A GRADIENT DETECTION AND CONTROL SYSTEM
FIELD OF THE INVENTION
[0001] The subject matter as described herein, relates generally to an
automotive vehicle and more particularly, but not exclusively, to a gradient detection and control system in a hybrid vehicle.
BACKGROUND OF THE INVENTION
[0002] A conventional two wheeled vehicle is powered by an internal
. combustion Generally, a hybrid vehicle,- combines -....the—advantages., of-a. conventional vehicle and an electric vehicle into one vehicle. It comprises of a dual powertrain in the form of an internal combustion engine and an electric traction motor which are either used jointly or separately depeding upon the user requirements of needing more power or more fuel efficiency. The electric traction motor is powered by a rechargable electric power unit.
[0003] While the vehicle is driven on the road, it is likely to encounter a
gradient. The gradient of the road is an angle of the slope of the road with respect to the horizontal plane. For a vehicle travelling on the road, it is important to know the angle of the slope. Unlike a conventional vehicle where the user downshifts a gear for increased engine torque to overcome a gradient encountered on road, the hybrid vehicle has lower user intervention because the vehicle is loaded with more electrical components than a conventional vehicle. With the existing limitations of the vehicle like wheel torque, controller power ratings, electric power unit capacity, the vehicle may not climb the gradient or the vehicle

may not ramp up using just the electric power source. Additionally, all gradients
encountered on road are not steeper and hence do not require dual power sources
to power the vehicle. .
[0004] There are several known technologies for determining the gradient
of the road on which the vehicle is traversing. The gradient of the road can be determined by including an additional inclination sensor in the vehicle, or by a road database stored in a GPS based navigation device. US Patent No. 6484086 teaches a similar technology wherein a camera equipped in a vehicle is used in determining the gradient. However, all these ways require some additional component to be included in the vehicle. This would increase the cost of the hybrid vehicle and make the electronic control unit associated with the vehicle more complex. In a two wheeled hybrid vehicle, it may also lead to packaging issues due to the presence of additional components.
SUMMARY OF THE INVENTION
[0005] It is, therefore, important that the hybrid vehicle detects a gradient
on the road or the 'onset' of gradient and also determines the 'extent' of gradient without using any additional component, and take necessary steps to sufficiently power the vehicle to overcome the gradient without any user intervention. It is therefore an object of the present invention to provide a system for gradient detection and control for a hybrid vehicle to detect the onset of a gradient and take subsequent corrective actions without using any additional components like inclination sensor or GPS based navigation device or a camera. It is also an object

of the present invention to detect the extent of the gradient and automatically change the vehicle mode or assist the vehicle to overcome the detected gradient.
[0006] To this end, the present subject matter discloses a hybrid vehicle
incorporating a gradient detection and control system and method thereof for detecting a gradient on the road and powering the vehicle according to the extent of the gradient. The hybrid vehicle is powered by a dual powertrain including an internal combustion engine and a traction motor. The traction motor is powered by an electric power unit. In an embodiment, the electric power unit is a Lithium ion based battery. According to an aspect, the gradient detection and control system determines the gradient and takes further action in assisting the vehicle to climb the gradient. The gradient is detected by sensing the throttle position value, brake position value and rate of change of vehicle RPM value. The brake position value is either one or zero stating the ON and OFF condition of the brake. The . rate of change of vehicle RPM is detected by the hall sensor inherently provided in the traction motor. The throttle position is detected by a throttle position sensor (TPS) inherently provided in the vehicle.
[0007] On sensing a gradient, the gradient detection and control system
first determines the magnitude of the gradient, compares the detected gradient with a set of predetermined gradient values and subsequently take steps to control the vehicle RPM to overcome the gradient. The gradient detection and control module is active only when the measured throttle position value is more than a predetermined throttle position value and the brake position value is zero. The gradient detection and control system includes an electronic control unit which is

