The Back Hoe Loader Design Engineering Essay

Backhoe loader is heavy equipment with very unique appearance. It consists of three pieces that combined into one unit: tractor, backhoe and loader. Each part is concerned with a particular sort of work and all of the pieces are integrated together to get job done.

The Tractor

Tractor is the main part and the core structure of a backhoe loader and it is designed to be appropriate and move easily over variety and rough terrain. It has a powerful, large, turbocharged diesel engine, rugged tires and a cab with basic steering controls such as steering wheel and brakes. Backhoe loader gives the operator protection by cabs that are completely enclosed or have an open canopy.

The loader

The loader is existed in the front and has many different functions. The operator usually cannot dig with it; it is used to pick up and carry large amounts of waste material. Loader also can be used to smooth things over or to push dirt like a plow and loader can be controlled by the operator while driving the tractor.

The Backhoe

The backhoe is the major device of the backhoe loader. It’s usually used in earth to dig up hard and compact material or to lift heavy loads, such as a sewer box. It also can lift this material and drop it in a pile to the side of the hole. Backhoe has three segments: boom, stick and bucket and the arrangement of backhoe is very similar to the human arm. The backhoe parts are connected by three joints and the boom bent upward to make it easier to dig in the way with obstacles. The backhoe suited for digging ditches and all sorts of holes.

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Another part of backhoe loader is the stabilizer legs and these legs are existed in the behind the rear wheels. The function of these legs is to take the brunt of the weight when a backhoe is digging and keeps the tractor steady in another word, minimizing the jostling effect with the backhoe while digging.

In the field of heavy equipment industry many manufacturer interested in producing backhoe loaders such as: Case, Volvo, CAT, JCB, New Holland and Sinoway.

1.2 History of Backhoe loader

Backhoe loader is reinvented from backhoe by Elton Long in 1957 after he had retired from the Case Corporation. Long’s backhoe loader had rubber tires for mobility and the right swing mechanism and buckets for specialized work. The loader provided weight and balance when the backhoe is working. By 1965, other evolutions of the backhoe had created machines exclusively for the construction industry which is powered by diesel engine, hydraulic linkages, four-wheel drive and other features were improved or added.

1.3 Backhoe loader hydraulic systems

Hydraulic systems simply used to transmit forces from point to point through fluid. The fluid that used in most systems is incompressible fluid such as oil.

Hydraulic systems in backhoe loader includes: hydraulic power, hydraulic valves, hydraulics in the backhoe, hydraulics in the loader and hydraulic pump.

Hydraulic power: The basic concept is a trade between distance and force. There are two components that determine how power will generate affect while the operator pressing downs the piston: amount of force that applied and how far that pushed in the piston. The fluid at every point in the system has the same pressure (pounds per square inch).

Hydraulic valves: the pressure in hydraulic backhoe loader comes from oil pump which is powered by a diesel engine and the appropriate oil that used is constant oil pressure because the piston is keep moving. The pump applies a lesser force to the oil at a high rate of speed. After that enough pressure will generate to move another piston more slowly but with greater force. The role of pump is to keep a steady supply of high-pressure oil flowing to a valve block system and valve will direct the pressure’s force. While backhoe is digging, it arms needs to be able to move in different directions. So the backhoe needs to use spool valve direct oil to either side of a ram.

Hydraulics in the backhoe: the three segment of backhoe (stick, boom and bucket) are connected together and each cylinder can either pull a connected segment closer or push it away. Spool valve controls in its own piston. The number of hydraulic pistons that located near the base of the boom arm in backhoe is two. The boom arm is connected to the tractor by a swing casting. Swing casting pistons makes the backhoe enable backhoe arm to swing from side to side.

Hydraulics in the Loader: the hydraulic rams of loader different from backhoe, they are work as pair. The function of rams to lift bucket and the valve system is responsible for pumps the same amount of oil to each ram, so that they move in unison.

