CN115199373A

CN115199373A - Fixed chain type engine braking mechanism

Info

Publication number: CN115199373A
Application number: CN202110399095.9A
Authority: CN
Inventors: 杨洲; 朱汝杰; 奚正
Original assignee: Shanghai Youshun Automobile Technology Co ltd
Current assignee: Shanghai Youshun Automobile Technology Co ltd
Priority date: 2021-04-14
Filing date: 2021-04-14
Publication date: 2022-10-18

Abstract

The invention provides a fixed chain type engine braking mechanism, which adopts a braking half rocker arm to drive a conventional exhaust rocker arm of an engine to generate an exhaust valve lift for engine braking, and the exhaust valve lift is superposed with the conventional exhaust valve lift. The semi-rocker arm comprises a connecting rod piston mechanism, the connecting rod piston mechanism comprises a first connecting rod, a second connecting rod and a connecting piston, one end of the first connecting rod is rotatably connected with one end of the second connecting rod, the other end of the first connecting rod is rotatably connected with the semi-rocker arm, the other end of the second connecting rod is rotatably connected with one end of the connecting piston, the length of the connecting rod piston mechanism is changed by contraction and extension between the first connecting rod and the second connecting rod and is used for losing or transmitting the motion of the brake cam, when the connecting piston straightens the first connecting rod and the second connecting rod, the other end of the connecting piston is connected with a conventional exhaust rocker arm, and the motion of the brake cam is transmitted to an exhaust valve of an engine. The invention can generate larger braking valve lift and increase the braking power of the engine.

Description

Fixed chain type engine braking mechanism

Technical Field

The invention relates to the field of machinery, in particular to the field of engine valve driving, and especially relates to a fixed chain type engine braking mechanism.

Background

Conventional valve actuation for vehicle engines is well known in the art and has been in use for over a hundred years. Conventional valve actuation utilizes a conventional valve actuator (including a rocker arm) to control the motion of an engine valve for conventional spark operation of the engine. But due to additional demands on engine fuel efficiency, exhaust emissions and engine braking, more and more engines employ variable valve actuation, including engine braking. Engine brakes have been widely used on commercial vehicle engines. The existing market adopts a fixed chain type engine braking mechanism, namely, only once compression release braking is carried out at the end of a compression stroke (near a compression top dead center) in one cycle (an air inlet stroke, a compression stroke, an expansion stroke and an exhaust stroke) of an engine.

One precedent of a fixed chain engine braking mechanism is disclosed in U.S. patent No. 3,220,392, by Cummins (Cummins), from which engine braking systems made have been commercially successful. However, such engine braking systems are engine-mounted accessories. To install the engine brake, a gasket is added between the cylinder and the valve cover, thus additionally increasing the height, weight, and cost of the engine. In addition, the cummins brake adopts hydraulic connection to drive the valve, and has the problems of three high hydraulic pressures (high load, high leakage and high deformation) and a hydraulic jack and the like.

Another four-stroke brake is disclosed in US 5,937,807 and US 5,975,251 (1999), which, instead of an overhead brake, use a brake exhaust rocker arm, arranged alongside a conventional exhaust rocker arm on a rocker shaft, the brake cam and the brake exhaust rocker arm actuating only one of the two exhaust valves during braking, in a hydraulic connection. Another drawback of this invention is the mounting/alignment compatibility of the rocker arms, when two exhaust valves are aligned parallel to the exhaust rocker arm, the brake exhaust rocker arm is unable to reach (short of) one of the exhaust valves.

U.S. Pat. No. 6,983,725 (2006) discloses another dual rocker arm braking device in which one rocker arm is a brake exhaust rocker arm and the other rocker arm is a conventional exhaust rocker arm. A conventional exhaust rocker arm houses a hydraulic brake actuation mechanism that includes two hydraulic pistons, one being a master piston and the other being a slave piston. When engine braking is not required, the master piston in the conventional exhaust rocker arm is in a retracted position, separated from the brake exhaust rocker arm, and the motion of the brake cam is skipped (lost). When the engine is required to be braked, the oil pressure of the engine enables a main piston in the conventional exhaust rocker arm to be in an extending position and connected with the brake exhaust rocker arm, the brake cam drives the brake exhaust rocker arm to press the main piston from the upper part, the main piston drives an auxiliary piston, the auxiliary piston presses the conventional exhaust rocker arm, and the conventional exhaust rocker arm opens two exhaust valves to brake the engine. It is clear that the load of such a hydraulically actuated opening of the two exhaust valve brakes is very high and that special methods, such as continuously variable back pressure control, must be used to control the cylinder pressure of the engine brake.

