FORM 2
The Patents Act 1970
(39 of 1970)
AND
THE PATENTS RULES, 2005
COMPLETE SPECIFICATION (See Section 10; Rule 13)
TITLE OF THE INVENTION
A DIAGNOSTIC SYSTEM AND METHOD FOR DIAGNOSING A SPEED SENSOR OF A VEHICLE
APPILICANT(S)
TATA MOTORS LIMITED
an Indian company
having its registered office at Bombay house,
24 Homi Mody Street, Hutatma Chowk,
Mumbai 400 001,
Maharashtra, INDIA.
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed.

A DIAGNOSTIC SYSTEM AND METHOD FOR DIAGNOSING A SPEED
SENSOR OF A VEHICLE
FIELD OF THE INVENTION
[0001] The present invention relates to a diagnostic system, and more specifically related to a diagnostic system and method for diagnosing a speed sensor of a vehicle.
BACKGROUND OF THE INVENTION
[0002] Vehicles such as cars, busses, trucks, etc. include an engine, an engine control unit, a transmission, a gearbox, a speed sensor, etc. The vehicle speed sensor is used for determining the rotating speed of the vehicle based on the gearbox. The gearbox transmits a torque of the engine for rotating the wheels of the vehicle. A vehicle speed sensor (VSS) signal is obtained by the speed sensor for controlling the torque of the engine. It is important to detect faults with the speed sensor. Diagnostic trouble code P0502 indicating “Vehicle speed sensor open circuit fault” is generated when the engine speed increased without corresponding change in vehicle speed. Misdetection of vehicle speed sensor fault (DTC P0502) can cause during below conditions:
[0003] First, if we accelerate the vehicle in stationary condition for more than a calibrated time limit. This is the main type of misdetection in the vehicle having mechanical throttle body. In this condition, the engine speed will be detected but not vehicle speed output (since vehicle is stationary). The engine control unit can't identify the vehicle is stationary or the vehicle is running with vehicle speed sensor fault (since no VSS signal is detected), and hence triggers the DTC P0502.
[0004] Second, during vehicle takeoff in first gear, especially in gradient. Even though the VSS relates engine relative torque and vehicle speed sensor signal,

misdetection can still happen in this case. Since in the gradient, greater torque is required to pull the vehicle. Usually the engine speed is raised in half clutch. This will create a condition of having engine speed but no vehicle speed output.
[0005] Further, engine control unit cannot distinguish between vehicle stationary condition (also to be referred as standstill condition) and open load condition. Both will lead to receiving no pules via Pulse-width modulation (PWM). Typically, drivers have a habit of accelerating the engine in vehicle stationary condition. If the vehicle speed sensor open circuit event trigger, it will impair the vehicle performance for wrong reasons. Also, if the gear is shifted and acceleration is provided inappropriately when the vehicle is not in motion, the performance of the vehicle is influenced. Therefore, the performance of the vehicle speed sensor directly affects the determination of the operating state of the vehicle.
[0006] There remains a need of a novel diagnostic approach by introducing a system for diagnosing a speed sensor of a vehicle. Detecting genuine condition of fault triggering is essential for overall vehicle performance.
OBJECT OF THE INVENTION
[0007] The principal object of the embodiments herein is to provide diagnostic system and method for diagnosing a speed sensor of a vehicle to avoid the misdetection of vehicle speed sensor fault. Based on inputs from clutch pedal, relative torque, engine speed and manifold air pressure signal during gear shifting, the vehicle speed sensor diagnosis is conducted only when vehicle is in motion.
[0008] Yet another object is to provide a new diagnostic system for a vehicle speed sensor open circuit is provided to avoid the misdetection. This will avoid misdetection of VSS signal and the vehicle can be driven normally.

