Ventilation – Vehicle – Pressure regulation
Patent
1996-08-08
1997-07-15
Joyce, Harold
Ventilation
Vehicle
Pressure regulation
454103, 454105, B61D 2700
Patent
active
056477937
DESCRIPTION:
BRIEF SUMMARY
The invention relates to apparatus and to a method for preventing sudden changes of pressure in vehicles, in particular in land vehicles.
The apparatus and the method of the invention for preventing sudden changes of pressure in vehicles is particularly applicable to high speed trains.
A vehicle moving through the atmosphere is subjected to pressure forces distributed over the outside wall of the vehicle in a manner that depends on the shape thereof and on its forward speed. When the vehicle passes close to an obstacle (tunnel mouth, bridge, various objects in the vicinity of a travel path, . . . ) or when going past an oncoming vehicle, the field of aerodynamic speeds entrained with the vehicle is deformed. This gives rise to rapid changes in pressure on the outside walls of the vehicle. This effect becomes more pronounced with increasing vehicle speed, since pressures are approximately proportional to the square of the speed.
In a vehicle where inside air is renewed from outside air by air conditioning or ventilation, inside pressure is close to outside pressure. Variations in outside pressure are transmitted almost instantaneously to the inside of the vehicle given the section sizes of the ventilation circuits. The time constant for transmitting pressure changes to the inside of air conditioned or ventilated vehicles is thus small, specifically because of the characteristics of the ventilation circuits. This rapid phenomenon does not occur when the inside of the vehicle is pressurized (e.g. airplanes).
For example, when high speed trains penetrate into tunnels or cuttings, rapid changes in pressure occur on the outside walls of the cars. These sudden changes propagate in the confined space constituted by the tunnel or the cutting and they are known as "pressure waves". In addition, these pressure waves propagate along the confined space outside the vehicle and reflect off the ends of the continued space, thus giving rise to return pressure waves that are just as large as the go waves. When the cars are well sealed, these changes are rapidly transmitted to the insides of the cars by the ventilation and air conditioning circuits, causing considerable discomfort to passengers. It is thus common to be subjected to pressure changes that may be as much as 2000 Pascals in less than one second.
To remedy this problem of pressure waves, certain high speed trains use "steep front" fans in the ventilation circuit. Those fans constitute, to some extent, an obstacle to pressure waves, but they have the drawback of being expensive and noisy. They constitute extra equipment of non-negligible weight and bulk even though great efforts are made to lighten cars as much as possible. They also consume large amounts of power. In addition, it is necessary to have two per car.
To mitigate those drawbacks, the present invention proposes constraining the inside pressure of an air conditioned or ventilated vehicle to vary at a rate that is fixed a priori whenever a sudden change in pressure occurs. To do this, appropriate apparatus operates in real time to create rapid changes to the geometrical characteristics of the ventilation or air conditioning circuits. These changes are such that the resulting change in the flow rate of air penetrating into the vehicle gives rise to a change in the pressure inside the vehicle that complies with the fixed rate. As soon as equilibrium is reestablished between inside and outside pressure, the ventilation circuit is put back into its configuration to enable normal fresh air renewal to proceed as before. Such a device placed on the ventilation circuits is equivalent to transforming a circuit designed for air renewal by ventilation or air conditioning very rapidly into a circuit that controls the inside pressure of the vehicle (and vice versa), whatever the sudden change in outside pressure (speed of the train, nature of the obstacle, outside topology, . . . ).
The invention thus provides apparatus for preventing sudden changes of pressure in an air conditioned or ventilated vehicle, the vehicle
REFERENCES:
patent: 5391111 (1995-02-01), Girard et al.
patent: 5439415 (1995-08-01), Hirikawa et al.
patent: 5462481 (1995-10-01), Riedel et al.
Gervais Yves
Mariaux Gilles
GEC Alsthom Transport SA
Joyce Harold
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