EP0548174B1

EP0548174B1 - Engine cooling system

Info

Publication number: EP0548174B1
Application number: EP91916280A
Authority: EP
Inventors: Thomas Tsoi-Hei Ma
Original assignee: Ford Werke GmbH; Ford France SA; Ford Motor Co Ltd; Ford Motor Co
Current assignee: Ford Werke GmbH; Ford France SA; Ford Motor Co Ltd; Ford Motor Co
Priority date: 1990-09-05
Filing date: 1991-09-04
Publication date: 1996-10-30
Anticipated expiration: 2011-09-04
Also published as: DE69122968T2; WO1992004534A1; GB2247745A; DE69122968D1; EP0548174A1; GB9019391D0

Abstract

An engine cooling system comprising integrating means for generating a signal representing the total heat rejection from the combustion chamber following engine startup, and an electrically operable valve (26) which is closed to prevent all circulation of coolant through at least the cylinder head (14) until the output signal of the integrating means attains a predetermined threshold.

Description

The invention relates to a cooling system for an internal combustion engine.

Background of the invention

In conventional liquid cooled engines, a thermostat is provided to improve warm up time. The engine block is isolated by a thermostat from the radiator until a certain coolant temperature is reached and thereafter that temperature is maintained by heat rejection to the radiator.
Before the opening temperature of the thermostat is reached, a small amount of circulation of the coolant in the engine block still takes places under the action of the circulation pump, the coolant passing from the engine block to the cylinder head and, from there, back through the passenger compartment heater to the intake side of the pump. This circulation is necessary to stop cavitation around the pump, to prevent local boiling and ensure that the warm coolant reaches the thermostat.
In order to minimise unburned hydrocarbon emissions, it is necessary to minimise the time taken for the combustion chambers to reach their normal operating temperature and even the small amount of coolant circulation taking place prior to the thermostat opening detracts from this objective.
Some proposals have been made to retain the heat within the cylinder head by forming a split cooling system. The main aim of such a system is to prevent the heat rejected to the cylinder head from being used to warm up the engine block unnecessarily. This modification reduces overall warm up time but is of assistance mainly in later parts of the warm-up phase.
GB-A-2097967 describes an engine cooling system in which a water jacket in the engine is connected by a water passage to the radiator. A thermostat valve opens the passage when the water temperature exceeds a predetermined value and a pump causes the cooling water to flow in the water jacket. A solenoid valve selectively connects a bypass or a circulation pipe with the inlet of the pump and a flow control valve is provided in the water passage to control the flow rate of water to the radiator. When the water temperature is higher than a given value the bypass is communicated with the inlet of the pump thereby to cause the water in the water jacket to circulate through the bypass. The flow control valve is operated in dependence upon the engine speed and the load on the engine and controls the water temperature at a water temperature higher than the predetermined value.
DE-A-38 10 174 describes a system that acts on the cooling system to vary the set desired engine coolant temperature as a function of the engine operating conditions. To prevent the system from reacting to changes in operating conditions that are only of a short duration, a low pass filter is used permit such rapid changes to be disregarded. The low pass filter may include an integrator.

Object of the invention

The present invention seeks to provide a coolant system in which heat retention in the immediate vicinity of the combustion chambers is maximised immediately after start-up.