the primary decision making unit of the hybrid vehicle: The electronic control unit overcomes the gradient by powering the vehicle according to the magnitude of the gradient detected and without any manual intervention.
[0008] Therefore, in a first condition where the magnitude of the gradient
is less than or equal to a first predetermined gradient value, the electronic control unit provides full power to the traction motor through the electric power unit if the vehicle is being driven in electric only mode. In a second condition where the magnitude of the gradient is more than the first predetermined gradient value but less than a second predetermined gradient value, the electronic control unit changes the prevailing vehicle operating mode to a hybrid power mode. Thus, the engine is assisted by the motor to climb the gradient. In a third condition where the magnitude of the gradient is equal to or more than the second predetermined gradient value, the electronic control unit changes the vehicle mode to hybrid power mode, provides full power to the traction motor and also communicates with the ignition unit to change the ignition timing curve of the engine for providing extra torque. The vehicle thus climbs and overcomes any gradient with full load.
[0009] Further, a condition is possible where the vehicle is suddenly
stopped while climbing a gradient. In this condition, the vehicle user switches on the vehicle and operates the throttle wide open while the brakes are on. This is done so that the vehicle does not move backwards on the gradient. Hence, in this condition where the measured throttle position value is more than a first predetermined throttle position value and brake position value is not zero, the

gradient detection and control system continuously determines the throttle position value and if the measured throttle position value is more than a second predetermined throttle position value, the system directly powers the vehicle in a . hybrid power mode and bypasses the rest of the steps. Thus, the hybrid vehicle is directly powered to overcome the gradient when stopping on a slope.
[00010] The disclosed system uses already present components in the
vehicle and is inexpensive because additional dedicated components like sensors, navigation systems, cameras are not required thus lowering the cost of hybrid vehicle.
[00011] - The foregoing objectives and summary is provided to introduce a
selection of concepts in a simplified form, and is not limiting. To fully appreciate these and other objects of the present subject matter as well as the subject matter itself, all of which will become apparent to those skilled in the art, the ensuing detailed description of the subject matter and the claims should be read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[00012] The above and other features, aspects, and advantages of the
subject matter will be better understood with regard to the following description and accompanying drawings where:
[00013] FIG. 1 illustrates a side view of a conventional scooter-type hybrid
vehicle in accordance with an embodiment of the present subject matter.

[00014] FIG. 2 shows a side view of a rear portion of the hybrid vehicle of
FIG. 1.
[00015] FIG. 3 illustrates a gradient detection and control system installed
in the hybrid vehicle in accordance with an embodiment of the present subject matter.
[00016] FIG. 4 shows a method of detecting gradient and further actions
taken by an electronic control unit of the hybrid vehicle in accordance with an implementation of the present subject matter.
DETAILED DESCRIPTION OF THE INVENTION ~ ---- —-■-—
[00017] The hybrid vehicle has an internal combustion engine and an
electrical power unit as power sources. The vehicle has many user selectable modes to operate the vehicle depending upon the user requirement of increased power or better fuel efficiency. When the hybrid vehicle encounters a gradient on the road with only the traction motor as the sole power source, it experiences an increase in load. With the existing limitations of the vehicle like wheel torque, controller power ratings, electric power unit capacity, the vehicle may not climb the slope or the vehicle may not ramp up. The load is aggravated with increase in number of vehicle occupants and escalation in the gradient. For example, more power is required to overcome the gradient with two people as vehicle occupants than a single occupant. Therefore, a situation is possible where the vehicle completely stops in the middle of the gradient due to such limitations.

[00018] In an implementation, it is possible to increase the capacity of the
electric power unit in the hybrid vehicle and make it more powerful to overcome a gradient. However, specifically in a two wheeled hybrid vehicle, the capacity and consequently the size of electric power unit is kept limited due to space issues and weight balance of the vehicle. A bigger electric power unit also affects the packaging of the other critical components in the vehicle and requires efficient cooling at its installed location to avoid any inconvenience.
[00019] Even when the vehicle operates with engine as the sole power
source, the vehicle experiences a significant decrease in speed when a gradient is encountered. This is because in a hybrid vehicle the power from engine is not immediately available at user's instance. The user can open the throttle but cannot himself shift the gears as the gear upshifting and downshifting in the hybrid vehicle is electrically controlled. In an embodiment where the hybrid vehicle has single speed transmission, the vehicle takes significant time for increase in engine torque to overcome the gradient. Thus, rather than the user, the electronic control unit of the vehicle has to know the onset of gradient on the road and take corrective actions. The power required to overcome the gradient is subject to the vehicle load.
[00020] Further, all gradients are not of equal inclination. Some are steeper
than the others. For example, the gradient of a steep hill is different from the gradient of a flyover with respect to the horizontal plane. Hence, the power made available to the vehicle by the electronic control unit for overcoming the gradient would be different. Generally, more power is required to climb a hill than in case

