Hydrodynamic brakes

Practically, aU data of friction measurements on wet tracks in the speed range of hydrodynamic lubrication exist as tire skid measurements. Figure 26.10 shows the results of a braking test on wet, finely structured concrete using a smooth tire and measuring the friction coefficient as function of... 

The propagation velocity of the TM does not exceed 85-87% of the theoretical detonation velocity DT. Calculation of DT is carried out under the assumption of a chemical reaction which runs after compression by the shock wave without any thermal or hydrodynamic losses. In the case of the TM, meanwhile, the very possibility of propagation of a fast flame with the velocity of the shock wave depends on a velocity redistribution as a result of braking of the layers adjacent to the wall. In constructing the equations for the motion as a whole, braking plays the role of a loss which reduces the velocity. In fact, the velocity will be even smaller than the value cited besides the losses in the hydrodynamic preparation zone (the zone of velocity redistribution between the shock wave front and the forward point of the flame front, zone I-II in Fig. 19) we must add the losses in the combustion zone (from the forward point of the flame front to the cross-section in which combustion has ended, zone II-III in Fig. 19). 

Hydrodynamic brakes are similar in construction to hydrodynamic couplings. The force or torque delivered by the machine to be braked is applied to the pump... 

FIG. B-12 Hydrodynamic brake schematic. (Source J.M. Voith GmbH.)... 

A hydrodynamic brake can either be controlled with the working fluid in closed circuit or in open circuit and, by adjusting the amount of fluid in the brake, it is possible to work at any point within the performance range of the brake concerned. 

With an open-drcuit hydrodynamic brake (Fig. B-14) the working fluid is fed to the brake from a tank by means of a pump. The required amount of fluid in the brake is maintained by a control element in the feed line. 

Hydrodynamic brakes are used wherever substantial masses have to be braked without the braking mechanism being subject to wear and where mechanical brakes would be overtaxed. Hydrodjmamic brakes are particularly well suited to applications involving continuous operation. Hydrodynamic brakes have been used over several decades as a means of measiuing power, particularly as absorption dynamometers (fluid friction brakes) in engine test stands. 

Specific hydrodynamic brake models (VHBI, VHBM construction and variants)... 

VHBI hydrodynamic brakes. These brakes are characterized by performance with small overall dimensions as a result of the inclined blading of the rotor and stator. The hydrodynamic brake is effective in only one direction of rotation. 

Non-self-supporting models. Where the hydrodynamic brake is fitted in a machine or drive element, use is made of the existing bearings. The rotor is fitted overhimg on the shaft and the braking torque is transmitted to the machine housing. 

Self-supporting models. Here the hydrodynamic brake is provided with its own bearings—roller bearings or, if requested, plain bearings. The hydrodynamic brake is either flange-mounted or separately mounted on the base plate as one of the elements in a drive assembly. See Fig. B-15. 

The control schematics shown in Figs. B-16 through B-21 are some of the many practical applications of controls for hydrodynamic brakes. 

FIG. B-18 Pump control with integral cooling. The supply to the hydrodynamic brake is effected by a pump by way of a pneumatically controlled pressure-regulating valve. The heated working fluid is cooled in a heat exchanger in the return line. (Source J.M. Voith GmbH.)... 

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