JP2870654B2 - Parallel 2-cylinder 4-cycle engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention can reduce a torque fluctuation generated on a crankshaft by a reciprocating portion of two cylinders, reduce vibration caused by inertial force, and reduce the size. The present invention relates to a parallel two-cylinder, four-stroke engine that is also suitable for realization.

(Background of the Invention) In a parallel two-cylinder reciprocating engine, a piston,
The vibration is reduced by balancing the inertial forces of the reciprocating parts such as the connecting rod and crankshaft. For this reason, in a conventional two-cylinder engine, for example, in the case of a four-stroke engine, the phase difference between the crank angles of the respective cylinders is set to 180 ° or 360 °. In a two-cycle engine, the phase difference of the crank angle is set to 180 °.

However, it has been found that in the conventional engine in which the crank angle phase difference is set as described above, the torque fluctuation of the crankshaft becomes large particularly during high-speed operation. This torque fluctuation generates gear noise in a transmission system such as a transmission, and is also a major cause of increasing noise in the entire transmission system.

(Object of the Invention) The present invention has been made in view of such circumstances,
It is an object of the present invention to provide a parallel two-cylinder four-stroke engine which reduces torque fluctuation of a crankshaft, and in particular, reduces engine vibration at high speed to prevent noise.

(Constitution of the Invention) According to the present invention, an object of the present invention is to provide three cylinders arranged in parallel with each other, in which the phase difference between the crank angles of the two cylinders is set to approximately 90 degrees, and three flat cylinders located between the two cylinders and on both outer sides thereof are provided. A crankshaft that is supported by a main bearing consisting of a bearing, rotates in the opposite direction at the same speed as the crankshaft, and periodically enters between the crank webs of each cylinder to reduce the inertial force due to the reciprocating portion of each cylinder. One balance shaft having a counterweight to be balanced, a balance shaft driving gear provided at one end of the crankshaft and positioned outside an outer main bearing, and the crankshaft adjacent to the central main bearing. A parallel two-cylinder 4 comprising a timing chain driving sprocket and an engine output extracting gear provided on the opposite side of the balance shaft driving gear.
Achieved by a cycle engine.

(Principle) The principle of the present invention will now be described with reference to FIG.

The inertia force I of the reciprocating part in a single cylinder engine is
If the third or higher order inertial force is omitted, it is expressed by the following equation.

Here, W is the equivalent mass (Kg) replaced on the piston side of the piston 1 and the connecting rod 2, and ω is the crankshaft 3
Is the angular velocity (rad / sec), and ρ is the ratio r / l of the crank diameter r to the connecting rod length l.

Therefore, inertia torque τ ₁ generated on crankshaft 3 by this inertial force I is: Here, the first term and the third term in parentheses indicate that ρ is usually 0.31 to 0.
Since it is about 25, it is much smaller than the second term,
This can be omitted. Therefore, In the case of two cylinders, assuming that the crank angle of the other cylinder lags behind the above cylinder by the phase angle β, the inertia torque τ ₂ of this cylinder becomes Therefore, the total inertia torque τ _t is The phase difference β that minimizes the total inertia torque τ _t is At this time, the total inertia torque τ _t becomes substantially zero. From this, it is understood that the torque fluctuation of the crankshaft becomes almost zero if the crank angle of the two cylinders is π / 2 rad (radian), that is, the phase difference is about 90 °.

In the calculation of the inertia torque τ ₁ , some of the terms are omitted by utilizing the fact that ρ is small, and the calculation is simplified. However, the present invention performs a strict calculation without this omission. Needless to say, the phase angle β at which the total inertia torque τ _t becomes substantially zero may be obtained.

(Embodiment) FIG. 2 is a side sectional view of one embodiment of the present invention, and FIG.
It is a II-II line development sectional view.

In these figures, reference numeral 10 denotes a cylinder body, and 12 denotes a vertically split crankcase. The crankshaft 14 is rotatably held by three main bearings A, B, and C between the split surfaces of the crankcase 12. These main bearings A, B and C are formed of flat bearings as is clear from FIG. Here, crank pins 16 for two cylinders (16a, 16b)
Has a phase difference β that makes the total inertia torque τ _t obtained as a result of the above calculation substantially zero, that is, a phase difference of approximately 90 °. A timing chain driving sprocket 18 is formed at a position between the cylinders of the crankshaft 14, and a timing chain for driving an overhead cam shaft (not shown) is formed on the sprocket 18.
Twenty is wound. The camshaft opens and closes the intake valve 22 and the exhaust valve 24 at a predetermined timing. Pistons 26, (26a, 26b) of each cylinder are connected to connecting rods 28 (28
a, 28b) to each of the crank pins 16a, 16b. Reference numeral 30 (30a, 30b) denotes a spark plug whose ignition portion faces near the center of the combustion chamber. The crankshaft 14 is provided with a gear 32 for taking out output at a position between the two cylinders.