U.S. Pat. No. 7,392,772 (2008) discloses another dual rocker arm brake device wherein one rocker arm is a brake exhaust rocker arm and the other rocker arm is a conventional exhaust rocker arm. A conventional exhaust rocker arm houses a hydraulic brake actuation mechanism, but includes only a hydraulic piston. When engine braking is not required, the hydraulic pistons in the conventional exhaust rocker arms are in a retracted position, separated from the brake exhaust rocker arms, and the motion of the brake cams is skipped (lost); when the engine is required to be braked, the oil pressure of the engine enables a hydraulic piston in the conventional exhaust rocker arm to be in an extending position and connected with the brake exhaust rocker arm, the brake cam drives the brake exhaust rocker arm to press the hydraulic piston from the upper part, the hydraulic piston presses the conventional exhaust rocker arm, and the conventional exhaust rocker arm opens an exhaust valve to brake the engine. Besides various failure modes (including hydraulic three-high) of hydraulic drive, the invention also has the problems of unbalance loading and the like when the conventional exhaust rocker arm is braked.

The fixed chain engine brakes that have emerged in recent years are replacing traditional hydraulic engine brakes. For example, chinese patent No. 103388505B (2016) of the present applicant discloses a double rocker arm brake device, in which one rocker arm is a brake exhaust rocker arm, and the other rocker arm is a conventional exhaust rocker arm. The conventional exhaust rocker arm has a fixed chain type brake driving mechanism disposed therein, including a ramp piston mechanism and a rod piston mechanism, which transmits or loses (jumps) the movement of the brake cam by the oscillation of a ramp or a rod (the raising and lowering of a piston). One drawback of the prior art fixed chain brakes is that the braking stroke (i.e. the braking valve lift) is limited or that the adjustable range is too small.

Disclosure of Invention

The invention provides a fixed chain type engine braking mechanism, which aims to solve the technical problems of three hydraulic heights (high load, high leakage and high deformation) of an engine brake adopting a hydraulic driving system in the prior art, eliminate the defects of failure modes such as 'water hammer' and 'hydraulic jack' inherent in a hydraulic system and the like and the defects of being easily influenced by external factors (such as oil temperature, oil pressure, air content and the like), and limit the too small adjusting range of the braking stroke (valve lift) of the conventional fixed chain type brake.

The invention provides a fixed chain type engine braking mechanism, which comprises a braking cam and a braking semi-rocker arm, wherein the braking semi-rocker arm is used for driving a conventional exhaust rocker arm of an engine to generate an exhaust valve lift for braking the engine, a connecting rod piston mechanism is arranged in the braking semi-rocker arm, the connecting rod piston mechanism comprises a first connecting rod, a second connecting rod and a connecting piston, one end of the first connecting rod is rotatably connected with one end of the second connecting rod, the other end of the first connecting rod is rotatably connected with the braking semi-rocker arm, the other end of the second connecting rod is rotatably connected with one end of the connecting piston, the contraction and the extension between the first connecting rod and the second connecting rod change the length of the connecting rod piston mechanism to lose or transmit the motion of the braking cam, when the connecting piston straightens the first connecting rod and the second connecting rod, the other end of the connecting piston is connected with the conventional exhaust rocker arm, and the motion of the braking cam is transmitted to an exhaust valve of the engine.

Furthermore, the brake half rocker arm and a conventional exhaust rocker arm of the engine are arranged on a rocker shaft of the engine side by side, when the engine is braked, oil pressure of the engine drives a connecting piston in the brake half rocker arm to straighten a first connecting rod and a second connecting rod, and the connecting piston acts on one end, close to an engine valve, of the conventional exhaust rocker arm to generate an exhaust valve lift of the engine brake.

Further, the engine braking exhaust valve lift comprises a compression release braking exhaust valve lift, the compression release braking exhaust valve lift is shown to open before compression top dead center and extend beyond the compression top dead center to expand and intersect with the conventional exhaust valve lift.

Furthermore, an exhaust clearance adjusting mechanism and a brake clearance adjusting mechanism are arranged at one end, close to the exhaust valve, of the conventional exhaust rocker arm, the exhaust clearance adjusting mechanism adjusts the clearance between the conventional exhaust rocker arm and the exhaust valve, and the brake clearance adjusting mechanism adjusts the clearance between the connecting piston and the conventional exhaust rocker arm.

Further, the rotationally coupling may include a cylindrical coupling or a spherical coupling.

Furthermore, the brake device also comprises an anti-flying off spring which pushes the brake half rocker arm to a brake cam of the engine.

