JP2001098913A - Compression pressure reliesing type engine brake - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compression pressure releasing type engine brake which can open an exhaust valve with optimum timing around the top dead center of compression stroke and the top dead center of intake stroke without the necessity of complicated oil passages. SOLUTION: This compression pressure releasing type engine brake is composed of a master piston 12 which is operated through the intermediately of a roller tappet 25 by an exclusive brake cam 24 added to a cam shaft 6 incorporating an intake cam and an exhaust cam, and operated around the top dead center of compression stroke and the top dead center of intake stroke, a slave piston 14 communicated with the master piston 12 through an oil passage 13 and adapted to open an exhaust valve when a hydraulic pressure is effected in the oil passage 13 through the operation of the master piston 12, and a solenoid valve 16 and a control valve 17 which serve as a hydraulic fluid supply means for selectively holding and releasing a hydraulic pressure in the oil passage 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compression-release type engine brake.

[0002]

2. Description of the Related Art Conventionally, large vehicles such as trucks and buses are originally heavy in weight and loaded with a load, so that a large inertia force acts upon deceleration, and a heavy load is imposed on a service brake device. .

Therefore, when braking is frequently performed on a downhill or the like, the engine brake is generally used together. However, when the loading load is large or the slope is steep, In some cases, sufficient engine braking effect may not be obtained.

[0004] For this reason, the exhaust valve is forcibly opened near the compression top dead center of the engine to release the compression pressure, thereby reducing the generation of the force for pushing down the piston in the next expansion stroke, thereby obtaining the compression stroke. In some cases, a compression-pressure-released engine brake, which effectively applies a braking force, is additionally provided.

FIG. 6 shows an example of the above-mentioned compression-release type engine brake, in which 1 is a cylinder, 2 is a combustion chamber,
3 indicates a piston, 4 indicates an exhaust valve, 5 indicates an exhaust flow path,
In the exhaust stroke, both exhaust valves 4 are pushed down through the crosshead 9 by the tip of the rocker arm 8 whose base end is pushed up via the roller 8a by the exhaust cam 7 mounted on the camshaft 6 via the roller 8a, and opened to operate. The exhaust gas 10 is scavenged from the chamber 2 to the exhaust passage 5.

When the two exhaust valves 4 are pushed down and opened by the tip of the rocker arm 8 via the crosshead 9, the base end of the rocker arm 8 is provided in the upper housing 11. Master piston 1
2 is raised to generate a pressure in an oil passage 13 formed in the housing 11 to cause a slave piston 14 above another cylinder 1 to follow the cylinder piston 1 and lower it. One of the exhaust valves 4 can be depressed by itself via the actuator pin 15 provided in the first embodiment.

In other words, the operation of the master piston 12 of another cylinder 1 in the exhaust stroke causes the slave piston 14 of the cylinder 1 near the compression top dead center to be driven, so that the cylinders 1 whose stroke timing matches each other are synchronized. The slave piston 14 and the master piston 12 are connected by an oil passage 13, and the oil passage 13 has a solenoid valve as a working oil supply unit for switching between holding and releasing the oil pressure of the oil passage 13. Hydraulic oil 18 (engine oil) is supplied via the control valve 16 and the control valve 17.

Here, the solenoid valve 16 controls the supply and supply of the hydraulic oil 18 according to a control signal 16 a from the control device 19.
The control valve 17 shuts off, and the control valve 17 functions as a check valve so that the oil pressure in the oil passage 13 is maintained when the solenoid valve 16 is open.
Is closed, the oil pressure in the oil passage 13 is reduced to the relief port 2.
It functions to open to zero.

In FIG. 1, reference numeral 21 denotes intake air, 22 denotes an intake passage, and 23 denotes a rocker shaft which rotatably supports a rocker arm 8 for taking in and exhausting air and forms a tilt axis of the rocker arm 8. .

[0010] In such a compression-pressure-release type engine brake, when the solenoid valve 16 is opened by the control signal 16a, the control valve 17 functions as a check valve and the oil passage 13 is closed. When each of the cylinders 1 approaches the pressure top dead center at a different timing, the master piston is moved through the rocker arm 8 by pushing up the exhaust cam 7 for opening the exhaust valve 4 of another cylinder 1 in the exhaust stroke. 12 is pushed up, pressure is generated in the oil passage 13 and the cylinder 1 near the compression top dead center
The slave piston 14 is driven to open one exhaust valve 4, and the compressed air is released from the combustion chamber 2 to the exhaust passage 5 to generate a force to push down the piston 3 in the next expansion stroke. As a result, the braking force obtained in the compression stroke is effectively used.

