Claims:We Claim:

1. A method to determine pressure at an injector, said method comprising the steps:
- reading engine speed
- reading accelerator pedal position
- reading fuel temperature
- reading from maps expected pressure at said injector corresponding
to engine speed and accelerator pedal pressure
- applying corrections to expected pressure in dependence of fuel temperature

2. A method according to claim 1 wherein said maps store values for engine speed, accelerator pedal position and expected pressure at injector
3. A method according to claim 1 wherein said maps are stored during testing of a fuel injection system
4. A method according to claim 1 wherein calculated pressure at injector is used for determining the energizing time of said injector
5. An electronic control unit 106 adapted to:
- read engine speed
- read accelerator pedal position
- read fuel temperature
- reading from maps expected pressure at said injector corresponding
to engine speed and accelerator pedal pressure
- apply corrections to expected pressure in dependence of said temperature to determine pressure

6. A fuel injection system 100 comprising:
- An electronic control unit 106 adapted to:
o Read engine speed
o Read accelerator pedal position
o Read fuel temperature
o reading from maps expected pressure at said injector corresponding to engine speed and accelerator pedal pressure
o apply corrections to expected pressure in dependence of said temperature to calculate pressure at said temperature
- a set of Maps stored in said ECU; said maps containing values for engine speed, accelerator pedal position and
- a pump to pressurize fuel to deliver it to an injector
- an injector to inject fuel into an engine; said injector energizing time controlled by said ECU in dependence of determined pressure at said injector
, Description:Complete Specification:

The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed.
Field of the invention
[001] This invention relates to the field of fuel injection systems in general. The invention relates to determining fuel pressure without using a pressure sensor.

Background of the invention

[002] Typical fuel injection systems in the prior arts use a pressure sensor to control the fuel injection. The pressure sensor may be disposed as part of a common rail system. Based on the fuel pressure and the quantity of fuel to be injected into the engine, the injector energizing time and the duration is controlled.

[003] It is also possible that the fuel pressure is modelled using look up tables or MAPS. MAPS are the tables which store graphs of different parameter. The US patent 6694953 discloses a rail pressure predictor model. The patent disclosure takes a rail pressure measurement Substantially before an injection event, and then utilizes a rail pressure predictor model to predict what the rail pressure will be at each injection event so in a succeeding injection sequence. This estimated rail, pressure is then used as the means for determining the fuel injection control signal characteristics for that Succeeding injection event.

Brief description of the accompanying drawing

[004] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:

[005] FIG. 1 illustrates a schematic of a fuel injection system

Detailed description of the embodiments

[006] Shown in fig. 1 is a fuel injection system 100. The main components of the fuel injection system are a fuel pump 102, a fuel injector 104 and an electronic control unit ECU 106. The fuel pump 102 is a high pressure pump. The fuel pump is just referred as pump. This pump 102 may be preceded by a low pressure pump. The pump 102 receives fuel from the fuel tank 110 and pressurizes the fuel. The pressurized fuel is delivered to the injector 104 to inject the fuel into an engine. Also shown in fig. 1 are a pressure sensor 110 to read fuel pressure, a temperature sensor 112 to read coolant temperature, engine sped sensor 114, accelerator load sensor 116 and a fuel filter 118.

[007] Here the pump 102 is a mechanical pump driven by a cam 108 which is driven by the engine. The injector is an electronic injector and is controlled by an electronic control unit ECU 106. The ECU 106 controls the injector by opening or closing the injector for fuel injection. The ECU 106 determines the quantity of fuel to be injected into the engine, based on various engine operating parameters like engine speed, engine load, fuel pressure, coolant temperature etc. Based on the quantity of fuel to be injected into the engine the ECU 106 determines the energizing time for the injector. The ECU 106 provides required power to the injector in terms of pulse width modulation for the duration of calculated energizing time. The injector valve opens and the fuel injection takes place. After the energizing time is over, the ECU stops power to the injector, the injector valve comes back to closed position thereby stopping the fuel injection.

