Browse Topic: Limited slip differentials
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.
This paper presents an integrated control of in-wheel motor (IWM) and electronic limited slip differential (eLSD) to enhance the vehicle lateral stability and maneuverability. The two actuators are utilized in the proposed controller to achieve separate purposes. The IWM controller is designed to modify the understeer gradient for enhanced handling characteristic and maneuverability. The eLSD controller is devised to improve the lateral stability to prevent oversteer in a severe maneuver. The proposed controller consists of a supervisor, upper-level controller and lower-level controller. The supervisor determines a target motion based on a target understeer gradient for IWM control and a yaw rate reference for eLSD control. The upper-level controller generates a desired yaw moment for the target motion. In the lower-level controller, the desired yaw moment is converted to the control inputs for IWMs in the two front wheels and eLSD at the rear axle. The proposed algorithm has been validated via computer simulation and vehicle tests. In the simulation results, the performance of the integrated control is compared with uncontrolled vehicle. The vehicle test results show that the integrated control of IWM and eLSD can enhance the cornering performance of the test vehicle.
The Electro actuated Limited Slip Differential (e-LSD) can help increasing the dynamic features of the vehicle, but to implement a well designed control logic it is necessary a deep knowledge of the actual friction torque built up by the differential clutch. This work presents the development of such a control law that takes into account the wear depth progression. To carry out this task, an alternative method has been used to study the clutch discs engagement depending on the wear rate. The method takes advantages from a mixed approach with a numerical and an experimental part. Using a general purpose block-on-ring test bench, the tribologic analyses were performed following the ASTM G77 standard; thus, the friction coefficient has been investigated in the contact between discs with molybdenum treatment and steel alloy discs, as well as its variation depending on the wear rate. The results were input in a numerical algorithm aimed at evaluating the friction torque of the clutch as a function of the pressure and the wear depth. The results, besides providing useful hints for the clutch design, were used to numerically assess the differential effects on a vehicle equipped with it. To accomplish this goal, a technique generally known as SiL - Software in the Loop was applied to multibody analyses. The paper is aimed at comparing the vehicle behavior using three different devices (open, self-locking and e-LSD) and performing standard (ISO) manoeuvers. The outcomes prove the advantages of the e-LSD in terms of handling, lateral dynamics and traction in comparison with the other solutions.
Basic driveline configurations offered in mid-size trucks have a standard “open” differential. Open differentials allow smooth cornering, as the outside tire must spin faster on corners as it travels a larger arc, when compared to the inner tire. This system has a main problem when traction is lost, due to slippery roads, different friction coefficients between pavements or even when the axle is submitted to a twist ditch. All of the power goes to the wheel with the least traction and the pickup is stuck. In order to improve traction on these situations, limited slip differentials were developed. A limited-slip differential will prevent excessive power from being allocated just to one wheel, and thereby keeping both wheels in powered rotation. There are several solutions offered in the market, each one presenting different torque transfer capabilities. Depending on the limited slip differential solution chosen for a determined pick-up truck, customer perception of this feature will not be considered as a value added to the vehicle. For these configurations, an open type differential with improved traction control features will provide a much better customer perception and effectiveness, as well as mass (and fuel economy) and price reductions for the product. This paper will provide some insights in order to choose traction control with open type differential instead of a limited slip differential when a pickup truck is on the early stages of its development, conciliating marketing requirements and the most effective solution to attend to the customer needs.
A new controllable limited slip differential is proposed and tested in software environment. It is characterized by the employment of a magnetorheological fluid, which presents the property of changing its rheology thanks to an applied magnetic field. A vehicle model has been designed and employed for the synthesis of a sliding controller. The control is based on a double level scheme: the upper controller aims to generate the target locking torque, while the lower controller generates, as control action, the supply current for the controllable limited slip differential. The obtained results show the effectiveness of the device in terms of vehicle dynamics improvement. Indeed, the results reached by the vehicle in presence of the new differential confirm the improved performances for both steady and unsteady state manoeuvres.
