INTAKE SYSTEM FOR ROTARY PISTON ENGINE

Abstract: An intake system for a rotary piston engine having a plurality of engine sections, each of said engine sections being separated by an intermediate housing (1), comprising com­ municating passage means for communicating said engine sec­ tions (F, R) so that intake air can be transferred between said working chambers (6f, 6r) in accordance with the difference in rotor phase between the engine sections, said communicating pas­ sage means being controlled so as to be closed at a timing after an intake port (5f, 5r) is closed in each engine section and positioned so that there remains a larger amount of intake air in each of the working chamber than the required amount of intake air under the lowest load driving condition when the communicating passage means is closed, and throttle valve means (14) for controlling the amount of intake air. Ac­ cording to the present invention, it is possible to obtain a rotary piston engine which can remarkably reduce pumping loss and desirably control the amount of intake air in accordance the engine driving condition.

Description: BACKGROUND OF THE INVENTION The present invention relates to an intake system for a rotary piston engine. DESCRIPTION OF PRIOR ART It is well known that since the Otto cycle engine is usually operated at an initial stage of compression stroke under a condition where the pressure within the combustion chamber is lower than the atomospheric pressure, a so-called pumping loss cannot be avoided. It is considered that the pumping loss amounts to about 30 % of the total energy loss caused by the operation of the engine. Therefore, the thermal efficiency of the engine can be remarkably improved if the pumping loss can be reduced. In order to reduce the pumping loss, there have been proposed a method in which an intake valve means is closed earlier or later than the standard timing, and a method in which a part of the intake air is recirculated to the intake system. An intake system for a rotary piston engine is known which is constituted so as to reduce the pumping loss in accordance with the latter method in which working chambers of two engine sections are connected by a communicating passage so as to be communicated with each other at a predetermined timing and in which a control valve, its opening being controlled in accordance with the engine load, is provided within the communicating passage. For example JP-A-58/172429 shows an intake system in a rotary piston engine comprising a plurality of engine sections each section having a rotor in a corresponding working chamber and at least one intake port communicating with intake passage means, each of said sections being separated by intermediate housing means, the engine further comprising communicating passage means between said sections which transfer intake air according to the rotor phase difference between said sections so as to be closed at a timing after the intake port has been closed, and the engine comprising throttle valve means which are located in said intake passage means for controlling the amount of intake air. An intake system in a rotary piston engine comprising a plurality of engine sections, each section having a rotor in a corresponding working chamber and at least one intake port communicating with intake passage means, each of said sections being separated by intermediate housing means, the engine further comprising communicating passage means between said sections which transfer intake air according to the rotor phase difference between said sections, said communicating passage means being connected with each working chamber by openings which are opened and closed by the respective rotor so as to be closed at a timing after the respective intake port has been closed, and the engine comprising throttle valve means which are located in said intake passage means for controlling the amount of intake air. However, in the prior art methods, since the timing of closing the intake valve or the timing of closing and opening the control valve has to be controlled in accordance with the engine load and the engine r.p.m., it is difficult to constitute the hardware of the controlling system and complicated software programs are necessary. As a result, the intake system based upon the prior art method has not been put into practice yet. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an intake system for rotary piston engines which can reduce the pumping loss with simple hardware and software. According to the present invention, the above and other objects can be accomplished by an intake system in a rotary piston engine comprising a plurality of engine sections, each section having a rotor in a corresponding working chamber and at least one intake port communicating with intake passage means, each of said sections being separated by intermediate housing means, the engine further comprising communicating passage means between said sections which transfer intake air according to the rotor phase difference between said sections, said communicating passage means being connected with each working chamber by openings which are opened and closed by the respective rotor so as to be closed at a timing after the respective intake port has been closed, and the engine comprising throttle valve means which are located in said intake passage means for controlling the amount of intake air characterized in that each opening connecting said communicating passage means