JP2012097712A - Sealing structure of dme supply pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sealing structure of a DME (Dimethyl Ether) supply pump, the structure capable of preventing an engine oil from mixing into DME fuel.SOLUTION: The sealing structure of the DME supply pump 1 is provided in which a plunger 7 is disposed so as to be reciprocatable in a cylinder 4 having a suction port 2 for DME fuel and a discharge port 3, the plunger 7 is connected to a driving part 15 of an engine, and one of the cylinder 4 and the plunger 7 includes a sealing device 8 for sealing a gap between the one and the other. In the sealing structure of the DME supply pump, the sealing device 8 includes: a rod seal 23 for DME, for sealing against the DME fuel from the cylinder 4; and a rod seal 24 for oil, disposed closer to the driving part 15 than the rod seal 23 for DME and sealing to prevent intrusion of an engine oil into the cylinder 4. The rod seal 24 for oil includes a check valve 40 for returning the engine oil, which intrudes into an intermediate chamber 36 between the rod seal 24 for oil and the rod seal 23 for DME, to the driving part 15 side.

Description

  The present invention relates to a seal structure of a DME supply pump.

  A diesel engine using DME (dimethyl ether) as a fuel has a low viscosity of DME itself and poor lubricity, and therefore, several hundred ppm of a lubricity improver is added to the DME fuel. Since this low viscosity makes it easy for DME to leak from a plunger gap of a supply pump or the like, a seal device such as a rod seal is generally used at the plunger site. Also, the cam chamber of the supply pump is lubricated with engine oil, and the pump cam and bearings are lubricated.

JP 2007-120423 A

  As shown in FIGS. 3, 4 (a) and 4 (b), when a seal device 50 such as a rod seal is used at the plunger portion, there is a case where a lip structure or the like is employed to seal DME fuel. This lip structure can seal DME fuel by appropriately adjusting the material, angle, and initial spring tension of the lip 51. However, engine oil adhering to the plunger 7 during the plunger ascending stroke may pass through the lip 51 and be sucked into the DME fuel. The engine oil includes various additives (antioxidants, antiwear agents, detergent dispersants, viscosity index improvers, antifoaming agents, pour point depressants) and the like. DME fuel also has a cleaning action, and the base oil component of engine oil will flow without sticking to the metal surface, but polymer polymers such as viscosity index improvers may adhere to the metal surface or staying places, There are cases where adhesion of a sliding portion or the like is promoted. Further, if the lip surface pressure during the stroke stroke of the lip 51 is increased for the purpose of preventing the engine oil from being sucked up, lip wear is promoted, and there arises a problem that the desired sealing performance cannot be maintained for a long time.

  The engine oil mixed in the DME fuel flows into the fuel injection devices (common rail, injector, etc.) after the supply pump, and the engine oil entering the injector is injected together with the DME fuel into the combustion chamber and burns. In addition, since components used in antioxidants such as Z-DTP contain metal components such as Ca, they adhere to the exhaust system (turbo, catalyst, etc.) and cause deterioration of PM emissions.

  Accordingly, an object of the present invention is to provide a seal structure for a DME supply pump that solves the above-described problems and can prevent mixing of engine oil into DME fuel.

  In order to solve the above-described problems, the present invention provides a plunger in a cylinder having a DME fuel suction port and a discharge port so as to be able to reciprocate, and an engine drive unit is connected to the plunger. A seal structure of a DME supply pump provided with a seal device for sealing between the other and the other, wherein the seal device includes a DME rod seal for sealing DME fuel from the cylinder, and the DME rod An oil rod seal that is disposed closer to the drive unit than the seal and seals the ingress of engine oil into the cylinder. The oil rod seal includes an oil rod seal and a DME rod seal. A check valve is provided to return the engine oil that has entered the intermediate chamber to the drive unit side. .

  The check valve may be a tapered hole formed so that the outlet is narrowed from the inlet.

