Heavy-duty engine with mechanical valve and two piston assemblies

Abstract

The invention relates to the field of piston type internal combustion engines, in particular to a heavy-duty engine with a mechanical valve and two piston assemblies. According to the variable hydraulic exhaust valve mechanism of the heavy-duty engine, the hydraulic energy storage assembly and the mechanical valve are arranged, so that the heavy-duty engine using the variable hydraulic exhaust valve mechanism can be switched between a four-stroke ignition mode main lifting mode and a two-stroke compression release brake compression mode; meanwhile, mechanical valves used by multiple cylinders can be driven in a centralized mode by arranging one pilot electromagnetic valve.

Description

Technical Field

[0001] The present invention relates to the field of piston internal combustion engines, and more particularly to a heavy-duty engine having a mechanical valve and two piston assemblies. Background Art

[0002] Most of the current mainstream heavy-duty engines use a single overhead camshaft SOHC (there is only one camshaft above the valves to drive the intake and exhaust valves) for the exhaust valve mechanism, and the exhaust valve is driven by a rocker arm.

[0003] Heavy-duty internal combustion engines may include a compression release function to provide auxiliary braking power for the vehicle. The compression release function is to open the exhaust valve before the top dead center TDC of the piston, so that the gas is released under the cylinder pressure (such as above 30 barA). During the compression release process, the reciprocating piston does negative work, thereby achieving the effect of generating braking torque.

[0004] In fact, the exhaust valve mechanism of the 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.

[0005] In order 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 change of valve lift; thus configured, 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.

[0006] 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

[0007] The object of the present invention is to provide a heavy-duty engine having a mechanical valve and two piston assemblies. The variable hydraulic exhaust valve mechanism of the heavy-duty engine can be switched between the main lift in the four-stroke ignition mode and the compression release braking compression in the two-stroke mode by setting a hydraulic energy storage component and a mechanical valve.

[0008] To achieve the above-mentioned invention object, the present invention provides a heavy-duty engine with a mechanical valve and two piston assemblies, which includes a variable hydraulic exhaust valve mechanism. The variable hydraulic exhaust valve mechanism includes: a first piston assembly, which includes a first cam and a first main piston unit drivingly connected to the first cam, and is used for the compression release brake of the heavy-duty engine; a second piston assembly, which includes a second cam and a second main piston unit drivingly connected to the second cam, and is used for the normal ignition of the heavy-duty engine; a mechanical valve, which is configured to disconnect and connect the first piston assembly and the second piston assembly to realize the switching of the heavy-duty engine between the compression release brake mode and the normal ignition mode; an energy storage assembly, which is respectively connected to the first piston assembly and the second piston assembly through the mechanical valve; and two valve return braking assemblies, which are controllably connected to the first piston assembly and the second piston assembly through the mechanical valve to simultaneously open two exhaust valves during the compression release brake process. Wherein, in the compression release brake mode of the heavy-duty engine, the mechanical valve hydraulically connects the first piston assembly and the valve return braking assemblies, and the rotation of the first cam pumps high-pressure oil into the two valve return braking assemblies to simultaneously open the two exhaust valves. In the exhaust main lift of the normal ignition mode of the heavy-duty engine, the mechanical valve hydraulically connects the second piston assembly and the valve return braking assemblies, and the rotation of the second cam pumps high-pressure oil into the two valve return braking assemblies through the mechanical valve. The outer peripheral profile of the first cam is formed with a first lift step and a second lift step arranged at intervals; the rising and falling stages of the first lift step cover a cam angle range of 90 degrees; the rising and falling stages of the second lift step cover a cam angle range of 45 to 50 degrees. The heavy-duty engine further includes a hydraulic circuit assembly, which is shared by each cylinder of the heavy-duty engine and includes an oil pump unit and a solenoid valve. The solenoid valve is hydraulically connected to the mechanical valve and is used to drive the mechanical valve to change the communication state between its different ports. The mechanical valve is a 4 / 2 mechanical valve. The solenoid valve is a 3 / 2 solenoid valve, and one solenoid valve controls the communication state between different ports of the mechanical valves of multiple cylinders of the heavy-duty engine.