Summary of the invention

According to the present invention, there is provided an engine cooling system comprising a coolant circuit that includes a radiator, the inlet of which is connected to the cylinder head of the engine via a first coolant passage and its outlet is connected to the cylinder block of the engine via a second coolant passage, a circulation pump in the second passage for pumping coolant around the circuit to cool the engine, the cylinder block and the cylinder head of the engine forming part of the coolant circuit, a thermostatic valve in the first passage that opens to allow coolant flow therethrough when the coolant temperature exceeds a threshold value, a third coolant passage connecting the cylinder head with the inlet of the circulation pump, and an electrically operable valve means arranged in said third coolant passage, characterised in that an integrating means is provided for generating a signal representing the total heat produced within the combustion chambers of the engine following engine start-up, and the electrically operable valve means is actuated to prevent all circulation of coolant through at least the cylinder head of the engine until the output signal of the integrating means attains a predetermined threshold.
Preferably, the valve means are additionally operative to prevent coolant from circulating through the engine block.
Advantageously, the cooling system further comprises a valve arranged in a by-pass passage connected across the coolant pump, the by-pass passage being normally closed and being opened only during the said predetermined time.
The integrating means may simply be a time integrator, the threshold being set to between zero and three minutes.
However, in this case, the time must be selected to be the shortest period in which boiling can occur assuming high speed and high load. In practice, a much longer period could still prove safe. For this reason, it is preferred to use another parameter, other than the coolant temperature, to estimate the heat rejection from the engine.
The total number of revolutions from start-up may be integrated and the valve means reset after a certain number of turns of the crankshaft. This is an improvement over measuring time alone since this measure is no longer affected by changes in engine speed. However, the heat production during a fixed number of engine revolutions is still load dependent and to eliminate this source of error, the count may be weighted to allow for the load as sensed for example from the manifold vacuum or throttle pedal position.
A preferred and more direct assessment of the total heat rejection after start-up can be gained by integrating the total fuel flow or the total mass air flow. In the case of an engine having a fuel injection system, integration either of the output of the air flow meter or the pulses applied to the fuel injectors provides a signal directly related to the total heat rejection.
The total heat which should be retained after start-up depends upon the initial engine temperature, that is to say the temperature before start-up. If the engine is already warm, then it may be unnecessary to retain any additional heat and if the engine is very cold, having for example been left inoperative for a long period in a cold ambient atmosphere, then an extended period may be safely be adopted to enable rapid warm up of the combustion chambers. It is therefore preferred to set the threshold in dependence upon the engine temperature before start-up.

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 is a block diagram of a coolant system in accordance with the invention, and
Figure 2 is a block diagram of a circuit for controlling the isolation valve of a coolant system.

Detailed description of the preferred embodiment

An engine 10 comprises a block 12 and a cylinder head 14 which form part of a cooling circuit around which a coolant, normally water, is pumped by means of an engine driven pump 24. The cylinder head 14 is connected to a radiator 20 by means of a thermostat 22 and the heat exchanger 18 of the passenger compartment heater is connected in a line 28 leading from the cylinder head 14 back to the return hose connecting the radiator 20 back to the pump 24.
As so far described, the cooling system and the engine are entirely conventional. Below the opening temperature of the thermostat 22, no circulation takes place through the radiator 20 and the smaller volume of coolant trapped in the block 12 and the cylinder head 14 can heat up more rapidly.
Even before the thermostat 22 opens, coolant can flow through the heat exchanger 18 of the passenger heater under the action of the pump 24. Heat is therefore lost to the passenger compartment from the engine and heat from the combustion chamber is encouraged to flow to warm up the entire engine instead of being retained where it is most needed, namely at the combustion chamber.
The present invention is aimed at preventing all circulation of coolant past the combustion chambers when the engine is cold and achieves its objective by the use of an electrically controlled isolation valve 26 which is closed to ensure that there is no closed coolant circuit powered by the pump 24. The pump 24 can be prevented from operating during cold starts, or it can be allowed to cavitate during the short time that the valve 26 is closed.
In the preferred embodiment illustrated, a by-pass valve 16 connected in shunt with the pump 24 and short circuits the inlet and outlet connections of the pump 24 to allow at least a small amount of circulation around the pump without the coolant needing to pass through the engine 10, in order to prevent cavitation.
The valve 26 is opened and closed by an integrating circuit (Figure 2) rather than in response to the sensing of a critical temperature. A sensing circuit 30 receives an input signal from the engine and its output is integrated by an integrating circuit 32. The output of the integrating circuit 32 is compared in a comparator 34 with a threshold set by a circuit 38 and if the set threshold is exceeded then the isolation valve 26 is opened to allow normal coolant circulation. The threshold setting circuit 38 in the illustrated embodiment also receives a signal from a temperature sensor 40 and sets the threshold in dependence upon the coolant temperature before starting.
The output of the integrating circuit 32 is required to represent the total heat production from the engine following the starting of the engine. To this end, the integrating circuit 32 can integrate time pulses, engine cycles, the durations of fuelling pulses, or samples of analogue signals derived from the mass air flow meter of a fuel injection system, and the sensing circuit 30 is designed accordingly.
Engine running time is a first approximation, total engine cycles is a better second approximation because it is not engine speed dependent but the most useful reading is to be derived by measurement of the fuel or air used in the combustion process.
At the commencement of operation, when the engine ignition is first turned on, the engine temperature is measured by the sensor 40 and the threshold setting circuit 38 provides a reference signal for the output of the integrating circuit which is inversely proportional to the difference between the measured starting temperature and the normal running temperature. The valves 16, 26 used to prevent circulation of the coolant past the combustion chamber are operated for as long as the output signal of the integrating circuit lies below the set reference threshold and thereafter the coolant is allowed to circulate normally.
It should be mentioned that when normally starting from cold, it is expected that the isolation valve 26 will be open and the valve 16 closed some time before the thermostat 22 begins to open so that the latter does not normally interfere in the operation described above. Of course, should the valve 26 malfunction and remain closed for too long, no serious harm will be done since the thermostat 22 will at such a time open and permit the coolant to circulate through the radiator 20. In this respect, it will be noted that the by-pass passage containing the valve 16 is only a restricted passage and there remains some pressure across the pump 24 to drive coolant around the radiator circuit even if the valve 16 is open.

