Description:TECHNICAL FIELD
[001] The embodiments herein generally relate to continuously variable transmission (CVT) systems of vehicles, and more particularly to the continuously variable transmission (CVT) system for an electric vehicle and a method of operating the CVT system.
BACKGROUND
[002] Continuously Variable Transmission (CVT) systems are widely utilized in two-wheeled, three-wheeled, and four-wheeled vehicles to provide seamless, step-less, and continuous variation of gear ratios. Unlike conventional gear systems, which rely on fixed gears to provide different speed ratios, CVT systems typically employ a belt and pulley mechanism to achieve a broad spectrum of gear ratios within predetermined limits.
[003] A conventional CVT system for a two-wheeled vehicle generally includes a primary pulley operatively connected to the vehicle’s engine, a secondary pulley operatively linked to the vehicle’s rear wheel(s), a power-transmitting belt coupled to the primary and secondary pulleys, and a centrifugal clutch coupled to the secondary pulley. The primary pulley is configured with movable sheaves whose axial position varies according to engine speed and load conditions, thereby modulating the effective diameter of the primary pulley. The secondary pulley incorporates a biasing spring mechanism to maintain appropriate belt tension and ensure the desired transmission ratio is preserved under varying operational conditions. The centrifugal clutch is configured to engage the secondary pulley once the engine speed exceeds a predefined threshold, enabling the vehicle to idle while stationary.
[004] The centrifugal clutch operates based on centrifugal force and typically includes a drum and multiple friction shoes. As the engine speed increases, the friction shoes are urged radially outward due to centrifugal force, establishing frictional engagement with the drum to transmit rotational power. While the centrifugal clutch arrangement facilitates simplified operation by obviating the need for manual clutch actuation, it introduces energy losses attributed to slippage during its engagement phase, thereby diminishing the overall transmission efficiency of the vehicle. Moreover, operation under high-load conditions accelerates the wear of the friction components, thereby necessitating frequent maintenance interventions. Further, the conventional CVT system is limited by inherent transmission losses, particularly when the power output is directed through the centrifugal clutch to a differential mechanism of the vehicle. At lower gear ratios, these losses, compounded by design inefficiencies, result in diminished output shaft speed and torque, thereby constraining the engine’s ability to achieve its maximum performance capabilities. A further limitation of conventional CVT systems utilized in two- and three-wheeled vehicles is the absence of reverse drive capability. The cam-and-pin mechanism responsible for controlling the movement of the secondary pulley sheave is specifically configured to permit forward motion exclusively, thereby limiting the implementation of reverse drive functionality in such vehicles.
[005] Further, adapting a conventional CVT system to electric two and three-wheeled vehicles presents significant challenges. The inherent transmission losses of the CVT system, particularly at the starting , diminish the efficiency gains achievable with electric motors, which are known for their high torque output at low speeds and broad efficiency ranges. Furthermore, the fixed cam-and-pin mechanism, limiting the CVT system to forward motion, conflicts with the ease of implementing regenerative braking and reverse functionality in electric vehicles through simple motor direction reversal. The mechanical complexity of the conventional CVT system becomes largely redundant in the context of electric vehicle powertrains, which prioritize simplicity, high efficiency, and precise electronic control.
[006] Therefore, there exists a need for a continuously variable transmission (CVT) system for an electric vehicle and a method of operating the CVT system which obviates the aforementioned drawbacks.
OBJECTS
[007] The principal object of embodiments herein is to provide a continuously variable transmission (CVT) system for an electric vehicle.
[008] Another object of the embodiments herein is to eliminate the centrifugal clutch, thereby reducing transmission losses and improving overall vehicle efficiency by directly coupling an electric motor of the vehicle with the CVT, ensuring optimal utilization of the motor's efficient rotational speed range.
[009] Another object of embodiments herein is to provide the CVT system that enables continuous gear ratio changes, facilitating operation of the electric motor with efficiency and enhancing vehicle performance.
[0010] Another object of embodiments herein is to provide a compact CVT system capable of seamless and continuous gear ratio adjustments across a wide gear ratio range, optimizing power delivery for various driving conditions.
[0011] Another object of embodiments herein is to integrate a reverse gear functionality within the CVT system, improving vehicle maneuverability and operational ease.
[0012] Another object of embodiments herein is to achieve a space-saving, compact design for the CVT system, facilitating easier installation and integration into electric vehicles.
[0013] Another object of embodiments herein is to provide a low-maintenance CVT system, ensuring reliable long-term performance and minimizing vehicle downtime.
[0014] Another object of embodiments herein is to disclose a method of operating the CVT system that optimizes the electric motor's performance through continuous and dynamic gear ratio adjustments.
