JP2828397B2 - Decompression type engine brake device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a decompression type engine braking device.

[0002]

2. Description of the Related Art A decompression type engine brake device used for a large vehicle or the like displaces a rocking center of a rocker arm at the time of deceleration of a vehicle, and opens an exhaust valve slightly even in a compression and expansion strokes. It is designed to increase power.

[0003] The present applicant has already proposed, as Japanese Utility Model Application No. 4-69276, a method in which the exhaust valve is mainly compressed and compressed as shown in FIG. The valve is opened during the expansion and exhaust strokes, while it is closed mainly during the intake stroke.

Further, when decompression is not performed to move the rocker arm swing center away from the cam, the exhaust valve is opened mainly in the exhaust stroke, and is closed mainly in the intake, compression and expansion strokes.

As shown in FIG. 8, the profile of a cam for opening and closing the exhaust valve is, as shown in FIG. 8, a first ramp portion 9d for seating the exhaust valve on the valve seat at a descending speed V when decompression is not activated, and an exhaust valve for decompression operation. Has a second ramp portion 9e for seating on the bulb seat at the same lowering speed V, and an inter-lamp communication portion 9f connecting the first and second ramp portions 9d, 9e.

The respective descending speeds V of the exhaust valves following the first and second ramp portions 9d and 9e are set so that the impact force when the exhaust valves are seated on the valve seats is suppressed to a predetermined value or less. As a result, the exhaust valve does not sit on the valve seat and does not bounce greatly, and the durability of the valve train is ensured.

[0007]

By the way, between the exhaust stroke and the intake stroke, there is a valve overlap period in which the exhaust valve and the intake valve are simultaneously opened. If the overlap period becomes longer, the work amount of the piston is reduced. The engine braking force is reduced. Therefore, there is a demand for reducing the valve overlap period as much as possible.

However, in such a conventional decompression type engine brake device, the profile of the cam is such that the first ramp portion 9d and the inter-ramp communication portion 9 are provided.
f, since the lowering speed V of the exhaust valve following the second ramp portion 9e is formed to be constant, there is a problem that the valve overlap period becomes longer and the engine braking force is weakened.

The present invention has been made in view of the above problems, and has as its object to increase engine braking force while ensuring sufficient durability of a valve train.

[0010]

According to the first aspect of the present invention,
Equipped with a rocker arm that opens and closes the exhaust valve following the cam, a mechanism that displaces the rocker arm's swing center with respect to the cam, and mainly compresses the exhaust valve during decompression operation that brings the rocker arm's swing center closer to the cam. A decompression engine brake that opens the exhaust valve mainly during the exhaust stroke and closes the intake valve mainly during the intake, compression, and expansion strokes when the decompression operation that moves the rocking arm of the expansion and exhaust row rocker arm away from the cam is not activated. in the device, the profile of the cam comprises a first ramp portion that is seated on the valve seat of the exhaust valve at a lowering speed V ₁ during decompression inoperative, is seated on the valve seat of the exhaust valve during decompression operation on the falling velocity V ₂ Connects the second ramp section with the first and second ramp sections In and a lamp intercellular communication unit is lowered by the lowering speed V _1, V ₂ higher lowering speed V _3, the maximum acceleration Ama exhaust valve to follow the contact portion between the lamp
x is a jump limit value A at which the exhaust valve follows the cam surface.
Set lower than limit.

[0011]

The descending speeds V ₁ and V ₂ of the exhaust valve following the first and second ramp portions are set so that the impact force when the exhaust valve is seated on the valve seat is suppressed to a predetermined value or less. As a result, the exhaust valve does not sit on the valve seat and does not bounce greatly, and the durability of the valve train is sufficiently ensured.

The descending speed V ₃ of the exhaust valve that follows the inter-lamp communication portion is set high within a range where the maximum acceleration Amax of the exhaust valve does not exceed the jump limit value Alim that the exhaust valve follows the cam surface. In addition, during the decompression operation, the valve overlap period during which the exhaust valve and the intake valve are simultaneously opened can be reduced without impairing the durability of the valve train.

