Field of the invention:

[0001] The present disclosure relates to a method for operating a Continuously Variable Transmission (CVT), and particularly relates to a controller and a method to operate a CVT which is assisted by an electrical actuator.

Background of the invention:

[0002] When a CVT vehicle is driven through gradient, driver has to open the throttle more. The throttle opening loads the CVT and causes vibration and affects drivability. For example: a mechanical CVT system of a scooter is assisted with an actuator comprising a DC motor. The actuator is operated by the ECU to achieve better fuel efficiency. The actuator is controlled based on the throttle position and vehicle speed. The ECU controls the gear ratio in the same manner on a flat surface as well as on a gradient surface, because there is no active gradient detection. So when the vehicle starts ascending an up gradient, the driver has to open the throttle more to maintain the acceleration (or speed). This leads to increased load on the CVT and cause vibrations, and thus affecting the drivability. [0003] Hence, there is a need for a solution to assist a vehicle with a CVT based on gradient of the driving surface and thereby maintain the drivability.

Brief description of the accompanying drawings:

[0004] An embodiment of the disclosure is described with reference to the following accompanying drawings,

[0005] Fig. 1 illustrates a system diagram of a Continuously Variable Transmission (CVT) assisted by an electrical actuator, according to an embodiment of the present invention;

[0006] Fig. 2 illustrates the process executed by a controller, according to an embodiment of the present invention;

[0007] Fig. 3 illustrates a method flow diagram for providing torque assistance to a CVT of the vehicle, according to an embodiment of the present invention, and

[0008] Fig. 4 illustrates a schematic of a vehicle travelling on two gradient surfaces, according to an embodiment of the present invention. Detailed description of the embodiments:

[0009] Fig. 1 illustrates a system diagram of a Continuously Variable Transmission (CVT) assisted by an electrical actuator, according to an embodiment of the present invention. A controller 102 to operate a CVT of a vehicle is provided. The CVT comprises at least two pulleys, i.e. primary pulley (not shown) and secondary pulley 122 coupled with a belt 124. One of the at least two pulleys (usually primary pulley) is controlled with a variator 118. The variator 118 is also assisted by an electrical actuator 116 based on a base gear ratio/ CVT ratio determined from a base map 202 (shown in Fig. 2). The base gear ratio is determined based on a vehicle speed and a throttle position. The controller 102 comprises an I/O interface, a processor, a memory element, all internally connected to each other. The controller 102 is adapted to determine a gradient of a driving surface 402 (shown in Fig. 4) based on signals received from output of at least one of, a sensor 110 and a combination of an engine speed, the vehicle speed and the throttle position. The controller 102 determines a desired gear ratio corresponding to the gradient using a gradient map 204. The controller 102 also determines an actual gear ratio based on the engine speed and the vehicle speed. The controller 102 then computes an offset between the desired gear ratio and the actual gear ratio. The controller 102 calculates a target gear ratio based on the offset and the base gear ratio. The controller 102 controls the variator 118 by the electrical actuator 116 corresponding to the target gear ratio. [0010] The sensor 110 is at least one selected from a group comprising a gradient sensor and an accelerometer. The sensor 1 10 is installed in the vehicle itself. Alternatively, a smartphone of a user such as driver or pillion rider comprising the accelerometer is used as the sensor 110. The smartphone of the user is connected to the controller 102 through known wired or wireless means.

[0011] The combination of the engine speed, a vehicle speed and said throttle position is received from an engine speed sensor 104, a vehicle speed sensor 108 and throttle position sensor 106, respectively. The controller 102 detects the gradient actively without having additional sensor by analyzing available inputs from the engine speed sensor 104, the vehicle speed sensor 108 and the throttle position sensor 106 in the vehicle.

[0012] The electrical actuator 116 is controlled when the target gear ratio is within a permissible range 206 (shown in Fig. 2). Otherwise the electrical actuator 116 is controlled as per the base gear ratio. [0013] In accordance to an embodiment of the present invention, the controller 102 is provided for a CVT vehicle as described below. The CVT comprises a primary pulley and a secondary pulley 122 each with respective fixed and movable sheaves. The fixed sheave is outside (away from the engine 112) and the movable sheave is at the engine 112 side. A crankshaft 114 of the engine 112 extends through said movable sheave to the fixed sheave. The electrical actuator 116 is coupled to the movable sheave through an assembly comprising a spindle, housing, bearing and a movable shaft. The spindle is coupled to the motor of the electrical actuator 1 16 and the housing. The housing in turn, is coupled to the movable shaft over bearings. The actuator moves the movable sheave towards and away from the fixed sheave as per the control signal provided by the controller 102. The controller 102 is provided for existing CVT vehicles irrespective of constructional changes.

[0014] Fig. 2 illustrates the process executed by the controller, according to an embodiment of the present invention. The controller 102 receives input from the engine speed sensor 104, a throttle position sensor 106 and a vehicle speed sensor 108. The controller 102 accesses the base map 202 from the memory element, and determines the base gear ratio corresponding to the vehicle speed and throttle position. The vehicle is operated at the determined base gear ratio by default.

[0015] The base gear ratio is determined by the controller 102 for operating points defined by vehicle speed and throttle position. The base gear ratio makes sure that fuel economy and drivability are better at those operating points. Clamping force generated by the roller weights 120 are also considered for ensuring that the force required to be generated by the electrical actuator 116 is optimum. The clamping force is computed as a function of the engine speed and characteristics of the roller weights 120 such as size, shape, weight and the like.