[0015] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating at least one embodiment and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
BRIEF DESCRIPTION OF FIGURES
[0016] Embodiments herein are illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the following illustrated drawings. Embodiments herein are illustrated by way of examples in the accompanying drawings, and in which:
[0017] Fig. 1 depicts a block diagram of a continuously variable transmission (CVT) system, according to embodiments as disclosed herein;
[0018] Fig. 2A depicts a top view of the CVT system, according to embodiments as disclosed herein;
[0019] Fig. 2B depicts a front view of the CVT system, according to embodiments as disclosed herein;
[0020] Fig. 2C depicts a sectional view of the CVT system, according to embodiments as disclosed herein;
[0021] Fig. 3A depicts an exploded view of a variable pulley mechanism of the CVT system, according to embodiments as disclosed herein;
[0022] Fig. 3B depicts an exploded view of a primary pulley of the variable pulley mechanism, according to embodiments as disclosed herein;
[0023] Fig. 3C depicts an exploded view of a secondary pulley of the variable pulley mechanism, according to embodiments as disclosed herein;
[0024] Figs. 4A to 4C depict isometric views of the secondary pulley showing a cam assembly of the variable pulley mechanism with a pin at different positions in a cam profile, according to embodiments as disclosed herein;
[0025] Fig. 4D depicts a sectional view of the cam profile, according to embodiments as disclosed herein; and
[0026] Fig. 5 depicts a flowchart of a method of operating the CVT system, according to embodiments as disclosed herein.
DETAILED DESCRIPTION
[0027] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[0028] The words/phrases "exemplary", “example”, “illustration”, “in an instance”, “and the like”, “and so on”, “etc.”, “etcetera”, “e.g.,”, “i.e.,” are merely used herein to mean "serving as an example, instance, or illustration. Any embodiment or implementation of the present subject matter described herein using the words/phrases "exemplary", “example”, “illustration”, “in an instance”, “and the like”, “and so on”, “etc.”, “etcetera”, “e.g.,” “i.e.,” is not necessarily to be construed as preferred or advantageous over other embodiments.
[0029] Embodiments herein may be described and illustrated in terms of blocks which carry out a described function or functions. These blocks, which may be referred to herein as managers, units, modules, hardware components or the like, are physically implemented by analog and/or digital circuits such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuits and the like, and may optionally be driven by a firmware. The circuits may, for example, be embodied in one or more semiconductor chips, or on substrate supports such as printed circuit boards and the like. The circuits constituting a block may be implemented by dedicated hardware, or by a processor (e.g., one or more programmed microprocessors and associated circuitry), or by a combination of dedicated hardware to perform some functions of the block and a processor to perform other functions of the block. Each block of the embodiments may be physically separated into two or more interacting and discrete blocks without departing from the scope of the disclosure. Likewise, the blocks of the embodiments may be physically combined into more complex blocks without departing from the scope of the disclosure.
[0030] It should be noted that elements in the drawings are illustrated for the purposes of this description and ease of understanding and may not have necessarily been drawn to scale. For example, the flowcharts/sequence diagrams illustrate the method in terms of the steps required for understanding aspects of the embodiments as disclosed herein. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the present embodiments so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Furthermore, in terms of the system, one or more components/modules which comprise the system may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the present embodiments so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
[0031] The accompanying drawings are used to help easily understand various technical features and it should be understood that the embodiments presented herein are not limited by the accompanying drawings. As such, the present disclosure should be construed to extend to any modifications, equivalents, and substitutes in addition to those which are particularly set out in the accompanying drawings and the corresponding description. Usage of words such as first, second, third etc., to describe components/elements/steps is for the purposes of this description and should not be construed as sequential ordering/placement/occurrence unless specified otherwise.
[0032] The embodiments herein achieve a continuously variable transmission (CVT) system for an electric vehicle. Further, embodiments herein achieve a method of operating the CVT system in the electric vehicle. Referring now to the drawings, and more particularly to Figs. 1 through 5, where similar reference characters denote corresponding features consistently throughout the figures, there are shown embodiments.
[0033] Fig. 1 depicts a block diagram of a continuously variable transmission (CVT) system (100) for an electric vehicle, according to embodiments as disclosed herein. The CVT system (100) includes an electric motor (102), a controller (104) provided in communication with the electric motor (102), a variable pulley mechanism (200), and an output shaft (110). For the purpose of this description and ease of understanding, the CVT system (100) is explained herein with below reference to achieving a continuously variable transmission in a three-wheeled electric vehicle. However, it is also within the scope of the invention to use/practice the components of the CVT system (100) for a two-wheeled, three-wheeled, and a four-wheeled electric vehicle, and any other hybrid vehicle without otherwise deterring the intended function of the CVT system (100) as can be deduced from the description and corresponding drawings.
