Browse Topic: Friction clutches
High-temperature hydraulic control in a Formula 1 drivetrain requires dimensional stability, controlled sealing force, and resistance to wear under sustained pressure cycling. Inside the limited-slip differential, the sealing architecture plays a defined mechanical role in maintaining consistent torque management under race conditions. In Formula 1, drivetrain reliability and performance are closely linked. The limited-slip differential (LSD) governs torque distribution between the rear wheels, allowing controlled transfer of power to the wheel with greater available grip. By limiting speed difference across the rear axle, the differential contributes directly to traction and cornering behavior, particularly where grip levels vary across the vehicle. At the center of this assembly is a hydraulic actuator that clamps a friction clutch inside the differential. The actuator modulates clutch engagement to redirect torque as grip levels change through corner entry, mid-corner load transfer, and acceleration on exit. Its performance depends on precise hydraulic control, which in turn depends on sealing integrity. Within this system, seal integrity is paramount, as significant leakage could cause a catastrophic loss of system function and force the team to retire the car.
During some critical maneuvers, transmission systems using Dual Mass Flywheel (DMF) may experience overtorques, which could lead to structural damages of the transmission components. In a dual mass flywheel, total inertia is divided into two parts: a primary mass connected to the engine and a secondary mass to the transmission. The torque delivered by the engine is transferred from one mass to the other through a drive plate and a set of arc springs, the latter absorbing the torsional oscillations coming from internal combustion engine and the shocks caused by fast clutch engagements. This paper investigates overtorque issues and proposes a solution based on a torque limiter, consisting of a friction clutch inserted between the two masses, that limits the maximum torque transmitted through it. The basic idea is to replace the classic flat drive plate with a tapered drive plate that functions as a Belleville spring. The experimental analysis carried out on dedicated benches has tested the elastic characteristic of the tapered drive plate, the durability of friction pads and the variation of the slipping torque over time. This article analyzes the torque limiter benefits through a detailed torsional dynamic model implemented in Simcenter Amesim. Overtorque phenomena are excited during cranking-in-gear vehicle launch tests on different slopes. Furthermore, a simplified multi-degree of freedom transmission model developed in Matlab/Simulink is shown; it allows calculating frequency response functions, natural frequencies, mode shapes and overtorque limitation. The comparison between the two models revealed that even the simplified model is capable of predicting the main dynamic aspects involved in the overtorque phenomenon and the positive effect of the torque limiter.
The following listed definitions are intended to establish terminology and criteria for describing the various kinds of automotive transmissions. A specific arrangement may be described by a combination of several of these definitions.
The inertial continuously variable transmission is a mechanical transmission which is based on the principle of inertia. This transmission has a lot of advantages, namely: compactness, minimum friction losses and high efficiency as a result of the relatively small number of rotating components, a wide range of transformation of the torque. It does not need any conventional friction clutches. This transmission protects the engine from overload when the output shaft is braked. This drive guarantees optimum conditions of work for the engine regardless of the changing of load, and smoothly changes output speed according to the load. Mostly, design of this transmission consists of a pulsed mechanism with unbalanced inertial units and two overrunning clutches. The objects of the investigation are structural dynamic analysis of the continuously variable transmission. The physical and mathematical models of this transmission are developed. For these models of the transmission the differential equations of structural dynamics in the form of second kind Lagrange's equations were developed. Dynamics of the transmissions is described by systems of substantial nonlinear differential equations. In general, precise methods of solution for such equations do not exist. Therefore, in practice, approximate analytical and numerical methods must be employed. Each approach has its advantages and disadvantages. Besides, the nonlinear differential equations were solved on the basis of Runge-Kutta numerical method. The described methods allow increasing the durability of the transmission and created transmission with higher level of reliability in comparison with existing designs of such a kind of transmissions. In this paper, a new design of the inertial transmission with only one overrunning clutch is suggested. This transmission provides a high level of the load ability. Besides, the periodic solutions of the equations were also received by means of the numerical methods. Optimal working modes of the transmission were found using these periodical solutions.
