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Chassis design of skid steer loaders

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The article provide analyzes the design features of the chassis components and assemblies of skid steer loaders. Describes the various options for frame design, engine layout and hydrostatic transmission. A comparison of the wheel and tracked propulsor used on loaders is given.
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Chassis design of skid steer loaders
To cite this article: Alexey Khomichev and Alexandr Volkov 2020 IOP Conf. Ser.: Mater. Sci. Eng. 709 033012
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ICMTMTE
IOP Conf. Series: Materials Science and Engineering 709 (2020) 033012
IOP Publishing
doi:10.1088/1757-899X/709/3/033012
1
Chassis design of skid steer loaders
Alexey Khomichev1,* and Alexandr Volkov2
1 Kurgan state university, Polytechnical Institute, Department of Tracked Vehicles and
Applied Mechanics, 640020, Kurgan, Russia
2 IES UB RAS, Department of Transportation Vehicles Mechanics, 620049,
Yekaterinburg, Russia
* khomichev.alexey@mail.ru
Abstract. The article provide analyzes the design features of the chassis components and
assemblies of skid steer loaders. Describes the various options for frame design, engine layout
and hydrostatic transmission. A comparison of the wheel and tracked propulsor used on loaders
is given.
1. Introduction
Skid steer loaders are widely used in the road construction industry, utilities and agriculture, as well as
in other areas due to their compactness, maneuverability and versatility. High accuracy and efficiency
when performing working operations is achieved through the use of hydrostatic transmission. At the
same time, the change of torque on the wheels and the speed of movement of the loader occurs
continuously. The possibility of using in combination with a loader of various attachments
significantly expands the functionality of the machine [1].
Currently, many models of skid steer loaders are on the world market. All of them have a similar
purpose, however, the design features of individual machines may differ significantly [2].
2. Purpose and objectives of design
The purpose of the skid steer loader design is to create a compact machine, capable of effectively and
safely fulfilling its function. In this regard, the design solves the problem: the choice of propulsion
(wheeled or tracked), the choice of the layout scheme, the selection of units (engine, transmission), the
selection of materials for the manufacture of loader parts.
3. Frame design
The basis of the chassis loader is a rigid frame, which is a welded construction of sheet steel (Fig 1).
The most loaded frame elements have a box-shaped cross section. High strength steel is used for their
manufacture. These are side sheets, rear pillars, bottom, front sheet, transverse beams. The choice of
the shape and thickness of the frame parts during design is usually determined by calculation using the
finite element method [3].
On the frame mounted the components and assemblies of the loader: engine, transmission, boom,
cab, running gear, etc. In addition, the frame can serve as tanks for the placement of fuel and hydraulic
fluid of the loader (Fig 1, b). In this case, the tanks are welded to the frame sheets. Placing the tanks
outside the frame makes the engine compartment more spacious, which has a positive effect on the
ICMTMTE
IOP Conf. Series: Materials Science and Engineering 709 (2020) 033012
IOP Publishing
doi:10.1088/1757-899X/709/3/033012
2
maintenance of the engine and its systems, and also makes it easy to place additional optional
equipment under the hood (air conditioner, preheater and others).
a. Frame without inegrated containers b. Frame with inegrated tanks
Figure 1. Construction of skid steer loader frame
Maximum tipping load - the characteristic of the loader, which determines its capacity. This load is
defined as the weight of the load that is in the bucket or other loading equipment, under the influence
of which the rear wheels of the loader will lift off the ground with the longest boom. To ensure a given
load capacity, as well as the stability of the loader during operation, the heaviest elements - the engine,
fuel and hydraulic tanks - are placed in the rear part of the frame.
4. Engine selection
Skid steer loaders are equipped with engines that have 30-40% more power compared to similar
machines that have steered wheels. This is due to the need to overcome considerable frictional force
when performing the bend, especially on a solid basis (asphalt, concrete). The most common on these
machines were diesel engines with direct fuel injection. The implementation of modern environmental
requirements for the power unit is ensured by the use of the Common Rail fuel injection system, the
installation of a diesel particulate filter and other measures. There are also machines with a gas and
electric power plant.
Engines for loaders are manufactured by both machine manufacturers and companies specializing
in the manufacture of engines (Hatz, Deutz, Perkins, Lister-Petter, Lombardini, Honda, Kubota,
Yanmar).
