Investigation Into the Causes of Propeller Shaft Failure of Dong Feng Trucks - a Case Study at the Base Workshop, Burma-Camp
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CHAPTER 1
INTRODUCTION
1.1 Problem Definition
The rated power generated from the engine of a heavy duty vehicle can only become useful when effectively transmitted from the engine via the fly wheel to the transmission system of the truck and finally to the final drive. The propeller shaft or the drive shaft which is the mechanical component used for transmitting torque and rotation is used in transmitting these generated power to the final drive.
However, when the Ghana Armed Forces introduced the Chinese made Dong Feng trucks which are five ton troop carrying vehicles (TCVs) for its operations, their propeller shafts recorded a high rate of failure. This inevitably affected the morale of troops and the operations of the Ghana Armed Forces. Some drivers of the truck fearing the propeller shaft failure could result in accident, hanged nylon rope or chain under the trucks to prevent a failed shaft from striking the ground. Below are pictures to that effect.
This project therefore aims at identifying the causes of the failures of propeller shafts and recommend mitigating measures to them.
Fig. 1.1 Nylon Rope Beneath the Propeller Shaft
1.2 Objectives
The objectives of this project work are: * To identify the causes of propeller shaft failure of heavy duty trucks at the Base Workshop. * To recommend mitigating and preventive measures to the problems.
1.3 Justification
It is anticipated that the findings of this project will bring to the knowledge of truck owners and users especially the Ghana Armed Forces the causes of propeller shaft failures and recommended measures to prevent them from occurring.
1.4 Methods Used
The methods to be adopted include: * Visit to the Dong Feng Base Workshop, Burma – Camp. * Consultation with Lecturers at the Mechanical Engineering Department of UMaT, Tarkwa. * Data collection and analysis.
1.5 Facilities Used for the Research
The facilities to be employed include: * The Base Workshop. * Relevant literature review. * Library facilities at UMaT. * Internet facilities at UMaT.
1.6 Scope of work
This project is limited to investigations into the causes of propeller shaft failures on Dong Feng trucks at the Base Workshop, Burma-Camp, Accra, Ghana.
1.7 Work Organization
This project work is organized into four chapters as follows:
Chapter one consists of the statement of the problem, objective, methods used, research facilities used, justification of the project objectives, scope of work and work organization.
The second chapter introduces relevant information about Base Workshop by way of an overview and some department at the Base Workshop and their maintenance procedure.
The third chapter gives a brief introduction to the truck and its technical data, detailed description of power train system and a general overview of the propeller shaft universal joint, General Causes of Propeller Shaft Failure and Mitigating Measures carried out in this chapter.
Chapter four will deal Investigation at the Base Workshop into the causes of propeller shaft failure, Outcome of the Investigation, conclusions and recommendations.
CHAPTER 2
RELEVANT INFORMATION ABOUT BASE WORKSHOP (B/WKSHP)
2.1 Introduction
After the first and second world wars, the Army thought of forming a workshop to undertake repair work in the Army. In 1946, a nucleus workshop was formed and located at Bubuashie at Accra to undertake the repairs of the Royal West African Frontier Force’s (RWAFF) weapons and equipments. Later it moved to a new site at United Africa Company (UAC) Workshop, opposite Accra Railways Station. In 1950, it was designated as No. 1 Station Workshop, West Africa Electrical and Mechanical Engineering (WAEME) and moved to a new location at Duala barracks, Giffard Camp, now Burma Camp. In 1952, the No. 1 Station Workshop was re - designated as No.4 Command Workshop with 300 military and civilian personnel. As a result of the dissolution of the West African Command, in 1954, the No. 4 Command Workshop was again re - designated as No. 4 Force Workshop. To differentiate the No. 4 Force Workshop from the Police Workshop, it was designated as No.1 Army Workshop (GEME) on 2nd April, 1956.
When Ghana attained independence in 1957, all foreign officers were seconded to the Ghana Army. The detachment of No.1 Workshop took part in the Congo Operations (July1960 - September 1963), partly under the British officers. The period 1961 - 1962 marked a complete transfer of command to the No.1 Army Workshop (EME) from the British seconded officers to the Ghanaian officers. The last British officer was Capt. FAC Williams and the first Ghanaian officer being Lt. N. Mantey.
