Compression release type in-cylinder braking system for engines

Abstract

The present invention discloses a compression release type in-cylinder braking system for an engine, which includes a valve train, an oil cylinder device, an oil pumping device and an oil supply device. The oil cylinder device and the oil pumping device of each cylinder are connected through a pressure transmission oil circuit. The pressure transmission oil circuit is connected to the oil supply device through a low-pressure relief valve, and an air release valve is provided at the high end of the oil circuit system. During in-cylinder braking, the air release valve is closed, the electromagnetic reversing valve is energized, and engine oil with a pressure of P1 is supplied to the pressure transmission oil circuit. The cam abuts against and pushes the oil pumping device to pump high-pressure oil to the oil cylinder device to push the rocker arm to open the valve, thereby realizing in-cylinder braking. During non-in-cylinder braking, the air release valve is opened, the electromagnetic reversing valve is de-energized, and engine oil with a pressure of P2 is supplied to the pressure transmission oil circuit, where P1 > P2. The oil cylinder device and the oil pumping device return to their original positions respectively, and the cam is disengaged from the oil pumping device. The compression release type in-cylinder braking system of the present invention has stable and reliable operation, a simple oil circuit structure, and is not limited by the number of engine cylinders.

Description

Technical Field

[0001] The invention relates to the technical field of engine variable valve technology, and in particular to a compression-release type engine cylinder brake system. Background Art

[0002] During normal engine operation, the engine completes four working cycles of intake, compression, power and exhaust every time the camshaft rotates 360 degrees. At the end of the compression stroke, the fuel burns in the cylinder and performs external work in the subsequent expansion stroke.

[0003] Engine cylinder braking is a form of auxiliary braking for the whole vehicle. The contribution of engine cylinder braking is that it can not only improve the braking capacity of the whole vehicle, but also reduce the braking load of the main brake of the whole vehicle. When the engine cylinder brakes, the engine performs auxiliary work externally during the compression stroke. When the compression stroke approaches the top dead center, the exhaust valve is opened with a small lift under the drive of the engine cylinder brake device, and the compressed high-pressure gas in the cylinder is quickly released. The pressure in the cylinder is rapidly reduced to reduce the energy of the power stroke. Therefore, in the next power stroke, the engine basically does not perform work externally, thereby slowing down the engine and achieving the purpose of engine cylinder braking.

[0004] The Chinese utility model patent with the announcement number CN201241740Y and the name of "A rocker arm integrated brake device for a four-stroke internal combustion engine" discloses an engine cylinder brake device, which is provided with two brake lobes on the exhaust cam, which is used to open the intake valve before the end of the intake stroke to increase the intake volume, and open the exhaust valve before the end of the compression stroke to release the pressure to achieve the engine cylinder brake. In order to offset the valve lift caused by the brake lobes when the engine is running normally, it is necessary to set a hydraulically controlled clearance compensation mechanism on the rocker arm. Since the normal operation state accounts for the vast majority of the entire engine operation state, the clearance compensation mechanism is in working state for most of the time when the engine is running, which puts forward high requirements on reliability, etc., and the structure is relatively complex.

[0005] To this end, the applicant developed a new type of engine in-cylinder braking device and submitted a patent application with publication number CN110566309A and name “Compression-release engine in-cylinder braking device”. However, in subsequent practical applications, the applicant found the following problems that need to be further improved: the structure is too complicated and can only be applied to multi-cylinder engines with an even number of engine cylinders, and each cylinder of the engine must have a cylinder with a phase of 360° crankshaft angle corresponding to it, which limits its application.

[0006] For this reason, the applicant has developed a new in-cylinder braking system for engines and submitted a patent application with the application number 201911383008.X and the title "Compression Release In-Cylinder Braking System for Engines" (referred to as the original application). However, in subsequent practical applications, the applicant found that the following problems exist in this patented technology and need to be further improved: For each cylinder of the engine, a pressure transmission oil circuit connecting its oil cylinder device and fuel pumping device is provided. The pressure transmission oil circuit needs to be connected to a common oil supply device through a one-way valve to supply engine oil during in-cylinder braking, and also needs to be connected to a low-pressure pressure relief oil circuit to release the oil in the pressure transmission oil circuit after in-cylinder braking ends, reduce the pressure, and facilitate the oil supply device to replenish oil to the pressure transmission oil circuit; in the in-cylinder braking system, there are many hydraulic components for oil supply and pressure relief, and the oil circuit structure is too complex.

[0007] After that, the applicant conducted further research and development and submitted a patent application with the application number 202010031654.6 and the title "Compression Release In-Cylinder Braking System for Engines" (referred to as the previous patent). However, in subsequent practical applications, the applicant found that at least the following problems still exist in the previous patented technology and need to be further improved:

[0008] Since the system transmits power through hydraulic oil, when the engine is in a stopped state, air is extremely likely to enter the pressure transmission oil circuit, seriously affecting the power transmission effect.

[0009] The fuel pumping device is provided with a plunger sleeve buffer oil hole 212. Although the impact caused by the sudden contact between the cam 16 and the top surface of the fuel pumping device II can be reduced through the flow buffering of the plunger sleeve buffer oil hole 212, however, since the camshaft drives the fuel pumping device to block the plunger sleeve buffer oil hole 212 before starting to pump oil, the size of the pumping stroke is not only controlled by the camshaft profile but also affected by the position of the plunger sleeve buffer oil hole 212, resulting in low control accuracy; moreover, each plunger sleeve buffer oil hole 212 is respectively connected to its own overflow pressure maintaining valve 300, resulting in a large number of valve parts and a complex system structure.

[0010] In addition, in the previous patent, when the fuel pumping device starts to work in the engine compression release mode, inevitably, a part of the high-pressure oil will flow back to the engine oil circuit L0 (i.e., the engine main oil circuit), causing an impact on the engine oil circuit L0. Summary of the Invention

[0011] In view of this, the technical problem to be solved by the present invention is: to provide a compression release in-cylinder braking system for engines, ensuring the power transmission effect of the oil circuit, with a simple oil circuit structure, high working reliability, low failure rate; good application performance, not limited by the number of engine cylinders.