of a series of steep speed-breakers. Therefore, the corrective action would be different based on the degree of the gradient. Hence, the detection of gradient should factor in the extent of the gradient and power the vehicle based on the degree of the gradient detected as same logic cannot be applied to gradients of different degrees.
[00021] On sensing a gradient, the gradient detection and control system as
proposed first determines the magnitude of the gradient, compares the detected gradient with a set of predetermined gradient values and subsequently take steps to control the vehicle RPM to overcome the gradient. A gradient detection and control module is active only when the measured throttle position value is more than a predetermined throttle position value and the brake position value is zero. The gradient. detection and control system includes an electronic control unit which is the primary decision making unit of the hybrid vehicle. The electronic control unit overcomes the gradient by powering the vehicle according to the magnitude of the gradient detected and without any manual intervention.
[00022] In order that those skilled in the art can understand the present
invention, the invention is further described below in detail so that various features of the invention thereof proposed here are discernible from the description thereof set out hereunder. However these descriptions and the appended drawings are only used for those skilled in the art to understand the objects, features, and characteristics of the present invention and not to be used to confine the scope and spirit of the present invention.

[00023] The present subject matter would now be described in greater
detail in conjunction with the figures in the following description. The description is to be understood as an exemplary embodiment and reading of the invention is not intended to be taken restrictively. FIG. 1 shows a side view of a conventional hybrid vehicle exemplified in the form of a scooter type, two-wheeled hybrid vehicle. The vehicle has a frame assembly made up of several tubes welded . together which usually supports the body of the said vehicle. The vehicle has a steerable front wheel 101 and a driven rear wheel 102. A handlebar assembly 109 and a seat assembly 113 are supported at opposing ends of the frame assembly and a generally open area is defined therebetween known as floorboard 110 which functions as a step through space. The seat for a driver and a pillion is placed forward to a fuel tank and rearwardly of the floorboard 110. A front fender 103 is provided above the front wheel 101 to avoid the said vehicle and its occupants from being splashed with mud. Likewise, a rear fender 104 is placed between fuel tank and rear wheel 102, and to.the outer side in the radial direction of rear wheel 102. Rear fender 104 inhibits rain water or other impurities from being thrown up by rear wheel 102. Further, as shown in FIG. 1, the frame assembly is covered by a plurality of vehicle body covers including a front panel 105, a leg shield 111, an under seat cover 112 and a side panel 114.
[00024] Suspensions are provided for comfortable steering of the vehicle
on the road. A front suspension assembly (not shown) is connected to a front fork 107 while the rear suspension assembly is connected to the body frame. The rear suspension assembly comprises of at least one rear suspension 121 preferably on

the left side of the vehicle. However, a vehicle with two rear suspensions namely on the left side and the right side is also possible. For the safety of the user and in conformance with the homologation requirements, a headlight 106 in the front portion of the vehicle and a taillight 120 in the rear portion of the vehicle is also included.
[00025] In a preferred embodiment, the scooter type motorcycle has an
electromechanical powertrain including an internal combustion engine 115 and a traction motor 118 as drive sources as shown in FIG. 2. In an embodiment, the engine is a four stroke single cylinder engine. The engine 115 is disposed substantially forwardly of the rear wheel 102. The traction motor 118 is powered by an electric power unit (also referred to as battery) 126 whereas the engine 120 is cranked by a starter motor (not shown) powered by the electric power unit 126. In a preferred embodiment, the battery 126 includes a lithium ion battery and provides 48 V of electromotive force. In an embodiment as shown in FIG. 2, the traction motor 118 is coupled to a hub 119 of the rear wheel 102. The direct coupling of traction motor 118 to the rear wheel hub 119 outside of the engine crankcase saves space and prevents transmission losses due to absence of any gear reduction.
[00026] The hybrid vehicle is provided with a plurality of vehicle operating
modes. These modes are user selectable and the vehicle user can select any of the operating modes for operating the vehicle and/or switch between the operating modes. The selected mode is displayed on a display panel of the hybrid vehicle forwardly of the vehicle user. The vehicle operating modes include an engine only

