Browse Topic: Continuously variable transmissions
This study investigates an optimal control strategy for a battery electric vehicle (BEV) equipped with a high-speed motor and a continuously variable transmission (CVT). The proposed dual-motor powertrain model activates only one motor at a time, with Motor A routed through a CVT and Motor B through a fixed gear. To improve energy efficiency, two optimization methods are evaluated: a quasi-steady-state map-based approach and a dynamic programming (DP) method. The DP approach applies Bellman’s principle to derive the globally optimal CVT ratio and motor torque trajectory over the WLTC cycle. Simulation results demonstrate that the DP method significantly improves overall efficiency compared to traditional control logic. Furthermore, the study proposes using DP-derived maps to refine practical control strategies, offering a systematic alternative to conventional experimental calibration.
This paper, explores the design and sizing of a planetary gear-based electronic continuously variable transmission (ECVT) for implementation of a parallel gas-electric hybrid helicopter propulsion system. The ECVT consists of a differential planetary gear transmission (PGT) and an electric motor/generator (MG) unit. The ECVT enables power-flow between engine, motor and helicopter main rotor. The parallel arrangement enables the main rotor speed to varied continuously based on the MG speed while the engine speed can remain constant. The performance benefits enabled by the main rotor speed variation capability are offset by the added weight penalties introduced by the ECVT system. By considering factors such a as gear tooth bending and contact stress, bearing loads, required motor torque, planetary gear kinematics and pitch-line velocity constraints, this paper conducts a minimum mass design study for several PGT / ECVT arrangements. Here, three different single stage PGT/ECVT arrangements are compared along with an improved two stage ECVT. The three single stage ECVT configurations can be summarized as; I) Sun-Engine / Carrier-Motor / Ring-Out, II) Sun-Engine / Ring-Motor / Carrier-Out, and III) Carrier-Engine / Sun-Motor / Ring-Out. Of these three types, it was found that type III was significantly lighter in weight compared with types I and II since type III would have the highest relative motor speed. When sized for a 3000 Hp engine-side power input at 6000 rpm, the minimum mass design for type III was on the order of 100 lbs compared to 400 lbs and 700 lbs respectively for types I and II. Despite the seemingly obvious advantage of design type III, it's drawback is that it is effectively a speed increasing stage with respect to the engine. To address this, a two-stage ECVT with compound planetary arrangement of Type III and II was designed which achieved an overall minimum weight of 219 lbs at the 3000 Hp level while providing 1:0.351 gear reduction form engine to output. The analysis tools developed and sizing results flowing from this study will provide a baseline for evaluating performance benefits and weight penalties introduced by parallel hybrid drive-systems for rotorcraft applications.
Due to the compact structure of the Bacha Racing vehicle, the continuously variable transmission (CVT) serves as a crucial transmission component. It is essential to tune and verify its performance to ensure the power matching and transmission efficiency of the entire vehicle. This paper conducts a kinematic analysis of CVT based on transmission theory, designs real vehicle traction experiments, and CVT bench tests. Additionally, it proposes a method to utilize Hall sensors for real-time monitoring of CVT motion to assist in its tuning. The results demonstrate that the optimal performance tuning of the CVT for the Bacha Racing vehicle has been achieved through various experiments.
In this paper, a comprehensive dynamic simulation of a parallel hybrid gas-electric single main rotor helicopter involving a motor/generator (MG) pair and a differential planetary gear transmission (PGT) arrangement forming an electronic continuously variable transmission (E-CVT) was performed. This notional hybrid electric helicopter was sized based on a retrofit of a dual engine, 10000 lb, 2500 Hp class helicopter. The total weight added by the electric components was 182 lbs which increased the propulsion system weight from 1184 to 1366 lbs. The simulation results found that at 110 kts cruise, the hybrid electric system enabled a 27% reduction in main rotor rpm which resulted in an 18% reduction in the fuel burn rate. It is concluded that use of an E-CVT parallel hybrid propulsion system offers potential for increased flight range and reduced fuel consumption in medium to large-scale helicopter applications.