With the introduction of new regulations on emissions, fuel efficiency, driving cycles, etc. challenges for the powertrains are significantly increasing. In order to fulfil these regulations, hybrid-electric powertrains are an unquestioned option for short and long-term solutions. Hybridization however, is not only fulfilling these challenging efficiency or emission targets, but also allows numerous new possibilities on control strategies of different powertrain elements as well as new approaches of designing them. A good example is transmissions where, hybridization allows a new transmission type called Dedicated Hybrid Transmission (DHT), which enables to use novel control strategies bringing improved performance, driveability, durability and NVH behavior. This paper focuses on the novel shift strategy where friction clutches do not have to slip. The strategy introduces a novel shifting control using the integrated electric motor and special power flow of the dedicated hybrid transmissions. The novel shift strategy significantly improves shift comfort, thermal losses and element durability. In addition, several design aspects are challenged by proposing questions like selection of dog clutches over friction clutches, usage of eCVT modes in DHT and how a DHT shall be designed,.
Electric Vehicles (EVs) with single-ratio gearbox provide high levels of smoothness, but using multi-speed gearbox can provide significant benefits in terms of vehicle acceleration, top speed, powertrain cost, mass, and energy consumption. In particular, Automated Manual Transmissions (AMTs) have characteristics of smooth shifts without torque interruption when coupled to a torque bypass clutch. However, conventional friction clutches are not best suited as torque bypass clutches because of their limited controllability and because large amount of heat must be dissipated to slow down the motor during gearshifts. This paper studies the feasibility of a seamless AMT architecture for EVs and Hybrid Electric Vehicles (HEVs) using an eddy current torque bypass clutch that is highly controllable, robust, low cost, and has no wearable parts. A system-level study using a backward-facing model is used to assess the advantages of multi-speed gearboxes for EVs in terms of energy consumption, powertrain cost, and mass. A full-scale clutch prototype is designed for a custom two-speed AMT of an 80 kW EV. Numerical simulations show that a two-speed gearbox can improve energy consumption by 7.2 % for a compact class EV such as the Nissan Leaf. Moreover, using two gear ratios allows a downsizing of the electric motor, which could reduce powertrain cost and mass by 23.1 % and 15.6 %, respectively. The clutch is characterized experimentally and its maximum torque agrees well with analytical results (within 6 %). The prototype performed a seamless shift on a test bench demonstrating the viability of using an eddy current clutch for torque bypass clutches in AMTs.
Higher demands on comfort and efficiency require a continuous improvement of the shift process. During the launch and shift process the clutch control is used to get a smooth and efficient behavior. In this short time of acting the shifting behavior can be rated. Many control concepts use a clutch characteristic to calculate the actuator signal based on the clutch torque. Therefore, a high quality of this characteristic is necessary. Because of the dynamic process during clutch engagement the clutch characteristic needs further information to reach a high accuracy for the control algorithm. In this paper an existing clutch torque characteristic is extended to a characteristic map where the clutch torque becomes a function of the current actuator signal of the clutch and the clutch slip. The extension of the torque characteristic describes the slip based dependencies, e.g. the friction coefficient. The model of the characteristic map consists of the multiplication of two separate functions in these two dimensions. The parameters of this model are estimated using different identification algorithms, in this case a non-linear recursive and a non-recursive identification algorithm. Both estimation algorithms result in a characteristic map of the clutch behavior. A further advantage of the presented approach is the normalization during the estimation process of the slip-based function with the cost function. Thus, the original torque characteristic can be used as fallback if the identification of the slip-based part still need reference data to converge or shows an implausible behavior.
This study aims to provide modeling and control approaches for automated manual passenger and commercial vehicle transmissions in order to improve the overall disengagement-gear shifting-engagement performance using electromagnetic powder clutch (EMPC). The rationale behind selecting this clutch is its rapid behavior. During the modeling procedure of the EMPC, the analogy between this type of clutches and dry plate friction clutches has been exploited and a simple control method is proposed. The study also includes modeling method for gear shifting and selecting mechanisms of the automated manual transmission gearbox as well as development and implementation of controllers which is designed for these mechanisms. Automated manual transmission gearbox is utilized due to its combination of ease of construction and ability for electronic automation.
