Lesson Notes By Weeks and Term v3 - Senior Secondary 1
PROPELLER SHAFT AND UNIVERSAL JOINT
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PROPELLER SHAFT AND UNIVERSAL JOINT
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Subject: Auto Mechanical Works
Class: Senior Secondary 1
Term: 3rd Term
Week: 3
Theme: Transmission & Braking System
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Identify various types of universal joints. Sketch a universal jointand propeller shaft. State the function of both
(spider) with its four arms.
3. Connect the arms of the spider to the eyes of the yokes, indicating the position of the needle roller bearings (often depicted as small circles or cross-hatched sections within the yoke eyes where the spider pins enter).
4. Show the axis of the input and output shafts at an angle to each other.
5. Label all key components: Input Yoke, Output Yoke, Spider/Cross, Bearings, Input Shaft, Output Shaft. * Propeller Shaft:
1. Draw a long, cylindrical shaft (the shaft tube).
2. At one end, draw a universal joint (as described above) connecting to a representation of the transmission output flange.
3. At the other end, draw another universal joint connecting to a representation of the differential input pinion flange.
4. Clearly indicate the slip joint mechanism, typically shown as splined sections where one part slides into another, allowing for length variation. This is often part of one of the universal joint yokes.
5. For a two-piece shaft, include a centre bearing assembly supporting the mid-section.
6. Label components: Shaft Tube, Front Universal Joint, Rear Universal Joint, Slip Joint, Transmission Flange, Differential Flange (and Centre Bearing if applicable). This section provides a detailed explanation of the propeller shaft and universal joint, their components, types, and functions.
A. The Propeller Shaft (also known as Driveshaft)
Definition: The propeller shaft is a rotating shaft that transmits torque and rotation from the gearbox (transmission) to the differential, which then distributes power to the driving wheels. It is a critical component in the driveline of rear-wheel-drive (RWD) and four-wheel-drive (4WD) vehicles.
Function:
1. Torque Transmission: Its primary function is to transmit the engine's torque (power) from the transmission output shaft to the differential input pinion.
2. Angular Alignment Accommodation: It must operate at varying angles due to the relative movement between the transmission (which is chassis-mounted) and the differential (which is axle-mounted and moves with the suspension).
3. Length Variation Accommodation: As the vehicle's suspension moves up and down (e.g., when driving over bumps or potholes common in Nigeria), the distance between the transmission and the differential changes. The propeller shaft must be able to change its effective length to accommodate this. Components of a Typical Propeller Shaft Assembly:
1. Shaft Tube: The main tubular body of the propeller shaft, usually made of steel or aluminum alloy for strength and lightness.
2. Universal Joints (U-joints): Typically, two or more U-joints are fitted at each end of the propeller shaft (one at the transmission end and one at the differential end) to accommodate angular changes.
3. Slip Joint (Sliding Yoke): This component, often integrated into one of the universal joints or as a separate spline, allows the propeller shaft to lengthen and shorten to compensate for changes in the distance between the transmission and the differential during suspension travel. It consists of splines on the shaft engaging with splines in a yoke.
4. Centre Bearing (for multi-piece shafts): In longer vehicles or those requiring better balance, a two-piece or three-piece propeller shaft may be used. A centre support bearing (also called a carrier bearing) is mounted to the chassis to support the intermediate section of the shaft, reducing vibration and critical speed issues.
Types of Propeller Shafts: Single-piece Propeller Shaft: Used in vehicles with shorter distances between the transmission and differential. Simpler construction.
Two-piece Propeller Shaft: Used in longer vehicles. Consists of two sections connected by a universal joint and supported by a centre bearing. This design helps reduce whipping and vibration.
Three-piece Propeller Shaft: Less common, used in very long vehicles.
B. The Universal Joint (U-joint)
Definition: A universal joint is a mechanical coupling that allows two shafts, which are not in perfect alignment, to transmit rotary motion. It is designed to accommodate angular misalignment and often allows for changes in distance (in conjunction with a slip joint).
Function:
1. Accommodates Angular Misalignment: Enables power transmission between shafts that are at an angle to each other, such as between the transmission and the propeller shaft, or the propeller shaft and the differential.
2. Allows for Suspension Travel: Permits the driving axle to move up and down relative to the transmission without binding the driveline. This is crucial for smooth ride quality and vehicle handling on uneven terrains.
Types of Universal Joints: (Meeting Performance Objective 1)
1. Hooke's Joint (or Cardan Joint): Description: This is the most common and simplest type of universal joint. It consists of two Y-shaped yokes and a cross-shaped central member (often called a spider or trunnion) with four needle roller bearings. Each yoke is attached to one shaft, and the spider connects the two yokes, allowing them to pivot relative to each other.
