occurring, especially when the vehicles pass through tunnels, and the
influences of forces acting on the body will become increasingly greater
as the train speed becomes higher.
If the car body expands or contracts when running, passengers would feel
uncomfortable and the vehicles would undergo rapid fatigue, resulting in
a deterioration of car body strength. To prevent these problems, the car
bodies must have an airtight and rigid structure with minimal expansion
and contraction. Aluminum alloy structural members have been used for
this purpose. [This is quite similar to constraints associated with
aircraft body construction.]
The car body framework, almost identical to that of a house, essentially
consists of pillars and main beam members, which are reinforced with
small beams, and mounting flooring and body shell. In the 0-series and
100-series cars, steel plates of 2-3mm thickness serve as the pillars to
provide the structural strength, and steel plates of about 1.6mm
thickness are mounted on the pillars. With the 200-series cars designed
for the frigid environment in the northern part of Japan, additional
equipment and body mount covering structures down to the floor are
required, making the body heavier. To achieve weight reduction, aluminum
material is used but the basic structure remains the same as previous
models. With the "Nozomi" 300-series, thick beams have been eliminated
and a new structure, in which the structural strength is sustained by
the structure made of thin structural members, has been introduced
reducing the body weight to 6.0tons. The 200-series body weighs as much
as 8.5tons.
What made this structural renovation possible was the remarkable
progress achieved in aluminum extrusion technologies, which allows
extruding aluminum into structural members of required shape and size
usable as large plates required for Shinkansen car bodies. The large
extruded plates (with a thickness of 2.2mm, width of 600mm and height of
15-25mm and the same length of 24.5m as that of the car body) are shaped
with longitudinal structural members installed at a spacing of 80-100mm.
These plates are welded together to make principal structural members of
the car body. The walls formed with these thin extruded aluminum plates
provide the overall structural strength by its finely tuned structure,
so the fabrication of these walls requires precision machining
technology. At Kasado Works, assembly of these precision structural
members is being conducted by the advanced machinery manufacturing
technologies fostered through years in the manufacture of trains.
The plates produced in conformance with fixed specifications of about
25m long and 60cm wide has enabled automatic welding in some parts of
the assembly process since welding can be performed in a straight line.
Automation not only improves the strength but also reduces the costs of
manufacturing these structural members.
* Truck
The truck is another key component which mounts the wheels, motors,
brakes and shock absorbers necessary for running on the railway, and
supports the car body weight. It serves to transmit the forward advance
motions of the wheels revolved by the motor to the body, controls the
oscillations generated by the rails and maintains good riding comfort.
With the 0-series the truck weighs 19.1tons, and with the 100-series
9.8tons. With the 300-series trains, whose top priority had been to
achieve maximum lightness, the bolsterless structure was introduced and
weight reduction of 30% was achieved. The bolster is a large beam
installed at the central part of the truck frame, and serves to absorb
the oscillations between the car body and the truck. The development of
the pneumatic spring has made oscillation prevention possible without
using the bolster.
When a train travels at curved sections, it can pass these curved parts
more smoothly if the truck has greater flexibility. However, the
movement of the long and rigid carriage body is largely restricted, so
the truck has to cope with the constraints of the body. If the truck was
overly flexible, it would generate oscillations by itself, prompted by
diverse factors on straight track, which lead to dangerous zigzag
running movement. Therefore, running stability at high speeds and stable
performance when traversing curved tracks had to be realized in concert
with body lightening. The levels of the longitudinal and lateral
stiffnesses and other values were studied in details at the design stage
through computer simulation. Meeting these requirements, the "Nozomi"
train bolsterless truck (with an oscillation absorption system based
primarily on the air spring) has been developed. Also, wheel diameter
has been reduced to 86cm, smaller than that of other series. In
addition, the axle was changed from the conventional rod type to bored
type, and the gear case and axle box changed to aluminum.
* Driving and control system
Each carriage of the 0-series train has 4 sets of motors, the train uses
a total of 64 sets of motors, and the total output is 11,840kW. With
the 100-series train, 48 motors are used and the total output is
11,040kW. The motors used through the 100-series trains were DC, and the
100-series motor, which is lighter than that of 0-series, weighs 825kg.
With the "Nozomi," which demands higher power for running at a faster
speed, an AC motor was introduced to meet the requirement without
increasing the weight.