This paper presents the design and experimental validation of an eddy current torque transfer clutch for use inside Automated Manual Transmissions (AMTs) to perform seamless gear upshifts. Electric vehicles (EVs) with a single-ratio gearbox may provide high levels of smoothness, but using a multi-speed gearbox provides significant benefits in terms of vehicle acceleration, top speed, powertrain cost, mass, and energy consumption. AMTs can provide smooth shifts without torque interruption when coupled to a normally-open torque bypass clutch. However, conventional dry friction clutches are not best suited for such torque bypass due to wear and controllability concerns, while wet clutches would decrease powertrain efficiency due to viscous losses. An eddy current clutch would be highly controllable, simple to manufacture, low-cost, robust, and do not wear compared to friction clutches. The potential of eddy current clutches is assessed from a representative case study consisting of a ∼190 Nm clutch for a seamless two-speed AMT. The clutch design is based upon Wouterse's model, which is further refined using a Finite Element Analysis (FEA) on the clutch magnetic circuit. A prototype clutch is built and installed inside an existing AMT. The measured clutch coupling torque agrees well with Wouterse's model results, with a maximum error of 6%. The AMT performed seamless gear upshifts on a test bench thanks to the eddy current clutch, which confirms their viability for torque bypass.
This paper presents three-dimensional thermal model, performed transient thermal analysis for the grooved dry friction clutches. A finite element technique has been used to study the effect of radial and /or circumferential grooves (classic models) on the temperature distribution for dry friction clutch during a single engagement. The friction clutch has been discretised using 20-noded brick elements. The effect of the groove area ratio (G.R=groove area / total contact area), number of grooves and their location are investigated. Furthermore, new groove shapes have been suggested, e.g., curved groove. The response of the new suggested groove has been compared to the already existing shapes. The commercial ANSYS13 has been used to perform the numerical computations in this paper.
A friction clutch is an essential component in the process of power transmission. Due to this importance, it's necessary to investigate the stresses and vibration characteristics of the rigid drive disc of clutch to avoid failure and obtain an optimal weight and cost. This work presents the numerical solution of computing the stresses and deformations during the steady-state period, as well as the vibration characteristics of the rigid drive disc of friction clutch. Furthermore, new models for rigid drive disc have been suggested. The response of the new suggested models have been compared to the classic model, the numerical results show that the stresses and vibration characteristics of rigid drive disc of clutch can be controlled by adjusting design parameters. They show as well that the suggested models improve the response of the friction clutch considerably. The ANSYS/WORKBENCH14 and SolidWorks 2012 have been used to perform the numerical calculation in this paper.
Most of failures in automotive friction clutches occur due to the excessive heat generated between the contact surfaces during the slipping period; for this reason, the accurate calculation of the heat generation during the slipping is considered an essential item in the successful design process to avoid the failures due to the high thermal stresses. A finite element technique has been used to study the temperature field, the heat generation and the contact pressure distribution when friction disc slides over the steel disc. Analysis has been completed using a three dimensional model to simulate the thermo-structural coupling in automotive clutches. ANSYS software has been used to perform the numerical calculation in this paper.
The inertial continuously variable transmission is a mechanical transmission which is based on the principle of inertia. This transmission has a lot of advantages, namely: compactness, minimum friction losses and high efficiency as a result of the relatively small number of rotating components, a wide range of transformation of the torque. It does not need any conventional friction clutches. This transmission protects the engine from overload when the output shaft is braked. This drive guarantees optimum conditions of work for the engine regardless of the changing of load, and smoothly changes output speed according to the load. Mostly, design of this transmission consists of a pulsed mechanism with unbalanced inertial units and two one-way clutches. The pulsed mechanism is well developed and possesses high reliability. However, the one-way clutches are the most unreliable parts of the transmission and restrain wide use of the transmission. In this paper a new design of the inertial transmission with the only one-way clutch is considered. This transmission provides a higher level of the load ability. The object of the investigation is the external characteristic of the inertial transmission with the only one-way clutch. The physical and mathematical models of this transmission are used. Besides, periodic solutions of the equations were received by means of the numerical methods. It was shown that the resulting external characteristic is close to an ideal one.
The aim of the work is to present the methodology for calculating the slippage parameters of friction clutches (the work and the time of slippage) for different installation options of such clutches in tractor gearboxes, and of the tractor acceleration time at different degrees of gear overlap. The authors suggest a universal diagram of tractor acceleration at gear shifting at different degrees of gear overlap in the gearbox, which is true for any interrelation of the times of gearing and slippage of the friction clutch. Based on the mathematical model of the tractor acceleration, suggested by the authors, a methodology was developed for calculating the slippage parameters of friction clutches (the work and the time of slippage) for a variety of installation options of such clutches in the gearbox during gear shifting with varying overlap degrees and the acceleration time of the tractor unit at each gear. The developed universal mathematical model allows defining - at the design stage of gearboxes with friction clutches - the time and work of their slippage, as well as the tractor acceleration time, making it possible to create reliable designs of friction clutches and gearboxes based thereon.