As part of the expansion program of the Army, a site was found, now called the Chiringa Barracks, Burma-Camp where buildings were put up to accommodate the No.1 Army Workshop. It was officially opened by the president of the Republic, Dr Kwame Nkrumah on 24th June, 1961. In the year 1973, the No. 1 Army Workshops was again designated as the Base Workshop (EME).
The Base Workshop is now the main workshop in the Ghana Armed Forces responsible for the servicing, repairs and maintenance of all electrical and mechanical equipment in the Army and other equipment common to the Ghana Air Force and Navy supported by Light Aide Detachments (LAD) attached to the various units. Figure 2.1 is the layout of the organizational structure of Base Workshop (Arkoful, 2000).
Fig. 2.1 The Organizational Structure of the Base Workshop (Arkoful, 2000)
2.2 Roles and Responsibility
The roles of the Base Workshop in general are: * Inspection * Repairs * Modification * Maintenance and * Recovery of all electrical and mechanical equipment common to the Air force and the Navy. It also provides other technical facilities, which are used to ensure that all the Armed Forces equipment are kept serviceable at all times during both war and peace times.
2.3 Maintenance Procedure
When a vehicle reports at the base workshop for repairs, it goes through the following stages:
2.3.1 Planning and Progress (P and P)
The driver reports at this section with a properly washed vehicle for processing and documentation.
2.3.2 Receipt and Inspection (R and I)
The vehicle is received at this outfit, an inspection is carried out in the presence of the driver to check the fuel level, notice is taken of any dents or bodily damage to the vehicle and the contents is also checked for the presence of tools, car jack, fire extinguisher among others after which the vehicle is sent to the servicing section.
2.3.3 Servicing Section
Here, all the various types of servicing in the workshop are carried out. It is also from this outfit that vehicles for repairs and maintenance are sent to the appropriate floors for work to be carried out. After the vehicles have been worked on, they are brought back to the servicing section, where personnel cross check with the job card to ensure that all that is on the job card was done before it is sent back to R and I where checks are once again conducted to ensure that the fuel gauge, tools fire extinguisher dents among others are intact as before the vehicle was sent to the workshop floor.
2.3.4 The Workshop Floor (Civil Pattern, Steyr, Land Rover, Tata, Heavy sections)
This is where the main vehicle repair works takes place. The workshop floor is divided based on specialization of personnel according to vehicle type. There is the civil pattern section that handles all civil pattern vehicles on charge to the Ghana Armed Forces, the steyr section, which handles only steyr trucks. Land Rover section handles only Land Lover as the name implies. The TATA section is responsible for buses and last but not the least, Heavy section that handles Dong Feng trucks (Arkoful, 2000).
CHAPTER 3
LITERATURE REVIEW
3.1 Introduction
In recent times, there have been many propeller shaft failures on the Dong Feng trucks at the Base Workshop, Burma- Camp, Accra. This could have been avoided with the proper care and attention to details. An investigation at the workshop into the causes of propeller shaft failures was undertaken to obtain an idea of the most common causes of propeller shaft failure of the Dong Deng truck. The results of this investigation indicate two main causes of the shaft failures at the Base Workshop i.e. Improper Assembly and Poor Lubrication.
3.2 The Dong Feng EQ1093F6D Truck
The Dong Feng EQ1093F6D 4x4 is a five-ton logistics and troop carrying vehicle (TVC) manufactured by The Dong Feng Motor Corporation of China. The original EQ240 vehicle, powered by EQ6100/6105 petrol engines, has been continually updated and a number of more `new technologies have been included into the design since the 1980s. The current model, designated EQ1093F6D is powered by an improved Cummins 6BT5.9 5.88 - litre diesel engine.
The layout of the truck is entirely conventional, with the engine forward, the steel cab seating the driver and two passengers, and the load area to the rear. A conventional C - section chassis is used, with beam - type axles sprung by leaf spring suspension. The standard cargo body of the truck has a steel and wood floor, steel side racks and a tailgate. Optional equipment includes a power take - off and a 4,500 kg winch mounted behind the front bumper (Anon., 2010).
The People's Liberation Army (PLA) of China uses a large number of these vehicles, which are similar in appearance to a wide variety of Dong Feng bonneted commercial 4 x 2 trucks. However, it was introduced into the Ghana Armed Forces a few years ago.
The Dong Feng Motor Corporation was originally known as the Second Automobile Works, and was established in 1967 by relocating part of the facilities and technicians of the First Automobile Works to the rural area in Hubei Province. Production began in the early 1970s and Dong Feng Corporation is now one of China's largest automotive manufacturers, producing a variety of designs used by the PLA (Anon., 2011a). Below is a table of the technical data of the Dong Feng EQ1093F6D truck (Fig.3.1).