The rotational speed of DC motor can be altered by changing the voltage,
so it has a simple structure and is easy to control. Its weak point is
that brushes (which are heavy and require regular inspection and
replacement) have to be used to transmit electricity to the rotator. An
AC motor uses no brush, but since it is essentially a mechanism that
revolves in conformance with the current frequency, its accurate control
at high speeds is quite difficult. However, progress in the pulse width
modulation (PWM) inverter has enabled stable control and a larger
capacity. The inverter serves to convert DC current into AC current, and
can set the frequency flexibly. Hitachi has the typical PWM inverter for
the large power electric carriage motors, the variable-voltage,
variable-frequency (VVVF) system that can flexibly change not only
frequency but also voltage. A semiconductor system known as the gate
turnoff (GTO) thyristor is used to turn on and off large currents of
several hundred amperes as rapidly as in a millionth of one second, and
the repeated ON-OFF generate the necessary frequency. The development of
equipment which can withstand high voltages and large capacities through
these new technologies led to the realization of the AC motor drive
system (3 phase asynchronous motor and powering circuit equipment) for
use on the "Nozomi" train. The compact high-power motor of "Nozomi"
requires a high level of rotational speed, but weighs only 390kg, has
output 300kW, and revolves at 5,470/minute.
* Regenerative braking
When power feed to motors is terminated during train operation, the
motors are kept revolving by the wheel rotation and become a sort of
electric current generator. With conventional driving systems, this
current is passed through resistors for dissipation as thermal energy.
However, the electromotive force becomes increasingly larger with
high-power motors for high-speed trains, making the resistors needed for
heat dissipation increasingly larger, conflicting with the weight
reduction requirement for high-speed electric vehicles. A regenerative
braking system has been designed to eliminate the use of resistors. The
electricity generated by the motors is raised to a voltage of over
25,000V and returned to the catenary line through the pantograph for use
by other nearby electric cars or for return to the substation to
comprise an energy conservation system. Various undesirable influences
would be exerted on power networks if AC currents of inappropriate
phases are returned to the power networks, so the AC electricity
generated by the motors is first converted temporarily into DC current
with a converter, then reconverted into AC current of the same frequency
and phase as those of the catenary line through an inverter. The
complicated controls of these inverters and converters are performed
using advanced microcomputer technologies. The recent remarkable
progress in semiconductor and electronics technologies, especially
large-capacity semiconductors, has been indispensable for "Nozomi".
In addition, the control functions of these drive systems are linked to
the central Shinkansen operating systems, safety control systems and
maintenance & inspection control systems to comprise an integrated
overall system.
* Train nose shape
The train nose shape affects the air resistance. The CD value is used to
represent this state, and the smaller this value, the less the air
resistance. The CD value is 0.15 with the 100-series and 0.11 with the
300-series. That of an ordinary passenger automobile is 0.3-0.5, and
that of a racing car 0.2-0.4.
* Pantograph
The 300-series trains use only three pantographs, two of which are
actually used when running and the other used mostly as a spare. In
contrast, the 0-series trains use 8 pantographs, while the 100-series
trains use 6 pantographs. The number of pantographs is decreased to
reduce the noise generated through the pantograph's contact with the
catenary line and through its friction with the air. To prevent
air-friction noise, a cover is used for the pantographs.
HITACHI'S KASADO WORKS
Kasado Works started manufacturing railway vehicles in 1921 by
manufacturing steam locomotives and in 1924 completed the country's
first large-sized electric locomotive, after which it engaged in the
manufacture of various innovative types of railway vehicles such as
monorail cars and linear motorcars. It completed the first Shinkansen
train in 1963, and has delivered a total of 1,060 trains by the end of
1993. The "Nozomi" train production started in 1991.
The fabrication of "Nozomi" starts with the assembly of aluminum
structural members, and the car body structure and truck are produced
through diverse subsequent operations such as welding. The truck is
fitted with motors, and the car body mounted on these trucks. After
this, the seats and interior furnishings are installed in the passenger
coaches. The completed vehicles are then inspected to confirm the
functions and performance of the braking and electrical systems, then
hoisted with cranes equipped in the port of the works and loaded onto
ships for transportation over the Seto Inland Sea to rolling stock
bases.