Global vehicle emissions reduction initiatives have warranted the development and usage of new materials and processes not traditionally used in the automotive industry besides exclusive applications. To support this mandate, vehicle lightweighting via metal replacement and design optimization has come into sharp focus as a doubly rewarding effect; namely, a lighter vehicle system not only requires less road load power for motivation, but also allows for smaller, usually more efficient powertrain options, which tend to be more efficient still. The automotive industry has begun to embrace adapting composite materials that have typically been available only to the upper end of the market and specialty racing applications. The specific component detailed in this paper highlights the challenges and rewards for metal replacement with an injection molded, fiber reinforced plastic for usage in mass produced drivetrain systems, namely the Electronic Limited Slip Differential (eLSD). The component detailed in this paper is a mechanical plenum that serves as a hydraulic supply, a fluid pressure control and a structural body for an eLSD system. Not only does the design approach for the component qualify for weight savings through material comparison, but its processing also allows for sub-component integration, further reducing final assembly complexity and lowering production cost. Material and production tooling costs are also favorable due to the net-shape processing allowed via injection molding. The injection molded design replaces a previously permanent molded aluminum with an injection molded, short glass fiber reinforced polymer. The paper describes the challenges and advantages of design and processing that have allowed the plenum to be optimized for the lightweighting of the eLSD system. A general design approach encompassing the myriad activities necessary for a transition from metal to plastic will be discussed also highlighting the lessons learned during the process of readying the component for the transition from research and development prototype into production acceptance.
Advanced research in ABS (Anti-lock Braking System), traction control, electronic LSD's (Limited Slip Differential) and electrical powertrains have led to an architecture development which can be used to provide a controlled yaw moment to stabilize a vehicle. A steer assistance mechanism that uses the same architecture and aims at improving the vehicle response to the driver steering inputs is proposed. In this paper a feed-forward approach where the steering wheel angle is used as the main input is developed. An optimal control system is designed to improve vehicle response to steering input while minimizing the H2 performance of the body slip angle. The control strategy developed was simulated on a 14 DOF full vehicle model to analyze the response and handling performance.
This SAE Recommended Practice outlines basic nomenclature in common use for truck and bus drive axle designs. Over a period of years there have been many different designs introduced; however, for this report, only the most common have been selected and only their general construction is illustrated to show the nomenclature of the various parts.
The open (standard) differential provides an important function in vehicle dynamics and handling by splitting the applied driveline torque and allowing each wheel or axle to spin at different speeds. This function is necessary to eliminate axle bind-up while negotiating turns. However, it inherently impedes optimal traction and mobility performance by allowing the available torque to be limited by the wheel or axle having the least amount of traction. Loss of traction could result in loss of driveline torque control and a resulting loss of vehicle control. This loss of control could be catastrophic in the case of higher speed maneuvers. The proposed electronically controlled hydraulic limited slip differential solution corrects this problem, seamless to the driver, while maintaining the fundamental open differential function. Furthermore, this system maintains efficient forward motion compared to other solutions that slow the vehicle down while expending valuable energy. A number of other systems available today govern and deprive the driver of the sense of confident unimpeded control while the proposed system maintains it. This paper will provide an overview of design considerations, development and testing of the electro-hydraulic limited slip differential. It will be shown that the optimal solution to this problem is to integrate the limited slip function into the differential and within the transaxle or axle assembly. The proposed design is a replacement for the open differential. Additionally, it provides OEMs with an integrated optimal solution that satisfies manufacturing drivers such as part complexity and weight reduction as well as the end customer.
Brake-based traction control systems (TC), which utilize the brake of a spinning wheel of the drive axle, are widely used in passenger cars and light trucks, and recently were applied to all-wheel drive construction equipment. Such machines employ various types of interwheel drive systems (i.e., axle drives such as open differentials, limited slip differentials, etc.) to control torque split between the drive wheels and, thus, improve vehicle traction performance. As experimental research showed, the interaction between the traction control system and the axle drive can lead to unpredictable changes in vehicle performance. Lack of analytical work in this area motivated this study of the interaction and impact of the two systems on each other and the dynamics and performance of a drive axle. The paper presents an analysis of the torque/force distribution between the driving wheels of an axle with open differential and limited slip differential with different torque bias characteristics when the traction control system is on and the driving wheels have the same/different gripping conditions. Also, the normal tire loads vary due to lateral inclination of the axle. Results of analytical research explain the nature of extra torque loads of the wheels, determine the yaw moment, and show energy losses in tires and the axle brake mechanisms. These results layout the requirements needed for the braking torque and control algorithm development of the traction control system to work “cooperatively” with limited slip differentials.
