Search Results

This paper presents an analysis of coupled longitudinal and lateral dynamics of a 4×4 hybrid-electric off-road vehicle (HEV) with two passive driveline systems, including drivelines with (i) an interaxle open symmetrical differential in the transfer case and (ii) a locked transfer case, i.e., positive engagement of two axles. The axle differentials are open. As the study proved, lateral dynamics of the 4×4 HEV, characterized by the tire side forces, vehicle lateral acceleration, yaw rate and tire gripping factors can be impacted by the tire longitudinal forces, whose magnitudes and directions (positive-negative) strongly depend on the driveline characteristics. At the same time, the tire side forces impact the relation between the longitudinal forces and tire slippages.

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.

Stability of motion, turnability, mobility and fuel consumption of all-wheel drive terrain vehicles strongly depends on engine power distribution among the front and rear driving axles and then between the left and right wheels of each axle. This paper considers kinematic discrepancy, which characterizes the difference of the theoretical velocities of the front and rear wheels, as the main factor that influences power distribution among the driving axles/wheels of vehicles with positively locked front and rear axles. The paper presents a new algorithm which enables minimization of the kinematic discrepancy factor for the improvement of AWD terrain vehicle dynamics while keeping up with minimal power losses for tire slip. Three control modes associated with gear ratio control of the front and rear driving axles are derived to provide the required change in kinematic discrepancy. Computer simulation results are presented for different scenarios of terrain and road conditions.

A new inter-disciplinary degree program has been developed at Lawrence Technological University: the Master of Science in Mechatronic Systems Engineering Degree (MS/MSE). It is one of a few MS-programs in mechatronics in the U.S.A. today. This inter-disciplinary program reflects the main areas of ground vehicle mechatronic systems and robotics. This paper presents areas of scientific and technological principles which the Mechanical Engineering, Electrical and Computer Engineering, and Math and Computer Science Departments bring to Mechatronic Systems Engineering and the new degree program. New foundations that make the basis for the program are discussed. One of the biggest challenges was developing foundations for mechanical engineering in mechatronic systems design and teaching them to engineers who have different professional backgrounds. The authors first developed new approaches and principles to designing mechanical subsystems as components of mechatronic systems.

All-wheel drive (AWD) vehicle performance considerably depends not only on total power amount needed for the vehicle motion in the given road/off-road conditions but also on the total power distribution among the drive wheels. In turn, this distribution is largely determined by the driveline system and its mechanisms installed in power dividing units. They are interwheel, interaxle reduction gears, and transfer cases. The paper presents analytical methods to evaluate the energy and, accordingly, fuel efficiency of vehicles with any arbitrary number of the drive wheels. The methods are based on vehicle power balance equations analysis and give formulas that functionally link the wheel circumferential forces with slip coefficients and other forces acting onto an AWD vehicle. The proposed methods take into consideration operational modes of vehicles that are tractive mode, load transportation, or a combination of both.

Running abilities of an off-road, all-wheel drive vehicle depend considerably not only on total traction effort but also on its distribution among the drive wheels. This distribution is largely determined by mechanisms and systems installed in power dividing transmission units. These are interwheel differentials, interaxle reduction gears, and transfer cases. To control the wheel driving forces for obtaining the optimum vehicle properties, a more creative and efficient way to design wheel drive systems and to control vehicle running abilities is being proposed. Optimization criteria for the tractive and velocity properties, fuel consumption, turnability, and ride stability of a vehicle have been used for the mathematical optimization of the wheel driving forces. The vehicle is modeled in motion with taking into account the kinematic requirements.

The field of Vehicle Dynamics as the theory of a vehicle in motion is to study the vehicle's properties (vehicle running abilities) in the interaction of the vehicle and it's surroundings. This interaction itself appears through forces acting on a vehicle. To control these forces leads to control the properties of a vehicle in motion such as tractive and velocity properties, fuel consumption, turnability, ride stability and others. This paper proposes a unique and novel theory of a vehicle in motion. This theory allows parallel control of the forces acting on a vehicle, which leads to considerable improvement of the vehicle's running abilities. This paper presents the interrelation between the criteria of vehicle running abilities and output characteristics of vehicle systems, which control the vehicle forces. To optimize a vehicle's running abilities require optimization of the combinations of forces acting on a vehicle.