The Kasado Works manufactured the 200-series Tohoku and Joetsu
Shinkansen line trains in 1963, and is presently manufacturing a new
model "MAX." By drawing on its most advanced technologies, in 1993 it
completed fabricating the next-generation Shinkansen experimental
trains, "STAR 21 " for East Japan Railway Co. and "WIN 350" for West
Japan Railway Co. At present, it is also manufacturing the 30OX train
that is the next-generation model of the "Nozomi" for Central Japan
Railway Co.
The factory is also engaged in the manufacture of products other than
railway rolling stock, such as chemical plants and semiconductor
manufacturing systems. Underpinning its activities which extend over
diverse sectors of industry are its advanced technologies for designing
and manufacturing large-sized structures such as pressure vessels and
vacuum equipment, supported by its precision machining technologies.
Other products include the helium-cooled systems supporting
superconducting technology and the artificial satellite vacuum testing
system in the field of space development, all of which are typical of
the most advanced modem technologies.
CAR BODY AIRTIGHTNESS & FATIGUE TESTING FACILITY
At the Kasado Works is a massive facility to test airtightness strength
for confirming the safety of "Nozomi" carriages, particularly for its
pressure resisting strength when passing through tunnels. This facility
consists of a tank with a diameter of 5m and length of 30m as well as a
pressurizing and depressurizing tank for rapid pressurization and
depressurization, also compressors for pressurization and vacuum pumps
for depressurization. The tank proper is capable of accommodating a
"Nozomi" car intact, so the influences exerted on the car when it passes
through tunnels, or the most severe conditions when running at superhigh
speeds, can be simulated. In the testing of "Nozomi" body,
pressurization to 3.7kPa and depressurization to -7.4kPa at a cycle of
45 seconds are repeated for three months (based on the values obtained
through research studies) by which accelerated deterioration is obtained
as if the vehicles ran for 15 years, leading to the confirmation of the
strength and safety of "Nozomi."
The Kasado Works is situated in Kudamatsu City, Yamaguchi Prefecture,
has a labor force of 1,500 employees, a land area of 538,000m^2 and a
floor area of 206,000m^2.
* Kasado Works, Hitachi, Ltd.
794 Higashitoyoi, Kudamatsu-shi, Yamaguchi Prefecture 744 Japan
Tel: +81-833-41-0123 Fax: +81-833-41-8683
NEW TYPE OF TRAIN RUNNING AT 300km/hr
West Japan Railway Company (JR-West) has announced it will fabricate a
train consisting of a new type of vehicle (500 Series) which will be
capable of running at a commercial speed of 300km/hr. The train is to be
completed in autumn next year [1995], commissioned into service as a
special train in the spring of 1996, and can be manufactured by a mass
production line.
The railway company conducted running tests on the test train WIN350
from June 1992, and acquired good results for commercialization based on
the test performances of riding comfort and environmental measures for
noise reduction.
The train is to consist of 16 coaches, and up to 1,323 passengers can be
accommodated in ordinary coaches and special luxury "Green Cars." These
coaches are smoothed and designed as a wing shape for weight reduction,
while the leading coach has a long, sharp shape, and the pantograph is
designed for suppression of aerodynamic noise to eliminate environmental
problems accompanying the increased speed. An aluminum honeycomb
material featuring excellent noise-shielding effect is used, and active
suspensions are used to minimize vehicle vibration.
The design concept is based on the long-nose design commensurate with
high-speed running, and aims to achieve functional excellence and
aesthetic form. The train manufacturing cost is roughly 4.5 billion Yen.
By commercial operation at a speed of 300km/hr, the same as that of the
French TGV system, the aim is to shorten the 2 hrs and 32 min required
for travelling the distance between Shin Osaka and Hakata stations to 2
hrs and 19 min, a reduction of 13 min. JR-West plans to continue further
tests on the WIN350 system and to commission the special train into
service in the spring of 1996 with the aim of putting the train into
full-scale operation from the spring of 1997.
West Japan Railway Company (JR-WEST)
Public Relations Dept., 4-24, Shibata, 2-chome, Kita-ku,
Osaka 530 Japan
Tel: +81-6-375-8889; Fax: +81-6-376-6053
---------------------------END OF REPORT-----------------------------
From:
Dr. David K. Kahaner
US Office of Naval Research Asia
(From outside US): 23-17, 7-chome, Roppongi, Minato-ku, Tokyo 106 Japan
(From within US): Unit 45002, APO AP 96337-0007
Tel: +81 3 3401-8924, Fax: +81 3 3403-9670
Email: kahaner@cs.titech.ac.jp
Re: Japanese Bullet train technology.
