FIELD OF THE INVENTION:

This invention relates to test system to test and calibrate an internal combustion engine.

BACKGROUND OF THE INVENTION:

It is known in prior arts that, a closed loop system is used to control air-fuel mixture to a stoichiometric air-fuel ratio. The closed loop system comprises an oxygen sensor provided in the exhaust passage of the internal combustion engine. The oxygen sensor senses the oxygen content of exhaust gases and generates an output dependent on the oxygen content.

The oxygen content represents the air-fuel ratio of the air-fuel mixture which is supplied to the engine. An engine control unit ECU checks whether the output of the oxygen sensor is higher or lower than a standard value corresponding to the stoichiometric air-fuel ratio. Depending upon the oxygen content, the ECU corrects the quantity of the fuel to be supplied to the engine. Typically the air-fuel ratio is controlled to the stoichiometric air-fuel ratio.

Typically the quantities of fuel to be supplied to the engine for each cycle of combustion under different working conditions of the engine are stored in look up tables. Depending upon the quantities of the fuel to be supplied to engine, the duration of opening of the injector valves is computed and accordingly the injector valves are opened.
The look up tables need to be refined from time to time because of some factors like ageing of the injector valves etc. This is achieved by computing correction factors for the look up tables.

The US patent 741312 discloses a control system to control the air-fuel ratio. The said patent also discloses a method to compute correction factors to maintain the air-fuel ratio.

ADVANTAGES OF THE INVENTION:

The invention has the advantage that there is no need to install an oxygen sensor as part of fuel supply system in vehicles. The calibration of the engine for the air-fuel ratio is done offline at the assembly line during the manufacturing of the vehicle or at the dealer show room or at the service stations. The initial data in look up tables or maps are stored during the manufacturing of the vehicle using the test system. The correction factors for the maps are stored during the servicing of the vehicle using the test system.
As the oxygen sensor is not installed in every vehicle, there is cost saving.

OBJECT OF THE INVENTION:

The object if the invention is to provide a device and method to test and calibrate the engine during manufacturing and servicing of the vehicle. The proposed invention works in open loop, but provides option to fine tune the parameters used for vehicle performance or emission controls, during the servicing of the vehicles.

BRIEF DESCRIPTION OF THE DRAWINGS:

Figure 1 Shows the schematic of the test system according to the
invention

Figure 2 Shows the schematic of the tester according to the invention

Figure 3 Shows the schematic of the ECU according to the invention

DESCRIPTION OF THE INVENTION:

Shown in Fig.1 is the test system used to test and calibrate the internal combustion engine in a vehicle 50, according to the invention. The test system comprises a tester 10 and an oxygen sensing means 52. The oxygen sensing means 52 is removably placed in the exhaust path of a vehicle 50 whose internal combustion engine needs to be calibrated. The oxygen sensing means 52 is so placed that it receives the exhaust gases and an output 54 is generated which represents the oxygen content in the exhaust gases.

The output 54 may be a voltage signal whose amplitude represents the level of oxygen content in the exhaust gases. The output 54 of the oxygen sensing means 52 which is an analog signal is delivered to the tester 10. The tester 10 converts the analog signal to digital domain for further processing.

The internal combustion engine is referred as engine in this document. Shown in fig. 2 is the tester 10 according to the invention. The tester comprises a first control means 12, an input means 14, an output means 16 and a communication means 18. The tester is typically built with a microcontroller, with memory and other peripheral devices.

The input means 14 may be a keyboard or a set of switches to provide user inputs to the tester 10. The output means 16 may be any kind of display to display status and other information to the user.

The input and output means may be combined into one in a touch screen display. The communication means 18 comprises required transmitter and receiver to establish communication with other devices which are external to the tester. The communication may take place through wired medium or wireless medium.

The first control means 12 may be a set of software functions supporting the input means, the out means and the control means.

The communication means 18 is used to communicate with an Engine Control Unit (ECU) 58 of the vehicle 50. The vehicle 50 may be a motorcycle which has no oxygen sensor permanently installed in its exhaust channel. The connection 56 connects the communication means to any other device.

The tester receives the output 54 of the oxygen sensing means 52 through one of the input pins. This signal may be in analog form and the tester may convert it into digital domain for further processing.

Shown in fig. 3 is the Engine control unit 58 shown with the internal blocks. Only the relevant parts of the control unit are shown. As the other parts of the ECU are well known, they are not explained in this document.

The ECU 58 comprises a second control means 60, a switching means 62, a second communication means 64, a set of maps 66, a set of first look up tables 68 and a set of second look up tables 70. The ECU operates in two modes, the first mode being the calibration mode and the second mode being the running mode. These modes are explained in detail in later parts. The switching mode selects one of the modes based on an event. The event may be a message from a tester. The second communication means is similar to the communication means in the tester.

The method to test and calibrate the engine is explained below. The vehicle 50 is placed on a dynamo so that the wheels can rotate but the vehicle remains stationery. The engine of the vehicle 50 is driven at a predefined speed. Once the predefined speed is attained, the tester 10 is activated through a switch or through an user interface to start the test and calibration.

The oxygen sensing means senses the level of oxygen content in the exhaust gases and generates an output 54. The first control means 12 in the tester 10 reads the output 54 of the oxygen sensing means 52. Typically the output 54 of the oxygen sensing means 52 should represent the stoichiometric ratio which is a standard value. But in reality the output 54 of the oxygen sensing means 52 may deviate from the standard value.

The first control means 12 in the tester 10 requests the communication means 18 to establish a link with the second communication means in the ECU 58 fitted in the vehicle 50. The communication may be through a wired link 56 or through wireless link.

