under the action of the coolant pump until a certain temperature is reached. Nevertheless the coolant is circulating around the engine and the intake port and combustion chamber are cooled by this recirculation.

It has been suggested to use a split cooling system that has separate coolant circuits for the cylinder head and the engine block. This proposal improves the warm up time of the cylinder head but the presence of coolant in the circuit for the cylinder head still contributes to the thermal capacity and convective cooling.

Object of the invention

The present invention seeks to provide an internal combustion engine in which the effectiveness of the cooling system in the vicinity of the combustion chambers is minimised during start up from cold. Summary of the invention

According to the present invention, there is provided an internal combustion engine having a cooling system with a closed coolant circuit which comprises coolant passages in the cylinder head, the block of the engine, a radiator connected in parallel with the engine, a circulation pump for circulating the coolant around the engine and the radiator, and a reservoir connected in parallel with the engine and disposed below the level of the cylinder head, the coolant being transferred between the reservoir and the engine by gravity and by the pressure head of the circulation pump, wherein the cooling system is only partially filled with coolant such that substantially all the coolant from the cylinder head is drained to the reservoir by the action of gravity when the engine is at a standstill while leaving coolant in the cylinder block and the circulation pump, the cylinder head being gradually refilled with coolant from the reservoir after engine startup as a pressure head is built up by the circulation pump.

In the present invention, when the engine is started from cold, there is no coolant in the upper part of the engine, including the cylinder head. The cylinder head therefore heats up rapidly. After startup, the engine block and cylinder head fill up gradually with coolant under the action of the circulation pump and when the coolant passages in the engine are completely full, the cooling system operates conventionally.

When the circulation pump ceases to the driven, that is to say^' after the engine is stopped, the pressure head across the pump drops and the coolant can find its own level under the action of gravity, during which time the coolant is drained from the cylinder head back into the reservoir. Preferred features of the invention

It is desirable to control the rate at which the transfer of coolant takes place between the cylinder head and the reservoir both on startup and when the engine is switched off. In the first case, it is important for the cylinder head to remain partially empty for long enough to achieve a significant improvement in the warm-up time, without of course risking overheating of the engine. In the second case, on the other hand, it is important to hold the coolant level in the cylinder head until the engine cools down so that the cylinder head should not be empty during a warm re¬ start .

It is therefore convenient to design the circuit using appropriate valves to control the rate at which fluid can transfer between the reservoir and the engine in different directions.

The lower and upper ends of the reservoir are connected to the engine and while the coolant flows in one direction at the bottom end of the reservoir, air flows in the opposite direction at the top end of the reservoir. Valves and/or flow restrictors may be placed in the connections at the upper or lower end of the reservoir but it is preferred to control the air passages at the upper end of the reservoir.

The valves in the air transfer connections at the upper end of the reservoir may include an externally controlled emergency valve to allow rapid refilling of the engine cylinder head when the risk of overheating is imminent. Such a risk may be detected from measurement of the engine temperature or estimated from the engine speed or the rate at which fuel is burned.

It is common in engines to use a top-up tank above the engine cylinder head level which acts as an overflow tank and maintains the system permanently full. De-gassing lines connect parts of the engine coolant circuit at which air pockets can be formed to the top of top-up tank. In the present invention, the de-gassing lines can be returned to the top of the reservoir and there is no need for a separate top-up tank. The valves and flow restrictor for regulating the fluid exchange rate between the engine and the reservoir may be included in the de-gassing lines.

Brief description of the drawings

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

Figure 1 shows an engine after a prolonged period at a standstill,

Figure 2 shows the engine of Figure 1 after it has reached its steady state operating temperature, and

Figure 3 shows a view similar to that of Figure 1 showing an engine in which the heater core is connected differently, to achieve more rapid warm-up of the passenger compartment.

Detailed description of the preferred embodiments

An engine shown schematically in Figure 1 has a block 20, a cylinder head 22 separated from one another by a gasket 21 having a connection opening 21' . A radiator 26 is connected in parallel with the engine and coolant is circulated around the engine and the radiator 26 by a pump 10. A thermostat 24, which opens only when the coolant reaches a threshold temperature is connected in the circuit to ensure that the radiator 26 remains ineffective while the engine is still warming up. A reservoir 30 is also connected in parallel with the engine by means of lower pipe 43 leading to the intake side 12 of the pump 10 and filled with coolant and an upper pipe 41 which in this state of the engine is filled with air. The upper pipe 41 leads from a point below the thermostat 24 to the air space at the top of the reservoir 30 and at its end near the reservoir 30 it branches into a first section 41a containing a non-return valve 34 and a second section 41b containing an emergency valve 40.

Still further connected in parallel with the engine, in a conventional manner, is a heater core 28. The lower end of the heater core is connected by a line 44 to the intake side 12 of the circulation pump 10 and the upper end of the core is connected by a pipe 42 to a point in the cylinder head 22 below the thermostat 24.

The reservoir 30 doubles as the top-up tank used in conventional cooling systems and to this end it is fitted with a filler cap 32 and its air space is connected by de¬ gassing lines 39 and 45 to the space 24' above the thermostat 24 and to the top of the heater core 28. The de¬ gassing lines contain flow restrictors 36 and 36' and non¬ return valves 38 and 38' .