12/27/94 (MM/DD/YY)
This file is named "train.94"
ABSTRACT. Summary of main technical issues associated with Japanese
"bullet" trains, (Shinkansen). This system is celebrating its 30th
anniversary in 1994, carries up to 130 million passengers annually
(3 billion in total), runs nearly 300 trains per day on the main line
from Tokyo through Osaka, has never had a derailment or collision
accident, and maintains a zero mortality rate for passengers and crew.
Japan's Shinkansen, bullet trains, are remarked on by all visitors, for
their speed and reliability as well as their frequency. There are three
routes, Tokaido (the first, and most heavily travelled, along the waist
of Japan from Tokyo through Osaka and Hiroshima, ending in Hakata on the
island of Kyushu) running west, Tohoku (from Tokyo to Sendai and
Morioka) running north east, and Joetsu (from Tokyo to Niigata on the
Japan Sea) running almost due north. The article below describes several
key technologies associated with this system, especially the car
construction and driving systems which are designed and manufactured at
Hitachi's Kasado Works (factory). System integration, scheduling and
related topics are not discussed.
This article appeared in JETRO's (Japan External Trade Organization) New
Technology Japan, Vol 22, No 9, Dec 1994. Several figures and photos in
the original article have been omitted here. This periodical is an
official Japanese government sponsored publication, providing
descriptions of various Japanese technologies, it is not a technical or
refereed journal. For further information contact the addresses listed
in the article or the following.
JETRO, Machinery & Technology Dept
2-5, Toranomon 2-chome, Minato-ku, Tokyo 105 Japan
Tel: +81 3 3582-4631; Fax: +81 3 3582-7508
or
Three "I" Publications
5-16, Uchikanda 1-chome, Chiyoda-ku, Tokyo 101 Japan
Tel: +81 3 5280-3100; Fax: +81 3 5280-2625
"NOZOMI" SHINKANSEN TRAIN MANUFACTURING AT KASADO WORKS, HITACHI LTD
The SHINKANSEN train "Nozomi," a symbol of Japan's advanced bullet train
technologies, was commissioned into service by Central Japan Railway Co.
on March 8, 1993. The "Nozomi" train has a running speed of 270 km/hr
and travels between Tokyo and Osaka in two and a half hours. And the
success of "Nozomi," both in commercial and technical aspects, has been
a positive addition to the 30th anniversary of Japan's Shinkansen train
operation. By October 1994, the Shinkansen had transported more than 3
billion passengers during the 30 years since the first Tokaido
Shinkansen bullet train started commercial operation in October 1964.
This article introduces the Kasado Works of Hitachi, Ltd. which is
presently assembling the "Nozomi." Hitachi participated in the
development of "Nozomi" from the initial stage and contributed to the
successful development with its accumulated expertise in both mechanical
and electric machinery technology. From the beginning of the Shinkansen,
the Kasado Works has been involved in the development and manufacture of
Shinkansen trains and about one-third of all Shinkansen vehicles
produced until now have been manufactured at this works of Hitachi.
NEW FRONTIER OF RAILWAY TRANSPORTATION
The construction of Shinkansen Line was a highly remarkable achievement
involving tremendous efforts, although at first glance it may appear as
if the development and progress of the Shinkansen has been achieved
without much trouble in the wake of the country's high economic growth.
When the Shinkansen construction project was launched, however, the
internationally prevailing consensus was that railway transportation was
destined to tread the path of gradual demise. What actually happened to
the railway in the United States seems to have proved the prediction had
some validity. Those widespread negative opinions were based on the
assumption that railway transportation cannot achieve an operational
speed exceeding 160 km/hr, so the railway would hardly be capable of
competing with airlines in the aspects of speed of travel and were being
overtaken by the convenience of the automobile that was rapidly being
popularized.
Despite this prevailing negative outlook, innovative-minded experts of
Japan National Railway (JNR) believed that the railway can compete with
aircraft in travel time considering the access time to the airport and
the waiting time for scheduled flight services, assuming that commercial
running speed of railways could be increased to 200 km/hr by advancing
existing railway technologies. JNR was also in an urgent need of
capacity expansion of the Tokaido line railway service-the main artery
for the Japanese economy-as it was heavily over-congested at that time.
