Vehicle dynamics

The dynamics is a specialty of the dynamics, the starting addresses of the laws of engineering mechanics and experiment consisting of found dependencies with the movement of land vehicles ( wheel, chain and rail vehicles ).

The dynamics includes investigations of distance, time, speed, acceleration, energy consumption, heating of motors, drivers, services, movement resistance, in rail- bound vehicles to be transported and the trailer loads and efficiencies of vehicles.

The dynamics uses technical, physical, mathematical and statistical foundations and in turn provides the basis for subsequent mechanical engineering, civil engineering, operational and economic investigations.

Directions of movement

A spatial movement of the bodies, the three dynamics considered translational movements in the direction of the main axes, namely

  • Longitudinal movement along the longitudinal axis, the actual change in location,
  • The transverse movement along the transverse axis. A pure lateral movement, the displacement of rolling stock on the sliding stage (s) and
  • The reciprocating motion along the vertical axis, usually combined with the longitudinal movement when driving on slopes or slope, a pure stroke realize lifting platforms and elevators,

The three rotational motions about the three principal axes ( resulting roll- pitch-yaw angle)

  • Yaw ( about the vertical axis ),
  • Nod (especially with watercraft also called stamping, about the transverse axis) and
  • Sway (especially with watercraft known as castors, around the longitudinal axis )

And two types of vibrations respectively characterized by the periodic return to the starting position (and not bonded to the main axis )

  • Translational and
  • Rotational vibration.

The order of the rotations is specified in DIN 70000 (terms of driving dynamics ) set to move from a stationary inertial system to build fixed coordinate system.

In a narrow focus (eg motor vehicles ) the dynamics is restricted to subregions, such as

  • Longitudinal dynamics (driving and braking, rolling resistance, fuel consumption, ... )
  • Transverse dynamics ( steering, cornering, steadiness, ...)
  • Vertical dynamics (comfort, cargo loading, pavement stress, ...)

The results of such consideration then find their way into the design of the drive train (engine, transmission, ...) and the chassis, especially the axle, but also increasingly in electronic driver assistance systems such as anti -lock braking system (ABS ), acceleration skid control (ASR), Electronic Stability Program (ESP ).

With two wheels ( bicycle, motorcycle, ...) can not be neglected weight and body measurements of the driver. Therefore, here driving dynamic considerations for the system are carried out driver / two-wheeler. The results are incorporated into the design of the frame, the wheels, any existing spring elements and for motorcycles as the installation position of the drive unit and the components mentioned above, if any.

The dynamics of rail vehicles which focuses on the translational locomotion of the vehicle.

Methods of driving dynamics

Analytical methods for railway vehicles

The analytical methods for kinematic analysis of vehicle movement on the rail is the simplifying assumption that the vehicle is concentrated in the form of a massless point. For resulting motion models in the form of differential equations, it is assumed here that the underlying forms of movement are continuous or sectionally continuous. The calculation is further assumed that the change in jerk, which is mathematically the 4th derivative of distance with respect to time is set equal to zero.

Driving test

Here, for example, various defined maneuvers such as

  • Straight ahead (with interference )
  • Steady state cornering
  • Load change response
  • ( single / double ) lane change ( ' elk test ' according to ISO 3888-2 )
  • Slalom maneuvers
  • Braking tests

Performed. This can be done

  • In " open loop" ( " open loop " ) with predetermined wheel torque and steering inputs and their gradients, without taking into account their impact on vehicle movement, or
  • In "closed loop" ( " closed-loop " ) with a given navigational task and performed by (mostly) experimental drivers, which take into account the vehicle reactions in their control inputs.

During these tests, a variety of different sizes usually be measured in order to derive parameters for the quantitative description of the dynamic behavior of the vehicle. However, some vehicle reactions are currently more reliable subjectively to experience and judge; it is research, with which measurable quantities correlate best Subjectively these judgments.

In contrast, longer-term test drives load parameters are measured, which are used for example, to ... to determine the load spectrum for the entire vehicle or individual components, or to the practice-relevant consumption depending on the route profile, load status, type of driver.

Vehicle dynamics simulation

Here are digital vehicle models of varying complexity, from the flat -track model of a solo vehicle to three-dimensional multi-body models (FMD), for example, multi-unit freight trains with sprung and unsprung masses, complex axle kinematics and elasto-kinematics (K & C), complex tire models and other effects used in simulation programs to specific driving virtually perform. To close the loop driver-vehicle - environment, an appropriate driver model and road model is also required. For the simulation of complex test scenarios, the driver model has to be embedded in a maneuver control to execute maneuvers instructions reliably. It is crucial that a dynamic switching between closed loop (driver - vehicle control loop) and open loop maneuver (open -loop ) in the individual phases maneuvers in the longitudinal and transverse dynamics.

Again, there are simulation calculations prolonged trips to ( engine etc., translations, switching points, masses) to determine, for example, fuel consumption or environmental impact depends on the design of the vehicle and powertrain. To simulate real driving routes such as the consumption round of " auto motor " and "sport virtually" the virtual driver must be able to (eg speed limit) to comply with relevant mandatory and prohibition signs.

An advantage of this method is the exact reproducibility, which can be different results clearly assign revised computation requirements. For this purpose it is often sufficient to replicate in detail only with respect to the vehicle of the observed effect size. Another benefit is the realization of complex causes, effects and relationships, which is heavier possible in the often limited perception / measurement reality.

On the test bench

  • Component testing ( component stress, strength)
  • Tilt test ( Oil circuit development )

Measuring equipment

The measuring equipment used in road tests are typically

  • Steering wheel angle meter
  • Accelerometer
  • Speedometer - Optical / Radar / impeller ( also 2-axis to determine the float angle )
  • Optical distance sensors
  • GPS / DGPS -based measurement systems ( position measurement)
  • Inertial Navigation System, often referred to as a centrifugal platform ( acquisition of all translational and rotational sizes)

The modern roundabout platforms are designed as GPS / INS systems. In this case ( Kalman filter ), the data of the two systems gyroplatform and GPS fused to advantageously utilize the advantages of satellite navigation and inertial navigation for the overall result with a special controller. This increases inter alia, the availability and measurement accuracy, and leads to other observable quantities (eg, float angle ).