If the solenoid valve 16 is closed by the control signal 16a, the hydraulic pressure in the oil passage 13 is released by the control valve 17 and no pressure is generated in the oil passage 13, so that the slave piston 14 is not driven. The exhaust valve 4 is opened only in the exhaust stroke by a normal valve opening operation, and is not opened near the compression top dead center.

[0012]

However, in recent years, the exhaust valve 4 has been forcibly opened even near the bottom dead center of the intake air, and the air has flowed back into the cylinder 1 from the exhaust flow passage 5 side. It has been proposed to increase the amount of working gas (intake air amount + backflow air amount) taken into the cylinder 1 in the stroke and increase the compression work in the next compression stroke to enhance the braking force. If the exhaust valve 4 is forcibly opened even near the bottom dead center, another cylinder 1
It is necessary to actuate a new master piston 12 by the rocker arm 8 responsible for intake and exhaust of the oil to drive the slave piston 14 via the oil passage 13, and the oil passage 13, which is more complicated than before, must be formed. In addition, since the valve opening / closing timing of each cylinder 1 is uniquely determined, the exhaust valve 4 of each cylinder 1 is set near the intake bottom dead center and near the compression top dead center. There is also a problem that it is difficult to perform the opening operation at an optimal timing.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and enables an exhaust valve to be opened at an optimum timing near an intake bottom dead center and a compression top dead center without a complicated oil passage. It is an object of the present invention to provide an improved compression-release engine brake.

[0014]

SUMMARY OF THE INVENTION The present invention provides a brake-dedicated cam which is additionally provided on a camshaft provided with an intake cam and an exhaust cam, and which is driven by the brake-dedicated cam via a roller tappet and which is located near a bottom dead center of the intake port. A master piston that operates near the compression top dead center, a slave piston that is connected to the master piston via an oil passage, and that opens an exhaust valve when oil pressure is generated by the operation of the master piston in the oil passage; And a hydraulic oil supply means for switching between holding and releasing the oil pressure of the oil passage.

When the hydraulic pressure in the oil passage is held by the hydraulic oil supply means, the master piston is driven by the brake dedicated cam via the roller tappet to operate near the intake bottom dead center and near the compression top dead center. As a result, oil pressure is generated in the oil passage and the exhaust valve is opened by the slave piston, so that the exhaust valve is forcibly opened near the bottom dead center of the intake air to flow air back into the cylinder from the exhaust flow path side. As a result, the amount of working gas (intake air amount + backflow air amount) taken into the cylinder in the intake stroke is increased, and the compression work in the next compression stroke is increased to increase the braking force. The compression pressure is released by forcibly opening the exhaust valve in the vicinity of the top dead center as in the past, thereby reducing the generation of the force that pushes down the piston in the next expansion stroke and reducing the pressure. It is possible to effectively act the resulting braking force stroke.

Further, when opening the exhaust valve near the intake bottom dead center and the compression top dead center in this way, the optimal timing is individually set by the brake dedicated cam independently of the stroke of another cylinder. Since the exhaust valve is opened, it is not necessary to form a complicated oil passage.

Further, a brake-dedicated cam that operates the master piston near both the intake bottom dead center and the compression top dead center has two cam ridges that are continuous in the circumferential direction. Since the roller tappet is driven via the roller tappet, the roller of the roller tappet can be reliably driven along the valley between the two cam peaks.

When the hydraulic pressure in the oil passage is released by the hydraulic oil supply means when the engine brake is not operating,
Even when the master piston operates, no oil pressure is generated in the oil passage, so the slave piston is not driven, and the exhaust valve is opened only during the exhaust stroke by a normal valve opening operation. Open operation is stopped near the point.

Also, in the present invention, it is preferable to provide a throttle means for appropriately narrowing the exhaust flow path. In this case, the exhaust path is narrowed by the throttle means to increase the back pressure on the exhaust flow path side. By promoting the backflow of air into the cylinder when the exhaust valve is opened near the intake bottom dead center, it is possible to increase the compression work in the compression stroke and further increase the braking force. Become.