They believed that the construction of new Tokaido Line, Shinkansen, was
commercially viable and socially needed.
After surmounting various obstacles, the Tokaido Shinkansen Line became
a reality and started operation at the revolutionary high speed of 200
km/hr. As a result, it is today indispensable for the Japanese social
and business activities, transporting an average of 350,000 passengers
daily and as many as 130 million passengers annually. This has been made
possible not only through the high-speed of individual trains but also
through the established total operation system which assures safe and
highly congested train operation.
HIGH SPEED ELECTRIC CAR SYSTEM
The Shinkansen trains consists of electrically powered cars--that means
basically all individual cars are equipped with electric motor driving
systems. This is in contrast to locomotive trains in which the
locomotive pulls the passenger coaches. The realization of the
high-speed Shinkansen with the electric train system had a great
significance. The French "Train a Grande Vitesse (TGV)" runs on a
centralized power system, in which the heavyweight, high-output
locomotives at both ends pull the passenger coaches via the friction
between the vehicle's wheels and rails. It is a system suitable to
European railways which run basically on straight tracks in wide plains
with solid foundations, but unsuitable in Japan where the ground is
flimsy and the tracks full of curves and undulations and inter-city
distances are short, making it necessary for the trains to accelerate
and decelerate frequently. One of the advantages of the electric car
system is that the motor functions as a brake to reduce the speed of the
train. When the power feed to the electric car motors is stopped, the
wheels continue revolving, keeping the motors rotating, resulting in
electricity generation by magnetic induction. As the force acts in the
direction opposite to the axle's motion it functions as a brake to the
train. All the motors equipped on each coach can be utilized effectively
to reduce the speed, making the electric train system advantageous on
Japanese railways which involve frequent deceleration and acceleration.
In addition, by virtue of the remarkable progress achieved recently in
semiconductor technologies, the electric train system has undergone
tremendous improvements in power, operability and safety administration,
so the system is becoming increasingly advantageous.
The most notable contribution of Japanese Shinkansen to the
international community is that it fully proved the economical viability
of railways through the achievement of mass-transportation system at
high-speed. The conditions unique to Japan, such as the dense population
and the concentration of economic activities in limited number of large
urban cities, may have prompted the Shinkansen project, but today the
necessity of mass transportation systems at high-speeds is realized
throughout the world and the vital importance of railway transportation
is recognized. As a result, new railway construction projects such as
the high-speed railway networks in Europe-the French Railway's TGV
system and the German Railway's Inter-City Express (ICE) system-are
being implemented. Also, due to the unceasing mass production of
automobiles, the limitations of automobile/highway network
transportation are being recognized in the environs of large cities due
to the deterioration of efficiency because of the inevitable heavy
traffic congestion. This is another major factor that is implementing a
reappraisal of the railway transportation worldwide.
HIGH SPEED WITH SAFETY
The viability of railway systems has been based on high-speed
transportation technology, and Japan's Shinkansen Line has taken the
lead in this respect. The Shinkansen trains, ever since they were
commissioned into service in 1964, have run for an aggregate distance of
1 billion kilometers, and while transporting over 3 billion passengers
at a speed of over 200 km/hr (currently operating 282 trains per day on
Tokaido Shinkansen alone) has had no derailment or collision accident
whatsoever, and has therefore established the highest level of safety
and reliability with no mortality whatsoever to passengers or crew
members.
Although the Shinkansen has been surpassed by the TGV in its maximum
speed, it is still highly praise-worthy in that it has realized
high-speed operation while constrained by Japan's geographical
conditions, which require operating on tracks with many curves built on
unsolid ground, while also coping with environmental problems such as
noise suppression due to densely populated regions. The overall
technologies which make the operation of the Shinkansen lines in Japan
possible despite these constraints -- advanced power electronics
technologies, vehicle weight reduction, energy conservation and safety
assurance -- may be regarded as the world's most advanced technologies.
THEMES RESOLVED FOR THE REALIZATION OF "NOZOMI"
[The original Shinkansen trains run at 200 km/hr. A newer "Hikari"
operates at 220 km/hr, and the current "Nozomi" operates at 270 km/hr.
See below for plans to put into service (1997) a 300 km/hr train.]
