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The demand to reduce noise in the passenger cars is increasing. Tire vibration characteristics must be considered when studying road noise because of the strong interaction between tire vibration characteristics and interior car noise. Car manufacturers are keenly interested in studies on the prediction of NVH (Noise, Vibration and Harshness) performance, including viewing tires as substructure. Recently, studies have illustrated the effect that tire lateral bending mode have has on road noise, while most past studies of tire vibration focused on the circumference mode, which excited the vertical spindle force. Therefore, further study of tire lateral bending mode is necessary. Modeling of the tire lateral bending mode is described in this paper. First, lateral spindle force is measured under tire rolling conditions. Second, experimental modal analysis is performed to grasp tire lateral bending mode. Finally, a tire vibration model is built using the cylindrical shell theory.

This study examined methods of machining a microsurface texture on the surface of the rolling elements of a toroidal continuously variable transmission (CVT) for improving the traction coefficient. The microsurface texture of the toroidal surfaces consists of tiny circumferential grooves (referred to here as micro grooves) and a mirror-like surface finish similar to the rolling surface of bearings. Hard turning with a cubic boron nitride (cBN) cutting tool, grinding with a cBN wheel and micro forming were applied to machine the micro grooves. The results made clear the practical potential of each method. A micro forming device was also developed for use in actual production. A mirror-like surface finish and micro crowning of the convex portions of the microsurface texture were simultaneously executed by superfinishing them with a fine-grained elastic superfinishing stone.

This paper proposes a method of estimating road friction and tire slip angle in a cornering maneuver. The method can estimate front tire road friction accurately at low lateral acceleration because it is based on the tire self-aligning torque (SAT) that exhibits high sensitivity to road friction at low slip angles. Road friction and tire slip angle, which are mutually interdependent, are estimated simultaneously using an extended Kalman filter designed around a model describing the relationship between road friction and SAT and a vehicle lateral dynamic model. The front tire SAT is calculated with a mathematical model that describes the torque transmission characteristics from the electric power steering torque to SAT. Therefore, the proposed method is readily applicable to production vehicles. Results of an experimental study show that the change in road friction is instantaneously estimated at low lateral acceleration.

Traction control systems (TCSs) serve to control brake pressure and engine torque, thereby reducing driving wheel spin for improved stability and handling. Systems are divided into two basic types by the brake control configuration. One type is a one-channel left-right common control system and the other is a two-channel individual control system. This paper presents an analysis of these two types of TCS configurations in terms of handling, acceleration, stability, yaw convergence and other performance parameters. The systems are compared with and without a limited-slip differential (LSD) under various road conditions, based on experimental data and computer simulations. As a result of this work, certain Nissan models are now equipped with a new Nissan Traction Control System with a rear viscous LSD (Nissan V-TCS), which provides both the advantages of a rear viscous LSD in a small slip region and a two-channel TCS in a large slip region.

This paper proposes a new hierarchical optimization technique for the vehicle body structure, by combining topology optimization and shape optimization based on the traction method. With the proposed approach, topology optimization is first performed on the overall allowable design domain in 3D. The surface is extracted from the optimization result and converted to a thin shell structure. Shape optimization based on the traction method is then applied to obtain an overall optimal body shape. In the shape optimization process, iterative calculations are performed in the course of consolidating parts by deleting those whose contribution is small. The result obtained by applying this method to the front frame structure of a vehicle is explained. The resultant optimal shape has stiffness greater than or equal to the original structure and is 35% lighter. This confirms the validity of the proposed technique. It was found, however, that some issues remain to be addressed.

In order to satisfy increasing customer demands on ride quality as well as expectations for off-road performance of sport-utility vehicles (SUVs), it is necessary to develop technologies which offer enhanced levels of both performances. For ride quality, it is important to minimize body roll angle during cornering, which is achieved by suppressing suspension travel, and also to reduce vertical motion during straight-ahead travel. While for off-road performance, it is necessary to allow a long suspension stroke to allow a high level of off-road traction by delivering driving force reliably to the surface. These two performance parameters require a tradeoff with respect to vehicle roll stiffness. To reconcile these conflicting performance requirements, for first time in the world we adopted for production vehicles the system which connects the four shock absorbers together.

The research into vibration characteristics of a loaded and rolling tire is essential for the prediction of spindle forces. There are tire vibration characteristics one of which is the first natural frequency of a loaded and rolling tire is lower than that of an unrolling tire. The vibration characteristics, for a loaded and rolling tire, are affected by the effect of rotation, restrictions of the vibration due to road contact, and the behavior of rubber dependent on amplitude strain. The consideration of the degradation of natural frequency is therefore necessary in the tire model for prediction of spindle forces. This paper describes an identification method for the tire equivalent stiffness of a tire model focused on vertical spindle forces. The first mode is dominant in vertical spindle forces. First, the natural frequencies in rolling and unrolling tires are identified by operational impact test.

Research into stability at high speed shows that rear suspension characteristics play an important role in vehicle control and stability. In order to improve the cornering limit steering performance and traction of front-wheel-drive vehicles, where the front wheels bear a large proportion of the load and transmit the driving force, and to maintain vehicle stability when decelerating while cornering, rear suspension characteristics are needed that will fully draw out the cornering force capacity of the rear tires. This requirement continues to grow every year, along with demands for higher levels of comfort in passenger cars, including improved ride quality and quietness. It was against this background that the new multi-link beam rear suspension, which is installed in the new Maxima and Sentra models, was developed. This paper describes the aims, construction, characteristics and effects of this new suspension, with focus on vehicle control and stability.

