GB2292602A

GB2292602A - Engine coolant temperature management

Info

Publication number: GB2292602A
Application number: GB9416514A
Authority: GB
Inventors: Thomas Tsoi-Hei Ma
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1994-08-16
Filing date: 1994-08-16
Publication date: 1996-02-28
Anticipated expiration: 2014-08-16
Also published as: GB2292602B; GB9416514D0

Abstract

An internal combustion engine has a coolant circuit with radiator 18, pump 10 for delivering coolant from the radiator 18 to the engine 12, 14 and a thermostatic valve 16 arranged in return line 24. A bypass pipe is provided to supply coolant directly from a point downstream of the pump 10 to a point upstream of the thermostatic valve 16 without passing through the engine and flow control valve 20 and fixed orifice 22 are provided within the bypass pipe for regulating the flow of coolant bypassing the engine. <IMAGE>

Description

ENGINE COOLANT TEMPERATURE MANAGEMENT The present invention relates to engine coolant temperature management.

It is desirable to operate an engine to a higher mean coolant temperature at part load for the benefit of lower friction and lower hydrocarbon emissions. However, it is also necessary to operate at a lower mean coolant temperature at high load to protect against the risk of knock and pre-ignition caused by local hot spots in the combustion chamber. With a fixed setting of the thermostatic valve it is necessary to select a safe mean coolant temperature suitable for high loads but this will not be able to realise the potential benefits at light loads.

There have for this reason already been proposed systems with electrically variable valves in place of mechanical thermostats to maintain a mean coolant temperature that varies as a function of engine operating conditions, in particular load. The valves have been closed loop controlled, based upon a temperature reading taken from a sensor, and because of the complexity of the systems, they have been rather costly to implement.

The present invention seeks to provide an engine with variable mean coolant temperature, in which the temperature control system is simple, inexpensive to manufacture and less prone to failure.

According to the present invention there is provided an internal combustion engine having a coolant circuit that includes a radiator, a pump for delivering coolant from the radiator to the engine and a thermostatic valve arranged in a return line from the engine to the radiator, wherein a bypass pipe is provided to supply coolant directly from a point downstream of the pump to a point upstream of the thermostatic valve without passing through the engine and means are provided within the bypass pipe for regulating the flow of coolant bypassing the engine.

The present invention relies on the mechanical thermostatic valve to effect internal closed loop temperature regulation of the coolant and there is no requirement for a further form of external closed loop control. The temperature within the engine is however stabilised at a different value from the regulated temperature of the thermostatic valve because the latter valve also receives a second flow of cold coolant that has passed through the radiator and the pump but not through the engine. The ratio of the rates of the two flows and the temperature of the two flows will determine the extent to which the engine temperature will exceed the regulated temperature of the thermostatic valve.

The control of the regulating means within the bypass pipe may be coarse and need not follow closely the changes in the engine operating conditions. It suffices to determine if the engine is operating under light load conditions or high load conditions and to open or close the bypass pipe accordingly. In this case the dimension of the pipe or an orifice therein may determine the ratio of the two flows at light load conditions. It is of course alternatively possible to effect finer open loop control and set several controlled bypass flow rates dependent upon different engine load conditions.

The determination of the load conditions may be effected by detecting throttle pedal position, engine intake manifold pressure or quantity of fuel injected per operating,cycle.

The invention will now be described further, by way of example, with reference to the accompanying drawing which is a block diagram of an engine and its coolant circuit.

In the drawing, an engine comprises a cylinder block 12 and a cylinder head 14. The coolant circuit for cooling the engine comprises a pump 10 that draws coolant from the radiator 18 and delivers it to the engine block 12. The coolant rises from the engine block 12 into the cylinder head 14 and returns to the radiator 18 after flowing through the cylinder head 12 and a return pipe 24 containing a thermostatic valve 16.

As so far described the engine and the coolant circuit are conventional. The thermostatic valve 16 is opened and closed automatically to a different extent by a wax filled element that expands and contracts as a function of the coolant temperature passing through it. In this way the temperature of the coolant at the valve 16 is automatically regulated to the temperature for which the thermostatic valve is designed. This temperature would normally be maintained the same under all operating conditions, the valve closing under light load and opening under high load to vary the rate of coolant flow through the radiator 18 to match the heat rejection from the engine.

The present invention introduces control over the temperature of the engine without modifying the thermostatic valve 16 and while continuing to rely upon it for internal closed loop control of coolant temperature. The engine temperature is varied by a bypass pipe containing a two position flow control valve 20 and a fixed orifice 22. When the flow control valve 20 is closed the engine operates in the manner in which it would conventionally and this is the position adopted by the flow control valve 20 under high load. During light load operation, however, the flow control valve 20 is fully opened and allows a flow set by the orifice 22 to bypass the engine. The thermostatic valve 16 will now therefore receive two flows comprising a hot flow from the engine and a colder flow taken directly from the radiator 18.The thermostat acts to maintain the temperature of the combined flows at its regulated temperature which results in the engine being run at a hotter temperature than when the flow control valve 20 is closed under high load. By this simple means the invention enables reduced emissions and more efficient operation to be achieved under light load conditions without impairing operation under high load conditions and risking knock or pre-ignition.

The setting of the flow control valve 20 may be determined in dependence upon the demand as indicated by the throttle pedal position but intake manifold pressure provides a better indication of load. The latter is preferred because the flow control valve 20 may simply be a two position valve operated directly by manifold vacuum and defaulting into its safer closed position. A still further possibility would be to vary the flow control valve 20 as a function of the quantity of fuel injected per cycle, this being directly related to the rate of heat rejection from the engine combustion chambers.

The arrangement as above described only allows the engine temperature to be regulated to one of two values but even this provides significant improvement in meeting emissions and fuel economy requirements. It is however possible, if desired, to provide continuous control over the position of the flow control valve 20 and thereby vary the temperature of the engine continuously as a function of the engine load.

In this case it is preferable to provide a temperature sensor in the engine as it may be difficult to correlate the temperature of the engine with the positions of the flow control valve 20. Though this does somewhat complicate the system and detract from the desired simplicity, it is still less costly to implement than the known electronic flow control valves arranged within the main coolant circuit, as it is only necessary to control a small bypass flow to achieve the desired engine temperature control.

It is also easier to achieve a fail safe condition, by not relying solely on an external closed loop system for coolant temperature control which, should the flow control valve 20 fail in any position, would still maintain continuous coolant temperature regulation with the mechanical thermostatic valve 16 operating as a backup.

Claims

1. An internal combustion engine having a coolant circuit that includes a radiator, a pump for delivering coolant from the radiator to the engine and a thermostatic valve arranged in a return line from the engine to the radiator, wherein a bypass pipe is provided to supply coolant directly from a point downstream of the pump to a point upstream of the thermostatic valve without passing through the engine and means are provided within the bypass pipe for regulating the flow of coolant bypassing the engine.

2. An engine as claimed in claim 1, wherein the flow regulating means in the bypass pipe comprise a two-position flow control valve arranged in series with a fixed orifice.

3. An engine as claimed in claim 1, wherein the flow regulating means in the bypass pipe comprise a continuously variable flow control valve.

4. An engine as claimed in claim 2 or 3, wherein the flow control valve of the flow regulating means is operated in dependence upon engine load.

5. An engine as claimed in claim 4, wherein the flow control valve of the flow regulating means is vacuum operated.

6. An engine constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawing.