ARTICULATED VEHICLE SYSTEMS

Articulated Wheeled Vehicles (AWVs) are a class of wheeled locomotion systems where the chassis is connected to a set of ground-contact wheels via actively- or passively-controlled
articulations, which can regulate wheel placement with respect to chassis during locomotion. In this paper the design, development and integration of vibration isolated mobile trailer platform, customized to meet the user’s requirements in general and optical requirements in particular is
discussed. The study also focusses on performance requirements, system requirements and technical details of the articulated vehicle system.

1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 7, July (2014), pp. 36-41 © IAEME
36











ARTICULATED VEHICLE SYSTEMS


Apoorv Prem

B.E Automobile Engineer, Manipal Institute of Technology



ABSTRACT

Articulated Wheeled Vehicles (AWVs) are a class of wheeled locomotion systems where the
chassis is connected to a set of ground-contact wheels via actively- or passively-controlled
articulations, which can regulate wheel placement with respect to chassis during locomotion. In this
paper the design, development and integration of vibration isolated mobile trailer platform,
customized to meet the user’s requirements in general and optical requirements in particular is
discussed. The study also focusses on performance requirements, system requirements and technical
details of the articulated vehicle system.

Keywords: Articulated, Trailer.

I. INTRODUCTION

An articulated vehicle is a large vehicle made in two separate sections, a tractor and a trailer,
connected by a pivoted bar. These vehicles can cary heavy loads and can take sharp turns. An
articulated truck is a vehicle that is most commonly used in construction work. Articulated trucks are
used to haul heavy loads, sometimes over difficult terrain, and they can be considered a type of
tractor-trailer unit.
The main feature of an articulated truck that puts it in a separate driving class is its drive
system. The drive system is based on the number of wheels on the axles used to pull the truck [1].
The most common system is the 6 x 6 system, in which the truck has six wheels on three axles and
all are used when driving the truck.
Another system used is the 6 x 4 drive, in which only the rear four wheels are used when
driving. The original drive system in articulated trucks is the famous 4 x 4 drive. This was designed
for trucks that drive over the roughest terrain on the planet [2]. The 4 x 4 drive system helps the truck
maneuver over terrain that could be a potential problem for the goods being carried.
Wheeled Mobile Platforms/Vehicles comprise of a platform supported by multiple wheels
which allow for relative motions between the platform and the ground. Wheeled vehicles have
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2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 7, July (2014), pp. 36-41 © IAEME
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traditionally offered simplicity of mechanical construction and control, very favorable payload-to-
weight ratio, excellent load and tractive-force distribution, enhanced stability and energy-efficiency,
making them the architecture of choice for most man-made terrestrial locomotion systems [3].
However, despite their incredible versatility, disk wheels impose severe constraints on the
design and control of the wheeled vehicle to which they may be attached. Multiple disk-wheels
cannot be arbitrarily attached to a single common platform/chassis without over-constraining the
system[4]. Kinematic over-constraint (as often seen in various machinery) occurs due to the lack of
compatibility between the instantaneous motions of all moving parts. However, unlike in traditional
machines, the violation of the wheel-ground contact-constraints (enforced only by force-closure) is
possible – and gives rise to undesirable kinematic wheel-slip (skidding/ slipping/scrubbing) seen in
poorly-designed wheeled vehicles [5]. Such wheel-slip is deleterious both from the perspective of
reduced efficiency (power is wasted by scrubbing) and poor performance (degraded odometric
localization, uncontrollable and unpredictable stick-slip behavior).
Kinematic over-constraint has traditionally been relieved by the addition of mechanical
compliance (in the form of bushings and couplings) in order to mitigate the undesired stick-slip
behavior at the wheel-ground contact. A case can be made for the systematic and careful introduction
of additional mechanical compliance – in the form of small articulated sub-chains with passive
(springs/dampers) or semi-active (adjustable spring-dampers) or active (motorized) actuation. The
resulting articulated leg-wheel systems form multiple closed-kinematic loops with the ground that
serve to constrain and redirect the effective forces and motions on the chassis.
Thus, viewing wheeled vehicles as yet another class of a parallel-kinematic chains (with
multiple articulated leg-wheel branches attached to a common chassis) allows the systematic
application of the rich theory of articulated multibody systems to design, analyze, simulate and
control of the ensuing systems. The nature and number of both the added wheels, together with the
intermediate articulations, has a significant influence on the mobility, maneuverability,
controllability, stability and efficiency of the wheeled vehicle [1].
From a design perspective, there is enormous diversity at various levels within selection of:
(i) the individual components, like the wheels (disk wheels vs Mecanum wheels) and the
articulations (lower-pair revolutes/prismatics vs higher-pair cam joints); (ii) the topology/number of
joints of each sub-chain; and (iii) the number of sub-chains/type-of-attachment to the chassis. The
suitable selection of topology, dimensions and actuation of the individual sub-chains together with
the selection of the number and attachment location to the common chassis creates enormous choice.
From the control perspective, the control and reconfiguration of the collaborating leg-wheel
subsystems to regulate the mobility and maneuverability of the chassis offers other challenges.
System configurations must be chosen in order to: (i) minimize singular configurations of the
system; (ii) enhance mutual cooperation (motions and forces) during task performance; and (iii)
improve robustness to local controller lapses and environmental disturbances [6]. Significant
freedom for implementation is also available by virtue of the re-configurability and the ability to
trade-off passive-equilibration versus active-actuation [7].
However, articulated wheeled vehicles are highly-constrained systems subjected to both
holonomic constraints (due to the multiple closed-loops) and non-holonomic constraints (due to
wheel/ground contacts). Violation of these constraints e.g. typically in terms of slipping and skidding
at the ground-wheel contacts, results both in energy-dissipation and estimation-uncertainty [5].
Hence considerable research has focused on both enhanced-suspension-design (kinematic and
kinetostatic), to avoid constraint violation without either sacrificing payload capacity or increasing
power consumption; and active-coordinated-control for enhancing mobility, stability and traction.

3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 7, July (2014), pp. 36-41 © IAEME
38

II. DESIGN AND DEVELOPMENT OF MOBILE TRAILER PLATFO RM

Following section discusses the design and development of a mobile trailer platform
undertaken at DRDO for military applications.
Sub-system of mobile trailor platform: The complete system of mobile trailer platform
consists of the following sub-systems;

Well bed full-trailer with Air Bag Suspension
Auto Leveling System
EMI shielded A/C control room
3 Axes alignment system
Metallic Sliding Canopy
Vibration Isolation System
Nitrogen Gas Purging System

Well bed full trailer wit airbag suspension: Fig. 1 shows a well bed full-trailer with air bag
suspension. It has a payload capacity of 8 tons. Depending on the load the overall trailer frame length
and width will be approximately 10000mm and 3000mm respectively. The pressure in the airbag is
15-20psi when loaded or when towing. Air bag suspension on both axes should be capable to reduce
the vibration during transportation by normal road/rough road to less than 0.75 g and impulse of 5 g
at the speed of 60 km/hr on plain road and 30km/hr on rough road. Input shock level at axle will be
from 5 to 10 g. The air should be tapped from the trailer brake circuit with suitable pressure
protection valve and air reservoir. One disadvantage of airbags is that they limit wheel travel because
they can only flex so far since they are attached to both the frame at the top and axle at the bottom.
Provision is made to mount four Nitrogen Cylinders at the front deck with suitable clamping facility.
Further, a floor sheet is provided to make the well bed dust proof. Provisions are also made to mount
other accessories like ladder, tool box etc.

III. STRUCTURE AND BRAKES

Welded structure shall be fabricated from Sailma Steel-350 (Specifications-Yield Strength
350Mpa and Ultimate Tensile Strength 610Mpa).
The trailer structure shall be optimally designed to withstand loading pattern, minimum
vibration during operation and transportation, meeting leveling accuracies and to suite mounting of 3
axes alignment system.
Trailer brakes are actuated from tractor. Twin line air brake system is coupled to tractor brake
system through palm coupling. Pressure protection valve is to be provided in the circuit. Fail safe
automatic braking and mechanical parking brakes are to be provided. The pneumatic lines from Air
bag suspension and anti-vibration air mounts charging shall be tapped from brake system through an
air reservoir.

