Claims:1. A method for detecting tampering of a vehicle speed sensor, said method comprising the steps:
- Checking if engine of said vehicle is running at an idle speed
- Checking if gear shaft is in neutral position
- checking whether the vehicle speed is above zero when said engine is running at idle speed and gear shaft is in neutral position
- Setting an error condition if the vehicle speed is above zero when said engine is running at idle speed and gear shaft is in neutral position
2. A method according to claim 1 where said vehicle speed signal is a stream of pulses
3. A method according to claim 1 where said vehicle speed signal is any coded signal indicative of vehicle speed
4. A method for detecting tampering of a vehicle speed sensor, said method comprising the steps:
- detecting a state where engine is not running
- computing vehicle speed by reading vehicle speed signal 106
- setting an error condition if the vehicle speed is above zero when the engine is not running
5. An engine control unit 102 to detect tampering of a vehicle speed sensor, said engine control unit 102 comprising:
- an interface to receive vehicle speed sensor signal 106 and a neutral gear switch signal 110;
said ECU 102 configured to detect tampering of said vehicle speed sensor by analyzing vehicle speed sensor signal 106 and neutral gear switch signal 110

6. An engine control unit 102 according to claim 5 wherein said ECU 102 further comprises a microcontroller, a memory and a set of input and out ports
7. An engine control unit 102 according to claim 5 wherein said interface is an input port of a microcontroller
8. A system 100 to detect tampering of a vehicle speed sensor, said system comprising:
- a vehicle speed sensor generating vehicle speed signal 106 indicative of vehicle speed
- a neutral gear switch indicative of whether gear shaft is in neutral position
- an ECU 102 to receive vehicle speed sensor signal 106, neutral gear switch signal 110; said ECU 102 configured to detect tampering of said vehicle speed sensor by analyzing vehicle speed sensor signal and neutral gear switch signal 110
, Description:Field of the invention
[0001] This invention relates to the field of detecting tampering of sensors used in vehicles, especially detecting the tampering of vehicle speed sensor.

Background of the invention
[0002] Normally the vehicles are fitted with speed governors to control the vehicle speed so that the maximum allowable vehicle speed does not exceed a pre-defined speed limit. The speed limit may vary depending upon the vehicle, depending upon the area where the vehicle is driven etc. These speed limits are set to ensure safety of the passengers and the vehicle. Normally the speed governors monitor the engine speed and the vehicle speed to activate or de-activate the peed limiting function.
[0003] In some cases the vehicle users may manipulate these signals in such a way that the speed governors do not activate the speed limiting function even when the vehicle is driven at a speed above the set speed limit. The manipulation is done by providing manipulated signals to the speed governors instead of providing the actual signals. The manipulated signal may always indicate a lower vehicle speed compared to the actual speed of the vehicle.
[0004] The US patent 58960683 discloses a method to detect tampering with a vehicle's speed sensor signal. The method includes determining a current gear ratio, comparing current gear ratio with a reference gear ratio. If the difference between current gear ratio and the reference gear ratio is above a pre-defined threshold, then an error condition is set.

Brief description of the accompanying drawing
[0005] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:
[0006] FIG. 1 illustrates a system for detecting vehicle speed sensor tampering