[0034] Figs. 2A, 2B, and 2C depict a top view, a front view, and a sectional view of the CVT system (100), according to embodiments as disclosed herein. Fig. 3A depicts an exploded view of the variable pulley mechanism (200), according to embodiments as disclosed herein. The variable pulley mechanism (200) includes a primary pulley (202) operatively coupled to the electric motor (102), and a secondary pulley (204) operatively coupled to the primary pulley through a belt (206), wherein each of the primary pulley (202) and the secondary pulley (204) have an adjustable effective diameter. The output shaft (110) is operatively coupled to the secondary pulley (204) and configured to transfer power to a differential (10) of the electric vehicle. Further, the controller (104) is configured to control the operation of the electric motor (102) to regulate its rotational speed. The effective diameters of the primary pulley (202) and the secondary pulley (204) are continuously adjustable based on the rotational speed of the electric motor (102). The continuous adjustment of the effective diameters of the primary pulley (202) and the secondary pulley (204) provides a continuously variable gear ratio, thereby enabling smooth power transmission and efficient torque delivery to the differential (10) based on the rotational speed of the electric motor (102).
[0035] The controller (104) is configured to receive a throttle position signal from a vehicle throttle (12). In response to this signal, the controller (104) regulates the rotational speed of the electric motor (102), thereby controlling the power output of the CVT system (100). The electric motor (102) operates within a plurality of rotational speed ranges, including a low rotational speed range, a high rotational speed range, and a maximum rotational speed range. Operation of the electric motor (102) in the low rotational speed range results in a high gear ratio and increased torque at the output shaft (110). Conversely, operation of the electric motor (102) in the high rotational speed range yields a low gear ratio and increased speed at the output shaft (110). Operation in the maximum rotational speed range provides a gear ratio of less than 1, optimizing speed at the output shaft (110). The gear ratio is dynamically adjusted by the continuous variation of the effective diameters of the primary pulley (202) and the secondary pulley (204) in response to changes in the rotational speed of the electric motor (102).
[0036] In an embodiment, the electric motor (102) is a permanent magnet synchronous motor (PMSM). However, it is within the scope of this invention to have any other type of electric motor (102) such as but not limited to axial flux motor, brushless DC motor, synchronous reluctance motor, switched reluctance motor, and induction motor. To facilitate precise control, the CVT system (100) incorporates a position-sensing module (120) configured to detect the rotor position of the electric motor (102). The controller (104) receives a rotor position signal from the position-sensing module (120) and determines both a current magnitude to supply to the electric motor (102) based on the throttle position signal, and a driving sequence for the electric motor (102) based on the rotor position signal, thereby accurately regulating the rotational speed of the electric motor (102).
[0037] Fig. 3B depicts an exploded view of the primary pulley (202), according to embodiments as disclosed herein. The primary pulley (202) is operatively coupled to the electric motor (102) via a connecting shaft (208), ensuring synchronous rotation. The primary pulley (202) includes a fixed sheave (202A) coaxially mounted on the connecting shaft (208), a movable sheave (202B) coaxially mounted on the connecting shaft (208) and axially displaceable, and a plurality of flyweights (202C) coupled to the movable sheave (202B). The centrifugal force generated by the flyweights (202C) due to the rotational speed of the electric motor (102) causes the movable sheave (202B) to axially displace, thereby adjusting the effective diameter of the primary pulley (202). Fig. 3C depicts an exploded view of the secondary pulley (204), according to embodiments as disclosed herein. The secondary pulley (204) includes a first sheave (204A) coaxially received on the output shaft (110) and axially displaceable, and a second sheave (204B) splined to the output shaft (110), ensuring synchronous rotation of the output shaft (110) with the secondary pulley (204). The axial displacement of the first sheave (204A) is mechanically linked to the axial displacement of the movable sheave (202B), such that the effective diameter of the secondary pulley (204) is adjusted relative to the effective diameter of the primary pulley (202), maintaining belt (206) tension and ensuring continuous power transmission to the output shaft (110) and the differential (10).
[0038] The variable pulley mechanism (200) further includes a tensioning member (210) coupled to the first sheave (204A) of the secondary pulley (204), mounted on the output shaft (110). The tensioning member (210) is configured to compress when the first sheave (204A) is displaced away from the second sheave (204B), thereby decreasing the effective diameter of the secondary pulley (204), and expand to displace the first sheave (204A) towards the second sheave (204B), thereby increasing the effective diameter of the secondary pulley (204).
