CN106762303B - An orifice type fuel injector for controlling the injection stability of a commercial vehicle diesel engine with a small amount of fuel - Google Patents

Abstract

A hole-type fuel injector for controlling the injection stability of a commercial vehicle diesel engine with a small amount of fuel, including a needle valve and a needle valve body. The head of the needle valve is composed of two steps, and the height of the first step is the maximum lift of the needle valve. The diameter of the first step is slightly larger than the diameter of the second step. When the needle valve lift is small, the annular flow cross-sectional area of the fuel between the needle valve head and the needle valve body in the pressure chamber is reduced. , so that it is smaller than the area of the nozzle hole, so as to realize the precise control of fuel injection at low flow rates; the inner diameter of the upper part of the needle valve body is the same as the outer diameter of the needle valve and the clearance fits to form an axial sealing surface for high-pressure fuel; the lower cone of the needle valve body And the boss of the needle valve head forms the sealing cone of the fuel injection nozzle to control the high-pressure fuel injection; the outer diameter d2 of the lower part of the needle valve body of the fuel injection nozzle is 11-13mm. The invention not only ensures the injection reliability and power performance in the large cycle fuel supply quantity, but also improves the fuel flow performance of the fuel injection nozzle in the small fuel quantity, and improves the injection stability in the small fuel quantity.

Description

An orifice type fuel injector for controlling the injection stability of a commercial vehicle diesel engine with a small amount of fuel

technical field

The invention relates to a fuel supply system for a commercial vehicle diesel engine, in particular to a hole-type fuel injection nozzle for controlling fuel injection stability when the commercial vehicle diesel engine has a small amount of fuel.

Background technique

In order to meet the increasing performance and emission requirements of diesel engines, electronic control has become an inevitable trend. The core of the electronic control of the diesel engine is the electronically controlled fuel injection system, and the common rail injector is the most critical and precise assembly in the electronically controlled common rail system. As well as the consistency requirements for basic parameters such as fuel injection volume and fuel injection duration under different working conditions, it is necessary to continuously optimize its structure and parameters.

The fuel injector is an important part in the fuel system of a diesel engine, and the fuel injector is a key component that affects the performance of the fuel injector. The traditional diesel fuel injectors currently used in commercial vehicles are all hole-type injectors. In order to ensure the dynamic performance at high speeds, high injection pressures are used, and the cycle fuel injection volume is relatively large. When the cycle fuel injection volume is small, the ratio between the maximum cycle fuel injection volume and the minimum cycle fuel injection volume of commercial vehicle diesel engine fuel injection system is large. Fluctuation in fuel volume: Under low-speed and low-load conditions, orifice injectors are prone to fluctuating injection phenomena caused by needle valve vibration, which makes it difficult to guarantee the injection stability of small fuel volumes at low idle speeds, which in turn affects fuel injection device performance. In addition, some electronically controlled injection systems use pre-injection, post-injection or multiple injections. Each injection has a small amount of fuel and requires stable and controllable injection, which requires higher injection stability.

The Chinese patent discloses a fuel injector for a diesel engine with a small bore swirl chamber. A fuel injector for a diesel engine (authorized publication number: CN 203248299 U), including a needle valve and a needle valve body. The needle valve is a rod-shaped cylindrical entity, and the needle valve body is a cavity-shaped entity. The needle valve is assembled in the needle valve body, and the two are ground and matched for use. By rationally designing the size of the needle valve and the head of the needle valve body, the flow area of the fuel injection nozzle is reduced, and the maximum lift h of the needle valve in the needle valve body is controlled to be 0.18-0.4mm. The flow area is not more than 0.18mm2. But this fuel injector is only applicable to the small bore vortex chamber diesel engine, and although the flow area of the fuel injector has been reduced, it does not involve the problem of fuel injection stability when the hole type injector of the direct-injection diesel engine has a small oil quantity.

