Redesign of the live axle in articulated lumber tractors.
Oltean, Andrei Ioan ; Pop, Grigore Marian ; Glad, Contiu 等
1. INTRODUCTION
Forestry tractors are subject to major strains. Problems with the
circuit transmitting the power from the engine to the wheels were
signaled in approx. 20% of the products in a family of Romanian forestry
tractors. Such problems were caused by the fact that the circuit
transmitting the power from the engine to the wheel had not been
correctly dimensioned (Radulescu, 1986). Likewise, a redesign was also
necessary, as the engine torque that the engine could transmit to the
wheel could have been higher than the current engine torque. An increase
in the engine torque automatically leads to an increase in the machine
output.
The continuous increase of the tractors output has been a general
trend and it explains the main orientations of the manufacturers within
this field. The power increase has enhanced the option of moving on to
the 4x4 drive with all four driving wheels. Such a technical solution is
needed because of the following advantages:
* In 4x4 drive tractors the entire operating weight is adherent;
* The 4x4 drive tractors have a 15-30% higher output;
* The propulsive efficiency is higher and the fuel demand lower as
compared to the tractive power. (Dobre & Barbu, 1998)
Depending on the type and size of the forces and torques exerted on
them, the wheels can be: driven (geared) wheels: these are wheels which
work due to the action of the power flow received from the engine
through the gear;--freewheel (drive-free wheel): these are wheels that
work under a pushing or pulling force having the same direction as the
cars travel speed, exerted on them by the cars frame or body; -brake
wheels: these are the wheels that work under a braking moment created in
the braking mechanisms of the wheel (active braking), or by the engine
set in geared motion (handbrake). In case of two-axle vehicles the drive
can be realized as a 4x2 or 4x4 solution, whereas the first figure
indicates the total number of the wheels and the second one the number
of driving wheels. For the 4x2 drive the live axle can be place in the
front or at the back, and for the 4x4 drive both axles have driving
wheels. The live axles, as compared to the non-live axles, ensure the
transfer of the self-propelling power flow depending on the drive type,
from the driven shaft of the gearbox or from the longitudinal drive
mechanism to the driving wheels. During the self-propelling process the
interaction between the driving wheels and the path gives birth to
reacting forces and moments. The axle's role is to take over all
these forces and moments and to transmit them to the elastic elements of
the suspension and the frame or the body of the vehicle. A building
assembly of the axle, called the wheel-steering system, performs such
takeover of the forces and the moments and their transmission to the
frame or the body of the vehicle through rigid directions. The steering
system defines the kinematics of the spring-suspended wheel by means of
the suspension. Rigid axles and articulated axes are thus defined.
According to the position within the vehicles configuration we
distinguish between front axles and rear axles(Vasu&Buladra, 1980).
2. THE INITIAL CONSTRUCTION OF THE AXLE
The axle is part of the drive assembly of the Articulated Lumber
Tractor, having a 4x4 drive, i.e. both axles have driving wheels. We
deal with a rigid drive with self-locking differential. While the power
is transferred from the engine to the driving wheels, the flow undergoes
a series of adjustments, such as:
* Geometric adjustment determined by the relative position between
the plane in which the engines crankshaft spins and the plane in which
the driving wheels rotate;
* Kinetic adjustment determined by the need to ensure the
transmission ratios necessary for the motion of the tractor;
* Splitting of the received power flow in two branches, one for
each of the driving wheels of the axle.
[FIGURE 1 OMITTED]
In order to perform the previously mentioned functions the
mechanisms transferring the power flow in the live axle are: the main
drive, the differential and the driving wheels.
3. REDESIGN OF THE DRIVE AXLE
The redesign of the drive axle in order to increase the engine
torque transmitted to the wheels with approx. 20%. In view of the said
objective we have applied the principles of "Integrated
Engineering" and the method of "Parametric Modelling",
while using the dedicated software "Autodesk Inventor Professional
2008".
[FIGURE 2 OMITTED]
Apart from the tehnical and technological factors we need to follow
aswell the economic component and the correlation of the accuracy
between the price factor and the time factor. It is far-famed the
alleged triangle of the pressure quality-price-time limit. (Popa, 2007)
[FIGURE 3 OMITTED]
The redesign activity involved up-to-date building solutions as
follows: for the first gear of the main drive one has used a curved
bevel gear, with the bevel pinion placed between the bearings, which has
led to a substantial increase of the transmitted torque and to
relatively small dimensions of the parts; one has used a self-locking
differential with friction disks which ensure a very good behavior in
limit situations, when the angular speeds of the wheels on the axle are
different (when turning, driving on rough grounds, when there are
differences between the operating diameters of the wheels as a
consequence of wear or inadequate pressure in the tyres);The second gear
of the main drive has been realized as a final drive while using a
planetary gear with three identical satellites, placed directly into the
wheel hub. This solution reduces the strains of the constitutive parts
with a value in direct ratio with the one of the transmission ratio for
this gear.
Before the actual execution one has modeled approx. 141 specific
markers, performed an optimal number of digital prototyping trials while
analyzing the kinetic behavior of the markers within the assembly they
are part of. This approach has enabled us to eliminate all design errors
and to optimize the construction of such markers in terms of quality and
manufacturing cost-effectiveness, as well. One has made dimensioning and
testing computations so as to ensure an optimal use of the execution
materials. Likewise, for the redesigned markers, based on the
prototypes, one has elaborated processing programs on numerically
controlled tools, thus significantly reducing the costs associated with
such operations.
4. CONCLUSIONS
The live axle has been redesigned because based on the available
bibliography and the documentation within the Romanian manufacturing
company for forestry machines and the "National Institute of
Research and Development for Machines and Installations in Agriculture
and Food Industry" we have noticed that an essential market
requirement was called for, i.e. the modernization of the machines used
in the field of forestry, while aiming at increasing the output by
increasing the engine torque, reducing the faults during the warranty
period, increasing operating safety and reducing the negative impact
that such machines have upon our environment. In order to achieve our
goal we have applied the principles of "Integrated
Engineering" and the method of "Parametric Modeling"
while using the dedicated software "Autodesk Inventor Professional
2010".
The computations have shown the following effects:
a) Upon the end product:
* An output increase with about 15 %, by increasing the driving
speed;
* Reduction of the pressure exerted by the wheels on the ground:
from 225 kPa to 175 kPa, with positive environmental effects, thanks to
the use of wider tyres (23,1-26, instead of 18,4/15-26 ; STAS 8258/1-86
).
b) Upon the manufacturing process:
* Reducing assimilation expenses with approx. 20%, as compared to
the classical methods;
* Reducing the expenses with the design and the execution of the
specialized SDV's, as a consequence of using group technologies.
* No need for personnel training as the technological processes is
similar.
[FIGURE 4 OMITTED]
5. REFERENCES
Dobre V.,Barbu V. (1998).Guide to the gear design and theoretical
computation basics,Scrisul Romanesc, ISBN 973-9187-63-3,Bucuresti
Fratila,GH.(1982). Vehicle computation and construction, Didactica
si pedagocica, Bucuresti
Popa,M.(2007).Manufacturing precision in modern production, Agir,
ISBN978-973-973-720-144-7, Cluj Napoca
Radulescu,GH. (1986)--"Design guide for the car
industry", Scrisul Romanesc, Craiova
Vasu T., Buladra, GH. (1980). Planetary drives with bevel
gears", Scrisul Romanesc, Craiova