Furthermore, the device also comprises a pre-tightening spring, wherein the pre-tightening spring enables an included angle between the upper connecting rod and the lower connecting rod to be reduced and the connecting rod piston mechanism to be shortened.

Furthermore, the oil cylinder also comprises a spring piston, one side of the spring piston comprises the pre-tightening spring, and the other side of the spring piston can bear the action of oil pressure.

Drawings

FIG. 1 is a schematic diagram of intake and exhaust valve lift during normal operation (firing) of an engine.

FIG. 2 is a schematic diagram of intake and exhaust valve lift during engine braking according to the prior art.

FIG. 3 is a schematic representation of a rocker arm arrangement of the fixed chain engine braking mechanism of the present invention.

Fig. 4 is a schematic view of the retracted state of the connecting rod piston mechanism in the braking half rocker arm of the fixed chain type engine braking mechanism of the present invention.

FIG. 5 is a schematic illustration of the brake cam lift and the conventional intake and exhaust cam lifts employed by the fixed chain engine braking mechanism of the present invention.

Fig. 6 is a schematic diagram of valve lift corresponding to the cam lift of fig. 5.

Detailed Description

Fig. 1 is a schematic diagram of intake and exhaust valve lifts during normal operation (ignition) of an engine in the prior art. Valve motion for conventional ignition of an engine is common knowledge. The exhaust cam of the engine drives a conventional (firing) exhaust rocker arm, which opens the exhaust valve during the exhaust stroke of the engine, discharging the combusted exhaust gases. The valve lift 20 (thin solid line in fig. 1) of the exhaust valve is opened before the expansion (power) bottom dead center of the engine and closed after the exhaust top dead center of the engine. An intake cam of the engine drives a conventional (ignition) intake rocker arm, and an intake valve is opened in an intake stroke of the engine to suck fresh air. The valve lift 30 (thick solid line in fig. 1) of the intake valve is opened before the exhaust top dead center of the engine and closed after the intake bottom dead center of the engine. It is particularly noted that the engine functions primarily to produce positive power upon ignition, and that whatever engine braking mechanism is employed, it must be ensured that the intake and exhaust valve lifts 20 and 30 shown in fig. 1 are present upon ignition of the engine.

FIG. 2 is a schematic diagram of intake and exhaust valve lifts during four-stroke braking of an engine in the prior art. The four-stroke engine braking valve motion is also well known and is generated in many ways, and one of the most widely used at present is that a braking cam drives the engine valve by braking an exhaust rocker arm. At engine braking, in addition to the exhaust valve lift 20 and the intake valve lift 30 that retain the engine's conventional firing, the exhaust valve lift 201 and 204 (thin dashed lines in fig. 2) of the engine brake are increased. Wherein the exhaust valve lift 201 is a compression release brake valve motion, occurring near the compression top dead center of the engine (open before compression top dead center, closed after compression top dead center), for releasing high pressure gas (air) compressed in the cylinder during the compression stroke of the engine; the exhaust valve lift 204 is the exhaust cycle brake valve motion, and occurs near the intake bottom dead center of the engine (the exhaust valve lift is opened before the intake bottom dead center and closed after the intake bottom dead center), so that the gas in the exhaust pipe reversely charges the cylinder of the engine near the closing of the intake valve, and the brake power is increased.

Fig. 3 and 4 are provided to illustrate one embodiment of the fixed chain engine brake mechanism of the present invention. In fig. 3 there is a conventional exhaust rocker arm 210 and a braking half rocker arm 220 for normal operation (ignition) of the engine, the braking half rocker arm 220 and the conventional exhaust rocker arm 210 being arranged side by side on a rocker shaft 205 of the engine. The conventional exhaust rocker arm 210 is provided with an exhaust lash adjustment mechanism 238 and a brake lash adjustment mechanism 248 (both typically including a lash adjustment screw, a lock nut, and a elephant foot pad) at one end 236 near the exhaust valve 300. The exhaust lash adjustment mechanism 238 adjusts the lash between the conventional exhaust rocker arm 210 and the exhaust valve 300, and the brake lash adjustment mechanism 248 adjusts the lash between the brake half rocker arm 220 (connecting piston 160) and the conventional exhaust rocker arm 210 (brake lash adjustment mechanism 248).

The conventional exhaust rocker arm 210 of the embodiment of the present application is unchanged except for the addition of the brake clearance adjustment mechanism 248 and will not be described herein. Also, conventional intake rocker arms of well-known engines are neither shown in the drawings nor need to be described herein. Only the newly added braking half rocker arm 220 will be described in detail below.

