Browse Topic: Limited slip differentials

Items (80)
Automatic Drive Train Management System for 4WD Vehicle Based on Road Situation Identification2018-01-09874/3/2018
The slip ratio of vehicle driving wheels is easily beyond a reasonable range in the complex and changeable driving conditions. In order to achieve the adaptive acceleration slip regulation of four-wheel driving (4WD) vehicle, a fuzzy control strategy of Automatic Drive Train Management (ADM) system based on road situation identification was proposed in this paper. Firstly, the influence on the control strategy of ADM system was analyzed from two aspects, which included the different road adhesion coefficients and the vehicle’s ramp driving state. In the meantime several quantitative expressions of relevant control parameters were derived. Secondly, the fuzzy logic control algorithm was adopted to design a road situation identification subsystem and a ramp driving state identification subsystem respectively. The former was based on the μ-S curve model, and the latter was based on the vehicle driving equilibrium equation. Thirdly, the physical model of limited slip differential was simplified appropriately and a spring damping model of the torque distribution was established. Finally, two typical working tests were carried out on the Matlab/Simulink-CarSim co-simulation platform to verify the proposed fuzzy control algorithm. The results show that 4WD vehicle equipped with ADM system can keep driving wheels’ slip ratio in the reasonable range rapidly by using the proposed control strategy, when its driving conditions are terrible such as low road adhesion coefficient. And so the vehicle trafficability is effectively enhanced.
Ke, MinZhu, BingZhao, JianDeng, Weiwen
Effect of Temperature on Braking Efficiency Stability of Magnetorheological Fluid Auxiliary Braking Devices2017-01-25109/17/2017
Fluid auxiliary braking devices can provide braking torque through hydraulic damping, fluid auxiliary braking devices can also convert vehicular inertia energy into transmission fluid heat energy during the braking, which can effectively alleviate the work pressure of the main brake. Traditional hydraulic auxiliary braking devices use transmission fluids to transmit torque, however, there is a certain lag effect during the braking. The magnetorheological fluid (MR fluid) can also be used to transmit torque because it has the advantages of controlling braking torque linearly and responding fast to the magnetic field changed. The temperature of MR fluid will increase when the vehicle is engaged in continuous braking. MR fluid temperature changes will cause a bad influence on the efficiency stability of auxiliary braking. So it is necessary to clear about the effect of temperature on MR fluid auxiliary braking torque in order to keep the braking efficiency stability through torque compensated by other factors, such as changing the magnetic field strength. In order to analyze the effect of temperature on MR fluid auxiliary braking torque, this study established the mathematical model of the MR fluid auxiliary braking device through the theory of one dimensional flow theory of hydraulic retarders, and the properties of MR fluid are described based on the Bingham model. This paper researched the change of the properties of MR fluid under the same magnetic field condition with different temperatures, and summarized how much compensated torque is needed to keep the braking efficiency stability. Research showed that when the vehicle is engaged in continuous braking, the temperature effect on the braking torque is non-linear. The braking torque increases with the increase of temperature under the same magnetic field condition, the braking torque increases fast at high rotating speed of the rotor.
Xiong, ShengguangTan, GangfengYang, BoXiao, LongjieXu, YongbingWang, Yishi
Evaluation of Stability and Control of Movement of 6x6 Truck for Different Operating Modes2017-01-15753/28/2017
Trucks are one of the most common modes of transport and they are operated in various road conditions. As a rule, all-wheel drive trucks are equipped with special systems and mechanisms to improve their off-road capability and overall efficiency. The usage of blocked mechanisms for power distribution is one of the most popular and effective ways to improve the off-road vehicle performance. However, the lock of differential may adversely affect the stability and control of vehicle because of the unobvious redistribution of reactions acting on wheels, which consequently leads to poor performance and safety properties. Problems of rational distribution of power in transmissions of all-wheel drive vehicles, as well as research in the field of improving directional stability and active safety systems are among the priorities in modern automotive industry. To study dynamics of a vehicle with wheel formula 6x6 a mathematical model of the vehicle was developed in an environment of LMS Amesim software package. The model includes the realization of the features of all major mechanical units of a vehicle: engine, transmission, suspension, drive wheels. Besides, the model takes into account the so called "external" dynamics of the vehicle and includes interaction of the wheels and pavement and implementation of possible changes in environmental conditions. With help of the mathematical model we have managed to estimate the trajectory and directional stability of all-wheel drive trucks with lockable differentials for different operating conditions. The results allowed us to develop the most effective, in terms of stability and control, algorithm for control of the power distribution system.