The commercial operation running speed of 220 km/hr of the "Hikari" is,
in itself, an astounding speed, therefore the realization of higher
speed of 270 km/hr for "Nozomi" required innovative solution of many
technical themes. The main constraining factors to be solved were as
follows:
* Constraint No. 1: Numerous curves
One of the biggest obstacles hampering speedup and shortening of travel
time was the existence of many curves on the line. About two-fifths of
the approximately 500km Tokaido Shinkansen Line between Tokyo and Osaka
consists of curves, and the sharpest curves with a curvature radius of
2,500m (R2,500) include about one-eighth of the total line length.
These curves would hardly be problematical in conventional lines with
lower speed trains, but when the running speed exceeds 200 km/hr, they
stand out as a formidable matter. Therefore, on the newer Shinkansen
lines (Sanyo Shinkansen [from Osaka to Hakata] as well as Tohoku/Joetsu
Shinkansen lines) the sharpest curves are suppressed to a radius of
4,000m.
The required shortening of travel time would have been impossible if the
maximum speed was attained only on the straight-line portions. Even the
speed at the difficult portions of tracks consisting of sharp curves
must be raised as much as possible. If the curved tracks could be
replaced with straight tracks, the problem would be quite simple, but
the problem faced by "Nozomi" was that the travel time had to be
shortened with the existing line consisting of numerous curves.
A maximum speed of 270 km/hr had already been attained in 1985 by a
rolling stock truck in a running test on the Tohoku Shinkansen Line, in
which case no serious problem was encountered, but attaining a speed of
250 km/hr at curved sections is a different matter. With the "Nozomi,"
the main objective was to attain a travel time of 2 hrs 30 minutes,
which was regarded necessary to make the Shinkansen line service
competitive with airlines.
* Constraint No. 2: Vibration and noise
The Tokaido Shinkansen Line runs through a route containing one city
after another. In the TGV and other railway systems in Europe which
mostly run through pastoral regions, environmental noise problems hardly
occur. In Japan, there is a requirement to suppress the noise at points
25m from railway lines to less than 70 phons due to the need of
protecting environments for citizens.
The main sources of noises are the wheel/rail noise generated by the
wheels rolling along the rails, the noise generated between pantograph
[device on the roof of the car providing electrical connection to the
catenary] and catenary [external wire power source], the aerodynamic
noise/air-friction noise generated by the vehicle's impact with the air,
and the structural noise generated when the train passes bridges or
other structures. Among these noise sources, the wheel/rail noise,
structural noise and vibrations increase with the vehicle's weight, so
the matter of rolling stock weight reduction is the most vital issue.
Railway engineers use the term "axle load" when discussing the
influences which the vehicle weight exerts on the railway track. It is
the load that is exerted on an axle linking the left and right wheels. A
Shinkansen car is equipped with 2 sets of trucks, each with 2 axles (4
wheels), so the axle load is obtained by dividing the vehicle weight by
4. [The underbody truck mounts wheels, motors, brakes and shock
absorbers.] With the 0-series car, the weight with passengers is 64tons,
so the axle load is 16tons. Experiments showed that suppressing the axle
load of the 270-km/hr "Nozomi" train to 11.3tons would suppress the
vibration to less than that of the 100-series "Hikari." This means a
vehicle weight of 45tons.
PURSUIT OF WEIGHT REDUCTION
To attain a high speed of 270 km/hr under these constraints, the most
vital issue was weight reduction for all main vehicle components-the
body, truck and the motor together with its related electrical parts.
The following basic technologies have been the focal points:
1) The body of 0-series and 100-series cars are made primarily of steel
structural members, but with the 200-series cars, aluminum structural
members were introduced. The "Nozomi " introduced further advanced use
of aluminum structural members.
2) As for the truck, the large central beam (bolster) of the
conventional type truck was eliminated. A lighter body require lighter
trucks, so additional weight reduction was made possible.
3) The motor and its related electrical equipment were changed to an AC
motor system. This enabled greater reduction in weight, and the control
equipment was made lighter.
NEW TECHNOLOGIES RELATING TO NOZOMI
* Strong, lightweight, high-speed car body
Achieving lightness by sacrificing structural strength is not
acceptable, so adequate rigidity has to be secured while achieving
significant weight reduction. However, the increased maximum speed
demands a proportional increase in body strength. The car body must
display efficient rigidity to withstand the atmospheric changes
