Heavy-duty combustion engine

Abstract

The invention relates to the field of combustion engines. A heavy duty combustion engine is provided. The heavy-duty combustion engine includes a variable hydraulic valve mechanism by combining a single cam member having a dedicated cam profile, a valve return brake assembly, and a switching solenoid valve, two-stroke compression release braking with two exhaust valves opened at the same time and advanced opening and closing of the exhaust valves in a normal ignition mode are achieved; specifically, the cam profile of the cam member is provided with four continuous ramp-up stages, so that the four continuous ramp-up stages cover a compression release lift in a CRB 1.5 compression release braking mode, an early exhaust valve opening / closing in an ignition mode, and an exhaust main lift in a normal ignition mode.

Description

Technical Field

[0001] The present invention relates to the field of combustion engines, and more particularly to a heavy-duty combustion engine. Background Art

[0002] Heavy-duty internal combustion engines may include a compression release function to provide auxiliary braking power for vehicles. The compression release function is to open the exhaust valve before the piston top dead center (TDC point), so that the gas is released under the cylinder pressure (such as above 30 barA). The reciprocating piston does negative work during the compression release process, thereby achieving the effect of generating braking torque.

[0003] In recent years, a much-concerned commercial vehicle engine thermal management is waste heat management, that is, actively heating the selective catalytic reduction (SCR) catalyst for nitrogen oxides reduction during cold start and low-load cycles. For future Euro 7 (EU7) exhaust emission regulations, actively reducing raw nitrogen oxide emissions and actively heating the aftertreatment device are one of the development roadmaps for many commercial vehicle engine manufacturers.

[0004] In terms of catalyst preheating measures, engine manufacturers have studied the possibility of directly using waste heat energy to actively preheat the aftertreatment path at idle speed. For example, in a double overhead cam engine, the exhaust cam phase realizes early opening and early closing, so that hotter exhaust gas flows to the catalyst. The effect of early closing is to increase the residual combustion gas in the cylinder, thereby helping to increase the average temperature of the cylinder gas. However, for a single overhead engine without a separate cam phase adjustment function, the active exhaust path temperature increase must be achieved through valve lift switching.

[0005] In fact, the exhaust valve mechanism of current mainstream heavy-duty engines usually can only achieve one valve lift function, specifically by switching between different rocker arms through a variable valve mechanism.

[0006] To provide more than two valve lift functions, independent rocker arms are required for switching; the mechanical strength of the switching mechanism plays a decisive role in the valve lift change; with such a setting, although more than two valve lifts can be achieved, since each valve lift requires independent rocker arm control, therefore, multiple rocker arms or cams need to be provided in the heavy-duty engine. However, the combination of multiple rocker arms or cams will occupy the installation space of the heavy-duty engine, resulting in a large volume of the equipment for installing the heavy-duty engine, which is not conducive to the installation and use of the heavy-duty engine.

[0007] In view of this, it is necessary to provide an integrated valve mechanism for a heavy-duty engine to solve or alleviate one of the above problems. Summary of the Invention

[0008] The object of the present invention is to provide a heavy-duty combustion engine, which includes a variable hydraulic valve mechanism. The variable hydraulic valve mechanism can achieve continuous change of valve lift by integrating compression release braking, the main lift of the exhaust valve, and early opening / closing into the cam profile of a cam member, and by calibrating the rotation trajectory of the cam member and cutting off the hydraulic pressure between the exhaust valve plunger.

[0009] To achieve the above object of the invention, the present invention provides a heavy-duty combustion engine, which includes a variable hydraulic valve mechanism. The variable hydraulic valve mechanism includes: a piston assembly configured with a cam member and a piston unit. Four continuous ramp-up stages and one ramp-down stage are formed circumferentially on the cam member. The ramp-up stages and the ramp-down stage together cover a crank angle of 550-570 degrees. The piston unit includes a pump roller abutting against the outer peripheral edge of the cam member; an energy storage assembly; a valve return braking assembly. The valve return braking assembly is arranged in pairs and connected to the exhaust valve. The two valve return braking assemblies are connected as a whole through a hydraulic bridge; a switching solenoid valve for controlling the connection of the piston assembly, the energy storage assembly, and the valve return braking assembly to achieve two-stroke compression release braking with both exhaust valves opening simultaneously, and early opening and closing of the exhaust valve in the normal ignition mode.

[0010] As a further improvement of the present invention, the energy storage assembly is connected to the switching solenoid valve through an intermediate pressure chamber or a first passage. The hydraulic bridge is connected to a high-pressure oil chamber or a second passage of the piston unit of the piston assembly. The high-pressure oil chamber or the second passage is connected to the switching solenoid valve. When the switching solenoid valve connects the high-pressure oil chamber or the second passage and the intermediate pressure chamber or the first passage, the movement of the cam member is transmitted to the energy storage assembly, disconnecting the valve return braking assembly and deactivating the exhaust valve; when the switching solenoid valve disconnects the connection between the high-pressure oil chamber or the second passage and the intermediate pressure chamber or the first passage, the movement of the cam member is transmitted to the valve return braking assembly to generate an exhaust lift.

[0011] As a further improvement of the present invention, each valve return braking assembly includes a braking unit for the exhaust valve and an exhaust valve assembly. Among them, the exhaust valve assembly includes a valve body, a valve stem, and an exhaust valve spring sleeved on the outer periphery of the valve stem. The hydraulic bridge is connected to an oil chamber of the valve body. The exhaust valve spring applies a force to the valve stem to make the valve stem tend to compress the oil chamber of the valve body.

[0012] As a further improvement of the present invention, the piston unit of the piston assembly further includes a pump piston connected to one side of the pump roller, a pump oil chamber for accommodating the pump piston, and a pump spring sleeved on the outer periphery of the pump piston. The high-pressure oil chamber or the second channel is connected to the pump oil chamber, and the pump spring presses the pump piston towards the cam member.

[0013] As a further improvement of the present invention, the switching solenoid valve is a 2 / 2 normally open solenoid valve.

[0014] As a further improvement of the present invention, the energy storage assembly includes an accumulator oil chamber, an accumulator piston movably connected in the accumulator oil chamber, and an accumulator spring sleeved on the outer periphery of the accumulator piston. The intermediate pressure chamber or the first channel is connected to the accumulator oil chamber, and the accumulator spring acts on the accumulator piston to tend to make the oil in the accumulator oil chamber flow towards the intermediate pressure chamber or the first channel.

[0015] As a further improvement of the present invention, the compression stiffness of the exhaust valve spring is greater than that of the accumulator spring, so that when the switching solenoid valve connects the high-pressure oil chamber or the second channel and the intermediate pressure chamber or the first channel, the movement of the cam member is transmitted to the energy storage assembly rather than to the valve return braking assembly.

[0016] As a further improvement of the present invention, the first ramp-up stage of the cam member covers the first compression release braking event of a heavy-duty engine; the second ramp-up stage of the cam member starts from the end point of the first ramp-up stage and includes opening the exhaust valve early in the ignition mode so as to release the exhaust gas energy to the aftertreatment path earlier compared with the normal main lift mode; the third ramp-up stage of the cam member is the longest ramp-up stage and covers the main lift opening sequence; the fourth ramp-up stage of the cam member is the second engine compression release braking event of the heavy-duty engine; the ramp-down stage of the cam member is to return to the base circle of the cam member.

[0017] The beneficial effects of the present invention include: the heavy-duty combustion engine of the present invention includes a variable hydraulic valve mechanism. The variable hydraulic valve mechanism combines a single cam member with a dedicated cam profile, a valve return braking assembly, and a switching solenoid valve to achieve two-stroke compression release braking with two exhaust valves opened simultaneously and early opening and closing of the exhaust valve in the normal ignition mode; specifically, by setting the cam profile of the cam member to be composed of 4 consecutive ramp-up stages, the 4 consecutive ramp-up stages cover the compression release lift in the CRB1.5 compression release braking mode, the early opening / closing of the exhaust valve in the ignition mode, and the main exhaust lift in the normal ignition mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic structural diagram of a variable hydraulic valve mechanism of a heavy-duty combustion engine according to the present invention.

[0019] Figure 2 is Figure 1 a three-dimensional sectional view of the variable hydraulic valve mechanism in

[0020] Figure 3 is Figure 1 a schematic structural diagram of the cam member in

[0021] Figure 4 For the working principle of the on-off solenoid valve control to generate exhaust lift.

