FUEL SUPPLY SYSTEM FOR INTERNAL COMBUSTION ENGINE USING AN ULTRASONIC ATOMIZER

Abstract: A fuel supply system (31) for an internal combus­ tion engine provided with a fuel injection valve (30) and an ultrasonic atomizer (1) on the inlet pipe (25) of the engine is disclosed. The tip of the oscillator member (10) of the ultrasonic atomizer (1) is formed with an inclined portion (10b) and a reduced portion (10c) ahead of the inclined portion (10b). By arranging a fuel supply passage (9) face-to-face with this in­ clined portion (10b), the shape of the oscillator tip is modified, and it is possible to maintain adequate atomizing angle (α) regardless of the quantity of fuel supply without fuel becoming attached on the inner wall of the inlet pipe (25), to increase the turndown ratio and to achieve even spraying all over the circum­ ference. Also, it is possible to shorten the engine starting time when the external air temperature is low, and to improve the combustion performance and the exhaust properties, particularly in an engine using a fuel which is difficult to ignite at low temperatures, such as alcohol, kerosene, etc.

Description: The present invention relates to a fuel supply system for an internal combustion engine using an ultrasonic atomizer for mixing of fuel and air. The system may be applied to a spark ignition type of engine, distributing the fuel-air mixture generated by a fuel injection valve to multiple cylinders, or to an engine using fuel difficult to ignite at low temperature (such as alcohol or kerosene) and the fuel and air are mixed by an ultrasonic atomizer to atomize the liquid fuel. A system to supply a fuel-air mixture to engines is known, in which an ultrasonic atomizer is provided on the inlet pipe of the internal combustion engine and fuel is atomized and mixed with intake air. For example. in JP-A-53-140416, it is proposed to provide a fuel supply system and an annular ultrasonic oscillator in the inlet pipe passage and to promote the mixing of atomized fuel obtained through annular ultrasonic oscillator with the intake air. In the above conventional system, however the fuel supply system and ultrasonic oscillator are fitted closely to the engine in the inlet pipe passage. Accordingly, the air flow is not stable and the intake air and the atomized fuel do not mix well, and fuel is often deposited as a film on the pipe wall. In such case, particularly, in a high-powered engine, the transfer speed of the fuel-air mixture is decreased during engine starting at a low external air temperature and at the pickup time to rapidly accelerate from low speed, and the desired power cannot be obtained. Also, because an annular ultrasonic oscillator is used, fuel is not atomized at the nodal portion of vibration. Thus, the stagnated fuel drips, and the fuel supply becomes unstable. On the other hand, an ultrasonic atomizer as shown in Fig. 16 is known as an atomizer to atomize liquid fuel. This consists of a cylinder 101, a nozzle body 102, an oscillator horn 103 and an electro-acoustic transducer 104. A fuel supply passage 105 is formed in the cylinder 101, and an injection hole 106 communicating with the fuel supply passage 105 is formed on the nozzle body 102. A plurality of injection holes 106 are formed around the nozzle body 102, and the fuel injected from the injection holes 106 is supplied to the vibrating oscillator horn 103 and is thus atomized. However, in this conventional type of ultrasonic atomizer, the atomized quantity is determined by the quantity of fuel supplied from the injection holes 106; therefore, the turndown ratio (ratio of maximum to minimum atomized amounts) cannot be increased. Also, because it is difficult to evenly distribute the fuel into a plurality of laterally placed injection holes 106, the fuel is unevenly atomized. Further, it is difficult to increase the number of injection holes 106 in order to distribute the fuel evenly. Also, the manufacturing cost may be increased because the injection holes 106 are difficult to fabricate. Because the oscillator horn 103 is in the shape of a horn with its outer diameter increasing toward the tip, the atomizing angle of the atomized fuel becomes larger when it is installed on an engine, and the atomized fuel becomes deposited on the inner wall of the inlet pipe. EP-A-0202381 describes a fuel supply system for an internal combustion engine, according to the preamble of claim 1, which system includes an ultrasonic injection nozzle having a fuel inlet port, a central vibrator (which is actuated by an ultrasonic oscillator) mounted in the central hole of the nozzle, and the tip of the vibrator extends a little beyond the housing and can have an inclined portion which terminates in a reduced diameter cylindrical end (see Fig. 2 thereof). Fuel from one or more injection holes is delivered to the surface of the vibrator just above this vibrating tip, where it