  The DME rod seal and the oil rod seal have a lip portion extending from the one side to the other side, the lip portion is formed so as to narrow the tip, and a surface of the lip portion on the sealing side is the lip portion. It is good to form so that it may become an angle of 40 degrees with respect to the stroke direction of a plunger, and the surface on the opposite side to the said sealing side may be formed so that it may become an angle of 20 degrees with respect to the stroke direction of the said plunger. .

  According to the present invention, mixing of engine oil into DME fuel can be prevented.

It is a schematic explanatory drawing of the DME supply pump which concerns on this Embodiment. It is side surface sectional drawing of the sealing device of the DME supply pump which concerns on this Embodiment. It is side surface sectional drawing of the conventional sealing apparatus. (A) is explanatory drawing of the sealing device of a plunger raising stroke, (b) is explanatory drawing of the sealing device of a plunger lowering stroke.

  As shown in FIG. 1, the DME supply pump 1 includes a cylinder 4 having a DME fuel suction port 2 and a discharge port 3, an electromagnetic valve 5 provided in the suction port 2, and a discharge port 3. A check valve 6, a plunger 7 provided in the cylinder 4 so as to be able to reciprocate, and a sealing device 8 provided in the cylinder 4 for sealing between the cylinder 4 and the plunger 7 are provided.

  The cylinder 4 is disposed so as to extend vertically. The suction port 2 is formed at the top of the cylinder 4. A pump gallery 9 is connected to the suction port 2 via an electromagnetic valve 5. A fuel tank 10 for storing DME fuel is connected to the pump gallery 9. The electromagnetic valve 5 includes a valve body 11 for opening and closing the suction port 2 and a solenoid 12 for driving the valve body 11. The solenoid 12 is connected to a control device (not shown). The control device controls the solenoid 12 to open the electromagnetic valve 5 when the plunger 7 is lowered and close the electromagnetic valve 5 when the plunger 7 is raised. The discharge port 3 is formed in the upper part of the cylinder 4 and is connected to a common rail (not shown) via a check valve 6. The check valve 6 opens only when the pressure on the cylinder 4 side is higher than the pressure on the common rail side. Further, a leak recovery path 13 for returning high-pressure DME fuel leaked between the plunger 7 and the cylinder 4 to the pump gallery 9 is connected to the side surface of the cylinder 4.

  The plunger 7 is inserted into the cylinder 4 from the lower end of the cylinder 4, and forms a cylinder chamber 14 in the cylinder 4 above the plunger 7. The volume of the cylinder chamber 14 changes as the plunger 7 moves up and down. Further, the plunger 7 is constantly urged downward by a return spring (not shown). An engine drive unit 15 is connected to the plunger 7.

  The engine drive unit 15 includes a cam 16 that is rotated by the power of the engine, and a cam follower 17 that is provided on the plunger 7 and abuts against the cam 16 and moves up and down according to the rotation of the cam 16. The cam follower 17 includes a tappet 18 provided at the lower end of the plunger 7, and a roller 19 provided on the tappet 18, abutted against the cam 16, and rotated according to the rotation of the cam 16. The engine drive unit 15 is accommodated in a cam chamber 20 formed in the engine, and is lubricated with engine oil.

  As shown in FIG. 2, the sealing device 8 is provided in a recess 21 formed on the inner peripheral surface of the cylinder 4. The recess 21 is formed so that the inner diameter of the lower end portion of the cylinder 4 is increased stepwise, and a seal presser 22 for holding the seal device 8 is provided on the inner periphery of the lower end of the recess 21. Yes. The sealing device 8 includes two upper and lower rod seals 23 and 24 made of resin using PTFE or the like having self-lubricating properties, and a spring 25 that elastically biases the tips of the rod seals 23 and 24 toward the plunger 7. With. The upper rod seal (DME rod seal) 23 is for sealing the DME fuel from the cylinder 4, and the lower rod seal (oil rod seal) 24 is for the engine oil into the cylinder 4. This is to seal the intrusion.

