With reference to the drawings, an embodiment of a gear pump according to the present invention will be described hereinafter. However, the present invention is not to be considered as being limited to the embodiment below. For example, it would be appropriately acceptable to combine the various structural elements of the embodiment with one another, and it would be acceptable to add or substitute other per se known structures.
As shown in
The fuel tank 1 is a tank in which fuel to be supplied to the jet engine 4 is reserved. The fuel pump 2 is disposed downstream of the fuel tank 1. The fuel measuring mechanism 3 is disposed downstream of the fuel pump 2. The fuel measuring mechanism 3 determines a flow rate of fuel in accordance with information transmitted thereto, e.g., positional information of a throttle lever provided in an aircraft. Based on the thus determined flow rate of fuel, it supplies to the jet engine 4 some of the fuel, which has been pumped out from the fuel pump 2, and returns the remaining or surplus fuel to an inlet of the fuel pump 2.
Referring now to
The fuel pump 2, which is the three-gear type gear pump as described above, has a driving gear 20 and two driven gears (a first driven gear 21 and a second driven gear 22) which are diametrically disposed with respect to one another in such a manner that the driving gear 20 is disposed therebetween. The driving gear 20 receives a rotational movement from a drive source including the jet engine 4 (see
As shown in
The driven gears 21 and 22 are respectively meshed with the driving gear 20 within a casing 23. Fuel is introduced between the driving gear 20 and the driven gear 21 via a first inlet port 24 and also between the driving gear 20 and the driven gear 22 via a second inlet port 25. In response to each rotation of the driven gears 21 and 22, the thus introduced fuel is retained in closed spaces one by one each defined by a tooth surface of each of the driven gears 21 and 22 and by an inner surface of the casing 23 such that each retained fuel is pressurized. Thereafter, the fuel is discharged via a first exhaust port 26 and a second exhaust port 27. In other words, the fuel pump 2 is structured and provided with a first booster section 9 which is mainly composed of the driving gear 20 and the first driven gear 21 and a second booster section 10 which is mainly composed of the driving gear 20 and the second driven gear 22. Accordingly, the first booster section 9 and the second booster section 10 have the same discharge rate in terms of the number of rotations of the driving gear 20.
The first inlet port 24 and the second inlet port 25 are connected to a first inlet line 28 and a second inlet line 29, respectively, both of the lines 28 and 29 being led out from the fuel tank 1 (see
The driving gear 20, the first driven gear 21, and the second driven gear 22 are rotatably supported by a main bearing 36, a first bearing 37, and a second bearing 38, respectively, each formed of a journal bearing or the like. Each of the bearings 36, 37 and 38 has a stationary side plate (36a, 37a, 38a) which is fixed at one side surface side of the gear corresponding thereto and a moveable side plate (36b, 37b, and 38b) which is provided so as to be axially moveable at the other side surface side. Further, the fuel pump 2 exerts fluid pressure (or fuel pressure) on high-pressure-bearing surfaces 36c, 37c, and 38c and low-pressure-bearing surfaces of the moveable side plates 36b, 37b, and 38b whereby the moveable side plates 36b, 37b, and 38b are pressed against the side surfaces of the respective gear so as to form a seal.
Returning to
The fuel-cooling oil cooler 7 is a heat exchanger for transferring heat from an engine lubricant to fuel and is disposed between the fuel measuring mechanism 3 and the jet engine 4.
As described above, the jet engine 4 is provided with the engine combustor 5 and the fan 6. In the jet engine 4, fuel supplied to the engine combustor 5 from the fuel-cooling-oil cooler is burned. By using energy obtained by this burning, the fan 6 is driven to thereby generate rotational power.
Next, the operation of the thus structured fuel supply system that is provided with the fuel pump 2 of the present embodiment will be described below.
Firstly, fuel that is stored in the fuel tank 1 is supplied to the fuel pump 2. At this time, fuel is supplied through the first inlet line 28 and the second inlet line 29 to the first inlet port 24 and the second inlet port 25 of the fuel pump 2. In response to rotation of the first driven gear 21 driven by the driving gear 20, the fuel which has been thus supplied to the first inlet port 24 is retained in the closed spaces each defined by the teeth of the first driven gear 21 and the inner surface of the casing 23 such that each retained fuel is pressurized. Thereafter, the fuel is discharged from the fuel pump 2 through the first exhaust port 26. Similarly, in response to rotation of the second driven gear 22 driven by the driving gear 20, the fuel which has been thus supplied to the second inlet port 25 is retained in the closed spaces each defined by the teeth of the second driven gear 22 and the inner surface of the casing 23 such that each retained fuel is pressurized. Thereafter, the fuel is discharged from the fuel pump 2 through the second exhaust port 27.