[0009] As a further improvement of the present invention, the first main piston unit includes a pump roller abutted and connected to the first cam, a pump piston connected to one end of the pump roller, and a pump oil chamber for accommodating the pump piston; the first main piston unit further includes a pump spring sleeved on the outer periphery of the pump piston.

[0010] As a further improvement of the present invention, the valve return braking assemblies are arranged in pairs, and the two valve return braking assemblies are connected through a hydraulic passage; each valve return braking assembly includes a braking unit for the exhaust valve and an exhaust valve assembly.

[0011] As a further improvement of the present invention, the energy storage component is connected to the mechanical valve through an intermediate pressure chamber or a first channel; the energy storage component 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. In the compression release braking mode of the heavy-duty engine, the mechanical valve hydraulically connects the second piston assembly to the energy storage component, and the rotation of the second cam pumps low-pressure oil into the energy storage component. In the exhaust main lift of the normal ignition mode of the heavy-duty engine, the mechanical valve hydraulically connects the first piston assembly to the energy storage component, and the rotation of the first cam pumps low-pressure oil into the energy storage component through the mechanical valve.

[0012] As a further improvement of the present invention, the oil pumping chamber of the first main piston unit is connected to port A of the mechanical valve through a high-pressure oil chamber or a second channel, the oil pumping chamber of the second main piston unit is connected to port B of the mechanical valve via a high-pressure oil chamber or a second channel, the two valve return braking components are connected to port P of the mechanical valve through a hydraulic passage, and the accumulator oil chamber of the energy storage component is connected to port T of the mechanical valve through an intermediate pressure chamber or a first channel.

[0013] The beneficial effects of the present invention include: the variable hydraulic exhaust valve mechanism of the heavy-duty engine of the present invention can switch between the main lift of the four-stroke ignition mode and the compression of the two-stroke compression release braking by setting a hydraulic energy storage component and a mechanical valve.

[0014] In addition, in at least one embodiment, a solenoid valve (such as a pilot solenoid valve) can be provided to centrally drive the mechanical valves used in multiple cylinders. Description of the Drawings

[0015] Figure 1 is a schematic structural diagram of the variable hydraulic exhaust valve mechanism of the heavy-duty engine of the present invention.

[0016] Figure 2 is Figure 1 a schematic structural diagram of the first cam in

[0017] Figure 3 a schematic diagram of the state of the variable hydraulic exhaust valve mechanism of the heavy-duty engine in the ignition mode.

[0018] Figure 4 a schematic diagram of the state of the variable hydraulic exhaust valve mechanism of the heavy-duty engine in the compression release braking mode.

[0019] Figure 5 a schematic diagram of the exhaust main lift on the crankshaft angle.

[0020] Figure 6 It is a schematic diagram of the main exhaust lift on the crankshaft angle and the expected cylinder pressure curve.

[0021] Figure 7 It is a schematic diagram of a two-stroke compression release brake and the expected cylinder pressure curve. Detailed implementation manners

[0022] 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 by referring to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0023] 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 indicating the number of the indicated technical features. Thus, the 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.

[0024] In the present invention, unless otherwise clearly specified and defined, the terms "mounted", "connected", "connected", "fixed" and other terms should be understood 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 elements or the interaction relationship between two elements. 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 situations.

[0025] In order to make the purpose, 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.

[0026] Heavy-duty engines (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).

[0027] One problem with the compression release function is how to improve the braking gas recirculation filling rate, which helps to improve the compression release braking power. Therefore, so-called brake gas recirculation (BGR) measures are usually introduced.

[0028] When a conventional heavy-duty engine implements the compression release function, it usually uses a variable valve mechanism to switch between different rocker arms to achieve more than two valve lift functions. However, limited by the rocker arm failure technology, usually one rocker arm can only drive one exhaust valve.

