GB2146386A - Control of temperature of air supplied to I.C. engines - Google Patents

Abstract

An air temperature control device comprises a thermoresponsive sensor 15, preferably of the wax pellet variety, and a plurality of pressure responsive poppet valves 25, 28, 32 arranged to regulate the relative proportions of pre- heated and ambient air supplied to the engine in accordance with both ambient air temperature and engine temperature by controlling the pressure in a servomotor 6 which actuates valve 5. <IMAGE>

Description

SPECIFICATION Improvements in and Relating to Air Filtration Background This invention relates to air temperature control devices for internal combustion engines. Such devices are well-known; they are used in an attempt to provide the engine air intake with air at a temperature appropriate to the operating conditions prevailing at a particular time. These operating conditions include such parameters as throttle setting, engine temperature and ambient air temperature.

Brief Description of the Prior Art Air temperature control devices together with some preferred operational features therefor are described in for example Patent Specifications GB1126157, 1313434 and 1361728. Thus it is known to use bimetallic strips and other thermo-responsive devices to actuate air valves of various kinds, either directly or thorough a servomotor. In particular, it is known to adjust the relative proportions of ambient air and pre-heated air to reflect the engine temperature and the ambient air temperature, especially under "cold start" conditions.

Objects of the Invention It is an object of the present invention to provide an air temperature control device having improved operating characteristics. It is a further object of the invention to provide an engine air intake system fitted with the device.

Brief Description of the Invention According to the present invention an air temperature control device for the air intake system of an internal combustion engine includes a sensor comprising a thermo-responsive actuator which is, in use, disposed to respond to the air temperature in said intake system, a first chamber vented to substantially ambient pressure and incorporating first and second valve means adapted to be progressively opened by the actuator in response to a progressive rise in said air temperature, the first valve means being biased so as to close a passageway from said first chamber to a second chamber which is further closed by a member incorporating a bleed orifice having third valve means therein adapted to move between one position in which said orifice is open and a second position in which it is closed, the orifice communicating with said second chamber which has a port connected, in use, to a vacuum servomotor and an outlet which is closed by the third valve means when in its first position and open when in its second position, said outlet communicating with a third chamber which has an outlet connected, in use, to a vacuum source dependant on engine throttle setting, the third chamber also having an inlet from the first chamber via the second valve means, together with means for biasing the latter towards the closed state.

Preferred Features of the Invention The valve means are preferably poppet valves and the biasing means are preferably springs. The thermo-responsive actuator is preferably of the wax pellet kind; advantageously it is arranged not to operate on either of the first and second valve means until the intake air temperature at least approaches a normal operating temperature for the associated internal combustion engine, (typically 25"C). The first chamber is conveniently vented into the engine air intake so that its temperature approximates that of the air in said intake, thereby helping to ensure that the sensor as a whole reflects the intake air temperature. The outlet to the vacuum source from the third chamber may include a restriction effective to limit the rate of flow from the chamber.

Description of Specific Embodiments of the Invention In order that the invention be better understood a particularly preferred embodiment of it will now be described by way of example with reference to the accompanying drawing in which: Figure lisa diagrammatic cross-sectional side view of an internal combustion engine air intake system incorporating an air temperature control device/sensor according to the invention, Figure 2 is a graphical representation of the preferred operating characteristics of the thermoresponsive actuator portion of the sensor of Figure 1, Figure 3 is a diagrammatic cross-sectional side view of the sensor of Figure 1, under cold start conditions and with an actuator temperature of 25"C, at a small throttle opening, Figure 4 is as Figure 3, but at full throttle during initial warm-up of the system (and associated engine-not shown), Figure 5 is as Figure 3, but with the engine warmed-up and a cold ambient air temperature (7"C), Figure 6 shows the sensor of Figure 1 under Figure 5 conditions, but at full throttle, Figure 7 shows the sensor of Figure 1 at normal to high ambient temperatures, with the engine fully warmed up and at low throttle openings, and Figure 8 shows the sensor of Figure 1 under Figure 7 conditions, but at full throttle opening.