mode, a motor only mode, a hybrid power mode and a hybrid economy mode. In the hybrid power mode, both the engine and the traction motor simultaneously power the hybrid vehicle whereas in the hybrid economy mode, the hybrid vehicle is first driven by the traction motor and after the vehicle attains a predefined speed, the engine is initiated and the traction motor is stopped. Thus, the rear wheel 102 in the vehicle is driven by driving force generated by either the engine 115 or the traction motor 118 or both.
[00027] An electronic control unit 125 controls the flow of power in the
vehicle and acts as the nerve centre for all decision making processes. In one of the embodiments as shown in FIG. 2, the electronic control unit 125 is located at the rear portion of the vehicle attached to the vehicle frame. The electronic control unit 125 starts the motor 122 or the engine. 120 or both according to the mode selected by the user. In case no mode is selected, the electric control unit starts the vehicle in default (pre-selected) mode which can be from any of the. vehicle oeprating modes. In a preferred embodiment, the default mode is hybrid economy mode.
[00028] FIG. 3 shows a block diagram of the gradient detection and control
system including an electronic control unit 125 and a memory 126 coupled to the electronic control unit 125. The electronic control unit 125 is configured to fetch and execute the data stored in the memory 126. The memory 126 may include any volatile memory or dynamic memory. The memory further includes one or more modules 130 and data 140. The modules include a throttle position sensing module 131, a brake position sensing module 132, a vehicle RPM sensing module

133 and a gradient detection and control module 134. The data 140 amongst other things serves as repositories for storing data processed, received, and generated by one or more module(s) 130. The data includes throttle position value (TPV) 141, brake position value (BPV) 142, rate of change of RPM value (RPV) 143 and gradient value (GV) 144. The data 140 and the modules 130 can be considered to be linked to each other such that the electronic control unit 125 continuously determines atleast one of the modules 130 to process the data 140.
[00029] The electronic control unit 125 is further electrically connected to
one or more sensors inherently provided in the vehicle. The throttle position sensing module 131 is configured to determine the TPV 141. The throttle position sensing module 131 is electrically linked to a throttle position sensor 151 provided in the vehicle and based on the electrical signals received determines the TPV 141. The brake position sensing module 132 is electrically connected to a brake position sensor 152 to determine at least one BPV 142. Similarly, the vehicle RPM sensing module 133 is electrically connected to a hall sensor present in the hub mounted traction motor 118 to determine RPV 143.
[00030] The gradient detection and control module 134 is active only when
the measured throttle position value is more than a predetermined throttle position value and the brake position value is zero. The gradient detection and control module 134 is configured to determine a gradient value 144 at least based on one of the TPV 141, BPV 142 and RPV 143. The determined gradient value 144 is compared to. a set of predetermined gradient values stored in the electronic control unit 125. Based on this comparison, the gradient detection and control module 134

controls the rate of change of the vehicle RPM to neutralize the effect of gradient by choosing, one or more power sources of the hybrid vehicle.
[00031] In an embodiment, the predetermined throttle position value is
85%. In an embodiment, the brake position value is either one or zero where one shows that the brake is operative and zero shows that the brake is not operative at that point of time.
[00032] The method of gradient detection and control is now explained in
detail through FIG.4 and 5. The gradient detection and control method begins at brock-501/At block 503, the TPV, BPV and RPV arecoritinuotisly1'mea'siired'in^ the vehicle so that as soon as a gradient is detected, additional power to the vehicle is made available immediately. Thus, the throttle position sensing module 131, the brake position sensing module 132 and the vehicle RPM sensing module 133 are always active in the electronic control unit 125. Till the measured throttle position value is less than the predetermined TPV, the gradient detection and control module 134 is not operative. When the vehicle encounters a gradient on the road, the user opens the throttle wider, for more torque irrespective of the prevailing vehicle operating mode. In this condition at block 505, the measured TPV becomes more than the predetermined TPV (say x%). If the BPV is zero as shown in block 509 indicating that the brakes are inactive, the gradient detection and control system starts a timer at block 511 and checks for any of the following conditions sequentially: (a) At block 515, whether the measured RPV is less than 1 kmph for a time interval of *P' seconds; (b) At block 517, whether the measured RPV is less than 20kmph for a time interval of 'Q' seconds, wherein Q is more

