EP2875232A1

EP2875232A1 - Piezo injector with hydraulically coupled nozzle needle movement

Info

Publication number: EP2875232A1
Application number: EP13736850.2A
Authority: EP
Inventors: Willibald SCHÜRZ
Original assignee: Continental Automotive GmbH
Current assignee: Continental Automotive GmbH
Priority date: 2012-07-18
Filing date: 2013-07-04
Publication date: 2015-05-27
Also published as: US10024285B2; WO2014012795A1; US20150184627A1; DE102012212614A1

Abstract

The invention relates to a piezo injector (100) with an actuator chamber (131) in which a piezo actuator (130) is arranged. The piezo injector (100) further comprises a valve plunger bore (151) in which a valve plunger (150) is arranged, said valve plunger (150) having a first end face (152) facing the piezo actuator (130). A valve plunger bore (151) portion which is delimited by the first end face (152) forms a first control chamber (153), and a valve plunger bore (151) portion opposite the first control chamber (153) forms a spring chamber (154). The valve plunger (150) is arranged between the first control chamber (153) and the spring chamber (154). Additionally, a nozzle needle (170) is provided comprising a second end face (172), said nozzle needle (170) guiding a nozzle needle sleeve (171). The nozzle needle sleeve (171) and the second end face (172) delimit a second control chamber (173). A connection bore (160) is provided between the first control chamber (153) and the second control chamber (173). Furthermore, a leakage pin (140) is provided which is arranged between the piezo actuator (130) and the first end face (152) of the valve plunger (150) in a leakage pin bore (141). Said leakage pin bore (141) is formed in an intermediate plate (112) which adjoins a control plate (114) on the side facing the piezo actuator (130), the valve plunger bore (151) being formed in said control plate (114).

Description

description

Piezoinj ektor with hydraulically coupled nozzle needle movement The invention relates to a piezoelectric actuator according to claim 1.

Direct fuel injection internal combustion engines are known. Become fuel direct injection

Piezoinj used sectors whose nozzle needle is driven by a piezoelectric actuator. In this case, a virtually backlash-free coupling between the piezoelectric actuator and the nozzle needle is required, which is difficult to maintain due to thermal change in the Piezoinj ector. Too little idle stroke between the piezo actuator and the nozzle needle can result in incomplete closing of a nozzle needle. Too large idle stroke between the piezoelectric actuator and the nozzle needle leads to an increase of the necessary for driving the Piezoinj ector drive energy. In the prior art, attempts have been made to compensate thermal length changes by suitable choice of material and geometry. However, this leads to high manufacturing costs and limits the constructive freedom in the design of Piezoinj ector a strong.

The object of the present invention is to provide a piezoelectric actuator in which length changes of

Piezoinj ector be compensated by itself. This object is achieved by a Piezoinj ector having the features of claim 1. Preferred developments are specified in the dependent claims.

An inventive Piezoinj ector comprises an actuator chamber in which a piezoelectric actuator is arranged, a valve piston bore in which a valve piston is arranged, which has a piezoelectric actuator facing the first end, wherein a limited by the first end portion of the valve piston bore forms a first control chamber, wherein a the first control chamber opposite portion of the valve piston bore forms a spring chamber, and wherein the valve piston between the first Control chamber and the spring chamber is arranged, a nozzle needle having a second end face, wherein the nozzle needle a

Düsennadelhülse leads, wherein the nozzle needle sleeve and the second end face define a second control chamber, a

Connecting bore between the first control chamber and the second control chamber, and a leakage pin which between the piezoelectric actuator and the first end face in a

Leakage pin hole is arranged. The leakage pin hole is formed in an intermediate plate which adjoins the piezoelectric actuator side facing a control plate, in which control plate, the valve piston bore is formed. Advantageously, in this Piezoinj ector, a hydraulic coupling between the piezoelectric actuator and the

Nozzle needle. This hydraulic coupling causes

advantageously a clearance compensation and a

Stroke step. Advantageously, by

Temperature effects, wear at contact points in the drive and by changing the polarization state of the piezoelectric actuator caused change in length in Piezoinj be compensated. This advantageously makes it possible to manufacture the injector from any material without thermal