is atomized and injected outwardly into the engine. It is an object of the present invention to maintain an adequate atomizing angle regardless of the quantity of the fuel supply by improving the shape of the oscillator tip of the ultrasonic atomizer and also to achieve even spraying all over the circumference with higher turndown ratio. It is another object of this invention to provide a fuel supply system for an internal combustion engine comprising an ultrasonic atomizer, by which it is possible to shorten the starting time when the external air temperature is low and to increase the combustion performance and exhaust property in a spark ignition type engine, using a fuel which is difficult to ignite at low temperature. According to this invention we provide a fuel supply system for an internal combustion engine furnished with a fuel injection valve and an ultrasonic atomizer on the suction pipe of the engine, said ultrasonic atomizer comprising: an oscillator member, to which ultrasonic vibration can be given by an ultrasonic vibration generating means, an inner cylinder provided on the outer periphery of said oscillator member, an outer cylinder engaged with and fixed on said inner cylinder and forming an annular fuel supply passage between itself and said inner cylinder, a fuel supply hole formed on said outer cylinder, and a circumferential groove communicating with said fuel supply hole and formed on said inner cylinder; the tips of the inner cylinder and outer cylinder having a tapered shape, so that an annular passage, an inclined passage and an opening are formed between the outer periphery of the tip of the inner cylinder and the inner periphery of the outer cylinder, and further comprising an inclined portion formed at the tip of said oscillator member, and a portion of reduced diameter formed at the tip of said inclined portion, characterized in that the opening of said fuel supply passage is arranged so as to direct the fuel onto said inclined portion. The invention extends to an internal combustion engine which is capable of burning alcohol or kerosene and is provided with a fuel supply system as aforesaid. By this invention, it is possible to maintain an adequate atomizing angle regardless of the quantity of the fuel supply, by improving the shape of the oscillator member tip of the ultrasonic atomizer, and to supply the fuel into the cylinder without the fuel being deposited on the inner wall of the inlet pipe. Also, because the turndown ratio can be increased and even circumferential atomization can be achieved, it is possible to use the ultrasonic atomizer in normal operation with an increased atomizing flow and to simplify the construction because a carburettor can be eliminated. In the accompanying drawings: Fig. 1 is a cross-sectional view showing a first embodiment of an ultrasonic atomizer for a system according to this invention; Fig. 2 is a cross-sectional view along the line II-II of Fig. 1; Figs. 3, 4, 5, 6 and 7 are enlarged partial views of showing the shape of the atomization plane of the oscillator member; Fig. 8 is a cross-sectional view of a first embodiment of the fuel supply system for an internal combustion engine of this invention; Fig. 9 is a cross-sectional view of a second embodiment of the fuel supply system for an internal combustion engine of this invention; Figs. 10, 11 and 12 are diagrams to explain the results of experiments on the fuel supply system of Fig. 9; Fig. 13 is a cross-sectional view of another embodiment of ultrasonic atomizer for use according to this invention; Fig. 14 is a plan view of the circumferential groove along the line X-X of Fig. 13; Fig. 15 illustrates further embodiments of an ultrasonic atomizer for use in this invention, showing respective plan views of the circumferential groove along the line X-X of Fig. 13; and Fig. 16 is a cross-sectional view showing a conventional type of ultrasonic atomizer. In the following, the embodiments of this invention will be described in connection with the drawings. In Fig. 1 and Fig. 2, the ultrasonic atomizer 1 comprises an oscillator member 10, having a base 2, a shaft 3 and an atomizing region 4. An inner cylinder 5 is provided on the outer periphery of the oscillator member 10. On the outer periphery of the tip 5a of the inner cylinder 5, an outer cylinder 6 having its inner diameter slightly larger than the outer diameter of the tip 5a is engaged and fixed, and a fuel supply passage 9 is formed between the tip 5a of the inner cylinder 5 and the outer cylinder 6. Also, the tips of inner cylinder 5 and outer cylinder 6 are formed in a tapered shape. Accordingly, an annular passage 9a, an inclined passage 9b and an opening 9c are formed between the outer periphery of the tip 5a of inner cylinder 5 and the inner periphery of outer cylinder 6. The inner cylinder is provided with a circumferential groove 5b at a suitable position on