than P; (c) At block 519, whether the change in vehicle RPM negative. The above mentioned conditions are checked 'sequentially' by the gradient detection and control system when the measured TPV is more than the predetermined TPV (x %) and the measured BPV is zero. In an embodiment, the x is 85. If none of the conditions are satisfied, the gradient detection and control system stops checks and the vehicle runs in the prevailing operating mode.
[00033] However, if any of these conditions is satisfied, as stated by 'Y'
meaning YES, the gradient detection and control module 134 determines a gradient value based on TPV, BPV and RPV at block 530. The determined gradient value is then compared to a set of predetermined gradient values stored in the electronic control unit 125. Based on the comparison, the gradient detection, and control system controls the rate of change of the vehicle RPM to neutralize the effect of gradient by choosing one or more power sources of the hybrid vehicle.
[00034] Three conditions are possible referred by alphabets 'A', 'B' and
'C\ In a first condition A at block 531, if the determined gradient value is less than or equal, to a first predetermined gradient value, the system provides full power to the traction motor for a particular time interval without changing the prevailing vehicle operating mode. This condition is applicable only when the vehicle is being operated in the motor only mode. Since the determined gradient value is less than or equal to a first predetermined gradient value, the gradient is not very steep and hence the traction motor is sufficiently capable of overcoming it if additional power is made available to it. The traction motor is usually

powered by the electric power unit at its rated power. However, the rated power may not be sufficient to overcome the gradient. Therefore additional power beyond the rate power for a particular time interval is made available to the traction motor through the electric power unit. However, the electric power unit would drain quickly in this condition. In an embodiment, the first condition A is able to overcome a gradient of less than or equal to 4°.
[00035] In a second condition B at block 532, the determined gradient
value is more than the first predetermined gradient value but less than a second predetermined gradient value wherein the second predetermined gradient value being more than the first predetermined gradient value. Therefore, the system changes the prevailing vehicle operating mode to a hybrid power mode since the gradient is steeper than the first condition. In this condition, the vehicle primarily uses the power of engine which is assisted by the traction motor in the hybrid power mode. In an embodiment, the second condition A is able to overcome a gradient of more than 4° but less than 10°.
[00036] In a third condition C at block 533, the determined gradient value
is more than or equal to the second predetermined gradient value which signifies steeper gradient. In this condition, as the gradient is very steep, the system changes the prevailing vehicle operating mode to the hybrid power mode, advances the engine ignition timing and provides full power to the traction motor beyond its rated power for a particular time interval. In an embodiment, an ignition unit associated with the engine advances the ignition timing of the engine to increase the engine torque. The electronic control unit communicates to ignition

unit through CAN communication or analogue signal. The combination of advanced engine timing and more powerful motor overcomes the gradient. In an embodiment, the third condition C is able to overcome a gradient of more than or equal to 10°.
[00037] As soon as the gradient is overcome, the rate of change of vehicle
RPM becomes positive and the gradient detection and control module is inactivated and the vehicle.returns to the prevailing operating mode.
[00038] In certain conditions, it is possible that the vehicle RPM drops to
zero while climbing' the gradient"; This may occur when the vehicle stops in the middle of the slope due to extremely lean air fuel mixture or due to any mechanical or electrical troubles in the vehicle. In this condition, the vehicle user will operate the brakes so that the vehicle does not travel backwards. During this condition, when the vehicle is again switched on, the measured TPV is more than the predetermined TPV x % but the determined BPV is not zero. The gradient detection and control system then diverts from block 509 to block 507. While starting the vehicle again, the user opens the throttle wider to immediately and sufficiently power the vehicle. However, the new determined TPV.say y % would be less than the predetermined TPV (x %) but more than the normal TPV at block 507. This is because the user opens the throttle wide but not wide enough to experience a jerk. In this condition, at block 533, the system immediately changes the prevailing vehicle operating mode to the hybrid power mode when the vehicle is started, advances the engine ignition timing and provides full power to the traction motor beyond its rated power for a particular time interval. This is

because more power is required for a static vehicle on a gradient than a moving vehicle.
[00039] From the foregoing description, it will be appreciated that the
present invention offers many advantages including those described above. The present invention ensures effective utilization of the available engine power and battery power and reduces vehicle cost. By boosting the vehicle power on encountering a gradient, the. invention ensures smooth ride on the slope while taking into account the load on the vehicle. The present invention not only detects the gradient but also takes into account the extent of the gradient for sufficiently powering the vehicle to neutralize the effect of gradient.
[00040] The present subject matter is thus described. The description is not
intended to be exhaustive nor is it intended to limit the invention to the precise form disclosed. It will be apparent to those skilled in the art that the disclosed embodiments may be modified in light of the above description. The embodiments described are chosen to provide an illustration of principles of the invention and its practical application to enable thereby one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore the forgoing description is to be considered exemplary 3 rather than limiting, and the true scope of the invention is that described in the appended claims.

