Design of hydraulic platform lift
2013
Chapter one Introduction Before the invention of weight lifting device such as screw jack, hydraulic jack, crane, etc., the early man apply a crude way of lifting objects to great heights through the use of ropes and rollers, which was mostly applied in the construction industry, where, it was used to raise mortar (cement, sand & water). After industrial revolution, with the advent of automobile, the automobile industry was also faced with the challenge of load lifting, because of the backlines of some automotive parts. Because of the interface between the the automobile automobile and human lives, lives, there is need for standardization standardization of of its component component part improves its performance, efficiency and reduces failure. For this reason car has to be taken during maintenance of its component parts. Because every machine is subjected to failure, maintenance is essential parts in handling machines. From time to time the need to improved and lasting maintenance has increased in the automotive industry in an attempt to reduce cost, for its reason, maintenance of vehicle needs to be efficient and reliable. To keep good quality of maintenance and to create good working conditions for the workers a convenient and easy way should be provided to identify and fix the problem. This report presents the study of a hydraulic platform lift.
1.1 Problem Statement In Bishoftu Automotive Industry light duty factory there is a problem to assemble and maintain the lower part of the vehicle. The method used is ditch and the use of this method does not allow free movement during assembly and maintenance and this leads to reduction in production produ ction rate and quality. 1.1.1
Proposed Solution
To create an easy and comfortable means for the maintenance of light duty vehicles Light duty vehicles in Bishoftu Automotive Industry, a mechanism is designed to lift the vehicle from the ground. This report presents the study of a h ydraulic lifting platform that utilizes the pressure power developed from hydraulic oil to raise or lower the vehicle. A single piston hydraulic lift platform is designed so that it would be convenient for the personnel working on the vehicle to freely move around during working.
1.2 Aims and Objectives The aim of this design is hydraulic platform lifting device that c an be used for the assembly and maintenance of light duty vehicles. The design conditions are to meet the following specifications; The device is limited to an average load of 1900kg Bishoftu Automotive Industry
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The device will have a maximum lift of 200 cm This objective is desirable to be achieved through the fluid power to raise or o r lower the platform. The system must be operated on a flat surface.
1.3 Scope of the Design The design project starts by stating the problem statement and proceeds by collecting background information on the problem type and the possible solution to it. The design of hydraulic platform lift for light duty vehicles involves:
The design of the platform for strength and bendi ng as well as determination of the dimensions. The design of the hydraulic circuit of the system. Calculations of the center of gravity for the model
double cabin pick-up car.
Selection of oil for the hydraulic pump, pump, pum p, reservoir, electric motor, hose, screw and other accessories of the hydraulic circuit.
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Chapter Two 2.0 Literature Review There are several distinct types of aerial work platforms, which all have specific features which make them more or less distinct for different applications. The ke y difference is in the drive mechanism which propels the working platform to the desired location. Most are powered by either hydraulics or possibly pneumatics. The different techniques also reflect in the pricing and availability of each type. An aerial work platform (AWP), also known as an aerial device or elevating work platform (EWP), is a mechanical device used to provide temporary access for people or equipment to inaccessible areas, usually at height. [1] In recent years, various platforms or devices with various means of applica tion have been produced for use in the automotive industry. The automotive industry have also experience the influx of various lifting platform, some of which are;
Electrically operated lifting device which is operated by th e turning effect of electric motor to drive the gear which will eventually eventua lly turn a screw shaft to raise or lower load. Hydraulic operated lifting platform which utilize the pressure power developed from hydraulic oil to raise or lower a load. Pneumatic lifting device which make use of o f air to create pressure or vacuum to raise or lower load. The use of a scissors mechanism with a table platform that will be horizontal at every level. Recent research also shows the use of air ba g for raising or lowering load. [2]
2.1 Various Lifting Platforms 2.1.1 Electric lifting Platform
These lift devices make use of electromagnetic po wer to raise or lower through the use of electric motor. The device could be very expensive and there is high probability of jerking during startup of the device through the torque created by the electric motor. [3] The challenges of this system are;
Due to frequent raising and lowering of the lift, there is possibility of snapping in the electric cable which could lead to exposure of the cable and could lead to electrocution. It requires other accessories to be operated It requires trained personnel to operate it successfully. It requires regular maintenance Overheating in electrical coil could damage the s ystem
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2.1.2 Pneumatic System
This device also operates like the hydraulic device, but it acquires its driving force/pressure from the air [3]. The limitations with this system are;
There is high risk of air leakage. Pneumatic systems are frequent with valve leakage. Precise control of movement is not possible due to high compressibility of air.
