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CHAP   1 - Introduction
CHAP   2 - Some Basic Specs
CHAP   3 - Locations of Major Equipment
CHAP   4 - the "TRACS" Computer System
CHAP   5 - the High Voltage, Auxiliary and Propulsion Systems
CHAP   6 - the Low Voltage Systems and Batteries
CHAP   7 - the Air System
CHAP   8 - the Braking System
CHAP 9 - the Suspension System
CHAP 10 - the Trucks
CHAP 11 - the HVAC Units
CHAP 12 - the PA and Intercom System
CHAP 13 - the Pantographs
CHAP 14 - the Doors
CHAP 15 - the Couplers
CHAP 16 - the Lighting System
CHAP 17 - the Destination Signs
CHAP 18 - Winterization
CHAP 19 - Operation
CHAP 20 - Maintenance
CHAP 21 - Floobydust

9.1    The Baltimore LRV’s utilizes two suspension systems, chevrons and airbags.  The chevrons are the primary suspension system, and the airbags make up the secondary suspension system.

9.2    The chevrons are made up of rubber and metal “V” shaped layers.  The rubber allows the truck to absorb the shocks and vibration transmitted by the axles.  The chevrons bolt to the truck frames, and pretty much sit in the top of the truck frame well.  Over time, they lose their rigidity, and will allow the truck (and car body) to get closer and closer to the rails.  Adjustments are made to the “car-height” as part of the annual inspection.  The height adjustment is made by inserting shims between the top of the chevron and the truck frame well.  The biggest problem with the adjustment procedure is that it only has provisions for either “new” or “old” chevrons, and doesn’t have any flexibility for accommodating chevrons that are “in-between”.  Someday engineering or management will wake up to this problem in performing car-heights.  Chevrons are graded and numbered after manufacturing, and like numbered chevrons must be used on the same truck.  The chevrons are also responsible for the trucks being of a radial-steering design, where the axles can supposedly follow minor variations in the straightness of the track, thereby reducing wheel, flange, and rail wear.  One of these days I will add a picture of the chevrons in here.

  Picture 9-1  A single Chevron, there are two per axle per side.

  Picture 9-2  One axle with both Chevrons.

9.3    The air bag suspension (picture 9-3) allows the LRV to react to changing loads (people getting on and off) and keep the car-height fairly constant.  Both powered trucks, on both sides, have a position sensing air valve (also shown in picture 9-3) mounted on them.  There is an arm on this valve, which mounts to the car body and senses any change in truck-to-car-body height.  The valve compensates for this change by adjusting the pressure going to the air bag.  Normal air bag pressure is around 70PSI.  Despite the fact that the air bag, or “donuts” as we call them, are exposed to the elements, they have performed quite well for the past 15 years (as of 2005)(no cracks or splits), and I don’t know of any that have been replaced.  They are manufactured by TOYO in Japan, and are made of rubber.  Pressure transducers are also connected to the output side of the position sensing valves – and the output feeds an analog weight signal to the computer.  The computer checks these values every time the doors are closed.

Picture 9-3  Air bag suspension and leveling valve

9.4    When we discuss the suspension, along with things such as acceleration, braking, and cooling, we have to consider how much the car weighs because the weight of the car directly affects those variables.  There are four key weight definitions that are used for testing and specifying purposes:
    AW0 is the weight of an empty car - around 54 tons, or 107,400 pounds.
    AW1 is with every seat filled, and is rated at 120,400 pounds.
    AW2 is with all the seats filled and one “body” every 3 square feet.
    AW3 is a fully loaded car with a crush load (one person every square foot in addition to those that are seated), and is 147,400 pounds.

9.5    In addition to making the ride smoother in the vertical plane, there are also dampers for travel in the horizontal plane.  Although they do not provide the same amount of " help" the air bags do, they nevertheless help to take the edge off of some of the jolts encountered when traversing a switch (for instance).  A horizontal stabilizer in shown below in picture 9-4.

  Picture 9-4   Horizontal stabilizer / shock

New 10/6/2006....
Last Modified Tuesday, 11 April 2017