Claims:We Claim:
1. A method (100) controlling speed in a vehicle, said method comprising:
Detecting (102), by a first sensor, the speed of an engine;

receiving (104) , by a control unit, said speed of said engine;

detecting (106), by a second sensor, speed of at least one wheel;

receiving(108), by said control unit, said speed of said at least one wheel;

validating (110), by said control unit, said received speed of said wheel with a corresponding engine torque based on said speed of said engine;

checking (112), by said control unit, based on said validation, for calibrated period of time, if said speed of said wheel corresponds to said engine torque;

maintaining(114), the magnitude of said calibrated time period constant upon non-correspondence between speed of said wheel and said engine torque.

2. The method of claim 1, further comprising supplying torque to said engine upon said non-correspondence between said speed of said wheel and said engine torque.

3. The method of claim 1, wherein said vehicle is one of an autonomous vehicle and semi-autonomous vehicle.

, Description:Complete Specification:

The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed.
Field of the invention
[0001]This invention relates to the field of vehicle speed control.

Background of the invention
[0002]Vehicle speed safety is one of the important areas for legislation worldwide. Vehicle speed plausibility involves checking if the speed of the vehicle as measured by sensor is in accordance with the legislation requirements. Vehicle speed regulation is defined and calibrated on a flat road and under no load condition. The time in which the vehicle reaches the rated top speed on a flat road is so determined and calibrated also called as the calibrated time. This regulation so defined conflicts with the parameters (speed and torque) that when a vehicle encounters a slope and is under fully loaded condition. In other words, since a threshold is defined for a speed in a vehicle, overcoming the same in order to clear a gradient under fully loaded condition becomes difficult. This is because a vehicle may have one particular threshold limit defined for engine torque and speed, however since it is fully loaded and is also encountering a gradient, there is a possibility of the vehicle being pulled back due to the action of gravity. In such a situation the driver of the vehicle tends to accelerate sharply, this sudden increase in acceleration conflicts with the vehicle speed regulation (speed of the engine increases while speed of the wheel is zero) so defined, the vehicle stalls, even though the vehicle has not crossed the threshold limit of speed.

[0003]Prior art patent application GB2520996 discloses a method of automatically starting an internal combustion engine. When performing an automated start, as part of a stop/start function, whilst on an uphill slope an engine of a vehicle can stall due to the brake torque from the wheels. This invention allows the engine to modify the torque it produces to compensate, and allows for wider use of the stop and start function. The disclosed method comprises the vehicle being provided with an internal combustion engine, a transmission, a brake system and a controller for automatically stopping and starting the internal combustion engine Wherein the method performs the following steps: determining a transmission ratio of the transmission, determining a vehicle inclination along a longitudinal plane of the vehicle, calculating a brake torque as a function of the transmission ratio and the vehicle inclination, and adjusting a torque to be delivered by the engine to compensate for the said brake torque and to perform an automatic engine start.

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 method controlling speed in a vehicle.

Detailed description of the embodiments
[0006]. FIG. 1 illustrates a method controlling speed in a vehicle. The speed of an engine is detected 102 by a first sensor, a control unit receives 104 the speed of the engine. The speed of at least one wheel of the vehicle is detected 106 by a second sensor. The speed of the wheel is then received 108 by the control unit. Based on speed of the engine, the speed of the wheel is validated 110 with a corresponding engine torque, by the control unit. The speed of the wheel is checked 112, based on the validation 110, for a calibrated period of time, with corresponding engine torque. The magnitude of the calibrated time period is maintained 114 constant, upon non-correspondence between speed of the wheel and the engine torque. Torque is supplied to the engine upon non-correspondence between the speed of the wheel and the engine torque. In an embodiment the vehicle may an autonomous vehicle or a semi-autonomous vehicle.