To take into account expansion properties of the material. Therefore, a particularly advantageous

high pressure resistant material can be used. Advantageously omitted in the assembly of Piezoinj ectors consuming

Adjustment processes for a no-load, which reduces the manufacturing costs of Piezoinj ectors. The elimination of a Leerhubs also reduces a required for driving the Piezoinj ector energy. Another advantage of Piezoinj ector is its improved injection quantity stability in dynamic engine operation. It is also advantageous that pressure losses are reduced in Piezoinj ector over the prior art. In a further embodiment, a connection plate is provided at the nozzle needle facing the end of the control plate, which limits the second control space. ^

Moreover, in a further embodiment of the invention, the intermediate plate and / or the control plate and / or the leakage pin can be made of a hard metal. In this case, the intermediate plate and / or the control plate and / or the leakage pin have a threefold higher modulus of elasticity than steel. According to the invention, the modulus of elasticity can be in the range of 500 to 700 GPa. This ensures that the bore for the leakage pin in the intermediate plate and the bore for the valve piston as a result of the clamping force through the

Do not constrict the nozzle retaining nut unduly (risk of jamming in the guides) and as a result of the effect of the

Do not unduly increase fuel high pressure. Excessive expansion, especially of the hole for the

Valve piston would cause the nozzle needle can not be kept stable in the open position.

It is expedient that a first leakage is made possible out of the first control chamber, a second leakage from the spring chamber into the first control chamber is made possible, and a third leakage from the high-pressure region into the second control chamber is made possible. In this case, a sum of the second leakage and the third leakage is at least as large as the first leakage. In addition, this sum of the second leakage and the third leakage is so small that when the nozzle needle is open, a pressure increase in the second control chamber caused by the second leakage and the third leakage does not lead to a closing of the nozzle needle. Advantageously, the second leakage and the third leakage prevent the first leakage from causing unintentional opening of the nozzle needle. The second and third leakage advantageously also prevent accidental opening of the nozzle needle at very steep

Pressure increases in the high pressure area.

Preferably, the piezoelectric injector has a high-pressure bore which is connected to the high-pressure region. It is the

High pressure area connected to the spring chamber.

Advantageously, the high pressure of the high-pressure bore always prevails in the spring chamber. It is expedient that a valve piston spring is arranged in the spring chamber, which acts on the valve piston with a force acting in the direction of the first control chamber.

Advantageously, the valve piston spring causes a return of the valve piston to its original position after an injection process has ended.

It is also expedient that the piezoelectric injector has a nozzle spring which acts on the nozzle needle with a force directed away from the second control chamber. Advantageously, the nozzle spring then assists in closing the nozzle needle to complete an injection process. In one embodiment of the Piezoinj ector there is a first between the leakage pin and the leakage pin hole

Mating game that allows the first leakage. The first mating game is less than two yards. Advantageously, experiments and model calculations have shown that such a first mating game leads to a sufficiently small first leak.

In one embodiment of the Piezoinj ector there is a third mating game between the nozzle needle and the nozzle needle sleeve that allows the third leakage. The third mating game is between 2 ym and 4 ym. Advantageously, it has been shown in model calculations and experiments that a third mating game of this magnitude leads to a suitable third leakage.

In one embodiment of the Piezoinj ector there is a second between the valve piston and the valve piston bore

Mating game that allows the second leakage. The second mating game is between 2ym and 4ym.

Advantageously, model calculations and experiments have shown that such a sized second mating clearance results in a second leakage of suitable size. In another embodiment of the Piezoinj ectors, the valve piston has a running between the first control chamber and the spring chamber throttle bore, which allows the second leakage. Advantageously, such a throttle bore allows a second leakage of suitable size.

Particularly preferred is the throttle bore through the

Leak pin closed when the leakage pin is against the valve piston. Advantageously, the second leakage is then interrupted in the open state of the nozzle needle, whereby the

Danger of caused by the second leakage unwanted closing of the nozzle needle is reduced.