[0012] To solve the above technical problems, the technical solution of the present invention is: a compression-release type in-cylinder braking system for an engine, which is applied to the valve train of the engine and includes: an oil cylinder device, an oil pumping device, and an oil supply device. All cylinders of the engine share one oil supply device;

[0013] The valve train includes a camshaft, rocker arms, and valves, and the camshaft is provided with cams;

[0014] The oil supply device includes an electromagnetic reversing valve, an oil supply oil path, a pressure reducing oil path, and a pressure relief oil path. An overflow pressure maintaining valve is provided in the pressure relief oil path. Define the engine oil pressure before pressure reduction as P1 and the engine oil pressure after pressure reduction as P2;

[0015] Each cylinder is respectively provided with the oil cylinder device and the oil pumping device. The oil cylinder device is communicated with the oil pumping device through a pressure transmission oil path, and the pressure transmission oil path is communicated with the oil supply oil path through a low-pressure pressure relief valve;

[0016] An air release valve is provided at the high end of the oil path system;

[0017] During in-cylinder braking, the air release valve is closed, the electromagnetic reversing valve is energized, and engine oil with a pressure of P1 is provided to the pressure transmission oil path through the oil supply oil path; the cam abuts against and pushes the oil pumping device, the engine oil pressure in the oil pumping device increases, and the oil pumping device pumps high-pressure engine oil with a pressure of P to the oil cylinder device through the pressure transmission oil path, and the oil cylinder device pushes the rocker arm to open the valve;

[0018] During non-in-cylinder braking, the air release valve is open, the electromagnetic reversing valve is de-energized, and engine oil with a pressure of P2 is provided to the pressure transmission oil path through the oil supply oil path; the oil cylinder device and the oil pumping device return to their original positions respectively, and the cam is disengaged from the oil pumping device;

[0019] When the oil pumping device is working, the low-pressure pressure relief valve is closed; when the oil pumping device is not working, the low-pressure pressure relief valve is open; the opening pressure difference of the low-pressure pressure relief valve is greater than P1 and less than P.

[0020] Among them, the air release valve includes:

[0021] A valve body, the valve body is provided with a valve body oil port one and a valve body oil port two communicated with its valve cavity. The valve body oil port one is connected to the pressure transmission oil path, and the valve body oil port two is connected to the engine oil sump;

[0022] A valve ball, the valve ball is arranged in the valve cavity;

[0023] A compression spring, which is arranged in the valve cavity and clamped between the valve ball and the second valve body oil port;

[0024] A limit pin, which is arranged on the valve body and located between the first valve body oil port and the valve ball;

[0025] The elastic force of the compression spring of the air release valve on the valve ball is greater than the acting force of the engine oil pressure P2 after decompression on the valve ball and less than the acting force of the engine oil pressure P1 before decompression on the valve ball.

[0026] Further, a throttle orifice is arranged behind the air release valve, and the throttle orifice communicates with the oil pan of the engine. Setting the throttle orifice can control the discharging speed of the oil and avoid waste of hydraulic oil.

[0027] Each cylinder oil passage between the low-pressure pressure relief valve and the oil supply oil passage is jointly connected to a high-pressure overflow pressure maintaining valve, and the high-pressure overflow pressure maintaining valve communicates with the oil pan of the engine.

[0028] A check valve is connected in front of the electromagnetic directional valve. Setting the check valve can further protect the main oil passage of the engine from the impact of the high-pressure oil flowing back.

[0029] A throttle orifice is arranged in the decompression oil passage. In the case of achieving the same function of decompressing the engine oil, compared with a pressure relief valve, using a throttle orifice has a simpler structure.

[0030] The oil pumping device includes:

[0031] A plunger sleeve, the bottom of which is closed, the top of which is open, and a plunger sleeve oil inlet / outlet hole is arranged on the sleeve wall of the plunger sleeve, and the plunger sleeve oil inlet / outlet hole is connected to the pressure transmission oil passage;

[0032] A plunger, which is slidably arranged in the inner cavity of the plunger sleeve. An oil cavity of the plunger sleeve is formed between the bottom of the plunger and the bottom of the plunger sleeve. The plunger sleeve oil inlet / outlet hole communicates with the oil cavity of the plunger sleeve. The top of the plunger extends out of the open top of the plunger sleeve. During in-cylinder braking, the top of the plunger contacts the cam, and during non-in-cylinder braking, the top of the plunger is disengaged from the cam;

[0033] A plunger tension spring, which is located in the oil cavity of the plunger sleeve and is connected between the bottom of the plunger sleeve and the bottom of the plunger;

[0034] A plunger limit device is provided at the open end of the plunger sleeve; the plunger includes a large-diameter section of the plunger located in the inner cavity of the plunger sleeve and a small-diameter section of the plunger connected to the large-diameter section of the plunger. A plunger step is formed at the transition between the large-diameter section of the plunger and the small-diameter section of the plunger. During in-cylinder braking, the plunger limit device limits the plunger step;

[0035] The plunger further includes a plunger abutting section located outside the plunger sleeve and connected to the small-diameter section of the plunger. During in-cylinder braking, the top surface of the plunger abutting section abuts against the cam; during non-in-cylinder braking, the top surface of the plunger abutting section is disengaged from contact with the cam, and the plunger limit device limits the plunger abutting section;

[0036] The top surface of the plunger abutting section is a flat surface or a curved surface.

[0037] Wherein, the oil cylinder device includes:

[0038] A cylinder block, the top of the cylinder block is closed, the bottom of the cylinder block is open, and a cylinder block oil inlet / outlet hole is provided on the cylinder wall of the cylinder block. The cylinder block oil inlet / outlet hole is connected to the pressure transmission oil circuit;

[0039] A piston, the piston is slidably arranged in the inner cavity of the cylinder block. An oil cavity of the cylinder block is formed between the top of the piston and the top of the cylinder block. The cylinder block oil inlet / outlet hole is communicated with the oil cavity of the cylinder block. A piston rod is provided at the bottom of the piston, and the piston rod extends out of the open end of the cylinder block. During in-cylinder braking, the bottom of the piston rod contacts the rocker arm and presses down the rocker arm to open the valve. During non-in-cylinder braking, the bottom of the piston rod is disengaged from contact with the rocker arm;

[0040] A piston pull spring, the piston pull spring is located in the oil cavity of the cylinder block and is connected between the top of the cylinder block and the top of the piston;

[0041] A cylinder block oil drain hole is further provided on the cylinder wall of the cylinder block. The cylinder block oil drain hole is communicated with the oil pan of the engine. During in-cylinder braking, the piston moves downward. When the fuel pumping device is working, the cylinder block oil drain hole is not communicated with the oil cavity of the cylinder block; when the cam opens the valve through the valve train and the fuel pumping device is not working, the cylinder block oil drain hole is communicated with the oil cavity of the cylinder block; during non-in-cylinder braking, under the action of the piston pull spring, the piston blocks the cylinder block oil drain hole;

[0042] A piston limit device is provided at the open end of the cylinder block; a piston step is formed at the transition between the piston and the piston rod. When the fuel pumping device is working during in-cylinder braking, the piston limit device does not limit the piston step, and the distance between the piston step and the piston limit device is S, S>0;

[0043] When the cam pushes open the valve through the valve train and the fuel pumping device is not working, the piston limiting device limits the step of the piston, and S = 0.

[0044] Among them, the low-pressure pressure relief valve includes:

[0045] A valve body provided with a first valve body oil port and a second valve body oil port communicating with its valve cavity. The first valve body oil port is connected to the pressure transmission oil path, and the second valve body oil port is connected to the oil supply oil path;

[0046] A valve ball disposed in the valve cavity;

[0047] A compression spring disposed in the valve cavity and clamped between the valve ball and the second valve body oil port;

[0048] A limit pin disposed on the valve body and located between the first valve body oil port and the valve ball.

[0049] Among them, the cam is an exhaust cam; or, the cam is an intake cam; or, the cam is a single-cylinder braking cam.

[0050] Among them, the cam can also be a total braking cam, and the fuel pumping device is disposed around the total braking cam, and the number of the fuel pumping devices is the same as the number of cylinders of the engine.

[0051] Among them, the electromagnetic reversing valve is a two-position three-way electromagnetic reversing valve.

[0052] After adopting the above technical solution, the beneficial effects of the present invention are as follows:

[0053] Since the compression-release type in-cylinder braking system of the present invention includes an oil cylinder device, an oil pumping device, and an oil supply device applied to the valve train of the engine, all cylinders of the engine share one oil supply device; the oil supply device includes an electromagnetic reversing valve, an oil supply oil path, a pressure reducing oil path, and a pressure relief oil path. The engine oil pressure before pressure reduction is P1, and the engine oil pressure after pressure reduction is P2; an oil cylinder device and an oil pumping device are respectively provided for each cylinder of the engine. The oil cylinder device and the oil pumping device are connected through a pressure transmission oil path. The pressure transmission oil path is connected to the oil supply oil path through a low-pressure pressure relief valve, and a gas release valve is provided at the high end of the oil path system; during in-cylinder braking, the gas release valve is closed, the electromagnetic reversing valve is energized, and engine oil with a pressure of P1 is supplied to the pressure transmission oil path through the oil supply oil path, and the piston of the oil cylinder device and the plunger of the oil pumping device extend; when the cam abuts against and pushes the oil pumping device, the engine oil pressure in the oil pumping device increases, and the oil pumping device pumps high-pressure engine oil with a pressure of P to the oil cylinder device through the pressure transmission oil path. The low-pressure pressure relief valve is closed, and the oil cylinder device pushes the rocker arm to open the valve, realizing in-cylinder braking; during non-in-cylinder braking, the gas release valve is open, the electromagnetic reversing valve is de-energized, and engine oil with a pressure of P2 is supplied to the pressure transmission oil path through the oil supply oil path. At the moment when the electromagnetic reversing valve is de-energized, the low-pressure pressure relief valve is in an open state, and the oil pressure in the pressure transmission oil path is relieved through the low-pressure pressure relief valve and drops to P2. The oil cylinder device and the oil pumping device return to their original positions respectively, the cam is disengaged from the oil pumping device, and the engine is in a normal operating state. The engine oil or air in the pressure transmission oil path is continuously discharged through the gas release valve, solving the problem that the power transmission effect is seriously affected due to air entering the pressure transmission oil path during the shutdown state. Since an oil cylinder device and an oil pumping device connected through a pressure transmission oil path are respectively provided for each cylinder of the engine, and the pressure transmission oil path is connected to the oil supply oil path of the oil supply device through a low-pressure pressure relief valve, only by controlling the on / off of the electromagnetic reversing valve, the braking / non-braking conversion of all cylinders of the entire engine can be realized. The requirement for the control circuit is low, the work is stable and reliable, and the failure rate is low; moreover, the structure is simple, the layout is flexible and convenient, and it is not limited by the number of engine cylinders, whether it is even or odd, and it has good application performance and is more widely applied.

[0054] Since the present invention removes the plunger sleeve buffer oil holes of the fuel pumping device in each cylinder and the overflow pressure maintaining valves connected thereto in the previous patent, and connects the oil circuits of each cylinder between the low-pressure pressure relief valve and the fuel supply oil circuit to a high-pressure overflow pressure maintaining valve, when the fuel pumping device starts to work in the engine compression release mode, inevitably, a part of the high-pressure engine oil will flow back to the engine main oil circuit through the low-pressure pressure relief valve, causing an impact on the engine main oil circuit. In the present invention, the high-pressure engine oil flowing back can be discharged through the high-pressure overflow pressure maintaining valve, avoiding the impact on the engine main oil circuit; moreover, the present invention only needs to set one high-pressure overflow pressure maintaining valve, while the previous patent sets multiple overflow pressure maintaining valves with the same number as the cylinders of the engine. The number of valves in the present invention is greatly reduced, and the structure of the oil circuit system is simpler; and, since the plunger sleeve buffer oil holes of the fuel pumping device in each cylinder in the previous patent are removed, in the present invention, the size of the fuel pumping stroke of the fuel pumping device is completely determined by the shape of the cam of the camshaft, and the control accuracy is higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 is a schematic diagram of the in-cylinder braking state of the compression release type in-cylinder braking system of the first embodiment of the present invention;

[0056] Figure 2 is Figure 1 the exhaust stroke state diagram after completing in-cylinder braking;

[0057] Figure 3 is a schematic diagram of the first embodiment of the present invention when the engine is in a normal working state;

[0058] Figure 4 is Figure 1 the hydraulic schematic diagram of the fuel supply device in;

[0059] Figure 5 is Figure 1 the structural schematic diagram of the fuel pumping device in;

[0060] Figure 6 is Figure 1 a structural schematic diagram of one kind of the oil cylinder device in;

[0061] Figure 7 is Figure 1 another structural schematic diagram of the oil cylinder device in;

[0062] Figure 8 is Figure 1 the schematic diagram of the closed state of the low-pressure pressure relief valve in;

[0063] Figure 9 is Figure 1 the schematic diagram of the open state of the low-pressure pressure relief valve in;

[0064] Figure 10It is a schematic diagram of the compression-release type in-cylinder braking system according to the second embodiment of the present invention;

[0065] In the figure: I-Valve train; II-Fuel pumping device; III-Cylinder device; IV-Fuel supply device;

[0066] 10-Valve; 11-Valve spring; 12-Rocker arm; 13-Rocker arm shaft; 14-Push rod; 15-Tappet; 16-Cam; 16a-Total braking cam;

[0067] 21-Plunger sleeve; 211-Inlet and outlet holes of the plunger sleeve; 213-Plunger limiting device; 22-Plunger; 221-Plunger top section; 2211-Top surface of the plunger top section; 23-Plunger pulling spring;

