JPH04241741A - Two/cycle engine - Google Patents

Abstract

PURPOSE:To arrange a balancer shaft by utilizing dead space, generated about a crankcase, so as to contrive compactness or the like of an engine by arranging the balancer shaft, which is rotated associated with a crankshaft to negate vibration of the engine, below the crankcase. CONSTITUTION:A crankshaft 5 is provided with a balance weight 15. A bottom surface of a crank chamber 4 for containing the balance weight 15 is approximate to a rotational locus of the balance weight 15. Further, a flywheel 19 is mounted to the other end of the crankshaft 5, and further a transmission case for covering the flywheel 19 is mounted to a rear plate 20. Here, a balancer chamber 33, overhung downward, is integrally formed in a lower case 3b of a crankcase 2 to contain a balancer shaft 36 in the inside of this balancer chamber. A balance weight 37 is mounted to the balancer shaft 36 and also connecting the balancer shaft associated with the crankshaft 5 through a timing belt 41 thus rotated at an equal speed in a reverse direction.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-stroke engine having a balancer shaft built into the crankcase for canceling engine vibrations.

0002

2. Description of the Related Art It is known that the source of vibration in an engine is the inertial force of the reciprocating parts generated when the pistons and connecting rods reciprocate. For this reason, in a normal engine, a balance weight is attached to the opposite side of the crankshaft from the crank pin, and the centrifugal force of this balance weight disperses the inertia force of the reciprocating part laterally, thereby reducing engine vibration. is being carried out.

However, although this method can disperse vibrations, lateral vibrations are newly generated due to the centrifugal force of the balance weight. For this reason, conventional engines have been designed to cancel out the lateral vibrations by arranging a balancer shaft around the crankshaft and having a weight of the same weight as the balance weight, and rotating this balancer shaft in the opposite direction to the crankshaft. Are known.

0004

By the way, in a four-stroke engine that has an oil pan at the bottom of the crankcase, the balancer shaft is placed on the side of the cylinder and crankcase to avoid interference with the oil pan. In many cases, this balancer shaft is driven by a timing belt stretched between it and the crankshaft. However, even in a 2-stroke engine that does not have intake/exhaust valves or an oil pan like a 4-stroke engine, if the balancer shaft is placed on the side of the cylinder, there will be a space to pass the balancer shaft around the cylinder.
Since it is necessary to provide a bearing portion to support the balancer shaft, the area around the cylinder and crankcase bulges out to the side.

[0005] This prevents the engine from becoming more compact, which is one of the characteristics of two-cycle engines, and also prevents various engine auxiliary equipment such as the alternator and power steering oil pump from being installed around the cylinder and crankcase. There is a problem where it is not possible to secure enough space to place the .

The present invention was made based on the above circumstances, and it is possible to arrange the balancer shaft by utilizing the dead space created around the crankcase, thereby increasing space efficiency and making it possible to make the engine more compact. ,
The purpose is to provide a two-stroke engine that can ensure sufficient minimum ground clearance.

[0007]

[Means for Solving the Problems] Therefore, in the present invention, the bottom surface of the crankcase is brought close to the rotation locus of the balance weight of the crankshaft, and a large diameter In a two-stroke engine, a transmission case is connected to the end face of the crankcase from which the crankshaft projects, and the transmission case covers the flywheel and extends below the bottom surface of the crankcase. It features a balancer shaft located below that rotates in conjunction with the crankshaft to cancel out engine vibrations.

[0008]

[Function] According to this configuration, the two-stroke engine does not have a downwardly protruding member such as an oil pan at the bottom of the crankcase, the dimension from the crankshaft to the bottom of the crankcase is short, and the crankcase Since the transmission case protrudes below the bottom surface of the crankcase, a space corresponding to the amount of protrusion of the transmission case is created between the end surface of the transmission case and the bottom surface of the crankcase. Therefore, the balancer shaft can be accommodated in this space, and the balancer shaft can be arranged easily by utilizing the dead space around the crankcase.

Moreover, since the distance from the crankshaft to the bottom of the crankcase is short, if the height of the crankshaft from the ground is the same as a 4-stroke engine, the balancer shaft should be placed below the crankcase. However, the position of this balancer shaft does not become extremely low, and the minimum ground clearance of the engine can be ensured sufficiently.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on an embodiment shown in the drawings.

In FIG. 1, reference numeral 1 indicates a two-stroke three-cylinder engine mounted in the engine room of an automobile, for example. The crankcase 2 of this engine 1 is
It is divided into two parts, an upper case 3a and a lower case 3b, and a crank chamber 4 is formed between these two cases 3a and 3b. A crankshaft 5 is housed inside the crank chamber 4, and the bottom surface of the crank chamber 4 is connected to the lower case 3b.
It is made up of.

