CLIAMS:We claim:
1. A device (100) to limit a speed of a vehicle when a vehicle speed sensor (118) is not working ,said device (100) comprising:
a clutch state sensor (101) adapted to check a state of a clutch;
a first calculating means (104) calculates a rate of change of an accelerator pedal (102) position for a predefined time and an accelerator pedal press percentage, if said state of said clutch is not in a pressed state;
a first comparing means (106) adapted to compare said calculated rate of change of said accelerator pedal (102) with a first threshold value and to compare said accelerator pedal percentage with a second threshold value;
- an engine speed sensor (112) adapted to measure a speed of an engine;
- a second calculating means (114) adapted to calculate a vehicle speed from an engine speed and a gear specific ratio when said calculated rate of change of said accelerator pedal (102) is less than said first threshold value or said accelerator pedal percentage is less than said second threshold value ;
-a gear position sensor (110) adapted to determine a gear position of a gear (108);
-an electronic control unit (121) adapted to determine a threshold speed for said gear position;
-a second comparing means (120) present in an electronic control unit (121) compares said calculated vehicle speed with said threshold speed ;
said electronic control unit (121) limits said speed of said vehicle when said calculated vehicle speed is more than said threshold vehicle speed.
2. A device (100) to limit a speed of a vehicle when a vehicle speed sensor(118) is working, said device comprising:
- a clutch state sensor (101) adapted to check a state of a clutch;
a first calculating means (104) calculates a rate of change of an accelerator pedal (102) position for a predefined time and an accelerator pedal press percentage, if said state of said clutch is not in a pressed state;
a first comparing means (106) adapted to compare said calculated rate of change of said accelerator pedal (102) with a first threshold value and to compare said accelerator pedal percentage with a second threshold value;
- an engine speed sensor (112) adapted to measure a speed of an engine;

a second calculating means (114) adapted to calculate a vehicle speed from an engine speed and a gear specific ratio when said calculated rate of change of said accelerator pedal (102) is less than said first threshold value or said accelerator pedal percentage is less than said second threshold value;
-said vehicle speed sensor (118) measures an actual vehicle speed;
-a second comparing means (120) compares said calculated vehicle speed with said actual vehicle speed;
-an electronic control unit (121) limits said speed of said vehicle when said calculated vehicle speed is more than said actual vehicle speed.
3. The device (100) according to claim (1), wherein said device (100) comprises a timer (103) adapted to set said predefined time.
4. The device (100) according to claim (1), wherein said predefiend speed value is set by a reference means (115).
5. The device (100) according to claim (1), wherein a determining means (116) activates said reference means (115) to set said threshold speed for said gear position, when said vehicle speed sensor (118) is not working.
6. A method for limiting a speed of a vehicle, said method comprising :
-checking a state of a clutch;
- calculating a rate of change of an accelerator pedal (102) for a predefined time and an accelerator pedal percentage, if said state of said clutch is not in a pressed state;
-comparing said rate of change of said accelerator pedal (102) with a first threshold value and said accelerator pedal percentage with a second threshold value;
-measuring a speed of an engine;
-calculating said speed of said vehicle from an engine speed and a gear specific ratio if said rate of change of said accelerator pedal (102) is less than said first threshold value or if said accelerator pedal percentage is less than second threshold value ;
-determining a gear position;
-determining a threshold speed for said gear position;
-determining the working of a vehicle speed sensor (118);
If said vehicle speed sensor (118) is not working,
-comparing said speed of said vehicle with said threshold speed;
-limiting said speed of said vehicle if said speed of said vehicle is more than said threshold speed;
if said vehicle speed sensor (118) is working,
-determining an actual vehicle speed;
-comparing said calculated speed of said vehicle with said actual vehicle speed;
-limiting said speed of said vehicle if said calculated speed of said vehicle is more than said vehicle speed. ,TagSPECI:Field of the invention
[001] This invention relates to a device to limit a speed of a vehicle and a method of operating the device.
