Outer Wheel Drive
- Smooth start-up of machines (e. g. conveyors)
- Avoids over exertion of engines during the acceleration of large masses
- Reduced power consumption with eased and shortened engine start-up
- Protection of machines (input and output) in case of overload or blockades
- Maintenance-free torque transmission since there is no mechanical transmission
- Vibration-reducing features due to oil as operating medium
- Easy torque regulation via oil filling level
The drive of the fluid coupling is provided via the rotation of the outer shell. The output is achieved via the induced rotation of the hollow shaft (solid shaft) with integrated paddle wheel.
Outer wheel drive (RM/MS) Advantages
- Good heat dissipation, mainly during the start-up phase, recommendable for frequent or long starting processes
- Easier oil setting, the outer shell can be turned without moving the drive or driven machine
- Type “MS“: Weight load of the fluid coupling is exerted on the engine shaft, not on the gear shaft
- Type “MS“: In combination with a fan on the output side, the distance between fluid coupling and fan is quite big, i.e. the heat dissipation of the fluid coupling has only a small impact on the fan
Outer wheel drive (RM/MS) General setup
The fluid coupling consists of a limited amount of main components. The two-part outer aluminium shell with integrated paddle wheel is the drive. On the driven side, the output is achieved via the inside paddle wheel in combination with the hollow shaft. One radial and one needle bearing ensure the bearing assembly while shaft seals ensure the seal against external influences. Standard design is the fluid coupling with a fusible safety plug (145°C – red) as well as an oil filler plug.
Outer wheel drive – Function
The function of the fluid coupling is based on the Föttinger principle.
Regarding the outer wheel drive, the outer shell works as a pump and the inside paddle wheel with the hollow shaft works as a turbine. The power provided by the engine generates a rotational flow of fluid via the outer shell with paddle wheel. This flow energy, in turn, gradually causes the inside paddle wheel to turn, thus transferring the mechanical energy to the driven side. Between input and output there occurs a slippage of 2-6%.
Outer wheel drive (RM/MS) Start-up factors
The fluid coupling type K can be extended by a small (SCF) or a large (DCF) delay chamber. Type K-CA has a large delay chamber and an additional chamber at the outside diameter. The start-up torque is reduced and the start-up time is extended, so that a smooth start-up is guaranteed. The following start-up factors can be implemented with the different delay chambers:
- ALFA K (without delay chamber): start-up factor 1.8-2.0
- ALFA K-SCF (with a small delay chamber): start-up factor 1.5-1.8
- ALFA K-DCF (with a large delay chamber): start-up factor 1.2-2.5
- ALFA K-CA (with a large delay chamber and additional chamber): start-up factor 1.0-1.2
Outer wheel drive (RM/MS) Accessories
To monitor temperature and speed several accessories are provided to complete the fusible safety plug.
Fusible safety plug (FP)
In case of overheating, the fusible link of the fusible safety plug melts allowing the oil to discharge and the torque transmission disabled.
The standard fluid coupling contains a fusible safety plug with a melting point of 145°C (red). Fusible safety plugs with the following temperatures are available: 96°C (blue); 120°C (white); 145°C (red); 180°C (green)
Fusible safety plug with pin (FTP)
To avoid oil leakage the use of a second fusible safety plug with pin is recommended, in addition to the standard fusible safety plug. This plug needs to be one temperature class lower than the standard screw. When reaching the trigger temperature of the fusible link of the pin, the plug is pushed out by a spring to actuate a mechanical switch which turns off the motor or triggers a signal. Fusible safety plugs with included pins are available with the following temperatures: 96°C (blue); 120°C (white); 145°C (red).
Contactless pulse generator (PM)
To avoid oil leakage, the use of a second temperature sensor is recommended, in addition to the standard fusible safety plug. The pulse generator needs to be one temperature class lower than the standard screw. When reaching the trigger temperature of the pulse generator it transmits the signal to the opposite sensor without any contact. This opposite sensor switches the motor off or triggers a signal. Pulse generators with the following temperatures are available: 100°C (blue); 120°C (white); 140°C (red); 160°C (yellow).
Mechanical temperature control (ET+FTP)
If the pin triggers the FTP because the temperature is exceeded, this actuates the mechanical switch installed. The motor is switched off or a signal is triggered.
Electronic speed control (SCD)
The electronic speed control can be installed as an additional coupling protection (for inner wheel drives). It compares the actual speed with the target speed. If the proportion is too high the motor switches off or a signal is triggered.
Contactless temperature and speed control (T09+PM)
If the temperature of the PM is achieved, it transmits a signal to the sensor, the motor switches off or a signal is triggered. In addition to the temperature control, a speed control is possible as well (only for inner wheel drives). The actual speed and the target speed are compared. If the difference is too big the motor switches off or a signal is triggered.