GB2431733A

GB2431733A - Reduction of Hydrocarbon Evaporative Emissions from Internal Combustion Engines

Info

Publication number: GB2431733A
Application number: GB0521816A
Authority: GB
Inventors: Adam Moorcroft
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2005-10-26
Filing date: 2005-10-26
Publication date: 2007-05-02
Also published as: GB0521816D0

Abstract

An engine control module (16) opens a throttle valve (13) during an engine run-down period thus allowing induction air to sweep residual fuel vapours away from an intake manifold (8) region and out through the exhaust port (9). Thus, residual fuel left in the intake areas after shutdown is much reduced, leading to better evaporative emissions performance.

Description

Reduction of Hydrocarbon Evaporative Emissions from Internal Combustion

Engines This invention relates to an apparatus and method for reducing hydrocarbon evaporative emissions from internal combustion engines.

On port injection engines, injectors fuel the inlet manifold or inlet port area. The port area then fuels the engine by vaporisation of the fuel into the inducted air. When the engine is shut down, there is residual fuel left in the port area. Over a period of time this fuel vaporises and escapes from the induction system of the engine into the atmosphere.

Legislation set limits for evaporative emissions which are tested by putting a recently-run vehicle in a sealed room and measuring the emitted hydrocarbons. As emissions requirements are becoming more stringent, there is a need for methods which minimise the amount of residual fuel left in the inlet manifold after the engine is shut down.

EP-A-1217195 discloses a strategy for clean shutdown of an engine incorporating variable valve timing. Actuation of the exhaust and intake valves in a particular way allows fuel and exhaust vapours to be purged from the engine intake and cylinders while the engine is running down.

US-A-2005/0011185 discloses a system which employs an air suction pump for drawing hydrocarbons from the intake port through a purge pipe and into a canister after the engine has been shut down.

In a first aspect, the present invention comprises an apparatus for reducing hydrocarbon evaporative emissions from an internal combustion engine, the engine being of the type which is provided with an intake duct, a throttle valve for controlling a flow of air through the intake duct, and an injector for supplying hydro-carbon based fuel to the intake duct for combustion, wherein the apparatus is adapted to; detect an engine shutdown request, thereafter, to curtail the operation of the injector so that no more fuel is supplied to the engine, and thereafter, to open the throttle valve thereby increasing the airflow through the intake duct into the engine.

In a second aspect, the present invention comprises a method for reducing hydrocarbon evaporative emissions from an internal combustion engine, the method including the steps of; (a) detecting an engine shutdown request (b) thereafter, ceasing a supply of hydrocarbon based fuel to the engine, and thereafter, (C) increasing a supply of induction air to the engine by opening a throttle valve.

Hence the present invention achieves a reduction in the amount of residual hydrocarbons left in the engine intake areas after engine shut-down by increasing the throughput of air into the induction system during the engine, run-down period.

When there is an increase in airflow through the engine, residual hydrocarbons will be swept through the engine and away from the intake areas.

The increased airflow also creates a significant reduction in the negative torque on the induction stroke during the run down period, i.e. reduced pumping loss. The net result is that the engine performs an increased number of induction strokes at a higher mass air flow before it stops completely. The increased airflow over a prolonged period of time pulls more of the residual hydrocarbons through the engine. After a short period, the fuel-air mixture will become too lean to combust. This lean hydrocarbon mixture will be expelled into the exhaust system's catalytic converter for conversion into harmless gases and some will be trapped in the cylinders.

In one embodiment, after the fuel supply has been curtailed (step (b)) the apparatus is adapted to close the throttle momentarily, preferably until combustion has ceased.

Thereafter, the throttle is opened (step (c)). This extra step of closing the throttle has the advantage of creating a high intake duct depression (after the last injected cylinder is inducted). This causes the residual fuel to vaporise and thus more fuel enters the engine's cylinders on the following inductions. The increased inducted fuel coupled with the reduced air flow entering the cylinders creates a mixture rich enough to combust. Thus, a greater number of combustions can occur during the run-down period between step (b) and step (c).

In this embodiment, the apparatus may be further adapted to detect when combustion has ceased, by monitoring of a signal from a crankshaft rotation sensor. When the apparatus detects a marked reduction in engine speed (crankshaft revolutions per second), it deduces that combustion has ceased. Thereafter, the throttle is opened. Alternatively, the apparatus may be adapted to delay opening of the throttle until a pre-determined time period has elapsed.

