Chapter 4- Vehicle Transmission System

BMCA 4643SISTEM KUASA KENDERAAN

(ENJIN DAN TRANSMISI)

CHAPTER 4:VEHICLE TRANSMISSION SYSTEM

Learning Objective

The objectives of this unit are to : i. Present the reason for a gearboxii. Introduce the different types of gear trainiii. Demonstrate the need for transmission design

and matchingiv. Indicate the terminology and the methods for

transmission design

REVIEW OF TYPICAL VEHICLE TRANSMISSION SYSTEM

• The job of the transmission is to change the speed ratio between the engine and the wheels of an automobile.

• The transmission uses a range of gears from low to high to make more effective use of the engine's torque as driving conditions change.

• The gears can be engaged manually or automatically. The typical vehicle transmission system can be categorized into three types namely – manual transmission– automatic transmission – continuously variable transmission (CVT).

Manual Transmission System• A manual transmission also known as manual gear box.

• It is a type of transmission used in motor vehicle application.

• This transmission allow the driver select any forward or reverse gear at any time by operate a pedal and gear shift.

• This operation is for regulating torque transfer from ICE to the transmission.

Figure 4.1: Mercedes-Benz Actros Manual Transmission

Manual Transmission System (Cont..)

• Power from ICE transfers its power in the form of torque and angular speed to the wheels - to produce motion.

• The object of the gearbox is to enable the engine’s turning effect and its rotational speed output to be adjusted by choosing a range of under-and overdrive gear ratios so that the vehicle responds to the driver’s requirements within the limits of the various road conditions.

Figure 4.1: Mercedes-Benz Actros Manual Transmission

Automatic Transmission System

Figure 4.2: Automatic Transmission System

• An automatic transmission is a transmission that can change gear ratios automatically as the vehicle moves.

• For automatic transmission, the driver only needs to operate a gear-shift once (forward and reverse) and do not need to control a clutch.

Automatic Transmission System (Cont…)

Figure 4.2: Automatic Transmission System

•The fuel consumption of an automatic transmission embodying a torque converter is inherently higher than that of equivalent manually controlled transmission.

• This is attributable to factors such as friction losses in the multi-plate clutches and brakes used to change gear ratios, losses in their hydraulic control systems, converter losses, and friction losses in the gears and preloaded rolling element bearings.

Gear Train

• Simple Gear Train– If two or more gearwheels meshed in series,

either in the same plane or in different plane, the gear wheels are said to form a gear train

Figure 4.3: (a) Simple Gear Train (b) Single Stage Gear Train

(a)

(b)

Gear Train (Cont…)

• The gear ratio of a gear train may be defined as the input speed, or it may be derived by using the formula

Example 1 (2 gears)

In a given gearbox, the primary-shaft second gearwheel has 18 teeth and the secondary output-shaft gearwheel has 36 teeth.

Calculate the gear ratio.

Solution (Example 1)

Gear Train (Cont…)

• If two or more pairs of gearwheels are joined in series and the driven gearwheel of one gear train is connected by a common shaft to the driver of the next gear train, these gears are said to form a compound gear train.

Example 2 (2 or more pairs of gears)

In a gearbox, the first-stage constant-mesh gearwheels have 16 teeth on the primary shaft and 30 teeth on the layshaft. The third-gear output main-shaft wheel has 18 teeth, and the meshing lay-shaft wheel has 27 teeth.

Calculate the third-gear ratio:

Solution (Example 2)

Continuously Variable Transmission (CVT)

Figure 5.4: Continuously Variable Transmission

CVT• Continously Variable Transmission (CVT) is based simply on the principle

of the belt running between two V-shaped pulleys. • The CVT is a flexibility transmission that allows the driving shaft to

maintain a constant angular velocity over a range of ouput velocities.

• The advantages of CVT are as follow:– Provide engine torque in optimum condition (roads/drive shaft

torque).– No shift clonk.– Transmission ratio can be adjusted continuously.– Improved fuel efficiency.– Better acceleration.– Eliminates gear hunting especially when going up a hill.

VEHICLE ENGINE AND TRANSMISSION CHARACTERISTIC

• An automobile can be divided into 4 major systems or basic components:-– The engine (which serves as a source of power).– The power train, or drive train, (which transmits

the engine’s power to the car’s wheel).– The chassis (which support the vehicle body)– The car’s body

• This chapter only covers on the vehicle engine and transmission system.

Engine Characteristics

• Although the engine is a major system, its should be considered a component of the drive train.