its outer periphery, and the outer cylinder 6 is furnished with a liquid fuel supply hole 6a, which communicates with said circumferential groove 5b and the passage 9a. To the liquid fuel supply hole 6a of the outer cylinder 6, liquid fuel is supplied from the fuel injection valve and it is supplied to all over the circumference of the circumferential groove 5b of the inner cylinder 5. The liquid fuel thus fed to the circumferential groove 5b is sent to the opening 9c through the passage 9a and the inclined passage 9b and reaches the atomizing annular region 4, where it is atomized by the ultrasonic vibration of the oscillator member 10. Fig. 3 shows the shape of the tip of the oscillator member 10 and said opening 9c. The tip of the oscillator member 10 consists of a portion with enlarged diameter 10a, an inclined portion 10b and a portion with reduced diameter 10c. Said portion with enlarged diameter 10a plays a role to increase the atomizing area. Said inclined portion 10b is formed in such manner that it maintains a predetermined angle to the axis of the oscillator member 10, and the portion with reduced diameter 10c maintains the angle γ to the axis of the oscillator member 10. The oscillator member 10 of this embodiment is characterized in that it is provided with a portion with enlarged diameter 10a, which maintains the flow of atomized liquid. If it is not necessary to maintain a high flow, there is no need to provide the portion of enlarged diameter 10a, and a portion of the same diameter may be used. An example of the dimension of each component is given below. It is assumed that the diameter D of the portion with enlarged diameter 10a of oscillator member is 9 mm, and that the axial length of the inclined portion 10b is 0.5 mm. The ratio L/D is 1/10 to 1/30, and more preferably, about 1/18. The atomizing angle α is set to 30° to 45°. The reason for this is that, when the engine is provided with the ultrasonic atomizer, it is important to maintain the atomizing angle in such degree that fuel is not attached on inner wall of suction pipe. However, it is also necessary to widen the angle to some extent in order to increase the mixing effect with the air. The angle β between the tip of fuel supply passage 9 and the inclined portion 10b should be 5 - 45° , or more preferably, 15°, so that the atomized fuel is not wastefully discharged and is easily attached on the atomizing surface 10b. The angle γ of the surface of the portion with reduced diameter 10c to the axis of the oscillator member 10 is 0 - 90° or more preferably, 40 - 50° . Fig. 4 shows an example with γ = 90° , and Fig. 5 an example with γ = 0° . The atomizing angle α is widened when the angle γ is decreased, and it becomes narrower when the angle γ is increased. The clearance D1 between the opening 9c of the fuel supply passage 9 and the portion with enlarged diameter 10a of the oscillator member 10 is set to 0.1 - 0.2 (D1/D = 0.01 - 0.02). The reason for this is that, if the clearance is smaller than the lower limit, the gap between the tip of fuel supply passage 9 and the oscillator member 10 is too narrow and they may contact each other. If it is larger than the upper limit, the liquid may drip without reaching the surface of the inclined portion 10b when liquid flow and pressure are low. The distance L1 from the opening 9c of fuel supply passage 9 to the portion with enlarged diameter 10a is 0 to 0.5 mm (L1/L = 0 - 1). When the distance L1 is decreased and the opening 9c is brought closer to the portion with enlarged diameter 10a, it is difficult to form a liquid film or membrane. If it is brought closer to the portion with reduced diameter 10c, incident angle is turned to minus, and the liquid runs through. Fig. 6 shows another example of the tip of the oscillator member 10, in which the portion with reduced diameter 10c is designed in two steps 10c′ and 10c″. Fig. 7 represents still another example of the tip of the oscillator member, in which the tip 10e is machined in such manner that the inclined portion and the portion with reduced diameter are formed continuously with a radius of curvature R. Fig. 8 is a cross-sectional view of a first embodiment of the fuel supply system 31 for an internal combustion engine mounted on a spark ignition type engine with multiple cylinders (MPI: multipoint injection). In this figure, numeral 21 denotes a cylinder, 22 a connecting rod, 23 a piston, 24 a combustion chamber, 25 an inlet pipe, 26 a suction or inlet valve, 27 an exhaust pipe and 28 an exhaust valve. At a predetermined position on the inlet pipe 25, a fuel supply unit 31 comprising an ultrasonic atomizer 1 and a fuel injection valve 30 is provided, and the atomizing plane 4 at the tip of the ultrasonic atomizer 1 is arranged face-to-face to the suction valve 26. Fuel is supplied from the fuel supply passage 33 of the fuel injection valve 30 to the atomizing plane 4, where