A cylinder block 6 is integrally formed on the upper surface of the upper case 3a and stands upright at an angle close to that of the upper case 3a. Inside the cylinder block 6, as shown in FIG. 2, three cylinders 8 are provided side by side in the axial direction of the crankshaft 5. These cylinders 8 are connected to the crankcase 2
It is connected to the crank chamber 4 inside. The crank chamber 4 is partitioned into cylinders 8 by a partition wall 9, and a journal portion 10 of the crankshaft 5 is rotatably supported by the partition wall 9 via a bearing 11. The crank pin 12 of the crankshaft 5 is connected to a piston 14 in each cylinder 8 via a connecting rod 13, and the reciprocating motion of the piston 14 causes the crankshaft 5 to rotate in the clockwise direction indicated by the arrow in the figure. It has become. Further, the crankshaft 5 includes a balance weight 15 that projects on the opposite side from the crank pin 12. The balance weight 15 is housed in the crank chamber 4, and the bottom surface of the crank chamber 4 is
It is close to the rotation locus X of the balance weight 15. Therefore, the lower case 3b, which serves as the bottom surface of the crank chamber 4, is formed in a substantially arc shape along the rotation locus of the balance weight 15.

One end of the crankshaft 5 is connected to the crankcase 2.
The first and second drive pulleys 17, 18 are attached to the leading end of the drive pulley. Further, the other end of the crankshaft 5 passes through the rear surface of the crankcase 2 and is led out. A large-diameter flywheel 19 is attached to the other end of the crankshaft 5, and the flywheel 19 projects below the bottom surface of the crankcase 2. As shown in FIG. 1, a rear plate 20 is attached to the rear surface of the crankcase 2 and the cylinder block 6 and extends radially outward from the flywheel 19. A transmission case 21 that covers the flywheel 19 is butted against the rear plate 20 from the rear and is fastened and fixed with bolts. This transmission case 21 protrudes below the bottom surface of the crankcase 2 by a distance L.

An exhaust port 23 and a scavenging port 24 are opened on the inner surface of the cylinder 8 and are opened and closed by the piston 14, and the scavenging port 24 is connected to the crank chamber 4. Further, three intake ports 25 are provided on the side surface of the crankcase 2 and are arranged axially in the axial direction of the crankshaft 5 . The intake port 25 is provided across the mating surface of the upper case 3a and the lower case 3b, and is led out substantially horizontally from the side surface of the crankcase 2 along a direction intersecting the crankshaft 5. The downstream end of each intake port 25 opens directly into the crank chamber 4, and the crank chamber 4 serves as a primary compression chamber for compressing intake air.

An intake manifold 26 is connected to the intake port 25 of the crankcase 2 . The intake manifold 26 has three intake pipes 27 connected to the open end of the intake port 25.
It is equipped with The upstream ends of the intake pipes 27 are joined to each other, and a throttle body 29 housing a throttle valve (not shown) is connected to this joining part 28 . Note that the intake port 25 is provided with a reed valve 30 that only allows intake air to flow from the intake pipe 27 toward the crank chamber 4 .

Lower case 3b constituting crankcase 2
A balancer chamber 33 projecting downward is integrally formed on the bottom surface of the balancer chamber 33 . The balancer chamber 33 includes a housing portion 33a that protrudes downward from the bottom surface of the lower case 3b, and a cover 33b that closes the lower end opening of the housing portion 33a. It is divided into 4. The balancer chamber 33 is located in a space 35 surrounded by the bottom surface of the crankcase 2 and the end surface of the rear plate 20.
It protrudes below the balancer chamber 33. A balancer shaft 36 is housed within the balancer chamber 33. The balancer shaft 36 includes a balance weight 37 for canceling the primary vibration of the engine 1. The balancer shaft 36 is located parallel to the crankshaft 5 and directly below the crankshaft 5, and both ends of the balancer shaft 36 are connected to the lower end via shield bearings 38 filled with lubricant. It is rotatably supported by the case 3b. One end of the balancer shaft 36 passes through the front surface of the crankcase 2 and is led out, and a pulley 39 is attached to this leading end. A timing belt 41 is stretched between this pulley 39 and a timing pulley 40 attached to one end of the crankshaft 5, and the balancer shaft 36 is connected to the crankshaft 5 via this timing belt 41.
It is designed to rotate at a constant speed in the opposite direction. Note that a tension roller 42 and an idle roller 43 are provided on the travel path of the timing belt 41.

Further, a cylinder head 45 is attached to the upper surface of the cylinder block 6. A wedge-shaped combustion chamber 46 is formed on the surface of the cylinder head 45 that meets the cylinder 8.
A fuel injection device 47 that injects fuel into the combustion chamber 46 together with compressed air and a spark plug (not shown) are attached.

