1 . Principle

1.1 Newton 's internal friction law

Newton 's internal friction law can be expressed as follows (see figure 1):

If there is viscous fluid （ e.g. lubricating oil ） full of the space between two parallel boards, and the thickness of the oil film is δ ,then, when the lower board keeps fixed and the upper board moves parallel to the lower one with velocity υ ,the fluid between the boards will be subjected to a shear force.

Fig.1 Newton 's internal friction law

The shearing force of oil film F is in direct proportion to the board area A and the velocity gradient υ / δ (or shearing rate):

There are a set of friction discs in the HVD, in which every pair of driving and driven discs correspond to the two parallel boards in Newton 's internal friction law. Therefore the output speed is in reverse proportion to the gap δ .

1.2 Structure

See figure 2.

There are external teeth on the left part of driving shaft, meshing with the internal teeth on driving friction discs. Thus the driving shaft and the driving friction discs can be connected and rotate synchronously. By the shearing effect of the oil film, the driven friction discs were driven by the driving ones. The driven friction discs with external teeth engage with the driven hub with internal teeth, and rotate with the driven hub (connected to driven shaft by driven plate) synchronously.

Fig.2 Structure and Principle of HVD

1  Driving shaft         2  Low box        3 Up box        4 Supporting plate        5 Driven hub        6 Driven friction discs 
7 Driving friction discs        8 Driven plate        9 Spring        10 Piston        11 Piston rings        12 Driven shaft 
13 Through cover        14 Screw stopper

When the pressure of controlling oil increases, the piston moves left against the spring force, making the gaps thinner between the friction discs, and consequently making the output speed higher. When the pressure of controlling oil becomes smaller, the piston moves left due to the spring force, which makes the gaps thicker and the output speed lower.

The function of lubricating oil system is to pump sufficient oil into the gaps between the discs, so that working oil film can be formed. Simultaneously, the heat due to the different the rotation speed is taken to the cooler and dispersed.

2. Technical Specifications

Type ： YL － 4 （ 4000 N · m ）、 YL － 8 （ 8000 N · m ）、 YL － 10 （ 10000 N · m ）、 YL － 12 （ 12000 N · m ）、 YL － 16 （ 16000 N · m ）

• Rating Speed: 750 ～ 3000r/min
• Rated Power:1000 ～ 4000kW
• Speed Range:30% ～ 100 ％
• Speed Accuracy ：± 0.1 ％

3 . Features

• Stepless speed regulating smoothly
• Remarkable energy-conservation effect
• Soft start
• No harmonic pollution to power network . Not reducing the power factor of network
• High reliability and maintainability

4 . Application fields

HVD is widely used in mining, metallurgy, petroleum, chemistry and water supply fields, etc., for large power fans, pumps and compressors to save energy, for loaded machines with large inertia to start smoothly, and for transmitting system to be protected when over-loaded.