This article presents an original methodology for the multi-objective optimization of Continuously Variable Transmission (CVT) for a wind turbine (WT). The objective functions of this optimization problem are to minimize the weight and maximize efficiency. This methodology also considers the variations of parameters caused by different factors (manufacturing tolerance, uncertainties in the operating conditions). Using a probabilistic model, the proposed algorithm combines a propagation of uncertainties and an optimization of the function objectives. The optimization is performed using the Non-dominated Sorting Genetic Algorithm (NSGA-II) with the advantage of exploring the global design space and finding the best compromise between the objectives. In order to verify the solution obtained by this approach, results were compared to the ones obtained by a previous study.
An all-terrain vehicle (ATV) is capable of traveling on any kind of surface or terrain. It is built especially for extreme road conditions. High ground clearance and soft suspension springs are some of the characteristics of an ATV. The use of a four-wheel-drive (4WD) transmission in a light ATV is in high demand. Power on all four tires provides better traction and increases the off-roading capabilities of the ATV. The methodology described in the paper discusses the design and validation of a four-wheel driveline for a light ATV using various modeling and simulation software. Briggs and Stratton engine is coupled with a continuously variable transmission (CVT) to provide infinite ratios within its tuned range to deliver effortless shifting. A two-stage reduction gearbox is used to multiply the torque received from the CVT to provide sufficient traction to the tires. Power is transferred to the front differential via a propeller shaft. A shifting mechanism is installed for shifting between two-wheel-drive (2WD) and 4WD. Components are designed in SolidWorks and Fusion 360 is used for parametric iterations. The analysis is done on driveline components using Ansys and HyperWorks for material selection and to validate their durability. The performance of the driveline is mapped using MATLAB Simscape and Simulink models. This research paper aims to lay a foundation for future developments in the driveline used in a light ATV.
Hydrostatic torque modulation is a new, at moment theoretical approach, to developing advanced AWD4WD transmissions. The basic component is a rotational hydrostatic modulator. It is derived from a low-speed high-torque hydrostatic machine. As such, it can be integrated into a standard mechanical AWD4WD transmission as a replacement for the clutch, where torque is controlled through energy dissipation. Controlled by a simple solenoid valve, it provides torque vectoring with a reaction time shorter than 0.5 s, and it provides additional safety features that result in a more robust AWD4WD transmission. As it can modulate torque with energy flow control/transfer, it offers much more than existing systems based on controlled clutches. Specifically, hydrostatic torque modulation, when it is integrated into the AWD4WD transmission, brings CVT or ICT performance. As torque modulation is performed through the control of the energy flow, it provides torque control from 0 km/h without using a clutch. This option is relevant in extreme situations where standard solutions cause heat buildup that slows the advancement in order to protect the clutch from burning out. With the introduction of a hydrostatic torque modulator, for each wheel, allows for maneuvering similar to tracked vehicles i.e. the option of 180° spot turns. In addition, the technology can be integrated into mild hybrid vehicles with 48 V starter-generators. Such vehicles are thus transformed it into AWD4WD vehicles with ZEV options in traffic jams at speed limits of 40 km/h, and optional torque vectoring at speed limits well above 100 km/h. In addition, advanced suspensions can be developed.
This SAE Aerospace Recommended Practice (ARP) outlines the design and performance requirements for a battery-powered electric tow tractor for the handling of baggage or cargo trailers in airline service. The use of “shall” in this document indicates a mandatory requirement. The use of “should” indicates a recommendation or that which is advised but not required.
The Continuously Variable Transmission (CVT) is a widely adopted transmission system. The operation of a CVT is simple, but successfully foretelling the longitudinal motion of a vehicle that utilizes this transmission is sophisticated. As a result, different vehicles taking part in BAJA-SAE competitions were developed using various strategies to model the vehicle’s longitudinal dynamics and CVT operation. This article aims to provide a tool for obtaining a quantitative estimate of the longitudinal performance of a CVT equipped vehicle and for the selection of an optimal drive-train gear ratio for such a vehicle. To this end, this article proposes a novel, relatively simple, and reasonably accurate mathematical approach for modeling the longitudinal motion of a vehicle utilizing a CVT, which was developed by a novel integration of existing vehicle dynamics concepts. The proposed technique splits the longitudinal motion into three distinct phases - low ratio acceleration, shifting, and over-run - and uses mathematical modeling to simulate each stage. The low ratio acceleration and over-run stages were modeled using an iterative approach based on Newton’s equations of motion, taking into account engine torque and aerodynamic drag variation. On the other hand, the shifting stage was modeled using a differential equation that governs the vehicle’s motion during the said stage. The technique was made more ‘realistic’, another novel aspect, by taking into account the effect of rotating masses. The proposed approach’s potency was validated through experimental validation studies on BAJA-SAE All-Terrain Vehicles (ATVs). It is concluded that the proposed modeling technique largely simplifies the motion simulation task while giving a relatively accurate estimate of the vehicle’s actual longitudinal performance. An All-Terrain Vehicle for the BAJA SAE collegiate competitions forms this cornerstone of this article.