BRIEF SUMMARY OF THE INVENTION
[0009] In one aspect the object is satisfied by providing a diagnostic system for diagnosing a speed sensor of a vehicle. The diagnostic system includes an engine control unit connected to the speed sensor of the vehicle, and vehicle speed sensor open circuit controller, connected to the engine control unit and the speed sensor of the vehicle. The engine control unit receive a gearshift command, and determine a speed of an engine of the vehicle, a torque of the vehicle, a speed of the vehicle, a status of a clutch pedal of the vehicle, a status of an acceleration pedal of the vehicle, and a manifold air pressure signal in response to receiving the gearshift command. The vehicle speed sensor open circuit controller is configured to receive a vehicle speed sensor (VSS) signal indicative of a speed of the vehicle from the speed sensor, determine whether the VSS signal is valid based on the speed of an engine of the vehicle, the torque of the vehicle, the speed of the vehicle, the status of the clutch pedal of the vehicle, the status of the acceleration pedal of the vehicle, and the manifold air pressure signal. Further, the vehicle speed sensor open circuit controller displays an error notification indicating the malfunction of the speed sensor of the vehicle in response to determining that the VSS signal is invalid.
[0010] In an embodiment, determine whether the VSS signal is valid includes: detect whether the engine speed meets an engine speed threshold, the torque of the vehicle meets a torque threshold, the speed of the vehicle is zero, the status of clutch pedal is pressed, the status of the acceleration pedal is off, and the manifold air pressure signal meets a manifold air pressure signal threshold; determine that the VSS signal is invalid in response to detecting that the engine speed meets the engine speed threshold, the torque of the vehicle meets the torque threshold, the speed of the vehicle is zero, the status of clutch pedal is pressed, the status of the acceleration pedal is off, and the manifold air pressure signal meets the manifold air pressure signal threshold; and determine that the VSS signal is valid in

response to detecting that the engine speed does not meet the engine speed threshold, the torque of the vehicle does not meet the torque threshold, the speed of the vehicle is not zero, the status of clutch pedal is not pressed, the status of the acceleration pedal is on, and the manifold air pressure signal does not meet the manifold air pressure signal threshold.
[0011] In an embodiment, the error notification is error code P0502 indicating low input of the speed sensor of the vehicle.
[0012] In one aspect the object is satisfied by providing a method for diagnosing a speed sensor of a vehicle by a diagnostic system. The method includes receiving a gearshift command and determining a speed of an engine of the vehicle, a torque of the vehicle, a speed of the vehicle, a status of a clutch pedal of the vehicle, a status of an acceleration pedal of the vehicle, and a manifold air pressure signal in response to receiving the gearshift command. Further, the method includes receiving a vehicle speed sensor (VSS) signal indicative of a speed of the vehicle from the speed sensor and determining whether the VSS signal is valid based on the speed of an engine of the vehicle, the torque of the vehicle, the speed of the vehicle, the status of the clutch pedal of the vehicle, the status of the acceleration pedal of the vehicle, and the manifold air pressure signal. Further, the method includes displaying an error notification indicating the malfunction of the speed sensor of the vehicle in response to determining that the VSS signal is invalid.
[0013] Furthermore, the method includes detecting whether the engine speed meets an engine speed threshold, the torque of the vehicle meets a torque threshold, the speed of the vehicle is zero, the status of clutch pedal is pressed, the status of the acceleration pedal is off, and the manifold air pressure signal meets a manifold air pressure signal threshold. The method includes determining that the VSS signal is invalid in response to detecting that the engine speed meets the engine speed threshold, the torque of the vehicle meets the torque threshold, the speed of the vehicle is zero, the status of clutch pedal is pressed, the status of the

acceleration pedal is off, and the manifold air pressure signal meets the manifold air pressure signal threshold; and determining that the VSS signal is valid in response to detecting that the engine speed does not meet the engine speed threshold, the torque of the vehicle does not meet the torque threshold, the speed of the vehicle is not zero, the status of clutch pedal is not pressed, the status of the acceleration pedal is on, and the manifold air pressure signal does not meet the manifold air pressure signal threshold.
[0014] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The proposed diagnostic system and method is illustrated in the
accompanying drawings, throughout which like reference letters indicate
corresponding parts in the various figures. The embodiments herein will be better
understood from the following description with reference to the drawings, in
which:
[0016] FIG. 1 illustrates a diagnostic system for diagnosing a speed sensor of a
vehicle, according to embodiments as disclosed herein;
[0017] FIG. 2 illustrates a method for diagnosing a speed sensor of a vehicle,
according to embodiments as disclosed herein;
[0018] FIG. 3 illustrates a method for validating a VSS single, according to
embodiments as disclosed herein; and

[0019] FIG. 4 illustrates an example graph of manifold pressure signal crossing manifold pressure signal threshold, according to embodiments as disclosed herein.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. The term “or” as used herein, refers to a non-exclusive or, unless otherwise indicated. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those skilled in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[0021] Referring now to the drawings, and more particularly to FIGS. 1 through 3, where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments.
[0022] FIG. 1 illustrates a diagnostic system (1) for diagnosing a speed sensor (6) of a vehicle. The diagnostic system (1) includes an engine control unit (2) and a vehicle speed open circuit controller (3) connected to the engine control unit (2).
[0023] The engine control unit (2) is connected to an engine (4) of the vehicle, a pressure sensor (5) of the vehicle, the speed sensor (6) of the vehicle, a clutch pedal (7) of the vehicle, an acceleration pedal (8) of the vehicle.