with a working chamber is positioned at a preselected position, said position being determined so that when the opening is closed by the respective rotor under lowest load driving condition the remaining amount of intake air in the respective working chamber is larger than the amount required under this condition. Improvements of the inventive intake system are defined in subclaims 2 to 9. According to the inventive solution the edge of the communicating passage means is positioned at the trailing side of an imaginary position thereof with respect to the rotating direction of the rotor, said imaginary position being determined so that when the communicating passage means is closed, the volume of the working chamber equals that of the amount of intake air required under the lowest load driving condition. Thus, it is possible to reduce the pumping losses under low load driving condition remarkably. The above and other objects and features of the present invention will become apparent from the following descriptions taking reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic drawing showing a longitudinal cross -sectional view of a rotary piston engine having an intake system which is an embodiment of the present invention. Figure 2 is a schematic drawing showing a longitudinal cross-sectional view of a front engine section of the rotary piston engine having an intake system which is the embodiment of the present invention. Figure 3 is a time chart showing timings of opening and closing intake ports and a communicating passage in the embodiment of the present invention. Figure 4 is a schematic drawing showing a control system for throttle valves and a control valve in the embodiment of the present invention. Figure 5 is a graph showing a method for controlling the opening of the first throttle valve and the control valve in the embodiment of the present invention. Figure 6 is a graph showing the relationship between the engine r.p.m. and the engine output torque characteristics as a function of the opening of the first throttle valve in the embodiment of the present invention. Figure7 is a schematic drawing showing a longitudinal cross-sectional view of the rotary piston engine having an intake system which is an embodiment of the present invention and further including a fuel feeding system. Figure 8 is a schematic drawing showing the structure of a fuel injection nozzle in the embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Figure 1, there is shown a two-rotor type rotary piston engine E consisting of a front engine section F and a rear engine section R. The engine sections F and R respectively have rotor housings 7f and 7r which are formed with inner walls of trochoidal configuration. An intermediate housing 1 is located between the rotor housings 7f and 7r to separate them one from the other. The outer sides of the rotor housings 7f and 7r are attached with side housings 3 and 4 the inner walls 3i and 4i of which are formed with second intake ports 5f and 5r. Thus, the rotor housing 7f and 7r, the side housing 3 and 4, and the intermediate housing 1 constitute a casing in which a pair of rotor cavities are defined. On the opposite faces of the intermediate housing 1, there are formed first intake ports 2f and 2r opening to respective rotor cavities. As well known in the art, in each of the rotor cavities, there is disposed a rotor 6f or 6r of substantially triangular configuration which is rotatable with apex portions in sliding contact with the inner wall of the rotor housing 7f or 7r. Thus, in each of the rotor cavities in the casing, there are defined working chambers 12f and 12r whose volumes cyclically change as the rotor 6f or 6r rotates. Each of the second intake ports 5f and 5r is located slightly toward the leading side of the first intake port with respect to the rotating direction of the rotor 6f or 6r. The two rotors 6f and 6r have 180 degree phase difference. Each of the first intake ports 2f and 2r is communicated with a first ramiform intake passage 8f or 8r ramified from a junction portion 8c of a first intake passage 8 and there is provided within the first intake passage 8 upstream of the junction portion 8c a first throttle valve 9 the opening of which is controlled in accordance with the engine load. Similarly, each of the second intake ports 5f and 5r is communicated with a second ramiform intake passage 10f or 10r ramified from a junction portion 10c of a second intake passage 10 and there is provided within the second intake passage 10 upstream of the junction portion 10c a second throttle valve 11 controlled so that it is opened when the opening degree of the first throttle valve 9 is larger than a predetermined value. As shown in Figure 1, there is provided in the intermediate housing 1 a communicating passage 13 communicating with the working chambers 12f and 12r of the engine section F and R and a control valve 14 is provided within the communicating passage 13. As shown in Figure 2 in connection with the front engine section F, said communicating passage 13 is arranged so that the front side opening 13f thereof is located at the leading side of both the first intake port 2f and the second intake port 5f with respect to the rotating direction of the rotor 6f. The edge of the front side opening 13f of the communicating passage 13 is positioned so that the opening 13f begins to be opened at the rotor phase as shown by a phantom line O and is closed at the rotor phase as shown by a