Fuel injection features of a two-cycle engine for motorcycles

A fuel injection type two-cycle engine for motorcycles. A fuel injection valve for injecting fuel into an air intake passageway at a predetermined timing is disposed on the upstream side of a reed valve in the air intake passageway communicating with an interior of the engine via the reed valve, with the injection port thereof directed towards the reed valve. An air intake pipe forming the air intake passageway extends nearly in the vertical direction from the upper surface of a crank case at an middle position between a crank shaft extending in the widthwise direction of the vehicle body and a transmission shaft separated from the crank shaft in the back and forth direction and extending in the widthwise direction of the vehicle body, and a fuel injection valve protrudes from this air intake pipe in the back and forth direction. The air intake pipe and the fuel injection valve are positioned between left and right vehicle body frame members above the engine, and a partition plate is provided between the vehicle body frame members and the engine main body.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a fuel injection type two-cycle engine for 
motorcycles and a motorcycle loaded with this engine. 
2. Description of the Relevant Art 
In a reed valve type two-cycle engine, a thin-plate-shaped reed valve which 
opens as attracted towards the side of a crank chamber in accordance with 
a pressure difference between the inside and the outside of the crank 
chamber produced by a piston motion and closes due to its own resilient 
force when the pressure difference has been lowered, is disposed at a 
suction port portion provided at the crank chamber or a cylinder portion 
and communicated with an air intake passageway, so that air would be 
sucked into the engine when the reed valve opens. Fuel is fed into the 
sucked air within the air intake passageway, and an engine designed so as 
to perform this fuel feed by means of a fuel injection valve has been 
known, for instance, such an engine is disclosed in Laid-Open Japanese 
Patent Specification No. 58-98632. 
In this engine, an amount of sucked air is detected on the basis of a 
magnitude of variation of an inner pressure within a crank chamber, and 
depending upon this detected value, an injection signal having a 
predetermined time width is output from a control device consisting of a 
digital computer or the like to a fuel injection valve. When the 
above-mentioned injection signal is input, the fuel injection valve opens 
only during the time width and injects an appropriate amount of fuel into 
the air intake passageway. 
However, in the above-described fuel injection device in the prior art, 
since a jet port of the fuel injection port is directed towards the wall 
of the air intake passageway and the injected fuel is at first blown onto 
this wall, fuel would adhere onto the wall, hence mistification of fuel 
would be prevented, and waste of fuel was liable to occur. 
In general, an engine for a motorcycle is desired to have a small width in 
view of its relation to a vehicle body, and also, as it is equipped by 
effectively utilizing a narrow space around a vehicle body frame, it is 
necessary to pay special attention to ease of maintenance and cooling of 
the engine and air intake. 
SUMMARY OF THE INVENTION: 
One object of the present invention is to provide a fuel injection type 
two-cycle engine for motorcycles, wherein fuel injected from a fuel 
injection valve is surely fed to an engine in a mistified state, and hence 
waste of fuel would not occur. 
Another object of the present invention is to provide a fuel injection type 
two-cycle engine for motorcycles, wherein the width of the entire engine 
is narrow, and when it is loaded on a motorcycle, maintenance is easy and 
effective cooling can be carried out. 
According to the present invention, the above-mentioned first object is 
achieved by an engine wherein a fuel injection valve adapted to inject 
fuel into the afore-mentioned air intake passageway at a predetermined 
timing is disposed on the upstream side of the aforementioned reed valve 
in the air intake passageway with its injection port directed towards the 
aforementioned reed valve. 
According to the present invention, since the injection port of the fuel 
injection valve is directed towards the reed valve, if the fuel injection 
timing is matched with the timing of opening the reed valve, fuel can be 
directly injected from the fuel injection valve through the opened reed 
valve into the engine. Accordingly, the fuel injected from the fuel 
injection valve can be surely fed to the engine in a mistified state, and 
there occurs no waste of fuel. In addition, response of an engine to fuel 
injection is improved, and for instance, breathing phenomena caused by 
delay of fuel feed upon abrupt opening of a throttle can be effectively 
prevented. 
The above-described second object is achieved by an engine comprising a 
crank shaft extending within a crank case in the widthwise direction of a 
vehicle body, a transmission shaft extending within the crank case in the 
widthwise direction of the vehicle body as separated from the 
aforementioned crank shaft in the back and forth direction, an air intake 
pipe extending nearly in the vertical direction from the upper surface of 
the aforementioned crank case at a middle position between the 
above-mentioned crank shaft and the above-mentioned transmission shaft, 
and a fuel injection valve mounted to the aforementioned air intake pipe 
and extending in the back and forth direction from the air intake pipe. 