[0039] In an embodiment, the controller (104) regulates the rotational speed range of the electric motor (102) by receiving the throttle position signal from the vehicle throttle (12), monitoring the real-time rotational speed of the electric motor (102) through the rotor position signal, comparing the real-time rotational speed with predefined threshold speed values stored in a memory, and adjusting the rotational speed by dynamically controlling the current magnitude and driving sequence supplied to the electric motor (102). The low rotational speed range is identified when the real-time rotational speed is below a first threshold speed value, the high rotational speed range is identified when the real-time rotational speed is between the first threshold speed value and a second threshold speed value, and the maximum rotational speed range is identified when the real-time rotational speed is equal to or above the second threshold speed value. In a non-limiting example, the first threshold value ranges between 2400 rpm to 2500 rpm, and the second threshold speed value ranges between 7499 rpm to 7999 rpm.
[0040] During operation of the electric motor (102) in the low rotational speed range, the primary pulley (202) rotates at a relatively low speed, resulting in minimal flyweight (202C) engagement. The tensioning member (210) expands, decreasing the distance between the first sheave (204A) and the second sheave (204B), increasing the effective diameter of the secondary pulley (204), thereby amplifying torque at the output shaft (110). During operation in the high rotational speed range, the primary pulley (202) rotates at a relatively high speed, resulting in outward flyweight (202C) movement and axial displacement of the movable sheave (202B). The tensioning member (210) compresses, increasing the distance between the first sheave (204A) and the second sheave (204B), decreasing the effective diameter of the secondary pulley (204), thereby increasing the rotational speed of the output shaft (110) without increasing the voltage supplied to the electric motor (102), providing efficient power transmission for high-speed operation.
[0041] The effective diameter of the primary pulley (202) is controlled by the flyweights (202C), which are pivotally mounted on the movable sheave (202B) of the primary pulley (202). As the electric motor’s (102) speed increases, the centrifugal force acting on the flyweights (202C) causes them to move radially outward, thereby decreasing the effective diameter of the primary pulley (202). Given that the distance between the primary pulley (202) and the secondary pulley (204) and the belt’s (206) length remain constant, simultaneous adjustment of both pulleys (202, 204) (one larger, the other smaller) is necessary to maintain proper belt tension. The tensioning member (210), utilized in conjunction with the secondary pulley (204), counteracts the centrifugal force of the flyweights (202C) as the electric motor’s (102) rotational speed decreases. The increasing force of the tensioning member (210) results in a reduction of the primary pulley’s (202) effective diameter and an increase in the secondary pulley’s (204) effective diameter.
[0042] Further, to optimize control and reduce transmission losses, the controller (104) is mounted directly on the electric motor (102). In an embodiment, the controller (104) implements a field-oriented control method, which involves decomposing a stator current into a magnetic field-generating current and a torque-generating current. This allows the controller (104) to independently control the magnetic field-generating current and the torque-generating current, providing precise and efficient control of the electric motor (102).
[0043] An example of the field-oriented control (FOC) technique, employed to regulate the speed of the electric motor (102), is as follows. The FOC method necessitates rotor position feedback, acquired from the position-sensing module (120). This module measures the rotor's position by varying its output voltage in response to the applied magnetic field's strength. The position-sensing module (120) may comprise sensors, including but not limited to, hall sensors and position encoders. For instance, when a current-carrying conductor or semiconductor is placed within a magnetic field perpendicular to the current flow, a Hall voltage is generated orthogonal to both the current and the magnetic field. This Hall voltage is proportional to the magnetic field's strength, enabling the sensor to detect its presence, absence, or intensity. In the electric motor (102), permanent magnets embedded within the rotor create a rotating magnetic field as the rotor spins. Hall sensors, positioned at specific intervals (typically 120° or 60° for three-phase motors) around the stator, detect the rotor's position relative to the stator windings. As rotor magnets pass over each Hall sensor, the sensor outputs a digital signal (HIGH or LOW), indicating the magnetic field's presence. The combination of signals from multiple sensors provides the rotor's precise position. In an embodiment, the position-sensing module (120) includes three Hall sensors, electrically spaced 120 degrees apart. This setup enables the electric motor (102) to provide six valid binary state combinations (e.g., 001, 010, 011, 100, 101, and 110). The Hall sensor provides the rotor's angular position in multiples of 60 degrees, which the controller (104) uses to compute angular velocity. Subsequently, the controller (104) computes the rotor's accurate angular position using this angular velocity.
[0044] In an embodiment, the controller (104) is further configured to convert a DC voltage and a DC current received from a power supply (14) of the electric vehicle into AC voltage and an AC current. This conversion is achieved using at least a pulse width modulation technique, specifically a space vector pulse width modulation technique. This technique ensures efficient and precise power delivery to the electric motor (102), optimizing performance and minimizing energy losses. In an embodiment, the power supply (14) includes one or more batteries, not explicitly shown. The controller (104) is configured to convert the input power into a three-phase current, which is then supplied to the electric motor (102). In an embodiment, the aforementioned batteries are the vehicle's primary power source. The controller (104) optimizes thermal dissipation using air cooling mechanisms, including but not limited to forced convection.