Here, it is preferable to employ a variable geometry turbocharger as the throttle means for appropriately narrowing the exhaust flow path. In this case, the opening degree of the nozzle vanes of the turbine is reduced to reduce the exhaust flow path side. Not only can it be possible to increase the back pressure, but also it is possible to increase the rotation speed of the exhaust gas in the turbine to increase the rotation speed of the turbine, thereby increasing the amount of intake air on the compressor side. The amount of working gas (intake air amount + backflow air amount) taken into the cylinder during the intake stroke is greatly increased by the synergistic effect of the increase in back pressure in the exhaust passage and the increase in supercharging in the intake passage. It becomes possible to further enhance the braking force obtained by the compression work in the stroke.

[0021] In addition, in the case of an engine having a variable geometry turbocharger as a turbocharger from the beginning, the variable geometries can be achieved without additional components such as a butterfly damper and a guillotine damper for narrowing the exhaust passage. It is only necessary to appropriately control the opening of the nozzle vane on the turbine side of the metrology turbocharger.

[0022]

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

FIGS. 1 to 4 show an example of an embodiment of the present invention, and the portions denoted by the same reference numerals as those in FIG. 6 represent the same components.

In this embodiment, as shown in FIG. 2, an intake cam 7 'for tilting a rocker arm 8 for opening the intake valve 4' during the intake stroke, and a rocker for opening the exhaust valve 4 '. For the camshaft 6 equipped with the exhaust cam 7 that inclines the arm 8 during the exhaust stroke, as shown in FIG. 1, a brake-dedicated cam 24 having two circumferentially continuous cam ridges is additionally provided. The master piston 12 is operated near the intake bottom dead center and near the compression top dead center via the roller tappet 25 by the brake dedicated cam 24.

Here, the roller tappet 25 illustrated in FIG. 1 is a lever whose base end is tiltably fitted to a rocker shaft 23 which is a tilting axis of the rocker arm 8 which takes in and exhausts. It has a structure, and comes into contact with a brake-dedicated cam 24 via a rollable roller 25a provided at a lower portion on the tip side thereof, and is pushed up by the brake-dedicated cam 24, thereby tilting around the rocker shaft 23. The master piston 12 is pushed up in the upper part on the tip side.

The slave piston 14 illustrated in FIG. 1 directly pushes down the upper end of the exhaust rocker arm 8 to open both exhaust valves 4 via the crosshead 9.

Further, in this embodiment, a variable geometry turbocharger 2 is used as the turbocharger.
6 (hereinafter abbreviated as VGT).
The intake air 21 is pressurized by the compressor 26a of T26, cooled by an intercooler (not shown), and then introduced into each cylinder 1 of the engine.

Here, the VGT 26 includes a turbine 26
The opening of the nozzle vane 27 can be adjusted by tilting the nozzle vane 27 of b by an actuator 28, and the actuator 28 is controlled by an opening command 28a from the control device 19. .

When, for example, the opening degree of the nozzle vane 27 is greatly increased with respect to a constant exhaust gas amount, the rotational speed of the exhaust gas 10 in the turbine 26b of the VGT 26 decreases, whereby the rotation speed of the turbine 26b decreases and the compressor 26a side In contrast, when the opening degree of the nozzle vanes 27 is reduced for a certain amount of exhaust gas, the rotational speed of the exhaust gas 10 in the turbine 26b of the VGT 26 increases, and thereby the rotation of the turbine 26b. As the number increases, the amount of intake air on the compressor 26a side increases.

In this embodiment, the actuator 29
Exhaust brake valve 3 that can be opened and closed by the
0 is provided in the exhaust flow path 5 downstream of the turbine 26b, and the exhaust brake valve 30 is closed by a control signal 30a from the control device 19 to compress the exhaust gas so that an exhaust brake can be obtained. I have.

When the solenoid valve 16 is opened according to the control signal 16a, the control valve 17 functions as a check valve to close the oil passage 13 and to close the oil passage 13.
Is held by the brake-dedicated cam 24 near the intake bottom dead center and near the compression top dead center.
5 is pushed up via a roller 25a and tilted, whereby the master piston 12 is pushed up to generate hydraulic pressure in the oil passage 13, and the slave piston 14 pushes down the tip end of the rocker arm 8 for exhaust, thereby causing the crosshead to move downward. The exhaust valve 4 is opened via 9.