2.1.3 Scissor Lift
A scissor lift is a device used for lifting purposes, its objectives is to make the table adjustable to desirable height. This mechanism comes with different actuation mechanisms like power screw and hydraulics. Its limitation is that it requires very large initial force to raise the mass from minimum height and these results in high probability of system failure. [3] 2.1.4 Hydraulic-operated Lifting Platform
The hydraulic lift makes use of fluid pressure to p roduce smooth movement during lifting. It has some benefits when compared to other lifting device; firstly, its dependency on power supply is eliminated. Secondly, it allows smooth movement without jerking due to steady increase in fluid pressure, majority of lift platform in market make use of hydraulic. Above all it has a high capacity in terms of load lifting. [3]
2.2 Components of the Hydraulic Platform Lift The hydraulic platform lift setup consists of the following parts:2.2.1 The electric motor
It is the prime mover of the system. It gets converts electrical energy to rotational mechanical energy. This is then made to drive the hydraulic pump via the belt that connects the shafts of the motor and the pump. [4] 2.2.2 Hydraulic pump
Hydraulic pump is the unit that drives oil from the tank in to the cylinder. It is driven by the electric motor. The pump, for this study, the ex ternal gear pump, which works by gears meshing and rotating opposite to each other. As the gears rotate they trap oil between the teeth and the pump housing and transfer it. [4] 2.2.3 Control valve
The control valve controls the flow of oil to the system and is used to stop when the desired height is reached. [4] 2.2.4 Reservoir
The reservoir is also called tank is a unit where oil is stored. Oil pumped to rise the system is made to flow back to the tank where it cools. [4]
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2.2.5 Hydraulic hoses
The hydraulic hoses used to transport oil to the cylinder and back to the tank. They are provided with fittings for installation on the cylinder and pump. [5] 2.2.6 Hydraulic cylinder
Hydraulic cylinder (also called a linear hydraulic motor) is a mechanical actuator that is used to give a unidirectional force through a unidirectional stroke. A hydraulic cylinder is the actuator or "motor" side of this system. The "generator" side of the hydraulic system is the hydraulic pump which brings in a fixed or regulated flow of oil to the hydraulic cylinder, to move the piston. The piston pushes the oil in the other chamber back to the reservoir. Hydraulic cylinders get their power from pressurized hydraulic fluid, which is typically oil. The hydraulic cylinder consists of a cylinder barrel, in which a piston connected to a piston rod moves back and forth. The barrel is closed on one end by the cylinder bottom (also called the cap) and the other end by the cylinder head (also called the gland), where the piston rod comes out of the cylinder. The piston has sliding rings and seals. The piston divides the inside of the cylinder into two chambers, the bottom chamber (cap end) and the piston rod side chamber (rod end / head end). [5] The hydraulic cylinder consists of Cylinder barrel, C ylinder base or cap, Cylinder head, Piston, Piston rod, seal glands, and seals. The seal gland contains a primary seal, a secondary seal / buffer seal, bearing el ements, wiper / scraper and static seal. In some cases, especially in small hydraulic cylinders, the rod gland and the bearing elements are made from a single integral machined part. 2.2.7 The Support Structure of the Top Platform The top support platform is a horizontal rectangular bar mounted at top of the piston rod. It is the structure that holds the vehicle’s chassis when lifting and during maintenance. It has two pairs of forks or arma that open outward to support the vehicle at the chassis.
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Figure: - 1 the platform lift setup
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Chapter Three 4.0 Design and Force Analysis of Components 4.1 Specifications for the System The hydraulic platform lift presented in this report is to be used in Bishoftu Automobile Industry for maintenance of light duty vehicles and it has the following specifications.
Overall vehicle weight of the model DD6479C to be lifted is 1740kg. [6] The maximum load on the piston of the hydraulic cylinder is taken as the sum of vehicle and platform self-weight plus allowance for safety factor. Stroke of the piston is taken as the maximum life and is 2000mm or 2m. The maximum system pressure should be greater than the pressure due to the load and is taken to be 63.4bar Due to cost and ease of maintenance and pressure specification, external gear pump is selected for the hydraulic system. The maximum system pressure is required to be greater than the pressure due to the load and is taken to be 63.4bar.
4.2 Determining Location for the Center of Gravity of the Vehicle Typical load distribution for double cabin pick up is shown as follows. [7]
Figure: - 2 Typical load distribution for double cabin pickup Bishoftu Automotive Industry
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Calculation for the axle load
Mass(M) Front bumper Power train Front pass/seat Rear pass/seat Fuel tank Luggage/spare wheel Rear bumper Exhaust Front structure Pass compartment structure
20 300 150 212.40 50 90 30 30 0.15x1625=243.75 0.18x2700=486
0.12x1065=127.8
Rear structure Total
1740kg
X – coordinate(mm) 0 760 2385 3715 3610 4880 5390 3050 812.5 4325+1625/2 =2975
4325+5390/2=4857.5
Mx(kg-mm) 0 228,000 357,00 789,067 180,500 439200 161700 92400 198,046.9 1445,850
620,7885 4251252.4
Table 1 Calculation for the axle load Longitudinal position for center of gravity
⃑ Moment about front axle
Moment about rear axle
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Check for equilibrium
4.2 Force Analysis for the Platform Design for plat form arms
The plat form pickup lifting position should be at the centroid where
Total length of the pickup is the position where power train lay.