In the above-described engine, since the air intake pipe is provided as 
erected in the vertical direction behind a cylinder protruding from the 
crank case on the side of the crank shaft, and moreover, since the fuel 
injection valve mounted to this air intake pipe extends in the back and 
forth direction from the air intake pipe, the air intake pipe and the fuel 
injection valve would not project sideways from the cylinder and the crank 
case, hence as viewed from the above, they are accommodated within a 
contour of the crank case, and accordingly, the width of the entire engine 
would not be broadened by the existence of the air intake pipe and the 
fuel injection valve. 
Accordingly, this engine can be loaded on a motorcycle with the 
aforementioned air intake pipe and fuel injection valve extended through 
the space between vehicle body frames above the engine, and in this case, 
by providing a partition plate between the vehicle body frames and the 
engine, intake air can be prevented from being heated with heat generated 
by the engine, and also by guiding running wind from the front to the air 
intake pipe by means of this partition plate, the engine is made to suck 
low-temperature air and thereby a filling efficiency can be enhanced. In 
addition, since a fuel system including the fuel injection valve is 
disposed as concentrated at the location above the partition plate, 
maintenance is easy.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the following, the present invention will be explained in connection to 
one preferred embodiment illustrated in the accompanying drawings. 
FIG. 1 is a general side view of a motorcycle loaded with an engine 1 
according to the present invention. Main frame members 3 extend obliquely 
downwards and backwards from a head pipe 2 which supports a front wheel 51 
via a front fork 52 in a freely steerable manner, and at the rear end 
portions of these main frame members 3 is supported a rear wheel 54 via a 
rear fork 53 in a vertically swingable manner. And between a seat rail 55 
extending backwards from the middle portions of the main frame members 3 
and the rear fork 53 is provided a rear cushion 56. 
The engine 1 is loaded on a central lower portion of a vehicle body as 
suspended from the main frame members 3, and in front of the engine 1 is 
disposed a radiator 57. Above the engine 1 is disposed a fuel tank 16 as 
straddling the main frame members 3 and the seat rail 55 so as to cover 
the engine 1. Behind the fuel tank 16 is disposed a seat (not shown). FIG. 
2 is a longitudinal cross-section view of the fuel tank 16. 
FIG. 3 is a side view of the engine 1. The engine 1 is supported as 
suspended from a pair of left and right main frame members 3 having a 
rectangular cross-section and connected with each other via a cross pipe 
3a. The engine 1 is a fuel injection type two-cycle engine of V-shaped 
two-cylinder class, in which two cylinders 5 protrude from the front 
portion of a crank case 4 as arrayed with respect to each other in a 
V-shape and juxtapositioned in the widthwise direction of the vehicle 
body. Reference numeral 6 designates an exhaust pipe which extends to the 
rear of the vehicle body as shown in FIG. 1. Reference numeral 7 
designates an ignition plug, and numeral 8 designates a coolant water pipe 
connected to the radiator 57 (FIG. 1) disposed in front of the cylinder 5. 
Reference symbols 0.sub.1, 0.sub.2, 0.sub.3 and 0.sub.4 respectively 
designate a crank shaft, a transmission shaft, a transmission output shaft 
and a water pump shaft, and as seen from the figures, these shafts are 
directed in the widthwise direction of the vehicle body. The crank shaft 
0.sub.1 and the transmission shaft 0.sub.2 are disposed as separated from 
each other in the back and forth direction. The interior of the crank case 
is partitioned into two crank chambers respectively corresponding to the 
left and right cylinders 5,5 by means of a central partition wall, the 
respective crank chambers are respectively provided with air intake ports 
10, and air intake pipes 9 are respectively connected to these air intake 
ports 10 and extend upwards. The air intake ports 10 are provided on the 
upper surface (back surface) of the crank case 4 at a middle position 
between the crank shaft 0.sub.1 and the transmission shaft 0.sub.2, and 
accordingly, as shown in FIG. 4, the left and right air intake pipes 9,9 
extend nearly in the vertical direction at the positions behind the 
respective corresponding cylinders 5,5. The upper end of the air intake 
pipe 9 forms an air intake 11 opening between the left and right main 
frame members 3. In the middle portion of the air intake pipe 9 is 
provided a throttle valve 12, and the air intake pipe 9 forms a throttle 
body supported by the crank case 4. To each air intake pipe 9 are 
respectively mounted a fuel injection valve 14a projecting forwards and a 
fuel injection valve 14b projecting backwards. Since these fuel injection 
valves 14a and 14b project in the back and forth directions from the air 
intake pipe 9 as described above, they would not interfere with the left 
and right main frame members 3,3, and also they would not interfere with 
members such as a throttle pulley provided on the side of the air intake 
pipe 9 for the purpose of operating the throttle valve 12. 