IV. AUTO LEVELING SYSTEM

Auto-Leveling System: Auto leveling system is used to check and monitor the land
irregularity. It has got two sensors to level the vehicle in longitudinal direction called X-sensor and
in transverse direction called Y-sensor. These sensors will sense the irregularities on the land and
send a signal to the four mechanical actuators. Each mechanical actuator is driven by a servomotor.
The actuation is further amplified by the amplifier and sends to controller. The controller is
connected to the computer through data acquisition system which will acquire the data, convert it in

4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 7, July (2014), pp. 36-41 © IAEME
39

to digital signal and display on the monitor. The land irregularities are red in minutes. The accuracy
of the measuring instrument is limited to ±5 min in longitudinal direction and ± 2 min in transverse
direction.
The trailer shall be provided with PLC based Auto-Leveling System to level the trailer
platform within accuracy as per required. Four electrically actuated mechanical jacks to be provided.
The mounting bracket surface shall be machined and leveled with trailer chassis frame and auto level
clino-meter mounting surface plate. The boring in jack mounting bracket shall be exactly vertical.
The other sub-assembly of auto leveling like power amplifier, connectors and cable-harness shall be
mounted suitable.

V. EMI SHIELDED CONTROL ROOM AND 3AXES ALINGNMENT S YSTEM

EMI shielded Air conditioned control room: The control room is shielded from
electromagnetic radiations to protect it from th laser system. There are many methods available for
making an enclosure shielded against EMI/RFI. To produce a
Faraday Cage, you need a metal enclosure, which will absorb/reflect the Electromagnetic energy.
Nonmagnetic metals, such as aluminum will not work at very low frequencies; a magnetic material;
for example, Iron or Nickel is required. At high frequencies, the conductivity of the material dictates
its effectiveness. Conductive Plastic is the best solution for some styles of plastic enclosures. The
plastic is compounded with stainless steel fibers, forming a 3 dimensional conductive matrix inside
the base material. This method provides a consistent enclosure, with no secondary coating quality
issues.

3 Axes alignment system: A platform to support 2ton load and to provide movements X axis-
150mm(±100mm) , Z axis-100mm(±50mm) and yaw ±5 degrees to facilitate alignment with another
system. It consists of a laser system to align two components in all the three directions. The
alignment accuracy of the system is ±0.5mm for linear alignment and ±0.5deg for rotational
alignment.

VI. METAL SLIDING CANOPY

This canopy is used to enclose equipment in trailer well bed. It is a dust proof, waterproof
sliding canopy made of galvanised iron. The canopy for the present system is designed for the
following specifications. The structural, members, foldable rails, front and rear panels shall be
integrated with the trailer.

Ground Clearance-350mm
-- Ramp Angle-6deg
-- TCD (along with suitable tractor)-<25m±1
-- Max speed-40 to 50 km/hr plain road and 30km/hr on Rough roads
-- Temperature- 10 to 55 deg C (operation)
-- Humidity-Humid < Salt, dusty condition
-- Wind speed-108km/hr for survival and 72km/hr for operation
-- Vibrations-1.5g during transportation

VII. VIBRATION ISOLATION SYSTEM AND NITROGEN GAS PU RGING

Vibration Isolation System: Sufficient number of vibration air mounts on the top of 3 axes
alignment system to support the optical equipment of average payload 1900 kg.

5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 7, July (2014), pp. 36-41 © IAEME
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Nitrogen gas purging system: Four Nitrogen Cylinders as per specifications are provided on
the front deck with suitable clamping. It is used to create an inert atmosphere. Moisture has a
damaging effect on the integrity and performance of electro-optical equipment and other sealed
enclosures, corroding electronics and condensing on optical surfaces. Dry gas purging is frequently
used to create very low dew points within sensitive equipment

FIGURES

NO 1 – AIR SUSPENSION NO 2 – AUTO LEVELLING SYSTEM




NO 3 – METAL SLIDING CANOPY





CONCLUSION

A study is made on the articulated vehicle system to explore the accessories such as auto
levelling system, 3-axis alignment system, and vibration isolation system etc., required for the testing
of various parts of an articulated vehicle.

6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print),
ISSN 0976 – 6359(Online), Volume 5, Issue 7, July (2014), pp. 36-41 © IAEME
41

ACKNOWLEDGMENT

Special thanks to Mr Raveesh Kumar, my guide, without whose help and valuable
suggestions this project wouldn’t have been possible. Also to DRDO, for allowing to work on their
prestigious project.

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