  The DME rod seal 23 is formed in an annular shape along the inner peripheral surface of the recess 21, and is formed in an annular shape along the inner periphery of the base portion 26, and protrudes inward in the radial direction. Includes a lip portion 27 which is in liquid-tight contact with the plunger 7. The base 26 is formed with a gap 28 for accommodating the spring 25. The air gap 28 is formed in a ring shape and a groove shape having an open upper end. The lip portion 27 is formed so as to narrow the tip, and has a DME sealing surface 29 formed on the upper side (side for sealing DME fuel) and a back surface 30 formed on the lower side. The DME seal surface 29 is inclined at an angle α of 40 ° with respect to the stroke direction of the plunger 7, and the back surface 30 is inclined at an angle β of 20 ° with respect to the stroke direction of the plunger 7.

  The oil rod seal 24 is formed in an annular shape along the inner peripheral surface of the recess 21, and is formed in an annular shape along the inner periphery of the base portion 31 and protrudes radially inward. Includes a lip portion 32 which is in liquid-tight contact with the plunger 7. A gap 33 for accommodating the spring 25 is formed in the base 31. The air gap 33 is formed in a ring shape and a groove shape having a lower end opened. The lip portion 32 is formed so as to narrow the tip, and has an oil seal surface 34 formed on the lower side (side for sealing engine oil) and a back surface 35 formed on the upper side. The oil seal surface 34 is inclined at an angle α of 40 ° with respect to the stroke direction of the plunger 7, and the back surface 35 is inclined at an angle β of 20 ° with respect to the stroke direction of the plunger 7. An intermediate chamber 36 is formed between the lip portion 27 of the DME rod seal 23 and the lip portion 32 of the oil rod seal 24 so as to accommodate the engine oil that has passed through the oil rod seal 24. It has become.

  In particular, the oil rod seal 24 is provided with a plurality of tapered holes 40 serving as check valves for returning the engine oil that has entered the intermediate chamber 36 to the drive unit 15 side. The tapered hole 40 is formed so as to constrict the outlet 38 from the inlet 37. The inlet 37 of the tapered hole 40 is formed in the back surface 35 of the lip portion 32, and the outlet 38 is communicated with the gap 33 of the base portion 31. The outlet 38 is formed to have an extremely small diameter so that engine oil does not enter the tapered hole 40 from the gap 33. The seal retainer 22 is formed with an oil discharge hole 39 extending vertically from the inside of the gap 33 into the cam chamber 20 so as to discharge engine oil.

  Next, the operation of this embodiment will be described.

  When the plunger 7 is lowered in accordance with the rotation of the cam 16 and the electromagnetic valve 5 is opened, the DME fuel in the pump gallery 9 is sucked into the cylinder chamber 14. At this time, the lip portion 27 of the DME rod seal 23 is in a state in which it is easy to seal DME fuel, so that the DME fuel in the cylinder chamber 14 does not leak through the sealing device 8.

  When the plunger 7 is raised and the electromagnetic valve 5 is closed, the DME fuel in the cylinder chamber 14 is pressurized. When the pressure in the cylinder chamber 14 becomes higher than the common rail pressure, the check valve 6 is opened, and the DME fuel in the cylinder chamber 14 is discharged from the discharge port 3 to the common rail side. At this time, the DME fuel in the cylinder chamber 14 may leak into the gap between the cylinder 4 and the plunger 7, but this DME fuel returns to the pump gallery 9 through the leak circuit 13. The pressure of will not act. Further, the engine oil rising together with the plunger 7 is scraped off by the lip portion 32 of the oil rod seal 24, while the extremely thin engine oil oil film adhering to the plunger 7 surface may enter the intermediate chamber 36 through the lip boundary surface. . The engine oil that has entered the intermediate chamber 36 is discharged from the taper hole 40 into the gap 33 of the oil rod seal 24 when the DME rod seal 23 and the oil rod seal 24 are deformed in accordance with the reciprocating movement of the plunger 7. Return from the discharge hole 39 into the cam chamber 20.