[0045] In an embodiment, the controller (104) is protected by a cover, which facilitates heat dissipation and shields the controller (104) and related components from external environmental factors such as rain, water, and dust. In certain embodiments, the controller (104) is IP65 protected. The controller (104) further comprises additional components, including but not limited to heatsinks, power cables, and fuses, not explicitly shown.
[0046] Further, in an embodiment, the variable pulley mechanism (200) incorporates a cam assembly (300). This cam assembly (300) includes a first sleeve (302) having a cam profile (302C), connected to the first sheave (204A) of the secondary pulley (204), and a second sleeve (304) connected to the second sheave (204B) of the secondary pulley (204). The first sheave (204A) is coaxially mounted on the second sleeve (304) and movably engaged by a plurality of pins (306) received within the cam profile (302C), facilitating axial displacement of the first sheave (204A) (shown in fig. 3C). The cam profile (302C) is configured to provide progressive resistance to the movement of the first sheave (204A) and, consequently, the movement of the tensioning member (210), as the belt (206) tension changes.
[0047] The cam profile (302C) of the cam assembly (300) has a generally triangular shape (shown in figs. 4A to 4D). Each pin (306) slides within the cam profile (302C) in response to changes in the rotational speed of the electric motor (102). Each pin (306) slides upward along a first side (302CF) of the cam profile (302C), guiding axial movement of the first sheave (204A) as the tensioning member (210) compresses with an increase in the rotational speed of the electric motor (102). Further, each pin (306) slides downward along the same first side (302CF) as the tensioning member (210) expands with a decrease in the rotational speed of the electric motor (102) (shown in figs. 4A). Each pin (306) also slides along a second side (302CS) of the cam profile (302C) (shown in figs. 4B and 4C), allowing rotation of the output shaft (110) in a reverse direction when the electric motor (102) operates in a reverse direction during operation of the electric vehicle in a reverse mode. The inclination of the first side (302CF) of the cam profile (302C) is configured to control the deflection of the tensioning member (210), allowing gradual compression of the tensioning member (210). The inclination of the second side (302CS) is configured to control the movement of the first sheave (204A) in the reverse direction, enabling rotation of the output shaft (110) in the reverse direction.
[0048] Furthermore, the CVT system (100) includes a support member (130) coupled to the output shaft (110). This support member (130) is preferably a needle bearing, configured to provide stable and efficient rotational support for the output shaft (110), minimizing friction and ensuring smooth power transfer to the differential (10) (shown in fig. 2C).
[0049] In an embodiment, the variable pulley mechanism (200) includes a first sleeve cover (230) configured to be coaxially mounted on the first sleeve (302), a plurality of O-rings (232), and a plurality of seals (234), positioned on the first sleeve (302) (shown in fig. 3C). The plurality of O-rings prevent leakage of lubricant from the variable pulley mechanism (200). The seals (234) guide the movement of the first sheave (204A), enabling smooth gliding over the first sleeve (302). The O-rings (232) and seals (234) are therefore provided to ensure a smooth gliding motion of the first sheave (204A), and also protect the inside components from dust and debris. Furthermore, the variable pulley mechanism (200) includes a stopper (236) (shown in fig. 3C), located at the tensioning member's (210) end, wherein the stopper (236) holds the tensioning member (210) in place, ensuring correct preload and alignment. In an embodiment, components mounted on the output shaft (110) are secured by a fastener (238) . Further, a lock nut (240) secures the entire assembly, ensuring proper preload and alignment, and preventing component loosening during operation (shown in fig. 3C).
[0050] In a non-limiting example, the gear ratio varies between 4 to 1 during the operation of the electric motor (102) in the low rotational speed range. During the operation of the electric motor (102) in the high rotational speed range, the gear ratio varies between 1 to 0.5. These specific gear ratio ranges provide optimal torque and speed performance for the electric vehicle. The CVT system (100), in conjunction with the electric motor (102), enables continuous gear changes and a wide gear ratio range by adjusting the primary (202) and secondary (204) pulley diameters. The CVT system (100), in conjunction with the electric motor (102), therefore allows for easy gear ratio adjustment to suit various vehicle installations.