phantom line C. The rotor 6r is shown by a phantom line in Figure 2. The operation mode of the communicating passage 13 will be hereinafter described in more detail based upon the time chart shown in Figure 3. The first intake port 2f and the second intake port 5f of the front rotor housing 7f begin to be opened with a slight time delay after the front rotor 6f passes through the top dead center TDC, for example, when the rotor 6f is rotated 32 degrees after TDC, and afterward the front side opening 13f of the communicating passage 13 begins to be opened with a further slight time delay, for example, when the rotor 6f is rotated 75 degrees after TDC. (See the phantom line O in Figure 2.) On the other hand, the first intake pore 2r and the second intake port 5r of the rear rotor housing 7r are still opened when the first intake port 2f and the second intake port 5f of the front rotor housing 7f begin to be opened and when the front side opening 13f of the communicating passage 13 begins to be opened, and they are shut some time after the front side opening 13f of the communicating passage 13 is opened. The rear side opening 13r of the communicating passage 13 is shut with a slight time delay after the first intake port 2r and the second intake port 5r of the rear rotor housing 7r is closed. Consequently, the communicating passage 13 is communicated with both the front and rear working chamber 12f and 12r for a time period T1 between the time when the front side opening 13f of the communicating passage 13 begins to be opened and the time when the rear side opening 13r thereof is closed. The working chamber 12r in the rear engine section R takes a position between the final stage of the intake stroke and the initial stage of the compression stroke in the time period T1 and the pressure therein is higher than that in the working chamber 12f in the front engine section F which takes a position at the first half stage of the intake stroke. As a result, the mixture of intake air and fuel flows from the working chamber 12r in the rear engine section R into the working chamber 12f in the front engine section F through the communicating passage 13 as shown by arrow A. Therefore, during the time period T1, the mixture is drawn through the communicating passage 13 into the working chamber 12f taking a position at the first half stage of the intake stroke and the pressure in the working chamber 12r is prevented from being undesirably increased. Then, the first intake port 2r and the second intake port 5r of the rear rotor housing 7r begin to be opened again just before the rear side opening 13r of the communicating passage 13 is closed and afterward the rear side opening 13r is opened. On the other hand, after the working chamber 12f passes through the bottom dead center BDC (when the crank angle is, for example, 40 degree from BDC), the first intake port 2f and the second intake port 5f of the front rotor housing 7f are closed and the front side opening 13f is closed with a predetermined time delay when the crank angle is, for example, 135 degree from BDC. Both the front side opening 13f and the rear side opening 13r of the communicating passage 13 are opened during the time period T2 ( T2 = T1 ) after BDC up to the time the front side opening 13f is closed. During this time period T2, the mixture flows from the working chamber 12f of the front engine section F into the working chamber 12r of the rear rotor housing 7r as shown by arrow B. As a result, increase in the pressure in the working chamber 12f of the front engine section F is prevented and the mixture is drawn into the working chamber 12r of the rear engine section R. After the front side opening 13f of the communicating passage 13 is closed, the compression stroke starts in the front engine section F. When the front side opening 13f of the communicating passage 13 is closed, the inner volume of the working chamber 12f is set so as to be larger than the intake air volume required under idling condition where the throttle valve 9 is fully opened, in other words, the volume of the minimum required amount of intake air. More specifically, the edge of the opening 13f is positioned at the trailing side of an imaginary position thereof with respect to the rotating direction of the rotor 6f, said imaginary position being determined so that when the front side opening 13f is closed, the volume of the working chamber 12f equals that of the minimum required amount of intake air. The operation mode of the control valve 14 and the throttle valve 9 and 11 will be hereinafter described. Referring to Figure 4, the opening of first throttle valve 9 is controlled by an accelerator pedal 16 and the second throttle valve 11 is interlocked with the first throttle valve 9 by a link 17. The control valve 14 is actuated by an actuator 18 consisting of diaphram. A pressure trasmitting passage 19 for transmitting the negative pressure of intake air from a downstream portion of the first throttle valve 9 in the first intake passage 8 to the actuator 13 is provided and a three-way solenoid valve 20 and a delay valve 21 are provided within the pressure transmitting passage 19. The three-way solenoid valve 20 is controlled by a control circuit 22. This control circuit 22 controls the three-way solenoid valve based upon a signal representing the opening of the first throttle valve 9 detected by a throttle opening sensor 23 as follows: When an ON signal is input to the three-way solenoid valve 22, the three-way