Components: Yokes: Two fork-like components, one attached to each shaft.
Spider/Cross: A cruciform (cross-shaped) component with four trunnions (pins).
Needle Roller Bearings (Caps): Fitted over the trunnions and inside the yokes to reduce friction and allow smooth pivoting.
Operation: As the input shaft rotates, the spider causes the output shaft to rotate.
However, a significant characteristic of a single Hooke's joint is that it transmits rotation with a non-constant angular velocity when the shafts are at an angle. This means the output shaft speeds up and slows down twice per revolution, Two fork-like components, one attached to each shaft.
Spider/Cross: A cruciform (cross-shaped) component with four trunnions (pins).
Needle Roller Bearings (Caps): Fitted over the trunnions and inside the yokes to reduce friction and allow smooth pivoting.
Operation: As the input shaft rotates, the spider causes the output shaft to rotate.
However, a significant characteristic of a single Hooke's joint is that it transmits rotation with a non-constant angular velocity when the shafts are at an angle. This means the output shaft speeds up and slows down twice per revolution, even if the input shaft rotates at a constant speed. This non-uniformity can cause vibration, especially at higher angles and speeds.
Solution to Non-constant Velocity: To overcome this, most drivelines use two Hooke's joints (a double Cardan arrangement), phased correctly, where the non-uniformity of one joint cancels out the non-uniformity of the other.
Applications in Nigeria: Widely used in propeller shafts of many RWD cars, SUVs, buses (e.g., Toyota Hiace, Mercedes buses), and trucks operating across Nigeria due to its robustness and cost-effectiveness.
2. Constant Velocity (CV)
Joint: Description: Unlike Hooke's joints, CV joints are designed to transmit rotational motion at a constant angular velocity regardless of the angle between the input and output shafts. This eliminates vibrations and torque fluctuations.
Necessity: Primarily used in front-wheel-drive (FWD) vehicles (e.g., most smaller cars, some SUVs common in Nigerian cities) where the drive shafts need to accommodate both steering angles and suspension movement, requiring large and variable angles without vibration. They are also used at the wheel ends of many 4WD and independent rear suspension (IRS) RWD vehicles.
Types of CV Joints: Rzeppa Joint (Ball Type): Description: Consists of an inner race, an outer race (housing), and a cage that holds several steel balls. The balls run in contoured grooves in both races.
Operation: As the shafts turn and angle changes, the balls roll and slide within the grooves, maintaining a constant velocity ratio between input and output.
Application: Typically used as the outer CV joint (at the wheel hub) in FWD vehicles due to its ability to handle large steering angles.
Tripod Joint: Description: Features three trunnions (like a small tripod) with needle roller bearings, which slide in a cup with three corresponding grooves.
Operation: Allows for both angular change and axial (length) movement.
Application: Commonly used as the inner CV joint (at the transmission side) in FWD vehicles because it can handle significant axial movement (plunge) required for suspension travel.
Birfield Joint: A type of Rzeppa joint, specifically designed for higher angles.
Maintenance: CV joints are typically sealed with a rubber boot (CV boot) filled with grease. Damage to this boot (common from road debris or age, especially on rough Nigerian roads) leads to grease leakage and contamination, causing rapid wear and failure. C. Relationship between Propeller Shaft and Universal Joint The propeller shaft is typically equipped with at least two universal joints (Hooke's joints are common for propeller shafts) to manage the fluctuating angles between the transmission and the differential. The slip joint integrated into the propeller shaft or one of its universal joints accounts for the varying length. In FWD vehicles, CV joints are used on the drive shafts that connect the transaxle to the front wheels, allowing steering and suspension movement while maintaining constant power delivery.
D. Sketching Guidelines (Meeting Performance Objective 2)
Universal Joint (Hooke's Joint):
1. Start by drawing the two Y-shaped yokes, clearly showing their attachment points to the respective shafts.
2. Draw the central cross (spider) with its four arms.
3. Connect the arms of the spider to the eyes of the yokes, indicating the position of the needle roller bearings (often depicted as small circles or cross-hatched sections within the yoke eyes where the spider pins enter).
4. Show the axis of the input and output shafts at an angle to each other.
5. Label all key components: Input Yoke, Output Yoke, Spider/Cross, Bearings, Input Shaft, Output Shaft.
Propeller Shaft:
1. Draw a long, cylindrical shaft (the shaft tube).
2. At one end, draw a
A. Introduction (5-10 minutes)
Teacher Activity: Begin by asking students to recall components of a vehicle's power train they have previously learned (e.g., engine, clutch, gearbox, differential).
