The speed variator is a kind of power transmission equipment that is used for speed control and torque management. The continuously variable transmission that is performed by the speed variators controls the output speed and torque of an engine. As the output speed of an engine increases, the gear ratio of the engine decreases and the torque decreases in accordance. On the other hand, when the gear ratio and the torque increase, the output speed of the machine decreases. By managing the speed and the gear ratio, the speed variator maintains the optimal efficiency of the engine while controlling the output speed of the machine at the same time.
By maintaining the efficiency of an engine, the fuel consumption can be controlled. Less fuel is needed to keep the machine running. In addition, the speed variator allows the engine to produce the maximum power over a wide range of speeds. The use of speed variator can be seen in many industrial settings such as vehicles, conveyor belts, food processors and many other machines. In general, the speed variators are used as a general speed changer. Based on the mechanisms that a speed variator applies, the variators can be categorized into two types: the mechanical variators and the hydraulic variators.
There is a wide selection of speed variators on the market. Regardless of the brands or types the machines are, they usually come with a full metal construction. The ideal material to build a speed variator is stainless steel or cast iron. Based on the type of variator, the material may vary but the steel-based material is preferred in most cases. The reason is that, when a variator is operating, the machine needs to deal with extreme conditions such as high pressure and high temperature. The material needs to withstand the extremes without causing metal fatigue or failure. As a result, the all metal construction is necessary when building a speed variator.
Typically speaking, the hydraulic speed variator applies the principle of hydrostatic transmission to control the speed of the machine. A hydraulic speed variator is basically comprised of a primary pump and a secondary pump. The primary pump is a hydraulic radial piston variable displacement pump and the secondary pump is a constant displacement pump. Both the primary pump and the secondary pump are contained in one case and mounted on a fixed shaft.
The constant displacement pump serves as a distributor of the fluid. Between the two pumps, there are pressure line and return line for the fluid to flow back and forth between the two pumps. The flow of the fluid in between the pumps hence creates a closed hydraulic circuit. There is an additional pump that connects to the primary pump. It serves as the fluid (oil) supply to the hydraulic circuit. The input shaft rotates the cylinder block of the radial piston pump; the pistons stroke in and out of their cylinders pumping hydraulic oil through the distributor shaft to the radial piston hydraulic motor.
The oil will then return directly to the pump. There is a set of eccentric rings that limits the stroke of the pistons in the pump and the motor. The position of the eccentric ring in the pump is controlled by a regulation pin. Therefore, this varies the flow rate from the pump to the motor. Since the eccentric ring in the motor is fixed, the speed of the hydraulic motor is directly proportional to the flow received from the pump. The pump eccentric ring can be moved to either side of the center position by the flow. When a torque load is applied to the output shaft, a pressure which is proportional to the torque is produced in the closed circuit. With the hydraulic circuit that controls the output shaft, the output speed can be regulated.
The mechanical speed variator applies the mechanical variable speed transmission system which is based on the transfer of power by friction between a moving part, drive and driven shafts. The moving component is moved by the control speed. The variation of speed is achieved mechanically by the gears inside the machine. The working principle of a mechanical speed variator is simpler than that of the hydraulic variators. The output speed and torque are changed by means of changing the gear ratios.
The gear ratio refers to the number of teeth on a gear. The calculation of gear ratio is simple too. It comes this way: if a driven gear has thirty six teeth and the driving gear has twelve teeth, the gear ratio here is three to one, as in 3: 1. The driven gear is also called the output gear and the driving gear input gear. As the teeth of the driven gear increases, the output torque of the machine becomes stronger. On the other hand, when the driven gear has fewer teeth, the output speed becomes higher but the output torque reduces.
Comparing to the hydraulic variators, the mechanical variators are easier to maintain due to the interior structure of the machine. The gears inside a mechanical variator are lubricated with engine oil. Therefore, the gears inside the machine can run more smoothly. Since the friction and impact between the gears are reduced, the moving components are less likely to wear out. To maintain the variator, it typically takes only the periodic replacement of the engine oil and the machine can last as long as possible.
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