Background of the invention
[002] A vehicle speed limiting devices enables the vehicle to run within a range of a preset vehicle speed limit. The vehicle speed limiting devices have been developed to avoid traveling of vehicles at speeds exceeding the upper speed limit set by law. Such a vehicle speed limiting device limits the power output of an engine in accordance with the relationship between the upper speed limit and the travel speed of the vehicle, such that travel speed does not exceed the set upper speed limit. In the vehicle industry there is widespread interest in limiting vehicle speed to improve fuel efficiency. In particular, trucking fleets can reduce costs and encourage safe vehicle operation by limiting the maximum allowable speed of a vehicle. Vehicle operators generally oppose and resist use of vehicle speed limiting systems because they tend to increase the time required to transport shipments that may marginally reduce their efficiency and productivity. Some operators have been known to attempt to frustrate the vehicle speed limiting devices by damaging, disconnecting or modifying such devices. Governors were originally proposed for speeds limiting that were integrated with vehicle fuel systems to limit the quantity of fuel supplied to a vehicle engine. The governors can be easily removed or re-calibrate rendering them ineffective.
[003] Many techniques are known in the state of art limiting a speed of a vehicle.
[004] A European patent application 624488 discloses a device includes at least one sensor to detect the speed of the motor vehicle, an actuating device to modify the power produced by the engine of the motor vehicle in order to limit the speed and a logic unit to drive the actuating device in response to the comparison between the value of the speed detected by the at least one sensor and a maximum value of the speed recorded in a memory belonging to the logic unit

Brief description of the accompanying drawings
[005] An exemplifying embodiment of the invention is disclosed in detail in the description and illustrated in the accompanying drawings:
[006] Figure 1 illustrates a block diagram of a device when a vehicle speed sensor is not working according to one embodiment of the invention;
[007] Figure 2 illustrates a block diagram of a device according when a vehicle speed sensor is working to one embodiment of the invention; and
[008] Figure 3 illustrates a flow chart of a method of working of the device according to one embodiment of the invention.
Detailed description of the invention:
[009] Figure 1 illustrates a block diagram of a device 100 to limit a speed of an vehicle when a vehicle speed sensor is not working according to one embodiment of the invention. The device 100 comprises a clutch state sensor 101 adapted to check a state of a clutch. The device also comprises a first calculating means 104 adapted to calculate a rate of change of an accelerator pedal 102 position for a predefined time and an accelerator pedal press percentage, if the state of the clutch is not in a pressed state. The device 100 comprises a first comparing means 106 adapted to compare the calculated rate of change of the accelerator pedal 102 with a first threshold value and to compare the accelerator pedal press percentage with a second threshold value. The device 100 comprises an engine speed sensor 112 adapted to measure a speed of an engine. The device 100 comprises a second calculating means 114 adapted to calculate a vehicle speed from a the engine speed and a gear specific ratio, if the rate of change of said accelerator pedal 102 is less than the first threshold value or if the accelerator pedal press percentage is less than the second threshold value. The device 100 comprises a gear position sensor 110 adapted to determine a gear position of a gear 108. The device 100 also comprises an electronic control unit 121 adapted to determine a threshold speed for the gear position. The device 100 also comprises a second comparing means 120 present in the electronic control unit 121 compares the calculated vehicle speed with the threshold speed. The electronic control unit 121 limits the speed of the vehicle when the calculated vehicle speed is more than the threshold speed.
[0010] Figure 2 illustrates a block diagram of a device 100 to limit a speed of a vehicle when a vehicle speed sensor 118 is working, according to another embodiment of the invention. The device 100 comprises a clutch state sensor 101 adapted to check a state of a clutch. The device also comprises a first calculating means 104 adapted to calculate a rate of change of an accelerator pedal 102 position for a predefined time and an accelerator pedal press percentage, if the state of the clutch is not in a pressed state. The device 100 comprises a first comparing means 106 adapted to compare the calculated rate of change of the accelerator pedal 102 with a first threshold value and to compare the accelerator pedal percentage with a second threshold value. The device 100 comprises an engine speed sensor 112 adapted to measure a speed of an engine. The device 100 comprises a second calculating means 114 adapted to calculate a vehicle speed from a speed of the engine and a gear specific ratio, if the rate of change of said accelerator pedal 102 is less than the first threshold value or if the accelerator pedal percentage is less than the second threshold value. The device 100 comprises a gear position sensor adapted to determine a gear position of a gear 108. The device 100 also comprises an electronic control unit 121 adapted to determine a threshold speed for the gear position. The vehicle speed sensor 118 measures an actual vehicle speed. The device 100 comprises a second comparing means 120 compares the calculated vehicle speed with the actual vehicle speed. The electronic control unit 121 to limits the speed of the vehicle when the calculated vehicle speed is more than the actual vehicle speed.