That is, the opening operation of the exhaust valve 4 is shown mainly by solid curves A, B and C in FIG. 3 with the vertical axis representing the lift of the valve opening operation and the horizontal axis representing the rotation angle of the crankshaft. More specifically, the rotation angle of the crankshaft 0 ° to 180 ° is the explosion stroke, 180 ° to 360 ° is the exhaust stroke, 360 ° to 540 ° is the intake stroke, and 540 ° to 720 °. Since (0 °) indicates the compression stroke, respectively, the vicinity of the compression top dead center of 0 ° or 720 ° and
540 ° intake cam near the bottom dead center 24
Opening operation (curves A and C) of the relatively small lift is performed, and the opening of the relatively large lift exhaust valve 4 by the normal exhaust cam 7 is performed in the exhaust stroke from about 180 ° to about 360 °. The operation (curve B) takes place.

The dashed curve D in FIG.
The opening operation of the intake valve 4 'of a relatively large lift performed by the normal intake cam 7' in the intake stroke from about 0 ° to about 540 ° is shown.

In this manner, the exhaust valve 4 is forcibly opened near the bottom dead center of the intake air to cause the air to flow back into the cylinder 1 from the exhaust flow path 5 side, whereby the cylinder 1 is moved in the intake stroke. The amount of working gas taken into the air (the amount of intake air +
The amount of backflow air) is increased, the compression work in the next compression stroke is increased, and the braking force can be increased, and the exhaust valve 4 is forcibly opened around the top dead center in the compression stroke as before. By doing so, the compression pressure is released, whereby the generation of the force for pushing down the piston 3 in the next expansion stroke is reduced, and the braking force obtained in the compression stroke can be effectively applied.

Further, when the exhaust valve 4 is opened near the intake bottom dead center and the compression top dead center in this way, the optimal timing is individually set by the brake dedicated cam 24 independently of the stroke of another cylinder 1. Since the setting is made to open the exhaust valve 4, it is not necessary to form a complicated oil passage 13.

As is apparent from FIG. 3, since the compression top dead center (0 ° or 720 °) continues after half a rotation from the intake bottom dead center (540 °), the intake bottom dead center is obtained. The master piston 12 both near the point and near the compression top dead center.
1 has two circumferentially continuous cam ridges as shown in FIG. 1. However, since the master piston 12 is driven via the roller tappet 25, The roller 25a of the roller tappet 25 can be reliably driven to follow the valley between the two cam peaks.

When the engine brake is not operating, the solenoid valve 16 may be closed by the control signal 16a. In this case, the oil pressure in the oil passage 13 is released by the control valve 17 and the oil passage 13 Since no pressure is generated inside the slave piston 14
Is not driven, and the exhaust valve 4 is opened only in the exhaust stroke by a normal valve opening operation, and is not opened near the intake bottom dead center or the compression top dead center.

Therefore, according to the above embodiment, the formation of the complicated oil passage 13 can be dispensed with, so that the braking force can be greatly improved without incurring a rise in cost, and the exhaust gas can be exhausted. It is also possible to realize the opening operation of the valve 4 at an optimum timing near the intake bottom dead center and near the compression top dead center.

Further, since the master piston 12 is driven via the roller tappet 25 with respect to the brake-dedicated cam 24 which has two cam ridges continuous in the circumferential direction, exhaust is performed near the bottom dead center of the intake. After the valve 4 has been opened, the valve opening operation can be accurately performed as intended by closing the valve 4 and reopening it near the compression top dead center. By adopting this, the durability can be improved by alleviating it.

Further, in the present embodiment, the VGT 26 can be used as a throttle means for appropriately narrowing the exhaust passage 5, and the control device 19 operates when the engine brake is operated.
When the opening degree of the nozzle vane 27 of the turbine 26b is reduced by controlling the actuator 28 in accordance with the opening degree command 28a from the engine, the airflow resistance in the turbine 26b increases, the back pressure on the exhaust passage 5 side increases, and the vicinity of the intake bottom dead center As a result, the backflow of air into the cylinder 1 when the exhaust valve 4 is opened can be promoted, so that the compression work in the compression stroke can be increased and the braking force can be further increased.