[0029] In fact, this technology switches between a mechanical bridge and single-valve movement. However, during the compression release braking process, the split rocker arm is difficult to withstand extremely high shear stress. Considering that the compression release braking of a heavy-duty engine is achieved through two exhaust valves instead of a single exhaust valve, and the compression release braking is two-stroke with two compression releases. The present invention sets a mechanical valve to switch between the normal ignition mode or the compression release braking mode. At the same time, by replacing the existing split rocker arm with a hydraulic switch technology, the variable hydraulic exhaust valve mechanism for a heavy-duty engine of the present invention can withstand a high oil pressure of up to 200 barA.

[0030] The heavy-duty engine of the present invention includes a variable hydraulic exhaust valve mechanism for a heavy-duty engine; please refer to Figure 1 As shown, the variable hydraulic exhaust valve mechanism for a heavy-duty engine of the present invention includes: a first piston assembly 1 for the compression release braking of a heavy-duty engine; a second piston assembly 2 for the normal ignition of a heavy-duty engine; a mechanical valve 3 configured to separately connect the first piston assembly 1 and the second piston assembly 2 to achieve the switching between the compression release braking mode and the normal ignition mode of a heavy-duty engine; an energy storage assembly 4 connected to the first piston assembly 1 and the second piston assembly 2 respectively through the mechanical valve 3; further, the variable hydraulic exhaust valve mechanism for a heavy-duty engine further includes a valve return braking assembly 5. Specifically, the valve return braking assembly 5 is controllably connected to the first piston assembly 1 and the second piston assembly 2 through the mechanical valve 3 to simultaneously open two exhaust valves during the compression release braking process.

[0031] Further, the variable hydraulic exhaust valve mechanism for a heavy-duty engine further includes a hydraulic circuit assembly 6. The hydraulic circuit assembly 6 is used in each cylinder of a heavy-duty engine. In other words, for multiple cylinders of a heavy-duty engine, or for multiple mechanical valves 3 for multiple cylinders, a single hydraulic circuit assembly 6 can be shared. The hydraulic circuit assembly 6 includes an oil pump unit 61 and a solenoid valve 62. Specifically, the hydraulic circuit assembly 6 includes a first oil passage 63 for connecting the engine oil sump 7 of an internal combustion engine and the solenoid valve 62, and a second oil passage 64 for connecting the engine oil sump 7, the oil pump unit 61, and the solenoid valve 62. In this application, the solenoid valve 62 is a 3 / 2 solenoid valve, and the solenoid valve 62 is arranged outside the cylinder head of the cylinder and is hydraulically connected to the mechanical valve 3 on each cylinder. The solenoid valve 62 is used to drive the mechanical valve 3 to change the communication state between its different ports. One solenoid valve can be connected to the mechanical valves 3 of multiple cylinders of a heavy-duty engine to control the communication state between different ports of the mechanical valves 3 of multiple cylinders.

[0032] The first piston assembly 1 includes a first cam 11 and a first main piston unit 12 that is drivingly connected to the first cam 11. As Figure 2 shown, the outer peripheral profile of the first cam 11 is formed with first lift steps 111 and second lift steps 112 that are spaced apart; the rising and falling phases of the first lift steps 111 cover a cam angle range of 90 degrees (i.e., a crank angle CrA of 180 degrees); the rising and falling phases of the second lift steps 112 cover a cam angle range of 45 to 50 degrees (i.e., a crank angle CrA of 90 to 100 degrees). Further, the first lift steps 111 include two consecutive lift ramps. With such a setting, the variable hydraulic exhaust valve mechanism for a heavy-duty engine can have the effect of braking exhaust gas recirculation BGR. It should be understood that Figure 2 the angles marked in the figure are the corresponding crank angles.

[0033] Further, the first main piston unit 12 includes a pump roller 121 that abuts and connects to the first cam 11, a pump piston 122 connected to one end of the pump roller 121, and a pump oil chamber 123 for accommodating the pump piston 122; the first main piston unit 12 further includes a pump spring 124 sleeved on the outer periphery of the pump piston 122.