fuel is atomized and sprayed into the inlet pipe 25. The operation of this fuel supply system according to this invention is as follows. Liquid fuel reaches the atomizing plane 4 through the circumferential groove 5b, the passage 9a, the inclined passage 9b, and the opening 9c. In this case, liquid fuel is supplied to all over the whole circumferential surface of the inclined portion 10b from the opening 9c through the circumferential groove 5b. During this process, liquid fuel is formed into a membrane of approximately even thickness, and it reaches the inclined portion 10b. After reaching the inclined portion 10b, liquid fuel is atomized by ultrasonic vibration of the oscillator member 10, and the fuel not atomized enough here flows into the portion with reduced diameter 10c, where all of the fuel is atomized. According to this invention, it is possible to maintain an adequate atomizing angle α regardless of the quantity of supply fuel by improving the shape of the oscillator member tip of the ultrasonic atomizer and also to supply the fuel into the cylinder without depositing the fuel on the inner wall of the inlet pipe 25. Also, because the turndown ratio can be increased and even spraying all over the circumference can be achieved, spray flow can be increased and ultrasonic atomizer can be used even during normal operation. The mechanism of the total system can be simplified because carburettor can be eliminated. Fig. 9 is a cross-sectional view of a fuel supply unit according to the present invention, mounted on the intake manifold of a spark ignition type engine of a single point injection (SPI) system, in which the fuel-air mixture generated from a fuel supply system is distributed to multiple cylinders. In this figure, each component has the same reference number as in the embodiment of Fig. 8. In this embodiment, the ultrasonic atomizer 1 is provided at the center of the inlet pipe 25, upstream of a throttle valve 35 which is connected to the accelerator pedal. The fuel injection valve 30 is fixed within the inlet pipe 25 which supplies fuel to the ultrasonic atomizer 1. The atomizer 1 is furnished upstream of the throttle valve 35. Accordingly, the air flows evenly in the suction pipe during the starting operation when the opening of the throttle valve is small. Thus, the mixing of the atomized fuel is promoted, and the starting time of the engine is shortened. The results of the experiments by the present inventors on this fuel supply system are given in Figs. 10, 11 and 12. A single point injection (SPI) engine performance was tested with a 1.8 liter, 4-cylinder commercial engine. The SPI engine fuel injector was mounted just over the throttle body. The fuel was sprayed from a centrally positioned injector and distributed to each cylinder. A/F Distribution among Cylinders The fuel distribution to each cylinder was a major concern in the development of a suitable atomizer for the SPI engine. Figure 10 shows the cylinder-to-cylinder A/F distribution with the rise of engine coolant temperatures. It is generally acknowledged that stable engine operation is not possible when the difference in A/F among cylinders exceeds 2.0. A/F distribution under low temperature conditions tends to deteriorate due to fuel oversupply. The ultrasonic atomizer, however, can maintain a constant fuel distribution through the whole temperature range, as shown in Figure 10. Cold Engine Performance The advantages under cold conditions were also clear in the cold startability tests. Tests were performed under a cold ambient temperature of -10°c. In order to determine cold startability, the tests were carried out without cold starter nozzles. Figure 11 shows the required cranking time and rough idling time at an ambient temperature of -10°c, the former indicating the time from the beginning of the rotation of the starter. motor to the start of complete combustion, and the latter a period of unstable engine vibration. These were measured by an accelerometer on the engine head, which monitors engine vibrations. This figure shows that the ultrasonic atomizer can reduce the cranking time of the conventional injector. Rough idling in engines equipped with ultrasonic atomizers was also significantly lower than in conventionally equipped engines. These advantages in cold engine performance can be explained by the effects of high delivery response and superior atomization. Transient Response Performance Transient response tests were also carried out in order to ascertain fuel delivery response. Figure 12 shows relations among brake torque response, A/F change and vacuum trend. From these results, it can be seen that the conventional injector demonstrates the lean spike and torque drop phenomena after fast throttle ramp. These characteristics impair response in accelerating operations. The ultrasonic atomizer reduces these undesirable phenomena, as shown. Figs. 13 