2.2 Vehicle Dynamics Fundamentals Flashcards
What is a driveable road vehicle?
A driveable road vehicle is characterized by:
- The driver is carried on board, thus undergoing the same dynamics
- Since a road is essentially a long, fairly narrow strip, a vehicle is an object with a clear heading direction
- Roads have curves, therefore, a vehicle must have the capability to be driven in a fairly precise way
What does vehicle control fundamentally require?
Controlling a vehicle fundamentally requires simultaneous control of:
- Vehicle speed
- Yaw rate
To fulfill this task, a car driver can act (at least) on:
- Brake or accelerator pedals
- Steering wheel
Why is vehicle dynamics important for drivers?
Vehicle dynamics is important because the outcome of driver actions strongly depends on the vehicle dynamic features and state. The relationship between driver inputs and vehicle response is governed by the principles of vehicle dynamics.
What are the key components of all road vehicles?
All road vehicles have:
- Wheels, in almost all cases equipped with pneumatic tires
- Wheel hubs connected to the chassis (vehicle body) by means of suspensions (linkages, springs, and dampers)
What makes a vehicle behavior acceptable?
Acceptable behaviors for road vehicles include:
- Predictable response to driver inputs
- Stability during maneuvers
- Controlled motion in turns and straight paths
- Ability to maintain desired path
What makes a vehicle behavior unacceptable?
Unacceptable behaviors for road vehicles include:
- Unpredictable responses
- Instability during maneuvers
- Loss of control
- Inability to maintain desired path
What are the key principles of mathematical vehicle models?
A mathematical model of a vehicle should be:
- Simple, yet significant
- Based on clearly stated assumptions
- Reliable in predicting the behavior of a real vehicle under specified conditions
Assumptions concern:
- Operating conditions
- Physical models of the vehicle
What are the main operating conditions considered in vehicle dynamics?
The main operating conditions include:
- Performance: The vehicle goes straight on a flat road, possibly braking or accelerating (nonconstant forward speed)
- Handling: The vehicle makes turns on a flat road, usually with an almost constant forward speed
- Ride: The vehicle goes straight on a bumpy road, with constant forward speed
Real conditions are typically a mixture of these.
What are the key physical model assumptions in vehicle dynamics?
The key physical model assumptions include:
- The vehicle body is a single rigid body
- Each wheel hub is connected to the vehicle body by a one-degree-of-freedom linkage (independent suspension)
- The steering angle of each (front) wheel is mainly determined by the angle of the steering wheel, as controlled by the driver
- The unsprung mass (wheels) is very small compared to the sprung mass (vehicle body)
- The wheels have pneumatic tires
- There are springs and dampers between the vehicle body and the suspensions, and between the two suspensions of the same axle (roll bars)
- There may be aerodynamic devices that significantly affect the downforce
What are the fundamental geometric parameters of a vehicle?
The fundamental geometric parameters include:
- Longitudinal axis x, and hence the vehicle heading direction i
- Lateral axis y, and hence direction j
- Vertical axis z, and hence direction k
- Height h from the road plane of the center of gravity G of the whole vehicle
- Longitudinal distances a and b of G from the front and rear axles respectively (the front and rear semi-wheelbases)
- Wheelbase L = a + b
- Front and rear track widths tF and tR
- Geometry of the linkages of the front and rear suspensions
- Position of the steering axis for each wheel
What is the basic scheme of a vehicle in terms of symmetry?
The vehicle is supposed to be symmetric with respect to the x axis (longitudinal axis).
What is CAMBER angle?
The CAMBER angle is the inclination of the wheel rim with respect to the vertical axis. It affects the contact patch geometry and tire grip characteristics.
What is TOE angle?
The TOE angle is the symmetric angle that each wheel makes with the longitudinal axis of the vehicle.
Toe settings include:
- Toe-in: Front of wheels angled inward
- Toe-out: Front of wheels angled outward (negative toe)
What is the Vehicle SIDESLIP (attitude) angle β?
The Vehicle SIDESLIP angle β is the angle between the vehicle’s longitudinal axis and the direction of the velocity vector of the center of gravity. It indicates how much the vehicle is “sliding” sideways during a maneuver.
What is tire SLIP angle α?
The tire SLIP angle α is defined as the angle made by the velocity vector VC with respect to the wheel longitudinal x-axis. It is a critical parameter that determines the lateral force generation of tires during cornering.