[0068] 31-Cylinder block; 311-Inlet and outlet holes of the cylinder block; 312-Oil drain hole of the cylinder block; 313-Piston limiting device; 32-Piston; 321-Piston rod; 33-Piston pulling spring;

[0069] 50-Check valve; 60-Oil pan; 70-Throttle hole; 80-Electromagnetic directional valve; 100-Overflow pressure maintaining valve; 200-Bleed valve; 2001-Throttle hole; 300-High-pressure overflow pressure maintaining valve;

[0070] 90-Low-pressure pressure relief valve; 91-Valve body; 92-Valve ball; 93-Compression spring; 94-Limit pin;

[0071] L0-Engine oil oil circuit; La-Fuel supply oil circuit; Lb-Pressure reduction oil circuit; Lc-Pressure relief oil circuit; L-Pressure transmission oil circuit; L1-Oil circuit of cylinder 1; L2-Oil circuit of cylinder 2; L3-Oil circuit of cylinder 3; L4-Oil circuit of cylinder 4; L5-Oil circuit of cylinder 5; L6-Oil circuit of cylinder 6; A-Plunger sleeve oil chamber; B-Cylinder block oil chamber. Detailed implementation manners

[0072] The present invention will be further described in detail and non-limitingly below with reference to the drawings and embodiments.

[0073] It should be noted that in this article, terms indicating positions such as "upper", "lower", "top", "bottom", etc. are defined for the purpose of facilitating description based on the drawings; terms such as "installation", "connection", "connection" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection between components; it can be a direct connection between components, or an indirect connection through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0074] Embodiment 1

[0075] As Figure 1As shown in the figure, the compression-release type in-cylinder braking system of Embodiment 1 of the present invention is applied to the valve train I of the engine, and includes: an oil pumping device II, an oil cylinder device III, and an oil supply device IV.

[0076] Among them, the rocker arm 12 of the valve train I is rotatably installed on the rocker arm shaft 13. The push rod 14 and the valve 10 are respectively arranged on both sides of the rocker arm shaft 13. When the tappet 15 and the push rod 14 push the rocker arm 12 to swing around the rocker arm shaft 13 from one side under the action of the cam 16 on the camshaft, the other side of the rocker arm 12 presses the valve 10, and the valve opens; when the camshaft rotates through a specified angle, the valve 10 returns to its original position under the action of the valve spring 11, and the valve closes. The above is the process of controlling the valve action in the valve train I during the normal operation of the engine.

[0077] As Figure 4 shown in the figure, among them, the oil supply device IV includes an oil supply oil path La, a pressure reduction oil path Lb, a pressure relief oil path Lc, and an electromagnetic reversing valve 80. One electromagnetic reversing valve 80 is provided, and the braking / non-braking conversion of all cylinders of the entire engine is realized through one electromagnetic reversing valve 80. Obviously, the electromagnetic reversing valve is not limited to one. Referring to Figure 1 , more than one electromagnetic reversing valve can also be provided. For example, two, or three, or more. Multiple electromagnetic reversing valves are connected in parallel to respectively control the oil paths of each cylinder, or group-control the oil paths of each cylinder to achieve multi-stage braking control. Among them, the electromagnetic reversing valve 80 is preferably a two-position three-way electromagnetic reversing valve. A check valve 50 is further provided in front of the electromagnetic reversing valve 80. The check valve 50 can further protect the engine oil oil path L0 from the impact of the high-pressure oil flowing back. An overflow pressure maintaining valve 100 is provided in the pressure relief oil path Lc. For the convenience of description, the oil pressure of the engine oil oil path L0 before pressure reduction is defined as P1, the oil pressure of the engine after pressure reduction is defined as P2, and the set pressure of the overflow pressure maintaining valve 100 is P2 or slightly higher than P2.

[0078] As Figure 1As shown, the situation of a six-cylinder engine is illustrated. Among them, each cylinder is respectively provided with an oil pumping device II and an oil cylinder device III. The oil cylinder device III is connected to the oil pumping device II through a pressure transmission oil path L. The pressure transmission oil path L is connected to the oil supply oil path La of a shared oil supply device IV through a low-pressure relief valve 90. An air release valve 200 is provided at the high end (preferably the highest end) of the oil path system. The air release valve 200 is connected to the pressure transmission oil path L. During in-cylinder braking, the air release valve 200 is closed; during non-in-cylinder braking, the air release valve 200 is opened, and the engine oil or air in the pressure transmission oil path L is continuously discharged through the air release valve 200, avoiding seriously affecting the power transmission effect due to air entering the pressure transmission oil path L during the shutdown state; in order to control the speed of the discharged engine oil and avoid waste of hydraulic oil, a throttle orifice 2001 is further provided behind the air release valve 200, and the throttle orifice 2001 is connected to the oil sump 60 of the engine. Specifically: the first cylinder is connected to the oil supply oil path La through the first-cylinder oil path L1, the second cylinder is connected to the oil supply oil path La through the second-cylinder oil path L2, the third cylinder is connected to the oil supply oil path La through the third-cylinder oil path L3, the fourth cylinder is connected to the oil supply oil path La through the fourth-cylinder oil path L4, the fifth cylinder is connected to the oil supply oil path La through the fifth-cylinder oil path L5, the sixth cylinder is connected to the oil supply oil path La through the sixth-cylinder oil path L6 and the low-pressure relief valve 90 in each oil path.

[0079] Among them, the oil paths of each cylinder between the low-pressure relief valve 90 and the oil supply oil path La are jointly connected to a high-pressure overflow pressure maintaining valve 300. The high-pressure overflow pressure maintaining valve 300 is connected to the oil sump 60 of the engine. The relief pressure of the high-pressure overflow pressure maintaining valve 300 is set equal to or slightly higher than the engine oil pressure P1. In the engine compression release mode, when the oil pumping device II starts to work, inevitably, a part of the high-pressure engine oil will flow back to the engine oil oil path L0 through the low-pressure relief valve 90, causing an impact on the engine oil oil path L0. In the present invention, the returned high-pressure engine oil can be discharged through the high-pressure overflow pressure maintaining valve 300, avoiding an impact on the engine oil oil path L0.

[0080] Among them, the decompression element in the decompression oil path Lb adopts a throttle orifice 70. In the case of achieving the same effect of decompressing the engine oil, compared with a pressure reducing valve, the throttle orifice structure is simpler.