and 14 represent another embodiment of the above ultrasonic atomizer 1. In the figure, the same component is referred to by the same number as in the embodiment of Fig. 1. In this embodiment, a circumferential groove 5b is provided on outer periphery of the inner cylinder 5 of ultrasonic atomizer, and it is eccentric to the circumference of the inner cylinder 5 as shown in Fig. 14. The depth of the circumferential groove 5b is maximized toward the fuel supply hole 6a, and the depth of the groove 5b is decreased toward the direction opposite from the fuel supply hole 6a. Accordingly, even when the liquid is supplied under pressure, liquid is not supplied excessively in the direction opposite from the fuel supply. Thus, the liquid supplied from the nozzle 9c to the atomizing region 4 of the oscillator member 10 is distributed evenly all over the circumference. (The box 4 represents the same parts as in the lower part of the oscillator in Fig. 1.) Therefore, it is possible to atomize the fuel evenly all over the circumference of the atomizing region 4 of the oscillator member 10, and the fuel can be sprayed evenly all over the circumference. By changing the depth of the circumferential groove 5b, it is possible to provide even spraying and to change the density of spray over the circumference for each application purpose. Next, description will be given of another embodiment of this invention in connection with Fig. 15. In this embodiment, the circumferential groove 5b is provided on the outer periphery of the inner cylinder 5 of the ultrasonic atomizer at an angle of 15, 45 or 90 degrees respectively as shown in Figs. 15 (a) to (c), leaving the remainder of the circumference intact. Because the circumferential groove 5b is not furnished on the opposite side of the fuel supply hole 6a, the liquid is not distributed too much on the opposite side of the liquid supply hole even when the liquid is supplied by pressurizing. In the embodiments of Figs. 8 to 15, the shape of the oscillator member is preferably as given in Figs. 3 to 7. It is also effective to adopt a horn-like shape, in which outer diameter is increased toward the tip of the oscillator member.

Claims: A fuel supply system for an internal combustion engine furnished with a fuel injection valve (30) and an ultrasonic atomizer (31) on the suction pipe (25) of the engine, said ultrasonic atomizer (31) comprising: an oscillator member (10), to which ultrasonic vibration can be given by an ultrasonic vibration generating means, an inner cylinder (5) provided on the outer periphery of said oscillator member (10), an outer cylinder (6) engaged with and fixed on said inner cylinder (5) and forming an annular fuel supply passage (9) between itself and said inner cylinder (5), a fuel supply hole (6a) formed on said outer cylinder (6), and a circumferential groove (5b) communicating with said fuel supply hole (6a) and formed on said inner cylinder (5); the tips of the inner cylinder (5) and outer cylinder (6) having a tapered shape, so that an annular passage (9a), an inclined passage (9b) and an opening (9c) are formed between the outer periphery of the tip (5a) of the inner cylinder (5) and the inner periphery of the outer cylinder (6), and further comprising an inclined portion formed at the tip of said oscillator member (10), and a portion (10c) of reduced diameter formed at the tip of said inclined portion (10b), characterized in that the opening (9c) of said fuel supply passage (9) is arranged so as to direct the fuel onto said inclined portion (10b). A fuel supply system as claimed in Claim 1, wherein said ultrasonic atomizer (31) is installed at the center of the engine suction pipe (25) upstream of the throttle valve (35). A fuel supply system as claimed in Claim 1 or 2, wherein said circumferential groove (5b) is provided on the outer periphery of said inner cylinder (5) and is eccentric to the circumference of said inner cylinder. A fuel supply system as claimed in Claim 1 or 2, wherein said circumferential groove (5b) is provided on the outer periphery of said inner cylinder (5), leaving a portion of the circumference intact at an angle. A fuel supply system as claimed in any preceding claim, wherein the tip of the oscillator member (10) has a portion (10a) of enlarged diameter above the inclined portion (10b). A fuel supply system as claimed in any preceding claim used in an internal combustion engine which is capable of burning alcohol or kerosene.

Inventors: HIGASHIMOTO, NOBORU, HOSOGAI, DAIJIRO, KOBAYASHI, TAIJI, KOKUBO, KAKURO, TSURUTANI, KAZUSHI, HIGASHIMOTO, NOBORU, C/O TONEN CORP. CORP. LAB., HOSOGAI, DAIJIRO, C/O TONEN CORP. CORP. LAB., KOBAYASHI, TAIJI, C/O TONEN CORP. CORP. LAB., KOKUBO, KAKURO, C/O TONEN CORP. CORP. LAB., TSURUTANI, KAZUSHI, C/O TONEN CORP. CORP. LAB.
Applicants: TONEN CORPORATION
Application year: 1990
Main classification: F02M69
IPC codes: B05B17, F02M69