FIELD OF THE INVENTION:

This invention relates to a method to operate an internal combustion engine.

BACKGROUND OF THE INVENTION:

Vehicle running on two fuels are referred as Bi-fuel vehicles. Typically one fuel is gasoline or diesel, and the other is an alternate fuel such as compressed natural gas (CNG) The two fuels are stored in separate tanks and the engine runs on one fuel at a time. Bi-fuel vehicles have the capability to switch back and forth from gasoline or diesel to the other fuel, manually or automatically.

The engines switching between the CNG and the gasoline under different operating conditions are known in the prior art. The prior art US 20040139944 discloses a method and a device to switch between liquid fuel and gaseous fuel. The switching happens under different operating conditions of the engine. In the prior art, during starting, the liquid fuel is used. A condition is previously established for switching from the liquid fuel to the gasiform fuel. Such a condition may be an individual one, such as an engine condition, or more specifically, a period of time elapsed after starting or a coolant temperature, or a combination of these individual conditions. The gasiform fuel is then selected when such a condition is met.

ADVANTAGES OF THE INVENTION:
The invention has the advantage that by selecting the gaseous fuel during the transient load condition, the fuel is controlled more accurately. Controlling the fuel more accurately yields better performance of the engine in terms of better torque output and also better control of the emissions of harmful gases in the exhaust.

The invention has the advantage that effort involved in modeling the wall film effect where a portion of the fuel gets stuck on to the walls of the intake manifold is reduced,

OBJECT OF THE INVENTION:

The object of the invention is to provide a device and a method to handle transient load in an internal combustion engine in such a way that the engine performance does not drop because of the transients in the load.

BRIEF DESCRIPTION OF THE DRAWINGS:

Figure 1 Shows the fuel injection system

Figure 2 Shows an Engine control unit according to the invention

DESCRIPTION OF THE INVENTION:

Shown in fig 1 is a fuel injection system. Many components of the fuel injection system are already known in the prior arts hence not explained in detail. Only the components which are specific to the invention are explained in detail.

The fuel injection system shown in fig. 1 is a bi-fuel fuel injection system along with an internal combustion engine 1. The internal combustion engine is referred just as engine in the document. In typical bi-fuel injection systems, two types of fuels are used, one being liquid fuel and the other being gaseous fuel. Out of the two fuels, only one fuel is used at any given time. The fuels can be switched between liquid and gaseous fuel either manually by the user or automatically by an engine control unit ECU.

The fuel injection system shown in fig 1 comprises two fuel tanks 10, 12 to store the two different types of fuels, two sets of fuel injectors 14, 16, a fuel ignition device 18 in the cylinder 20, an engine control unit (ECU) 22 to control the fuel injection system. The fuel injected in the intake manifold 24 reaches the cylinder 20 where it is burnt. The exhaust gases go out through the exhaust path 26.

The ECU may decide automatically which fuel is to be supplied to the engine 1 depending upon operating conditions of the engine 1 or the user can select manually.

Shown in fig. 2 is the ECU 22. The typical ECU is built around a microcontroller, memory and all other components to handle any inputs and outputs. Hence the common components in the ECU are not shown. The ECU 22 comprises a receiving means 200 to receive a load signal 202 which is indicative of load on the engine. The load on the engine is indicated by an accelerator pedal position, air mass passing through the intake manifold etc. The receiving means 200 receives the signal 202 and computes the transients in the load signal 200 which indicates the transients in the load. The information on transients is passed to switching means 203 which monitors the transients and automatically switches between the liquid fuel and the gaseous fuel which is supplied to the engine 1 based on the amount of transients. For this effect ECU 22 generates actuation signals 204 and 206 which are used to control the liquid fuel and gaseous fuel respectively.

In internal combustion engines, the amount of fuel to be injected in to the cylinders is computed by the ECU based on engine operating conditions. The parameters which influence the engine operating conditions may comprise the air mass coming into the intake manifold, air temperature, engine temperature, engine load etc. The listed parameters are only for reference and not for limiting. The engine load is determined by the torque demand which is determined by the accelerator pedal position. If the user suddenly presses the accelerator pedal, then there is a sudden increase in torque demand and the amount of fuel to be injected needs to be increased suddenly. Similarly if the user suddenly releases the accelerator pedal, then there is a sudden decrease in torque demand and the amount of fuel to be injected needs to be decreased suddenly. Such state where the torque demand changes rapidly is referred as transient state. As the torque demand is indicative of the engine load, transient state of torque also refers to the transient state of the load. The state where the load is stable is referred as stable state.