[0081] As Figure 1 shown, the oil pumping device II is installed at an appropriate position of the cam 16. By reasonably designing this position, it is ensured that when the cam 16 acts on the oil pumping device II, the moment when the oil pumping device II pumps oil and pushes the piston 32 in the oil cylinder device III to move to open the valve 10 to achieve exhaust braking is exactly near the compression top dead center. As Figure 5As shown in the figure, the oil pumping device II includes a plunger sleeve 21, a plunger 22, and a plunger spring 23. Among them, the bottom of the plunger sleeve 21 is closed and the top is open. A plunger sleeve oil inlet / outlet hole 211 is provided on the sleeve wall of the plunger sleeve 21, and the plunger sleeve oil inlet / outlet hole 211 is connected to the pressure transmission oil path L. The open end of the plunger sleeve 21 is further provided with a plunger limit device 213 for restricting the movement position of the plunger 22. Among them, the plunger 22 is slidably arranged in the inner cavity of the plunger sleeve 21. A plunger sleeve oil cavity A is formed between the bottom of the plunger 22 and the bottom of the plunger sleeve 21. The plunger sleeve oil inlet / outlet hole 211 communicates with the plunger sleeve oil cavity A. The top of the plunger 22 extends out of the open end of the plunger sleeve 21. The plunger 22 includes a plunger large-diameter section located in the inner cavity of the plunger sleeve 21 and a plunger small-diameter section connected to the plunger large-diameter section. A plunger step is formed at the transition between the plunger large-diameter section and the plunger small-diameter section. The plunger 22 further includes a plunger abutting section 221 located outside the plunger sleeve 21 and connected to the plunger small-diameter section. The radial dimension of the plunger abutting section 221 is larger than the radial dimension of the plunger small-diameter section. The top surface 2211 of the plunger abutting section can be a flat surface or an arc surface matching the cam surface of the cam 16 so as to have a larger contact area with the cam 16. Among them, the plunger spring 23 is located in the plunger sleeve oil cavity A and is connected between the bottom of the plunger sleeve 21 and the bottom of the plunger 22. The pulling force of the plunger spring 23 is much smaller than the pushing force of the engine oil pressure P1 on the plunger 22, but much larger than the pushing force of the engine oil pressure P2 on the plunger 22.

[0082] Among them, the plunger limit device 213 can specifically be a closed ring, or an unclosed ring, or a strip, and its shape is not limited here.

[0083] As Figure 1 shown, during in-cylinder braking, the plunger limit device 213 limits the plunger step. As Figure 3 shown, during non-in-cylinder braking, the plunger limit device 213 limits the plunger abutting section 221.

[0084] Among them, fixedly installing the plunger limit device 213 at the open end of the plunger sleeve 21 is an optimized design of the structure of the plunger sleeve 21. Obviously, the plunger limit device 213 can also not be provided at the open end of the plunger sleeve 21. In this case, the limit function can be achieved by the base circle of the cam 16 abutting against the top surface 2211 of the plunger abutting section.

[0085] As Figure 1 shown, the oil cylinder device III is installed on the top of the rocker arm 12 (or other valve mechanisms). As Figure 6As shown in the figure, the oil cylinder device III includes: a cylinder block 31, a piston 32, and a piston tension spring 33. Among them, the cylinder block 31 is fixed relative to the engine. The top of the cylinder block 31 is closed and the bottom is open. A cylinder block oil inlet / outlet hole 311 is provided on the cylinder wall of the cylinder block 31, and the cylinder block oil inlet / outlet hole 311 is connected to the pressure transmission oil circuit L. Among them, the piston 32 is slidably arranged in the inner cavity of the cylinder block 31. An oil cavity B of the cylinder block is formed between the top of the piston 32 and the top of the cylinder block 31. The cylinder block oil inlet / outlet hole 311 is communicated with the oil cavity B of the cylinder block. A piston rod 321 is provided at the bottom of the piston 32. A piston step is formed at the transition between the piston 32 and the piston rod 321. The piston rod 321 extends out of the open end of the cylinder block 31. By reasonably designing the diameter d of the piston 32, it is ensured that the thrust generated by the engine oil pressure P1 on the piston 32 is much smaller than the valve spring force. Among them, the piston tension spring 33 is located in the oil cavity B of the cylinder block and is connected between the top of the cylinder block 31 and the top of the piston 32. The tension of the piston tension spring 33 is much greater than the thrust of the oil pressure P2 on the piston 32, but much smaller than the thrust of the oil pressure P1 on the piston 32.

[0086] As Figure 6 shown in the figure, further, an oil drain hole 312 of the cylinder block is also provided on the cylinder wall of the cylinder block 31, and the oil drain hole 312 of the cylinder block is communicated with the oil pan 60 of the engine. On the one hand, part of the oil in the oil cavity B of the cylinder block can flow through the oil drain hole 312 of the cylinder block and be drained off, taking away part of the heat to prevent the oil temperature in the oil cylinder device III from being too high. On the other hand, the oil drain hole 312 of the cylinder block also plays a role in restricting the position of the piston 32. As Figure 6 shown in the figure, the thrust of the oil with pressure P1 on the piston 32 is greater than the elastic force of the piston tension spring 33. The high-pressure oil in the oil cavity B of the cylinder block pushes the piston 32 to move downward. When the piston 32 moves downward to a certain position, the top edge of the oil drain hole 312 of the cylinder block starts to be higher than the top surface of the piston 32. The oil drain area formed by the edge of the oil hole and the top surface of the piston will drain off part of the oil, reducing the oil pressure. The piston 32 continues to move downward, and the oil flow area formed by the edge of the oil hole and the top surface of the piston gradually increases, and the oil pressure continues to decrease. When the thrust of the oil pressure on the piston 32 is equal to the elastic force of the piston tension spring 33, at this time, the piston 32 will no longer move downward and stop at a certain position, becoming the equilibrium position. At this time, the oil drain hole 312 of the cylinder block plays a role in limiting the position of the piston 32.

[0087] As Figure 7 shown in the figure, on the basis of Figure 6 , a piston limiting device 313 for restricting the axial movement of the piston 32 is further provided at the open end of the cylinder block 31. The design of the piston limiting device 313 ensures that when it limits the position of the piston 32, the top edge of the oil drain hole 312 of the cylinder block slightly protrudes from the top surface of the piston 32, but the piston 32 has not reached the equilibrium position. At this time, the oil drain hole 312 of the cylinder block only plays a role in draining oil and cooling.

[0088] Among them, the piston limiting device 313 may specifically be a closed ring, or an open ring, or a strip, and its shape is not limited herein.