Fig. 4 is used to describe the connecting rod-piston mechanism 100 in the braking half rocker arm 220 of the fixed chain engine braking mechanism of the present invention. The connecting rod-piston mechanism 100 includes a first connecting rod 152, a second connecting rod 154, and a connecting piston 160. One end of the first link 152 is rotatably connected to one end of the second link 154, the other end of the first link 152 is rotatably connected to the brake half rocker arm 220, and the other end of the second link 154 is rotatably connected to one end of the connecting piston 160. When the connecting rod-piston mechanism 100 is deployed, the other end face of the connecting piston 160 is connected to a conventional exhaust rocker arm 210 (see fig. 3) to which the brake clearance adjustment mechanism 248 is secured, and transmits the motion of the brake exhaust cam 230 to the exhaust valve 300. When the connecting rod-piston mechanism 100 is retracted (see fig. 4), the contraction between the first connecting rod 152 and the second connecting rod 154 creates a gap between the connecting piston 160 and the conventional exhaust rocker arm 210, canceling (losing) the motion of the brake exhaust cam 230.

The angle of the first link 152 and the second link 154 of the rod-and-piston mechanism 100 is greater than 0 ° to less than or equal to 180 °, and the minimum angle can be controlled by a stop mechanism. When the included angle is a straight angle (180 °), the first and

second links

152 and 154 are straightened by the connecting piston 160, and the connecting piston 160 is fully extended. As the angle decreases, the connecting piston 160 retracts and the clearance with the conventional exhaust rocker arm 210 increases. The change range of the telescopic included angle between the first connecting rod 152 and the second connecting rod 154 is large, the stroke of the corresponding connecting rod piston 160 is also large, the lift of the generated brake valve 300 is also large, and the defect that the lift of the brake valve is too small in the prior art is overcome.

The present embodiment further includes a fly-off prevention spring 298 for preventing a gap between the brake half rocker arm 220 and the conventional exhaust rocker arm 210 from generating an impact when the link piston mechanism 100 is retracted by pushing the brake half rocker arm 220 toward the brake exhaust cam 230 through the roller shaft 231 and the roller 235.

The operation of this embodiment is as follows. In the normal (or default) state, the brake control valve (not shown) is disconnected from oil discharge, the oil pressure in the spring piston oil chamber 132 and the drive piston oil chamber 162 is zero, the pre-load spring 136 pushes the spring piston 130 out (upward), pushing the connecting piston mechanism 100 to the retracted (contracted) position shown in fig. 4, the clearance between the connecting piston 160 and the normal exhaust rocker arm 210 eliminates the motion of the brake exhaust cam 230, and the exhaust valve can only obtain motion from the normal (firing) exhaust cam 215 through the normal exhaust rocker arm 210 (see thin solid lines 22 in fig. 5 for cam lift), resulting in the normal exhaust valve lift 20 of the engine (thin solid lines in fig. 1 and 2).

When engine braking is required, the brake control valve (not shown) is turned on to supply oil, the oil of the engine is supplied to the driving piston oil chamber 162 through an oil passage (such as an oil hole (not shown) in the rocker shaft 205 and an oil passage 214 in the brake half rocker arm 220), the oil pressure pushes out the driving piston 160 (note that the connecting piston and the driving piston are the same piston here) (to the left), the connecting

rods

152 and 154 in the contracted position in fig. 4 are pulled straight, the connecting piston 160 is extended, the brake half rocker arm 220 (the connecting piston 160) is connected with the conventional exhaust rocker arm 210 (brake clearance adjustment mechanism), the motion of the brake exhaust cam 230 (the cam lift is shown by thin

dotted lines

237 and 239 in fig. 5) is transmitted to the exhaust valve 300 of the engine, and the exhaust valve lifts 201 and 204 (the thin dotted lines in fig. 6) for engine braking are generated. Of course, oil may also be simultaneously supplied to spring piston oil chamber 132 through oil bore 213 to push spring piston 130 back (downward in fig. 4) against the force of preload spring 136, which makes it easier to pull rod piston mechanism 100 in the retracted position of fig. 4 up to the fully extended deployed position.

Due to the larger piston stroke of the connecting piston 160 of the fixed chain engine brake mechanism 100 of the present application, a higher braking exhaust valve lift may be obtained in addition to the braking valve lifts 201 and 204 of the prior art shown in fig. 2. Such as the compression release brake cam lift 237 of fig. 5, is substantially the same as the prior art before compression top dead center, but extends beyond compression top dead center, intersects the conventional exhaust cam lift 22 at 238, and finally ends (back to cam base circle) during the exhaust stroke.