[0022] Figure 5 For the working principle of the on-off solenoid valve control to deactivate the movement of two valves.

[0023] Figure 6 is Figure 3 the lift coverage crankshaft angle curve that the cam member in

[0024] Figure 7 is Figure 3 the lift curve of each stage of the lift part of the cam member in

[0025] Figure 8 For the current control curve of the on-off solenoid valve during exhaust lift and the expected in-cylinder pressure curve under normal ignition mode.

[0026] Figure 9 For the solenoid valve current control curve during early exhaust valve opening (EEVO) and early exhaust valve closing (EEVC) stages and the cylinder pressure curve under early exhaust opening and closing mode.

[0027] Figure 10 For the solenoid valve current control curve of the CRB1.5 compression release braking function and the cylinder pressure curve during two-stroke CRB1.5 compression release braking. Detailed implementation manners

[0028] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention, and should not be construed as limiting the present invention.

[0029] In the description of the present invention, it should be understood that the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality of" means two or more unless otherwise specifically defined.

[0030] In the present invention, unless otherwise clearly specified and limited, the terms "mounted", "connected", "coupled", "fixed", etc. shall be construed in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0031] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail below with reference to the drawings and specific embodiments.

[0032] Please refer to Figure 1 and Figure 2 The heavy-duty engine provided by the present invention includes a variable hydraulic valve mechanism; the variable hydraulic valve mechanism of the present invention includes: a piston assembly 1, an energy storage assembly 2, a valve return braking assembly 3 connected to the exhaust valve, and a switching solenoid valve 4; the switching solenoid valve 4 is used to control the connection of the piston assembly 1, the energy storage assembly 2, and the valve return braking assembly 3; to achieve two-stroke compression release braking with two exhaust valves opening simultaneously, and the early opening and closing of the exhaust valve in the normal ignition mode.

[0033] The piston assembly 1 includes a cam member 11 and a piston unit 12 drivingly connected to the cam member 11. As Figure 3 shown, the circumferential direction of the cam member 11 is formed with 4 continuous ramp rising stages (the first ramp rising stage 1a, the second ramp rising stage 1b, the third ramp rising stage 1c, the fourth ramp rising stage 1d) and 1 ramp falling stage (1e); the rising stage and the falling stage together cover a crank angle (CrA) of 550 - 570 degrees (i.e., a cam angle of 275 - 285 degrees).

[0034] Further, the piston unit 12 includes a pump roller 121 abutted against the outer peripheral edge of the cam member 11, a pump piston 122 connected to one side of the pump roller 121, a pump oil chamber 123 for accommodating the pump piston 122, and a pump spring 24 sleeved on the outer periphery of the pump piston 122. The piston assembly 1 further includes a high-pressure oil chamber or a second passage 13 connected to the pump oil chamber 123. The pump spring 24 presses the pump piston 122 towards the cam member 11.

[0035] The energy storage assembly 2 is connected to the switching solenoid valve 4 through an intermediate pressure chamber or a first passage 21, and then is respectively connected to the piston assembly 1 and the valve return braking assembly 3 through the switching solenoid valve 4. The energy storage assembly 2 includes an accumulator oil chamber 22, an accumulator piston 23 movably connected in the accumulator oil chamber 22, and an accumulator spring 24 sleeved on the outer periphery of the accumulator piston 23. The intermediate pressure chamber or the first passage 21 is connected to the accumulator oil chamber 22, and the accumulator spring 24 acts on the accumulator piston 23 to tend to make the oil in the accumulator oil chamber 22 flow into the intermediate pressure chamber or the first passage 21.