Claims

An engine cooling system comprising:
- a coolant circuit that includes a radiator (20), the inlet of which is connected to the cylinder head of the engine via a first coolant passage and its outlet is connected to the cylinder block of the engine via a second coolant passage;

- a circulation pump (24) in the second passage for pumping coolant around the circuit to cool the engine (10), the cylinder block (12) and the cylinder head (14) of the engine forming part of the coolant circuit,

- a thermostatic valve (22) in the first passage that opens to allow coolant flow therethrough when the coolant temperature exceeds a threshold value,

- a third coolant passage (28) connecting the cylinder head with the inlet of the circulation pump (24), and

- an electrically operable valve means (26) arranged in said third coolant passage (28),
characterised in that
- an integrating means (32) is provided for generating a signal representing the total heat produced within the combustion chambers of the engine following engine start-up, and

- the electrically operable valve means (26) is actuated to prevent all circulation of coolant through at least the cylinder head (14) of the engine until the output signal of the integrating means (32) attains a predetermined threshold.
An engine cooling system as claimed in claim 1, wherein the valve means (26) are additionally operative to prevent coolant from circulating through the engine block.
An engine cooling system as claimed in claim 1 or 2, further comprising valve means (16) arranged in a by-pass passage connected across the coolant pump (24), which valve is normally closed and is opened only when circulation is prevented through the cylinder head (14).
An engine cooling system as claimed in any preceding claim, wherein the said threshold is predetermined as a function of the engine temperature prior to start-up.
An engine cooling system as claimed in any preceding claim, wherein the integrating circuit (32) is operative to integrate time pulses commencing with engine start-up.
An engine cooling system as claimed in any one of claims 1 to 4, wherein the integrating circuit (32) is operative to integrate engine cycles commencing with engine start-up.
An engine cooling system as claimed in any one of claims 1 to 4, wherein the integrating circuit (32) is operative to integrate fuel injection pulses commencing with engine start-up.
An engine cooling system as claimed in any one of claims 1 to 4, wherein the integrating circuit (32) is operative to integrate signals representative of mass air flow to the engine commencing with engine start-up.