[0007]The working of the above mentioned method in a control unit will be explained in further detail. The above mentioned method is explained with respect to a vehicle traversing from a flat road condition to a gradient and back to a flat road condition. It should be understood that this is for the sake of explanation only and the above mentioned method would hold good whenever the vehicle encounters a gradient and or stop and go traffic irrespective of the previous road condition. Consider the case of a vehicle being under fully loaded condition and the vehicle encounters a gradient after traversing along a flat road. The first sensor detects 102 the speed of the engine. The speed of the wheel is detected 106 by a second sensor. The speed of the wheel and the engine is then received (104 and 108) by the control unit. Based on the speed of the engine, the control unit validates 110 the speed of the wheel with a corresponding engine torque. The relationship between speed of the wheel and engine torque is derived during calibration and is stored in the form of a data map in the control unit. The values of engine torque so stored in the data map is used as reference for vehicle speed regulation. When the vehicle is under gradient condition, the engine speed increases and the vehicle needs to be under motion, however since it is loaded, the vehicle is not able to move forward with ease as it happens in case of a flat road condition. Hence there is an error condition in this case. This diagnosis of this error condition is referred to as debounce. The error condition is determined by checking (112), by the control unit, based on the validation 110, for calibrated period of time, if the speed of the wheel corresponds to the engine torque. The magnitude of the calibrated time is maintained constant 114 upon non-correspondence between the speed of the wheel and the engine torque. By keeping the magnitude of calibrated time constant, the control unit gets additional time to check if error condition is valid or not. The use of the term maintaining the calibrated time constant implies that at the end of calibrated time, the diagnosis of the error condition is not reset. In case the error condition is valid, due to misdiagnosis, torque is supplied to the wheels of the vehicle to keep it in motion and to prevent the vehicle from stalling in a gradient under loaded condition.

[0008]The calibrated time disclosed above refers to the time for which the control unit will wait to detect an error condition. Upon completion of the calibrated time period, the control unit may trigger further action, like displaying an error condition, stalling the vehicle, causing the vehicle to be under torque limitation mode.

[0009]For the purpose of better understanding the said method will be explained in the case of the vehicle having a speed limitation (rated speed) of 40Km/Hr., for the above mentioned speed, assuming the calibrated time to be 5 second. That is, at the expiry of 5 second period the vehicle should have reached the rated speed and speed limitation should be implemented once the vehicle exceeds the above mentioned speed limit. The instant explanation is for the purpose of better understanding and does not limit or restrict the disclosed method to the above mentioned speed and time. Also, the above mentioned method may be incorporated in a control unit of a vehicle that may be a manually driven vehicle, an autonomous vehicle or a semi-autonomous vehicle. Consider the scenario of a fully loaded vehicle starting from a flat road condition. As the driver (in the case of a manually driven vehicle) accelerates the vehicle, the control unit receives the speed of the wheel and the engine. The control unit validates the speed with the engine torque, and upon the completion of the time period, that is 5 seconds in this case, the control unit checks if the speed of the wheel corresponds to the engine torque. In case of correspondence, the control unit implements speed limitation and the calibrated time is reset, that is control unit repeats the above mentioned steps of receiving the vehicle and engine speed, validating with engine torque and further checks if the speed of the wheel corresponds to the engine torque for the next five seconds and so on, so as to keep the vehicle within the rated speed.