Keller, AndreiAliukov, SergeiAnchukov, Vladislav
Torque Vectoring of a Formula SAE through Semi Active Differential Control2014-32-008811/11/2014
In a Formula SAE car, as for almost all racecars, suppressing or limiting the action of the differential mechanism is the technique mostly adopted to improve the traction exiting the high lateral acceleration corners. The common Limited Slip Differentials (LSDs) unbalance the traction torque distribution, generating as a secondary effect a yaw torque on the vehicle. If this feature is electronically controlled, these devices can be used to manage the attitude of the car. The yaw torque introduced by an electronically controlled LSD (which can also be called SAD, “Semi-Active Differential”) could suddenly change from oversteering (i.e. pro-yaw) to understeering (i.e. anti-yaw), depending on the driving conditions. Therefore, controlling the vehicle attitude with a SAD could be challenging, and its effectiveness could be low if compared with the common torque vectoring systems, which act on the brake system of the car. In addition, unlike common ESC (“Electronic Stability Control”) systems do, a SAD can modify the vehicle attitude without limiting its traction performance, which is a crucial factor for racecars. This paper shows the SAD designed at the University of Florence, highlighting its technical features and discussing its torque vectoring capabilities through the results of the simulation performed with a numerical vehicle model. These results show that this system is capable of improving the performance of the vehicle, in terms of both vehicle stability and traction.
Annicchiarico, ClaudioCapitani, Renzo
Mobility and Energy Efficiency Analysis of a Terrain Truck2013-01-06724/8/2013
While much research has focused on improving terrain mobility, energy and fuel efficiency of terrain trucks, only a limited amount of investigation has gone into analysis of power distribution between the driving wheels. Distribution of power among the driving wheels has been shown to have a significant effect on vehicle operating characteristics for a given set of operating conditions and total power supplied to the wheels. Wheel power distribution is largely a function of the design of the driveline power dividing units (PDUs). In this paper, 6×6/6×4 terrain truck models are analyzed with the focus on various combinations of PDUs and suspension systems. While these models were found to have some common features, they demonstrate several different approaches to driveline system design. In order to further investigate the effect of wheel power split on mobility and energy/fuel efficiency in conjunction with suspension characteristics, this paper provides an analytical method and mathematical model for the entire truck, including driveline system (sets of PDUs), suspension, and tires under various typical operating conditions. Interactions between longitudinal and normal truck dynamics are first modeled and their influence on vehicle mobility and energy efficiency is analyzed. A computational algorithm is presented, which integrates equations for the driveline system with the suspension model (i.e., wheel normal reactions), along with a method for solving the integrated equations. Finally, an analysis of the effects of PDU combinations on truck mobility and energy efficiency is demonstrated.
Vantsevich, Vladimir V.Murphy, DennisBortolin, Gianantonio
Development of Front-Wheel-Drive ELSD for Efficient Performance and Safety2012-01-03054/16/2012
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.
Fox, MatthewGrogg, John
Axle Drive and Brake-Based Traction Control Interaction2011-01-21609/13/2011
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.
Vantsevich, Vladimir V.Bortolin, Gianantonio
High-Performance Differentials, Axles, & DrivelinesC11137/27/2011
Every automobile has a differential and most have axles, yet the exact function of these is not common knowledge. This comprehensive seminar introduces participants to the function and interfaces of axles and their individual components. As we modify cars for street performance or all out race applications, it is important to know the trade-offs in the drivetrain system. The theory and practice of axle systems is introduced along with a hands-on style approach to repairing and modifying axles for high performance applications. For this hands-on approach, actual hardware will be reviewed in an informal setting. The seminar begins by defining the axle fundamentals and operation followed by an in-depth review of original equipment axles, differentials, torque bias, hypoid gears, and rebuild steps. The different manufacturing and service techniques required for different gear architectures is also reviewed. The seminar concludes with a unique applications-specific workshop and industry trends discussion. Upon completion of the seminar, attendees will have a working knowledge of axles, hypoid gearing, and differentials (open and limited slip), along with typical performance enthusiast modifications for race teams and weekend warriors. The book, "High-Performance Differentials, Axles, and Drivelines," by Joseph Palazzolo is included in the course materials. By attending this seminar, you will be able to: Identify vehicle specific axle types Evaluate the differences between open and limited slip differential (LSD) Distinguish between the different torque transfer characteristics of the different LSD technologies Identify how to correctly set and adjust bearing preload and hypoid contact patterns Describe how to assemble and disassemble a differential Explain the steps to set-up a new gear set and bearings Recognize the difference required between typical passenger car applications and high-performance, race style axles CEUs
Permeability Measurements of Sintered and Paper Based Friction Materials for Wet Clutches and Brakes2010-01-222910/25/2010
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.
