Transmission Advances Create Easier-to-Drive Vehicles

June 1, 2005
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Transmission Advances Create Easier-to-Drive Vehicles
David Kolman  
With the increasing difficulty in recruiting and retaining drivers, a truck’s “driveability” has become more of a priority. Trucks that are easy to operate and have enhanced driver comfort and convenience features are selling points to potential drivers.
To this end, many advances have been made to automatic and automated truck transmissions. Basically, automated transmissions are a compromise between a manual and an automatic. Compared to manual transmissions, automatic and automated transmissions offer a number of advantages.
For one thing, they are simpler to operate. The driver can more easily use both hands for steering and can better focus his attention on traffic and the road rather than having to switch gears according to his changing speed. Furthermore, automatic shifting helps make the driver’s working environment less fatiguing. All of this improves overall safety, which can reduce insurance costs.
Automatic and automated transmissions can help with recruiting drivers because not as much experience in driving a truck is required. Since the new generation of drivers is not familiar with manual shift transmissions, automatics and automateds widen the pool of potential drivers.
Driver training costs are lowered because the amount of training necessary to get a driver from “street-to-seat” with automatic and automated transmissions is significantly reduced. Learning to shift a non-synchronized manual truck transmission is challenging and usually requires a large investment in both time and money.
Another advantage over manuals is that shift quality is better and consistent, which helps increase component life as well as efficiency and performance. Automatics and automateds are less complex products than manuals and so are less expensive to maintain. Plus, drivetrain protection features reduce the potential for drivetrain abuse.
A lot more choices in automatic and automated transmissions are available nowadays. Advances in electronics, controls and technology have allowed engineers to create various systems for automating gear controls that perform properly under more of the conditions medium and heavy trucks encounter.
Simply put, the primary function of a transmission — whether manual, automatic or automated — is to transfer the rotational energy of the engine to the vehicle’s rear wheels, enabling it to move. The transmission allows the engine to operate in its best narrow range of speeds while providing a wide range of output speeds through various gear combinations.
A clutch’s main purpose is to allow engine power to be applied gradually when a vehicle is starting out, and interrupts power to avoid gear grinding when shifting. Engaging the clutch allows power to smoothly transfer from the engine and transmission to the drive wheels. Disengaging the clutch stops the power transfer and allows the engine to continue turning without sending force to the drive wheels.
Automatic transmissions use a torque converter instead of a clutch. The torque converter multiplies the engine’s torque so the first gear offers similar ratio coverage as the first couple gears of a manual transmission. There is no power interruption between or during shifts, which can provide smoother acceleration and ride, along with reduced shock loading of the drivetrain compared to a manual. Electronic controls continuously monitor operating conditions to keep the vehicle operating at peak performance.
Automated transmissions are basically a manual transmission that is partially or fully electronically controlled and pneumatically or hydraulically actuated. Electronic controls on the engine and transmission work together to select and change gears. There is some power interruption between and during shifts.
Some automated transmissions are three-pedal versions which require the use of the clutch pedal when starting and stopping. Two-pedal versions have no clutch pedal.
Two-pedal automated transmissions work like automatic transmissions. When starting from a stop, the driver presses the accelerator and the clutch automatically engages; when stopping, the driver disengages the clutch.
Automated transmissions usually offer the driver some level of shift control for certain types of driving and road situations.
Manual transmissions — which require a driver-operated clutch and a movable gear selector — come in models with a variety of speeds, up to 18. More transmission speeds means closer gear ratio splits and greater overall ratio. Closer gear ratios usually translates into a better driving transmission and a greater overall ratio gives the transmission better starting power.
Another consideration with manual transmissions is direct drive versus overdrive. In low gear, a direct-drive transmission gives a higher ratio starting gear for easier starts but provides 1-to-1 (input-to-ouput) ratio in top gear. An overdrive transmission provides less startability in low gear but gives more efficient operation in top gear.
A good rule of thumb: If the truck is operating in stop-and-go start applications, direct-drive manuals are the way to go. If the truck will be traveling at highway speeds for extended periods of time, overdrive transmissions are better suited.
Keep in mind all transmissions are rated to a maximum input torque. So the torque of the engine rating will dictate the transmissions that are compatible. The higher the input torque, the larger the transmission needs to be. Another consideration is that some transmissions have gross vehicle weight rating limits. BI

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