Here, especially when the VGT 26 is used as the throttle means, the nozzle vanes 27 of the turbine 26b are used.
Not only can the back pressure on the exhaust flow path 5 side be increased by reducing the opening degree of the exhaust gas 10, but also the rotational speed of the exhaust gas 10 in the turbine 26b is increased to increase the rotational speed of the turbine 26b, thereby increasing the compressor 26a side. The amount of working gas taken into the cylinder 1 during the intake stroke by the synergistic effect of the increase in the back pressure on the exhaust passage 5 side and the increase in the supercharging on the intake passage 22 side (intake of (Air volume + backflow air volume) can be greatly increased,
In the next compression stroke, the braking force obtained by the compression work can be further enhanced.

Further, as in the present embodiment, with respect to an engine provided with the VGT 26 as a turbocharger from the beginning, it is not necessary to newly install extra parts such as a butterfly damper and a guillotine damper to narrow the exhaust passage 5. Vanes 2 of the turbine 26b of the VGT 26
The exhaust passage 5 can be appropriately narrowed only by appropriately controlling the opening of the nozzle 7, and the number of parts can be suppressed from increasing as much as possible, thereby avoiding an increase in equipment costs.

As a throttle means for appropriately narrowing the exhaust passage 5, an exhaust brake can be used instead of the VGT 26. When the engine brake is activated, the actuator 29 is controlled by a control signal 30a from the control device 19. Is controlled and the exhaust brake valve 30 is closed, the back pressure on the exhaust flow path 5 side rises and the exhaust valve 4 closes at the intake bottom dead center.
When the valve is opened, the backflow of air toward the inside of the cylinder 1 can be promoted. In this case, the compression work in the compression stroke can be increased and the braking force can be further increased. .

The combined use of such a restricting means makes it possible to use the exhaust passage 5
It is particularly effective in the low speed rotation region where the back pressure on the side is low,
As shown in FIG. 4, the braking force obtained by the operation of the normal compression pressure release type engine brake (only the opening operation of the exhaust valve 4 near the compression top dead center) is shown by a solid straight line x with respect to the engine speed. , The exhaust valve 4 even near the intake bottom dead center
Is opened, the braking force may be weakened in the low-speed rotation region as shown by the dashed straight line y. When the back pressure on the fifth side is increased, the braking force can be reliably increased even in the low-speed rotation region as indicated by the two-dot chain line z.

That is, in the low-speed rotation region where the back pressure on the exhaust passage 5 side is low, when the exhaust valve 4 is opened near the intake bottom dead center, air flows out of the cylinder 1 to the exhaust passage 5 side. This is because, in some cases, the amount of working gas (intake air amount + backflow air amount) taken into the cylinder 1 during the intake stroke cannot be increased as intended.

When the exhaust brake as described above is used in combination with the throttle means, it is mainly used in the low-speed rotation region in consideration of the fact that the back pressure on the exhaust passage 5 side is sufficiently increased in the high-speed rotation region. It is preferable to limit it to.

FIG. 5 shows another embodiment of the present invention.
A short rod-shaped roller tappet 31 is integrally formed below the master piston 12 in place of the roller tappet 25 having a lever structure in which the base end side is tiltably fitted to the rocker shaft 23 as shown in FIG. The roller tappet 31 is slidably held by a cylindrical guide portion 11a formed on the housing 11 side, and is brought into contact with a brake-dedicated cam 24 via a rollable roller 31a provided thereunder. It is configured to be pushed up by the brake dedicated cam 24. Even if such a roller tappet 31 is employed, the same operation and effect as those of the embodiment described with reference to FIGS. .

It should be noted that the compression-release engine brake of the present invention is not limited to the above-described embodiment, and the throttle means for appropriately narrowing the exhaust passage may include a variable geometry turbocharger or an exhaust brake. It goes without saying that various changes can be made without departing from the spirit of the present invention.

[0049]

According to the above-mentioned compression-release type engine brake of the present invention, various excellent effects as described below can be obtained.

(I) According to the first aspect of the present invention, the optimal timing is individually set by the brake-dedicated cam independently of the stroke of another cylinder, and the exhaust valve is set near the intake bottom dead center and Since the opening operation can be performed near the compression top dead center, it is not necessary to form a complicated oil passage, and the braking force can be significantly improved without incurring a rise in cost. The opening operation can be realized at an optimum timing near the dead center and near the compression top dead center.