During the transient state if the engine is using liquid fuel, the sudden increase in the quantity of fuel injected causes inaccurate air fuel ratio. This is because of the following reason Wall Film effect: The sudden increase in the fuel mass injected into the intake manifold 24 does not remain entirely in the air in the form of fuel droplets or fuel vapor, but a certain portion of the fuel gets deposited on the walls of the intake manifold 24, in the form of a wall film. This wall film varies according to engine speed, manifold pressure, intake manifold wall and air temperatures. The higher the sudden change in the fuel mass injected, higher is the wall film effect. This means that higher the transients in the load, the larger is the wall film effect, hence larger inaccuracy in the air-fuel ratio.

The wall film causes less amount of fuel to reach the cylinder 20 thereby affecting the air fuel ratio. This in turn affects the torque output of the engine 1.

The wall film effect has more influence when the liquid fuel is used compared to the gaseous fuel. The gaseous fuel is not affected or the effect is not significant compared to the liquid fuel. This is because of the fact that the liquid fuel sticks to the walls of the intake manifold. This is not seen with the gaseous fuel.

The invention proposes a method to handle the transient state of the load without affecting the engine performance. The working of the invention is explained below.

The engine performance is determined by the demand in the torque and the actual torque generated. If the demand in the torque and the actual torque generated are comparable to each other, then the performance of the engine is said to be as expected. If there is a gap in the two and the gap is beyond an acceptable limit, then the engine performance is said to be deviating from expected performance. In other words the engine should generate the torque within an acceptable limit of the torque demand. The torque demand is proportional to the position of the accelerator pedal which is not shown in fig. 1.

According to the invention, during the transient state, if there is sudden increase in the torque demand, the fuel is automatically switched to gaseous fuel if the engine is currently using the liquid fuel. This is achieved as explained below:

The ECU 22 continuously monitors the torque demand by monitoring the rate of change of accelerator pedal position. The rate of change of accelerator pedal position indicates the amount of transient in the torque demand which is indicative of the amount of transient in the load. An accelerator pedal position sensor which is not shown in fig. 1 is used to sense the accelerator pedal position and ECU 22 computes the rate of change of accelerator pedal position to determine the transients in the load.
In another embodiment, there may not be accelerator pedal position sensor. In this embodiment, the transients are determined by other means, for example, by monitoring the air mass passing through the intake manifold 24.

If the transients in the load are greater than a predefined threshold, then the ECU 22 automatically switches the fuel from liquid to gaseous. The ECU activates the required components like fuel pump, sensors etc. required for the gaseous fuel injection and at the same time deactivates the components supplying the liquid fuel.

The gaseous fuel is injected proportional to the torque demand. The torque demand is determined by monitoring the accelerator pedal position or by monitoring the air mass passing in the intake manifold.
As the wall film effect is not present during the use of the gaseous fuel, more fuel will reach the cylinder 20, maintaining the air fuel ratio. This results in better combustion and better torque generation. This results in better engine performance.

The ECU 22 keeps monitoring the transients in the torque demand. Once the torque demand is stabilized, the ECU 22 will switch back to the liquid fuel, if liquid fuel was used before switching to gaseous fuel.
Thus by automatically switching to the gaseous fuel during the transient load conditions of the engine, the air-fuel ratio is maintained thereby maintaining the performance of the engine. The user will not experience any jerks or deceleration in the vehicle conditions.

WE CLAIM:

1. A method to operate an internal combustion engine running on bi-fuel, said method comprising:

Monitoring the transients in the load on the engine

If the transients are above a predefined threshold, then determining whether the engine is running on liquid fuel or gaseous fuel

If said engine is running on liquid fuel, then switching the engine to gaseous fuel
Switching back to liquid fuel once the transients are below the predefined threshold

2. A method to operate an internal combustion engine according to claim 1 wherein said transient is monitored by monitoring rate of change of accelerator pedal position

3. A method to operate an internal combustion engine according to claim 1 wherein said transient is monitored by monitoring the expected torque to be delivered by the engine

4. An engine control unit ECU (22) to control an internal combustion engine 1, said engine control unit characterized by:

a receiving means (200) to receive a load signal 202 indicative of load on said internal combustion engine 1; said receiving means (200) further adapted to compute transients in the load signal (202);

a switching unit (203) to switch from a liquid fuel to a gaseous fuel if the transients in the load are above a predefined threshold and the current fuel used is liquid fuel

5. An engine control unit to control an internal combustion engine 1 according to claim 4 wherein ECU (22) monitors transients in said load by monitoring the expected torque to be delivered by the engine