On a side cover 4a covering a side portion of the crank case 4 is provided 
a fuel pump 15 which is interlocked with the crankshaft and mechanically 
driven by the crank shaft. Reference symbol 0.sub.5 designates a pump 
shaft of this fuel pump 15. Fuel within the fuel tank 16 disposed above 
the main frame members 3 is sucked through a cock 17 and a fuel suction 
pipe 18 into the fuel pump 15. Fuel delivered from the fuel pump is sent 
through a fuel delivery pipe 19 to a fuel feed pipe 20 made of metal. 
The fuel suction pipe 18 and the fuel delivery pipe 19 are disposed so as 
to pass the above of a clutch cover portion 25 formed on the side cover 4a 
of the crank case 4 as projected sideways in order to cover the clutch 
within the crank case 4, also an air vent valve 26 provided in the fuel 
pump 15 for the purpose of venting air within the fuel system is disposed 
at the front portion of the fuel pump 15 as directed forwards, and thus it 
is attempted to reduce the entire width of the engine 1 by eliminating 
members protruding sideways from the engine 1 as much as possible. 
As shown in FIGS. 4 and 5, the fuel feed pipe 20 is arranged in a U-shape 
so as to surround the left and right air intake pipes 9,9, and two 
connecting tubes 21a made of pressure-proof rubber hoses are branched from 
a front portion 20a of this fuel feed pipe 20 and connected respectively 
to the above-described fuel injection valves 14a on the front side of the 
left and right air intake pipes 9,9. From a rear portion 20b of the fuel 
feed pipe 20 are also branched two similar connecting tubes 21b, and they 
are respectively connected to the fuel injection valves 14b on the rear 
side of the air intake pipes 9,9. In addition, the fuel feed pipe 20 is 
provided with a pressure regulating valve 22, and by returning surplus 
fuel to the fuel tank 16 through a return tube 23 connected to this 
pressure regulating valve 22, a fuel pressure within the fuel feed pipe 20 
would be maintained constant. As shown in FIG. 2, the return tube 23 rises 
within the fuel tank 16, so as to eject the return fuel from the top of 
the tube and a cylinder 59 having a communication hole 58 at its lower 
portion is disposed around the return tube 23, and thereby bubbling of 
fuel within the fuel tank 16 is prevented. 
The fuel injection valve 14 contains therein electromagnetic 
opening/closing means 24 consisting of an electromagnetic solenoid or the 
like, and the fuel sent through the connecting tube 21 to the fuel 
injection valve 14 is injected from the fuel injection valve 14 into the 
air intake pipe 9 only when the electromagnetic opening/closing means is 
actuated to open the fuel injection valve 14. An electric signal is input 
to the electromagnetic opening/closing means 24 through an electric wire 
27 and the electromagnetic opening/closing means 24 is actuated by this 
electric signal. The electric signal is controlled by an electronic 
control device in such manner that the electric signal may be input only 
at the timing when the reed valve 28 provided at the above-described air 
intake port 10 is opening and it may be sustained only during a period 
corresponding to a desired fuel feed amount at that time. Accordingly, 
when the reed valve 28 opens, fuel of the amount corresponding to the 
desired fuel feed amount is injected from the fuel injection valve 14, and 
efficient engine operation can be effected. 
The above-mentioned electronic control device is well-known one consisting 
of an electronic circuit including a microcomputer and its interfaces, and 
its principal portion is assembled as a control unit (ECU) 60. To the 
control unit 60 are input signals sent from a throttle angle sensor, an 
engine rotational speed sensor, a crank angle sensor and the like disposed 
at the respective portions of the engine 1, and the control unit 60 
processes these input signals by means of a microcomputer and sends the 
above-mentioned control signal to the fuel injection valve 14. 
The control unit 60 is provided at the front end upper portion of the fuel 
tank 16 as shown in FIGS. 1 and 2. 
More particularly, at the front end of the upper surface of the fuel tank 
16 is formed a recessed portion of the shape conformed to the contour of 
the control unit 60, that is, a control unit loading section 61, and the 
control unit 60 is loaded on the loading section 61 via a cushion member. 
It is to be noted that the fuel tank 16 itself is also mounted to the 
vehicle body frame via a cushion member such as a rubber mount 62 or the 
like. The control unit 60 is firmly fixed on the control unit loading 
section 61 by means of a fastening band 63, and further the top of the 
control unit 60 is covered by an openable cover member 64. 
It is to be noted that in the illustrated embodiment, since each air intake 
pipe 9 is provided with two front and rear fuel injection valves 14a and 
14b, control is effected in such manner that upon low rotational speed low 
output operation, fuel may be injected only from, for instance, the front 
fuel injection valve 14a, and when it becomes a high rotational speed high 
output condition, the rear fuel injection valves 14b also may be opened 
and fuel may be injected from the two fuel injection valves 14a and 14b. 
