Report on Transmission Gear Ratios

Added on - 21 Apr 2020

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Project 2 Report on Transmission gear ratios via Vehicle DynamicPrepared by: Group XDated:EXECUTIVE SUMMARYThe report hereinafter entails a comprehensive work done in the area of vehicledynamics; specifically the power and transmission system of the vehicle. It seeks touncover different aspects such as the design, construction and operating conditions of arange of transmissions. A case study is selected from which critical technicalinformation is derived as provided in this report.CHAPTER 1: INTRODUCTIONThe transmission system is a critical component of the vehicle as it guaranteesmovement of vehicle from one point to another. Because of the prohibitive speed andtorque that results from the engine, these two parameters are normally passed through aspecial box within the mechanically connected powering system of the vehicle. Thisspecial box is known as the gearbox. It houses a set of gears that engage with each otherto transmit the required torque, power and speed to the wheel drive via the clutch. Now,there are basically two modes of transmission which are being used today; namely:Manual and automatic transmissions. The former will be the focus of discussion in thisreport. Notably, a 5-speed manual transmission is chosen; specifically we did select the1990 made Porsche car (928 S4) of engine type: M28.42. In this report, therefore, agreater effort is made in comparing and contrasting the design, construction features andthe operating principles of the transmission. More specifically, we paid a special interestin discovering the relationship between gear ratios, maximum engine power and outputtorque of the selected vehicle model. This is done using an analytical approach wherevarious vehicle dynamics are considered.Page |1Update November 2017
CHAPTER 2: ANALYSIS AND DISCUSSION2.1 The Case StudyThis section presents the selected case study which entails, as mentioned earlier, a 1990 madePorsche 928 S4 with an engine of type: M 28.42. This car is still considered a sly automobilethat can roar miles while conserving its fuel consumption. It comes built with a staggering V-8 engine design. Due to its affordable price and fuel economy, the car dominated the scenefor a very long time. Notably, the car has a 5-speed manual transmission and the critical inputparameters as provided by the Porsche Technical Specifications (1992) are given in the table1:Table 1: Input Parameters of the Porsche 1990; 928 S 4Input parametersActual ValuesEngine Max Power235kWMax. Engine Torque450Nm at max. 3000 rpmTop Vehicle Speed275 km/hrHeight1282mmTrack1551mmBody Drag Coefficient0.457Wheel/Tires details-Wheel base2500mmRolling resistance coefficient values at extremedriving conditions?0.34Curb & Gross Weights1580kg; 1920kgFinal Drive Ratio2.7272Page |2Update November 2017
Engine Layout & estimated Drive train EfficiencyV-8 design with 80 % DTEIn our calculations, the following assumptions were made:Take-off Engine Torque at 80% of Max Engine TorqueTake-off Engine Torque available at 2000 rpm engine speedTransfer Box Hi Ratio: 1:1Max Gradient Climbable for Hi Range in 1stSpeed gear: 30 %Max Gradient Climbable for Lo Range in 1stSpeed gear: 70 %And the Gearbox Speed Steps as percentages of the total gearbox gearingrange:1-2 step : 48%2-3 step : 30%3-4 step : 15%4-5 step : 7%2.2 The Vehicle Driving Conditions and ApplicationsThe drive train mechanism is composed of the clutch, gearbox transmission, drive shaftand differential. Its functionality, according to Global Fundamentals (2001) is tofacilitate required torque transfers to the wheel drive, either 4 wheel or front/rear wheeldrives. The clutch is normally placed between the transmission and the engine; if thedriver wants to shift gears, she would disengage the clutch and pressure on the plate isreleased while allowing the engine to run and at the same time the gear selector isactuated to make the shift possible. Then, the driver engages the clutch to apply pressureon the plate and once again a mechanical connection is created between the engine andthe transmission. The gearbox transmission houses a set of gears that must be engaged atdifferent times to ensure required power and torque are transmitted. The gear ratioselection for manual transmission is normally done via a hand lever while the clutch isbeing disengaged to allow engine run without stopping during ride condition and alsominimize wear as this is normally accompanied by greater frictional forces as the changeoccurs (Global Fundamentals, 2001). But, how are the forward and reverse drivesachieved in this case? Now, inside the gearbox, there is an idler gear such that to achievereverse drive, the idler gear meshes with gear1&2 synchronizer which is located at thedrive pinion while the drive gear is mated with the main shaft hence facilitating reversemovement (Viosin, 2008). Figure 1 illustrates the gearbox transmission where it can benoted that the gear selector is actuated by a system of lever.Page |3Update November 2017
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