It is widely accepted that the plug-in hybrid vehicle is the most economically viable near-term solution to the petroleum and CO₂ problems associated with passenger vehicles. The battery and electrics costs of gas/electric plug-in hybrid vehicles can be significantly reduced with the use of a hydraulic transmission and the implementation of hydraulic regenerative braking. This has not been done to date due to the unavailability of a low cost, reliable, compact, and efficient hydraulic transmission. This paper describes a conceptual design of such a transmission and evaluates its performance using the attributes of existing components. The main causes of the lack of past success with hydraulic transmissions are the many drawbacks of variable-displacement hydraulic pumps and motors. This transmission is based on fixed displacement pumps and motors to avoid these drawbacks. The efficiency of the transmission is evaluated under various driving conditions and is equal to or better than present day automatic transmissions due in part to the use of an all-mechanical bypass when cruising. The transmission is configured to allow a continuously variable level of braking torque. The design, construction and performance of this digital hydraulic transmission are detailed. The use of internal gear type pump/motors results in a small size that will allow the transmission to fit within the outline of a typical SUV transmission, offering a low cost way to convert existing vehicles to hybrids. The required accumulator size is discussed. The design eliminates the need for either a friction clutch or torque converter and is scalable such that it is applicable from compact cars to large trucks and buses. A variation is described that is suitable for adding hydraulic regenerative braking to an all-electric vehicle. The technical trend in hydraulic pumps and motors is to higher operating pressures and speeds. Both these trends result in proportional reductions in the size and cost of this style of transmission and increased power handling capability.
For control of most automatic transmissions with wet clutches (e.g. dual clutch transmission), it is important to know the kiss point with high accuracy. The kiss point describes the value of the control variable for which the friction clutch begins to transmit torque. Another significant value during the filling process of a wet clutch is the takeoff point. This is the hydraulic pressure which causes the clutch piston to begin to move. This paper presents an innovative approach that enables the joint determination of the kiss point as well as the takeoff point in only one identification procedure. In contrast to existing methods, this method is able to identify both points without the necessity for undesired auxiliary system excitation. Therefore it is possible to reduce wear on system components such as synchronization rings. The method presented in this paper analyzes the measured filling pressure characteristic over time as the system response to a defined excitation. The innovation of this method consists of dividing this pressure characteristic into three phases, where the separation is motivated by physical considerations. Each of these phases is approximated by appropriate linear and nonlinear functions. With the help of offline methods for system identification, the parameters of the approximation function are adjusted to reach the optimal approximation of the pressure characteristic. The takeoff point and the kiss point are distinct points between the approximating functions of the neighboring phases of the filling pressure characteristic. These points can be analytically determined for all phases of the characteristic. The choice of a suitable identification method has to take into account the electronic control units used for transmission control in modern vehicles and the capabilities they have. These methods are designed to work with noisy signals and allow for the accurate determination of the system parameters.
AEI travels to Friedrichshafen for an exclusive look at the development and technology behind the 9HP-the industry's first nine-speed transaxle slated for MY2013 production. With its 9.84 ratio spread, clever controls, and compact packaging, ZF's new nine-speed automatic transaxle will offer OEMs capability to increase fuel economy in their front-wheel-drive vehicles by 10-16% at 75 mph (121 kph), based on the NEDC cycle, when the gearbox is launched for MY2013 production next year. Few new transmissions have caused as much buzz within the industry as the 9HP. ZF announced it at the 2011 Detroit auto show but provided almost no details of its inner workings. But this summer, ZF's top engineers gave a select group of media, including AEI, a look inside the 9HP and its development. The visit to the company's Friedrichshafen R&D center included a long test drive of three 9HP-equipped mules (see sidebar).