Marklund, Pär
Next Generation Torque Control Fluid Technology, Part IV: Using a New Split-μ Simulation Test for Optimizing Friction Material-Lubricant Hardware Systems2010-01-223010/25/2010
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.
Whitticar, DavidBasu, ShubhamitaGreene, GalenHenley, MatthewParham, DwightPrengaman, ChristopherSchiferl, ElizabethBaker, MarkBartley, StuartHuston, Michael E.
Effect of Limited Slip Clutch Friction on the Driveline Dynamics of a Rear Wheel Drive Vehicle Coasting in a Turn2008-01-15826/23/2008
A model and simulation results are presented for the torsional dynamics of a rear wheel driveline while the vehicle is coasting in a turn. The model includes the effects of road load and powertrain drag, limited slip differential clutch friction, the inertias of the vehicle, wheels, axles, differential carrier, and driveshaft, the final drive ratio, torsional stiffnesses of the axles and driveshaft, vehicle track width, and radius of the turn. The dynamics of coasting in a turn differ from powered driving due to changes in the inertia loading the driveshaft, the damping effect of the disengaged transmission, and nonlinearities in the clutch friction. Specific focus is given to vibration in the axles and driveshaft due to variations in the torque-speed slope of the clutches, which is determined by the slope of the friction coefficient ‘μ’ versus sliding speed ‘v’ in the limited slip clutches. The clutch μ-v slope is strongly influenced by the lubricant in the differential and understanding its effect on driveline vibration will help in the development of future lubricants. Three cases are presented: (1) two clutches with the same static breakaway torque and positive torque-speed slopes, (2) one clutch with a lower breakaway torque and zero torque-speed slope, and (3) one clutch with a lower breakaway torque and negative torque-speed slope.
Cameron, T. M.Jao, T. C.Hewette, C.McCombs, T.DeGonia, D.
Limited Slip Additive Testing and Development: New Products with Improved Thermal Stability2007-01-19887/23/2007
Limited slip differentials, developed over 40 years ago to counter drive wheel slippage when different traction conditions exist on either side of an axle, are still widely employed by the automotive industry to improve driving control. In a limited slip differential (LSD) frictional couplings connect the axle shafts to the differential and provide the means of transmitting power to the wheels. The friction plates in the coupling may contain a variety of friction materials including metal, paper, sintered bronze, and carbon. Each one of these materials has very different frictional and wear characteristics and each one requires a different response from the gear additive package. Each plate must be durable over the course of the vehicle lifetime irrespective of the material used. As the demands on rear axles increases with the application of greater horsepower and the increasing requirements of aerodynamic engineers, the lubrication of these friction plates remains an ongoing challenge. Lubricant frictional characteristics are very important in determining the quiet and smooth operation of LSD's. Fully formulated API GL-5 J 2360 gear lubricants are unable to fulfill all the lubrication requirements of LSD's. Special additives have therefore been developed to improve the frictional response in the coupling to eliminate noise, vibration, and stick slip problems. There is a requirement to provide limited slip additives that give excellent friction plate lubrication. The goal of lubricant formulators is to develop new products that retain frictional performance with minimal effect on the thermal stability of the gear lubricant. Test methodology has been developed that correlates friction characteristics with known field performance and testing has been performed on a variety of friction plate materials. The results of testing with current commercially available limited slip additives and new additives with much improved thermal characteristics in different gear lubricants and with different hardware configurations are discussed. This paper adds to previous work in this area and brings to a conclusion the development, design and experimentation associated with this extensive program.
Vettel, PaulaLindsay, David
Traction and Clutch Effects on the Natural Frequency and Vibration Stability of Limited Slip Differential Axles2007-01-22955/15/2007
The torsional natural frequencies of axles equipped with limited slip differential clutches depend on whether or not the tires and clutches are slipping since the effective inertia at each end of the axle is different for slipping and non-slipping conditions. Limited slip axle vibrations are typically analyzed for one tire slipping and the other not since that is the case for which the limited slip clutches are used. Vibrations often arise, however, during normal turning when both drive tires have good traction. Models for estimating the torsional natural frequencies of limited slip axles are presented for the cases of: Non-slipping clutches, neither tire slipping Non-slipping clutches, both tires slipping Non-slipping clutches, one tire slipping, one tire not slipping Slipping clutches, neither tire slipping Slipping clutches, both tires slipping Slipping clutches, one tire slipping, one tire not slipping Vibration frequencies varying from below 1 Hz to about 500 Hz are shown to arise due to differing conditions, and experimental data are presented that support the theoretical conclusions. The damping on each axle provided by the clutches is shown to be the average damping rate of the clutches due to coupling through the differential. To ensure vibration stability the sum of the μ-v slopes of the clutches should be positive. Understanding axle torsional vibrations under different operating conditions will assist in the development of future generations of lubricants that extend gear life and suppress vibration in limited slip differential axles.