[0024] The engine control unit (2) receives a gearshift command from the vehicle. Upon receiving the gearshift command, the engine control unit (2) determines a speed of the engine (4) of the vehicle, a torque of the vehicle, a speed of the vehicle, a status of the clutch pedal (7) of the vehicle, a status of the acceleration pedal (8) of the vehicle, and a manifold air pressure signal.
[0025] In an embodiment, the engine control unit (2) determines the speed of the engine (4) based on a tire size, an axle ratio, and a final transmission gear ratio. The speed of the engine (4) is defined as the number of times a crankshaft of the engine (4) rotates within a span of one minute.
[0026] In an embodiment, the engine control unit (2) determines the torque of the vehicle based on horsepower of the engine (4). The torque indicates rotating force produced by the crankshaft of the engine (4). If the engine (4) generates more torque, the greater its ability to provide vehicle performance.
[0027] In an embodiment, the engine control unit (2) determines speed of the vehicle based on the distance traveled in a given space of time.
[0028] In an embodiment, the engine control unit (2) determines the status of the clutch pedal (7) of the vehicle based on a single received from a sensor placed on or in proximity to the clutch pedal (7).
[0029] In an embodiment, the engine control unit (2) determines the status of the acceleration pedal (8) of the vehicle based on a single received from a sensor placed on or in proximity to the acceleration pedal (8).
[0030] In an embodiment, the engine control unit (2) determines the manifold air pressure signal using the presser sensor (5) such as manifold pressure signal sensor embedded in the engine control unit (2) of the vehicle.

[0031] The vehicle speed open circuit controller (3) is connected to the engine control unit (2) and the speed sensor (6) of the vehicle. The vehicle speed open vehicle circuit receive a vehicle speed sensor (VSS) signal indicative of a speed of the vehicle from the speed sensor (6) and determine whether the VSS signal is valid based on the speed of an engine (4) of the vehicle, the torque of the vehicle, the speed of the vehicle, the status of the clutch pedal (7) of the vehicle, the status of the acceleration pedal (8) of the vehicle, and the manifold air pressure signal.
[0032] In an embodiment, in order to determine whether the VSS signal is valid or invalid, the vehicle speed open circuit controller (3) detects whether the speed of the engine (4) meets an engine speed threshold, the torque of the vehicle meets a torque threshold, the speed of the vehicle is zero, the status of clutch pedal (7) is pressed, the status of the acceleration pedal (8) is off, and the manifold air pressure signal meets a manifold air pressure signal threshold. When the torque of the vehicle meets the torque threshold, the speed of the vehicle is zero, the status of clutch pedal (7) is pressed, the status of the acceleration pedal (8) is off, and the manifold air pressure signal meets the manifold air pressure signal threshold, the vehicle speed open circuit controller (3) determines that the VSS signal is invalid. When the speed of the engine (4) does not meet the engine speed threshold, the torque of the vehicle does not meet the torque threshold, the speed of the vehicle is not zero, the status of clutch pedal (7) is not pressed, the status of the acceleration pedal (8) is on, and the manifold air pressure signal does not meet the manifold air pressure signal threshold, the vehicle speed open circuit controller (3) determines the VSS signal is valid.
[0033] Upon determining that the VSS signal is invalid, the vehicle speed open circuit controller (3) display an error notification indicating the malfunction of the speed sensor (6) of the vehicle. In an embodiment, the error notification is error code P0502 indicating low input of the speed sensor (6) of the vehicle.