If such provision is made, a fuel feed amount can be regulated over a 
broad range in accordance with an operating condition of the engine. 
As shown in FIG. 3, between the main frame member 3 and the engine 1 is 
provided a partition plate 29, and this partition plate 29 extends 
forwards so as to cover the top of the cylinder 5 and the radiator 57 
disposed in front of the cylinder 5. And the air intake pipe 9 extends 
upwards penetrating through this partition plate 29, and jointly with the 
fuel injection valves 14a and 14b it is positioned between the left and 
right main frame members 3. 
Accordingly, as the heat radiated from the cylinder 5 and the radiator 57 
and the air heated by the heat are intercepted by the partition plate 29, 
the air intake pipe 9, the fuel injection valves 14 and the fuel system 
connected to the fuel injection valves 14 can be maintained at a low 
temperature. Furthermore, at the above of the partition plate 29, running 
wind .omega. is introduced through an opening provided appropriately in 
the front portion, the running wind .omega. reaches the neighborhood of 
the air intake pipe 9 as guided by the partition plate 29 and the main 
frame members 3 and cools this portion, and also the air is sucked into 
the engine through the air intake 11. Since low-temperature air can be fed 
in this way, a filling efficiency is improved, and further since the rear 
portion 29a of the partition plate 29 rises so as to block the rear of the 
air intake pipe 9, a dynamic pressure of air is produced in the proximity 
of the air intake 11 by this partition plate portion 29a, and owing to 
this dynamic pressure also, the filling efficiency is improved. 
In addition, as the fuel system consisting of the fuel injection valves 14, 
the connecting tubes 21, the fuel feed pipe 20, the pressure regulating 
valve 22 and the like is provided as concentrated at the above of the 
partition plate 29, maintenance is easy. 
As shown in FIG. 6, the air intake pipe 9 forming an air intake passageway 
9a is mounted to an air intake port 10 via a rubber member 67 which is 
fixed to the outer circumferential surface of the air intake pipe 9 as 
fastened by means of a band 66. An injection port 65 of the fuel injection 
valve 14 faces the air intake passageway 9a at a middle position between 
the above-described throttle valve 12 and a reed valve 28, and the 
injection port 65 is directed towards the reed valve 28. More 
particularly, the axis of the injection port 65 inclines largely with 
respect to the axis of the air intake passageway 9a, and fuel .function. 
injected in a circular cone shape from the injection port 65, at least a 
most part thereof, would directly reach the reed valve 28 without striking 
against the wall of the air intake passageway 9a. 
The reed valve 28 is a valve having a conventional structure, in which thin 
plate-shaped reeds 28f having resiliency are openably attached onto the 
both upper and lower surfaces of a support frame 28a of triangular shape 
as shown in FIG. 7, and when a pressure within a crank chamber has been 
lowered, the reeds 28b are sucked towards the side of the crank chamber 
and open as shown in FIG. 8, and hence the air within the air intake 
passageway 9a is sucked through an aperture section 28c into the crank 
chamber. 
As described above, when the reed valve 28 has opened, fuel of the amount 
corresponding to a desired feed amount is injected from the injection port 
65, and as shown by an arrow .function. in FIG. 8, this fuel is injected 
directly aiming at the aperture section 28c. Upon low speed rotation of 
the engine 1, only the front fuel injection valve 14a, for instance, feeds 
fuel, and as the rotational speed rises, the injection valve opening 
period becomes long. If the engine rotate at a further high speed, the 
rear fuel injection valve 14b would additionally feed fuel. Upon the 
highest output rotation, both injection valves would feed fuel at the 
largest rate. 
Thus, in the illustrated embodiment, since the fuel injected from the fuel 
injection valve 14 directly enters into the crank chamber through the 
aperture section 28c of the reed valve 28 rather than after it has once 
struck against the inner wall of the air intake passageway 9a it is 
carried into the crank chamber by an intake air flowing through the air 
intake passageway 9a as is the case with the prior art engine, the 
injected mistified fuel can be efficiently and surely fed to the engine. 
In addition, it would never occur that fuel stagnated within the intake air 
passageway 9a is blown back towards the air intake 11 by an inverse flow 
from the side of the crank chamber immediately before the reed valve 28 is 
closed. 
Furthermore, response of the engine to fuel feed is excellent, and 
breathing phenomena caused by delay of fuel when the throttle valve 12 has 
opened abruptly, can be effectively prevented. 
While two fuel injection valves 14a and 14b were provided for one air 
intake passageway in the illustrated embodiment, in the case where an air 
intake passageway is provided with a single fuel injection valve, 
preferably the axis of the fuel injection port is directed to the center 
of the reed valve.