Fig. 6 shows the brake valve lift corresponding to the cam lift of fig. 5. Since the brake half rocker arm 220 acts on the conventional exhaust rocker arm 210 (fig. 3) during engine braking, the motion of the brake cam 230 and the motion of the conventional exhaust cam 215 are superimposed on the exhaust valve 300, resulting in a combined brake exhaust valve lift as shown in fig. 6. Where 201 and 204 (thin dashed lines) are the braking exhaust valve lifts produced by braking the half rocker arm 220 by the cam lifts 237 and 239 of the brake cam 230, and 20 (thin solid lines) are the braking exhaust valve lifts produced by the conventional exhaust rocker arm 210 by the cam lift 22 of the conventional exhaust cam 215. The compression release brake exhaust valve lift 201 opens before compression top dead center, expands after compression top dead center and intersects the conventional exhaust valve lift 20 at 28. It is clear that the portion of the braking exhaust valve lift 201 during the expansion stroke of the engine is beneficial for creating exhaust gas recirculation (second exhaust gas recirculation) increasing the engine braking power. The braking exhaust valve lift 204 near bottom dead center at the end of the conventional intake valve lift 30 (the thick solid line in fig. 6, produced by the conventional intake cam lift 33 in fig. 5) is the first exhaust gas recirculation.

The above description should not be taken as limiting the scope of the invention, but as being a representative of the invention in which many other variations are possible. For example, the engine braking mechanism shown herein may be used not only with exhaust rocker arms, but also with intake rocker arms. Also, the connecting rod-piston mechanism herein may be used not only for engine braking, but also to generate auxiliary valve movements for other engines, such as waste-to-recycle valve movements. In addition, the rotary connection between the connecting rod and the piston can be a pin (cylindrical surface) or a ball (spherical surface).

Claims

1. A fixed chain type engine braking mechanism is characterized by comprising a braking exhaust cam and a braking half rocker arm, wherein the braking exhaust cam and the braking half rocker arm are used for driving a conventional exhaust rocker arm of an engine to generate an exhaust valve lift of engine braking, a connecting rod piston mechanism is arranged in the braking half rocker arm and comprises a first connecting rod, a second connecting rod and a connecting piston, one end of the first connecting rod is rotatably connected with one end of the second connecting rod, the other end of the first connecting rod is rotatably connected with the braking half rocker arm, the other end of the second connecting rod is rotatably connected with one end of the connecting piston, the length of the connecting rod piston mechanism is changed by contraction and extension between the first connecting rod and the second connecting rod, the movement of the braking cam is lost or transmitted, when the connecting piston straightens the first connecting rod and the second connecting rod, the other end of the connecting piston is connected with the conventional exhaust rocker arm, and the movement of the braking cam is transmitted to an exhaust valve of the engine.

2. The fixed chain engine brake mechanism of claim 1, wherein: when the engine is braked, the oil pressure of the engine drives the connecting piston in the braking half rocker arm to straighten the first connecting rod and the second connecting rod, and the connecting piston acts on one end of the conventional exhaust rocker arm close to the engine valve to generate the exhaust valve lift for braking the engine.

3. The fixed chain engine brake mechanism as claimed in claims 1 and 2, wherein: the engine braking exhaust valve lift comprises a compression release braking exhaust valve lift which is shown as opening before compression top dead center and extending beyond and intersecting with a conventional exhaust valve lift.

4. The fixed chain engine brake mechanism as claimed in claims 1 and 2, wherein: the conventional exhaust rocker arm is provided with an exhaust clearance adjusting mechanism and a brake clearance adjusting mechanism at one end close to an exhaust valve, the exhaust clearance adjusting mechanism adjusts a clearance between the conventional exhaust rocker arm and the exhaust valve, and the brake clearance adjusting mechanism adjusts a clearance between the connecting piston and the conventional exhaust rocker arm.

5. The fixed chain engine brake mechanism of claim 1, wherein: the rotationally coupling may comprise a cylindrical coupling or a spherical coupling.

6. The fixed chain engine brake mechanism of claim 1, wherein: the anti-flying-off device further comprises an anti-flying-off spring, and the anti-flying-off spring pushes the braking half rocker arm to a braking cam of the engine.

7. The fixed chain engine brake mechanism of claim 1, wherein: the hydraulic cylinder further comprises a pre-tightening spring, and the pre-tightening spring enables an included angle between the upper connecting rod and the lower connecting rod to be reduced and the connecting rod piston mechanism to be shortened.

8. The fixed chain engine brake mechanism according to claims 1 and 7, wherein: the oil pressure control valve further comprises a spring piston, one side of the spring piston comprises the pre-tightening spring, and the other side of the spring piston can bear the oil pressure effect.