Vehicle handling is heavily influenced by the torque distribution to the driving wheels. This work presents a newly developed differential, designed to actively control the driving torque distribution to the wheels. The new device incorporates an electric machine, which can operate either as a motor or generator. A control unit monitors signals from various sources in the vehicle, such as steering angle, yaw acceleration and wheel rotational speed. Then, a control algorithm takes into account the steering angle rate and the vehicle speed in order to determine the suitable difference between output torque values. The handling improvement capabilities are evaluated by simulating in ADAMS/Car the driving behavior of a vehicle equipped with the new differential. The model that has been used to simulate vehicle handling is that of a Formula SAE type racing car. Results are obtained using the following three types of differentials: an open differential, a limited slip differential and the new actively controlled device. In all simulations, the same vehicle model has been used. Swept sine steering and split coefficient of friction (μ) acceleration driving conditions are tested for each differential type and the results are compared and evaluated. The aim of the paper is to shed some light on the advantages of the new torque distributing differential device. This is achieved by comparing simulation results such as trail, speed and yaw rate for the chosen driving conditions against those obtained by using the two common differential types.
Wet clutches are important components used in the transmission and drive trains of many modern vehicles. The clutches transfer torque via the friction between a number of friction discs and the friction characteristics is therefore of great importance for the overall behavior of the vehicles. The friction characteristics is governed by a number of parameters such as lubricant base oil and additives, type and permeability of the friction material and temperature and surface roughness of the interacting surfaces. The permeability is considered to influence time of engagement and supply the sliding interface with lubricant and additives during engagement. In this work, a permeability measurement method suitable for wet clutch friction materials is thus used to measure the permeability of friction materials of different types; sintered bronze and paper based materials. The investigated friction materials come from different vehicle applications such as Limited Slip Differentials and Automatic Transmissions. The investigation also includes measurements made with different types of lubricants such as mineral based lubricants, mineral based VHVI lubricants and ester based lubricants. As comparison similar permeability measurements are made with water since the permeability, according to Darcy's law, should not be influenced by the percolating fluid. It is found that even though permeability is considered to be a material parameter the measured permeability for a certain material will vary depending on which fluid that is used in the measurements. Therefore, if a detailed absolute value of the permeability is of interest, i.e. for use in simulations models, the permeability should be measured with the fluid that is going to be used in the clutch or brake application in order to obtain a detailed result. However the results show that if the permeability only is compared between different materials the test fluid is of less importance as long as the same fluid is used in all investigations.
Wet clutch friction devices are the primary means by which torque is transmitted through many of today's modern vehicle drivelines. These devices are used in automatic transmissions, torque vectoring devices, active on-demand vehicle stability systems and torque biasing differentials. As discussed in a previous SAE paper ( 2006-01-3271 - Next Generation Torque Control Fluid Technology, Part II: Split-Mu Screen Test Development) a testing tool was developed to correlate to full-vehicle split-mu testing for limited slip differential applications using a low speed SAE #2 friction test rig. The SAE #2 Split-Mu Simulation is a full clutch pack component level friction test. The purpose of this test is to allow optimization of the friction material-lubricant hardware system in order to deliver consistent friction performance over the life of the vehicle. In this paper we will describe the development of a new test based on the previous work including equipment modifications, data analysis and correlation to full-vehicle split-mu testing. This new tool allows the validation of new friction modifiers tailored to OEM-specific friction materials.