On skid steer loaders, air or liquid cooling engines are used. Preferably the use of diesel engines
with a liquid cooling system, as they have a lower noise level, which is important when working in
urban environments. In addition, it is possible to install a cheaper dependent loader cabin heater. The
radiator installation of such a loader usually includes a monoblock radiator, consisting of two sections:
engine cooling fluid and hydraulic system oil cooling. Sometimes a third section is needed - charge air
cooling - in the case of using an engine with a turbocharger and intermediate air cooling. The radiator
is installed in the back of the loader frame and is blown by a fan mounted on the shaft of the water
pump of the engine, driven by the crankshaft. In the case of a transverse engine arrangement, the
cooling fan has a hydraulic or electric drive.
To facilitate starting at low ambient temperatures, the engine is equipped with an air charge heater.
The heating element is installed in the intake manifold or in the engine cylinders. Also apply fuel
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IOP Conf. Series: Materials Science and Engineering 709 (2020) 033012
IOP Publishing
doi:10.1088/1757-899X/709/3/033012
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filters with integrated heater. As an option, some manufacturers offer preheaters that run on diesel
fuel, or electric heaters, powered by an external energy source.
5. Transmission design
Hydrostatic transmission of loader consists of two hydraulic pumps and two hydraulic motors, forming
a running circuit. On modern loaders, axial-piston hydraulic machines with an inclined disk are most
often used. Changing the speed and direction of movement of the machine is infinitely variable by
controlling the volume of working fluid supplied by the hydraulic pump [4].
The tandem pump is preferably connected to the flywheel of the engine through a friction clutch.
The clutch somewhat reduces the dynamic load from the engine to the pumps, and also allows the
engine to be disconnected from the transmission. This is necessary when starting the engine at low
ambient temperatures. More viscous transmission oil may cause the engine to stop. As the engine
warms up, the clutch smoothly turns on, the hydraulic pumps start working, they warm up, after which
the loader can begin work.
The option of driving the right and left side pumps through separate shafts is possible. In this case,
it is necessary to use a gear distributing gearbox, in which the gear ratio from the engine to the pumps
can also be converted. This is necessary if the engine speed does not allow the pumps to create the
necessary flow of hydraulic oil to the hydraulic motors. The use of a gearbox also reduces the length
of the power unit.
Depending on the torque value, there are "high-torque" and "low-torque" hydraulic motors. The
torque on the shaft of "high-torque" hydraulic motors is 10 or more times greater than that of the "low-
torque" at the same pressure values in the pressure line. On skid steer loaders, axial-piston or radial-
piston hydraulic motors are used.
For transmission of torque to the wheels of one side, a gear onboard gear or chain transmission is
used. The onboard gearbox is designed as a separate unit and is attached to the loader frame (Fig 2). It
includes 11-13 gears, has a gear ratio of more than 20 and is used in combination with "low-torque"
hydraulic motors.
Figure 2. Onboard gearbox
In case of using "high-torque" hydromotors, an onboard chain transmission with a gear ratio of not
more than 3 will be used (Fig 3). The chain must have sufficient resource comparable to the life of the
loader. The drive sprocket is usually made as one unit with the motor shaft. Chain onboard gear can be
mounted in the housing, which is part of the loader frame. The wheels are mounted through the hubs,
on the shaft of which the driven chain sprockets are mounted.
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IOP Conf. Series: Materials Science and Engineering 709 (2020) 033012
IOP Publishing
doi:10.1088/1757-899X/709/3/033012
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Figure 3. Onboard chain
There are also options to increase the gear ratio through the use of a two-stage chain drive or the
installation of planetary gears on the hubs of all wheels.
To lock the wheels of the loader, a parking brake is used that is integrated in the hydraulic motor.
There is also a version of this unit as part of the loader side gearbox. The brakes are normally closed
and to start driving it is necessary to create a hydraulic oil pressure in the booster to open the friction
discs.
The maximum speed of the skid steer loader is usually 12 km/h. However, some manufacturers
offer loaders, the transmission of which has two modes: transport and operating. The transport mode is
used when the loader moves for fairly long distances along a flat road surface at a speed of up to 20
km / h. The operating mode is used when performing loading operations and other operations
performed with attachments. The possibility of using these two modes is achieved by using double-
volume hydraulic motors in the transmission of the loader [5].
6. Propulsion selection
The most widely used wheel skid steer loaders. The onboard turning process is associated with
overcoming significant frictional forces; therefore, multi-layer pneumatic tires with a special tread
pattern are used on the loaders. Intensive use of the machine on a hard surface leads to rapid tire wear.
Some manufacturers (Michelin, Trelleborg) offer airless tires that have a greater resource. Load in
such tires perceive polyurethane knitting needles. They perform the depreciation function. The wheel
rim has several layers of steel elements that increase lateral stiffness and improve resistance to damage
from shocks and jams of sharp objects. However, airless tires are still more expensive than pneumatic
tires.