In one embodiment of the Piezoinj ectors is in the

Connecting bore between the first and the second

Control room arranged a choke.

Particularly preferably, the piezoelectric actuator is a fully active

Piezo stack. Advantageously, the piezoelectric actuator can be hermetically separated from the fuel and therefore does not have any

Have fuel resistance.

The invention will now be described in more detail below with reference to the accompanying drawings, in which:

Figure 1 is a cross-sectional view of an upper part of a

Piezoinj ektor, ·

FIG. 2 is a cross-sectional view of a lower part of FIG

Piezoinj ektor.

In the figures 1 and 2, a cross-sectional view of a Piezoinj ector 100 is shown. FIG. 1 shows an upper part 101 of the piezo injector 100. FIG. 2 shows a lower part 102 of the piezo injector 100. The piezo injector 100 can be used for

Injecting fuel into an internal combustion engine. The Piezoinj ector 100 can be used for example for injecting diesel fuel in a common rail internal combustion engine. The piezoelectric injector 100 has an injector housing 110. The injector housing 110 may consist of a largely arbitrary material, since the thermal expansion properties of the injector 110 are irrelevant. In particular, the injector housing 110 need not be Invar.

In the injector housing 110, a high pressure bore 120 is arranged, which can be supplied via a high pressure port 121 under high pressure fuel. The high pressure bore 120 extends longitudinally through the injector housing 110, through an intermediate plate 112, a control plate 114 and a

Connecting plate 116 up to a subsequently discussed high-pressure area 178 in the lower part 102 of the Piezoinj ector 100. The upper part 101 of the piezo injector 100 further includes a leakage connection 111 on. Next, the injector 110 has in the upper part 101 of the piezo injector 100 ector an actuator chamber 131 in which a piezoelectric actuator 130 is arranged. The piezoelectric actuator 130 is preferably a fully active piezo stack. The piezoelectric actuator 130 has approximately a cylindrical shape and can be acted upon via an electrical connection 132 with an electrical voltage to change the length of the piezoelectric actuator 130 in the longitudinal direction.

In the lower part 102, the piezoelectric injector 100 has a

Valve piston bore 151 which is formed in the control plate 114. In the valve piston bore 151 is the

Valve piston 150 is arranged. The valve piston 150 has a first end 152 pointing in the direction of the piezoactuator 130. A limited by the first end face 152 portion of the valve piston bore 151 forms a first control chamber 153 in the control plate 114. At its the first control chamber 153th

opposite longitudinal end, the valve piston bore 151 forms a spring chamber 154, which is also arranged in the control plate 114. The valve piston 150 is thus arranged between the first control chamber 153 and the spring chamber 154. Furthermore, the first control chamber 153 is delimited by the intermediate plate 112, which is arranged on the side facing the piezoelectric actuator adjacent to the control plate 114. In the spring chamber 154 is a valve piston spring 155, which may be formed for example as a spiral compression spring. A first longitudinal end of the valve piston spring 155 is supported on the valve piston 150. A second longitudinal end of the valve piston spring 155 is supported on an end face of the valve piston bore 151. The valve piston spring 155 acts on the valve piston 150 with a force acting in the direction of the first control chamber 153.

The spring chamber 154 is connected to the high-pressure region 178 via a high-pressure connection 157. The high-pressure connection 157 is formed in the connection plate 116, which delimits the spring space 154 on the side remote from the piezoactuator and adjoins the control plate 114. Thus, there is always fuel in the spring chamber 154 in the operation of the piezoelectric injector 100 with the pressure prevailing in the high-pressure bore 120 and the high-pressure region 178.