[0034] The second piston assembly 2 includes a second cam 21 and a second main piston unit 22 that is drivingly connected to the second cam 21. In the present invention, the second cam 21 has a different outer peripheral profile from the first cam 11. Further, the second main piston unit 22 includes a pump roller 121 that abuts and connects to the second cam 21, a pump piston 122 connected to one end of the pump roller 121, and a pump oil chamber 123 for accommodating the pump piston 122; the first main piston unit 12 further includes a pump spring 124 sleeved on the outer periphery of the pump piston 122. The pump spring 124 tends to make the pump roller 121 abut against the outer peripheral profile of the first cam 11. The pump oil chamber 123 of the first main piston unit 12 can be connected to port A of the mechanical valve 3 through a high-pressure oil chamber or a second passage L1.

[0035] Specifically, the first piston assembly 1 and the second piston assembly 2 are connected to the mechanical valve 3 through a high-pressure oil chamber or a second passage L1, and the first cam 11 and the second cam 21 are separated; preferably, the mechanical valve 3 is a 4 / 2 mechanical valve.

[0036] The energy storage component 4 is connected to the mechanical valve 3 through the intermediate pressure chamber or the first channel 41, and then is respectively connected to the first piston assembly 1 and the second piston assembly 2 through the mechanical valve 3. The energy storage component 4 includes an accumulator oil chamber 42, an accumulator piston 43 movably connected in the accumulator oil chamber 42, and an accumulator spring 44 sleeved on the outer periphery of the accumulator piston 43. The accumulator spring 44 tends to discharge the oil in the accumulator oil chamber 42 through the intermediate pressure chamber or the first channel 41. The accumulator oil chamber 42 of the energy storage component 4 can be connected to the T port of the mechanical valve 3 through the intermediate pressure chamber or the first channel 41.

[0037] The valve return braking components 5 are arranged in pairs, and the two valve return braking components 5 are communicated through the hydraulic passage L2; each valve return braking component 5 includes a braking unit 51 for the exhaust valve and an exhaust valve assembly 52, wherein the exhaust valve assembly 52 includes a valve body 521, a valve stem 522, and an exhaust valve spring 523 sleeved on the outer periphery of the valve stem 522.

[0038] For the convenience of better understanding of the variable hydraulic exhaust valve mechanism for a heavy-duty engine of the present invention, the following description part will detail the motion states of each component in the variable hydraulic exhaust valve mechanism for a heavy-duty engine during the working process.

[0039] Please refer to Figure 3 As shown, it is a schematic diagram of the state of the exhaust main lift in the ignition mode of the variable hydraulic exhaust valve mechanism for a heavy-duty engine in the present invention. During the exhaust main lift in the ignition mode, the solenoid valve 62 is in the closed state, and the spring in the mechanical valve 3 pushes the mechanical valve 3 to the reference position PB||AT connection state (that is, the P port and the B port of the solenoid valve are connected, and the A port and the T port are connected). Since the oil pumping chamber 123 of the second piston assembly 2 is connected to the B port of the mechanical valve 3 through the high-pressure oil chamber or the second channel L1, and the hydraulic passage L2 is connected to the P port of the mechanical valve 3. At this time, the rotation of the second cam 21 pumps the high-pressure oil into the two valve return braking components 5 through the mechanical valve 3, and the braking units 51 of the two exhaust valves push the valve stem 522 in the exhaust valve assembly 52 downward; at the same time, the first cam 11 rotates, so that the low-pressure oil is pumped into the energy storage component 4.

[0040] Please refer to Figure 4, in the compression release braking mode, the solenoid valve 62 is energized, and the oil flow from the oil pump unit 61 pushes the mechanical valve 3 to the position where PA||BT is connected (i.e., the P port and A port of the solenoid valve are connected, and the B port and T port are connected). Since the oil pumping chamber 123 of the first piston assembly 1 is connected to the A port of the mechanical valve 3 via the high-pressure oil chamber or the second channel L1, and the hydraulic passage L2 is connected to the P port of the mechanical valve 3, at this time, when the first cam 11 rotates, high-pressure oil is pumped into the two valve return braking assemblies 5 through the high-pressure oil chamber or the second channel L1, while when the second cam 21 rotates, low-pressure oil is pumped into the energy storage assembly 4.