[0009] Moving further, consider the scenario where the vehicle after reaching a gradient or under stop and go traffic or any other scenario where the vehicle may not show a valid vehicle speed(the vehicle speed sensor reads 0Km/hr until the vehicle is in motion) within the calibrated time. In the case of a gradient, as the driver accelerates the vehicle, the control unit receives the speed of the wheel and the engine. The control unit validates the speed of the wheel with the engine torque, and upon the completion of the time period, that is 5 seconds in this case, the control unit checks if the speed of the wheel corresponds to the engine torque. Since, the vehicle is fully loaded and/or is also encountering a gradient, the speed of the engine may not be sufficient enough to provide drive to the wheels within the calibrated time period (5 seconds). Hence, even though the vehicle has accelerated to the maximum extent, this may not result in drive to the wheels. This results in a condition wherein the speed of the wheel is in non-correspondence with the engine torque. Since this is an error condition the control unit may implement torque limitation by stalling the vehicle because the speed of the engine may be higher compared to the wheel speed. In order to avoid the above mentioned scenario, the disclosed method, maintains the magnitude of the calibrated time period constant. In other words, if the magnitude of the calibrated time is not maintained constant, the diagnosis will have to be completed in lesser time of 3 seconds (as the non-correspondence may be encountered for example if gear changes and the diagnosis time will be reset. With the implementation of the disclosed method, the control unit waits to see if the engine speed, torque are in not in correspondence for reasons like gear change. The calibrated time of diagnosis is maintained constant at this instance and the diagnosis resumes once the engine speed and torque are in correspondence. In order words upon expiry of 3 seconds period (in this example), the control unit will not allow the calibrated time period to be reset to 0 seconds (starting from 3 second and resuming diagnosis until 5 second). In the absence of reset, torque limitation may not be implemented as further input about vehicle speed is not available. This gives the wheels additional time to receive torque. Further, diagnosis of vehicle speed with respect to engine torque, resumes again from the instant of stoppage of reset, the control unit further repeats the above mentioned steps for the next 5 seconds and so on.

[0010]Under normal running condition, for 40Km/hr. speed limitation, this speed is achieved in second gear under flat road condition. The correspondence of engine speed and torque in first gear is active for approximately 2.5 seconds and the vehicle reaches a maximum speed of 28Km/hr. The vehicle speed reaches 40Km/hr. in second gear with correspondence of engine speed and torque valid for lesser than 1.5 seconds in second gear. This means it is required to have a calibrated time of 2.5 seconds for diagnosis in case of failure in vehicle speed sensor and the top speed is limited to 40 Km/hr.
In case of stop and go traffic or gradient condition and/ or the vehicle being fully loaded, the vehicle is sometimes not able to move within 2.5 seconds (vehicle speed is shown as 0Km/hr.). This will lead to misdiagnosis of the vehicle speed sensor and the torque limitation mode may be activated, which will not allow the complete torque transmission and results in stalling of vehicle in the gradient.

[0011]In the disclosed method, the correspondence time of 2.5 seconds in first gear is kept constant when the engine speed and torque are not in correspondence during the gear change to second gear. The correspondence time in second gear of 1.5seconds is accumulated to the calibrated time. This results in 5 seconds of calibrated time as explained below. Gear 1 correspondence time (2.5 seconds) plus Gear change time (approximately 1second) plus correspondence time under second gear before the speed of 40Km/hr. is reached (1.5seconds). The example with respect to the disclosed method provides a total diagnosis time of 5seconds. This time is enough for the fully loaded vehicle to traverse in gradient and provide a valid vehicle speed. Thus the misdiagnosis is avoided. Correspondence time disclosed herein implies that the magnitude of engine speed and torque are in way such that the vehicle will move during that time period.

[0012]The above mentioned method gives additional time for the control unit to check if the vehicle is in motion under gradient condition. This avoids the problem of misdetection that would occur due to wrong signal being generated in case of from second sensor on wheel. The problem of a fully loaded vehicle stalling under a gradient is thus avoided. In absence of the above disclosed method the vehicle would stall under a gradient condition, and repeated attempts to re-start the same would fail due to the fact any increase in engine speed would not result in corresponding increase in speed of the wheels because of vehicle speed limitation. This vehicle speed or torque limitation under an error condition as disclosed, and in the absence of the disclosed method, would deny the vehicle of the torque that is required to keep the vehicle in motion under gradient condition. The above mentioned method allows to have the flexibility of greater magnitude of the calibrated time and thus avoids misdiagnosis which causes the vehicle to be under torque limitation mode which may not allow the fully loaded vehicle to negotiate the gradient slope. In addition the above mentioned method is applicable whenever the vehicle is not able to reach the rated speed due to a non-correspondence or mismatch between speed of the wheel and the corresponding engine torque.

[0013] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention in terms of the type of vehicle used. 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.