Table 3.1 Technical Data of Dong Feng EQ1093F6D Truck GVW | 9715 kg | Curb Weight | 4480 kg | Fron | 2280 kg | Rear | 2200 kg | Wheel base | 3950 mm | Min turning radius | 8 m | Overall length | 6910 mm | Overall width | 2470 mm | Overall height | 2460 mm4052 L | Interior dimension of cargo body | 2294 W550 H | Approach Angle | 42.5° | Min. Ground Clearance | 260 mm | Passengers | 3 | Max. Speed | 94 km/h | Max. Gradeability | 55 % | Engine | EQB160 20 | Type | Diesel, 6 cylinders in line, water-cooled, turbo-charged, direct injection | Displacement | 5880 cc | Max. Output | 118 kw (160 hp) @ 2600 rpm | Max. Torque | 559 N.m @ 1400-1600 rpm | Clutch | Single dry plate, diameter 350mm, hydrauliccontrol with air booster | Gear-box | five forward-speeds, one reverse | Ratios | 4.763/2.808/1.594/1.00/0.815/4.99 (Re) | Rear axle | Full floating, single reduction by hypoid gearing | Capacity & Ratios | 7600 kg, 6.33 | Front axle | full floating, single reduction by hypoid gearing | Capacity & Ratios | 2800 kg, 6.33 | Transfer Case | Two speeds, mechanical control, 1.08 (H)-2.05 (L) | Service brake | Full air brake system split pneumatic circuit | Parking brake | Mechanical control, acting on transfer case | Auxiliary brake | Exhaust brake | Frame | Riveted pressed steel ladder type | Suspension | Front: Leaf spring with shock absorbersRear: Leaf spring with auxiliary leaf spring | Steering | Integral power steering | Cab | Normal control type | Tire and wheel | 9.00-20 14 PR | Fuel tank | 160 L | Starter | 24V, 4.5 kw | Battery | 12V, 100 Ah |
(Source: Huijuan ke, 2011)
Fig. 3.1 The Dong Feng EQ1093F6D Truck (Anon., 2011b)
Fig. 3.2 The Dong Feng EQ1093F6D Trucks (Anon., 2011b)
3.3 Major Transmission Units The main components in the transmission system or power train of the Dong Feng truck include the engine, transmission, differential, propeller shaft, axle and final drive.
Shaft between Transfer Case and Front Axle
Shaft between Transfer Case and Rear Axle
Gear Box
Transfer Case
Shaft between Gear Box And Transfer Case
Fig. 3.3 Line of Power Transmission (Anon., 2005)
1. Front axle | 2. Transmission | 3. Propeller shaft between transfer case and front | 4. Propeller shaft between transmission and transfer case | 5. Transfer case | 6. Propeller shaft between transfer case and rear axle | 7. Rear axle | |
3.3.1 The Engine
The Dong Feng trucks are powered by diesel engines of mechanical fuel system with displacement volume of 3.9L (60 - 150HP), which comply with Euro II emission standards for motor vehicles and Tier I emission standards for off-highway mechanical equipment in Europe. The engine is the component that produces power which moves or propels the vehicle. A flywheel mounted on the crankshaft minimizes the cyclic variation in speed. It absorbs energy during the working strokes and supplies it during the non working strokes. This ensures uniform turning moment at the crankshaft.
Torque which is a measured ability of a rotating element (gear or shaft) is generated to overcome the turning resistance. In addition, various engine support systems such as air induction, fuel injector, exhaust, lubrication, and cooling work together to keep the engine running properly. Fig. 2.3 shows a Dong Feng Engine built to Cummins technology standards (Anon., 2011c).
Fig. 3.4 Cummins Engine (Anon., 2011c)
3.3.2 Transmission and Transfer Case
The transmission has the following functions: * To vary the ratio and the extend the variation range and speed of the driving wheel for satisfying requirements under different conditions, at the same time, to allow the engine to operate under a favorite condition, i.e. high power and low fuel consumption. * To satisfy the requirement of the truck backing with the engine rotation direction unchanged. * By making use of the neutral gear position, to interrupt power transmission for the engine to state, engine running idle and for convenience of gear shifting or power delivering.