Numeral 34 denotes a balancer shaft, which is supported in parallel with and near the crankshaft 14. The balancer shaft 34 rotates in the opposite direction at the same speed as the crankshaft 14 by the balancer shaft driving gears 36 and 38. On the balancer shaft 34, counterweights 34a, 34b facing between the crank webs of the respective cylinders are integrally formed, and the inertial force due to the reciprocating portion of the piston 26 and the connecting rod 28
The weight and the mounting phase are set so as to cancel each other in cooperation with the crank webs W1, W2, W3, W4 provided in the above. Here, the counterweights 34a and 34b of the balancer shaft 34 periodically enter between the crank webs W1 and W2 and between W3 and W4 of each cylinder.
By bringing the balancer shaft 34 closer to the crankshaft 14, the size of the engine can be reduced.

Therefore, according to this embodiment, while the inertial force of the reciprocating portion is canceled by the crank web of the crankshaft 14 and the balancer shaft 34, the torque fluctuation generated on the crankshaft 14 due to this inertial force depends on the crank angle. It is reduced by setting the phase difference β to 90 degrees.

FIG. 4 is a graph showing the effect of this embodiment. For engines of various specifications in which the phase difference β and the ignition timing phase difference are different, the torque fluctuation of the crankshaft 14 is plotted on the vertical axis, and the crank angle Is shown on the horizontal axis. It should be noted that the data used in FIG.
That is, it is obtained at the fully closed position. The reason for using the data of η = 0 is that the throttle valve is fully open (η =
In the data of 1), the peak of the torque fluctuation due to the combustion pressure appears, whereas when η = 0 shown in the figure, the effect of the combustion pressure is hidden, and the effect of the inertial force of the moving part of the engine appears remarkably. This is because the effect of the present invention becomes clear.

Specifications A and B are for the embodiment according to the present invention, in which the crank angle phase difference β is 90 ° and the ignition timing is 90 ° and 450 °, respectively. Specifications C, D, E
Are the cases of the conventional engine in which the phase difference β of the crank angle is 180 ° and 360 °, respectively. From these results, the torque fluctuations in the specifications A and B according to the present invention are the same as those of the conventional engine. Significantly reduced compared to E,
This effect is particularly remarkable in a high speed range.

(Effect of the Invention) As described above, since the crank angle phase difference β of the two cylinders arranged in parallel is set to approximately 90 °,
The reciprocating portion can reduce the torque fluctuation generated on the crankshaft. For this reason, it is possible to satisfactorily reduce noise generated in the gears of the transmission system. Further, since the balancer shaft is provided, the vibration due to the inertial force is further reduced.

Since the balance weight of the balancer shaft periodically enters between the crank webs of the respective cylinders, the size of the engine can be reduced by bringing the balancer shaft closer to the crankshaft. Here, the crankshaft is supported by three main bearings from the main bearing, and a gear for the balancer shaft drive shaft is provided outside the main bearing at one end, and on the opposite side of the balancer shaft drive gear adjacent to the central main bearing. Since the engine output extracting gear and the timing chain driving sprocket are disposed, the two main bearings are sandwiched between the balancer shaft driving gear, the engine output extracting gear and the timing chain driving sprocket, The bending vibration of the crankshaft can be suppressed by reliably preventing the bending of the crankshaft.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view for explaining the principle of the present invention, FIG. 2 is a side sectional view of one embodiment of the present invention, FIG.
The figure is a diagram showing a torque fluctuation for showing the effect of the present invention. 14 ... Crank shaft, 18 ... Sprocket for driving the timing chain, 20 ... Timing chain, 26 ... Piston, 32 ... Gear for taking out engine output, 34 ... Balancer shaft, 36,38 ... Driver for balancer shaft Gear, A, B, C …… Main bearing, W1, W2, W3, W4 …… Crank web, β …… Crank angle phase difference,

Claims (1)

(57) [Claims] 1. A two-cylinder cylinder arranged in parallel has a crank angle phase difference of about 90 degrees and is supported by a main bearing consisting of three flat bearings located between and outside the two cylinders. A crankshaft and a counterweight that rotates in the opposite direction at the same speed as the crankshaft, periodically enters between the crank webs of each cylinder, and reduces the inertial force due to the reciprocating portion of each cylinder. A balance shaft, a balance shaft driving gear provided at one end of the crankshaft and located outside the outer main bearing,
A parallel two-cylinder four-stroke engine, comprising: a timing chain drive sprocket and an engine output take-out gear provided adjacent to the central main bearing on a side of the crankshaft opposite to the balance shaft drive gear.