There are also tracked skid steer loaders, which have a greater maneuverability on soils with a
weak bearing capacity. Tracked loaders have a chassis system with track rollers, guide wheels and
drive wheels. Such machines have a greater mass and carrying capacity compared to the wheel, they
are more stable, so they can work with heavier attachments.
It is also possible to equip the loader with removable tracks that are mounted on tires.
Skid steer loaders do not have suspension. Vibration loads acting on the operator during operation
are perceived by the elastic parts connecting the cab to the frame and the loader tires. It is also possible
to install a seat with suspension.
7. Conclusions
Based on the analysis, it can be concluded that the most rational design of the chassis is the skid steer
loader. A modern machine of this type should be equipped with an economical diesel engine of liquid
cooling with a power supply system using Common Rail technology, equipped with means to facilitate
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IOP Conf. Series: Materials Science and Engineering 709 (2020) 033012
IOP Publishing
doi:10.1088/1757-899X/709/3/033012
5
starting at low ambient temperature. The engine must have a power take-off shaft for driving the
hydraulic pump of the working equipment. The design of the loader frame should provide sufficient
space for servicing the engine and its systems during operation, as well as for installing additional
optional equipment. Therefore, the most rational is a frame with integrated fuel, hydraulic tanks and
onboard gear housings. The loader's transmission should include a tandem-type axial-piston hydraulic
pump, high-torque radial-piston hydraulic motors and onboard chain transmissions.
Manufacturers of skid steer loaders regularly launch new models on the market that are more
economical and comfortable to operate. Successful competition depends on progressive constructive
solutions and technologies introduced at the same time.
References
[1] Boyarintsev A K 2016 Design features of universal mini-loaders // Scientific community of
students of the XXI century. Technical science: collection of articles based on the XLI
International Student Scientific-Practical Conference № 4(40)
[2] Zaichka S A, Volkov E A 2015 Design features of skid steer loaders // Proceedings of the VIII
International Student Scientific Conference "Student Scientific Forum"
[3] Shestakov V, Babenkov P, Horoshavin S 2018 Features of designing hydraulic excavator in
APM WinMachine. MATEC Web of Conferences 224, 02046
[4] Zhao L, Wang J, Zhang Z 2017 Research on Parameter Design of Multi - axis Hydrostatic
Transmission Vehicle. MATEC Web of Conferences 139, 00215
[5] Zhao L, Wang J, Zhang Z 2017 Research on Travel Control System of Hydrostatic
Transmission Chassis. MATEC Web of Conferences 139, 00212
... The hinges of the boom are fixed at the rear, the working equipment is at the front (Fig. 1). The components with the largest mass (engine, fuel and hydraulic tanks) are located at the rear of the machine to provide the necessary tipping load [3]. ...
... On modern loaders, axial-piston hydraulic pumps mounted on one drive shaft in the form of a tandem are most often used. This design option allows you to reduce the number of links for transmitting torque from the engine to the transmission [3]. ...
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The article analyzes the layout of the main components and units of a skid steer loader. The effect of placing the heaviest components on the tipping load is estimated. The necessity of increasing the duration of the loader without refueling is substantiated. An option is proposed to improve the layout of the machine to increase its operational performance. A test arrangement made using a 3D-modeling system is given.
... Modern skid steer loaders are equipped with a diesel internal combustion engine and hydrostatic transmission. [12] To create a loader with an electric traction drive, it is necessary to replace the hydrostatic transmission with an electromechanical one. ...
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In order to obtain reasonable parameters in the design of driving system of multi-axis hydrostatic transmission vehicle, the working principle of single-side drive of hydrostatic transmission vehicle is introduced. The matching and control of engine and hydraulic pump are analyzed. According to the driving equation of vehicle, The driving force required for driving system is determined, and the parameters of hydraulic motor, hydraulic pump, system working pressure and braking system are designed and calculated, which provides the parameter design for driving system of multi-axis hydrostatic transmission Reliable theoretical basis.
Design features of universal mini-loaders // Scientific community of students of the XXI century
  • A Boyarintsev
Boyarintsev A K 2016 Design features of universal mini-loaders // Scientific community of students of the XXI century. Technical science: collection of articles based on the XLI International Student Scientific-Practical Conference № 4(40)
Design features of skid steer loaders // Proceedings of the VIII International Student Scientific Conference
  • S A Zaichka
  • E Volkov
Zaichka S A, Volkov E A 2015 Design features of skid steer loaders // Proceedings of the VIII International Student Scientific Conference "Student Scientific Forum"
Design features of universal mini-loaders
  • Boyarintsev
Design features of skid steer loaders
  • Zaichka