[0016] Further, the controller 102 determines the gradient of the driving surface 402 either directly from the sensor 110 or derives by processing the inputs from the engine speed sensor 104, the vehicle speed sensor 108 and the throttle position sensor 106. The controller 102 then accesses a gradient map 204 from the memory element, and determines the desired gear ratio corresponding to the gradient. The effect of the gradient on the gear ratio is taken into consideration. The controller 102 also calculates the actual gear ratio from engine speed and vehicle speed. The controller 102 then computes an offset between the actual gear ratio and the desired gear ratio. The controller 102 calculates a target gear ratio after applying the offset to the base gear ratio. The controller 102 then assists the variator 1 18 with the electrical actuator 1 16 with respect to the target gear ratio. [0017] Before controlling the electrical actuator 1 16, the controller 102 checks the validity of the target gear ratio with a permissible range 206. If the target gear ratio is outside the range 206, then the target gear ratio is discarded and the electrical actuator 1 16 is operated as per the base gear ratio. [0018] In accordance to an embodiment of the present invention, the gradient of the driving surface 402 is detected by smartphone of the driver or pillion rider or both. The smartphone is connected to the controller 102 either through wired means such as Universal Serial Bus (USB) cables or through wireless means such as Bluetooth, Wi-Fi and the like. The smartphone is mounted on the vehicle. The accelerometer signal from the smartphone is utilized. Using the accelerometer signal, the controller 102 is able to measure position, motion, tilt and acceleration. Further, since the smartphone is mounted on the vehicle or carried by the user, the orientation of the vehicle is also obtained. Once the gradient is detected, the controller 102 determines and provides more torque to the wheels based on the intensity of the gradient by controlling the electrical actuator 1 16.

[0019] In accordance to an embodiment of the present invention, an active gradient detection is provided. The controller 102 learns/ detects the gradient through which the vehicle is being driven. The controller 102 is able to detect the gradient and its intensity without having additional sensors by monitoring the variations in engine speed, vehicle speed with respect to the driver demand (throttle position). Alternatively, a sensor 1 10 is used. In still another alternative, the controller 102 combines the sensor 1 10 input with the inputs received from the engine speed sensor 104, the vehicle speed sensor 108 and the throttle positon sensor 106, to determine more accurate gradient. [0020] Fig. 3 illustrates a method flow diagram for providing torque assistance to a CVT of the vehicle, according to an embodiment of the present invention. The CVT comprising at least two pulleys, i.e. primary pulley (not shown) and secondary pulley 122, coupled with a belt 124. One of the at least two pulleys is controlled with a variator 1 18 comprising roller weights 120. The variator 1 18 is operatively assisted with an electrical actuator 1 16. The method comprises, a step 302 comprising determining a base gear ratio from a base map 202 based on vehicle speed and throttle position. A step 304 comprises determining a gradient of the driving surface 402 based on output of at least one of, a sensor 110 and a combination of engine speed, vehicle speed and a throttle position. A step 306 comprises determining a desired gear ratio corresponding to the gradient from a gradient map 204. A step 308 comprises estimating an actual gear ratio based on the engine speed and the vehicle speed. A step 310 comprises computing an offset between the desired gear ratio and the actual gear ratio. A step 312 comprises calculating a target gear ratio based on the offset and the base gear ratio. A step 314 comprises assisting the variator 118 with the electrical actuator 116 corresponding to the target gear ratio.

[0021] The sensor 110 is at least one selected from a group comprising a gradient sensor and an accelerometer. The gradient sensor and the accelerometer are either installed in the vehicle or components of a smartphone carried by the driver or the pillion rider or both.

[0022] The combination of the engine speed, a vehicle speed and the throttle position is received from the engine speed sensor 104, the vehicle speed sensor 108 and the throttle position sensor 106, respectively. [0023] The electrical actuator 116 is controlled when the target gear ratio is within a permissible range 206. Otherwise the electrical actuator 116 is calculated as per the base gear ratio.

[0024] Fig. 4 illustrates a schematic of a vehicle travelling on two gradient surfaces, according to an embodiment of the present invention. The vehicle is shown to be a scooter 400 but is also allowed to be any other vehicle such as motorcycle, moped, car and the like. The vehicle is shown traveling on a flat driving surface 402. When a driver when starts driving on a inclined driving surface 402 in continuation from the flat driving surface 402, then the drivability is affected. Alternatively, if the driver starts on the inclined driving surface 402 directly such as from parked state, stop-go traffic, then the drivability is affected. The controller 102 maintains the drivability by keeping the same acceleration based on the detected gradient or gradient assist feature. The controller 102 automatically detects an up gradient, and correspondingly calculates extra/additional torque needed. Then this additional torque is realized by controlling the electrical actuator 116. The electrical actuator 116 reduces the gearratio and allows more power to be transmitted to the wheels, needed for easy up gradient ascending and maintaining the acceleration. Once the gradient is over, the controller 102 switches back to the normal state (base map 202).

[0025] In accordance to an embodiment of the present invention, the controller 102 provides dedicated function for automatic gradient detection and gradient compensation by torque assistance. The controller 102 also supports the CVT of those vehicles which comprises driving modes such as ECO mode, Sport mode and the like. The present invention provides an add-on (retro-fit) feature for electronically controlled CVT vehicles. So while driving an up gradient, the driver does not open more throttle. The drivability is not affected and same acceleration and stability are maintained.

[0026] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. 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.