The Chinese patent also discloses a standard fuel injector flow section adjustment mechanism (authorized publication number: CN 85201403U). By adopting the screw mechanism and adjusting the cone head to change the flow section of the nozzle hole, the flow section can be continuously adjusted to meet the adjustment of the fuel injection pump within the range of various fuel injection quantities. In the case of small fuel injection volume, it solves the problems of unstable measurement readings and poor measurement accuracy due to poor classification, but this mechanism is only used in throttle standard fuel injectors ) is not applicable to the current high-pressure common rail injectors.

The Chinese patent also discloses a novel internal combustion engine fuel injector needle valve coupling, including a needle valve and a needle valve body (authorized publication number: CN 202937394 U). By designing the head of the needle valve as a three-stage cone surface, an annular step is processed between the first-stage cone surface and the second-stage cone surface, and the annular step constitutes a sealing ring between the needle valve and the needle valve body. Arc transition between the secondary cone surface and the tertiary cone surface. Although the needle valve coupler can form the minimum flow cross section at the needle valve sealing ring when the needle valve lift is very small, and realize the control of the small lift fuel injection volume of the injector, it is from the needle valve and the needle valve sealing surface. The fuel injector has been improved in terms of machining error. Like conventional fuel injectors, the relationship between the circular flow section of the needle valve cone surface and the area of the nozzle hole has not been controlled to solve the problem of small fuel injection stability.

Contents of the invention

Aiming at the problem of small fuel injection stability of traditional diesel engine orifice injectors, the present invention discloses a novel orifice injector. By rationally designing the structure and size of the needle valve head of the orifice injector, the needle valve The head is a stepped cylinder. When the needle valve lift is small, it can ensure the minimum flow cross section between the needle valve and the pressure chamber, so as to realize the precise control of the injection volume of the injector needle valve with small lift. When the valve has a large lift, the minimum flow cross-sectional area is only controlled by the cross-sectional area of the injection hole, thereby improving the stability of the fuel injection and improving the reliability of the nozzle; while ensuring the injection performance of the large cycle fuel injection volume, it can It can effectively improve the injection stability when the oil quantity is small, and at the same time reduce the volume of the pressure chamber, which can reduce HC and soot emissions, and improve the economy and the overall performance of the diesel engine.

At low idle speed, due to the small amount of circulating fuel injection and the large flow area, the lift of the needle valve is not fully opened, and the phenomenon of fluctuating injection is very easy to occur. The flow area of the fuel injection nozzle is reduced when the fuel injection volume is small, so that the lift of the needle valve is increased when the fuel flow is small, which can reduce the fuel injection fluctuation phenomenon and improve the fuel injection stability.

The present invention is for realizing the above object, and the technical scheme that adopts is:

A hole-type fuel injector for controlling the injection stability of a commercial vehicle diesel engine with a small amount of fuel, including a needle valve and a needle valve body, the inner diameter of the upper part of the needle valve body is the same as the outer diameter of the needle valve and the gap fits to form a high-pressure fuel injection nozzle Axial sealing surface; the boss is reasonably designed on the needle valve head to reduce the circular cross-sectional area of the fuel in the pressure chamber between the needle valve head and the needle valve body, making it smaller than the area of the injection hole, so as to realize fuel injection at low flow rates precise control; the lower cone of the needle valve body and the boss of the needle valve head form the sealing cone surface of the fuel injection nozzle that controls high-pressure fuel injection; the lower edge of the pressure-bearing cone surface of the needle valve and the edge of the sealing cone surface The inner diameter of the needle valve within the length is 0.6-0.9mm larger than the outer diameter of the needle valve, forming a fuel passage from the oil tank to the nozzle hole of the injector head; the outer diameter d2 of the lower part of the needle valve body of the injector is 11-13mm.

Further, the head of the needle valve is a cylindrical surface and changes in steps.

Further, the needle valve head is composed of two steps, and the height of the first step is 0.2 to 0.8 times the maximum lift of the needle valve, and the height of the second step does not exceed the maximum lift of the needle valve; the first step The diameter of the fuel injector is slightly larger than the diameter of the second step to ensure that the circulating fuel injection volume is relatively large, and the minimum flow section of the injector when the needle valve is fully opened is the cross-sectional area of the nozzle hole.