[0034] Hence the proposed diagnostic system is provided to avoid the misdetection of faults. Based on inputs from the clutch and accretion pedals, relative torque, engine speed and manifold air pressure signal during gear shifting, the vehicle speed sensor diagnosis is conducted only when vehicle is in motion. This will avoid misdetection of the VSS signal and the vehicle can be driven normally.
[0035] FIG. 2 illustrates a method for diagnosing the speed sensor (6) of a vehicle, according to embodiments as disclosed herein. At S1, the method includes receiving, by the diagnostic system (1), a gearshift command. At S2, the method includes determining a speed of an engine (4) of the vehicle, a torque of the vehicle, a speed of the vehicle, a status of a clutch pedal (7) of the vehicle, a status of an acceleration pedal (8) of the vehicle, and a manifold air pressure signal in response to receiving the gearshift command. At S3, the method includes receiving, by the diagnostic system (1), a vehicle speed sensor (VSS) signal indicative of a speed of the vehicle from the speed sensor (6). At S4, the method includes determining, by the diagnostic system (1), whether the VSS signal is valid based on the speed of an engine (4) of the vehicle, the torque of the vehicle, the speed of the vehicle, the status of the clutch pedal (7) of the vehicle, the status of the acceleration pedal (8) of the vehicle, and the manifold air pressure signal. In response to determining that the VSS signal is invalid, at S5, the method includes displaying, by the diagnostic system (1), an error notification indicating the malfunction of the speed sensor (6) of the vehicle.
[0036] FIG. 3 illustrates a method for validating the VSS single, according to embodiments as disclosed herein. At S41, the method includes receiving the VSS signal indicative of a speed of the vehicle from the speed sensor (6). At S42, the method includes detecting whether the speed of the engine (4) meets an engine speed threshold.

[0037] In response to detecting that the speed of the engine (4) meets the engine speed threshold, at S43, the method includes detecting whether the torque of the vehicle meets a torque threshold.
[0038] In response to detecting that the torque of the vehicle meets the torque threshold, at S44, the method includes detecting whether the speed of the vehicle is zero.
[0039] In response to detecting that the speed of the vehicle is zero, at S45, the method includes detecting whether the status of clutch pedal (7) is pressed.
[0040] In response to detecting that the status of clutch pedal (7) is pressed, at S46, the method includes detecting whether the status of the acceleration pedal (8) is off.
[0041] In response to detecting that the status of the acceleration pedal (8) is off, at S47, the method includes detecting whether the manifold air pressure signal meets a manifold air pressure signal threshold.
[0042] In response to detecting that the manifold air pressure signal meets the manifold air pressure signal threshold, at S48, the method includes determining that the VSS signal is invalid and display an error notification comprising error code.
[0043] In an embodiment, the VSS signal is considered as valid when the speed of the engine (4) does not meet the engine speed threshold, the torque of the vehicle does not meet the torque threshold, the speed of the vehicle is not zero, the status of clutch pedal (7) is not pressed, the status of the acceleration pedal (8) is on, and the manifold air pressure signal does not meet the manifold air pressure signal threshold.

[0044] FIG. 4 illustrates an example graph manifold pressure signal crossing manifold pressure signal, according to embodiments as disclosed herein. During gear shifting the intake manifold pressure signal (psrg_w) will goes below a manifold pressure signal threshold value as shown at (100 in the FIG. 4. This is a very unique and will only happen when the vehicle is in motion and the gear is shifting and hence can be used to ensure that the proposed diagnosis system (1) diagnose the vehicle speed only when the vehicle is in moving condition so as to avoid misdetection of the VSS signal and drive the vehicle normally.
[0045] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

[0046] List to reference numerals:

Sr. No. Description
1 diagnostic system
2 engine control unit
3 vehicle speed open circuit controller
4 Engine
5 manifold Air pressure sensor
6 speed sensor
7 clutch pedal
8 acceleration pedal
9 manifold pressure signal threshold