The Continuously Variable Transmission (CVT) is a popular form of automotive transmission that uses friction between a belt and pulley to transmit power. Due to the sliding and other losses associated with the belt, power is lost in the form of heat, which must be dissipated to enhance the belt’s life. The task of heat dissipation is, however, complicated by the use of a CVT casing, which serves to protect the transmission from mud, debris, etc. Consequently, the design of an optimum CVT casing for efficient cooling is a challenging task. Experimental approaches or 3D numerical simulation approaches to tackling such problems are either involved or time-consuming or both. This article discusses a novel and simplified strategy for optimizing a CVT casing for maximum heat removal, using computational fluid dynamics (CFD). The rotating pulleys are approximated as heated, rotating cylinders inside a two-dimensional flow domain of the casing. Transient CFD calculations are carried out on a practical CVT configuration in Ansys® Fluent, using the Shear Stress Transport k-ω turbulence model, for a total of nine different geometrical configurations. The effectiveness of a configuration is judged based on the surface heat flux from the pulleys. The practicality of the proposed approach is verified by a systematic comparison with three-dimensional simulations. It is observed that the simplified two-dimensional methodology can effectively supplant extensive three-dimensional simulations for determining the best CVT casing configuration. The novelty of this study is an emphasis on CVT casing optimization and in the reductionist nature of the simulations which allows for time-efficient transient simulations and simulating the boundary layers effectively. Transient boundary-layer simulations are computationally intensive for 3D simulations and have been neglected in the existing literature. The methodology proposed in this article also aims to provide grounds for further fluid flow research specific to the domain of cooling of continuously variable transmissions.
Passenger utility vehicles like car, SUVs, MPVs are used in wide application all over the world. Luxuries are becoming essential features of product mix along with comfort and ergonomics. Customer desires best shift quality with emerging technologies like AT, DCT, CVT, etc. and every OEM is working hard to achieve it. It is very difficult to satisfy the customer desire because of diversities in demographics and geographic. Gear shift quality (GSQ) is very crucial touch point in overall drive feel of vehicle. It consist of various parameters like mode selection feel, precision, comfort, select Noise, etc. It demands tradeoff practices among various parameters as stated. In this paper, external mode selection system of automatic transmission is explained. Various contributing parameters are explained with practical design approach for detent profile, mode selection mechanism, cable & dampers, etc. Among various GSQ parameters, in-cabin noise occurred during mode selection is also one of the crucial parameters. This paper thoroughly explains inter-relation between different parameters of GSQ and its effect on mode selection noise and feel; this is explained with help of various DOEs and relation matrix. In this study various practical approaches are explained to reduce in-cabin noise and to improve shift feel without making any changes inside gearbox parameters. The intensity and causes of different parameters are explained with help problem solving tool and fish bone diagrams in the later part of paper. The conclusion is derived by referring the interrelationship matrix to decide the priority of critical contributing factors with optimized cost for reducing cabin noise & thereby improve gear shift feel.
A new Cruise Control Algorithm (CCA) commanding the Internal Combustion Engine (ICE) and the Continuous Variable Transmission (CVT) of a 200 hp tractor was implemented on a Rapid Prototyping System (RPS) and successfully tested with an empty vehicle and with 16 t trailer from 0.5 to 50 kph. Low velocities required an extra controller and a good concept for transition to higher velocities.
