GB2463055A

GB2463055A - A method of controlling fuel injection timing in a turbo charged ic engine as a result of acceleration

Info

Publication number: GB2463055A
Application number: GB0815832A
Authority: GB
Inventors: Pierluigi Rellecati
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2008-09-01
Filing date: 2008-09-01
Publication date: 2010-03-03
Anticipated expiration: 2028-09-01
Also published as: GB2463055B; GB0815832D0

Abstract

A combustion engine comprising a cylinder 2, a turbocharger 13 driven by exhaust gas from said cylinder 2, a fuel injector 4 which injects fuel into the cylinder 2, and fuel injection control means 16 for controlling the amount of fuel that is injected from this fuel injector and the timing t1, t2, t3, t4 of this fuel injection. The injection control means 16 controls injection of at least a main injection amount 22 in the vicinity of the top dead centre position (TDC) of the cylinder. The injection control means 16 is adapted to delay the average injection timing of fuel 22, 23 injected during an engine stroke after top dead centre position (TDC) beyond a steady state timing in case of acceleration of the engine. The delay may be proportional to an increase in the main injection amount. The delay to the average timing may be achieved by increasing a post-injection quantity which may be proportional to an increase in the main injection quantity. The acceleration may be judged by monitoring an air intake sensor measuring airflow or intake pressure. The acceleration may be judged via a crankshaft sensor.

Description

Combustion Engine with a Turbocharger

Description

The present invention relates to a combustion engine, in particular to a diesel engine, comprising a turbocharger. It is generally known to use a turbocharger driven by exhaust gas from the combustion engine to pre-compress intake air of the engine, in order to increase the amount of oxygen present in a cylinder filling, and, hence, the amount of work that can be obtained from one engine stroke.

Although a turbocharger can increase significantly the amount of engine power that can be generated per unit of cylinder volume under steady state operating conditions, the inertia of the turbocharger causes a problem whenever the engine accelerates. Under acceleration, the air intake rate of the combustion engine increases, but the throughput of the turbocharger lags behind, so that there is a drop in the air pressure at the intake side of the cylinders of the engine, causing the engine power to be less than what could be expected at the same engine speed in the steady state.

The turbocharger thus prevents a fast increase of engine power. Firther, if the fuel metered into the cylinders does not take account of the decrease of the intake air pressure, excessively fat combustion may result, causing a high concentration of pollutants such as soot, carbon monoxide or nitric oxides in the exhaust gas.

The object of the present invention is to relieve one ore more of the above mentioned defects of

the prior art.

The subject is achieved by a combustion engine comprising:a cylinder, a turbocharger driven by exhaust gas from said cylinder for compressing intake air supplied to said cylinder, a fuel injector which injects fuel into the cylinder; and fuel injection control means for controlling the amount of fuel that is injected from this fuel injector and the timing of this fuel injection; the injection control means being adapted to control injection of at least a main injection amount in the vicinity of the top dead centre position of the cylinder, characterized in that the injection control means is further adapted to delay, in case of acceleration of the engine, the average injection timing of fuel injected during an engine stroke after the top dead centre position beyond a steady state timing.

Under steady state conditions, the injection of fuel will be timed so as to derive from its combustion the maximum possible amount of work. By delaying the average injection timing, it should be expected that the efficiency of the engine is reduced. However, this reduction in efficiency causes an increase of the exhaust gas temperature, and, hence, a steeper increase of the pressure of the exhaust gas driving the turbocharger than would occur if the engine accelerated without a delay of the injection timing. Accordingly, in case of acceleration of the engine, the turbocharger receives more driving power from the exhaust gas than it would from the engine running at the same power under steady state conditions. This causes the turbocharger to accelerate very quickly and thus to provide the required additional compressed fresh air with a minimum delay.

In some combustion engines, in particular Diesel engines, the injection control means may conventionally be adapted to inject a pilot injection amount before top dead centre, for starting combustion, and a main injection amount after top dead centre, which is ignited in the cylinder by the pilot injection amount.

In case of acceleration of the engine, such an injection control means may be adapted to delay said average injection timing by delaying the main injection amount.

In such a case, it may also be necessary to delay the timing of the pilot injection in order to insure that the main injection is safely ignited.

The delay of the average injection timing of the main injection amount may be set proportional to an increase rate of the main injection amount, so that the increase of the exhaust gas temperature will be the more pronounced, the higher the increase rate of the injection amount is, i.e. the faster the engine is intended to accelerate.

According to a second embodiment, the injection control means is adapted to control injection of a post-injection amount after a main injection amount and, in case of acceleration of the engine, to delay said average injection timing by increasing the quantity of said post-injection above a steady state amount. The timings of main and post-injection amounts as such may remain unchanged.

In this case, the increase of the post-injection amount is preferably set proportional to an increase rate of the main injection amount.

The steady state amount may be zero, i.e. while the engine is operating under steady state conditions, there is no post-injection.

Many combustion engines have an intake air flow rate sensor which is used for metering injected fuel in proportion to the intake air flow rate, so as to obtain a predetermined air-fuel ratio. Such a flow rate sensor may be used according to the present invention for judging an acceleration of the engine from an increase of the intake air flow detected by said sensor.

