JPH04109424U - diesel engine - Google Patents

Abstract

(57) [Abstract] [Purpose] In a diesel engine in which a camshaft equipped with an intake and exhaust cam is driven by a timing chain, the interference between the exhaust valve and the piston due to the delay in valve opening/closing timing due to the elongation of the timing chain can be avoided. ,
Extends the usable engine of the timing chain and reduces maintenance costs for chain replacement. [Configuration] When the timing chain extends by a set amount, the lower end of the exhaust valve umbrella interferes with the top surface of the piston of a diesel engine in which a camshaft equipped with an intake and exhaust cam is driven by a timing chain. A dish-shaped recess that can be received without any problem is provided. Even if the timing chain stretches to the set limit due to long-term operation and the timing of the intake and exhaust valves is delayed, the lower end of the exhaust valve head is received within the recess and does not interfere with the piston, so the timing chain can no longer be used. It is possible to extend the possible period and reduce the maintenance cost of replacing the same chain.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

The present invention relates to a diesel engine.

0002

[Conventional technology]

The valve train camshaft that opens and closes the intake and exhaust valves is driven through a chain transmission. In a diesel engine that is driven in conjunction with the rank shaft, the engine The chain for driving the camshaft (hereinafter referred to as the chain in some cases) may become damaged due to long-term engine operation. The opening and closing timing of intake and exhaust valves is affected by the timing of the opening and closing of intake and exhaust valves. will be gradually delayed. On the other hand, in a diesel engine, the compression ratio is usually large and the piston reaches top dead center. When The gap is extremely small. This causes the timing chain to stretch beyond a certain limit and cause the intake valve to If the opening/closing timing of the exhaust valve is significantly delayed, the exhaust valve and piston may interfere with each other. There are problems with the exhaust valves being damaged and causing excessive noise. Now, this is shown by taking the crank angle θ or time on the horizontal axis and the valve lift on the vertical axis. To explain the valve lift diagram of FIG. 2, the curves Le and L indicated by solid lines in the diagram i is the exhaust valve lift and intake valve in the initial state when the timing chain is not stretched The curves le and li shown by dotted lines in the figure each indicate the lift, and the timing Exhaust valve lift and Furthermore, the curve P indicated by a dashed line in the figure indicates the piston It shows displacement. The shaded area A in the diagram is the delay in the opening and closing timing of the exhaust valve. indicates the area where the exhaust valve and piston interfere near the piston top dead center; The intake valve does not interfere with the piston due to the delay in opening and closing timing. This prevents interference between the exhaust valve and piston due to timing chain stretching as described above. To avoid this, it is necessary to replace the timing chain early. The service life of the chain is shortened, and therefore frequent chain replacement is required and maintenance work is reduced. There are problems such as increased business costs.

0003

[Problem that the idea aims to solve]

This invention eliminates the problem of the exhaust valve and piston caused by the timing chain stretching as described above. Extends the usable period of the timing chain by effectively avoiding interference with The purpose is to extend the chain replacement period and reduce maintenance costs. It is.

0004

[Means to solve the problem]

This invention was devised to achieve the above purpose, and it The valve train camshaft, which opens and closes, is connected to the engine crank via a chain transmission. In those driven in conjunction with a shaft, there is a piston on the top surface facing the exhaust valve, A dish-shaped recess is provided to accommodate the lower end of the exhaust valve without interfering with the umbrella. This paper proposes a diesel engine characterized by:

[0005]

[Effect]

According to the present invention, the lower end portion of the exhaust valve umbrella is provided on the top surface of the piston facing the exhaust valve. A dish-shaped recess is provided that can receive the timing check without interfering with the timing check. interference between the exhaust valve and the piston due to delays in valve opening/closing timing due to stretch of the valve. This can be effectively avoided, in other words, increasing the allowable amount of stretch of the timing chain. You can extend the usable period of the chain by setting

[0006]

