US 3267987 A
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7 Aug. 23, 1966 FOR VEHICLE HEATERS Filed Nov. 8. 1963 United States Patent 3,267,987 SUPPLY ()F FUEL TU EURWERS MGRE ESPECIALLY FOR VEHICLE HEATERS Rainer Friedl, Starnberg, Upper Bavaria, and Robert von Linda, Grafeifing, near Munich, Germany, assignors to Webasto Wei-k G.m.b.H., Stochdorf, near Munich, Germany Filed Nov. 8, 1963, Ser. No. 322,490 Claims priority, application Switzerland, Nov. 30, 1962, 14,692/62 2 Claims. (U. 158-363) This invention relates to the supply of liquid fuel to burners, more especially for vehicle heaters, by means including a pump which delivers fuel from a storage tank into an intermediate tank from which a second pump withdraws fuel and supplies it to the burner.
Devices of this type are already known, e.g. in connection with central heating burners. Here the problem of ventilation has been solved by a return pipe connected to the interemediate vessel and leading to the storage tank.
In the case of fuel supply devices for internal combustion engines a separate vent pipe, usually incorporating a throttle, has been connected to the intermediate vessel, its other end leading into the return system.
In both of the aforesaid cases the use of a return system is essential for the venting of the fuel supply device, and the installation of this device (especially in vehicle heaters) is rendered difiicult and expensive by this requirement, so that hitherto float ventilation has generally been provided. This, however, entails other disadvantages, such as sensitivity to vibration and a reduced degree of safety, and also necessitates a less satisfactory arrangement of the fuel supply.
The present invention aims at providing a fuel supply device more especially for vehicle heaters, suitable for readily volatile fuels and which ensures a continuous flow of fuel to the burner, even when large air bubbles are formed in the fuel pipe running from the storage vessel to the first pump.
In accordance with the invention a pipe which bypasses the second fuel pump, and through which fuel is fed to the burner, may be connected to the intermediate fuel tank. By this means the air bubbles delivered by the first pump are fed to the burner through the by-pass pipe, particularly when its entry into the intermediate vessel is at a higher level than the mouth of the pipe leading to the second pump, and a continuous flow of fuel is always ensured from the quantity of fuel delivered by the second pump. Instead of the above-mentioned different levels of the entries of the by-pass pipe and of the pipe leading to the second pump, it may alternatively be arranged that the air bubbles will always be delivered through the by-pass pipe by providing a partition inside the intermediate vessel and a corresponding entry of the pipe coming from the first pump.
If the by-pass pipe does not lead directly into the burner, but into the delivery pipe coming from the second pump, the cross-section of the portion of the delivery pipe which lies after the entry point should be so proportioned in relation to the total fuel delivery fiowing through it that a lower pressure always prevails in it than in the intermediate vessel. Owing to the fact that the by-pass pipe leads into a common delivery pipe, the obstruction of the by-pass pipe, which is generally in the form of a capillary is to a very considerably extent prevented, although obstruction would occur in the case of direct entry into the burner.
In a preferred form of construction of a device according to the invention the suction and delivery pipes of the second pump are so proportioned in relation to the flow "ice resistance of the by-pass pipe that the pump delivers at least and preferably at least of the total amount of fuel supplied to the burner. In the preferred embodiment, the amount of fuel delivered through the by-pass pipe is typically approximately 5% of the total fuel supplied to the burner. The by-pass pipe is preferably constructed as a capillary having a relatively small bore. By such dimensioning the supply device according to the invention also enables the supply system to be adapted to fuels of different viscosities. Thus, for example, when use is made of fuel of lower viscosity, more fuel is delivered through the by-pass pipe and hence the lower calorific value of this fuel as compared with a fuel of higher viscosity is to a large extent compensated. This additional advantage of the fuel supply device according to the invention enables a heating device having a substantially constant heating power to be provided, with a high degree of independence of the viscosity of the fuel used, for example, petrol or diesel oil.
If the bypass pipe is in the form of capillary, its end connected to the intermediate vessel is according to a further feature of the invention fitted with a filter body, for example a sintered metal.
The by-pass pipe advantageously enters the intermediate vessel substantially centrally in relation to the side walls of the vessel, preferably in a tower-like attachment in the roof wall. The volume of the intermediate vessel is thereby fully utilised and greater inclinations are also possible without any difficulties arising in respect of the removal of air bubbles through the by-pass pipe.