Optionally, after the throttle valve has been opened (step c) and the engine has subsequently stopped completely, the throttle valve may be closed completely in order to prevent leakage of any remaining hydrocarbons escaping from the intake duct, and into the atmosphere. Alternatively, the throttle valve may be moved to a slightly open position to prevent it sticking closed and causing engine starting problems at a later time. In either case, throttle valve movement is controlled by the apparatus which is adapted to be able to detect when the engine has stopped.

The apparatus may, optionally, be further adapted to control engine ignition.

Preferably, ignition is not disabled until combustion has ceased. Prolonging ignition, (preferably for just one or two engine cycles after curtailing the fuel supply) ensures combustion of any residual mixture entering in the cylinders. Hence, ignition may be disabled once the apparatus has detected that combustion has ceased or when a pre-determined time period after ceasing the fuel supply has elapsed.

Some embodiments of the invention will now be described by way of example only, with reference to the drawings of which; Fig. 1 is a partially sectioned schematic view of an engine incorporating the emission reduction apparatus in accordance with an embodiment of the invention, Figs 2 and 3 are flow charts illustrating two alternative methods of operating the engine and emission reduction apparatus of Fig. 1.

In Figure 1, one cylinder 1 of a multicylinder internal combustion engine 2 houses a reciprocating piston 3. A connecting rod 4 connects the piston 3 with a crankshaft 5. A cylinder head 6 closes off one end of the cylinder 1, a combustion chamber 7 being defined between the cylinder head 6 and the top of the piston 3.

The combustion chamber 7 communicates with an intake port 8 and an exhaust port 9 by way of an intake valve 10 and exhaust valve 11 respectively. A spark plug 12 is mounted in the cylinder head 6 for igniting the air-fuel mixture in the combustion chamber 7. The flow of air which is supplied to the intake port 8 is controlled by an electrically-operated throttle valve 13. Fuel supplied to the intake port 8 is controlled by an injector 14.

A sensor 15 detects crankshaft rotation and has an output connected to an engine control module ([CM) 16. Thus the ECM 16 can continuously monitor engine spped.

The ECM 16 is also electronically connected with and controls the operation of the injector 14, the throttle valve 13 and the spark plug 12.

An ignition switch 17 provides a further electrical input to the ECM.

While only one cylinder, piston, intake valve, exhaust valve, spark plug and injector are shown, it will be understood that the invention can be used with any typical multicylinder, port fuel-injected engine.

Operation of a first embodiment will now be described with reference to Figure 2.

Initially, the switch 17, which is operated by a driver of the vehicle incorporating the engine 2, is closed so that the engine is running normally with the throttle valve 13 being controllable by the driver (via an accelerator pedal) and the spark plug 12 and injector 14 under the control of the ECM 16.

When the driver turns the ignition switch 17 off, this signifies an engine shutdown request. By way of the electrical connection between the switch 17 and ECM 16, the ECM 16 detects that shutdown has occurred (step 18). In response to this, the ECM 16 sends a control signal to the injector 14 so that the fuel supply is curtailed. At this point, although the injector 14 is no longer feeding fuel into the intake port 8, there will be some residual fuel left in the intake port area. In order to allow residual fuel vapours to be swept through the cylinder 7 and out through the exhaust port 9, the throttle valve 13 is opened in response to a control signal from the ECM 16 (step 20). The throttle valve is opened sufficiently wide so that the airflow is not throttled at all. This may be only a few percent of the maximum position at low engine speeds. While the throttle valve 13 is in its open position, the ECM 16 monitors crankshaft rotation via the sensor 15.

Once the ECM 16 detects that the crankshaft has stopped rotating i.e. the engine has stopped (step 21) it sends a further control signal to the throttle valve 13, thereby closing the valve 13 (step 22). The throttle valve 13 then remains closed until the ignition switch 17 is turned on again whereupon the normal engine running regime resumes with the throttle valve 13 being controllable by the driver.

A second embodiment of the invention will now be described with reference to Figure 3. In step 23 an engine shutdown condition is detected by the ECM 16 and the fuel supply is curtailed (step 24) in the same way as described with reference to the first embodiment.