[0041] Specifically, in this process, the first cam 11 is specifically used for the engine compression release braking. Please refer to Figure 5 , Figure 2 As shown, when the first cam 11 rotates to the first lift ramp 1a1 stage of the first lift step 111, the heavy-duty engine performs the first compression release braking. This braking process starts at 50 - 60 CrA degrees (crank angle) before TDC ignition and ends at the high point 3 - 5 CrA after TDC ignition.

[0042] At the second lift ramp 1a2 stage of the first lift step 111, starting from the end point of the first lift ramp 1a1, that is, 3 - 5 CrA ATDC after TDC ignition until 70 CrA ATDC, and then smoothly ramping down between 120 - 150 CrA ATDC. In this way, the effect of braking exhaust gas recirculation BGR can be generated at the second lift ramp 1a2 stage.

[0043] Furthermore, when the first cam 11 rotates to the second lift step 112, that is, at the third lift ramp 1a3, the second engine compression release braking of the heavy-duty engine is performed; specifically, this process starts from 315 CrA ATDC and ends at 355 CrA ATDC, and after experiencing a ramp-down stage, it returns to the base circle of the first cam 11 between approximately 400 - 420 CrA ATDC to complete the compression release braking.

[0044] Please refer to Figures 5 - 7 As shown (the ordinate is the valve lift), compared with the main exhaust lift and the expected cylinder pressure curve on the 720 crankshaft rotation angle ( Figure 6 ), the variable hydraulic exhaust valve mechanism for the heavy-duty engine of the present invention transfers the cam lift to the valve lift through the second cam 21, and the movement of the first cam 11 is all transferred to the energy storage assembly 4.

[0045] Compared with the two-stroke compression release braking and the expected cylinder pressure ( Figure 7), the variable hydraulic exhaust valve mechanism for a heavy-duty engine of the present invention transfers the cam lift to the valve lift through the second cam 21, and the movement of the first cam 11 is entirely transferred to the energy storage assembly 4, so that the second compression release at 360° TDC of the heavy-duty engine with the variable hydraulic exhaust valve mechanism for a heavy-duty engine will generate a cylinder pressure higher than 30 barA.

[0046] In summary, the variable hydraulic exhaust valve mechanism for a heavy-duty engine of the present invention combines the energy storage assembly 4 and the mechanical valve 3, and centrally controls the mechanical valve 3 by setting the solenoid valve 62, realizing the switching between the main lift in the four-stroke ignition mode and the compression release brake compression in the two-stroke mode; at the same time, by setting the first cam 11 and the second cam 21, the independent drive of the exhaust main lift in the ignition mode and the compression release brake lift in the brake mode is realized; further, the transmission of the cam movement is carried out hydraulically, further improving the operating stability of the heavy-duty engine; in addition, by setting the first lift step 111 of the first cam 11 to include two consecutive lift ramps, the variable hydraulic exhaust valve mechanism for a heavy-duty engine has the effect of brake exhaust gas recirculation BGR.