Between the piezoactuator 130 and the valve piston bore 151 is a leakage pin 140 in a leakage pin bore 141

arranged. This leakage pin bore 141 is in the

Between plate 112 is formed. The length of the leakage pin 140 is dimensioned such that an increase in the length of the

Piezoactuator 130 is transmitted via the leakage pin 140 to the valve piston 150. Next is in the lower part of the

Piezoinj ector of the high-pressure region 178 arranged, in which the high-pressure bore 120 opens. In the high-pressure region 178, a nozzle needle 170 is arranged, which guides a nozzle needle sleeve 171. In the direction of the upper part 101 of the piezo injector 100, the longitudinal end of the nozzle needle 170 has a second end face 172. Above the second end face 172 is a second

Control chamber 173 formed by the second end face 172 of the nozzle needle 170, the nozzle needle sleeve 171 and the

Terminal plate 116 is limited. The second control chamber 173 is connected via a connecting bore 160 with the first control chamber 153. Wherein the connecting hole 160 through the

Control plate 114 and the connection plate 116 extends. ₀

O

The nozzle needle 170 has a fixed collar 174 connected to the nozzle needle 170. Between the collar 174 and the nozzle needle 171, a nozzle spring 175 is arranged, which may be formed for example as a spiral compression spring. A first longitudinal end of the nozzle spring 175 is supported on the

Nozzle needle sleeve 171 from. A second longitudinal end of the nozzle spring 175 is supported on the collar 174. The nozzle spring 175 acts on the nozzle needle 170 with a second control chamber 173 directed away force.

In the closed state of the piezoelectric injector 100, the nozzle needle 170 is located at a lower tip of the lower part 102 of the piezo injector 100 at. The piezoactuator 130 is discharged and has its minimum length. The piezo injector 100 does not fuel injection.

If the piezoelectric actuator 130 is charged via the electrical connection 132 and thereby increases the length of the piezoactuator 130, then the piezoactuator 130 exerts a force on the valve piston 150 via the leakage pin 140, through which the valve piston 150 in the

Valve piston bore 151 is moved in the direction of the spring chamber 154. As a result, the volume of the first control chamber 153 increases, as a result of which the pressure in the first control chamber and in the second control chamber 173 decreases. Thus, the reduced pressure in the second control chamber 173 exerts a now reduced force on the second end face 172 of the nozzle needle 170. The further acting on the lower end of the nozzle needle high pressure of the high pressure area 178 subsequently causes a movement of the nozzle needle 170 upwards in the direction of the second control chamber 173. As a result, the piezoelectric injector 100 is opened, and fuel is injected.

By the ratio of the diameter of the valve piston 150 and thus the diameter of the first control chamber 153 to the diameter of the nozzle needle 170 at its second end face 172 and thus to the diameter of the second control chamber 173 is a

Translation ratio between a change in length of the piezoelectric actuator 130 and a stroke of the nozzle needle 170 is fixed. If the diameter of the valve piston 150 is, for example 5 mm and the diameter of the nozzle needle 170 at its second end face 172, for example, 3.5 mm, this results in a transmission ratio of about 2. After opening the nozzle needle 170, the stroke of the nozzle needle 170 can be controlled by varying the length of the piezoelectric actuator 130 , In turn, the length of the piezoactuator 130 can be varied via a variation of the energy supplied to the piezoactuator 130 via the electrical connection 132. If the piezoelectric actuator 130 is subsequently discharged and thereby shortened, then the pressure prevailing in the spring chamber 154 and that caused by the

Valve piston spring 155 on the valve piston 150 force exerted a movement of the valve piston 150 in the direction of the first control chamber 153. This increases the pressure in the first control chamber 153 and, because of the first control chamber 153 and second control chamber 173 existing communication bore 160, and the pressure in the second Control chamber 173. This has a retraction of the nozzle needle 170 to the lower end of the lower part 102 of the piezoelectric injector 100 result, through which the piezoelectric injector 100 is closed and the fuel injection is terminated.

The force exerted by the valve piston spring 154 on the valve piston 150 spring force ensures that the valve piston 150 in the closed state of the Piezoinj ector 100 always on

Leakage pin 140 is applied and the drive formed by the piezoelectric actuator 130, the leakage pin 140 and the valve piston 150 is always free of play. This has the consequence that changing thermal boundary conditions, changes in length of the piezoelectric actuator 130 and wear in the contact areas have no appreciable effect on the output by the piezoelectric injector 100 injection quantities.