The transmission used in the Dong Feng EQ1093F6D truck adopts a two-axle gear structure. It has five forward gears (the fifth is a direct gear) and one reversing gear.
Transmission ratios of different gears are as follows: the 1st – speed gear, 7.58; the 2nd speed gear, 4.30; the 3rd speed gear. 2.44; the 4th - speed gear, 1.49; the 5th gear - speed gear, 1.00 and the reversing gear, 7.69 (Anon., 2005).
3.3.3 Gear Mechanism
A lock – pin type inertial synchronizer is installed respectively between the second and the third gears and between the fourth and fifth gears for convenience of gear shifting and reduction of impact noises of gears. The powers drive in the second, third, the fourth and fifth - speed gears is realized by constantly meshing oblique tooth gears. The power drive in the first-speed and reserving gears is realized by straight tooth gears, and gear shifting is realized by sliding gears on different shafts. Refer to Fig. 3.6.for the structure of the transmission gear mechanism.
Fig. 3.5 Transmission Assembly (Anon., 2005)
1. Primary shaft | 2. Constant meshing driving gear | 3. Gear seat, fourth and fifth gears | 4. Synchronizer, fourth and fifth gears | 5. Driven gear fifth gear | 6. Driven gear, third gear | 7. Synchronizer, second and third gears | 8. Driven gear, second gear | 9. Driven gear, first and reverse gears | 10. Main shaft | 11. Inter mediate shaft | 12. Driven gear, first gear | 13. Reversing gear shaft | 14. Reversing gear | 15. Driving gear, second gear | 16. Driving gear, reversing gear | 17. driving gear, third gear | 18.driving gear, forth gear | 19. constant meshing driven gear | |
The primary shaft 1 is the power input shaft of the transmission and is manufactured in an integral part with constant meshing driving gear 2.
The main shaft 10 is the power output of the transmission. The forward end of the main shaft sits on the inner hole of the primary shaft constant meshing gear through a needle bearing, and its rear end, on the rear end face of the transmission case through a ball bearing.
The intermediate shaft 11 is seated on the front and rear end faces of the transmission case through bearings. The front bearing is a ball bearing without inner face, it allows the intermediate shaft moves a little axially forward whenever the shaft is exerted by external force and becomes deformed, or is heated and becomes longer. The rear bearing is a common bearing which bears the axial force and is fixed by a big nut.
The reverse shaft 13 is installed in the case by press fit and the reversing gear is floating on the shaft through a pair of needle bearings with a metallic retainer brackets.
The synchronizer 4 of the fourth and fifth gears can slid on the gear seat 3 of the main shaft through a sliding toothed sleeve, while the synchronizer 7 of the second and third gears can slid directly on the main shaft by means of a sliding toothed sleeve. By moving the sliding toothed sleeve of the fourth and fifth gears or that of the second and third gears to make it engage with the constant meshing gear 2of the primary shaft or with engaging teeth of driven gears 5, 6 or 8. Gear shifting to the fifth, forth, the third or the second gear can be realized.
Driven gear 9 of the 1st- speed and reversing gears is installed at the rear part of the main shaft through its rectangular splines. Moving the driven gear forward and make it engage with the reversing gear 14 can shift to the reversing gear. Moving the driven gear backward and make it engage with the first driving gear 12 can shift to the first gear (Anon., 2005).
3.3.4 The transfer case
The function of the transfer case is to distribute the power from the transmission to the drive axles and to vary drive ratio of the power train for the purposes of making the truck better adapt to the complicated and difficult riding conditions.
The Dong Feng EQ1093F6D truck transfer case has a high- speed gear that is commonly used, and allow-speed gear that is used for power boosting. By means of the transfer case, the front axles can be engaged and disengaged. There is a window on the upper part of the transfer for the installation of power take-off devices. The transfer case is composed of three assemblies i.e. the casing and cover, the gear drive mechanism and the gear-shift control mechanism. (Anon., 2005) Refer to fig. 2.2.7 for its construction.
