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11
. ECAS introduction
11.1 ECAS introduction
The name ECAS stands for Electronically Controlled Air Suspension.
ECAS is an electronically controlled air suspension system with a large
number of functions.
Air suspension systems have been used in motor vehicles since the mid 50s-especially in buses. Air suspension
systems are used in them as a standard and are increasingly being used in trucks and trailers. The advantages of air
suspension over mechanical suspension (steel springs) are listed below:
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Increase in ride comfort due to lower spring rate and low natural frequency
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constant vehicle height irrespective of the load
•
precise load-dependent activation of the brakes through use of the air bellows pressure as control pressure for the
proportioning valve
•
Kneeling function (lowering of one side of the vehicle to facilitate entry and exit)
The control system was initially designed with pure mechanically operating leveling valves, soon afterwards
electromechanical control systems were developed. This served to enhance ease of operation and to facilitate
raising/lowering processes.
ECAS is the most advanced development in this direction. Using electronic control units enabled decisive
improvements in the conventional system; it enabled many functions for the first time ever:
•
Reduction of the air consumption-none while the vehicle is moving. Air savings of approximately 25 % were
determined using ECAS compared to a conventional air suspension system in low-floor buses for scheduled route
services.
•
High speed of all control processes due to large valve cross-sections (nominal size 7 per air bellows).
•
Easy installation. Only one air line is required from the solenoid valve block to each bellows and one to the
storage tank.
•
Raising/ lowering function and kneeling conform to the legal requirements
•
High system flexibility for different kneeling types
•
Extensive safety concept, error storage and diagnostics capabilities.
In mechanically controlled air suspension systems, the device that measures the level also controls the air spring.
With ECAS, an electronic system takes over control, regulating the air springs by means of solenoid valves
informed by measured values from sensors.
Apart form controlling the normal level, the electronic unit also covers control of the other functions: working
together with control switches and sensors for the tyre deflection compensation, the ECU achieve this without the
need for numerous additional valves required by conventional air suspension control. ECAS at different
configuration levels can be fitted in various bus types.
The ECAS system in a bus consists of the following components:
•
an ECAS electronic unit (ECU)
•
a solenoid valve (solo vehicle)
•
3 distance sensors
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optionally 1 pressure sensor