Glossary
Automotive
The term Automotive relates to the application of Torotrak’s technology in cars, light commercial vehicles, light utility vehicles and engine auxiliary devices.
CVT
A variable ratio drive connects a drive mechanism (engine or motor) to a load (road wheels or generator etc). In its simplest form it will operate between two ratio limits without a speed reversal between and is known as a continuously variable transmission (CVT). If however the ratio limits are of opposite sign (clockwise to anticlockwise) it is known as an infinitely variable transmission (IVT) since at a particular point the drive must produce an infinite reduction.
Commercial vehicles
The term Commercial vehicles relates to the application of Torotrak’s technology in trucks, buses, truck-and bus-derived vehicles, heavy military vehicles and heavy commercial off-road or on-road vehicles.
Contact patch
The contact patch refers to the area where the roller contacts the disc.
EHL, EHD
Highly loaded mechanisms such as rolling element bearings (ball bearings for example) suffer elastic deformation at the point of contact as the elements roll one on the other. When lubricated, oil is entrained at the contact point, separating the surfaces by a thin oil film. The phenomenon is known as either elasto-hydrodynamic-lubrication (EHL) or alternatively elasto-hydro-dynamic lubrication (EHD).
Epicyclic gear train
In its simplest form an epicyclic gear train is an assembly of gears that provide three coaxially rotating elements (known as the sun gear, planet gears and annulus – or ring gear) such that the speed of one element is a function of the speeds of the other two elements and the torque distribution across the system is dependent upon the load applied to any single element.
Geared neutral
A variable ratio transmission may be capable of infinite reduction meaning it can mechanically connect a running engine to stationary road wheels without a slipping mechanism such as a clutch or torque convertor. This condition is termed Geared neutral.
IP
Active development of an engineering concept such as variable ratio traction drives yields inventions, protected by patents and design or operational understanding termed know-how. Collectively these are known as intellectual property (IP), the ownership of which leads to intellectual property rights (IPR).
IVT
A variable ratio drive connects a drive mechanism (engine or motor) to a load (road wheels or generator etc). In its simplest form it will operate between two ratio limits without a speed reversal between and is known as a continuously variable transmission (CVT). If however the ratio limits are of opposite sign (clockwise to anticlockwise) it is known as an infinitely variable transmission (IVT) since at a particular point the drive must produce an infinite reduction.
KERS
A kinetic energy recovery system (KERS) recovers kinetic energy otherwise wasted during the braking of a vehicle, stores it in an energy storage device such as a flywheel or battery, and then re-uses such energy at a time when the vehicle requires it eg during launch or acceleration.
KERS CVT
A KERS CVT is a variable drive unit engineered specifically to connect a high-speed flywheel (which acts as an energy storage device) to a vehicle’s driveline. This provides a highly efficient, power-dense, cost-effective and environmentally friendly mechanical hybrid solution, ideal for applications with regular stop-start operation.
Off-highway
The application of Torotrak’s technology in tractors, agricultural and construction vehicles and also materials handling vehicles (eg forklift trucks) is termed the Off-highway market.
OPE
Outdoor power equipment (otherwise known as OPE) is the application of Torotrak’s technology in lawn tractors and mowers, small utility vehicles and outdoor powered tools and equipment.
Power splitting
The variable ratio traction drive may be integrated with an epicyclic gear system such that power is transmitted by the variator and via a simple gear train i.e. the power is split. The power transmitted by the variator is thereby reduced allowing a smaller unit and improved overall transmission efficiency.
Ratio
The relationship between the variator input (driven) speed and output (load) speed is expressed as the variator speed ratio. It is conventionally defined as input speed / output speed but at geared neutral, output speed is zero and the ratio becomes infinite. For this reason it may be usefully expressed as output speed / input speed.
Ratio spread
An important transmission performance parameter is its ratio spread. It is defined as maximum ratio / minimum ratio and is typically between 5.0 and 6.0 for a car. The traction variator is capable of 6.5 to 7.0.
Regime
The load transmitted by the variable ratio element of a transmission can be reduced by splitting the total ratio spread of the transmission into a series of regimes engaged sequentially as the transmission progresses from lowest to highest ratio. Each regime change occurs synchronously at one or other of the ratio extremes produced by the variator. So, for example the maximum transmission ratio produced in regime 1 will be identical to the minimum transmission ratio produced in regime 2. Consequently the transmission can operate in both regimes 1 and 2 allowing imperceptible shifts with no transmitted power interruption.
Shunt
Associating the traction drive with a simple gear ratio will change the overall speed and torque ratios produced but not the ratio spread, defined as minimum ratio / maximum ratio.
Replacing the simple gear ratio with an epicyclic gear system, forming a shunt changes both the overall ratio and the ratio spread. It is used to match the variator to a particular application including the introduction of an infinite overall reduction ratio.
Synchronous ratio
A multi-regime variable ratio transmission shifts from one regime to the next at synchronous ratio. This occurs at one variator ratio, usually close to its maximum or minimum ratio and is typified by the transmission producing the same overall ratio in either regime at that variator condition. This enables a shift without power interruption since the next regime clutch is engaged before releasing out of the current regime.
Toroid
The space produced between the traction drive discs is defined as toroidal. It results in a constant variator length for any roller operating angle.
Torque
Mechanical torque is the turning force (momentum) applied, for example by an engine, to driven a load.
Tribology
In general, the science of oil based lubrication applied to moving mechanisms is termed Tribology.
TVAD
Toroidal variable auxiliary drives (TVADs) provide a variable drive between the engine of a vehicle and engine auxiliary devices such as a supercharger or air conditioning system. Such a variable drive provides a rapid, stepless change in drive ratio, ensuring optimum operation of the auxiliary device, regardless of engine rpm.
Variator
A variator is a device capable of transmitting drive at a ratio externally defined and capable of continuous variation between two limits.