By reducing the valve overlap period, the amount of air entering the cylinder via the exhaust valve during the intake stroke when the intake valve is opened is reduced, the work amount of the piston is increased, and the engine braking force is increased. .

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

In FIG. 3, reference numeral 1 denotes an exhaust valve of an engine, and reference numeral 2 denotes a cam which rotates in synchronization with a crankshaft. The valve lifter 3 reciprocates following the rotation of the cam 2.
The rocker arm 5 swings via the push rod 4 and the rocker arm 5 drives the exhaust valve 1 to open and close.

As shown in FIG. 4, the rocker shaft 6
Support shaft 6a supporting rocker arm 5 for exhaust valve
And a support shaft 6b for supporting the intake valve rocker arm
Having. As shown in FIG. 5, the exhaust valve support shaft 6
a is formed eccentrically about the central axis X of the rocker shaft 6.

The rocker shaft 6 is rotatably supported by the engine body and an actuator (not shown) for driving the rocker shaft 6 to rotate with respect to the engine body.
And a device for controlling the operation of the actuator in accordance with the operating conditions.

At the time of the decompression operation, the control device drives the rocker shaft 6 via the actuator to rotate as shown by the arrow in FIG.
Is lowered to lower the rocking center of the rocker arm 5 from Y to Z.

As shown in FIG. 7, the profile of the cam 2 includes a lift portion 2A for opening and closing the exhaust valve 1, a base circle portion 2B, and an under base for closing the exhaust valve 1 during an intake stroke when the vehicle is decelerated. It has a circle portion 2C.

FIG. 2 shows the lift characteristics of the exhaust valve 1 and the intake valve during the decompression operation. The exhaust valve 1 has a cam 2 during the compression and expansion strokes.
Is slightly opened by the base circle portion 2B, the valve is largely opened by the lift portion 2A of the cam 2 in the exhaust stroke, and is closed by the under base circle portion 2C of the cam 2 in the intake stroke.

As described above, when the exhaust valve 1 is slightly opened during the compression and expansion strokes, a predetermined amount of air flows in and out of the cylinder through the exhaust valve 1 with the reciprocation of the piston. The amount is increased and the engine braking power is increased.

When the exhaust valve 1 closes during the intake stroke, air enters the cylinder only through the intake valve as the piston descends, so that the work of the piston increases and the engine braking force increases.

However, between the exhaust stroke and the intake stroke,
There is a valve overlap period in which the exhaust valve 1 and the intake valve open at the same time. If the overlap period is long, the work of the piston is reduced, and the engine braking force is weakened. Therefore, there is a demand for reducing the valve overlap period as much as possible.

In response to this, the profile of the cam 2 is
As shown in FIG. 1, the valve seat 7 and the first lamp unit 2d seating the exhaust valve 1 at the time of decompression inoperative the valve seat 7 at a lowering speed V _1, the exhaust valve 1 at the time of decompression operation by lowering speed V ₂ It has a second ramp portion 2e for seating, and a first, second lamp section 2d, between lamps contact portion 2f for lowering by connecting 2e each lowering speed V _1, V ₂ higher lowering speed V ₃ in.

The lowering speeds V ₁ and V ₂ of the exhaust valve 1 following the first and second ramp portions 2d and 2e are such that the impact force when the exhaust valve 1 is seated on the valve seat 7 is suppressed to a predetermined value or less. It is set as follows. Thereby, the exhaust valve 1
Is not seated on the valve seat 7 and does not bounce greatly, and the durability of the valve train is sufficiently ensured.

The maximum acceleration Amax of the exhaust valve 1 following the inter-lamp communication portion 2f is set lower than the jump limit value Alim that the exhaust valve 1 follows the cam surface.
Here, the jump limit value Alimt is a limit value of acceleration at which the exhaust valve 1 does not follow the cam surface of the cam 2 and is obtained in advance by an experiment or the like.