As proven, both friction in the gearing and movement of the contact point of the teeth in mesh along the pressure line generate vibrations of the axial components of the resultant force acting in a couple of mating straight bevel gears. The vibrations of the real forces in gearings cause an increased dynamic pressure on and, accordingly, damage of frictional surfaces of differential parts. The law of summing up the axial components of all the gearings in two and four pinion differentials depends on combinations of numbers of the side gear's and pinion's teeth. A classification of bevel gear differentials into four groups depending on those combinations has been carried out. Differentials of the four groups have different degrees of the axial force vibration. The paper presents a detailed method to evaluate theoretically the axial forces in each of the groups. As shown, differentials from one of the four groups (Group III) have decreased axial force vibrations.

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.

To evaluate traction and velocity performance and other operational properties of a vehicle requires data on some tire parameters including the effective rolling radius in the driven mode (no torque on a wheel), the effective radii in the drive mode (torque applied to the wheel), and also the tire longitudinal elasticity. When one evaluates vehicle performance, these parameters are extremely important for linking kinematic parameters (linear velocity and tire slip coefficient) with dynamic parameters (torque and traction net force) of a tired wheel. This paper presents an experimental method to determine the above tire parameters in laboratory facilities. The facilities include Lawrence Technological University's 4x4 vehicle dynamometer with individual control of each of the four wheels, Kistler RoaDyn® wheel force sensors that can measure three forces and three moments on a wheel, and a modern data acquisition system. The experimental data are also presented in the paper.

In the absence of a physical driveline between the wheels powered by individual electric motors, in this paper, a concept of the virtual driveline system was applied to a small skid-steering unmanned ground vehicle (UGV) for the purpose of controlling its maneuverability, i.e., for fulfilling desired maneuvers in terrain zones constrained by natural and man-made objects. The virtual driveline concept supposes that the UGV driving wheels are connected via a virtual driveline that is a computational code to manage the power split among the wheels by using characteristics of a mechanical driveline system. The kinematic discrepancy factor (KDF) as a mechanical driveline characteristic is utilized to mathematically link the angular velocities and the drive torques of the electrically driven wheels.

When a vehicle moves over uneven ground, motion of the sprung and unsprung masses causes dynamic shifting in the load transmitted to the ground, making the normal reaction in the tire-soil patch a continuously changing wheel parameter that may affect vehicle performance. At high loads, sinkage of the wheel can become high as the wheel digs into the soil. At low loads, the wheel can have difficulty acquiring sufficient traction. Additionally, steerability of the wheel can be diminished at very low loads. Controlling the damping forces in the suspension that is usually used to improve ride quality and stabilize motion of the sprung mass can result in an increase in the dynamic variation of the wheel normal reaction and cause vehicle performance deterioration. In this paper, a method is developed to establish boundary constraints on the dynamic normal reaction to maintain reasonable tire-terrain mobility characteristics.

In-wheel electric motors open up new prospects to radically enhance the mobility of autonomous electric vehicles with four or more driving wheels. The flexibility and agility of delivering torque individually to each wheel can allow significant mobility improvements, agile maneuvers, maintaining stability, and increased energy efficiency. However, the fact that individual wheels are not connected mechanically by a driveline system does not mean their drives do not impact each other. With individual torques, the wheels will have different longitudinal forces and tire slippages. Thus, the absence of driveline systems physically connecting the wheels requires new approaches to coordinate torque distribution. This paper solves two technical problems. First, a virtual driveline system (VDS) is proposed to emulate a mechanical driveline system virtually connecting the e-motor driveshafts, providing coordinated driving wheel torque management.