WE CLAIM:
1. A diagnostic system (1) for diagnosing a speed sensor (6) of a vehicle, wherein
the diagnostic system (1) comprises:
an engine control unit (2), connected to the speed sensor (6) of the vehicle, is continued to
receive a gearshift command, and
determine a speed of an engine (4) of the vehicle, a torque of the vehicle, a speed of the vehicle, a status of a clutch pedal (7) of the vehicle, a status of an acceleration pedal (8) of the vehicle, and a manifold air pressure signal in response to receiving the gearshift command;
a vehicle speed open circuit controller (3), connected to the engine control unit (2) and the speed sensor (6) of the vehicle, configured to:
receive a vehicle speed sensor (VSS) signal indicative of a speed of the vehicle from the speed sensor (6);
determine whether the VSS signal is valid based on the speed of an engine (4) of the vehicle, the torque of the vehicle, the speed of the vehicle, the status of the clutch pedal (7) of the vehicle, the status of the acceleration pedal (8) of the vehicle, and the manifold air pressure signal; and
display an error notification indicating the malfunction of the speed sensor (6) of the vehicle in response to determining that the VSS signal is invalid.
2. The diagnostic system (1) as claimed in claim 1, wherein determine whether the
VSS signal is valid based on the speed of an engine (4) of the vehicle, the torque
of the vehicle, the speed of the vehicle, the status of the clutch pedal (7) of the
vehicle, the status of the acceleration pedal (8) of the vehicle, and the manifold
air pressure signal comprises:
detect whether the speed of the engine (4) meets an engine speed threshold, the torque of the vehicle meets a torque threshold, the speed of the vehicle is

zero, the status of clutch pedal (7) is pressed, the status of the acceleration pedal (8) is off, and the manifold air pressure signal meets a manifold air pressure signal threshold;
determine that the VSS signal is invalid in response to detecting that the speed of the engine (4) meets the engine speed threshold, the torque of the vehicle meets the torque threshold, the speed of the vehicle is zero, the status of clutch pedal (7) is pressed, the status of the acceleration pedal (8) is off, and the manifold air pressure signal meets the manifold air pressure signal threshold; and
determine that the VSS signal is valid in response to detecting that the speed of the engine (4) does not meet the engine speed threshold, the torque of the vehicle does not meet the torque threshold, the speed of the vehicle is not zero, the status of clutch pedal (7) is not pressed, the status of the acceleration pedal (8) is on, and the manifold air pressure signal does not meet the manifold air pressure signal threshold.
3. The diagnostic system (1) as claimed in claim 1, wherein the error notification is error code P0502 indicating low input of the speed sensor (6) of the vehicle.
4. A method for diagnosing a speed sensor (6) of a vehicle by a diagnostic system (1), wherein the method comprises:
receiving, by the diagnostic system (1), a gearshift command;
determining, by the diagnostic system (1), a speed of an engine (4) of the vehicle, a torque of the vehicle, a speed of the vehicle, a status of a clutch pedal (7) of the vehicle, a status of an acceleration pedal (8) of the vehicle, and a manifold air pressure signal in response to receiving the gearshift command; receiving, by the diagnostic system (1), a vehicle speed sensor (VSS) signal indicative of a speed of the vehicle from the speed sensor (6);
determining, by the diagnostic system (1), whether the VSS signal is valid based on the speed of an engine (4) of the vehicle, the torque of the vehicle, the speed of the vehicle, the status of the clutch pedal (7) of the vehicle, the status

of the acceleration pedal (8) of the vehicle, and the manifold air pressure signal; and
displaying, by the diagnostic system (1), an error notification indicating the malfunction of the speed sensor (6) of the vehicle in response to determining that the VSS signal is invalid.
5. The method as claimed in claim 4, wherein determining whether the VSS signal is valid based on the speed of an engine (4) of the vehicle, the torque of the vehicle, the speed of the vehicle, the status of the clutch pedal (7) of the vehicle, the status of the acceleration pedal (8) of the vehicle, and the manifold air pressure signal comprises:
detecting whether the speed of the engine (4) meets an engine speed threshold, the torque of the vehicle meets a torque threshold, the speed of the vehicle is zero, the status of clutch pedal (7) is pressed, the status of the acceleration pedal (8) is off, and the manifold air pressure signal meets a manifold air pressure signal threshold;
determining that the VSS signal is invalid in response to detecting that the speed of the engine (4) meets the engine speed threshold, the torque of the vehicle meets the torque threshold, the speed of the vehicle is zero, the status of clutch pedal (7) is pressed, the status of the acceleration pedal (8) is off, and the manifold air pressure signal meets the manifold air pressure signal threshold; and
determining that the VSS signal is valid in response to detecting that the speed of the engine (4) does not meet the engine speed threshold, the torque of the vehicle does not meet the torque threshold, the speed of the vehicle is not zero, the status of clutch pedal (7) is not pressed, the status of the acceleration pedal (8) is on, and the manifold air pressure signal does not meet the manifold air pressure signal threshold.

6. The method as claimed in claim 4, wherein the error notification is error code P0502 indicating low input of the speed sensor (6) of the vehicle.