Referring firstly to Figure 1 an air intake duct has an ambient air inlet 2 and a pre-heated air inlet 3, the latter being provided by passing ambient air over an exhaust manifold 4. Where the inlets 2 and 3 meet there is a flap valve 5 movable by a vacuum servomotor 6 between two extreme positions, in one of which the ambient air inlet 2 is completely closed and in the other of which the pre-heated air inlet 3 is closed. Between those two positions, the relative proportions of pre-heated and ambient air vary in response to operation of the flap valve 5 by the motor. The flap valve is spring biased towards closure of the inlet 3. The inlet duct 1 leads into a conventional air cleaner 7.

The latter discharges into a carburettor 8 containing a conventional throttle valve 9. The downstream side 10 of the latter (the carburettor throat) supplies a fuel/air mixture to the engine inlet manifold, in the usual way.

Upstream of the throttle valve 9 and in the airstream from the air cleaner 7 there is a sensor 11.

The sensor is connected through a pipe 12 to the servomotor 6 and to a tapping point 13 in the carburettor throat 10, by another pipe, 14.

The sensor is best seen in Figures 3 to 8 inclusive; it incorporates a wax pellet type thermo-responsive actuator 15 whose preferred characteristics are as shown in Figure 2, further discussed below.

Referring now primarily to Figures 3 to 8 inclusive the sensor 11 comprises the actuator 15 mounted on top of a casing 16 which is divided internally into three chambers 17,18 and 19 by a plug member 20.

The first chamber 17 is vented to atmosphere through ports 21; the latter being open to the airstream inside the cleaner 7. A coil spring 22 inside the first chamber serves to bias the actuator piston 23 towards its unoperated, i.e. cold, state. The first chamber 17 is connected to the second chamber 18 by a passageway 24 containing a first one-way poppet valve 25 biased towards a closed position by a coil spring 26. The first chamber 17 is also connected to the third chamber 19 by a passageway 27 containing a second one-way poppet valve 28 biased towards a closed position by a coil spring 29.

The opposite (lower) end of the passageway 25 opens into the second chamber through a port 30 containing one part 31 of a third, two-part poppet valve, whose stem 32 extends through from the second chamber into the third chamber 19 through a port 33 closeable by another part 34 of the valve.

The arrangement is such that the third valve can 'float' between two positions, in one of which port 30 is closed and port 33 is open and in the other of which the opposite applies, (as best seen by comparing figures 3 and 8, for example).

The second chamber 18 is connected, in use, to the servomotor 6 (see also Figure 1) by pipe 12. The third chamber 19 is connected, in use, to the carburettorthroat 10 by pipe 14 (see also Figure 1).

Although the vacuum motor 6 is shown in Figures 3 to 8 inclusive, in order to assist with the following description of the operation of the air temperature control device, it will be appreciated that other parts of Figure 1 have been omitted in the interests of clarity.

Referring to all the figures, the 'cold start' condition is that immediately prior to starting, the pre-heated air inlet 3 is closed by the flap valve 5, due to its associated biasing spring (not shown).

The actuator piston 23 is fully retracted under cold start conditions and does not contact the stems of either of the two poppet valves 25 and 28. Both valves are therefore closed. Under light to moderate throttle openings a high vacuum exists in the carburettor throat 10. This is applied through pipe 14 to chamber 19 where it causes the two part valve to adopt the position shown in Figure 3 in which port 30 is closed by valve part 31, whilst port 33 is open. Full vacuum is therefore applied to the servomotor 6 through pipe 12, resulting in the flap valve being moved to close the ambient air inlet 2.

All air drawn into the intake 1 therefore comes from the pre-heated air inlet 3 and as the engine begins to warm up the exhaust manifold 4, the air supplied to the intake also warms up.