the position of arm that support frontal part should set at
Figure: -3 the total length of the pick-up The position of front arm from centroid is calculated as
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Figure: -4 structure of the platform Calculation for the link length CD (front arm)
Using Pythagoras theorem calculating for CD and,
The angle θ will be
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Calculation for the arm length AB (rear arm)
Using Pythagoras theorem calculating for AB and,
And the angle
will be
Shear and bending moment diagram for arm AB (rear arm)
,
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Design of hydraulic platform lift
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Figure: -5 bending moment for the platform arm
– – ,
Figure: -6 bending moment diagram for the platform arm Bishoftu Automotive Industry
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Shear and bending diagram for arm CD (front arm)
,
–
Fig shear and bending diagram for arm CD (front arm) Design of link AB with the cross section Rectangular steel with hollow section with yield stress σ yield=855Mpa is selected. [8] Bishoftu Automotive Industry
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Figure: -7 cross section of the arm Data taken:-
Design stress
for arm AB
Safety factor n Bishoftu Automotive Industry
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So the design is safe
The total mass of the rear arms Design stress
2013
for arm CD
Safety factor n
,
So the design is safe
The total mass of the rear arms
The overall weight of the structure
That means weight of the four arms and the weight of the plate.
Figure: -8 top plate Bishoftu Automotive Industry
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Plate design, fixed at mid-point by bolt
From mechanical properties some typical material, we select that material steel form with yield strength of which is steel with grade . [8]
And h is thickness of the plate
Safety factor (n)
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Where,
Selection of screw
Specification on selection of the screw
Standard dimension of screw threads [9] Table 11; 1 design dimension of screw threads, bolts and nuts according to IS: 4218(part iii) 1997 Pitch(mm) Designation
M36
4
Major diameter Nut and bolt 36
Effective or pitch dia nut and bolt d p(mm) 33.42
Minor or core diameter dc bolt
Nut
31.093
31.670
Depth of thread bolt(mm) 2.454
Stress area(
)
817
Checking for crushing stress on the threads and shear stress
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S
Since yield crushing stress is greater than design crushing stress the design is safe. Checking for shear stress
And A is stress area
Since yield shear stress is greater than design stress the design is safe
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Design of bolt
Figure: -9 dimensions for bolt From mechanical property of steel bolts we select the bolt material to be medium carbon (Q and T) with property class and the min tensile strength of
Where p is
From Table 11.1 (coarse series), machine design by Khurmi and Gupta we find that the standard core diameter is and corresponding size of the bolt is
And also for bolt diameter of 28 we have hexagonal nut diameter of for this diameter of nut we have width and height and washer internal diameter of 30mm and outside diameter of 56mm which have maximum thickness of 5mm from appendix Shigleys mechanical design book [12]
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Where
is length of threaded part.
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= 92mm
Design of pin
Assuming the pine material is steel with tensile stress having Reaction moment at the pin is calculated
.
Maximum design stress of pin
Where d is the diameter of the pin.
Diameter of knuckle pin and collar
Thickness of pin head
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Outer diameter of head
It is not such much necessary to design pin for other two arms because if it is designed for maximum bending moment it will be safe for other, which have less bending moment. Design of the cover plate for the cylinder rod
We select the cover plate material will be mild steel with
Section modulus
Where w – width of the plate and
Where
outside diameter of the plate and
Hole diameter of the bolt
Circumferential pitch of bolts
√
Size of the bolt
Let size of the bolt hole would be
Minimum circumferential pitch of bolts
√ , 20
Maximum circumferential pitch of bolts
We know that for a leak joint the circumfrential pitch of bolts should lie between , so that lets take the circumferential pitch will be
to
Circumferential pitch of the bolt
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Where n is number of bolts
Outside diameter of cover plate
Width of the plate
=
Suction modulus
We know that moment acting on the cover plate
From bending equation of
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4.3 Design of the Hydraulic Circuit
Specification of the job
Force requirement of the job is
Length of the stroke
This relates to the maximum lifting height and is taken to be
.
Speed of piston and rod assembly
Minimum time is taken to be
. The speed is therefore.
Cylinder Size
Rod diameter is taken to be
Cylinder selected with bore diameter of Area of rod is
And the pressure on the rod side is; - from
we can get the pressure as
This is the total pressure due to the weight of the vehicle. So the pressure applied by the pump should exceed the above pressure and for this a pump pressure of is selected.
The capacity of pump needed
Maximum cylinder speed is; -
Flow rate: -
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But area of piston
So flow rate becomes
The size of electric motor needed.