[0011] The clutch state sensor 101 checks the state of the clutch. The clutch state sensor 101 provides a signal to the first calculating means 104 if the clutch is not in the pressed state. The first calculating means 104 is programmed in such a way that, the first calculating means 104 will not receive any signals from the accelerator pedal 102, if the clutch is in the pressed state. The device 100 also comprises a timer 103 adapted to set the predefined time. The first calculating means 104 calculates a rate of change of accelerator pedal 102 position for a predefined time. For instance, the first calculating means 104 calculates a rate of change of accelerator pedal 102 as 10% in 0.2sec.The first calculating means 104 calculates an accelerator pedal press percentage which is a variation in a position of the accelerator pedal 102 after the predefined time. The rate of change of accelerator pedal 102 and accelerator pedal percentage are given as inputs to first comparator means 106 and the output of the first comparator means 106 is given to the electronic control unit 121. The gear position sensor 110 provides the gear position to the electronic control unit 121. The engine speed sensor 112 provides input to the second calculating means 114 to calculate the vehicle speed from the engine speed and the gear specific ratio, if the rate of change of said accelerator pedal 102 is less than the first threshold value and if the accelerator pedal percentage is less than the second threshold value. The calculated vehicle speed is fed as an input to the second comparing means 120. Simulatenously, the determining means 116 determines the working of the vehicle speed sensor 118.The determining means 116 provides a signal to a reference means 115 to set the threshold speed value associated with the selected gear position as a reference value if the vehicle speed sensor 118 is not working. The threshold speed will be different for different gear positions. The second comparing means 120 compares the calcualted vehicle speed with the threshold speed. The electronic control unit 121 limits the vehicle speed by limiting an injection quantity into an engine or by limiting an air flow into the engine or by controlling an ignition angle of the engine or by combination of the above. If the vehicle speed sensor 118 is working, the determining means 116 provides a signal to the vehicle speed sensor 118 to provide the actual vehicle speed as one of the inputs to the second comparing means 120.The threshold vehicle speed will be replaced by the actual vehicle speed and the actual vehicle speed is considered as a threshold speed. The second comparing means 120 compares the calculated vehicle speed with the actual vehicle speed. The electronic control unit 121 reduces the speed of the vehicle if the calculated vehicle speed is more than the actual vehicle speed.

[0012] Figure 3 illustrates a flowchart of a method of working of a device 100 to limit a speed of a vehicle according to one embodiment of the invention. In step s1, determining a state of a clutch .In step S2, a rate of change of an accelerator pedal 102 for a predefined time and an accelerator pedal percentage is calculated, if said state of said clutch is not in a pressed state. In step S3, the rate of change of the accelerator pedal 102 is compared with a first threshold value and the accelerator pedal percentage is compared with a second threshold value. In step S4, a speed of an engine is measured. The speed of the vehicle is calculated from the engine speed and a gear specific ratio, if said rate of change of said accelerator pedal 102 is less than said first threshold value or if said accelerator pedal percentage is less than second threshold value in step S6. In step S7, a gear number is determined. In step 8, a reference speed associated for the selected gear position. In step S8, the working of a vehicle speed sensor 118 is determined. If the vehicle speed sensor 118 is not working, the speed of the vehicle that is calculated is compared with a threshold speed value in step S9 (b).In step S10 (b), the speed of said vehicle is limited, if the speed of the vehicle is more than the predefiend speed value. If the vehicle speed sensor 118 is working, an actual vehicle speed is determined in Step S9 (a).In Step S10 (a), the calculated speed of the vehicle is compared with the actual vehicle speed. In Step S11, the speed of the vehicle is limited if the calcualted speed of the vehicle is more than the actual vehicle speed.
[0013] With this device 100, the drivability can be improved even when the vehicle speed sensor 118 is not working. The method operating the device 100 can be used to determine the speed of the vehicle when there is no vehicle speed sensor 118 present in the vehicle, by which, the manufacturing cost can be reduced.The method disclosed can be applied in any vehicle irrespective of the electronic control unit logics.Additonal hardware or any change in the existing hardware units can be avoided.
[0014] It must be understood that the examples and embodiments of the components explained in the detailed description are only illustrative and do not limit the scope of the invention. The scope of this invention is only limited by the scope of the claims.