The leakage pin 140 is fitted with a first mating clearance 142 into the leakage pin bore 141. Because of the first mating clearance 142, a first leakage 143 takes place from the first control chamber 143 along the leakage pin 140 into a region of the piezoelectric injector 100 arranged above the leakage pin 140, from where the first leakage 143 via the leakage connection ₁

111 can escape. Because of the high pressure prevailing in the first control chamber 153, the first mating clearance 142 must be selected to be small in order to obtain a small first leakage 143. The first mating game 142 is preferably less than 2 ym, more preferably about 1 ym.

The valve piston 150 is fitted with a second mating clearance 158 in the valve piston bore 151. If the pressure in the first control chamber 153 is less than the pressure in the spring chamber 154, the second mating clearance 158 causes a second leakage 159 from the spring chamber 154 along the valve piston 150 into the first control chamber 153. The valve piston 150 can also be a

Have throttle bore 156 which extends from the spring chamber 154 through the valve piston 150 to the first control chamber 153. In this case, a fourth leakage 180 from the spring chamber 154 into the first control chamber 153 is possible through the throttle bore 156. If the throttle bore 156 is absent, the second mating clearance 158 is preferably between 3 ym and 10 ym, more preferably between 2 ym and 4 ym, to allow a sufficient second leakage 159. If the throttle bore 156 is present and thus the fourth leakage 180 is possible, then the second mating clearance 158 can be selected to be very small and, for example, amount to 1 μm. The nozzle needle 170 is fitted with a third mating clearance 176 in the nozzle needle sleeve 171. If the pressure in the second control chamber 173 is less than the pressure in the high-pressure region 178, then it can pass along the nozzle spring 175 through the third

Mating game 176 to a third leak 177 from the

High-pressure region 178 come into the second control chamber 173. The third mating game 176 is preferably between 3 and 10 ym, more preferably between 2 and 4 ym. If the throttle bore 156 is present, then the third leakage 177 can be dispensed with and the third mating clearance 176 can likewise be formed very small, for example in the size of approximately 1 μm. In the closed state of the Piezoinj ector it comes through the first leakage 143 along the leakage pin 140 to a drain of fuel from the first control chamber 153. So this Fuel drain from the first control chamber 153 does not lead to a pressure drop in the first control chamber 153, the one

Inadvertent opening of the nozzle needle 170 would result in the loss of fuel caused by the first leakage 153 having to be compensated for by the second leakage 159, the third leakage 177 and / or the fourth leakage 180. If the throttle bore 156 does not exist and thus the fourth leakage 180 does not take place, then the sum of the second leakage 159 and the third leakage 177 must be at least as large as the first leakage 143. If the throttle bore 156 is present, then the sum from the second leakage 159, the third leakage 177 and the fourth leakage 180 be at least as large as the first leakage 143.

In the open state of the nozzle spring 175 and thus of the

Piezoinj ektors 100 it comes through the second leakage 159, the third leakage 177 and / or the fourth leakage 180 to a drain of fuel in the first control chamber 153 and the second control chamber 173. The inflow of fuel causes an increase in pressure in the first control chamber 153 and in the second control chamber 173. However, the pressure increase must be so small that it does not come to an unintentional premature closing of the nozzle needle 170 and thus the Piezoinj ector 100.

Particularly preferred are the throttle bore 156 and the

Leakage pin 130 is formed so that the leakage pin 140 closes the throttle bore 156 when the nozzle needle 170 is opened. As a result, when the nozzle needle 170 is open, the fourth leakage 180 is prevented, so that premature, undesired closing of the nozzle needle 170 is precluded.

In the connecting bore 160 between the first control chamber 153 and the second control chamber 173, a throttle may be arranged.

The second leakage 159 and the third leakage 177 are also necessary to prevent accidental opening of the nozzle needle 170 at very steep pressure increases in the high pressure region 178. The components intermediate plate 112, control plate 114 and

Leakage pin 140 may be made of hard metal. Such hard metals are characterized by the fact that they have a threefold higher modulus of elasticity than steel. Preferably, the modulus of elasticity is in the range of 500 GPa to 700 GPa. As a result, the intermediate plate 112 and the control plate 114 in the entire operating range of the injector a stable

Guide play to the leakage pin or to the valve piston safe.