Accordingly, the fuel in the first and second exhaust ports 26 and 27 is in a state such that the pressure is raised higher than the fuel in the first and second inlet ports 24 and 25. Therefore, if a gap exists between the driving gear 20 and the first driven gear 21 and a gap exists between the driving gear 20 and the second driven gear 22, the fuel in the first exhaust port 26 easily leaks into the first inlet port 24 and the fuel in the second exhaust port 27 easily leaks into the second inlet port 25.
In contrast, as described above, in the fuel pump 2 according to the present embodiment, the driving gear 20 has a gear diameter about twice the gear diameter of each of the first driven gear 21 and the second driven gear 22 and a larger number of teeth than the number of teeth of each of the first driven gear 21 and the second driven gear 22. Therefore, since a speed of rotation of each of the first driven gear 21 and the second driven gear 22 is increased as compared to a conventional gear pump, it is possible to substantially reduce a face-width of each of the first driven gear 21 and the second driven gear 22 as compared to the conventional gear pump. Accordingly, as compared to the conventional gear pump, it is possible to reduce an area of each tooth tip of the gears. As a result, it is possible to prevent leakage of fuel from between the driving gear 20 and the first driven gear 21 and from between the driving gear 20 and the second driven gear 22.
Additionally, if a gap exists between the driving gear 20 and the inner surface of the casing 23, the fuel in the first exhaust port 26 easily leaks into the second inlet port 25. In contrast, since the driving gear 20 according to the present embodiment has about twice the number of teeth of a conventional driven gear, a pressure drop between the driving gear and the inner surface of the casing 23 is increased such that leakage of fuel from the first exhaust port 26 to the second inlet port 25 can be prevented.
Incidentally, when the number of teeth of the driving gear 20 changes from N to (N+M), where N denotes the number of teeth of each of driven gear 21 and 22, the leakage of fuel from between the driving gear and the driven gears 21 and 22 decreases or becomes (N+M)0.5. Accordingly, theoretically speaking, the greater the number of teeth of the driving gear 20, the smaller the leakage of fuel. Whereas, the greater the number of teeth of the driving gear 20, the greater the diameter of the driving gear 20. That is, the size of the fuel pump inevitably becomes large. Therefore, empirically speaking, it is preferable that the number of teeth of the driving gear 20 be about twice the number of teeth of the driven gears 21, 22.
Further, with the driving gear 20 having a large diameter, the flow rate of fuel can be increased even under the same conditions in rotation. Conversely, when the flow rate of fuel is set at substantially the same level that used conventionally, a face-width of the gears can be N/(N+M), whereby leakage of fuel can potentially be prevented.
As described above, in the fuel pump 2 according to the present embodiment, it is possible to prevent leakage of fuel from a high pressure side to a low pressure side, and hence, to increase the volumetric efficiency of the fuel pump.
The thus pressurized fuel is discharged from the fuel pump 2 and is supplied to the fuel measuring mechanism 3 through the first discharge line 30 and the second discharge line 31. Some of fuel or a predetermined amount of fuel in the fuel measuring mechanism 3 is supplied to the jet engine 4, and the remaining fuel or surplus fuel in the fuel measuring mechanism 3 is pressure-released and returned to the fuel pump 2.
Next, the thus discharged/supplied fuel from the fuel supply system (the fuel measuring mechanism 3) to the jet engine 4 is thermally interchanged with an oil used in the jet engine 4, and thereafter, supplied to the engine combustor 5 of the jet engine 4. Then, the fuel in the engine combustor 5 is burned. The use of energy generated by the fuel burning allows the fan 6 to be rotated and thereby generate rotational power.
Although the preferred exemplary embodiment according to the present invention has been described with reference to the appended drawings, it goes without saying that the present invention is by no means limited to the above-described embodiment. Shapes of such structural elements and a combination thereof as described in the aforesaid embodiment are simply an example, and therefore, they can be modified in accordance with a design need or the like without departing from the scope or subject matter of the present invention
For example, as an application, in the aforesaid embodiment, the fuel supply system provided with the fuel pump 2 as a structural component has been described. However, a gear pump according to the present invention is not limited to a gear pump that is provided in such a fuel supply system. The present invention can be applied to all three-gear type gear pumps in which a fluid is pressurized and then discharged.
Additionally, although the engine lubricant (oil) is cooled by only using fuel in the aforesaid embodiment, the cooling means is not limited to this. For example, the oil may be further cooled by using some of the air discharged from the fan 6 as a bleed air for cooling the oil.