• An engine develops a rotary motion or torque that, when multiplied by transmission gears, it will move the car under a variety conditions.

• The engine produces power by burning a mixture of fuel and air in its combustion chamber.

Engine Characteristics (Cont..)

• Combustion causes a high pressure in the cylinders, which forces the pistons downward.

• Connecting rods transfer the downward movement of the pistons to the crankshaft, which rotates by the force on the pistons.

Transmission Characteristics

• The transmission is mounted to the rear of the engine.

• It is design to allow the car to move forward and in reverse.

• It also has a neutral position. In this position, the engine can run without applying power to the drive wheels.

Transmission Characteristics (Cont..)

• There is an input to the transmission when the vehicle is in neutral, there is no output from transmission because the driving gears are not engaged to the output shaft.

How Manual Transmission Works?

How Manual Transmission Works?

• The transmission is connected to the engine through the clutch.

• The input shaft of the transmission therefore turns at the same rpm as the engine.

• A five-speed transmission applies one of five different gear ratios to the input shaft to produce a different rpm value at the output shaft.

Typical 5-speed transmission ratio

How Manual Transmission Works? (Cont..)• The green shaft comes from the engine through the clutch which are connected as a single unit.

• (The clutch is a to connect and disconnect the engine and the transmission).

•When you push in the clutch pedal, the engine and the transmission are disconnected so the engine can run even if the car is standing still. When you release the clutch pedal, the engine and the green shaft are directly connected to one another. The green shaft and gear turn at the same rpm as the engine.)

Neutral Condition

How Manual Transmission Works? (Cont..)• The green shaft and the red shaft are directly connected through their meshed gears so that if the green shaft is spinning, so is the red shaft. In this way, the layshaft receives its power directly from the engine whenever the clutch is engaged.

•The yellow shaft is a splined shaft that connects directly to the drive shaft through the differential to the drive wheels of the car. If the wheels are spinning, the yellow shaft is spinning.

Neutral Condition

How Manual Transmission Works? (Cont..)• The blue gears ride on bearings, so they spin on the yellow shaft. If the engine is off but the car is coasting, the yellow shaft can turn inside the blue gears while the blue gears and the layshaft are motionless.

•The collar is connected, through the splines, directly to the yellow shaft and spins with the yellow shaft.

Neutral Condition

How Manual Transmission Works? (Cont..)When shifted into the first gear,• The green shaft from the engine turns the layshaft, which turns the blue gear on the right.

• This gear transmits its energy through the collar to drive the yellow drive shaft.

• Meanwhile, the blue gear on the left is turning, but it is freewheeling on its bearing so it has no effect on the yellow shaft.

First Gear Condition

How Automatic Transmission Works?

How Automatic Transmission Works? (Cont..)

• There are two big differences between an automatic transmission and manual transmission:– There is no clutch pedal in an automatic

transmission car. – There is no gear shift in an automatic transmission

car.


• The key difference between a manual and an automatic transmission is that the manual transmission locks and unlocks different sets of gears to the output shaft to achieve the various gear ratios, while in an automatic transmission, the same set of gears produces all of the different gear ratios. The planetary gear set is the device that makes this possible in an automatic transmission.


• Any planetary gear set has three main components:

– The sun gear – The planet gears and the planet gears'

carrier – The ring gear

• Each of these three components can be the input, the output or can be held stationary. Choosing which piece plays which role determines the gear ratio for the gearset. Let's take a look at a single planetary gearset.

Planetary Gear Set


• An example of the planetary gear sets has a ring gear with 72 teeth and a sun gear with 30 teeth. We can get lots of different gear ratios out of this gear set.

• Use a formula above and insert the number of teeth of ring and sun gear to find the gear ratio.Sun Gear

Carrier Gear

Ring Gear

Example 1

Ring Gear: 72 teeth, Sun Gear: 30 teethFind the gear ratio if the output speed is slower than the

input speed (reduction)Solution:

Gear ratio= 1 + R/S = 1 + (72/30) = 1 + 2.4 = 3.4

So, the gear ratio is 3.4:1

Example 2

Ring Gear: 72 teeth, Sun Gear: 30 teethFind the gear ratio if the output speed is faster than the

input speedSolution:

Gear ratio= 1 / (1 + S/R) = 1 / (1 + 30/72) = 1 / 1.42 = 0.71

So, the gear ratio is 0.71:1

Chapter 4- Vehicle Transmission System

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