[0089] As Figure 8 shown, among them, the low-pressure pressure relief valve 90 includes: a valve body 91, a valve ball 92, a compression spring 93, and a limit pin 94. Among them, the valve body 91 is provided with a first valve body oil port and a second valve body oil port communicating with its valve cavity. The first valve body oil port is connected to the pressure transmission oil path L, and the second valve body oil port is connected to the oil supply oil path La; the valve ball 92, the compression spring 93, and the limit pin 94 are all arranged in the valve cavity. The compression spring 93 is clamped between the valve ball 92 and the second valve body oil port, and the limit pin 94 is located between the first valve body oil port and the valve ball 92.

[0090] As Figure 8 shown, if the thrust on the valve ball 92 due to the pressure difference between the first valve body oil port and the second valve body oil port of the low-pressure pressure relief valve 90 is greater than the acting force of the compression spring 93, then the valve ball 92 seals the inner conical surface of the valve cavity, and the low-pressure pressure relief valve 90 is in the closed state. As Figure 9 shown, on the contrary, if the thrust on the valve ball 92 due to the pressure difference between the first valve body oil port and the second valve body oil port of the low-pressure pressure relief valve 90 is lower than the acting force of the compression spring 93, the valve ball 92 disengages from the inner conical surface of the valve cavity, the engine oil circulates, and the low-pressure pressure relief valve 90 is in the open state.

[0091] By designing the spring force of the compression spring 93, when the pressure difference △P between the first valve body oil port and the second valve body oil port of the low-pressure pressure relief valve 90 exceeds P1, the low-pressure pressure relief valve 90 can be closed.

[0092] When the oil pumping device II is working, the low-pressure pressure relief valve 90 is closed; when the oil pumping device II is not working, the low-pressure pressure relief valve 90 is open; the opening pressure difference of the low-pressure pressure relief valve 90 is greater than P1, but much smaller than the pressure P of the high-pressure engine oil pumped to the oil cylinder device III through the pressure transmission oil path L when the oil pumping device II is working. The closer the opening pressure difference of the low-pressure pressure relief valve 90 is to P1, the better.

[0093] As Figure 1 、 Figure 8 、 Figure 9 shown, among them, the air release valve 200 has basically the same structure and principle as the low-pressure pressure relief valve 90. The air release valve 200 includes a valve body, a valve ball, a compression spring, and a limit pin. The valve body is provided with a first valve body oil port and a second valve body oil port communicating with its valve cavity. The first valve body oil port is connected to the pressure transmission oil path L, and the second valve body oil port is connected to the oil sump 60 of the engine through a throttle hole 2001; the valve ball is arranged in the valve cavity; the compression spring is arranged in the valve cavity and is clamped between the valve ball and the second valve body oil port; the limit pin is arranged on the valve body and is located between the first valve body oil port and the valve ball.

[0094] The elastic force of the compression spring inside the bleed valve 200 on the valve ball is greater than the acting force of the engine oil pressure P2 on the valve ball after pressure reduction and less than the acting force of the engine oil pressure P1 on the valve ball before pressure reduction.

[0095] When in the in-cylinder braking state, the engine oil pressure in the pressure transmission oil passage L is P1, and the bleed valve 200 is closed. When not in the in-cylinder braking state, the engine oil pressure in the pressure transmission oil passage L is P2, the bleed valve 200 is opened, and the engine oil or air in the pressure transmission oil passage L is continuously discharged through the bleed valve 200 and the throttle hole 2001.

[0096] In the first embodiment, the cam 16 can be the exhaust cam on the camshaft; the cam 16 can also be the intake cam on the camshaft; the cam 16 can also be a single-cylinder braking cam specifically applied to braking, and the number of single-cylinder braking cams is the same as the number of cylinders of the engine. Whether using the exhaust cam, the intake cam, or the single-cylinder braking cam, during in-cylinder braking, it can be used to abut against and push the plunger 22 of the oil pumping device II, increasing the engine oil pressure in the plunger sleeve oil cavity A, pumping high-pressure engine oil to the oil cylinder device III through the pressure transmission oil passage L, and the oil cylinder device III pushing the rocker arm 12 to swing downward to open the valve 10, realizing in-cylinder braking.

[0097] The working process of the compression release type in-cylinder braking system of the engine of the present invention is as follows:

[0098] As Figure 1 shown, when the engine enters the in-cylinder braking mode, the bleed valve 200 is closed. When the cam base circle abuts against the top surface of the plunger of the oil pumping device II, at this time, the oil pumping device II has not yet worked, the hydraulic oil pressure in the pressure transmission oil passage L is P1, the pressure difference across the low-pressure relief valve 90 is zero, and the low-pressure relief valve 90 is opened; the electromagnetic directional valve 80 is energized, and the engine oil with a pressure of P1 passes through the one-way valve 50, the electromagnetic directional valve 80, and the low-pressure relief valve 90 and enters the pressure transmission oil passage L, and respectively enters the oil cylinder device III and the oil pumping device II;

[0099] Under the action of the engine oil pressure P1, the piston 32 in the oil cylinder device III overcomes the force of the piston tension spring 33, and the piston rod 321 extends out and abuts against the top end of the rocker arm 12, but it cannot yet open the valve 10;

[0100] Under the action of the engine oil pressure P1, the plunger 22 in the oil pumping device II overcomes the acting force of the plunger tension spring 23, and the plunger step extends to the plunger limiting device 213 position;

[0101] The camshaft rotates. When it rotates to Figure 1When in the position shown, the convex part of the cam 16 gradually abuts against the top surface of the oil pumping device II and pushes the plunger 22 to move. The oil pressure of the engine oil in the plunger sleeve oil chamber A of the oil pumping device II continuously increases, and the reaction force of the plunger 22 on the cam 16 continuously becomes larger;

[0102] The oil pumping device II works and starts pumping oil. The high-pressure engine oil with a pressure of P in the pressure transmission oil path L is transmitted through the pressure transmission oil path L to the cylinder block oil chamber B of the cylinder device III. Since P >> P1, the pressure difference ΔP at both ends of the low-pressure pressure relief valve 90 >> P1, and the low-pressure pressure relief valve 90 quickly closes. The cylinder device III starts to work, and the high-pressure engine oil pushes the piston 32 downward to open the valve 10 to complete the pressure release;

[0103] When the oil pumping device II starts to work, inevitably, a part of the high-pressure engine oil will flow back to the engine oil oil path L0 through the low-pressure pressure relief valve 90, causing an impact on the engine oil oil path L0. In the present invention, the high-pressure engine oil flowing back can be discharged through the high-pressure overflow pressure maintaining valve 300 to avoid an impact on the engine oil oil path L0.