When the opening amount of the needle valve is small, the minimum flow section of the injector is the annular flow section between the needle valve head and the pressure chamber, which is slightly smaller than the sum of the flow areas of the nozzle holes.

Beneficial effects of the present invention:

(1) Compared with the conical shape of the needle valve head in the existing fuel injector, the multi-step stepped cylindrical needle valve head proposed by the present invention can effectively reduce the impact force of the needle valve on the needle valve seat surface, and improve the injection efficiency. The working reliability and service life of the nozzle;

(2) The volume of fuel in the pressure chamber is reduced, so that the phenomenon of post-dripping after fuel injection is reduced, and the combustion is timely, which is conducive to fuel atomization and mixing, and improves the resulting carbon deposits at the end of the fuel injection nozzle and the emission of HC and soot from the diesel engine ;

(3) The pump suction volume is reduced, the energy generated by the fuel injection pump pressure oil is absorbed by the pump suction effect caused by the rise of the needle valve in the oil tank, which is more used for fuel injection, and the injection pressure is increased;

(4) A fuel flow section is added between the guide section of the needle valve and the sealing cone surface of the seat surface, which improves the fuel flow performance. The fuel nozzle is stuck due to local heating of the nozzle, and the reliability of the fuel injector is high;

(5) By rationally designing the dimensions of the stepped cylinders at all levels of the needle valve, while ensuring the reliability and dynamics of the injection when the fuel supply is large in circulation, the fuel flow performance of the fuel injection nozzle is improved when the fuel is small, ensuring that the needle valve The minimum flow cross section is formed with the pressure chamber, which improves the injection stability when the oil volume is small.

Description of drawings

Fig. 1 is a schematic diagram of the structure of the fuel injector of the present invention.

Fig. 2 is a schematic diagram of the structure of the nozzle head of the present invention.

Fig. 3 is a partially enlarged view of the pressure chamber of the fuel injector of the present invention.

Fig. 4 is a schematic diagram of the structure of the head of the original fuel injector.

Marks in the figure: 1-needle valve, 2-needle valve body, 3-first step, 4-second step, 5-spray hole, 6-axial sealing surface, 7-pressure bearing cone, 8- Oil tank, 9-compression fit surface, 10-sealing cone.

Detailed ways

In order to have a clearer understanding of the technical features, purposes and effects of the invention, the specific implementation of the present invention will now be described with reference to the accompanying drawings. The accompanying drawings are only used to illustrate the present invention, and do not represent the actual structure and true proportion of the present invention.

The implementation of the present invention takes a commercial vehicle diesel engine supporting a hole-type fuel injector as an example. In order to control the injection stability of the commercial vehicle diesel engine with a small amount of fuel, the structure of the fuel injector is designed as shown in Figure 1-4. The needle valve of the injector is a rod-shaped cylindrical entity, and the needle valve body is a cavity-shaped entity. The needle valve is assembled in the needle valve body. The outer diameter d2 of the lower part of the needle valve body is 11-13mm, and the outer diameter d1 of the upper part of the needle valve body is 1.8 of d2. -2.1 times; the height of the second step 4 does not exceed the maximum lift of the needle valve 1; the diameter d3 of the needle valve 1 is 7-9 mm. The inner diameter of the upper part of the needle valve body is the same as the outer diameter of the guide section of the upper part of the needle valve, and the clearance fit forms the axial sealing surface of the high-pressure fuel; The sealing cone of the seat surface, the fuel flow section is added between the needle valve guide section and the sealing cone of the seat surface; there is a large gap (above 0.5mm) between the needle valve and the needle valve body below the oil tank, providing fuel to the injection hole at the channel.

According to the relationship between the annular flow cross-sectional area and the area of the nozzle hole, the following formula can be obtained

Tidy up

Among them, i is the number of injection holes, d is the diameter of the injection holes, D is the diameter of the pressure chamber, δ is the thickness of the annular flow section, and the value of α is 0.2-0.8.

