Progressive shifting
Encyclopedia
Progressive shifting is a technique for changing gears commonly practiced by driver
s of semi-trailer truck
s. It is meant to reduce fuel
consumption — something very important for drivers who travel several hundred miles each day.
Progressive shifting is accomplished by changing gears upward as early as possible when accelerating. After each shift is completed, the engine
and transmission
should be operating at or near the lowest rpm
speeds recommended by the manufacturers of those parts.
When done properly, progressive shifting often results in quicker acceleration because diesel engine
s produce the most torque
in lower rpm ranges. Additionally, this technique reduces wear on the transmission because synchronizers only need to compensate for relatively small differences in rotational speed between different components in the gearbox.
As defined by KE =1/2 mv^2, acceleration is the process of gaining kinetic energy, so greater the power delivered, the quicker it gains kinetic energy.
The best average acceleration in a truck with a Caterpillar C15 engine is achieved by going all the way up to 1950RPM, then shifting to a gear that will put the engine at 1500RPM, so that the truck is receiving as close as possible to maximum power throughout the entire time it is accelerating.
Shifting at peak torque doesn't provide the maximum acceleration as even the engine maybe making the maximum torque
, with each up shift, the mechanical advantage of the transmission is reduced.
Driving
Driving is the controlled operation and movement of a land vehicle, such as a car, truck or bus.Although direct operation of a bicycle and a mounted animal are commonly referred to as riding, such operators are legally considered drivers and are required to obey the rules of the road...
s of semi-trailer truck
Semi-trailer truck
A semi-trailer truck, also known as a semi, tractor-trailer, or articulated truck or articulated lorry, is an articulated vehicle consisting of a towing engine , and a semi-trailer A semi-trailer truck, also known as a semi, tractor-trailer, or (in the United Kingdom and Ireland) articulated truck...
s. It is meant to reduce fuel
Fuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...
consumption — something very important for drivers who travel several hundred miles each day.
Progressive shifting is accomplished by changing gears upward as early as possible when accelerating. After each shift is completed, the engine
Engine
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...
and transmission
Transmission (mechanics)
A machine consists of a power source and a power transmission system, which provides controlled application of the power. Merriam-Webster defines transmission as: an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a...
should be operating at or near the lowest rpm
Revolutions per minute
Revolutions per minute is a measure of the frequency of a rotation. It annotates the number of full rotations completed in one minute around a fixed axis...
speeds recommended by the manufacturers of those parts.
When done properly, progressive shifting often results in quicker acceleration because diesel engine
Diesel engine
A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...
s produce the most torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
in lower rpm ranges. Additionally, this technique reduces wear on the transmission because synchronizers only need to compensate for relatively small differences in rotational speed between different components in the gearbox.
As defined by KE =1/2 mv^2, acceleration is the process of gaining kinetic energy, so greater the power delivered, the quicker it gains kinetic energy.
The best average acceleration in a truck with a Caterpillar C15 engine is achieved by going all the way up to 1950RPM, then shifting to a gear that will put the engine at 1500RPM, so that the truck is receiving as close as possible to maximum power throughout the entire time it is accelerating.
Shifting at peak torque doesn't provide the maximum acceleration as even the engine maybe making the maximum torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
, with each up shift, the mechanical advantage of the transmission is reduced.