Manual Transmission Fundamentals Chapter 71 2012 Delmar Cengage

Manual Transmission Fundamentals Chapter 71 © 2012 Delmar, Cengage Learning

Objectives • Describe the relationship between gears and torque • Understand the basic types of gears • Calculate gear ratios • Trace the power flow through three-, four-, and five-speed transmissions • Name all of the transmission parts © 2012 Delmar, Cengage Learning

Introduction • Manual transmission • Used with clutch – Shifted between gears manually • Transmission – Used in rear-wheel-drive cars • Transaxle – Used in front-wheel-drive cars © 2012 Delmar, Cengage Learning

Purpose of a Transmission • Provide a means of changing torque to fit engine operating requirements • Low gear – Crankshaft turns three times to one turn of transmission output shaft – Small gear drives a larger gear • Gears provide leverage © 2012 Delmar, Cengage Learning

Using Gears to Increase Torque and Gear Ratio • Driving gear smaller than driven gear – Output speed decreases – Output torque increases • Gear radius – Distance from center of a gear to its outside edge • Gear ratio – Number of teeth on driven gear divided by number of teeth on driving gear © 2012 Delmar, Cengage Learning

Transmission Gear Ranges and Overdrive • Transmissions in cars and light trucks – Three-six forward gear ranges • Overdrive – Opposite of gear reduction • Output shaft turns faster than input shaft – Ratio a step beyond 1: 1 ratio of high gear • Planetary gears – Automatic transmission with lock-up torque converter © 2012 Delmar, Cengage Learning

Final Drive Ratio and Gear Types and Operation • Final drive ratio – Ratio between transmission output shaft and differential ring gear • Gear tooth shape – Allows teeth to roll into and out of mesh with minimum friction • Contact pattern: where teeth of two gears meet • Pitch diameter: diameter of meshed gear – Manual transmission uses two types of gear • Spur and helical gear © 2012 Delmar, Cengage Learning

Spur Gears • Simple gears with straight-cut teeth – One tooth carrying the load at time • No end thrust • Transmission will not attempt to pop out of gear • Backlash – Clearance between meshing gear teeth • Clicking sound results as one gear rolls out of contact and new one rolls in • As backlash noise gains speed, it turns into gear whine © 2012 Delmar, Cengage Learning

Helical Gears and Idler Gears • Helical gears replaced spur gears – Quieter – Continuous flow of power across gear teeth • Minimum backlash – Greater gear strength • More area of tooth contact – Cause end thrust under load • Idler gears – Used between two other gears • Changes output rotation direction © 2012 Delmar, Cengage Learning

Transmission Parts • Power flows from clutch disc to input shaft • Each forward gear has a synchronizer – Keeps two meshing gears from clashing – Shift linkage acts on shift forks within transmission to select gear range • Power flows from input shaft to countergear – Then to mainshaft or output shaft • Parts are housed in transmission case – Has drain and fill plugs for adding and draining oil © 2012 Delmar, Cengage Learning

Transmission Lubrication and Transmission Bearings • Transmission parts – Separated by oil at all times • Splash lubrication – Oil moved throughout case by rotating gears • Bearings support ends of almost all rotating parts – Allow parts to rotate with very little friction • Reverse idler shafts and gears – Supported by bushings © 2012 Delmar, Cengage Learning

Transmission Gears and Shafts • Countergear – Single part made of a series of gears that mesh with various gears on mainshaft • Mainshaft – Includes all transmission gears and synchronizers • Manual transmission – Forward gears in constant mesh • Reverse idler gear is only gear that moves into mesh with another gear © 2012 Delmar, Cengage Learning

Synchronizer Assembly • Helps two gears spinning at different speeds mesh without clashing • Blocking ring synchronizers – Shift collar fits around hub outside – Gears are in constant mesh – Rotate freely on bearing areas – Splines on outside of hub become meshed with gear teeth • Synchro assembly – Locks input shaft gear to output shaft gear © 2012 Delmar, Cengage Learning

© 2012 Delmar, Cengage Learning

Gear Shift Mechanisms and Shift Patterns • Major components: – Shift forks: fit into grooves cut in outside of synchro collar – Shift linkage: internal shift rail or external rod – Detent mechanism: holds transmission in gear – Spring tension: holds detent balls into detent notches in shift rail – Interlock mechanism: prevents selection of two gears at once – Shift patterns: various patterns for different transmissions © 2012 Delmar, Cengage Learning

Transmission Power Flow • Modern transmissions are constant mesh – Synchro collar: only thing that moves • All manual transmissions operate in a similar fashion – Whethere are three speeds or six speeds – Five-speed transmissions: most common today • Most have direct power in fourth gear • Fifth gear provides an overdrive © 2012 Delmar, Cengage Learning

Four-Speed Transmission Power Flow • Four-speed transmission without overdrive – Neutral: synchro sleeves centered and do no mesh with clutch teeth of any gear – High gear: power runs straight through the transmission from input to output shaft – Third gear: power enters through input shaft – Second gear: rear synchro sleeve engages engage the second-gear clutch teeth – First-gear: rear synchro sleeve is moved toward rear to engage first-gear clutch teeth – Reverse: synchro sleeves are in neutral position © 2012 Delmar, Cengage Learning

Five-Speed Transmission • Gear flow in five-speed – Same as in first four speeds • Extra gears in extension housing – Fifth gear: synchro sleeves in transmission case in neutral position • Power flow through end of countergear to gear at the end of countergear – Some have both reverse and fifth gear in extension housing or rear section of case © 2012 Delmar, Cengage Learning

Speedometer Drive • Some cars use electric speedometers – Receive signal from vehicle speed sensor (VSS) • Vehicles with VSS – If the tire diameter is changed: computer can often be programmed with new tire information • Speedometer will be accurate • Speed inputs to the computer will be meaningful © 2012 Delmar, Cengage Learning

Switches and Sensors • Computer technology – Provided several electronic features to transmissions • • VSS on late-model transmissions Shift blocking solenoids Reverse lockout Gear range selector switch – Sensors are not prone to wear like a switch that has electrical contacts © 2012 Delmar, Cengage Learning