The tester 10 and the ECU 50 may follow a defined protocol so that each knows what the other device is sending. Also there may be exchange of authentication codes so that only authorized testers are allowed to calibrate the engines of particular manufacturer.

This is required so that unauthorized tampering of the engine is avoided. The ECU has two modes of operations; first mode being the calibration mode where the ECU receives the data from the tester; the second mode being running mode where the ECU is controlling the engine when the vehicle is running.

In the second mode the ECU makes use of the data received from the tester for injecting fuel into the engine.Once the tester 10 and the ECU 58 establish the communication, the ECU enters into the calibration mode.

The first control means sends the data regarding the oxygen content in the exhaust gases to the ECU 58. The ECU 58 receives the data regarding the oxygen content and analyses the data. The ECU 58 has pre-stored look up tables which contain the values of expected oxygen content for different operating conditions of the engine. These are referred as first look up tables 68.

The ECU compares the values from the first look up tables with the data received from the tester. The data received from the tester represents the actual oxygen content in the exhaust gases. Based on the comparisons, the ECU 58 computes the deviation between the actual oxygen content and the expected oxygen content. This deviation is stored as correction factor in the second look up table 70. There may be a set of second look up tables 70 which are used to store the correction factors for different operating conditions of the vehicle.

The ECU has pre-stored data referred as Maps 66 which contain the data regarding quantity of fuel versus different operating conditions of the engine. The operating condition of the engine is determined by parameters like engine speed, engine load, engine temperature, air temperature, air pressure etc. This list is only for reference and is not a complete list.

The above test is repeated for different operating conditions of the engine and the corrections are stored by the ECU in different second look up tables 70.

Once the entire operating range of the engine is covered and the corrections are stored, the test is complete. The Tester sends a message indicating the end of the test. The oxygen sensing means is removed from the exhaust path. The ECU changes the mode from calibration to running.

Now the vehicle is ready for use with the calibrated data which is stored in the form of correction factors in the second look up tables. During the running of the engine, the ECU uses the data from the maps 66 along with the correction factors to compute the right quantity of fuel to supply to the engine.

Also it is possible that the user wants to run the engine under rich air-fuel ratio where the engine generates more power. This can be adjusted through the tester so that the correction factor is computed accordingly by the ECU. Similarly it is possible that the user wants to run the engine under lean air-fuel ratio where the engine gives more mileage for the given amount of fuel. This can be adjusted through the tester so that the correction factor is computed accordingly by the ECU.

The tester provides different options for the user to fine tune the engine, the options being rich air-fuel mixture, lean air-fuel mixture and air-fuel mixture at stoichiometric ratio. These options can be exercised through user inputs. The user inputs may be entered through an user interface using the input and output means. Alternatively these options may be exercised through simple switches.

WE CLAIM:

1. A test system to test and calibrate an internal combustion engine, said test system comprising a tester (10) and an oxygen sensing means (52); said oxygen sensing means removably placed in an exhaust path of said combustion engine; said oxygen sensing means (52) adapted to sense the oxygen content in the exhaust gases in said exhaust path and adapted to deliver the data regarding the oxygen content to said tester 10; said tester (10) adapted to send the data regarding the oxygen content to an Engine Control Unit (ECU) (58) which is in communication with said tester (10).

2. A test system according to one of the previous claims wherein the oxygen sensing means (52) is an oxygen sensor.

3. A test system according to one of the previous claims wherein the oxygen sensing means (52) is an emission analyzer which provides information regarding oxygen content in the exhaust gases.

4. A test system according to one of the previous claims wherein the tester (10) configures the ECU (58) to use one of the air-fuel ratios, the air-fuel ratios being rich air-fuel mixture, lean air-fuel mixture and air-fuel mixture with stoichiometric ratio.

5. A test system according to one of the previous claims wherein the test system starts the test and calibration by activation of a switch on the tester (10)

6. A test system according to one of the previous claims wherein the test system stops the test and calibration by activation of the switch on the tester (10)

7. A test system according to one of the previous claims wherein the data i regarding the oxygen content is displayed on a display of the tester (10)

8. An engine control unit (ECU) (58) to control an engine, said (ECU) comprising

a switching means (62) to switch between a calibration mode and a running mode;
a set of maps (66) containing data regarding quantity of fuel to be injected in the engine for different operating conditions of the engine

a second control means (60) to receive the data regarding oxygen content in the exhaust gases of said engine from a tester and store said data in a second look up table (70) when the ECU (58) is in said calibration mode; said second control means (60) adapted to use the data from the said maps (66) along with the data in the second look up table (70) to compute the quantity of fuel to be injected into the engine during the running mode

9. A method to operate a test system to test and calibrate an engine, the said method comprising the steps :

- Placing an oxygen sensing means (52) in the exhaust path of said engine

- running the engine at a predetermined speed by injecting a predetermined quantity of fuel

- reading the oxygen content in the exhaust gases using the said oxygen sensing means 52

- establishing a communication between a tester (10) and an ECU (58) controlling the said engine

- Sending data to the ECU (58) regarding the said oxygen content

- Computing by the ECU (58), a correction factor in dependence of the oxygen content

- Storing the correction factor by the ECU (58) in a second look up table for future use

10. A method according to one of the previous claims wherein the tester uses a wired communication with the ECU (58)

11. A method according to one of the previous claims wherein the tester uses a wireless communication with the ECU (58)

12. A method according to one of the previous claims wherein the communication etween the tester and the ECU (58) is established after checking for authentication

13. A method according to one of the previous claims wherein the tester (10) starts the test and calibration of the engine by sending a first command

14. A method according to one of the previous claims wherein the tester (10) stops the test and calibration of the engine by sending a second command

15. A method according to one of the previous claims wherein the tester (10) sends the data to the ECU (58) regarding the oxygen content in a predefined format