We claim:
1. A hybrid vehicle comprising:
an internal combustion engine (115);
a battery driven traction motor (118);
a plurality of vehicle operating modes including an engine only mode, a motor only mode, a hybrid power mode and a hybrid economy mode; and
a gradient detection and control system linked with the hybrid vehicle
--including airetectronrc -control unit (125) and a memory. (126)-coupled to~--*-~ "■
the electronic control unit (125), the memory (126) further comprising:
a throttle position sensing module (131) configured to determine a throttle position value (141);
a brake position sensing module (132) configured to determine at least one brake position value (142);
a vehicle RPM sensing module (133) configured to determine a rate of change of vehicle RPM value (143); and
a gradient detection and control module (134) configured to:
determine a gradient value (144) at least based on one of the throttle position, value (141), the brake position value (142) and the rate of change of vehicle RPM value (143),

compare at least the determined gradient value (144) to a set of predetermined gradient values stored in the electronic control unit (125), and
control the rate of change of the vehicle RPM to neutralize the effect of gradient by choosing one or more power sources of the hybrid vehicle.
2. The hybrid vehicle as claimed in claim 1, wherein the gradient detection and control module (134) determines the gradient value (144) by determining any of following ''condition^^sequentlally, whether the measured rate of change of vehicle RPM value is less than 1 kmph or whether the measures rate of change of vehicle RPM value is less than 20 kmph for a time interval of 'Q' seconds or whether the change in vehicle RPM is negative.
3. The hybrid vehicle as claimed in claim 1 or claim 2, wherein the gradient detection and control module (134) is active only when the throttle position value (141) is more than a predetermined throttle position value and the brake position value (142) is zero.
4. The hybrid vehicle as claimed in claim 1, wherein if the determined gradient value (144) is less than, or equal to a first predetermined gradient value, the electronic control unit (125) provides full power to the traction motor (118) without changing the prevailing vehicle operating mode.

5. The hybrid vehicle as claimed in claim 1, wherein if the determined gradient value (144) is more than the first predetermined gradient value but less than a second predetermined gradient value, the electronic control unit (125) changes the prevailing vehicle operating mode to a hybrid power mode.
6. The hybrid vehicle as claimed in "claim 1, wherein if the determined gradient value (144) is more than or equal to the second predetermined gradient value, the electronic control unit (125) changes the prevailing vehicle operating mode to the hybrid power mode, provides full power to the traction motor and advances the engine ignition timing.
7. The hybrid vehicle as claimed in claim 1, wherein the electronic control unit (125) is electrically connected to a throttle position sensor (151) and the traction motor (118).
8. The hybrid vehicle as claimed in claim 1, wherein if the throttle position value (141) is more than a predetermined throttle position value and the brake position value (142) is not zero, the electronic control unit (125) changes the prevailing vehicle operating mode to the hybrid power mode, provides full power to the traction motor and advances the engine ignition timing.
9. A method for detecting a gradient and assisting a hybrid vehicle having anf electronic control unit (125) configured to propel the vehicle through an internal combustion engine (115) and a traction motor (118), the vehicle

being driven in any of a plurality of operating modes, the method comprising the steps of:
measuring a throttle position value (141) from a throttle position sensing module (131);
determining the brake position value (142) from a brake position sensing module (132),
measuring rate of change of vehicle RPM value (143) through a vehicle RPM sensing module (133),
comparing the measured value of vehicle RPM for a corresponding measured value of throttle position continuously with a predetermined threshold value of vehicle RPM for a corresponding threshold value of throttle position stored in the electronic control unit,
determining a gradient value (144) at least based on one of the throttle position value, brake position value and rate of change of vehicle RPM value and comparing the measured gradient value to a set of predetermined gradient values stored in the electronic control unit,
wherein if the determined gradient value (144) is less than or equal to a first threshold value, the electric control unit provides full power to the traction.motor without changing the prevailing vehicle operating mode;
if the determined gradient value (144) is more than the first predetermined
unit changes the prevailing vehicle operating mode to a hybrid power mode; and
if the determined gradient value (144) is more than or equal to the second threshold value, the electronic control unit changes the prevailing vehicle operating mode to the hybrid power mode, providing full power to the traction motor and advancing the engine ignition timing.