At the subsequent step 25 and in contrast with the first embodiment, the throttle valve 13 is closed in response to a signal from the ECM 16. This has the effect of creating an enriched mixture in the cylinder 7 which has a greater chance of combusting. While the throttle valve 13 is closed, the ECM 16 monitors crankshaft rotational speed via a signal from the sensor 15. When the ECM 16 detects a marked decrease in rotational speed, it deduces that combustion has ceased (step 26), whereupon it disables ignition and sends a further control signal to the throttle valve 13 causing the valve 13 to open (step 27). The open valve 13 allows induction air to sweep residual fuel vapours through the intake manifold 8, into the cylinder 7 and out through the exhaust port 9. While the valve 13 is open, the ECM 16 continues to monitor crankshaft rotation (via the sensor 15). When the ECM 16 detects that the crankshaft is no longer rotating and therefore the engine has stopped (step 28), it sends out a further control signal causing the throttle valve 13 to close (step 29).

Claims

CLAIMS

1. An apparatus for reducing hydrocarbon evaporative emissions from an internal combustion engine, the engine being of the type which is provided with an intake duct, a throttle valve for controlling a flow of air through the intake duct, an injector for supplying hydro-carbon based fuel to the intake duct for combustion, wherein the apparatus is adapted to; detect an engine shutdown request, thereafter, to curtail the operation of the injector so that no more fuel is supplied to the engine, and thereafter, to open the throttle valve thereby increasing the airflow through the intake duct into the engine.

2. An apparatus as claimed in claim 1 in which the apparatus is further adapted to detect when combustion in the engine has ceased and, after curtailing operation of the injector and before opening the throttle valve, close the throttle valve until combustion has ceased.

3. An apparatus as claimed in claim 1 in which the apparatus is further adapted to, after curtailing the operation of the injector and before opening the throttle valve, close the throttle valve for a pre-determined time period..

4. An apparatus as claimed in claim 2 in which the apparatus is further adapted to control an engine ignition system and, to disable the ignition system after combustion has ceased.

5. An apparatus as claimed in claim 1 or claim 3 in which the apparatus is further adapted to control an engine ignition system and to detect when combustion has ceased and to disable the ignition system after combustion has ceased.

6. An apparatus as claimed in any of claims 1 to 3 in which the apparatus is further adapted to control an engine ignition and to disable ignition after a predetermined time interval has elapsed after curtailing the operation of the injector.

7. An apparatus as claimed in any preceding claim in which the apparatus is further adapted to detect when the engine has stopped running and, to close the throttle valve completely after the engine has stopped running.

8. An apparatus as claimed in any of claims 1 to 6 in which the apparatus is further adapted to detect when the engine has stopped running and, to partially close the throttle valve after the engine has stopped running.

9. A method for reducing hydrocarbon evaporative emissions from an internal combustion engine, the method including the steps of; (a) detecting an engine shutdown request, (b) thereafter, ceasing a supply of hydrocarbon based fuel to the engine, and thereafter, (c) increasing a supply of induction air to the engine by opening a throttle valve.

10. A method as claimed in claim 9 and including the further step of after step (b) and prior to step (C), restricting a supply of induction air to the engine by closing the throttle valve until combustion has ceased.

11. A method as claimed in claim 9 including the further step of after step (b) and prior to step (c), restricting a supply of induction air to the engine by closing the throttle valve for a pre-determined time period.

12. A method as claimed in any of claims 9 to 11 and including the further step of disabling engine ignition after combustion has ceased.

13. A method as claimed in any of claims 9 to 11 and including the further step of disabling engine ignition after a pre-determined time interval has elapsed after ceasing the supply of fuel to the engine (step (b)).

14. A method as claimed in any of claims 9 to 13 and including the further steps of; after step (c), (d) detecting that the engine has stopped running, and thereafter, (e) closing the throttle valve completely 15. A method as claimed in any of claims 9 to 13 and including the further steps of; after step (c), (d) detecting that the engine has stopped, and thereafter, (e) partially closing the throttle valve.

16. An apparatus for reducing hydrocarbon evaporative emissions from an internal combustion engine substantially as hereinbefore described with reference to the drawings.

17. A method for reducing hydrocarbon evaporative emissions from an internal combustion engine substantially as hereinbefore described with reference to the drawings.