solenoid valve 22 is driven so that the pressure transmitting passage 19 is communicated with the actuator 18 and when an OFF signal is input, it operates so that the communication between the pressure transmitting passage 19 and the actuator 18 is cut off and that an atmospheric port 20a is communicated with the the actuator 18 to apply the atmospheric pressure onto the actuator 18 through a filter means 24. The actuator actuates so that when the negative pressure is applied from the pressure transmitting passage 19 thereto, the control valve 14 is fully opened as shown in Figure 4 and that when atmospheric pressure is applied thereto, the control valve is closed. The delay valve 21 provided between the actuator 13 and the three-way solenoid valve 20 delays said switching operation of the control valve 14 to prevent the driving condition from suddenly changing. As shown in Figure 5, the control valve 14 is fully opened under the low load driving condition where the opening of the first throttle valve 9 is not larger than the predetermined opening value X0 and it is closed under the condition where the opening of the first throttle valve 9 exceeds the predetermined opening value X0. Referring to Figure 4, when the control circuit 22 detects that the opening of the first throttle valve 9 has reached the predetermined opening value X0, it changes the signal to be input to the three-way solenoid valve 20 from ON to OFF and cuts off the negative pressure of intake air to shut the control valve 14. Provided, however, that the control valve 14 may be closed under the idling condition. The predetermined opening value X0 is determined based upon the output characteristics of the engine. More specifically, the predetermined opening value X0 is experimentalily determined as follows: The opening of the first throttle valve 9 is increased under the condition where the front engine section F and the rear engine section R are communicated with each other by the communicating passage 13 and a critical opening value at the time when the output of engine cannot be increased any more is set as the predetermined opening value X0. When the opening of the first throttle valve 9 exceeds said predetermined opening value X0, the control valve 14 is shut primarily in order to ensure the engine a sufficient amount of intake air. The relationship between the engine r.p.m. and the engine output torque characteristics in the above intake system is shown in Figure 6 as a function of the opening value X of the first throttle valve 9. In the intake system of this embodiment, the opening value X of the first throttle valve 9 is set slightly larger than that in the prior art system in which the communicating passage is not provided and the engine is operated under a lower intake pressure. Thus, the pumping losses under low load driving condition can be remarkably reduced while, nevertheless, the intake system can be controlled in a similar manner to that in the prior art system. In this embodiment, since there are formed the first intake ports 2f and 2r on the opposite faces of the intermediate housing 1 and there are formed the second intake ports 5f and 5r on the inner walls 3i and 4i of the side housings 3 and 4, each facing the intermediate housing 1, the mixture flowing into the working chamber 12f or 12r from the other 12r or 12f is prevented from directly entering into the first ramiform intake passage 8f or 8r during the period that the communicating passage 13 communicates the working chambers 12f and 12r with each other under the low load driving condition. On the other hand, since the second intake ports 5f and 5r are closed under the low load driving condition, they can be located so as to face the front side and rear side opening 13f and 13r of the communicating passage 13 and that is advantageous from the point of the layout of respective means. Figure 7 shows an engine including an intake system which is an embodiment of the present invention and further a fuel feeding system. Fuel injection nozzles 25 are usually provided for each of the first intake ports 2f and 2r to feed required fuel over the whole range of driving conditions, but, in this embodiment, a third fuel injection nozzle 26 is provided in the vicinity of the center portion of the communicating passage 13 to feed fuel into the communicating passage 13 during the control valve 14 is opened. In other words, the opening of the first throttle valve 9 is not larger than the predetermined opening value X0. Therefore, during this period, the third fuel injection nozzle 26 feeds fuel in place of the fuel injection nozzles 25 provided for the first intake ports 2f and 2r. In this embodiment, since the flow rate of the mixture gas of fuel and intake air within the communicating passage 13 is larger than that at the first intake ports 2f and 2r under the low load condition where the control valve 14 is opened, it is possible to improve the vaporization and atomization of fuel by injecting fuel into the communicating passage 13 at the timing when the communicating passage 13 communicates the front rotor housing 7f and the rear rotor housing 7r. Further, since the fuel injection nozzle 26 is provided nearer to an ignition plug (not shown) than the fuel injection nozzles 25 and the distance for transferring fuel becomes shorter, the amount of fuel remaining on the inner wall of the working chambers 12f and 12r, especially the amount of unburned fuel remaining in the end zone at the