Cab Access Steps with Coplanar Door Extension for Drag Reduction
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Solution Overview
Problem
Conventional semi-tractor vehicles experience increased aerodynamic drag due to turbulent airflow around the cab access steps and the interface between the cab and chassis, with existing solutions often being complex and difficult to use.
Innovation Solution
The design features a cab with recessed steps covered by a lower door extension that matches the outboard extension of the fender, creating a smooth, angled transition between the cab and chassis, reducing the complexity of step deployment and shielding the steps from road spray, while the angled gap between the cab and chassis fairing directs airflow around the vehicle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If access steps are reduced in size and placed in shallow recesses to minimize aerodynamic drag, then aerodynamic performance is improved, but the steps become more difficult to use
Solution Approach 1:
The step assembly is made movable between a retracted position (flush with vehicle body) and an extended position (protruding for use). The door extension automatically deploys the steps when the door is opened, and retracts them when the door is closed, allowing the system to adapt its configuration based on operational needs versus aerodynamic requirements
2Loss of energy
If concealed or deployable step designs with mechanical linkages or actuators are used to improve aerodynamic performance, then aerodynamic drag is reduced, but the system complexity increases
Solution Approach 1:
The door extension serves multiple functions: it provides the necessary structural support for the steps, acts as the deploying mechanism when the door is opened, and serves as the aerodynamic fairing when closed. This eliminates the need for separate mechanical linkages or actuators, reducing system complexity while maintaining deployable functionality
Solution Approach 2:
The invention combines the door extension, step support structure, and aerodynamic fairing into a single integrated assembly. The lower door extension both covers the recesses to maintain aerodynamics and provides the structural framework for mounting and deploying the steps, merging multiple components into one unified structure
3Adaptability or versatility
If a horizontal gap is created between the cab and chassis to allow cab movement, then cab independence is enabled, but aerodynamic drag increases due to airflow through the gap
Solution Approach 1:
The lower door extension features a curved leading edge that smoothly guides airflow around the corner of the door and along the vehicle body. This curved geometry prevents sharp flow separation and reduces turbulence, allowing the gap to remain open for cab movement while minimizing its aerodynamic penalty
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration reduces aerodynamic drag by minimizing turbulence and improving airflow around the vehicle, making the steps easier to use and providing enhanced security by concealing them from potential intruders.
Implementation Method 1
Aerodynamics is a prime consideration in the design of vehicles... There are several factors that contribute to the aerodynamic drag caused by friction of air flowing around the sides of a truck or vehicle
Implementation Method 2
A key to minimizing drag is the reduction or elimination of turbulence... the lower door extension extends outboard to match the outboard extension of a fender or exterior cab side panel to provide a coplanar transition
Implementation Method 3
In conventional semi-tractor vehicles, the transition between the front fenders and the chassis fairing is often fairly abrupt due to the cab access steps. This leads to airflow separation and increased drag
Data Source
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AI summary
Vehicles are described including a cab having a door opening on a side thereof, a chassis that supports the cab, two or more steps leading to the door opening, each of which is supported by the cab or the chassis, wherein the steps are placed within the recesses in the cab or chassis, and a door connected to the cab, wherein the door fits within the door opening, and the door comprises a lower door extension having a lower edge that terminates near to an upper surface of a lowermost step, the lower door extension covers a majority of the one or more recesses, and the lower door extension extends outboard to match the outboard extension of a fender or exterior cab side panel to provide a coplanar transition from the fender to the door, or from the door to the exterior cab side panel, or both.