It is known that the hole diameter of the commercial vehicle diesel engine is 0.155mm, the number of holes is 7, and D is 1mm. According to the formula (2), when the value of α is 0.2, the calculated δ is equal to 0.0084mm; when the value of α is 0.8 , the calculated δ is equal to 0.0336mm, which all meet the current machining accuracy requirements for fuel injectors.

When the present invention is installed and used on a diesel engine, the head of the needle valve is changed from a cone to a multi-stage stepped cylinder, which reduces the impact force of the needle valve on the seat surface of the needle valve and increases the working life of the fuel injection nozzle assembly; Increase the volume of the pressure chamber, reduce the drop after fuel injection, make the combustion timely, and improve the resulting carbon deposits at the nozzle end and the emission of HC and soot from the diesel engine; reduce the pump suction volume, so that the pressure fluctuations in the oil tank The fuel flow section is increased between the needle valve guide section and the sealing cone surface of the seat surface, which improves the fuel flow performance. At the same time, the flowing fuel cools the needle valve, reducing the Nozzle sticking failure caused by local heating of the fuel injector; improved fuel flow performance of the fuel injector when the needle valve lift is small, ensures the minimum flow cross section between the needle valve and the pressure chamber, and improves injection stability when the fuel volume is small sex.

The detailed description listed above is only a specific description of the feasible embodiments of the present invention, and is not intended to limit the protection scope of the present invention. All equivalent embodiments or changes made without departing from the technical spirit of the present invention shall include Within the protection scope of the present invention.

Claims (3)

1. jetting stability hole type nozzle when a kind of commercial diesel engine for automobile of control small oil mass, including needle-valve (1) and needle-valve Body (2), which is characterized in that it is characterized in that, the needle-valve (1) head is cylindrical body, and be in step variation, the needle-valve head Portion specifically by the different cylindrical body of diameter be connected constitutes, and in inverted steps formula change, stepped cylindrical diameter with needle-valve head with The diminution of pressure chamber's distance from bottom and reduce；

Needle-valve (1) head is made of two-stage cylinder ladder；First order ladder (3) is highly the 0.2 of needle-valve (1) maximum lift ~0.8 times, second level ladder (4) is highly no more than the maximum lift of needle-valve (1)；The diameter of first order ladder (3) is slightly larger than the The diameter of second level ladder (4)；Circulating fuel injection quantity is larger, needle-valve standard-sized sheet when, fuel injector minimum flow area is each spray orifice (5) stream The sum of logical area；When needle-valve open amount is smaller, fuel injector minimum flow area is annular flow at needle-valve (1) head and pressure chamber The sum of logical section, and be slightly less than each spray orifice (5) circulation area；

The head sizes and annular flow cross-section relation of the needle-valve (1) are as follows:

Wherein, i is orifice number, and d is injection diameter, and D is pressure chamber's diameter, and δ is the thickness in annular flow section, and α value is 0.2 ~0.8.

2. jetting stability cellular type oil spout when a kind of commercial diesel engine for automobile of control according to claim 1 small oil mass Mouth, which is characterized in that needle-valve body (2) upper inner diameter is identical as needle-valve (1) top outer diameter and clearance fit, forms high compression ignition Oily axial seal face (6)；Between the lower edge of the pressure-bearing conical surface (7) of needle-valve (1) and the upper edge of atomizer sealing cone (10) Length inner needle valve body (2) internal diameter is 0.6-0.9mm bigger than needle-valve (1) outer diameter, forms oil holding slot (8) and arrives atomizer head spray orifice (5) Fuel flow path.

3. jetting stability cellular type oil spout when a kind of commercial diesel engine for automobile of control according to claim 1 small oil mass Mouth, which is characterized in that needle-valve body (2) the lower outer diameter d2 of the atomizer is in 11-13mm, the 1.8- that top outside diameter d 1 is d2 2.1 times, the diameter d3 of the needle-valve (1) is in 7-9mm.