Pose a question: "How does the power get from the gearbox to the wheels, especially in big vehicles like buses or trucks where the gearbox is at the front and the driving wheels are at the back?" Introduce the propeller shaft as the "bridge" and universal joints as the "flexible elbows" that allow this connection despite movement. Display a diagram or actual propeller shaft/U-joint if available in the workshop.
Student Activity: Respond to recall questions. Engage in brief discussion. Observe diagrams/components.
B. Development (40-50 minutes) Explanation of Propeller Shaft (15 minutes)
Teacher Activity: Explain the definition, primary function (power transmission, length/angle accommodation), and key components (shaft tube, universal joints, slip joint, centre bearing). Use analogies relevant to Nigerian daily life (e.g., a long bridge connecting two moving parts, a telescopic antenna). Discuss why a slip joint is essential (suspension travel, rough roads). Show a diagram of a propeller shaft assembly, pointing out each part.
Student Activity: Listen attentively, take notes. Ask clarifying questions. Identify components on diagrams. Explanation of Universal Joints - Types and Functions (25 minutes)
Teacher Activity: Introduce the universal joint as the component that allows flexibility.
Focus on Hooke's Joint: Explain its components (yokes, spider, needle bearings). Describe its operation, emphasizing the non-constant velocity aspect and how two joints are used to mitigate this. Show a physical Hooke's joint (if available) and demonstrate its movement. Discuss its common applications in RWD vehicles (e.g., commercial buses, 4WD pickups prevalent in Nigeria).
Introduce Constant Velocity (CV)
Joint: Explain its advantage (constant velocity transmission). Briefly describe the Rzeppa (ball type) and Tripod types, highlighting their components (balls, races, cage for Rzeppa; trunnions, cup for Tripod). Discuss their primary application in FWD vehicles (steering and suspension angles) and at wheel ends in advanced RWD/4WD systems. Emphasize the importance of the CV boot and the consequences of its failure (dust ingress, grease loss, joint damage – a common repair in Nigerian workshops). Use diagrams to illustrate the differences and components of each U-joint type.
Student Activity: Observe demonstrations keenly. Take detailed notes on definitions, components, and functions of each joint type. Compare and contrast the two main types of U-joints. Sketching Activity (10 minutes)
Teacher Activity: Project or draw a simplified diagram of a Hooke's joint and a propeller shaft on the board. Guide students step-by-step through sketching a basic Hooke's joint, then a simple propeller shaft. Circulate, providing individual feedback and assistance.
Student Activity: Attempt to sketch a universal joint (Hooke's type) and a propeller shaft in their notebooks, labeling key parts.
C. Conclusion (5 minutes)
Teacher Activity: Recap the main points: functions of propeller shaft and universal joints, types of universal joints (Hooke's, CV). Connect the knowledge to practical applications, such as identifying components during vehicle inspection or understanding common driveline problems (e.g., vibrations due to worn U-joints, squeaking from dry slip joints). Assign homework.
Student Activity: Participate in a brief Q&A session for review. Note down homework assignment.
Vehicle Maintenance and Repair in Nigerian Workshops: Students will encounter propeller shafts and universal joints frequently in Nigerian auto repair shops. Understanding their function and common failure modes (e.g., worn U-joints causing clunking or vibration, torn CV boots leading to joint failure) is crucial for diagnosis and repair. Mechanics in Nigeria regularly replace U-joints and CV boots on commercial vehicles like Danfo buses, Molue, and trucks due to the demanding conditions of Nigerian roads. This knowledge directly translates to practical skills for aspiring mechanics.
Driving and Vehicle Safety: A failing universal joint or propeller shaft can lead to severe vibrations, loss of power, or even complete driveline failure, posing significant safety risks, especially at high speeds on expressways. Understanding their role helps drivers recognize symptoms of failure early, promoting timely repairs and safer road usage. For commercial vehicle drivers (e.g., luxury bus drivers, trailer drivers), this knowledge is critical for pre-trip inspections and preventing breakdowns that could lead to accidents or delays.
Career Opportunities: This topic lays the foundation for various automotive careers in Nigeria, including: Automotive Mechanic/Technician: Specializing in driveline repair.
Auto Parts Sales/Distribution: Understanding the different types and applications of U-joints and propeller shafts for proper inventory management and customer advice.
Vehicle Inspection/Road Worthiness: Identifying faulty components during vehicle inspections for roadworthiness compliance, contributing to safer transportation within the country.