Fig. 3.6 Transfer Case Construction (Anon., 2005)
1. Driven gear, low-speed gear | 2. Driven gear, high speed gear | 3. Driving shaft, front axle | 4. Engagement sleeve, front axle | 5. Intermediate shaft | 6. Driving shaft | 7. Casing, transfer case | 8. Transfer case cover | 9. Bearing cap | 10. Adjusting shim | 11. Engagement sleeve, high and low gear. | 12. Adjusting shim | 13. Hand break assembly | 14. Driving shaft rear axles | 15. Oil filter | 16. Driving gear, mileage counter | 17. Driven gear, mileage counter | 18. Hand break arm | 19. Gear-shift arm, high and low gear | 20. Gear shift arm, front axle | |
The driving shaft 6, intermediate shaft 5 and the rear axle driving shaft 14 are seated on the casing 7 and cover 8 through a pair of conical roller bearings respectively. The forward end of the front axle driving shaft 3 is seated in the bearing seat through a single-row centripetal ball bearing, while its rear end, through a needle bearing with a retainer bracketed, is going through the front hole of the middle and rear driving shaft. Constant meshing oblique-tooth cylindrical gears are adopted for power drive for the purpose of improving the strength of gears, reducing noises and bringing about convenience for gear shifting.
The driving gears are manufactured in an integral part with the driving shaft. The driving gear of high speed gear is fixed on the intermediate shaft by means of a semicircular key, while the driving gear of low speed gear is made in an integral part with the intermediate shaft. The driven gear 1 of the low- speed gear is slipping over the middle and rear gear axle driving shaft through two parallel niddle bearing containing retainer brackets. While driven gear 2 of the high-speed gear is slipping directly over the middle and rear driving shaft, i.e. without any bearing. This is because when the high-speed gear is selected, driven gear 2 is synchronized with the shaft, while the low-speed gear is rarely used.
The transfer case adopts a mechanical control unit. Changing to high or low gear and engagement of the front axle are realized by engagement sleeve and gear-shift turning forks respectively, that makes gearshift easy and smooth. The engagement sleeve 11 of high and low gear and the engagement sleeve 4 of front axle are installed on gear seats of rear and middle axle shaft and front axle driving shaft respectively. (Anon., 2005)
3.3.5 The Propeller Shaft
In automobile parlance the propeller shaft, also known as the drive shaft in effect, are lightweight hollow carbon steel tube which is strong enough to resist twisting and bending that are used to connects the gear box of the automobile with the rear differential for the purposes of transmitting the engine drive force to the wheels. The propeller shafts used in contemporary automobiles are typically more rigid that their earlier counterparts. This enables them to deliver maximum power to the wheels form the transmission. They are generally used in pairs and shorts propeller shafts are used to provide power to the wheels. This can be from the differentials, Transaxle or the transmission.
In the case of rear - drive vehicles or ones that have a rear engine, the propeller shafts that are used are longer. This enables the power to be transmitted through the length of the vehicle. Two forms of the propeller shafts are extensively used in the world of automobiles namely the Hotchkiss shaft that has two or more joints, and the torque tube that has a single universal joint. The propeller shaft is used when the engine and axle are not together but are separated from each other. This scenario occurs in vehicles that come under the category of four-wheel drive and rear-wheel drive. In these cases, it is the definitive propeller shaft that transmits the engine generated drive force to the axles of the vehicle. (Agustus, 2010)
There are altogether three propeller shafts on the Dong Feng truck, i.e. Propeller shaft between transmission and transfer case, the propeller shaft between transfer case and rear axle, propeller shaft between transfer case and the front axle. Among them, the propeller shaft between the transmission and the transfer case is relatively short and without shaft tube, the other two are open tube structure. (Anon., 2005)
Below, Fig.3.7 shows details of a typical propeller shaft, Fig.3.8 Propeller Shaft between Transmission and Transfer Case. Fig. 3.9 Propeller Shaft between Transfer Case and Rear Axle and Fig.3.10 Propeller Shaft between Transfer Case and the Front Axle.
Fig. 3.7 Components of a Typical Propeller Shaft (Anon, 2011d)
Fig. 3.8 Propeller Shaft between Transmission and Transfer Case
Fig. 3.9 Propeller Shaft between Transfer Case and Rear Axle
Fig. 3.10 Propeller Shaft between Transfer Case and the Front Axle
3.3.6 Driving axles
The driven axles have the following functions: * To reduce the speed coming from the transmission and increase the torque exerted on driving wheels. * To make driving wheels on two sides of the truck rotates at different angular velocities, ensuring a pure rolling of the truck wheels. * To change the direction of torque coming from the engine and make it the same as that of driving wheel rotation. * To carry the weight of the truck
The Dong Feng EQ1093F6D adopts a two axle driving system. Its front axle is a steering and driving axle and the front and rear axles are single-stage speed reducing driving axles as shown in Fig.3.12 and Fig.3.13. The driving and driven conical gears adopted in the main reduction gearbox of the driving axles are quasi - hyperbolidal gears with the drive ratio of 5.83.