The following article aims to compare the performance parameters between a continuously variable transmission (CVT) and a 6-gear manual transmission. The manual transmission is a usual type of transmission system, consisting in a clutch and a transmission gearbox, containing a set of gears which, according to the coupling chosen, creates a reduction between the speed of the engine and the gearbox output. Meanwhile, the continuously variable transmission (CVT) is a type of transmission that outputs any reduction, between certain limits, in a continuous way, from two pulleys linked through a metallic belt. Due to the characteristics of both transmission systems, it is possible to infer that there are differences on the vehicle’s performance. The comparison between both types of transmissions, applied to a passenger’s vehicle is done through the mathematical modeling considering the same usage profile. Thus, parameters such as vehicle speed, traveled distance, engine speed and transmission reduction were obtained by the dynamic computational analysis and compared, explicating advantages and disadvantages of each system.
In order to improve the mode switching performance of parallel hybrid electric vehicles (PHEV) and make better use of the dynamics of the vehicle, this paper proposes a three-stage control method for the start-up mode of start-up, speed synchronization, and clutch slip based on the response characteristics of actual vehicle components and the complex working conditions of the actual road. In the speed synchronization phase, a coordinated control method of “engine speed active following + continuously variable transmission (CVT) speed ratio motor speed limiting” is proposed. The real vehicle test results show that the engine starting-up coordinated control method can significantly accelerate the speed synchronization and shorten the starting-up mode duration during the rapid acceleration, so that the vehicle’s power performance can be well played and the ride comfort can be effectively guaranteed.
Baja SAE is an intercollegiate competition where teams design and build a single-seat off-road vehicle that is powered by a 10 HP Briggs & Stratton engine. Due to this power constraint, it is crucial to optimize the vehicle’s weight and performance. The design process began by creating a vehicle dynamics simulation, which included engine performance, continuously variable transmission (CVT) shifting, tire slipping, vehicle mass, rotational inertia, air drag, rolling resistance, weight shift, and drivetrain efficiency. These calculations predicted the time to reach 100 ft and the top speed for various gear box ratios to aid in gear ratio selection. The rotational inertia of the drivetrain is 40% of the total effective mass of the vehicle when the CVT primary is engaged and 12% when the CVT has fully shifted into a numerically lower gear, with the largest contribution coming from the inertia of the CVT primary pulley. A sensitivity analysis showed that the vehicle mass and coefficient of friction between the tires and ground have the largest effect on gear ratio selection and times to reach 100 ft. A compound gear train was designed with gears having a minimum diameter and face width to reduce the inertia of the system and included calculation of static and fatigue failure from contact and bending stresses. The gearbox housing, shafts, and bearings were designed, manufactured, and integrated into the vehicle. Vehicle simulations were compared to testing results and showed good agreement in the cases tested. The final gearbox weighed 36% lighter than previous designs and had a 4% decrease in 100 ft times.
This research paper concentrates on BAJA ATV CVT premises thermal cooling. BAJA event has a 4-hour endurance run, which demands full potential from the drivetrain. In our drive train assembly, we have used CVT coupled with fixed reduction gearbox, while having long run the temperature of CVT unit increases so much that it hinders the efficiency. The main heat generation sources in the CVT chamber is the engine, friction between belt and sheaves, and high ambient outside. It is learned that CVT working temperature should be reduced. Hence cooling was much required for optimum performance of our vehicle, implemented cooling system involves insulation of CVT from engine while having a passive heat exchanger using super absorbent polymer inside our vehicle to inject cool air on CVT and using insulating material on CVT cover to reduce the overall temperature, whereas passive heat exchanger cools down the injected air. All this leads to significant temperature drop in whole assembly.
The RADIALcvt is a traction drive continuously variable transmission (CVT) implemented in a new novel radial configuration mechanical assembly. The RADIALcvt functions as a multi-parallel power path (at least six) type of CVT, which consists of only one steel-on-steel, line contact, traction drive interface in each power path. A constant input radius on the traction drive input makes it possible to use a constant clamping force, which is provided by mechanical springs, thus eliminating the need for a hydraulic control system. The RADIALcvt has a very large radius variation on the traction drive output, which provides the ratio variation. The test and simulation results of the first RADIALcvt prototype was published in [1] and presented mechanical efficiencies above 90%. This article presents the simulation and test results of the second-generation RADIALcvt prototype, which presents mechanical efficiencies above 94% and includes measured parameters of mechanical efficiency, slip, traction curves, and ratio torque at different loads while providing excellent partial load versus mechanical efficiency properties. A methodology for predicting the efficiency map using the no load torque loss is also proposed.
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