The descending speed V ₃ of the exhaust valve 1 following the inter-lamp communication portion 2f is the maximum acceleration Ama of the exhaust valve 1.
x is set as high as possible within a range where x does not exceed the jump limit value Alimt.

As a result, the valve overlap period during which the exhaust valve 1 and the intake valve are simultaneously opened during the decompression operation without impairing the durability of the valve operating system is reduced, and the exhaust valve 1 is moved with the lowering of the piston. , The amount of air entering the cylinder is suppressed, the work amount of the piston is increased, and the engine braking force can be increased.

[0029]

As described above, the invention according to claim 1 includes a rocker arm that opens and closes an exhaust valve following a cam, and has a mechanism for displacing the rocking arm swing center with respect to the cam. During decompression operation, when the swing center is close to the cam, the exhaust valve is mainly opened during the compression, expansion, and exhaust strokes, while it is mainly closed during the intake stroke, and when the compression center that moves the rocker arm's swing center away from the cam is not operated. In a decompression type engine brake system in which the exhaust valve is mainly opened during the exhaust stroke, while the exhaust valve is mainly closed during the intake, compression and expansion strokes, the profile of the cam lowers the exhaust valve when decompression is not activated. a first ramp section to seat on the valve seat at a velocity V _1, Dekonpuresshi A second lamp unit to the exhaust valve when down operation at a descending speed V ₂ is seated on the valve seat, a first lamp is lowered by the second lamp connecting in each descending speed V ₁ of the section, V ₂ higher lowering speed V ₃ And the maximum acceleration Ama of the exhaust valve following the lamp-to-lamp communication part.
x is a jump limit value A at which the exhaust valve follows the cam surface.
Since the lower limit is set lower than the limit, the valve overlap period during the decompression operation can be shortened and the engine braking force can be increased while ensuring the durability of the valve operating system.

[Brief description of the drawings]

FIG. 1 is an enlarged view of a main part of a lift characteristic diagram of an exhaust valve according to an embodiment of the present invention.

FIG. 2 is a lift characteristic diagram of the intake and exhaust valves.

FIG. 3 is a configuration diagram of a valve train.

FIG. 4 is a plan view of the rocker shaft.

FIG. 5 is a view taken in the direction of the arrow A in FIG. 4;

FIG. 6 is an explanatory view of the operation of the rocker shaft.

FIG. 7 is a sectional view of the cam.

FIG. 8 is an enlarged view of a main part of a lift characteristic diagram of an exhaust valve showing a conventional example.

[Description of Signs] 1 Exhaust valve 2 Cam 2A Lift section 2B Base circle section 2C Under base circle section 2d First ramp section 2e Second ramp section 2f Inter-lamp communication section 5 Rocker arm 7 Valve seat

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F01L 13/06 F01L 1/08

Claims (1)

(57) [Claims] A rocker arm for opening and closing an exhaust valve following the cam; a mechanism for displacing a rocker arm swing center with respect to the cam; and a decompression operation for bringing the rocker arm swing center closer to the cam. While the valve is mainly opened during the compression, expansion, and exhaust strokes, the valve is mainly closed during the intake stroke, and the decompression operation that moves the rocker arm swing center away from the cam is not performed, while the exhaust valve is mainly opened during the exhaust stroke. primarily intake, compression, in decompression engine brake system where the structure is closed in the expansion stroke, profile of the cam, the first lamp unit which is seated on the valve seat of the exhaust valve during decompression inoperative by lowering speed V ₁ If, decompression operating lowering speed V ₂ knife the exhaust valve at the time of The second ramp portion to be seated on the lube seat and the first and second ramp portions are connected to each other to lower the speed V
_1, and a lamp intercellular communication unit is lowered at a high lowering speed V ₃ than V _2, the maximum acceleration Am of the exhaust valve to follow the contact portion between the lamp
ax is set lower than a jump limit value Alimt at which the exhaust valve follows the cam surface.