  Since the tapered hole 40 has a small diameter at the outlet 38, it is difficult for the engine oil in the gap 33 to enter the tapered hole 40 from the outlet 38. In addition, the presence of the engine oil oil film on the lip portion 32 of the oil rod seal 24 maintains the boundary lubricating film on the lip surface. The boundary lubrication film on the lip surface is maintained on the lip portion 27 of the DME rod seal 23 with a lubricity improver mixed as DME fuel. In other words, mixing of engine oil into the DME fuel can be suppressed while maintaining the boundary lubricating film between the lip portions 27 and 32.

  In this way, the seal device 8 is disposed on the drive unit 15 side of the DME rod seal 23 for sealing the DME fuel from the cylinder 4, and the engine oil from the cam chamber 20 into the cylinder 4. And an oil rod seal 24 that seals intrusion of the oil, and the oil rod seal 24 has a check valve (taper hole) for returning the engine oil that has entered the intermediate chamber 36 to the drive unit 15 side (cam chamber 20). 40), it is possible to prevent the engine oil from being sucked up while maintaining the DME sealing performance, and to prevent the engine oil from being mixed into the DME fuel. In addition, this makes it possible to prevent sticking of components of the fuel injection device and poor sliding, and to prevent variations in injection amount between cylinders, idle vibration, and the like. Further, the sealing performance can be continuously maintained.

  Since the check valve comprises a tapered hole 40 formed so as to constrict the outlet 38 from the inlet 37, the check valve effect can be exhibited with a simple structure, and the DME supply pump with a plunger diameter of several millimeters It can be easily applied to one sealing device 8.

  The rod seal 23 for DME and the rod seal 24 for oil have lip portions 27, 32 extending from the cylinder 4 to the plunger 7, and are formed so that the lip portions 27, 32 narrow the tip. The surface to be sealed (DME seal surface 29 or oil seal surface 34) is formed at an angle of 40 ° with respect to the stroke direction of the plunger 7, and the surface opposite to the side to be sealed (rear surfaces 30, 35). ) Is formed at an angle of 20 ° with respect to the stroke direction of the plunger 7, the DME rod seal 23 can seal DME fuel, and the oil rod seal 24 can engine. Oil uptake can be suppressed satisfactorily.

  Although the sealing device 8 is provided on the cylinder 4, it may be provided on the plunger 7.

  Moreover, although the drive part 15 demonstrated what was a cam mechanism, it may comprise not only this but the other mechanism which uses engine oil.

  The oil rod seal 24 is provided with a plurality of tapered holes 40, but may be a single one.

DESCRIPTION OF SYMBOLS 1 Supply pump 2 Suction port 3 Discharge port 4 Cylinder 7 Plunger 8 Sealing device 15 Drive part 23 DME rod seal 24 Oil rod seal 27 Lip part 29 DME seal surface (surface on the seal side)
30 Back (surface opposite to the side to be sealed)
32 Lip part 34 Oil seal surface (surface to seal)
35 Back (surface opposite to the side to be sealed)
36 Intermediate chamber 40 Tapered hole (check valve)

Claims (3)

  A plunger is provided in a cylinder having a DME fuel suction port and a discharge port so as to be able to reciprocate, and an engine drive unit is connected to the plunger, and one cylinder or the plunger is sealed between the other and the other. In the seal structure of the DME supply pump provided with the seal device for the DME rod seal for sealing the DME fuel from the cylinder, the DME rod seal is disposed closer to the drive unit than the DME rod seal, and An oil rod seal that seals the ingress of engine oil into the cylinder. The oil rod seal contains the engine oil that has entered the intermediate chamber between the oil rod seal and the DME rod seal. A check valve for returning to the drive unit side is provided. Structure.   The seal structure of the DME supply pump according to claim 1, wherein the check valve comprises a tapered hole formed so as to narrow the outlet from the inlet.   The rod seal for DME and the rod seal for oil have a lip portion extending from the one side to the other side, the lip portion is formed so as to narrow the tip, and the surface of the lip portion on the sealing side is the plunger The surface of the side opposite to the sealing side is formed so as to have an angle of 20 ° with respect to the stroke direction of the plunger. Or the sealing structure of the DME supply pump of 2.