[0104] The cam 16 continues to rotate. After passing the highest point, the piston 32 moves downward to push the rocker arm 12 to reach the limit position. At this time, the distance between the piston 32 and the limiting device is S, and S is the safety distance, and S > 0. As Figure 1 shown, at this time, the cylinder block oil drain hole 312 is completely blocked by the piston 32, and no oil is drained (the engine oil pressure in the cylinder block oil chamber B is too high, and oil drainage is not desired);

[0105] The cam 16 continues to rotate, and the top surface of the plunger of the oil pumping device II gradually disengages from the cam 16. Under the action of the engine oil pressure P1, the plunger 22 moves in the direction of the cam 16, and the pressure in the plunger sleeve oil chamber A decreases. The piston 32 in the cylinder device III gradually returns to its original position under the action of the valve spring force, and the valve 10 closes, ending a braking process.

[0106] As Figure 2 shown, the cam 16 continues to rotate and pushes the tappet 15 and the push rod 14 to move. The top of the rocker arm 12 disengages from the piston rod 321. The piston 32 moves to the limiting position under the action of the engine oil pressure P1. At this time, the top surface of the piston 32 is slightly lower than the top edge of the cylinder block oil drain hole 312, and the cylinder block oil drain hole 312 starts to drain oil; The cam 16 continues to rotate, and the valve 10 gradually closes. The rocker arm 12 re-abuts against the piston rod 321 and, under the action of the valve spring force, pushes the piston 32 upward. The engine oil in the cylinder device III is transmitted to the oil pumping device II through the pressure transmission oil path L.

[0107] During this process, under the reaction force of the piston 32 in the oil cylinder device III on the rocker arm 12, the closing moment of the valve 10 may be slightly delayed, which is beneficial in the in-cylinder braking state. In the subsequent intake stroke, a certain amount of charge can enter the cylinder through the exhaust valve additionally, increasing the total charge entering the cylinder and improving the braking power in the compression stroke.

[0108] As Figure 3 shown, the air release valve 200 is opened, the electromagnetic reversing valve 80 is de-energized, the oil supply device supplies oil with a pressure of P2, the pressure at the second oil port of the valve body of the low-pressure pressure relief valve 90 is P2, and the pressure at the first oil port of the valve body remains instantaneously at P1; when the cam base circle abuts against the top surface of the plunger of the oil pumping device II, since the pressure at the first oil port of the valve body of the low-pressure pressure relief valve 90 is not greater than P1, the pressure difference △P across the low-pressure pressure relief valve 90 is not greater than P1, and the low-pressure pressure relief valve 90 is in an open state. The hydraulic oil in the pressure transmission oil passage L flows through the first oil port of the valve body of the low-pressure pressure relief valve 90 to the second oil port, and the pressure transmission oil passage L is quickly depressurized to P2; the plunger 22 in the oil pumping device II returns under the action of the plunger return spring 23, and the piston 32 in the oil cylinder device III returns under the action of the piston return spring 33 to the Figure 3 position shown, ending the in-cylinder braking process.

[0109] The above-mentioned low-pressure pressure relief valve 90 is only in a closed state when the oil pumping device II is working, and is in an open state at other times.

[0110] Embodiment 2

[0111] As Figure 10 shown, the compression release type in-cylinder braking system of the engine according to the second embodiment of the present invention is basically the same as that of the first embodiment, except that: the cam for abutting against and pushing the plunger 22 of the oil pumping device II is a total braking cam 16a, and the total braking cam 16a is a cam added at an appropriate position on the camshaft, different from the original exhaust cam and intake cam on the camshaft; and, the oil pumping devices II corresponding to all cylinders of the engine are arranged around the total braking cam 16a, and the number of oil pumping devices II is the same as the number of cylinders of the engine.

[0112] As Figure 10 taking a six-cylinder engine as an example, it shows the situation where the oil pumping devices II of the six cylinders of the engine are arranged around the total braking cam 16a.

[0113] Obviously, the compression release type in-cylinder braking system of the present invention is not limited to Figure 1 and Figure 10 the six-cylinder engine shown. The compression release type in-cylinder braking system of the present invention is not limited by the number of cylinders, and the number of cylinders can be increased or decreased on the basis of six cylinders. The number of cylinders can be even or odd.

[0114] The present invention discloses an exhaust braking solution for an engine with a camshaft located below. For engines with a camshaft located on the side or at the top, the same can be implemented by reference.

[0115] The above are examples of the preferred embodiments of the present invention. Those parts not described in detail are known technologies to those skilled in the art. The protection scope of the present invention shall be subject to the content of the claims. Any equivalent transformation based on the technical inspiration of the present invention shall fall within the protection scope of the present invention.

Claims

1. Compression release type in-cylinder engine braking system, applied to the valve train of the engine, comprising: An oil cylinder device, an oil pumping device and an oil supply device, and all cylinders of the engine share one of the oil supply devices; The valve train includes a camshaft, rocker arms and valves, and the camshaft is provided with cams; The oil supply device includes an electromagnetic reversing valve, an oil supply oil path, a pressure reducing oil path and a pressure relief oil path; the electromagnetic reversing valve is a two-position three-way electromagnetic reversing valve, and one end of the oil supply oil path is connected to one oil port of the two-position three-way electromagnetic reversing valve; one end of the pressure reducing oil path is connected to the engine oil oil path, and the other end is connected to another oil port of the two-position three-way electromagnetic reversing valve; another oil port of the two-position three-way electromagnetic reversing valve is connected to the engine oil oil path; one end of the pressure relief oil path is connected to the pressure reducing oil path, and the other end is connected to the oil pan of the engine. An overflow pressure maintaining valve is arranged in the pressure relief oil path. Define the engine oil pressure before pressure reduction as P1 and the engine oil pressure after pressure reduction as P2; Each of the cylinders is respectively provided with the oil cylinder device and the oil pumping device. The oil cylinder device and the oil pumping device are communicated through a pressure transmission oil path, and the pressure transmission oil path is communicated with the oil supply oil path through a low-pressure pressure relief valve; characterized in that, A gas release valve is arranged at the high end of the pressure transmission oil path; During in-cylinder braking, the gas release valve is closed, the electromagnetic reversing valve is energized, and oil with a pressure of P1 is supplied to the pressure transmission oil path through the oil supply oil path; the cam abuts against and pushes the oil pumping device, the oil pressure in the oil pumping device increases, and the oil pumping device pumps high-pressure oil with a pressure of P to the oil cylinder device through the pressure transmission oil path, and the oil cylinder device pushes the rocker arm to open the valve; During non-in-cylinder braking, the gas release valve is opened, the electromagnetic reversing valve is de-energized, and oil with a pressure of P2 is supplied to the pressure transmission oil path through the oil supply oil path; the oil cylinder device and the oil pumping device return respectively, and the cam is separated from the oil pumping device; When the oil pumping device works, the low-pressure pressure relief valve is closed; when the oil pumping device does not work, the low-pressure pressure relief valve is opened; the opening pressure difference of the low-pressure pressure relief valve is greater than P1, and the opening pressure difference of the low-pressure pressure relief valve is less than P; 2. The compression release type in-cylinder braking system for an engine according to claim 1, wherein The gas release valve includes: A valve body, the valve body is provided with a valve body oil port one and a valve body oil port two communicated with its valve cavity, the valve body oil port one is connected to the pressure transmission oil path, and the valve body oil port two is connected to the oil pan of the engine; A valve ball, the valve ball is arranged in the valve cavity; A compression spring, the compression spring is arranged in the valve cavity and is clamped between the valve ball and the valve body oil port two; A limit pin, the limit pin is arranged on the valve body and is located between the valve body oil port one and the valve ball; The elastic force of the compression spring of the gas release valve on the valve ball is greater than the acting force of the engine oil pressure P2 after pressure reduction on the valve ball and less than the acting force of the engine oil pressure P1 before pressure reduction on the valve ball; 3. The compression-release type in-cylinder braking system for an engine according to claim 2, wherein A throttle hole is arranged behind the gas release valve, and the throttle hole is communicated with the oil pan of the engine.