Cameron, T. M.Hewette, C.McCombs, T.DeGonia, D.Jao, T. C.
This SAE Information Report was prepared by the SAE Fuels and Lubricants Technical Committee for two purposes: (a) to assist the users of automotive equipment in the selection of axle1 and manual transmission lubricants for field use, and (b) to promote a uniform practice for use by marketers of lubricants and by equipment builders in identifying and recommending these lubricants by a service designation.
Fuels and Lubricants TC 3 Driveline and Chassis Lubrication
All-Wheel Driveline Mechatronic Systems: Principles of Wheel Power Management2006-01-05804/3/2006
All-wheel driveline systems with electronic torque control on each and all wheels, torque vectoring and torque management devices, hybrid electro-mechanical systems, and individual electro (hydraulic) motors in the wheels have been gaining a bigger interest in the industry for recent years. The majority of automotive applications are in vehicle stability control that is performed by controlling the vehicle yaw moment. Some devices also improve vehicle traction performance. The proposed paper develops a methodology that includes the key-principles in all-wheel driveline systems design and is based on the wheel power management as a broader analytical approach. The proposed principles relate to the optimization of power distributions to the drive wheels in both rectilinear and curvilinear vehicle motion. Inverse dynamics is the basis for the developed methodology. Combinations of optimal power distributions at the drive wheels and proactive estimation of the road conditions (friction coefficient estimation) lead to developing adaptive control algorithms for a new generation of mechatronic driveline systems. Mechatronic systems designed with the proposed methodology can improve not only stability of vehicles, but can provide vehicles with better operational properties such as traction/velocity properties, energy/fuel efficiency, vehicle turnability, and handling.
Vantsevich, Vladimir V.
Redesign of a Differential Housing for a Formula Car (FSAE)98307711/16/1998
A unique differential assembly was needed for the Lawrence Technological University (LTU) SAE Formula race car. Specifically, a differential was required that had torque sensing capabilities, perfect reliability, high strength, light weight, the ability to withstand inertia and shock loading, a small package, no leaks, the ability to support numerous components. In that regard, an existing differential was selected that had the torque sensing capabilities, but had deficiencies that needed to be fixed. Those deficiencies included the following: Differential unit was over 4 kg unmounted, with no housing. This was considered too heavy, when housed properly. Bearing surface was provided on only one end of the carrier. This design provides insufficient bearing surface to support either the differential housing or half-shafts The internal drive splines integral to the case are not optimized for a perpendicular drive/axle arrangement, such as, a chain drive. Differential unit is an open cased frame, lacking in any shields to protect internal gearing. The differential was re-engineered for the SAE Formula car to address each of the above deficiencies, and helps better achieve an optimized axle that meets all of the race car objectives. To make use of the selected differential, the internal gearing was removed and placed in an all new multipurpose casing. This new casing is the centerpiece for the lightweight final drive assembly. The differential casing and its positioning have been optimized to reduce part count and improve functionality. This design increases reliability and reduces manufacturing time and cost. Design weight of the differential casing is considerably lighter with a dramatically reduced final package size.
Jawad, Badih A.Fowler, John G.