One embodiment of a fuel supply in accordance with the invention will now be described, by way of example, with reference to the accompanying drawing from which further features of the invention will be understood.
Referring to the said drawing the fuel, which enters a displacement blower 2 through the delivery pipe 3 providing communication between the outlet of a pump 4 and the inlet of the blower 2, is fed by the blower 2 to a burner 1. The blower 2, at the same time, delivers air for combustion.
The pump 4, which is preferably constructed as a constant-volume delivery pump, and consequently always delivers the same volume of fuel with a high degree of independence on the fluctuations of pressure in the pipe 3, withdraws the fuel from an intermediate tank 5 through a suction pipe 6. As will be noted from the drawing, the open end of the suction pipe 6 is in communication with the bottom portion of the tank 5 to reduce the possibility of any air bubbles being entrained in the fuel passing through the suction pipe 6. The fuel passes into the intermediate vessel 5 through a diaphragm pump 7, which sucks the fuel from a storage tank 9 through a pipe 8 and then delivers the fuel through a pipe 16 into the intermediate vessel 5. It is of importance that the pump 7 shall maintain a constant pressure in the intermediate vessel 5, and this is most simply achieved if the pump 7 is constructed as a spring-controlled diaphragm pump. The pump 7 includes a spring 11 effecting the pressure impulse, and, for example, a cam, or, as illustrated, an electro-magnet 12, provided to effect the suction stroke. By selecting and/or adjusting the strength of the spring 11, a constant pressure can thus be maintained in the intermediate vessel 5, thereby insuring a constant delivery capacity of the pump 4 and of a by-pass pipe 13 between the intermediate vessel 5 and the delivery pipe 3. The constant delivery capacity through the by-pass pipe 13 is in particular achieved if the bypass pipe is constructed as a capillary, or if it incorporates a throttle valve.
In the delivery device illustrated, air bubbles which pass through the pipe 10 into the intermediate vessel 5, collect in the upper portion of the latter and are passed through the capillary 13 (which offers no appreciable resistance to the bubbles, in contrast to the resistance which it offers to the passage of fuel) and the bubbles proceed by way of the delivery pipe 3 to mix with the fuel coming from the pump 4, so that the bubbles are no longer able to interrupt the fiow of fuel. The end of the capillary 13 is mounted in association with a sintered body 14 which to a large extent eliminates fouling, the sintered body lying inside a tower-like attachment 15 provided on the cover wall of the intermediate vessel 5.
The invention is not restricted to the details of the embodiment illustrated, but can be supplemented and modified in difierent ways. Thus, for example, instead of the diaphragm pump illustrated there may be employed a spring-controlled piston pump or a gear pump provided with a pressure relief valve and recycling pipe. The burner or other parts, for example the displacement blower, may also be replaced or omitted.
What we claim is: 1. A device for supplying liquid fuel to a burner comprising:
a first pump, said pump having a suction port and a discharge port; a storage tank for liquid fuel connected to the suction port of said first pump; an intermediate tank connected to the discharge port of said first pump; a second pump, said pump having a suction port and a discharge port; a suction pipe connected between the suction port of said second pump and said intermediate tank;
a delivery pipe means connected between the discharge port of said second pump and the burner, said delivery pipe means having a cross-sectional area to maintain a lower pressure therein than the pressure maintained in said intermediate tank; and
a by-passing pipe providing communication between said intermediate tank and said delivery pipe means.
2. A device as defined in claim 1 wherein the end of said by-passing pipe connected to said intermediate tank is vertically higher than the end of said suction pipe communicating with said intermediate tank, whereby air bubbles collected in said intermediate tank are allowed to pass through said by-passing pipe and into said burner through said delivery pipe.
References Cited by the Examiner UNITED STATES PATENTS 1,532,326 4/1925 Lent et al 158-363 XR 1,631,454 6/1927 Bambach et al. 158-363 XR 2,157,737 5/1939 Janssen 158-363 XR 2,412,019 12/1946 Walker 158-363 XR 2,447,008 8/1948 Gouy 158-363 2,521,270 9/1950 Vanni 158-363 XR 2,865,442 12/ 1958 Halford et a1. 158-36 3,010,509 11/1961 Scherenberg 158-363 FOREIGN PATENTS 568,529 1/ 1959 Canada.
FREDERICK L. MATTESON, Jn., Primary Examiner.
ROBERT A. DUA, Examiner.