To optimize the performance of continuously slipping wet friction clutches, it is vital to predict the maximum temperature at the friction surface. Prediction necessitates an accurate mathematical model of the heat transfer coefficient in and around the transmission oil grooves of the wet friction facing. All the relevant dimensionless variables in and around the oil grooves with respect to heat transfer coefficients were identified using Buckingham's ‘Pi’ theorem. Computational fluid dynamics (CFD) was used to create empirical formulas for heat transfer coefficients from relevant dimensionless variables and to study the dynamics of the oil flow through the grooves. Maximum transient temperature at the friction interface was predicted via finite element (FE) code using developed empirical formulas of heat transfer coefficients. Transient temperatures were then measured using thermo-couples for various conditions and groove geometries. An excellent agreement was found between the prediction and the measured data.
In its global development process General Motors Company-Powertrain follows a consequent "Road to Lab to Math" strategy, substituting road and laboratory tests with virtual tests. Hence simulation increasingly becomes a central aspect in the vehicle development process. With increasing accuracy of the single tools and a smart combination of different tools the credibility of the whole simulation chain comes closer to testing results. Furthermore the simulation gives us the possibility to change early and easily the product attributes in regard to functionality, robustness, comfort, etc. The enormous product cost resulting from a high amount of different test samples can be decreased by an early screening of the desired product functionality. Within General Motors Company-Powertrain a combined clutch simulation approach is used which joins the simulation tools Matlab/Simulink, LMS AMESim, Abaqus, Fortran, StarCCM+, NX Unigraphics to a powerful development process. A dry friction clutch is beside its main functionality, building the connecting link between engine and transmission, often the weakest link in the complete powercube (P₃). The customer expectations on the clutch system are that it is comfortably operable over lifetime under consideration of all known cases of tolerances out of the serial production.
This paper covers the development of a closed loop transaxle synchronization algorithm which was a key deliverable in the control system design for the L3 Enigma, a Battery Dominant Hybrid Electric Vehicle. Background information is provided to help the reader understand the history that lead to this unique solution of the input and output shaft synchronizing that typically takes place in a manual vehicle transmission or transaxle when shifting into a gear from another or into a gear from neutral when at speed. The algorithm stability is discussed as it applies to system stability and how stability impacts the speed at which a shift can take place. Results are simulated in The MathWorks Simulink programming environment and show how traction motor technology can be used to efficiently solve what is often a machine design issue. The vehicle test bed to which this research is applied is a parallel biodiesel hybrid electric vehicle called the Enigma. This vehicle is believed to be the world's first diesel hybrid electric sports car designed in the late 1990's and fabricated in 2001 at San Diego State University. The powertrain couples an AC-Propulsion AC-150 induction motor and a Volkswagen 1.2 direct injection turbo diesel together with a significant energy storage system. This powertrain can propel the vehicle 20 miles on electric power alone with lead acid battery technology and much farther with modern lithium ion. To couple these two power sources together, a custom transaxle was designed. Due to vehicle geometry and powertrain robustness constraints the transaxle design utilizes helical gears for power transmission that are larger than in a standard passenger vehicle. The inertia is further increased by that of the motor rotor. The engine has a dedicated friction clutch and thus can be removed from the synchronization operation. Normal mechanical synchronization methods are not desirable due to the required large size of a conventional synchronizer in this application and amount of rework required to integrate such assembly. Instead, the control system does this job by monitoring input and output shaft speeds as it modulates motor torque to bring the difference between these two shaft speeds within acceptable limits in less than 1 second. Results are presented in units of time to synch vs. RPM delta between the two transaxle shafts. Application of control system development in this area has the potential to mechanically simplify and reduce the mass of a transaxle or transmission in a hybrid powertrain while maintaining robust operation and shift related drive quality. Here, the transaxle is easily synchronized in less than 1 second allowing for smooth engagement of the transaxle's gears to their respective shaft.
The following listed definitions are intended to establish terminology and criteria for describing the various kinds of automotive transmissions. A specific arrangement may be described by a combination of several of these definitions.
A proposed mechanical breakaway clutch would not rely on friction. The clutch would be useful in environments in which the inherent inaccuracies of friction would make friction clutches erratic. The proposed clutch would comprise two primary assemblies: a driver assembly and a slip flange. The slip flange would be an internally splined cup driven by the driver assembly. The driver assembly would feature a sliding spring that would provide full adjustability. Roller bearings could be used to deflect the spring simultaneously as they were forced inward by the splines of the slip flange. In an alternate configuration, rotating cams would be used in place of the ball bearings. By varying the linear position of the spring assembly, one could adjust the level of torque at which the clutch would slip.
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