This paper presents a new electronic torque split four-wheel-drive system called All-Mode 4WD, which has been adopted in the latest generation of sport-utility vehicles (SUVs). As a torque split system designed specifically for SUV use, it provides stable driving performance matching the driver's intentions under all sorts of operating conditions, from a completely natural on-road driving feel to powerful traction for off-road travel.

Judging from viewpoint of automotive safety and more space by eliminating a spare tire, the development of the run-flat tires is important. Many problems relating to weight increase and usability had to be solved in the course of the development of such tires. The “ N ” type run-flat tire, described in this paper, has a simple structure with reinforced side walls and additional beads to fit the rim flanges. Though this tire system brought about a small amount of weight increase, it needs no special part, therefore the conventional road wheels, air valves and tire changers may be used. We have tested and evaluated this tire system equipped with passenger cars as well as on the test machines. Especially vehicle dynamics such as steering, stability and so forth were tested. The test results indicated that this tire system is practical enough.

From the view point of vehicle weight reduction and saving resources, it would be desirable to decrease the steering effort eliminating the assistance of power. Therefore, we have analyzed the steering effort at low vehicle speeds where steering effort is great, and have introduced a theoretical model based on the contact surface deflection recovering process of rolling tires. This deflection comes from the lateral rigidity and the total deflection of tires. The following results were obtained from this study. As the vehicle speed increases, the steering effort decreases exponentially. As the steering speed increases or as the vehicle speed decreases, the steering effort increases and the effort approaches the final value which equals the static steering effort. The static steering effort is not relative to steering speed. These theoretical results are supported by vehicle experiments.

Basic vehicle performance, such as Safety, Comfort and Economy, are by dependent on tire performance, and it is the air pressure in the tire which assures this performance. However, tire air has a tendency to leak naturally, making it necessary to check them periodically. Since a deterioration in vehicle performance resulting from a drop on tire air pressure can not be directly felt by the driver, the number of people maintaining their tires sufficiently is relatively few. There have been many tire pressure warning devices developed which advise the driver when the pressure drops below a prescribed level. Differing from conventional devices, the TWD-III features a 7-step digital display (at a pitch of 0.1 kgf/cm2) which shows the pressure of each tire within an optional range, and it also has a flat tire warning function. The employment of echo effect from clystal vibrator resonance precludes the need to attach a power source on the tire.

This paper presents a new system for controlling the braking force between the inner and outer wheels in a turn independently. Vehicle cornering performance has improved noticeably in recent years thanks to advances achieved in tire and suspension technology. Due to this improvement, vehicle handling characteristics during braking have taken on added importance. To achieve stabler handling properties during braking in a turn, a new evaluation method is being used at Nissan to analyze vehicle directional stability. The analytical results show that decreasing the yaw moment before wheel locking occurs is effective in achieving stabler handling. An effective approach to decreasing the yaw moment is to control the braking force between the inner and outer wheels independently. Base on these analytical results and experimental data obtained with actual vehicles, a new system has been developed that provides such independent control over the braking force.

Road Noise is generated by the change of random displacement input inside the tire contact patch. Since the existing 3 or 6 directional electromagnetic shakers have a flat surface at the tire contact patch, these shakers cannot excite the vehicle in a manner representative of actual on-road road noise input. Therefore, this paper proposes a new experimental method to measure the road noise vehicle transfer function. This method is based on the reciprocity between the tire contact patch and the driver's ear location. The reaction force sensor of the tire contact patch is newly developed for the reciprocal loud speaker excitation at the passenger ear location. In addition, with this equipment, it is possible to extract the dominant structural mode shapes creating high sound pressure in the automotive interior acoustic field. This method is referred to as experimental structure mode participation to the noise of the acoustic field in the vibro-acoustic coupling analysis.

At Nissan we have developed a new parallel hybrid system for rear-wheel-drive hybrid vehicles. As the main components of the hybrid system, both the motor and the inverter have been developed and are manufactured in house to attain high power density for providing responsive acceleration, a quiet EV drive mode and improved fuel economy. Because the motor is located between the engine and the transmission, it had to be shortened to be within the length allowed for the powertrain. Therefore, new technologies have been developed such as high-density, square-shaped windings and an optimized magnetic circuit specially designed for concentrated winding motors. The inverter is sized to a 12V battery, which it replaces in the engine compartment. Despite its compact size, the inverter must have rather large current capacity to drive a high-power motor. Heat management is critical to the design of a small but high-power inverter.

Early studies on the tire vibration characteristics of road noise focused on radial modes of vibration because these modes are dominant in vertical spindle force. However, recent studies of Noise, Vibration and Harshness (NVH) prediction have suggested that tire modeling not only of radial modes, but also of lateral vibration, including lateral translational and lateral bending modes, affect interior noise. Thus, it is important to construct tire dynamic models with few degrees of freedom for whole-vehicle analysis of NVH performance. Existing tire dynamics model can't express tire lateral vibrations. This paper presents a new approach for tire vibration analysis below 200Hz, and a formula for tire natural frequencies. First, a tire dynamic model is developed based on the thin cylindrical shell theory. Kinetic and potential energies are derived. Mode shape function is also derived by the assumption of inextensility in the neutral of the tread ring.