In Figure 1, there is no pressure head across the pump 10 and the coolant finds its own level under gravity. The filling level for the coolant system is marked on the side of the reservoir 30 and when filled to the recommended level, there is insufficient coolant to fill the passages within the engine completely.

When the engine is now started, a pressure head is developed across the pump 10 which raises the coolant level in the engine and lowers the level in the reservoir 30 as shown in Figure 2. As coolant is transferred from the reservoir 30 to the engine block 20, and from there to the cylinder head 22, the air trapped in the cylinder head 22 is returned to the reservoir 30 by way of the pipe 41. The resistance of the non-return valve 34 in the forward direction regulates the air flow so that the transfer of coolant does not occur too rapidly. Under normal conditions of use, the non-return valve 34 should allow the cylinder head to fill up in a period of two to five minutes. In case the engine is driven hard during this time, the valve 40 can be opened by a suitable control system to allow the cylinder head to fill more rapidly. The valve 40 may be opened for example if the head temperature rises excessively or if the metered quantity of fuel exceeds a given threshold within the time that the non-return valve 34 alone would allow the cylinder head 22 to fill with coolant.

During the initial period, therefore, the head contains no coolant at all and will warm up more rapidly than in a conventional system. The block also warms up more rapidly because no circulation takes place until the cylinder head 22 is full of coolant. However, once the cylinder head is full and the coolant reaches the return pipe 41, the cooling system operates normally and eventually the thermostat will reach its operating temperature to open and bring the radiator 26 into operation.

Once the cylinder head 22 is full and coolant reaches the thermostat 24, the coolant will also commence to circulate through the heater core 28 to begin warming up the passenger compartment. Air pockets are prevented from forming above the thermostat 24 and the top of the heater core 28 by the de-gassing lines 39 and 45, respectively, which lead back to the space at the top of the reservoir 30.

In^'this embodiment, the heater core 28 receives no heat at all until the engine cylinder head has filled up but when this occurs the temperature of the coolant is already high enough to begin heating the passenger compartment. However, the total absence of heat in the passenger compartment during the warm up period of the engine may be undesirable. The embodiment of Figure 3 seeks to avoid this problem by altering the connections to the heater core 28. The supply to the heater core 28 now comes from the top of the cylinder block, below the coolant level, and enters the bottom of the core 28 through a line 50. The return flow from the top of the core 28 passes through a line 52 to the intake side of the circulation pump 10. With this direction of coolant flow, one can dispense with a de-gassing line for the heater core 28 and furthermore, circulation through it takes place immediately.

In the case of both embodiments, when the engine is stopped, the pressure head across the pump 10 drops immediately but the coolant is prevented from draining too rapidly under gravity back to the level shown in Figure 1. During this draining of the engine coolant, air must be returned from the reservoir 30 to the cylinder head 22 but this is inhibited by the non-return valves 34, 38 and 38' . These valves are designed to leak slightly to permit a slow transfer of coolant but the transfer takes long enough for the engine to have cooled down significantly, the period for the coolant to reach its own level under gravity being typically of the order of thirty minutes. Therefore, should the engine be re-started while still warm, overheating will be avoided by the fact that the cylinder head will still be at least partly full from previously.

Claims

1. An internal combustion engine having a cooling system with a closed coolant circuit which comprises coolant passages in the cylinder head (22) , the block (20) of the engine, a radiator (26) connected in parallel with the engine, a circulation pump (10) for circulating the coolant around the engine and the radiator, and a reservoir (30) connected in parallel with the engine, the coolant being transferred between the reservoir and the engine by gravity and by the pressure head of the circulation pump, characterised in that the reservoir (30) is disposed below the level of the cylinder head (22) and, in use, the cooling system is only partially filled with coolant such that substantially all the coolant from the cylinder head (22) is drained to the reservoir (30) by the action of gravity when the engine is at a standstill while leaving coolant in the cylinder block (20) and the circulation pump (10) , the cylinder head (22) being gradually refilled with coolant from the reservoir (30) after engine startup as a pressure head is built up by the circulation pump (10) .

2. An internal combustion engine as claimed in claim 1, wherein valves and flow restrictors are provided to control the rate at which fluid can transfer between the reservoir and the engine in different directions.

3. An internal combustion engine as claimed in claim 2, wherein the valves include non-return valves (38,38') .

4. An internal combustion engine as claimed in claim 2 or claim 3 , wherein the valves include an electrically or thermally controlled valve (40) for allowing the cylinder head to refill under emergency conditions.

5. An internal combustion engine as claimed in any of claims 2 to 4, wherein the valves serve to control the transfer of air between the engine and the reservoir.

6. An internal combustion engine as claimed in any preceding claim, wherein the reservoir (30) serves as a top-up tank and has a filler cap and de-gassing lines connected to avoid air pockets in selected parts of the coolant circuit.

7. An internal combustion engine as claimed in any preceding claim, further comprising a heater core (28) , the coolant supply to the heater core being taken from a point above or below the coolant level when the engine is at a standstill.