Actuating Vehicle Systems and Unified Limited Slip Differentials9727519/8/1997
A peculiarity of all-wheel drive off-highway vehicles is that their running abilities (cross-country mobility, tractive and velocity properties, turnability and the like) depend not only on total traction effort but also on its distribution between driving wheels. The latter is in great measure determined by actuating vehicle system and characteristics of the mechanisms installed in power dividing transmission units, i.e. in interwheel, interaxle reduction gears, and transfer cases. The characteristics of locking performance of these mechanisms regulate the circumferential force distribution between driving wheels and, respectively, a vehicle's performance indicators. Such mechanisms have been created and are being created in a multitude. The classification of power dividing mechanisms and system is given. They provide a high level of the traction performance of all-wheel drive off-highway vehicles and agricultural tractors, in particular. The article features a statistical analysis of all-wheel-drive agricultural tractors and their differentials with data on more than 4000 tractor models produced since 1970. It is shown that limited slip differentials with 6 various characteristics developed on the basis of various constructional elements enjoy a wide spread. Limited slip differentials with various characteristics must be used in different transmission units in order to provide maximum efficiency of tractors. Lack of unification among those differentials impedes employment of such mechanisms with various characteristics on one and the same tractor. This problem is solved in the article: unified limited slip differential systems have been developed, in which various interaction of differential's primary constructional elements provides different characteristics. This has been implemented not only for the mentioned differentials with 6 various characteristics. Using those, one more differential (the seventh) has been designed. The description of the developed differentials and the differentials' locking performance is included.
Vantsevich, V. V.
The Effect of a Viscous Coupling Used as a Front-Wheel Drive Limited-Slip Differential on Vehicle Traction and Handling9408753/1/1994
The viscous coupling is known mainly as a driveline component in four wheel drive vehicles. Developments in recent years, however, point toward the probability that this device will become a major player in mainstream front-wheel drive application. Production applications in European and Japanese front-wheel drive cars have demonstrated that viscous couplings provide substantial improvements not only in traction on slippery surfaces but also in handling and stability even under normal driving conditions. This paper presents a series of proving ground tests which investigate the effects of a viscous coupling in a front-wheel drive vehicle on traction and handling. Testing demonstrates substantial traction improvements while only slightly influencing steering torque. Factors affecting this steering torque in front -wheel drive vehicles during straight line driving are described. Key vehicle design parameters are identified which greatly influence the compatibility of limited-slip differentials in front-wheel drive vehicles. Cornering tests show the influence of the viscous coupling on the self steering behavior of a front-wheel drive vehicle. Further testing demonstrates that a vehicle with a viscous limited-slip differential exhibits an improved stability under acceleration and throttle-off maneuvers during cornering.
Huchtkötter, H.Taureg, H.
Advanced Development of Self-Controlled Torque Sensitive Limited-Slip Differential by Means of Helical Gears9407333/1/1994
This paper compares and contrasts several types of torque-sensitive limited slip differential designs while focusing on the self-controlled helical gear differential. Cone-and plate-type locking differentials in common use today offer a low production cost but tend to change locking characteristics as they wear and influence vehicle handling and braking. Current worm gear type limited slip differentials present a disadvantage in that they have a limited range of available locking ratios as a function of cost and also present long-term durability issues. Thus, attention has turned in recent years to the self-controlled helical gear approach. This method offers a wide range of locking ratios thus making it possible to tune the performance of the differential to match virtually any vehicle. Applications involving use of this design as a rear wheel differential and as a center differential are described. Uneven distribution of torque is often desirable in a center differential and the design principles involved in achieving this effect are explained. Finally, a test rig was developed to measure the locking effect and service life of the helical gear differential and it showed that these devices maintain consistent performance over their service life, as compared to current torque sensitive devices.
Rohregger, W.Amborn, P.Kaufmann, O. A.
A New Form of Limited Slip Differential9306723/1/1993
Improved performance creates a need for a limited slip differential for widespread application. Existing types suffer from the disadvantage of high cost and they are generally not well suited to front wheel drive applications. The ‘Suretrac’ differential meets this enhanced requirement. In this new design torque is transmitted through the unit using a cam and follower principle. Any relative rotation of the cams on the output shafts is opposed by friction forces which generate a torque ratio between the output shafts. The design is novel in using helical faces to give large contact areas and avoid high Hertzian stresses. The performance of this type of differential differs from viscous types or traction control because the torque difference is established before any relative motion takes place. The tyre dynamics dictate the torques generated so that the differential always provides the optimum torque balance. This maintains tyre adhesion and enhances directional stability and safety. The complexity of the shapes involved precludes machining as an economic production process, so nett shape forming methods are used. This also has to apply to the prototype phase, and so simultaneous engineering has been implemented throughout the product development. The operation of the differential should normally not impinge on the driver's consciousness, so the performance can only be established by special tests carried out with full instrumentation. These tests include acceleration with the wheels on different surfaces, “split mu”, and acceleration on a curve to give unequal wheel loading. Test results are presented. Durability tests have also been completed. The differential is shown to give substantial advantages in operation, is capable of being installed in the same space as a conventional differential and has a minimum additional cost and so should gain widespread acceptance in all types of vehicle.
Jarvis, Roger P.Young, Alastair J.
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