Fig 3.11 Main Reduction Gearbox and Differential of Front and Rear Axles
(Anon., 2005)
The main reduction gearbox and differential in front and rear axles (see Fig 3.12). Gears of the main reduction gearbox and differential and other parts are all installed in the main reduction gearbox casing 5 constituting an independent assembly, which is fixed to the axle case by bolts made of 40 Cr steel alloy. The reduction gearbox and differential assemblies of the front and rear axle are identical to each other. The conical driving gears are left-handed gears, while conical driven gears are right-handed ones.
The conical driving gears are supported by a pair of conical roller bearings 2 (front bearings) and a short roller bearing 2 (rear bearing). The outer race and rollers of the short bearings are installed in the main reduction gearbox casing %, while a pair of conical roller bearings is places in bearing seat 18. (Anon., 2005)
Propeller shafts can also be connected using spline joints. Spline connections have corresponding male and female sides, which interlock to maintain shaft-angle consistency and transfer torque efficiently. Spline joints are used to transfer rotational torque at larger angles than U-joints. Spline units are covered with rubber boots to protect the inner steel balls from the buildup of dirt and grime (Agustus, 2010).
3.4.2 Yokes and Flanges
Yokes and flanges are located at the ends of drive shafts. Different systems utilize many combinations and types of connecting yokes and flanges. In automobiles, the yoke at one end of the shaft is slid into the transmission, and the other end's flange is bolted to the rear differential's pinion flange. These connections ensure transfer from a machine's rotational source to its moving parts. (Agustus, 2010)
3.4.3 Carrier Bearings
On two-or-more piece propeller shafts, carrier bearings, along with U-joints, connect the separate propeller shafts. Carrier bearings are attached to a chassis with a cross member. Carrier bearings must sit in their cross members correctly to maintain proper alignment in transferring the torque through the two shafts it is connecting (Agustus, 2010).
3.4.4 Universal Joints
Universal or "U" joints are used at the ends of propeller shafts to transfer torque from input and output sources that are not located on the same plane in a machine. They consist of two "C" shaped hinges connected by a multi-directional cross shaft. U- joints are used on vehicles that must maneuver inclines or difficult terrain. For systems that use a two-or-more shaft design, U-joints are used to connect the propeller shafts (Agustus, 2010).
The universal joint adopted in the EQ1093F6D truck is of a common cross joint structure. It is composed of spiders, grease and oil seals, winged bearings and so on, as shown in Fig.3.16. The universal joint of the EQ1093F6D truck has the following features:
* The two ends of the spiders are fixed by a bearing pressing plate and a lock piece respectively. * The ends of the propeller shaft are coupled through winged bearings and fastened by hexagonal head bolts.
Such a configuration of the universal joint makes it simple in construction, easiness in the assembling, and improves the bearing working conditions (Anon., 2005).
Fig. 3.15 Universal Joints (Anon., 2010)
The sizes and specifications of shaft tubes, spiders and splined shafts of the three propeller shafts are given in the following table:
Table 3.2 Sizes and Specifications of Shaft Tubes, Spiders and Splined Shafts of the Four | Shaft tube | spider | Splined shaft | | Outer dia. | Wall thickness | Shaft dia. | Length | Outer dia. | Tooth width | Tooth quantity | 1 | Propeller shaft between transmission and transfer case | / | / | 31.66 | 130 | 60 | 4 | 24 | 2 | Propeller shaft between transfer and rear axle | 89 | 2.5 | 25 | 108 | 50 | 5 | 16 | 3 | Propeller shaft between transfer and front axle | 89 | 2.5 | 25 | 108 | 50 | 5 | 16 | (Source: Anon., 2005) 3.4.5 Requirements The requirements expected of a universal joint. These are: * Strength: high torque must be transmitted with the minimum energy loss due to friction. * Compactness: space is limited to the joint must be small and robust. * Large drive angle: modern road spring allows large wheel deflections so that joints must be able to accommodate the large drive angle given by this movement. * Shaft balance: severe vibrations occurs if the shaft runs-out-of true so the joint must maintain good alignment * Operating speed: the joint must operate efficiently at high speed under conditions of high torque and variable drive angle. This requirement must be combined with the need for the joint to have a long life and minimum maintenance (Agustus, 2010).