【Example】

Embodiments of the present invention will be described in detail below with reference to FIGS. 1 and 3. Number 10 in the figure generally indicates an OHC type diesel engine for trucks, and 12 indicates a crankcase diesel engine. 14 is a cylinder head mounted on the upper end of the crankcase 12, and 16 is a cylinder head mounted on the upper end of the crankcase 12. It is a rocker cover. 18 is a crankshaft housed in the crankcase 12, and 20 is the same crankshaft. A crank gear 18 is fixed, and 22 is an idler that meshes with the crank gear 20. A gear 24 is located in front of a front plate 26 attached to the front end of the crankcase 12. The idler shaft 28 is fixed to one side, and the main idler shaft 28 is rotatably supported by the idler shaft 24. It is a dynamic sprocket vehicle, and the idler tooth is provided on the hub 30 of the sprocket vehicle 28. A wheel 22 is fitted onto the outside and fixed integrally. A plurality of cylinders 32 are formed within the crankcase 12, and each cylinder 32 has a A piston 34 is slidably fitted. The piston 34 is connected to the piston pin 36 and and the crank pin portion 40 of the crankshaft 18 via the connecting rod 38. is connected to. The cylinder head 14 also includes an intake port for each cylinder. An intake port 42 and an exhaust port 44 are provided, and these intake ports 42 and exhaust ports 44 and the cylinder 32 are connected through a mushroom-shaped intake valve 46 and an exhaust valve, respectively. Controlled by valve 48. The intake valve 46 and the exhaust valve 48 are each operated by a valve spring. It is always biased in the closing direction. Further, the valve stem of the intake valve 46 is connected to the intake valve 46 via the intake tappet 50 on the camshaft 52. Similarly, the valve stem of the exhaust valve 48 is connected to the cam 54 via the exhaust tappet 56. It is in contact with the exhaust cam 58 on the camshaft 52. The above camshaft 52 is A plurality of cam brackets 60 and bearing caps formed on the driver head 14 The camshaft 52 is rotatably supported by the camshaft 62, and the shaft end of the camshaft 52 is A driven sprocket wheel 66 is fixed by a bolt 64 extending in the direction and screwed together. There is a timing gap between the driving sprocket wheel 28 and the driven sprocket wheel 66. The chain 68 is wrapped. As shown in FIG. A fixed chain guide 70 is provided, and a chain guide 70 is provided along the running path on the other side of the chain 68. A tensioner 72 is provided. The tensioner 72 is connected to the It is pivoted to the front plate 26 or the crankcase 12 and has a built-in spring. It is always elastically pressed against the chain 68 by a pressing member 76. A shallow dish-shaped recess is formed on the top surface of the piston 34 in a portion facing the exhaust valve 48. 78 is provided, and the recess 78 is shaped to have a larger diameter than the outer diameter of the lower end portion of the umbrella of the exhaust valve 48. The depth of the timing chain 68 is determined by the timing chain 68 being When the exhaust valve 48 is extended to the set limit and the opening/closing timing of the exhaust valve 48 is delayed due to this extension. However, it is set so that it does not come into contact with the lower end surface of the exhaust valve umbrella.

[0007] In the above device, if the engine 10 is a four-stroke engine, the crank gear The number of teeth 20 is 1/2 of the number of teeth of the idler gear 22, and the number of teeth fixed to the idler gear 22 is The driven sprocket wheel 28 is fixed to the camshaft 52 and the driven sprocket is fixed to the camshaft 52. The cutting wheel 66 is formed to have the same diameter. Therefore, the rotation of the crankshaft 18 is , crankshaft 20, idler gear 22, main drive sprocket wheel 28, and main drive sprocket The signal is transmitted to the camshaft 52 via the clutch wheel 66, and the camshaft 52 is connected to the crankshaft 52. It rotates at 1/2 the rotation speed of the link shaft 18. The intake power is increased by the rotation of the camshaft 52. The cam 54 and the exhaust cam 58 push down the intake tappet 50 and the exhaust tappet 56, respectively. 2, the intake valve 46 and the exhaust valve 48 are arranged, for example, as shown in the valve lift diagram of FIG. It opens and closes in various ways. Due to long-term operation, the timing chain 68 gradually stretches, causing the intake valves 46 and Although the opening and closing timing of the exhaust valve 48 is delayed as shown by the dotted line in FIG. A recess 78 is recessed in the top surface of the tongue 34 in a portion facing the exhaust valve 48, The diameter of the recess is larger than the lower end portion of the umbrella portion of the exhaust valve 48, and the recess has a depth. , the exhaust valve 48 reaches its maximum open/close position due to the preset maximum elongation of the chain 68. Even if a timing delay occurs, the lower end of the exhaust valve head will not come into contact with the bottom of the recess. Since the engine 10 is formed to have the same size as the exhaust valve 48 and the piston 34, It can be operated safely for a long period of time without causing interference. As a result , the usable period of the timing chain 68 can be extended, and the chain This has the advantage of effectively reducing maintenance costs for engine replacement.

[0008]

[Effect of the idea]

As mentioned above, the diesel engine according to the present invention opens and closes the intake valve and the exhaust valve. The valve train camshaft is connected to the engine crankshaft via a chain transmission. In those that are driven by moving, the same exhaust valve is placed on the top surface of the piston facing the above exhaust valve. It has a dish-shaped recess that can receive the lower end of the valve head without interfering with it. This feature prevents exhaustion caused by timing chain elongation caused by long-term operation. Extends the usage life of the timing chain by reliably avoiding interference between the air valve and the piston. This has the advantage of increasing the length and reducing maintenance costs for chain replacement.

[Brief explanation of drawings]

FIG. 1 is a schematic front view, partially in cross section, showing an embodiment of the present invention.

FIG. 2 is a valve lift diagram of an intake valve and an exhaust valve in a diesel engine.

FIG. 3 is an enlarged cross-sectional view of essential parts of the engine according to the present invention.

[Explanation of symbols] 10 engine 12 Crank case 14 Cylinder head 18 crankshaft 20 crank gear 22 Idler gear 28 Main drive sprocket car 32 cylinder 34 Piston 46 Intake valve 48 Exhaust valve 52 Camshaft 66 Driven sprocket car 68 Timing chain 78 Recess

Claims (1)

[Scope of utility model registration request] 1. A valve-driving camshaft that opens and closes intake and exhaust valves is driven in conjunction with the crankshaft of the engine via a chain transmission device, in which a piston top face facing the exhaust valve is provided with: A diesel engine characterized by having a dish-shaped recess that can receive the lower end portion of the exhaust valve without interfering with the exhaust valve.