[0036] The valve return braking assemblies 3 are arranged in pairs and connected to the exhaust valve. The two valve return braking assemblies 3 are connected as a whole through a hydraulic bridge 5 and are connected in the high-pressure oil chamber or the second passage 13 of the piston assembly 1 through the hydraulic bridge 5. Further, each valve return braking assembly 3 includes a braking unit 31 for the exhaust valve and an exhaust valve assembly 32. The exhaust valve assembly 32 includes a valve body 321, a valve stem 322, and an exhaust valve spring 323 sleeved on the outer periphery of the valve stem 322. The hydraulic bridge 5 is connected to the oil chamber of the valve body 321. The exhaust valve spring 323 applies a force ( Figure 1 in which, presses the valve stem 322 upward) to make the valve stem 322 tend to compress the oil chamber of the valve body 321. Here, only the exhaust valve spring 323 is schematically shown. Figure 1 in which, the upper end of the exhaust valve spring 323 can act on the lower surface of the flange on the valve stem 322, and the lower end of the exhaust valve spring 323 can be supported on the housing (for example, the cylinder head or the supporting part thereon).

[0037] The compression stiffness of the exhaust valve spring 323 can be greater than that of the accumulator spring 24, so that when the switching solenoid valve 4 connects the high-pressure oil chamber or the second passage 13 and the intermediate pressure chamber or the first passage 21, the movement of the cam member 11 is transmitted to the energy storage assembly 2 rather than to the valve return braking assembly 3, that is, the oil in the piston unit 12 enters the accumulator oil chamber 22 to compress the accumulator spring 24, rather than entering the valve body 321 to compress the exhaust valve spring 323.

[0038] Further, the piston assembly 1, the energy storage assembly 2, and the valve return braking assembly 3 connected to the exhaust valve are connected to the switching solenoid valve 4. Specifically, when the switching solenoid valve 4 is energized, the switching solenoid valve 4 disconnects the connection between the high-pressure oil chamber or the second passage 13 and the intermediate pressure chamber or the first passage 21, and the movement of the cam member 11 is transmitted to the valve return braking assembly 3 (in Figure 4 , the valve stem 322 moves downward), to generate an exhaust lift ( Figure 4 ); when the switching solenoid valve 4 is de-energized, the switching solenoid valve 4 connects the high-pressure oil chamber or the second passage 13 and the intermediate pressure chamber or the first passage 21, and the movement of the cam member 11 is transmitted to the energy storage assembly 2, to disconnect the valve return braking assembly 3 (that is, the oil in the intermediate pressure chamber or the first passage 21 does not enter the valve body 321), and deactivate the exhaust valve ( Figure 5 ).

[0039] Refer to Figure 3 and combine with Figure 6 , Figure 7 shown. In a four-stroke internal combustion engine, four continuous ramp-up stages (the first ramp-up stage 1a, the second ramp-up stage 1b, the third ramp-up stage 1c, the fourth ramp-up stage 1d) and one ramp-down stage (1e) are formed on the outer periphery of the cam member 11; together they cover a crank angle of 550 - 570 degrees.

[0040] Among them, the first ramp-up stage 1a of the cam member 11 covers the first compression release braking event of a heavy-duty engine; it starts at 50 - 60 CrA degrees before TDC ignition (0 CrA) and ends at 3 - 5 CrA high points after TDC ignition.

[0041] The second ramp-up stage 1b of the cam member 11 starts from the end point of the first ramp-up stage 1a, that is, 3 - 5 CrA after TDC ignition (ATDC), until 70 CrA ATDC, and then reaches 90 CrA ATDC. The second ramp-up stage 1b includes opening the exhaust valve in advance in the ignition mode, so as to release the exhaust gas energy to the aftertreatment path earlier compared with the normal main lift mode.

[0042] The third ramp-up stage 1c of the cam member 11 is the longest ramp-up stage, covering the main lift opening sequence. It gradually accelerates from 90 CrA ATDC to 230 CrA ATDC, and then is in a steady stage until 315 CrA ATDC.

[0043] The fourth ramp-up stage 1d of the cam member 11 is the second engine compression release braking event of a heavy-duty engine; it starts from 315 CrA ATDC to 355 CrA ATDC, and then reaches 365 CrA ATDC.

[0044] The ramp-down phase 1e is the base circle of the return cam member 11; it starts at 365 CrA ATDC and ends between 500 and 510 CrA ATDC.