[008] In fuel injection systems, the pressure of the fuel entering the injector plays a major role. Typically in the prior arts there will be a pressure sensor disposed in one of the high pressure paths which provides the pressure value to the ECU. The ECU uses the pressure value to determine the injector energizing time to inject the required quantity of fuel into the engine.

[009] In some of the low cost fuel injection systems, there may not be a pressure sensor to sense the pressure of the fuel. The invention proposes a method to determine the pressure of the fuel using other parameters of the engine. The two parameter which can be used are engine speed and the accelerator pedal position. The engine speed provides an indication towards the fuel pressure. Similarly the accelerator pedal position influences the fuel pressure at the injector.

[010] The invention proposes a method to calculate fuel pressure using stored MAPs. During the testing and calibration of the fuel injection system in the engine, the parameters influencing the fuel pressure are stored as MAPs in the ECU. MAPs are the graphs of one parameter Vs another parameter. The MAPs stored in the ECU may be Accelerator pedal position Vs pressure for different ranges of engine speeds.

[011] In the proposed method, in the step S1, the ECU 106 reads the engine speed, the accelerator pedal position and the temperature of the fuel. The temperature of the fuel may be determined by reading coolant temperature.
In step S2, the ECU106 reads the expected pressure value from the MAPs corresponding to the engine speed and the accelerator pedal position.
In step S3, the ECU 106 applies correction to the expected pressure value based on the temperature of the fuel and computes the fuel pressure.

[012] Based on the computed fuel pressure and the required quantity of fuel to inject, the ECU calculates the energizing time and duration to operate the injector to inject required quantity of the fuel into the engine. The required fuel quantity is calculated based on various engine parameters and this is commonly known, hence not described in this document.

[013] Based on the calculated energizing time and duration to operate the injector, the ECU 106 controls the injector to inject fuel in the engine.

[014] The ECU 106 comprises a typical microcontroller, memory, input and output interfaces. The input and output interfaces may be input and output ports and may be additional circuits for signal conversion etc. The output interfaces may be connected to actuators to control the injector. The ECU 106 receives engine speed from a speed sensor and accelerator pedal position from an accelerator pedal position sensor. These are received by ECU 106 through the input interfaces. The ECU 106 computes the fuel pressure and the energizing timing and duration of energizing of the injector. The ECU 106 activates actuators through the output interfaces to initiate the injection of fuel. The injection of fuel is carried out by injector when the ECU 106 provides it with a signal, ex. a PWM signal.

[015] Shown in Fig. 2A and 2B are table 1 and table 2 respectively. These show a MAP of graphs for accelerator pedal position Vs pressure for different engine speeds. These MAPs are stored during calibration of the engine. The X axis represents the accelerator pedal position and Y axis represents pressure. The lines S1, S2 etc. are for different engine speeds. Table 1 may be for coolant temperature T1 and table 2 may be for coolant temperature T2. The ECU reads the accelerator pedal position and engine speed. Then the ECU reads the pressure value ‘p’ from the MAP corresponding to the accelerator pedal position and the engine speed. This pressure ‘p’ is the expected pressure. The ECU reads the coolant temperature and using a known relationship between pressure and temperature, applies a correction to expected pressure ‘p’ to compute the corrected pressure of the fuel. Using this corrected pressure, the ECU calculates the energizing time of the injector as explained above and injects the required quantity of fuel into the engine.

[016] In another embodiment, it is possible that the MAPs similar to shown in table 1 are stored for different temperatures. In this case the ECU, depending upon the temperature, reads the pressure ‘p’ from a MAP corresponding to accelerator pedal position, engine speed, ex. either Table 1 or table 2 depending upon the temperature.

[017] Thus the invention proposes a simple method to calculate fuel pressure thereby eliminating a need to have a pressure sensor. The invention makes use of the MAPS to calculate the pressure. Also the correction is applied for variations in the temperature.

[018] The invention has advantages that the pressure sensor is eliminated and the pressure is calculated using MAPs.