Referring now to Figure 4, the full throttle cold start condition results in a reduction of vacuum in the carburettor throat. This causes a corresponding loss in chamber 19 and because the pressure in chamber 18 is now lower, the two part valve moves to its other position, ciosing port 33 and opening port 30. This prevents vacuum from affecting the servomotor, but it exposes the latter to the control of poppet valve 25. Depending on the strength of spring 26 the valve 25 allows some air to enter chamber 18 from chamber 17 and the ports 21. This causes the servomotor to permit the entry of some ambient air into the intake duct 1, but pre-heated air will predominate, as required for the warm up period.

Referring to Figure 5, as the engine warms up and as the pre-heated air warms the actuator 15 towards its operating temperature (see Figure 2) the piston 23 begins to move downwardly towards the poppet valve 28, which is thereafter progressively opened.

This results in a progressive reduction in vacuum in chamber 19 due to air entering through passageway 27. To ensure this, the outlet 14 may incorporate a restriction effective to limit the rate of flow from chamber 19. Consequently, the servomotor allows progressively more ambient air into the intake 1.

This has the effect of controlling intake air temperature, since the proportion of ambient air also affects the temperature attained by the actuator and accordingly, the extent to which valve 28 is opened. At ambient temperatures below say 7"C very iittle ambient air is needed to achieve the desired intake air temperature, typically 25 to 30"C.

At higher ambient temperatures much more ambient air can be used. However, under the full throttle conditions of Figure 6 it is still necessary to prevent carburettor icing and to this end the sequence of events described in relation to Figure 4 applies. The reduction in engine vacuum causes the two part valve to close port 33, whilst opening port 30. The servomotor is therefore isolated from the effect of the reduced vacuum to a significant extent and as a result, enough pre-heated air is admitted to prevent icing.

When the engine is warm and the ambient temperature is high, Figure 7 applies at low to moderate throttle settings. The actuator piston 23 is fully extended, opening both poppet valves 25 and 28. The vacuum applied to the servomotor is therefore considerably reduced, allowing mainly ambient air into the intake duct 1. At full throttle (Figure 8) the reduction of engine vacuum again causes the two-part valve to close port 33 and at the same time to open port 30. Because both of the other valves are held open the vacuum applied to the servomotor is rapidly relieved, so that the servomotor ceases to have any effect; the spring biased float valve closes off the supply of pre-heated air and the intake is entirely at ambient temperature.

Claims (8)

1. An air temperature control device for the air intake system of an internal combustion engine, the device including a sensor comprising a thermoresponsive actuator which is, in use, disposed to respond to the air temperature in said intake system, the sensor comprising a first chamber vented to substantially ambient pressure and incorporating first and second valve means adapted to be progressively opened by the actuator in response to a progressive rise in said air temperature, the first valve means being biased so as to close a passageway from said first chamber to a second chamber which is further closed by a member incorporating a bleed orifice having third valve means therein adapted to move between one position in which said orifice is open and a second position in which it is closed, the orifice communicating with said second chamber which has a port connected, in use, to a vacuum servomotor and an inlet closed by said third valve means when in its first position and open when its second position, said inlet communicating with a third chamber having an outlet connected, in use, to a vacuum source dependant on engine throttle setting, the third chamber also having an inlet from the first chamber via the second valve means, together with means for biasing the latter towards the closed state.

2. An air temperature control device according to claim 1 in which the thermo-responsive actuator is of the wax pellet kind.

3. An air temperature control device according to claim 2 wherein the actuator is arranged not to operate on either of the first and second valve means until the air intake temperature at least approaches a normal operating temperature for the associated engine.

4. An air temperature control device according to any preceding claim wherein the valve means are poppet valves.

5. An air temperature control device according to any preceding claim wherein the first chamber is vented into the air intake.

6. An air intake system for an internal combustion engine incorporating the temperature control device of any preceding claim.

7. An air temperature control device comprising a sensor substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.

8. An air intake system for an internal combustion engine substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.