[0045] Furthermore, when the switching solenoid valve 4 controls the operation of the variable hydraulic valve mechanism, the control strategies and the number of energizations of the switching solenoid valve 4 for compression release braking (CRB1.5), early exhaust valve opening / closing (EEVO / EEVC), and normal ignition exhaust main lift are different; specifically, in the case of early exhaust valve opening / closing (EEVO / EEVC) and normal ignition exhaust main lift, the switching solenoid valve 4 is energized and de-energized once every four strokes; and during compression release braking CRB1.5, the switching solenoid valve 4 is energized and de-energized twice every 720° of crankshaft rotation.

[0046] Refer to Figure 8 As shown, for the exhaust main lift, the switching solenoid valve 4 is energized briefly after the second ramp-up phase 1b and before the exhaust main lift, for example, between 45 and 60 CrA ATDC, so that the lift is generated around 90 to 100 CrA ATDC. The switching solenoid valve 4 is de-energized between 270 and 30 CrA ATDC, and the exhaust valve pushes the oil in the valve return braking assembly 3 back to the energy storage assembly 2, thus returning the exhaust valve to its seat. At the same time, the closing time can be calibrated so that the exhaust valve closes after TDC (for example, around 405 CrA ATDC).

[0047] Refer to Figure 9 As shown, in the early opening (EEVO) and early closing (EEVC) functions, compared with the normal exhaust lift mode, the switching solenoid valve 4 is energized approximately 60 CrA earlier. Compared with the closing time of the normal exhaust lift mode, the switching solenoid valve 4 closes approximately 30 degrees of crank angle earlier, so that the exhaust valve closes 10 to 30 degrees earlier (EEVC). EEVO and EEVC together increase the exhaust temperature and the residual gas in the heavy-duty engine cylinder.

[0048] Refer to Figure 10As shown, in the two-stroke compression release braking function with two compression release processes, when performing compression release braking, there will be two exhaust opening instants: For the first time, the switching solenoid valve 4 is energized starting from 90 CrA BTDC, and the first valve lift is generated at approximately 45 CrA BTDC. The actual valve opening event depends on the dynamic mechanical balance among the cylinder pressure, exhaust manifold pressure, spring force, and movement inertia. Then, the switching solenoid valve 4 is de-energized at approximately 90 CrA ATDC, the exhaust valve moves back to the reference position, and closes at approximately 140 CrA ATDC. The second energization of the switching solenoid valve 4 starting from 290 CrA ATDC generates the second valve lift between 315 and 325 CrA ATDC; similarly, the actual valve opening event depends on the dynamic mechanical balance among the cylinder pressure, exhaust manifold pressure, spring force, and movement mass inertia. Then, the switching solenoid valve 4 is de-energized at 365 CrA ATDC, the exhaust valve moves back to the reference position, and closes between 380 and 390 CrA ATDC.

[0049] In summary, the variable hydraulic valve mechanism of the present invention combines a single cam member 11 with a dedicated cam profile, a valve return braking assembly 3, and a switching solenoid valve 4 to achieve two-stroke compression release braking with two exhaust valves opening simultaneously, as well as early opening and closing of the exhaust valve in the normal ignition mode; specifically, by setting the cam profile of the cam member 11 to consist of 4 consecutive ramp-up stages, the 4 consecutive ramp-up stages cover the compression release lift in the CRB1.5 compression release braking mode, the early opening / closing of the exhaust valve in the ignition mode, and the main exhaust lift in the normal ignition mode; in addition, the variable hydraulic valve mechanism can also achieve the dynamic cylinder deactivation (i.e., selective cylinder deactivation) function. Further, by setting the switching solenoid valve 4 as a 2 / 2-way high-speed solenoid valve, it cooperates with the movement trajectory of the cam member 11 to switch the valve lift mode; and in all valve lifts, including decompression release braking, the two exhaust valves operate simultaneously.

[0050] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A heavy-duty combustion engine, characterized in that, including a variable hydraulic valve mechanism, which includes: a piston assembly (1) configured with a cam member (11) and a piston unit (12), the circumferential direction of the cam member (11) being formed with 4 continuous ramp-up stages and 1 ramp-down stage, the ramp-up stages and the ramp-down stage together covering a crank angle of 550-570 degrees, the piston unit (12) including a pump roller (121) abutting against the outer peripheral edge of the cam member (11); an energy storage assembly (2); a valve return braking assembly (3), the valve return braking assemblies being arranged in pairs and connected to the exhaust valves, the two valve return braking assemblies (3) being connected as a whole through a hydraulic bridge (5); a switching solenoid valve (4) for controlling the connection of the piston assembly (1), the energy storage assembly (2), and the valve return braking assembly (3) to achieve two-stroke compression release braking with both exhaust valves opened simultaneously, and early opening and closing of the exhaust valves in the normal ignition mode.