Hydraulic pump: hydraulic pump provide all hydraulic pressure needs for the hydraulic systems on a backhoe. The most common types of pump hydraulic are: gear pump and Variable-displacement pumps. In a gear pump, the hydraulic oil can be pressurized by using a pair of intermeshing gears. The drawback of gear pumps is that pressure rises and falls with engine speed. So, the only way to get high pressure is to run the engine at full power.

1.4 Attaching Different Tools to backhoe loader

Some backhoe loader gives chance to connect variety tools to the backhoe stick or to the loader. The purpose of attaching several tools to backhoe loader is expanding the backhoe’s versatility a great deal and let the backhoe loader do a number of different things. These tools could be Hydraulic hammers, Augers, Asphalt grinders and Grapples. Each tool has many functions to serve, for example: hydraulic hammer is used for breaking up asphalt and grapple is used for gripping and pulling rooted material.

Backhoe tools: hammer, ditching bucket, spreader, rotary finishing mower, patch planer, augers, trapezoidal bucket, and compactor plate.

Loader tools: pole planters, fork-mounted crane hook, industrial forks and concrete skip.

2. Hydraulic system Calculations:

The hydraulic system contains many parts which are:

1- Hydraulic cylinders

a- four cylinders in the loader mechanism; (2) lift cylinders and the others bucket cylinders

b- three cylinders is used in backhoe mechanism; the first one connects between the body and the boom, the second hydraulic cylinder connects between the stick and boom and the final cylinder connects between the stick and bucket.

2- Gear pump, this pump is used to pump the oil from the tank to the cylinder in this assignment the working pressure of the pump was assumed 250 bar.

3- The mechanical valves controllers, these valves can be extended the piston rod in two different directions pushing and pulling. Depending on the pressure difference on the both chambers of piston when the pressure in the one chamber more than other ; piston moves back which means the loader arm at initial position. When the pressure increases within the other chamber more than the first one the piston moves forward, loader in operation. The difference in pressure can be performed by the mechanical controller which has a five port

2.1 Hydraulic calculation

2.2 Loader pistons

The force that required from this piston should be enough to carry the total load, where

F total= total mass *9.81*factor of safety

Factor of safety =2

Total mass = 310+600=910 kg

F total= 17854.2 N

In the proposed design, two lift pistons will be used, so the force on each piston is

F hydraulic = F total

F hydraulic =17854.2 N

Area of bore cylinder = force hydraulic/ working pressure

Working pressure = 250 bar (assumed)

Area of bore cylinder =( 17854.2 /250 * 105)

= 7.14164 * 10 -3 m2

Diameter of bore cylinder = ((7.14164 * 10 -3 /π) *4) 1/2

Diameter of bore cylinder = 95.36 mm

The total oil volume

Vc= A x S

Vr= Ar x S

Where:

Vc = Total Cylinder Volume in Cubic meters in the Rear or Cap End

A = cylinder Area in Square meters = 7.14164 * 10 -3 m2

S = Cylinder Stroke in mm = 400

Vr = Piston Rod Volume

Ar = Piston Area in Square meters =3.5707 * 10 -3 m2

Vc =2.8566* 10-3 m3

Vr = 1.42828 * 10-3 m3

V = Vc – Vr

V =1.4282 m-3

3. Backhoe cylinder

F hydraulic =8927.1 N

Area of bore cylinder = force hydraulic/ working pressure

Working pressure = 250 bar (assumed)

Area of bore cylinder =( 8927.1 /250 * 105)

= 3.57084 * 10 -4 m2

Diameter of bore cylinder = ((3.57084 * 10 -4 /π) *4) 1/2

Diameter of bore cylinder = 21.32 mm

The total oil volume

Vc= A x S

Vr= Ar x S

Where:

Vc = Total Cylinder Volume in Cubic meters in the Rear or Cap End

A = cylinder Area in Square meters = 3.57084 * 10 -4 m2

S = Cylinder Stroke in mm = 400

Vr = Piston Rod Volume

Ar = Piston Area in Square meters =2.38 * 10 -4 m2

Vr =9.522* 10-5 m3

Vc = 1.43* 10-4 m3

V = Vc – Vr

V = 4.778 * 10-5 m3

4. Loader dimensions

4.1 Arm one

The dimensions of this arm can be calculated as following:

The factor of safety = 2

The total mass =910

The total force that affects on arm one is 17854.2

L 1 =1.3409 (Assumed)

The area moment of inertia of this part is

I = FL3 / (3EY) (m4)

Where:

E = 200 GPa (for steel)

Y = 2 * 10 -3 (m) (maximum allowable deflection)

I = 3.5834 * 10 -5 m4

Also I = 1/12 (B * H 3 – b * h 3)

Fig.2: Cross sectional area

Where

B = .1625 m

H = .1625 m

b = .1 m

(h) Can be calculated using area moment of inertia equations

h = (-(I *12 – B * H 3) / b) 1/3

h = 13.877 cm

Thicknesses of material are:

t1 = (H – h) /2

t1 = (.1625 – .13877) / 2

t1 = 1.2 cm

t2 = (B – b ) / 2

t2 = 3.125 cm

The thicknesses of material was calculated at the most weakness area along the arm, where this area has the most stress concentration so if the thicknesses of material are suitable for this area absolutely it are suitable for others cross sectional area. The dimensions of this arm are shown in Fig. 3 and Fig.4 respectively

Fig.3: Arm one – 2D

Fig.4: Arm one, 3-D

4.2 Arm two design

This arm connects the hydraulics system to loader mechanism and it control the angle of rotate for the bucket ; the forces that affect on this arm are two hydraulic forces from lift and bucket cylinders , this part isn’t a hollow but it is fitting on both sides of arm one

The dimensions of this arm can be calculated as following:

The total length = .394 m

The minimum width = .21 m

Length and width of arm two are assumed to be applicable with arm one dimensions.

During the same procedure of the first arm based on forces calculation

I = 5.621566 * 10-5 m4

I = 1/12 (B * H 3)

H = 8.12 cm

Where: H is the thickness of the arm two

The diameters of the pin hollows can be calculated based on shear stress calculation

The permissible shear stress = 22.19 MPa (assumed from material properties)

The total force = 17854.2 N

Area of the hollow = 22.19 * 10 6 / 17854.2

Area of the hollow = 8.042477 * 10 -4 m2

The diameter of the hollow = 32 mm

The all dimensions of this arm are shown in Fig.5

Fig.5: a) Arm two 2-D

Fig.5: b) Arm two 3-D

4.3 Arm three

This arm is connected with the bucket hydraulic cylinder, also arm four push or pull the loader bucket case. The dimensions of this arm can be analyzed base on the hydraulic force that affects on them.

The area moment of inertia for this arm

I = 5.47443 * 10 -6 m4

The thickness of this arm = 8.14 cm

The pin hollows should be applicable with the dimensions of hollows for arm two

The dimensions of this arm can be presented as shown in Fig.6

Fig.6: a) Arm three 2-D

Fig.6: b) Arm three 3-D

4.4 Arm four dimensions

This arm connects arm three with the bucket the area moment of inertia for this arm is 5.39 * 10 -6 m4.

Where

The total length = .893 m

The width = .1281

So the thickness of this arm = 81 mm

Dimensions of this arm are shown in Fig.7

Fig.7: a) Arm four 2-D

Fig.7: b) Arm four 3-D

5. Bucket dimensions

The bucket dimensions should be suitable for the total load weight that requerd from the bucket also the pin hollows design the other arms, the bucket dimensions are shown in Fig.8

Fig.8: a) Bucket dimensions 2-D

Fig.8: b) Bucket dimensions 3-D

6. Backhoe design

6.1 Boom dimensions

Boom is a first linkage in the backhoe mechanism

The factor of safety = 2

The total mass =910

The total force that affects on arm one is 17854.2

L 1 = 2 m (Assumed)

The area moment of inertia of this part is

I = FL3 / (3EY) (m4)

Where:

E = 200 GPa (for steel)

Y = 2 * 10 -3 (m) (maximum allowable deflection)