4. The compression release type in-cylinder braking system for an engine according to claim 1, wherein, The oil circuits of each cylinder between the low-pressure pressure relief valve and the oil supply oil circuit are jointly connected to a high-pressure overflow pressure maintaining valve, and the high-pressure overflow pressure maintaining valve is communicated with the oil pan of the engine.

5. The compression-release type in-cylinder braking system for an engine according to claim 1, characterized in that, A check valve is connected in front of the electromagnetic directional control valve.

6. The compression release type in-cylinder braking system for an engine according to claim 1, characterized in that, A throttle orifice is provided in the pressure reducing oil circuit.

7. The compression release type in-cylinder braking system for an engine according to claim 1, characterized in that, The oil pumping device includes: A plunger sleeve, the bottom of the plunger sleeve is closed, the top of the plunger sleeve is open, and a plunger sleeve oil inlet / outlet hole is provided on the sleeve wall of the plunger sleeve, and the plunger sleeve oil inlet / outlet hole is connected to the pressure transmission oil circuit; A plunger, the plunger is slidably arranged in the inner cavity of the plunger sleeve, a plunger sleeve oil cavity is formed between the bottom of the plunger and the bottom of the plunger sleeve, the plunger sleeve oil inlet / outlet hole is communicated with the plunger sleeve oil cavity, the top of the plunger extends outside the open end of the plunger sleeve, during in-cylinder braking, the top of the plunger contacts the cam, and during non-in-cylinder braking, the top of the plunger is disengaged from the cam; A plunger tension spring, the plunger tension spring is located in the plunger sleeve oil cavity and is connected between the bottom of the plunger sleeve and the bottom of the plunger; A plunger limiting device is provided at the open end of the plunger sleeve; the plunger includes a plunger large-diameter section located in the inner cavity of the plunger sleeve and a plunger small-diameter section connected to the plunger large-diameter section, and a plunger step is formed at the transition between the plunger large-diameter section and the plunger small-diameter section, and during in-cylinder braking, the plunger limiting device limits the plunger step; The plunger further includes a plunger abutting section located outside the plunger sleeve and connected to the plunger small-diameter section, and during in-cylinder braking, the top surface of the plunger abutting section abuts against the cam; during non-in-cylinder braking, the top surface of the plunger abutting section is disengaged from the cam, and the plunger limiting device limits the plunger abutting section.

8. The compression-release type in-cylinder braking system for an engine according to claim 1, characterized in that, The oil cylinder device includes: A cylinder block, the top of the cylinder block is closed, the bottom of the cylinder block is open, and a cylinder block oil inlet / outlet hole is provided on the cylinder wall of the cylinder block, and the cylinder block oil inlet / outlet hole is connected to the pressure transmission oil circuit; A piston, the piston is slidably arranged in the inner cavity of the cylinder block, a cylinder block oil cavity is formed between the top of the piston and the top of the cylinder block, the cylinder block oil inlet / outlet hole is communicated with the cylinder block oil cavity, a piston rod is provided at the bottom of the piston, and the piston rod extends out of the open end of the cylinder block, and during in-cylinder braking, the bottom of the piston rod contacts the rocker arm and presses down the rocker arm to open the valve, and during non-in-cylinder braking, the bottom of the piston rod is disengaged from the rocker arm; A piston tension spring, the piston tension spring is located in the cylinder block oil cavity and is connected between the top of the cylinder block and the top of the piston; A cylinder block oil drain hole is further provided on the cylinder wall of the cylinder block, and the cylinder block oil drain hole is communicated with the oil pan of the engine. During in-cylinder braking, the piston moves downward, and when the oil pumping device works, the cylinder block oil drain hole is not communicated with the cylinder block oil cavity; when the cam pushes open the valve through the valve train and the oil pumping device does not work, the cylinder block oil drain hole is communicated with the cylinder block oil cavity; during non-in-cylinder braking, under the action of the piston tension spring, the piston blocks the cylinder block oil drain hole; A piston limiting device is provided at the open end of the cylinder block; a piston step is formed at the transition between the piston and the piston rod. When the in-cylinder braking pump oil device is working, the piston limiting device does not limit the piston step, and the distance between the piston step and the piston limiting device is S, where S > 0; When the cam pushes open the valve through the valve train and the pump oil device is not working, the piston limiting device limits the piston step, and S = 0.

9. The compression release type in-cylinder braking system for an engine according to claim 1, characterized in that, The low-pressure relief valve includes: A valve body, which is provided with a first valve body oil port and a second valve body oil port communicating with its valve cavity. The first valve body oil port is connected to the pressure transmission oil path, and the second valve body oil port is connected to the oil supply oil path; A valve ball, which is arranged in the valve cavity; A compression spring, which is arranged in the valve cavity and is clamped between the valve ball and the second valve body oil port; A limit pin, which is arranged on the valve body and is located between the first valve body oil port and the valve ball.

10. The compression release type in-cylinder braking system for an engine according to claim 1, characterized in that, The cam is an exhaust cam; alternatively, the cam is an intake cam; alternatively, the cam is a single-cylinder braking cam.

11. The compression release type in-cylinder braking system for an engine according to claim 1, characterized in that, The cam is a total braking cam, and the pump oil device is arranged around the total braking cam. The number of the pump oil devices is the same as the number of cylinders of the engine.

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