Wet clutch friction devices are the primary means by which torque is transmitted in many of today's modern vehicle drivelines. These devices are used in automatic transmissions, torque vectoring devices, active on-demand vehicle stability systems, and torque biasing differentials. As discussed in a previous SAE paper ( 2006-01-3270 - Next Generation Torque Control Fluid Technology, Part I: Break-Away Friction Slip Screen Test Development), a testing tool was developed to simulate a limited slip differential break-away event using a Full Scale-Low Velocity Friction Apparatus (FS-LVFA). The purpose of this test was to investigate the fundamental interactions between lubricants and friction materials. The original break-away friction screen test, which used actual vehicle clutch plates and a single friction surface, proved a useful tool in screening new friction modifier technology. This paper describes upgrades to the FS-LVFA as well as improvements in the test method including statistical data analysis. The combination of these new tools is facilitating the development of new friction modifier technology tailored to OEM specific friction materials.
SAE members voted Toyota's new microcar the Best Engineering Vehicle for 2009. The iQ shows its smarts with brilliant packaging, city-friendly efficiency, and superb overall execution. What a difference a year makes in SAE International's annual Best Engineered Vehicle (BEV) award voting. Last year SAE members gave the top BEV honors to GM's Chevrolet Tahoe and GMC Yukon and their clever two-mode hybrid powertrain. This year, however, members shifted their interest to the opposite end of the vehicle spectrum. They awarded the BEV to Toyota's new iQ-a diminutive “micro premium” four-seat car that almost appears capable of fitting into a full-size SUV's cargo area with room to spare. The iQ is a lesson in ultra-efficient vehicle packaging and superb overall execution. Its exterior dimensions put it squarely in Europe's A segment. But its performance is superior to Toyota's own B-segment Yaris, and its quality and attention to detail rival that of many midsize D-segment offerings-all from a vehicle with an overall length shorter than 3.0 m (9.8 ft).
The important new model from General Motors Europe is based on the Epsilon II architecture expected to underpin many GM models for markets around the world. Flowery language laced with hyperbole is part of the communication philosophy of some European car companies, but the language from General Motors Europe (GME) at the world premiere of their Opel/Vauxhall Insignia was comparatively modest. True, the company spoke at the British International Motor Show of “breathtaking design and leading technology” and “sculptural artistry meets German precision,” but the overall message was a balanced and sensible description of a precisely designed and engineered car. It is certainly a very significant model (built in sedan, hatchback, and wagon forms) not just for GME, but also for the GM business empire as a whole. The Insignia's Epsilon II mechatronic chassis architecture is expected to be the basis of the Saab 9-5's replacement as well as for numerous other models including the Saturn Aura.
Jeep engineers give the 2005 model more on-road comfort, with all the off-road capability. The 2005 Jeep Grand Cherokee follows closely in the tracks of the 1992 Grand Cherokee in its mission to marry off-road competence with smooth, stable highway ride and handling. The original Range Rover was the first to try to combine these often-contradictory traits, but it was Jeep that addressed this challenge for mainstream customers. The company's latest effort is its best yet, with independent front suspension installed to provide the ride and handling suburban customers demand, but configured to preserve Jeep's trademark off-road prowess. “Just as when it first debuted on the market, the 2005 Jeep Grand Cherokee sets the benchmark for off-road capability and continues to do so for on-road refinement,” said Jeff Bell, Vice President, Jeep.
Linear back-drive differentials have been proposed as alternatives to conventional gear differentials for applications in which there is only limited rotational motion (e.g., oscillation). The finite nature of the rotation makes it possible to optimize a linear back-drive differential in ways that would not be possible for gear differentials or other differentials that are required to be capable of unlimited rotation. As a result, relative to gear differentials, linear back-drive differentials could be more compact and less massive, could contain fewer complex parts, and could be less sensitive to variations in the viscosities of lubricants.
This SAE Recommended Practice outlines basic nomenclature in common use for truck and bus drive axle designs. Over a period of years there have been many different designs introduced; however, for this report, only the most common have been selected and only their general construction is illustrated to show the nomenclature of the various parts.
Items per page:
50
1 – 50 of 70