2. The heavy-duty combustion engine according to claim 1, characterized in that, The energy storage assembly (2) is connected to the switching solenoid valve (4) through an intermediate pressure chamber or a first passage (21), the hydraulic bridge (5) is connected to a high-pressure oil chamber or a second passage (13) of the piston unit (12) of the piston assembly (1), and the high-pressure oil chamber or the second passage (13) is connected to the switching solenoid valve (4). When the switching solenoid valve (4) connects the high-pressure oil chamber or the second passage (13) and the intermediate pressure chamber or the first passage (21), the movement of the cam member (11) is transmitted to the energy storage assembly (2), disconnecting the valve return braking assembly (3) and deactivating the exhaust valve; when the switching solenoid valve (4) disconnects the connection between the high-pressure oil chamber or the second passage (13) and the intermediate pressure chamber or the first passage (21), the movement of the cam member (11) is transmitted to the valve return braking assembly (3) to generate an exhaust lift.

3. The heavy-duty combustion engine according to claim 2, characterized in that, Each valve return braking assembly (3) includes a braking unit (31) for the exhaust valve and an exhaust valve assembly (32), wherein the exhaust valve assembly (32) includes a valve body (321), a valve stem (322), and an exhaust valve spring (323) sleeved on the outer periphery of the valve stem (322), the hydraulic bridge (5) is connected to the oil chamber of the valve body (321), and the exhaust valve spring (323) applies a force to the valve stem (322) to make the valve stem (322) tend to compress the oil chamber of the valve body (321).

4. The heavy-duty combustion engine according to claim 2, characterized in that, The piston unit (12) of the piston assembly (1) further includes a pump piston (122) connected to one side of the pump roller (121), a pump oil chamber (123) for accommodating the pump piston (122), and a pump spring (124) sleeved on the outer periphery of the pump piston (122), the high-pressure oil chamber or the second passage (13) is connected to the pump oil chamber (123), and the pump spring (124) presses the pump piston (122) towards the cam member (11).

5. The heavy-duty combustion engine according to claim 1, characterized in that, The switching solenoid valve (4) is a 2 / 2 normally open solenoid valve.

6. The heavy-duty combustion engine according to claim 3, characterized in that, The energy storage assembly (2) includes an accumulator oil chamber (22), an accumulator piston (23) movably connected in the accumulator oil chamber (22), and an accumulator spring (24) sleeved on the outer periphery of the accumulator piston (23). The intermediate pressure chamber or the first passage (21) is connected to the accumulator oil chamber (22). The accumulator spring (24) acts on the accumulator piston (23) to tend to make the oil in the accumulator oil chamber (22) flow to the intermediate pressure chamber or the first passage (21).

7. The heavy-duty combustion engine according to claim 6, characterized in that, The compression stiffness of the exhaust valve spring (323) is greater than that of the accumulator spring (24), so that when the switching solenoid valve (4) connects the high-pressure oil chamber or the second passage (13) and the intermediate pressure chamber or the first passage (21), the movement of the cam member (11) is transmitted to the energy storage assembly (2) rather than to the valve return braking assembly (3).

8. The heavy-duty combustion engine according to claim 1, wherein The first ramp-up stage (1a) of the cam member (11) covers the first compression release braking event of the heavy-duty engine; The second ramp-up stage (1b) of the cam member (11) starts from the end point of the first ramp-up stage (1a) and includes opening the exhaust valve in advance in the ignition mode so as to release the exhaust gas energy to the aftertreatment path earlier than in the normal main lift mode; The third ramp-up stage (1c) of the cam member (11) is the longest ramp-up stage and covers the main lift opening sequence; The fourth ramp-up stage (1d) of the cam member (11) is the second engine compression release braking event of the heavy-duty engine; The ramp-down stage (1e) of the cam member (11) is to return to the base circle of the cam member (11).

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