(II) According to the first aspect of the present invention, the master piston is driven via the roller tappet with respect to the brake-dedicated cam having two cam ridges continuous in the circumferential direction. The opening of the exhaust valve near the bottom dead center of the intake and then closing it again near the top dead center of the compression can be performed exactly as intended. The surface pressure of the tappet against the cam can be reduced to improve durability.

(III) According to the second aspect of the present invention, the exhaust passage can be appropriately narrowed by the throttle means to increase the back pressure on the exhaust passage side. It is possible to promote the backflow of air into the cylinder when the exhaust valve is opened, thereby increasing the compression work in the compression stroke and further increasing the braking force.

(IV) According to the third aspect of the present invention, not only can the back pressure on the exhaust passage side be increased by reducing the opening of the nozzle vane of the turbine,
Since the rotation speed of the exhaust gas in the turbine is increased to increase the rotation speed of the turbine, thereby increasing the intake air amount on the compressor side, the back pressure on the exhaust passage side and the supercharging on the intake passage side increase. The amount of working gas (the amount of intake air + the amount of backflow air) taken into the cylinder during the intake stroke can be greatly increased by the synergistic action with the above, and the braking force obtained by the compression work in the next compression stroke is further enhanced. can do.

(V) According to the third aspect of the present invention, an engine provided with a variable geometry turbocharger as a turbocharger from the beginning, such as a butterfly damper or a guillotine damper for narrowing an exhaust passage. Even without adding extra parts,
By appropriately controlling the opening of the nozzle vane on the turbine side of the variable geometry turbocharger, the exhaust flow path can be appropriately narrowed, and the number of parts can be suppressed as small as possible to avoid an increase in equipment costs. it can.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an embodiment for implementing the present invention.

FIG. 2 is a plan view showing a structure around the camshaft of FIG. 1;

FIG. 3 is a graph illustrating a timing of an opening operation of an exhaust valve.

FIG. 4 is a graph showing a relationship between a braking force and an engine speed.

FIG. 5 is a partial sectional view showing another embodiment of the present invention.

FIG. 6 is a schematic diagram showing a conventional example.

[Explanation of symbols]

Reference Signs List 4 exhaust valve 5 exhaust passage 6 camshaft 7 exhaust cam 7 'intake cam 12 master piston 13 oil passage 14 slave piston 16 solenoid valve (hydraulic oil supply means) 17 control valve (hydraulic oil supply means) 24 dedicated cam for brake 25 roller Tappet 25a Roller 26 Variable geometry turbocharger (throttle means) 30 Exhaust brake valve (throttle means) 31 Roller tappet 31a Roller

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 9/04 F02D 9/06 A 9/06 13/04 A 13/04 23/00 N 23/00 F02B 37/12 301Q (72) Inventor Kazuhiro Higuchi 3-1-1 Hinodai, Hino-shi, Tokyo Hino Motor Co., Ltd. (72) Inventor Masanori Yamaguchi 3-1-1 Hinodai, Hino-shi, Tokyo Hino Motor Co., Ltd. F term (reference) 3G005 EA04 EA16 FA00 GA04 GB24 GD03 GD17 HA09 HA19 3G065 AA09 CA00 DA04 EA05 EA10 GA00 GA10 KA02 3G092 AA11 AA18 DA02 DA06 DA12 DA14 DA15 DB03 DC12 DF04 DG05 DG09 FA34 FA50

Claims (3)

[Claims] 1. A brake-dedicated cam additionally provided on a camshaft provided with an intake cam and an exhaust cam, and the brake-dedicated cam is driven via a roller tappet and operates near an intake bottom dead center and a compression top dead center. A master piston, a slave piston connected to the master piston via an oil passage, and opening a discharge valve when a hydraulic pressure is generated in the oil passage by the operation of the master piston; and holding oil pressure in the oil passage. -A compression-pressure-released engine brake, comprising: a hydraulic-oil supply means for switching release. 2. The compression-release engine brake according to claim 1, further comprising a throttle means for appropriately narrowing an exhaust passage. 3. The compression-pressure-release type engine brake according to claim 2, wherein the throttle means is a variable geometry turbocharger.