[0051] Fig. 5 depicts a flowchart of a method (400) for operating the continuously variable transmission (CVT) system (100) in the electric vehicle, according to embodiments as disclosed herein. At step (402) the method (400) includes receiving, by the controller (104), the throttle position signal from the vehicle throttle (12). At step (404), the method (400) includes, regulating, by the controller (104), the rotational speed of the electric motor (102) in response to the throttle position signal, wherein the electric motor (102) operates within the plurality of rotational speed ranges. In an embodiment, step (404) includes at step (404A), determining, the current magnitude to supply to the electric motor (102) based on the throttle position signal. Further, step (404) includes at step (404B), determining, the driving sequence for the electric motor (102) based on the rotor position signal received from the position-sensing module (120). At step (406), the method (400) includes, adjusting, based on the rotational speed of the electric motor (102), the effective diameters of the primary pulley (202) and the secondary pulley (204), thereby providing a continuous variable gear ratio. In an embodiment, step (406) includes at step (406A), axially displacing, the movable sheave (202B) of the primary pulley (202) in response to centrifugal force generated by flyweights (202C) coupled to the movable sheave (202B). Further, step (406) includes at step (406B), axially displacing, the first sheave (204A) of the secondary pulley (204) in coordination with the movable sheave (202B) displacement, wherein the tensioning member (210) coupled to the first sheave (204A) restricts the axial displacement. Furthermore, at step (408), the method (400) includes, transferring, via the output shaft (110), power from the secondary pulley (204) to the differential (10) of the electric vehicle, wherein the continuously variable gear ratio enables smooth power transmission and efficient torque delivery.
[0052] The technical advantages of the CVT system (100) for the electric vehicle, along with the method (400) for operating this system, are as follows. The CVT system (100) enhances the efficiency of the electric vehicle by reducing transmission losses through a direct coupling with the vehicle's electric motor (102), eliminating the need for a centrifugal clutch, which ensures optimal utilization of the motor's efficient rotational speed range. Additionally, the CVT system (100) allows for continuous gear ratio changes, promoting efficient operation of the electric motor (102) and improving vehicle performance. Moreover, the CVT system (100) integrates reverse gear functionality, enhancing vehicle maneuverability and operational ease. Furthermore, the CVT system (100) supports compact packaging, facilitating easier installation and integration into electric vehicles. It also boosts the electric motor’s electromagnetic, mechanical, and thermal efficiency, resulting in longer ranges with reduced battery consumption. The method (400) optimizes the electric motor's performance through continuous and dynamic gear ratio adjustments.
[0053] The embodiments disclosed herein may be implemented through at least one software program running on at least one hardware device and performing network management functions to control the network elements. The elements include blocks which may be at least one of a hardware device, or a combination of hardware device and software module.
[0054] The embodiments disclosed herein describe systems and methods for controlling an electric vehicle continuously variable transmission. Therefore, it is understood that the scope of the protection is extended to such a program and in addition to a computer readable means having a message therein, such computer readable storage means contain program code means for implementation of one or more steps of the method, when the program runs on a server or mobile device or any suitable programmable device. The method is implemented in at least one embodiment through or together with a software program written in e.g., Very high speed integrated circuit Hardware Description Language (VHDL) another programming language, or implemented by one or more VHDL or several software modules being executed on at least one hardware device. The hardware device i.e. the controller (104) may be any kind of portable device that may be programmed. The controller (104) may also include means which could be e.g., hardware means like e.g., an ASIC, or a combination of hardware and software means, e.g. an ASIC and an FPGA, or at least one microprocessor and at least one memory with software modules located therein. The method embodiments described herein could be implemented partly in hardware and partly in software. Alternatively, the invention may be implemented on different hardware devices, e.g., using a plurality of CPUs.
[0055] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others may, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of embodiments, those skilled in the art will recognize that the embodiments herein may be practiced with modification within the scope of the embodiments as described herein.
, Claims:We claim:
1. A continuously variable transmission (CVT) system (100) for an electric vehicle, the CVT system (100) comprising:
an electric motor (102) configured to operate at a plurality of rotational speed ranges;
a controller (104) provided in communication with the electric motor (102), wherein the controller (104) is configured to control the operation of the electric motor (102) to regulate its rotational speed;
a variable pulley mechanism (200) comprising:
a primary pulley (202) operatively coupled to the electric motor (102), the primary pulley (202) having an adjustable effective diameter; and
a secondary pulley (204) operatively coupled to the primary pulley (202) through a belt (206), the secondary pulley (204) having an adjustable effective diameter; and
an output shaft (110) operatively coupled to the secondary pulley (204) and configured to transfer power to a differential (10) of the electric vehicle,
wherein:
the effective diameters of the primary pulley (202) and the secondary pulley (204) are continuously adjustable based on the rotational speed of the electric motor (102); and
the continuous adjustment of the effective diameters of the primary pulley (202) and the secondary pulley (204) provides a continuously variable gear ratio, thereby enabling smooth power transmission and efficient torque delivery to the differential (10) based on the rotational speed of the electric motor (102).