As an alternative, an intake air pressure sensor may be provided, and the injection control means is adapted to judge an acceleration of the engine from a decrease of the intake air pressure detected by said sensor.

As a further alternative, the control means may be adapted to judge an acceleration directly from the speed detected by a crankshaft sensor.

The object is also achieved by a method for controlling fuel injection in a turbocharged combustion engine comprising the steps of judging whether the engine is accelerating or not, and, in case of the engine being judged to accelerate, delaying beyond a steady state timing the average injection timing of fuel injected into a cylinder of the combustion engine after top dead centre position of said cylinder.

The invention further relates to a computer program product enabling a microprocessor, when executed on said microprocessor, to carry out the method defined above.

Further features and advantages of the invention will become apparent from the subsequent description of embodiments thereof referring to the appended drawings.

Fig. 1 is a schematic diagram of the combustion engine system according to the invention; Fig. 2 is a diagram illustrating the injection of fuel into a cylinder of the engine according to a first embodiment of the invention; and Fig. 3 is a diagram analogous to Fig. 2 illustrating fuel injection according to a second embodiment of the invention.

The Diesel engine system of Fig. 1 comprises an engine block 1 having a plurality of cylinders 2 formed in it. The cylinders 2 drive a crankshaft, not shown, the angular position and/or rotation speed of which is detected by a crankshaft sensor 3. Each cylinder 2 has a fuel injection valve 4 associated to it for injecting fuel from a common fuel rail 5. The fuel rail 5 is pressurized by a fuel pump 6 which draws fuel from a tank 7.

J

The cylinders 2 are connected to a fresh air intake manifold 8 and to an exhaust manifold 9 by conventional intake and exhaust valves, not shown. An exhaust gas reduction channel 10 forms a flow path between the exhaust manifold 9 and the intake manifold 8.

It joins the intake manifold 8 at a downstream side of a throttle 11. An exhaust gas reduction valve (EGR valve) 12 is located in the channel 10.

A turbocharger 13 comprises a turbine 14 located at a downstream end of the exhaust manifold 9 and driven by the flow of exhaust gas from the cylinders 2, and a compressor 15 which is driven by turbine 14 to compress fresh air emitted into intake manifold 8 via an intercooler 19.

A microprocessor-based electronic controller 16 controls the flow of exhaust gas through EGR valve 12 and the fuel injection timings and quantities at injection valves 4 based on the position of accelerator pedal 17 detected by sensor 18, the crankshaft rotation speed detected by sensor 3, and, if appropriate, other parameters.

Fig. 2 is a diagram illustrating the fuel injection flow rate IF of one of injectors 4 as a function of time t. While the engine is running under steady state conditions, two pilot injection pulses 20, 21 having a duration öt and centred at times ti, t2 are generated shortly before the piston of the cylinder 2 associated to injector 4 reaches its top dead centre position TDC. Fuel injected in these pilot injection pulses 20, 21 is heated along with fresh air in the cylinder by adiabatic compression of the latter, so that in the vicinity of top dead centre TDC the fuel ignites.

While the fuel of the pilot injection pulses 20, 21 is still burning, a main pulse 22 of duration T centred around t3 is injected after top dead centre.

Controller 16 is adapted to detect an acceleration of the engine. This detection may be carried out according to various schemes.

According to a first scheme, a fresh air flow rate sensor 24 is provided at an adequate position in the fresh air supply system of the engine. In Fig. 1 flow rate sensor 24 is shown in the fresh air duct between intercooler 19 and throttle 11, but it might be provided anywhere downstream of compressor 15 and upstream of cylinders 2. Sensor 24 continuously provides fresh air flow rate data to controller 16, and controller 16 calculates a time derivative of this flow rate. This time derivative is representative of an increase of engine speed because if the speed of the crankshaft increases, fresh air throughput of the engine will do so, too, and this reflects in the air flow data from sensor 24.

This first scheme is rather economic, since many combustion engines have an intake air flow rate sensor for other purposes, which may be used for the purposes of the present invention at no extra cost.

However, air flow rate measurements may be corrupted by the inertia of compressor 13, in particular if flow rate sensor 24 is very close to compressor 15.

According to a second scheme, controller 16 uses crankshaft sensor 3 for monitoring the crank shaft speed and calculating its rate of change.

A third scheme uses a pressure sensor 25 which may be located anywhere in the fresh air supply system between compressor 15 and the cylinders 2, preferably at a downstream side of throttle 11. When the engine is running at steady state conditions, the intake air pressure measured by sensor 25 is essentially constant at a value determined by the design of turbocharger 13.

Whenever the engine accelerates and the turbocharger 13 lags behind, the cylinders 2 take in more fresh air than th.e compressor 15 can provide, causing the pressure seen by sensor 25 to drop. The deviation between the steady state pressure and an instantaneous pressure detected by sensor 25 may therefore directly be taken as proportional to an acceleration of the engine, without having to calculate a time derivative in controller 16.

