Field of the invention
[0001] This invention relates to the field of a method to determine engine
RPM in a vehicle.
Background of the invention
[0002] In conventional system engine speed recording is possible with alternator W+ terminal. However, in the alternators without W+ terminal, detecting the engine speed is impossible and determining the vehicle operation is therefore not possible. Enabling the engine speed sensing on the vehicle can be then be used for determining the usage duration and pattern of usage. [0003] Prior art patent application US7032545 discloses a method and apparatus for determining the balanced condition of an engine having a balancer is provided. An engine balancer tester includes a sensor coupled to the engine. The engine generates first- and second-order vibrations that have vibration levels and the sensor generates a signal corresponding to the vibrations. A meter coupled to the sensor receives the signal and calculates a ratio between the vibration level of the first-order vibrations and the vibration level of the second-order vibrations. A comparator compares the ratio to a predetermined value to assess the balanced condition of the engine.
Brief description of the accompanying drawing
[0004] Different modes of the invention are disclosed in detail in the description
and illustrated in the accompanying drawing:
[0005] FIG. 1 illustrates a control unit in a vehicle in accordance to one embodiment of the invention; and
[0006] FIG.2 illustrates a flowchart of a method of determining engine RPM in the vehicle.

Detailed description of the embodiments
[0007] FIG. 1 illustrates a control unit 12 to determine an engine 22 RPM in a vehicle 10 in accordance with one embodiment of the invention. The control unit 12 comprises a band pass filter 14 adapted to filter impact noise from a vibration frequency signal of at least one component of the vehicle 10, received from an accelerometer 18. The control unit 12 comprises a pulse width modulator 16 adapted to convert the filtered vibration frequency signal into a chain of pulses. The control unit 12 adapted to determine the engine 22 RPM based on the generated chain of pulses.
[0008] Further the construction of the control unit 12 in the vehicle 10 and the working of the control unit is explained as follows. The vehicle 10 is a conventional vehicle having an alternator without a W+ terminal. The band pass filter 14 as disclosed above filters out the structural noises and the impact noises from the detected vibrational frequency signal of at least one component in the vehicle 10. The band pass filter 14 is chosen from a group of filters like a low pass filter, a high-pass filter, a sacitzky-golay filter. At least one component in the vehicle 10 is a moving component chosen from a group of components like an injector, a cylinder head or the like. The vibration experienced by the moving component of the vehicle 10 during combustion is detected by the accelerometer 18 present in the vehicle 10. The accelerometer 18 detects the vibrational loads during each rotational operation and generates a peak signal. Using at least one signal synthesis, which is known to a person skilled in the art, the generated peak signal is used to generate chain of pulses. According to one embodiment of the invention, the accelerometer 18 is a MEMS accelerometer mounted at a suitable position to sense reciprocating vibration loads. The control unit 12 further comprises

a pulse counter 24 adapted to count the number of pulses generated from the pulse width modulator 16.
[0009] Fig 2 illustrating a flowchart for a method to determine an engine 22 RPM in a vehicle 10. The vehicle 10 comprises an alternator without a W+ type output terminal. In step S1, a vibration frequency signal is detected from at least one moving component of the vehicle 10 during combustion, by an accelerometer 18. In step S2, a band pass filter 14 filters impact noises from the detected vibration frequency signal. In step S3, the filtered vibration frequency signal is converted into a chain of pulses by a pulse width modulator 16 of the control unit 12. In step S4, the engine 22 RPM is determined based on the chain of pulses generated from the pulse width modulator 16.
[0010]The control unit 12 upon receiving the vibrational frequency signal of the moving component from the accelerometer 18 filters the impact noises and the structural noises. The filtered impact noise signal is fed to the pulse width modulator 16 of the control unit 12, wherein the vibration frequency signal is converted into chain of pulses. The control unit 12 determines the engine RPM based on the chain of pulses generated. The pulse counter 24 present in the control unit 12 counts the number of pulses generated from the pulse width modulator 16.
[0011] With the above method and the control unit, additional sensing unit to detect the engine RPM is avoided making it a cost effective solution. The engine speed unit is not vehicle dependent design and the scope can be extended on other applications for rotation speed detection (bearing life determination application). As the design is made to work as stand-alone, the unit itself can be

used independently for engine speed determination, or can be integrated with additional control system for closed loop operations .
[0012] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.

We Claim:
1. A method of determining an engine (22) RPM in a vehicle (10), said vehicle
(10) having an alternator without a W+ type output terminal , said method
comprising :
- detecting a vibration frequency signal from at least one moving component (20) of said vehicle (10) during combustion, by an accelerometer (18);
- filtering impact noises from said detected vibration frequency signal, by a band pass filter (14);
- converting said filtered vibration frequency signal into a chain of pulses by a pulse width modulator (16); and
- determining said engine (22) RPM based on said chain of pulses generated from said pulse width modulator (16).
2. A control unit (12) to determine an engine (22) RPM in a vehicle (10) ,said
control unit (12) comprising :
- a band pass filter (14) adapted to filter impact noise from a vibration frequency signal of at least one component (20), received from an accelerometer (18) ;
- a pulse width modulator (16) adapted to convert said filtered vibration frequency signal into a chain of pulses;
said control unit (12) adapted to determine said engine (22) RPM based on said generated chain of pulses.
3. The control unit (12) of claim 2, wherein said accelerometer (18)
positioned in proximity to at least one moving component (20) of said
vehicle (10), adapted to detect said vibration frequency signal of said at
least one moving component (20).

4. The control unit (12) as claimed in claim 2, wherein said at least one moving component (20) of said vehicle (10) is chosen from a group of components comprising an injector, a cylinder head or the like.
5. The control unit (12) as claimed in claim 2, wherein said band pass filter (14) is adapted to separate structural noise and to filter said impact noise from said vibration frequency signal.
6. The control unit (12) as claimed in claim 2, wherein said filter (14) is chosen from a group of filters like a high-pass filter, a low- pass filter, a sacitzky-golay filter or the like.
7. A control unit (12) in a conventional vehicle (10) having an alternator without a W+ type output terminal, said control unit (12) adapted to :

- detect a vibration frequency signal from at least one moving component (20) of said vehicle (10) during combustion, by an accelerometer (18) of said vehicle (10);
- filter impact noises from said detected vibration frequency signal, by a band pass filter (14) of said control unit (12);
- convert said filtered vibration frequency signal into a chain of pulses by a pulse width modulator (16) of said control unit (12);
- determine said engine (22) RPM based on said chain of pulses generated from said pulse width modulator (16).