3 - Chapter2-Vehicle Performance_1_

3 - Chapter2-Vehicle Performance_1_ - Road Vehicle...

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Road Vehicle Performance: Introduction and Resistance TTE 4004 Lecture 3 8/26/11
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Outline Recap – Introduction to Transportation Introduction to vehicle performance Resistance Aerodynamic resistance Rolling resistance Grade resistance Tractive effort Maximum tractive effort Engine-generated tractive effort Vehicle acceleration Braking
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Role of the Transportation Engineer To move people and goods safely and efficiently
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Vehicles vs Drivers
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Transportation Technology Traffic control strategies Advanced detection and control technologies Advanced traffic management systems Traffic management centers Ramp metering Managed lanes ITS Advanced traveler information systems
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Vehicle Performance
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Introduction Roadway design is governed by two main factors: Vehicle capabilities acceleration/deceleration braking cornering (chap. 3) Human capabilities (chap. 2, chap. 3) perception/reaction times eyesight (peripheral range, height above roadway)
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Introduction Performance of road vehicles forms the basis for roadway design guidelines such as: length of acceleration / deceleration lanes maximum grades stopping-sight distances passing-sight distances setting speed limits timing of signalized intersections
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Introduction Studying vehicle performance serves two important purposes: 1. provides insight into roadway design and traffic operations and the compromises that are necessary to accommodate the wide variety of vehicles that use roadways 2. it forms a basis on which to assess the impact of advancing vehicle technologies on existing roadway design guidelines
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Tractive Effort and Resistance These are the opposing forces that determine straight-line performance of road vehicles Tractive effort is simply the force available at the roadway surface to perform work (expressed in lbs [N]) Resistance (expressed in lbs [N]) is defined as the force impeding vehicle motion
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Resistance Three major sources of vehicle resistance are: Aerodynamic Rolling (originates from the roadway surface/tire interface) Grade or gravitational
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Resistance Illustration of forces with vehicle force diagram F f   +  F r   =  ma  +  R a   +  R rlf   +  R rlr   +  R g F  =  ma  +  R a  +  R rl  +  R g Fig. 2.1 (Eq. 2.1) (Eq. 2.2)
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Aerodynamic Resistance Can have significant impacts on vehicle performance, particularly at high speeds. Aerodynamic resistance originates from a number of sources: Turbulent flow of air around the vehicle body (≈ 85%) Function of shape of vehicle, particularly the rear Friction of air passing over vehicle body (≈ 12%) Air flow through vehicle components such as radiators and air vents (≈ 3%)
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Aerodynamic Resistance Based on these sources, equation for determining aerodynamic resistance is: R a         =   Aerodynamic resistance in lb (N)
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This note was uploaded on 12/07/2011 for the course TTE 4004 taught by Professor Staff during the Fall '08 term at University of Florida.

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3 - Chapter2-Vehicle Performance_1_ - Road Vehicle...

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