When the controller 16 decides that the engine is accelerating, it shifts the timings of pilot injections 20, 21 and main injection 22 by times, E proportional to the rate of acceleration of the engine, as shown by dashed outlines in Fig. 2. While the pilot injections 20, 21 are only delayed, the main injection 22 also has its amount increased, in order to compensate for a loss of efficiency cause by the delayed injection and to provide extra power for accelerating. Due to the reduced efficiency, the exhaust gas becomes hotter than under steady state operating conditions, and the pressure at the input side of turbine 14 increases accordingly.

The turbocharger 13 thus accelerates very quickly, so that enough compressed intake air becomes available for driving a fast acceleration of the crankshaft.

Fig. 3 illustrates an alternative injection procedure. In this procedure, the pilot injections 20, 21 at times tl, t2 prior to TDC are similar in amount and timing to those under steady state operating conditions in Fig. 2. Under these conditions also the main injection 22 at t3 is similar to that of Fig. 2. If the controller 16 detects an acceleration of the engine, it does not only increase the amount of the main injection 22, as illustrated by solid and dashed outlines of the main injection in Fig. 3, but it produces a post injection 23 at a time t4, subsequent to the main injection 22, the amount of which is proportional to the detected engine acceleration. Combustion of this post injection 23 does not have a substantial influence on the force driving the pistons of cylinders 2, but it increases the thrust of the exhaust gas blowing out of the cylinders 2, so that more driving power is available at the turbine 15. Like in the case of Fig. 2 the turbocharger 13 accelerates quickly, so that sufficient pressurized intake air for driving an acceleration of the crankshaft is available with little delay.

It should be noted that the concepts of Fig. 2 and Fig. 3 can be combined by both delaying the main injection 22 and generating the post-injection 23 if controller 16 detects acceleration of the engine.

Reference to the Drawings List of reference signs 1 engine block 2 cylinder 3 crankshaft sensor 4 fuel injection valve fuel rail 6 fuel pump 7 tank 8 intake manifold 9 exhaust manifold exhaust gas reduction channel 11 throttle 12 EGR valve 13 Turbocharger 14 Turbine Compressor 16 Controller 17 accelerator pedal 18 sensor 19 intercooler pilot injection 2]. pilot injection 22 main injection 23 post-injection 24 flow rate sensor pressure sensor

Claims

Claims 1. A combustion engine comprising: a cylinder (2), a turbocharger (13) driven by exhaust gas from said cylinder (2) for compressing intake air supplied to said cylinder (2), a fuel injector (4) which injects fuel into the cylinder (2), and fuel injection control means (16) for controlling the amount of fuel that is injected from this fuel injector and the timing (ti, t2, t3, t4) of this fuel injection; the injection control means (16) being adapted to control injection of at least a main injection amount (22) in the vicinity of the top dead centre position (TDC) of the cylinder, characterized in that the injection control means (16) is further adapted to delay the average injection timing of fuel (22, 23) injected during an engine stroke after top dead centre position (TDC) beyond a steady state timing in case of acceleration of the engine.
2. The combustion engine of claim 1, wherein the injection control means (16) is adapted to inject a pilot injection (20, 21) amount before top dead centre (TDC) and a main injection amount (22) after top dead centre (TDC), and, in case of acceleration of the engine, to delay said average injection timing (t3) by delaying (E) the main injection amount (22).
3. The combustion engine of claim 2, wherein the delay (E) of said average injection timing (t3) is proportional to an increase rate of said main injection amount (22).
4. The combustion engine of claim 1, wherein the injection control means (16) is adapted to control injection of a post-injection amount (23) after a main injection amount (22), and, in case of acceleration of the engine, to delay said average injection timing by increasing the quantity of said post-injection (23) above a steady-state amount.
5. The combustion engine of claim 4, wherein the increase of said post-injection amount (23) is proportional to an increase rate of said main injection amount (22)
6. The combustion engine of claim 4 or 5, wherein the steady-state amount is zero.
7. The combustion engine of any of the preceding claims, further comprising an intake air flow-rate sensor (24), wherein the injection control means (16) is adapted to judge an acceleration of the engine from an increase of the intake air flow detected by said sensor (24)
8. The combustion engine of any of claims 1 to 6, further comprising an intake air pressure sensor (25), wherein the injection control means (16) is adapted to judge an acceleration of the engine from a decrease of the intake air pressure detected by said sensor (25)
9. The combustion engine of any of claims 1 to 6, further comprising a crankshaft sensor (3) for measuring the speed of a crankshaft, wherein the injection control means (16) is adapted to judge an acceleration of the engine from the speed detected by said sensor (3)
10. A method for controlling fuel injection in a turbocharged combustion engine, comprising the steps of -judging whether the engine is accelerating or not, and, in case of the engine being judged to accelerate, -delaying beyond a steady state timing the average injection timing of fuel injected into a cylinder (2) of the combustion engine after top dead centre position (TDC) of said cylinder (2).
11. A computer program product enabling a microprocessor (16), when executed on said microprocessor, to carry out the method of claim 10.