3.4.6 Requirement of Propeller Shaft:
For achieving efficient functions, the following are expected in a propeller shaft * High Torsional Strength: Therefore, they are made of solid or hollow circular cross section * Toughened and Hardened: Therefore, they are made of superior quality steel and are induction hardened * Efficiently Jointed: Therefore they are generally welded by submerged are carbon dioxide welding process. * Dynamically Balanced: Since the phenomenon of whirling may be critical at higher speeds, therefore, propeller shafts are tested on electronic balancing machine. * Reduced Thrust Loads. Since resonance is dangerous for the life of shaft, it also transmits excessive dynamic force to the shaft's end supports, and so its occurrence should be avoided.
3.5 General Causes of Propeller Shaft Failures and Ways of Mitigating Them:
A properly “sized” propeller shaft should never fail or wear out if it is properly installed and properly maintained. When a propeller shaft or a part of it fractures, it is usually the result of some sort of shock load.
The components of a propeller shaft will wear prematurely if they are not properly serviced. All propeller shaft manufacturers provide recommended service intervals and recommend the proper lubricant to use for their products
3.5.1 Types of Failures and Analysis (i) U - joint cross, broken at a bearing surface * U-joints seldom break off at the bearing surface. It takes a very large shock load to cause this type of failure. It is also very difficult to inspect for this type of failure because they, start as a small crack and progress into a complete failure.
(ii) U-joint cross, broken through lubrication fitting hole * This failure is usually caused by someone who does not install the U-joint in the correct orientation with the drive shaft. The front U - joint of a drive shaft MUST be installed so the driving torque compresses the U - joint lube fitting.
(iii) A lube related failure might include: * A U-joint with a completely “burned off” journal. * A U-joint with needle marks in the bearing surface. (Called brinelling) (Needle marks that can be felt with a thumbnail.) * A U - joint with “scrape” marks, (called spalling) on the bearing surface.
(iv) Spalling occurs when dirt or moisture enters the bearing area of the U - joint and is not “flushed out” during normal service because: * The service mechanic did not follow service interval recommendations or… * Did not take care to “purge” all four seals of the U - joint.
(v) A U - joint having one or more “blackened” bearing surfaces. * A U - joint bearing surface can “burn” if it is operated at a high U - joint angle (more on U - joint angles later) or if it is installed in a drive shaft yoke or end fitting yoke that has ears that are not in correct alignment. * A key indicator of a defective yoke is a U - joint that has two burned bearing surfaces, 180 degrees from one another (Anon., 2011d).
3.6 Propeller Shaft Vibrations
There are five types of drive shaft induced vibrations that are associated with the installation parameters of a drive shaft.
Transverse Vibrations are caused by imbalance:
All drive shafts should be balanced at their application speeds. * Drive shafts are much heavier than a tire. * Drive shafts rotate much faster than a tire.
All drive shafts should be inspected for missing balance weights at every service interval. A transverse vibration always occurs at drive shaft speed, and occurs at once per revolution.
3.5.2 Torsional vibrations
Are caused by two things:
* The U-joint operating angle at the “drive” end of the drive shaft
* The orientation (phasing) of the yokes at each end of the drive shaft
A torsional vibration is a twice per revolution vibration. This vibration will cause the drive shaft, “downstream” of the front U - joint, to “speed up” and “slow down” twice per revolution. That means that a power supply producing a constant speed of 3,000 RPM can actually be attached to a propeller shaft is changing speed 6,000 times per minute. The amount of that change in speed, called the magnitude, or size of the change, is proportional to the size of the angle at the drive end of the drive shaft, or the amount of misalignment between the yokes at the drive and driven end of the drive shaft (Anon., 2011d).
3.5.3 Phasing Affects Torsional Vibrations.
A propeller shaft that is “in phase” and has the correct operating angles at the drive end of the shaft does not create a torsional vibration.
Propeller shafts that are not in phase will vibrate with the same twice per revolution vibration as a propeller shaft with incorrect operating angles.
The easiest way to make sure your propeller shaft is in its correct phase is to mark the tube and slip yoke every time it is taken apart so it can fixed back in its original orientation when it is re-assembled. Re-assembling a propeller shaft out of phase is the main cause of torsional vibration.