[0047] 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 engine with a mechanical valve and two piston assemblies, characterized in that, Comprising a variable hydraulic exhaust valve mechanism, the variable hydraulic exhaust valve mechanism including: A first piston assembly (1), which includes a first cam (11) and a first main piston unit (12) drivingly connected to the first cam, for the compression release brake of the heavy-duty engine; A second piston assembly (2), which includes a second cam (21) and a second main piston unit (22) drivingly connected to the second cam (21), for the normal ignition of the heavy-duty engine; A mechanical valve (3), the mechanical valve being configured to disconnect and connect the first piston assembly and the second piston assembly to achieve the switching of the heavy-duty engine between the compression release brake mode and the normal ignition mode; An energy storage assembly (4), which is connected to the first piston assembly and the second piston assembly respectively through the mechanical valve; and Two valve return braking assemblies (5), which are controllably connected to the first piston assembly and the second piston assembly through the mechanical valve to simultaneously open two exhaust valves during the compression release brake process, wherein, in the compression release brake mode of the heavy-duty engine, the mechanical valve (3) hydraulically connects the first piston assembly (1) to the valve return braking assembly (5), and the rotation of the first cam (11) pumps high-pressure oil into the two valve return braking assemblies (5) to simultaneously open the two exhaust valves, in the exhaust main lift of the normal ignition mode of the heavy-duty engine, the mechanical valve (3) hydraulically connects the second piston assembly (2) to the valve return braking assembly (5), and the rotation of the second cam (21) pumps high-pressure oil through the mechanical valve (3) into the two valve return braking assemblies (5), the outer peripheral contour of the first cam (11) is formed with a first lift step and a second lift step arranged at intervals; the rising and falling stages of the first lift step cover a cam angle range of 90 degrees; the rising and falling stages of the second lift step cover a cam angle range of 45 - 50 degrees, the heavy-duty engine further includes a hydraulic circuit assembly (6), the hydraulic circuit assembly (6) being shared by each cylinder of the heavy-duty engine, including an oil pump unit (61) and a solenoid valve (62), the solenoid valve being hydraulically connected to the mechanical valve (3) for driving the mechanical valve (3) to change the communication state between its different ports, the mechanical valve is a 4 / 2 mechanical valve, the solenoid valve is a 3 / 2 solenoid valve, and one solenoid valve controls the communication state between different ports of the mechanical valves (3) of multiple cylinders of the heavy-duty engine.

2. The heavy-duty engine according to claim 1, characterized in that, The first main piston unit (12) includes a pump roller (121) abuttingly connected to the first cam (11), a pump piston (122) connected to one end of the pump roller, and a pump oil chamber (123) for accommodating the pump piston; the first main piston unit further includes a pump spring (124) sleeved on the outer periphery of the pump piston.

3. The heavy-duty engine according to claim 1, characterized in that, The valve return braking assemblies (5) are arranged in pairs, and the two valve return braking assemblies (5) are connected through a hydraulic passage (L2); each valve return braking assembly includes a braking unit (51) for the exhaust valve and an exhaust valve assembly (52).

4. The heavy-duty engine according to claim 1, characterized in that, The energy storage assembly (4) is connected to the mechanical valve (3) through an intermediate pressure chamber or a first passage (41); the energy storage assembly (4) includes an accumulator oil chamber (42), an accumulator piston (43) movably connected in the accumulator oil chamber (42), and an accumulator spring (44) sleeved on the outer periphery of the accumulator piston. In the compression release braking mode of the heavy-duty engine, the mechanical valve (3) hydraulically connects the second piston assembly (2) to the energy storage assembly (4), and the rotation of the second cam (21) pumps low-pressure oil into the energy storage assembly (4). In the main exhaust lift of the normal ignition mode of the heavy-duty engine, the mechanical valve (3) hydraulically connects the first piston assembly (1) to the energy storage assembly (4), and the rotation of the first cam (11) pumps low-pressure oil into the energy storage assembly (4) through the mechanical valve (3).

5. The heavy-duty engine according to claim 1, characterized in that, The oil pumping chamber (123) of the first main piston unit (12) is connected to port A of the mechanical valve (3) through a high-pressure oil chamber or a second passage, the oil pumping chamber (123) of the second main piston unit (22) is connected to port B of the mechanical valve (3) via a high-pressure oil chamber or a second passage, the two valve return braking assemblies (5) are connected to port P of the mechanical valve (3) through a hydraulic passage (L2), and the accumulator oil chamber (42) of the energy storage assembly (4) is connected to port T of the mechanical valve (3) through an intermediate pressure chamber or a first passage (41).

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