Power required to run the pump is calculated as; -
Efficiency of pump
The type of pump selected is gear pump with efficiency of
Shaft size, tape and electric source
Reservoir size needed
Reservoir size should be and this becomes
times the pump capacity
So the reservoir size is taken to be
Pump capacity is
Pressure vessel and stress concentration in the hydraulic cylinder
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Figure:- 10 hydraulic cylinder cross-section
The force exerted by the fluid must be equal to the force exerted by the pipe walls; that is the sum must be zero.
The force exerted by the fluid is
, where
is inside diameter
The stress acts around the circumference; that is the stress is hoop stress. [10]
The stress in the walls of the pipe is equal to the fluid force divided b y the cross sectional area of the pipe wall. So the hydraulic cylinder has a pressurized fluid which would push the rod end and the stress will develop along the length of the pipe to resist the pressure on the rod end. The shape of the cup does not affect the longitudinal stress in the pipe.
Figure:- 11 pressure lines inside the cylinder The force exerted by the fluid equals the force along the length of the pipe walls. Pressure acts on a circular area of fluid, so the force exerted by the fluid is:-
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=
The stress along the length of the pipe is
Figure:- 12 hydraulic circuit
4.4 Selection of Hydraulic Pump External gear pump is selected for this system. External gear pu mps are less efficient than internal gear pumps, but have some advantages. They offer ease of maintenance, steady flow, and are less expensive to buy and repair. These pumps can produce pressures ranging from to i, and their viscosity range is limited to (centistokes).
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4.5 Selection of Hydraulic Oil With hydraulics there are two primary considerations – the viscosity grade and the hydraulic oil type. The specifications are typically determined by the type of hydraulic pump employed in the system, operating temperature, and the operating pressure. The type of hydraulic oil suitable for this application and the external gear pump is found to be full synthetic oil with viscosity of
4.6 Selection of Hoses and Fittings There are places on many machines where rigid pipe or tubing cannot be used because of their inflexibility. Rigid lines can cause problems at cylinders with pivot mou ntings, pumps on noiseisolation mounts, or connections between separate un its. Hose avoids these problems. Wire braised hydraulic hose selection for hydraulic platform lifter is based on the following specifications: -
For rated internal pressure of
, a hydraulic hose with the following
specifications is selected.
Part number
Hose internal diameter 1in
Hose outer diameter
Minimum burst 4000Psi
Minimum bend radius
Weight per foot
4.7 Selection of Electric Motor
The electric motor horsepower needed to drive a positive displacement pump is calculated from the formula assuming a pump efficiency of which would be representative of most positive displacement pumps.
The motor most often used to drive a hydraulic pump is a 3-phase, induction type, design B motor. The service factors on most open frame sizes is which means that the motor can be overloaded about above current shown on its nameplate, assuming it is being operated in a normal temperature environment.[11]
The motor selected is therefore, as per the calculation, a 3-phase, motor
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, induction
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4.8 Installation and Operation of the Platform The hydraulic cylinder with the support platform at the top of the piston rod is mounted below ground with its fully retracted position and the support arms on the ground. The pump control valves, reservoir, and electric motor are mounted on the ground and are connected to the cylinder via hydraulic hoses. This is because when the piston is initially at its fully retracted position, it is in such a way that the top platform is just on the ground at its lowest level. The vehicle comes along and the chassis is made to align with the platform arms at the position of the center of gravity. Oil is then allowed to be pumped to the cylinder which raises the piston thereby lifting the vehicle. The height can be adjusted anywhere in the range of the maximum limit as per the requirement of the personnel working on it by controlling the oil flow via control valves.
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Chapter Five 5.0 Conclusion and Recommendation 5.1 Conclusion In this project, the design of a h ydraulic lifting platform is done for an average vehicle load of 1740kg and lifting height of 1.8m. The analysis includes the design of the hydraulic circuit, the design of the support platform arms, the design of screws, bolts and other fasteners. Selection of various components of the hydraulic system is also made based on the system maximum pressure. From the results obtained in the analysis, the following can be concluded:
Position for the center of gravity for the model double cabin pick up is at 2443.25mm left to right from front to back. The prime mover for the system (electric motor) is found to be a 3-phase, 220-240V, 60 Hz induction motor. The top T-platform that supports the vehicle is subject to bending due to vehicle weight. Pressure on the rod side (pressure due to the load) is found to be 6.69bar
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5.2 Recommendation The design in this report is based on some specifications and assumptions. However the system can be redesigned for any required applications and specifications Based on the design specifications of the job, the following are recommended for use:
It is recommended that the vehicle is checked for proper alignment on the platform at its center of gravity before lifting. It is also recommended to fix the vehicle chassis on the arms with the provided clamps and screws for balance during work. It is recommended to check the hoses and change them continually.
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