trailing side can be reduced and, as a result, emmissions of hydrocarbons can be reduced. In Figure 7, the second intake system is omitted for simplicity and the basic arrangements of the rotary piston engine are similar to those of the previous embodiment as shown in Figure 1 so that corresponding parts are designated by the same reference numerals as in the previous embodiment. Figure 8 shows a example of the structure of the fuel injection nozzle 26 to be provided within the communicating passage 13. As shown in Figure 8, there is provided a block 27 having a hole portion 13' for forming a part of the communicating passage 13 at a lower portion thereof and the fuel injection nozzle 26 is fixed so as to face the hole portion 13' in said block 27. Then, the block 27 is fixed in a cavity 28 provided for the intermediate housing 1. The block 27 and the cavity 28 are sealed by two O-rings 29 and the fuel injection nozzle 26 and the block 27 are sealed by O-rings 30. As described above, in accordance with the present invention, since the communicating passage is closed so that there remains a larger amount of intake air than the minimum required amount of intake air in the working chamber and the amount of intake air is controlled by the throttle valve, it is possible to obtain a rotary piston engine capable of reducing the pumping loss remarkably and desirably controlling the amount of intake air in accordance with the engine driving condition without controlling the opening of the control valve located within the communicating passage closely and accurately. Changes and modifications may be made without departing from the scope of the appended claims. For example, although, as described in the above embodiment, the present invention is preferably applied to a two-rotor type rotary piston engine, the present invention can be applied to other types of rotary piston engines such as a three-rotor type rotary piston engine. Further, a rotary valve can be employed for the control valve in place of the butterfly valve.

Claims: An intake system in a rotary piston engine (E) comprising a plurality of engine sections (F, R), each section having a rotor (6f, 6r) in a corresponding working chamber (12f, 12r) and at least one intake port (2f, 2r, 5f, 5r) communicating with intake passage means (8f, 8r, 10f, 10r), each of said sections (F, R) being separated by intermediate housing means (1), the engine (E) further comprising communicating passage means (13) between said sections (F, R) which transfer intake air according to the rotor phase difference between said sections (F, R), said communicating passage means (13) being connected with each working chamber (12f, 12r) by openings (13f, 13r) which are opened and closed by the respective rotor (6f, 6r) so as to be closed at a timing after the respective intake port (2r, 2f, 5r, 5f) has been closed, and the engine (E) comprising throttle valve means (9, 11) which are located in said intake passage means (8f, 8r, 10f, 10r) for controlling the amount of intake air characterized in that each opening (13f, 13r) connecting said communicating passage means (13) with a working chamber (12f, 12r) is positioned at a preselected position, said position being determined so that when the opening (13f, 13r) is closed by the respective rotor (6f, 6r) under lowest load driving condition the remaining amount of intake air in the respective working chamber (12f, 12r) is larger than the amount required under this condition. An intake system in accordance with Claim 1 in which said communicating passage means (13) is provided in the intermediate housing means (1). An intake system in accordance with Claim 1 or 2 which further includes control valve means (14) provided in the communicating passage means (13) for controlling the opening thereof. An intake system in accordance with Claim 3 in which the opening of said control valve means (14) is controlled according to the engine load to be opened under the low load and to be closed under the heavy load driving condition. An intake system in accordance with Claim 4 in which said control valve means (14) is further controlled to be closed under idling condition. An intake system in accordance with at least one of the Claims 1 to 5 in which the required amount of intake air is the amount required under idling condition where the throttle valve means (9, 11) is fully opened. An intake system in accordance with at least one of the Claims 1 to 6 which further includes fuel feeding means (26) provided in the communicating passage means (13). An intake system in accordance with at least one of the Claims 1 or 3 to 7 and Claim 2 which includes two engine sections (F, R) each being attached with a side housing (3, 4) whereas in each section (F, R) an opening (13f, 13r) of said communicating passage means (13) is located at the preselected position so that each opening is closed with the same time delay after the closing of the corresponding intake port (2f, 2r, 5f, 5r). An intake system in accordance with Claim 8 in which in each section (F, R) a first intake port (2f, 2r) is formed on the face (1f, 1r) of the intermediate housing (1) and a second intake port (5f, 5r) is formed on the inner wall (3i, 4i) of the side housing (3, 4) and controlled to be closed under the low load driving condition.

Inventors: KARIYAMA, SISO, NAGAO, AKIHITO, YOSHIOKA, SADASHICHI
Applicants: MAZDA MOTOR CORPORATION
Application year: 1986
Main classification: F02B53
IPC codes: F02B53, F02B1