3.5.4 Secondary Couple Vibrations
* Secondary couple vibrations are also caused by the operating angle at the drive end of the propeller shaft * Every U-joint that operates at an angle creates a secondary couple load that traverses down the centerline of the propeller shaft
3.5.5 Critical Speed Vibrations
Critical speed occurs when a propeller shaft rotates too fast for its length. It is a function of its rotating speed and mass and it is the RPM where a drive shaft starts to bend off of its normal rotating centerline. As it bends, it does two things:
* It gets shorter. If it gets short enough, it can pull out of its slip and drop to the floor or ground. * It starts to “whip” up and down or back and forth like a jump rope. If it whips far enough, it will fracture in the middle of the tube.
Every propeller shaft, no matter what its length and mass, has a critical speed. The shorter the propeller shaft, the higher its critical speed. Conversely…the longer a propeller shaft, the lower its critical speed. When a propeller shaft runs at its critical speed, it always fails, and the failure is always catastrophic. Below in table Fig.3.18 are the causes of wear in bearings and the mitigating measures to employ. (Anon., 2011d)
Table 3.3 General Causes of Propeller Shaft Failure and Mitigating Measure Problem | Causes | Mitigating measure | Vibration | Bent propeller shaft | straighten it/replace it | | Broken or worn universal joint crosses and bearings | replace them | | Loose propeller shaft supporting mounting | tight it | | Loose universal joint bolt nuts | tighten them | | Splines not properly aligned at sliding joint | align them with the help of arrows | | Intemediate flange not properly aligned with forward propeller shaft yoke | realign them | Squak, metalliuc rattle, click or growl | Due to lack of lubrication | grease the joints | | Worn or broken universal joint cross, joint bearing and joint seals | replace them | | Universal joint bearings not seated properly in yoke or flange | adjust them | | Propeller shaft support mounting cap screws, loose | Tighten them | | Propeller shaft support improperly installed and loose intermediate flange | Install properly and tighten the flange. | Lubricant loss at the joints | worn out joint seals, worn out universal joint cross as well bearings, and the bearings not seated properly in the yokes or flangers | Replace seals, universal joint cross and bearings. Fix bearings well into yoke. |
(Source: Anon., 2011d)
CHAPTER 4
INVESTIGATIONS, CONCLUSION AND RECOMMENDATIONS
4.1 Investigations at the Base Workshop
At the Base Workshop, data of accident report collected and analyzed indicated that five of the reports attributed the cause of accident of the Dong Feng trucks to the failure of propeller shafts. Armed with this information and working with the Officer in Charge of the Dong Feng Section of the workshop with his mechanics, trouble shooting was done against each of the general causes of propeller shaft failure and two identified causes were arrived at to be the main causes of the propeller shaft failure on the trucks. These are:
* Improper Assembly
* Improper lubrication
4.1.1 Outcome of Investigations at the Base Workshop
Data collected and analyzed at the base workshop revealed the following: * It was observed that some of the propeller shaft failures were due to the fact that the shafts were not properly secured to the drive axle or to the transfer case of the trucks. It was detected that, the bolt and nuts holding the shaft were not given the right tightening torque therefore the continuous running of the truck lead to further loosening of the nuts and eventually the shaft failed/dropped.
* The other observation made was that the lubricant that came with the trucks was too light and therefore looses it properties/qualities quickly in our tropical region. This lead to the Brinelling and End Galling i.e. The grooves made by the needle roller bearings on the trunnion of the universal cross which eventually led to the failure of the shaft. This occurs because the oil is unable to serve its purpose of reducing friction and wear.
Fig. 4.1 Damaged Roller Bearing
Fig. 4.2 Brinelling of Universal Joint
Fig. 4.3 End Galling
4.3 Conclusion
There are many factors that can cause a propeller shaft to fail. However, the investigation conducted at the Base Workshop shows that the causes of the propeller shaft failures on the Dong Feng EQ1093F6D where due improper tightening of bolts and nuts that secure the shaft to the transfer case and the drive axle and improper lubrication. However, these failures could have been prevented if due diligence had prevailed.
4.4 Recommendations
* Trucks imported should undergo inspection and where necessary, the various bolts and nuts securing the propeller shaft to the drive axle and the transfer case should be given the right tightening torque. * Lubrication oil that arrives with the trucks should be replaced with lubricant that suites the climatic condition of Ghana. * Regular inspection and maintenance should be carried out on the propeller shaft and the appropriate action carried out. * The Armed Forces should adopt a mechanism of evaluating equipment purchased to ensure they meet acceptable standards before they are accepted into the system. * The findings of this investigation are communicated to the manufactures of the trucks for correction.