Around the crankcase 2 and cylinder block 6 of the engine 1, an air pump 50 and an alternating current generator are installed as engine auxiliary equipment driven by the crankshaft 5, and serve as a source of compressed air guided to the fuel injection device 47. In addition, an air conditioner compressor 52 and a power steering oil pump 53 are arranged. Of these engine auxiliary machines, the air pump 50 and the alternator 51 are arranged vertically in front of the intake manifold 26, and the compressor 52 and oil pump 53 are arranged in a manner that the cylinder block 6 is sandwiched between the intake manifold 26 and the air pump 50 and the alternator 51. They are arranged one above the other on the opposite side. These engine accessories 50, 51, 52, 5
3 includes drive shafts 54 that are parallel to the crankshaft 5, and pulleys 55 are attached to these drive shafts 54. A first belt 56a is stretched between the pulleys 55 of the air pump 50 and the alternator 51 and the first drive pulley 17 of the crankshaft 5, and a first belt 56a is stretched between the pulleys 55 of the air pump 50 and the alternator 51, and the first drive pulley 17 of the crankshaft 5. 55 and the second drive pulley 18 of the crankshaft 5, a second belt 56b is stretched, and the various engine auxiliary machines 50, 51, 52, 53 are driven simultaneously.

A tension roller 57 and an idle roller 58 are provided on the traveling path of the belt 56b, and these rollers 57 and 58 are supported by the cylinder block 6.

According to this configuration, the two-cycle engine 1 has the bottom surface of the crankcase 2 close to the rotation locus X of the balance weight 15 of the crankshaft 5, and the bottom surface of the crankcase 2 has a lower part such as an oil pan. Since there is no member protruding from the bottom of the crankcase 2 and the transmission case 21 protrudes downward from the bottom of the crankcase 2, there is no part of the transmission case 21 between the end of the transmission case 21 and the bottom of the crankcase 2. A space 35 corresponding to the amount of protrusion L is created. Therefore, the balancer shaft 36 can be accommodated in the space 35, and the balancer shaft 36 can be easily arranged using the dead space created below the crankcase 2.

Therefore, the space efficiency of the engine 1 can be increased, and the crankcase 2 and cylinder block 6 can be formed compactly.
Engine auxiliary equipment 50, 5 is installed around the cylinder block 6.
1, 52, and 53, and the degree of freedom in laying out the engine accessories 50, 51, 52, and 53 increases.

Moreover, since the engine 1 can be made compact, there is an advantage that when the engine 1 is mounted in the engine room of an automobile, no extra space is required in the engine room.

Furthermore, when the engine 1 is installed in the engine compartment of a car, the position of the crankshaft 5 from the ground is approximately the same height regardless of the engine type or displacement, so the above-mentioned If the bottom surface of the crankcase 2 is close to the rotation locus X of the balance weight 15 and the dimension from the crankshaft 5 to the bottom surface of the crankcase 2 is short as shown in FIG. However, the position of the balancer shaft 36 does not become extremely low. Therefore, a sufficient minimum ground clearance for the engine 1 can be ensured.

[0024] In the above embodiment, a two-stroke engine was explained in which the crank chamber was used as a primary compression chamber for intake air. The same method can be applied to a forced scavenging two-stroke engine in which the crank chamber is separated from the intake air supply path by connecting to a scavenging pump. In addition, balancer shafts are not limited to those driven by timing belts.
It may also be driven via a gear that meshes with the crankshaft.

Furthermore, the balancer shaft does not necessarily need to be placed directly below the crankshaft, but may be placed at any position within the space surrounded by the bottom surface of the crankcase and the end surface of the transmission case.

[0026]

[Effects of the Invention] According to the present invention described in detail above, the balancer shaft can be arranged easily by utilizing the dead space created below the crankcase, and the space efficiency of the engine is increased accordingly. The entire engine including the balancer shaft can be made compact. Therefore, sufficient space can be secured around the engine for arranging the engine auxiliary equipment, and the degree of freedom in laying out the engine auxiliary equipment is increased. Furthermore, even if the balancer shaft is disposed below the crankcase, the position of the balancer shaft does not become extremely low, so there is an advantage that a sufficient minimum ground clearance for the engine can be ensured.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a two-stroke engine incorporating a balancer shaft.

FIG. 2 is a sectional view of the two-stroke engine showing the drive path of the balancer shaft.

FIG. 3 is a side view showing the position of an engine auxiliary machine with respect to the engine and the running path of a belt that drives the engine auxiliary machine.

[Explanation of symbols]

1...2-stroke engine, 2...Crank case, 5...Crankshaft, 15...Balance weight, 19...Flywheel, 21...Transmission case, 36...Balancer shaft.

Claims (1)

[Claims] Claim 1: The bottom surface of the crankcase is brought close to the rotation locus of the balance weight of the crankshaft, and a large-diameter flywheel is provided at one end of the crankshaft protruding from the end surface of the crankcase. In a two-cycle engine, a transmission case is connected to the end surface of the protruding crankcase, and the transmission case covers the flywheel and protrudes below the bottom surface of the crankcase. A two-stroke engine characterized by having a balancer shaft arranged to cancel engine vibration.