Detailed description of the embodiments
[0007] FIG. 1 illustrates a system 100 for detecting tampering of a vehicle speed sensor signal. The system 100 comprises an engine control unit (ECU) 102 controlling an engine 104. The various sensors are not shown in the figure. The ECU 102 receives vehicle speed signal 106, engine speed signal 108, neutral gear switch signal 110. The ECU 102 also receives various other signals which are not shown. The ECU 102 generates control signals 112 for the engine 104. The control signals 112 may be used to control injectors, spark plugs and other components which are not shown and which are necessary for fuel injection.
[0008] The ECU may receive other various signals 107 to process and then control the engine.
[0009] The ECU 102 typically comprises a microcontroller, a memory block, a set of input and out ports etc. These are typical components for any engine control unit hence are not shown. The input ports are used as interface to connect various signals which the ECU needs to monitor, for example, vehicle speed signal, engine speed signal, neutral gear switch signal etc. The neutral gear switch is an electro mechanical switch coupled to the gear shaft. The neutral gear switch generates the neutral gear switch signal 110 depending upon whether the gear shaft is in neutral position or not. When the gear shaft is in neutral position the neutral gear switch signal 110 is high. When the gear shaft is in any other position other than neutral position, the neutral gear switch signal 110 is low.
[0010] Typically an engine speed sensor, which is not shown in the fig, is coupled to a crankshaft of the engine. The engine speed sensor is also referred as crankshaft position sensor. The engine speed sensor generates a stream of pulses indicative of engine speed. These stream of pulses are provided to ECU as engine speed signal 108.
[0011] Typically the vehicle speed signal 106 comes from vehicle sped sensors which are not shown. Vehicle speed signal 106 is also a stream of pulses.
[0012] By counting the number of pulses in the engine speed signal and the vehicle speed signal per unit time, the ECU computes the engine speed and vehicle speed respectively. The engine speed and vehicle speed may be represented as Revolutions Per Minute (RPM) and KMPH respectively.
[0013] The ECU is configured to detect tampering of vehicle speed signal by monitoring the various signals. The ECU is configured through a set of instructions stored in the memory block, to read and analyse the signals. These instructions are typical instructions used for any microcontroller and hence not explained.
[0014] According to one embodiment of the invention, the ECU detects the tampering of the vehicle speed sensor using the method comprising the steps of checking if engine of said vehicle is running at an idle speed; checking if gear shaft is in neutral position; checking whether the vehicle speed is above zero when said engine is running at idle speed and gear shaft is in neutral position; setting an error condition if the vehicle speed is above zero when said engine is running at idle speed and gear shaft is in neutral position;
[0015] In another embodiment of the invention the ECU detects the tampering of the vehicle speed sensor using the method comprising the steps of detecting a state where engine is not running; reading vehicle speed; setting an error condition if the vehicle speed is above zero when the engine is not running.
[0016] The vehicle speed sensor 106 signal may be tampered by disconnecting the original vehicle speed sensor signal and providing a signal from a signal generator to the ECU. Signal generators may be simple resistance and capacitance based circuits or based on any integrated circuits. The frequency and amplitude of these circuits can be configured to match the functioning of the ECU.
[0017] The signal generator may be connected directly to the vehicle battery or connected through the cranking circuit. When the signal generator is directly connected to the battery, the signal generator is always on and it keeps always generating the signal irrespective of whether engine is running or not.
[0018] In another case the signal generator may be connected through a cranking circuit. In this case, the signal generator is activated when the cranking of the engine happens. The signal generator generates the signal as long as the engine is running. Once the engine stops from running, the signal generator is de-activated and it stops generating the vehicle speed signal 106.
[0019] Now the detection of the tampering of the vehicle speed signal is explained in detail.
[0020] In one embodiment, assume that the user of the vehicle disconnects the original vehicle speed sensor signal and connects the signal generator output at the input 106 of the ECU. In this case assume that signal generator is connected directly to the battery and the output of the signal generator is provided to the ECU at 106.
[0021] When the ignition key is inserted and turned to the ignition-on position, the ECU becomes activated. Still the cranking of the engine has not happened, hence engine is not running. The ECU gets initialized and starts checking for the vehicle speed signal 106. It detects the pulses on the vehicle speed signal 106. As the cranking has not happened the engine speed signal 108 will be zero. The ECU 102 detects that the engine is not yet running by monitoring engine speed signal 108. When the engine is not running, ideally the vehicle speed should be zero. But in this case the ECU 102 detects that the engine is not running and the vehicle speed signal 106 indicates that vehicle speed is above zero. This is treated as tampering of vehicle speed sensor and an error condition is set. Also if required, a timer is incremented to keep count of error conditions. After a certain count of errors, an indication to user or service personnel is generated. This indication may be an LED or a beep or any other audio visual indication.
[0022] In another embodiment, assume that the user of the vehicle disconnects the original vehicle speed sensor signal and connects the signal generator output at the input 106 of the ECU. In this case assume that the signal generator is connected to the battery through a cranking circuit. The output of the signal generator is connected to the ECU at 106. In this case the signal generator is activated only when the cranking of the engine happens.
[0023] The ECU monitors the engine speed signal 108 to compute the engine speed. From the computed engine speed, ECU checks whether the engine is running at idle speed. Typically the idle speed is the speed at which engine runs when the gear shaft is in neutral condition and vehicle is not moving. As the ECU keeps monitoring the vehicle speed signal, it detects that the vehicle speed signal has pulses coming after the cranking takes place and as long as engine is running. The ECU reads the vehicle speed signal 106 and computes the vehicle speed. The ECU 102 reads the neutral gear switch signal 110 to determine whether the gear shaft is in neutral position.
[0024] If the engine is running at idle speed and if the gear shaft is in neutral position, ideally the vehicle speed should be zero.
[0025] Because the vehicle speed sensor is tampered with and signal generator is connected to the ECU 102, the signal generator provides some fixed frequency signal to the ECU 102 even when engine is in idle speed and the gear shaft is in neutral position.
[0026] When the ECU detects that the engine is running at idle speed and the gear shaft is in neutral position and the vehicle speed signal is indicative of vehicle speed above a zero, ECU 102 sets an error condition. Also if required a timer is incremented to keep count of error conditions. After a certain count of errors, an indication to user or service personnel is generated. This indication may be an LED or a beep or any other audio visual indication.