2. The CVT system (100) as claimed in claim 1, wherein the controller (104) is configured to:
receive a throttle position signal as input from a vehicle throttle (12);
regulate the rotational speed of the electric motor (102) by selectively increasing or decreasing the rotational speed of the electric motor (102) corresponding to the throttle position,
wherein the plurality of rotational speed ranges of the electric motor (102) comprise:
a low rotational speed range, wherein operation of the electric motor (102) in the low rotational speed range results in a high gear ratio and increased torque at the output shaft (110);
a high rotational speed range, wherein operation of the electric motor (102) in the high rotational speed range results in a low gear ratio and increased speed at the output shaft (110); and
a maximum rotational speed range, wherein operation of the electric motor (102) in the maximum speed range provides the gear ratio of less than 1, providing optimum speed at the output shaft (110),
wherein the gear ratio is adjusted by the effective diameters of the primary pulley (202) and the secondary pulley (204) changing in response to a change in the rotational speed of the electric motor (102).
3. The CVT system (100) as claimed in claim 2, wherein:
the electric motor (102) is a permanent magnet synchronous motor (PMSM);
the CVT system (100) includes a position-sensing module (120) configured to detect a rotor position of the electric motor (102); and
the controller (104) is configured to:
receive a rotor position signal from the position sensing module (120);
determine a current magnitude to supply to the electric motor (102) based on the throttle position signal; and
determine a driving sequence for the electric motor (102) based on the rotor position signal, thereby regulating the rotational speed of the electric motor (102).

4. The CVT system (100) as claimed in claim 3, wherein:
the primary pulley (202) is operatively coupled to the electric motor (102) via a connecting shaft (208), enabling synchronous rotation of the primary pulley (202) with the electric motor (102);
the primary pulley (202) comprises:
a fixed sheave (202A) coaxially mounted on the connecting shaft (208);
a movable sheave (202B) coaxially mounted on the connecting shaft (208) and axially displaceable; and
a plurality of flyweights (202C) coupled to the movable sheave (202B), wherein centrifugal force generated by the flyweights (202C) due to the rotational speed of the electric motor (102) causes the movable sheave (202B) to axially displace, thereby adjusting the effective diameter of the primary pulley (202);
the secondary pulley (204) comprises:
a first sheave (204A) coaxially received on the output shaft (110) and axially displaceable along the output shaft (110); and
a second sheave (204B) splined to the output shaft (110), thereby ensuring synchronous rotation of the output shaft (110) with the secondary pulley (204),
wherein the axial displacement of the first sheave (204A) of the secondary pulley (204) is mechanically linked to the axial displacement of the movable sheave (202B) of the primary pulley (202), such that the effective diameter of the secondary pulley (204) is adjusted relative to the effective diameter of the primary pulley (202), maintaining belt (206) tension and ensuring continuous power transmission to the output shaft (110) and the differential (10).
5. The CVT system (100) as claimed in claim 4, wherein the variable pulley mechanism (200) includes:
a tensioning member (210) coupled to the first sheave (204A) of the secondary pulley (204), mounted on the output shaft (110), wherein the tensioning member (210) is configured to:
compress when the first sheave (204A) is displaced away from the second sheave (204B), thereby decreasing the effective diameter of the secondary pulley (204); and
expand to displace the first sheave (204A) towards the second sheave (204B), thereby increasing the effective diameter of the secondary pulley (204).
6. The CVT system (100) as claimed in claim 5, wherein the controller (104) is configured to regulate the rotational speed range of the electric motor (102) by:
receiving the throttle position signal from the vehicle throttle (12) indicative of a desired power output;
monitoring a real-time rotational speed of the electric motor (102) through the rotor position signal received from the position-sensing module (120);
comparing the real-time rotational speed of the electric motor (102) with predefined threshold speed values stored in a memory associated with the controller (104),
wherein:
the low rotational speed range is identified when the real-time rotational speed is below a first threshold speed value;
the high rotational speed range is identified when the real-time rotational speed is between the first threshold speed value and a second threshold speed value;
the maximum rotational speed range is identified when the real-time rotational speed is equal to or above the second threshold speed value;
adjusting the rotational speed of the electric motor (102) by dynamically controlling the current magnitude and driving sequence supplied to the electric motor (102) based on the identified rotational speed range and throttle position signal.
7. The CVT system (100) as claimed in claim 5, wherein:
during the operation of the electric motor (102) in the low rotational speed range:
the primary pulley (202) rotates at a relatively low speed, resulting in minimal flyweight (202C) engagement;
the tensioning member (210) expands, decreasing the distance between the first sheave (204A) and the second sheave (204B), increasing the effective diameter of the secondary pulley (204), thereby resulting in high gear ratio, amplifying torque at the output shaft (110);
during the operation of the electric motor (102) in the high rotational speed range:
the primary pulley (202) rotates at a relatively high speed, resulting in outward flyweight (202C) movement and axial displacement of the movable sheave (202B);
the tensioning member (210) compresses, increasing the distance between the first sheave (204A) and the second sheave (204B), decreasing the effective diameter of the secondary pulley (204), thereby resulting in low gear ratio, increasing the rotational speed of the output shaft (110) without increasing the voltage supplied to the electric motor (102), providing efficient power transmission for high-speed operation of the vehicle.