I = 1.19028 * 10 -4 m4

Also

I = 1/12 (B * H 3 – b * h 3)

Fig.9: Cross sectional area

B = .25 m

H = .25 m

Let b=h

h= .2231 m

t1 = (.25 – .2231) / 2

t1 = 1.344 cm

The all dimensions of this arm are shown in Fig. 10

Fig.10: a) Boom dimensions 2-D

Fig.10: b) Boom dimensions 3-D

6.2 Stick dimensions

Stick arm used to transmute the mechanical power from the boom to bucket holder also this arm contains three gudgeon pins, the forces that affect on the stick arm is hydraulic load from the lift cylinder and bucket weight, these forces cause shear stress on the gudgeon pins and normal stress on the arm. The dimension of this arm was calculated as the previous arms design, during these calculations the thickness of the material that used in manufacturing process can be obtained, the dimensions of this arm was presented in Fig.11 in two and three dimensions sketch.

Fig.11: a) Stick dimensions 2-D

Fig.11: a) Stick dimensions 3-D

6.3 Bucket Holders dimensions

These arms are used to control the rotate angle of the bucket and it are connected with the hydraulic bucket cylinder, by calculating the area moment of inertia for these arms thicknesses of material can be calculated where these arms are not hollows in other words it’s a raged body These arms are affected by three loads; hydraulic load, bucket weight and the load that transmitted by the stick, the dimensions of these arms are shown in Fig.12

Fig.12: a) Bucket holders dimensions 2-D

Fig.12: b) Bucket holders dimensions 3-D

Backhoe bucket dimensions

This part is used to dig the hollows and to extract the demolitions waste , Backhoe bucket is affected by the weight of the shovel, each dimension of the bucket was designed based on the load weight and shovel weight, the capacity of bucket was estimated as shown in Fig.13

Fig.13: a) Backhoe bucket dimensions 2-D

Fig.13: b) Backhoe bucket dimensions 3-D

7. Body design

The design of loader backhoe body can be designed based on many factors such as

1 – Operator’s weight

2- Operational conditions, in other words where the backhoe loader is operated

3 – The different climate, such as the outside temperature and moisture rate

4- The weight of the operational machines those are carried by them such as the engine and the hydraulic pump.

5- The volume of these parts

6 – The height o f the body that required above the ground

7- The tires size

8- The wheel base

The design of the body is shown in Fig.14

Fig.14: Body dimensions 2-D

Tires size:

The tire size was selected from the tires stander as following

The rear tires size 40”

The front tire size 35”

Fig.15: a) Front tire dimensions 2-D

Fig.15: b) Front tire dimensions 3-D

Fig.16: a) Front rim dimensions 2-D

Fig.16: b) Front rim dimensions 3-D

8. Finite Element Method Analysis

Using finite element method to analyze the stress distribution along the arms, the result was as shown following

Boom arm

Using solid work software the stresses destitute normally without any critical points the factor of safety very applicable and the max deflection doesn’t exceed over the allowable deflections as shown in Fig.17,18.19 ,20

Fig.17: the deflection over the boom

Fig.18: the static strain

Fig.19: the factor of safety

Fig.20 : the stress distribution

Arm one loader

Fig.21: the deflection

Fig.22: The factor of safety

Fig.23: the strain

Fig .24: the stress distribution

Stick arm

Fig.25: the deflections

Fig.26: the factor of safety

Fig.27: the static strain

Fig.28: The stress distribution

Conclusion

Backhoe loader is heavy equipment with very unique appearance contain three main parts: The Tractor, The loader and The Backhoe .Hydraulic systems simply used to transmit forces from point to point through fluid. The fluid that used in most systems is incompressible fluid such as oil. The hydraulic system contains many parts which are: Hydraulic cylinders four cylinders in the loader mechanism; (2) lift cylinders and the others bucket cylinders, the mechanical valves controllers and Gear pump. The area moment of inertia is a suitable method to analyze the dimensions. Using solid work software the stresses destitute normally without any critical points the factor of safety very applicable and the max deflection doesn’t exceed over the allowable deflections

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