8. The CVT system (100) as claimed in claim 1, wherein the CVT system includes a support member (130) coupled to the output shaft (110), wherein the support member (130) is a needle bearing configured to support rotation of the output shaft (110).
9. The CVT system (100) as claimed in claim 1, wherein the controller (104) is mounted on the electric motor (102) to reduce transmission losses, and wherein the controller (104) implements a field-oriented control method, and is configured to:
decompose a stator current into a magnetic field-generating current and a torque-generating current; and
control the magnetic field-generating current and the torque-generating current independently.
10. The CVT system (100) as claimed in claim 1, wherein the controller (104) is configured to convert a DC voltage and a DC current received from a power supply (14) of the electric vehicle into AC voltage and an AC current using at least a pulse width modulation technique which is supplied to the electric motor (102), and wherein the pulse width modulation technique comprises a space vector pulse width modulation technique.

11. The CVT system (100) as claimed in claim 4, wherein the variable pulley mechanism (200) comprises a cam assembly (300), comprising:
a first sleeve (302) having a cam profile (302C), connected to the first sheave (204A) of the secondary pulley (204);
a second sleeve (304) connected to the second sheave (204B) of the secondary pulley (204);
wherein
the first sheave (204A) is coaxially mounted on the second sleeve (304) and movably engaged by a plurality of pins (306) received within the cam profile (302C), enabling axial displacement of the first sheave (204A);
the cam profile (302C) is configured to provide progressive resistance to the movement of the first sheave (204A) and thereby movement of the tensioning member (210) as the belt (206) tension changes.
12. The CVT system (100) as claimed in claim 11, wherein:
the cam profile (302C) of the cam assembly (300) has a generally triangular shape;
each pin (306) slides within the cam profile (302C) in response to changes in the rotational speed of the electric motor (102);
each pin (302C) slides upward along a first side (302CF) of the cam profile (302F) guiding axial movement of the first sheave (204A) as the tensioning member (210) compresses, with an increase in the rotational speed of the electric motor (102);
each pin (306) slides downward along the first side (302CF) of the cam profile (302C) guiding axial movement of the first sheave (204A) as the tensioning member (210) expands, with a decrease in the rotational speed of the electric motor (102);
each pin (306) slides along a second side (302CS) of the cam profile (302C) allowing rotation of the output shaft (110) in a reverse direction, when the electric motor (102) operates in a reverse direction during operation of the electric vehicle in a reverse mode;
an inclination of the first side (302CF) of the cam profile (302C) is configured to control the deflection of the tensioning member (210) allowing gradual expansion and compression of the tensioning member (210);
an inclination of the second side (302CS) is configured to control the movement of the first sheave (204A) in the reverse direction, allowing rotation of the output shaft (110) in the reverse direction.

13. The CVT system (100) as claimed in claim 2, wherein:
the gear ratio varies between 4 to 1 during the operation of the electric motor (102) in the low rotational speed range; and
the gear ratio varies between 1 to 0.5 during the operation of the electric motor (102) in the high rotational speed range.

14. A method (400) for operating a continuously variable transmission (CVT) system (100) in an electric vehicle, the CVT system (100) comprising an electric motor (102), a controller (104), a variable pulley mechanism (200) including a primary pulley (202) and a secondary pulley (204) coupled by a belt (206), and an output shaft (110), the method (400) comprising:
receiving (402), by the controller (104), a throttle position signal from a vehicle throttle (12);
regulating (404), by the controller (104), a rotational speed of the electric motor (102) in response to the throttle position signal, wherein the electric motor (102) operates within a plurality of rotational speed ranges, and wherein the regulating (404) comprises:
determining (404A), a current magnitude to supply to the electric motor (102) based on the throttle position signal; and
determining (404B), a driving sequence for the electric motor (102) based on a rotor position signal received from a position-sensing module (120);
adjusting (406), based on the rotational speed of the electric motor (102), effective diameters of the primary pulley (202) and the secondary pulley (204), thereby providing a continuously variable gear ratio,
wherein the adjusting (406) comprises:
axially displacing (406A), a movable sheave (202B) of the primary pulley (202) in response to centrifugal force generated by flyweights (202C) coupled to the movable sheave (202B); and
axially displacing (406B), a first sheave (204A) of the secondary pulley (204) in coordination with the movable sheave (202B) displacement, wherein a tensioning member (210) coupled to the first sheave (204A) restricts the axial displacement; and
transferring (408), via the output shaft (110), power from the secondary pulley (204) to a differential (10) of the electric vehicle, wherein the continuously variable gear ratio enables smooth power transmission and efficient torque delivery.