Claims

claims

1. Piezoinj ector (100) having an actuator chamber (131) in which a piezoelectric actuator (130) is arranged,

a valve piston bore (151) in which a valve piston (150) is arranged,

wherein the valve piston (150) has a first end face (152) facing the piezoactuator (130), wherein a section of the valve piston bore (151) delimited by the first end face (152) forms a first control chamber (153), wherein the first control chamber (15) 153) opposite section of

Valve piston bore (151) forms a spring chamber (154), wherein the valve piston (150) between the first control chamber (153) and the spring chamber (154) is arranged,

a nozzle needle (170) having a second end face (172), wherein the nozzle needle (170) guides a nozzle needle sleeve (171), wherein the nozzle needle sleeve (171) and the second end face (172) define a second control chamber (173),

a communication bore (160) between the first control chamber (153) and the second control chamber (173),

and a leakage pin (140) disposed between the piezoactuator (130) and the first end face (152) of the valve piston (150) in a leakage pin bore (141),

characterized in that

the leakage pin bore (141) is formed in an intermediate plate (112) which, on the side facing the piezoactuator (130), adjoins a control plate (114) in which

Control plate (114), the valve piston bore (151) is formed.

2. Piezoinj ector (100) according to claim 1, characterized in that at the nozzle needle (170) facing the end of

Control plate (114) is provided a connection plate (116) which limits the second control chamber (173).

3. Piezoinj ector (100) according to any one of the preceding claims, characterized in that the intermediate plate (112) and / or the control plate (114) or / and the leakage pin (140) are made of a hard metal.

4. Piezoinj ector (100) according to any one of the preceding claims, characterized in that the intermediate plate (112) and / or the control plate (114) and / or the leakage pin (140) have a threefold higher modulus of elasticity than steel.

5. Piezoinj ector (100) according to claim 4, characterized in that the modulus of elasticity is in the range of 500 GPa to 700 GPa.

6. Piezoinj ector (100) according to any one of the preceding claims, characterized in that a first leakage (143) from the first control chamber (153) out is possible, wherein a second leakage (159, 180) from the spring chamber (154) in the first

Control space (153) is possible, wherein a third leakage (177) from a high-pressure area (178) in the second control chamber (173) is possible, wherein a sum of the second leakage (159, 180) and the third leakage (177) at least is as large as the first leakage (153), wherein the sum of the second leakage (159, 180) and the third leakage (177) is so small that when the nozzle needle (170) is open by the second leakage (159, 180 ) and the third leakage (177) effected increase in pressure in the second control chamber (173) does not lead to a closing of the nozzle needle (170).

7. Piezoinj ector (100) according to any one of the preceding claims, characterized in that the piezoelectric injector (100) has a high pressure bore (120), wherein the high pressure bore (120) with the high pressure region (178) is connected, wherein the high pressure region (178 ) is connected to the spring chamber (154).

8. Piezoinj ector (100) according to any one of the preceding claims, characterized in that in the spring chamber (154) a valve piston spring (155) is arranged, which acts on the valve piston (150) in the direction of the first control chamber (153) acting force ,

9. Piezoinj ector (100) according to any one of the preceding claims, characterized in that the piezoelectric injector (100) has a nozzle spring (175) which acts on the nozzle needle (170) directed away from the second control chamber force.

10. Piezoinj ector (100) according to any one of the preceding claims, characterized in that between the leakage pin (140) and the leakage pin bore (141) a first mating game (142), wherein the first mating game (142) the first leakage (143) allows, wherein the first mating game (142) is less than 2 ym.

11. Piezoinj ector (100) according to any one of the preceding claims, characterized in that between the nozzle needle (170) and the nozzle needle sleeve (171), a third mating game (176), wherein the third mating game (176), the third leakage (177) wherein the third mating game (176) is between 2 ym and 4 ym.

12. Piezoinj ector (100) according to any one of the preceding claims, characterized in that between the valve piston (150) and the valve piston bore (151) a second mating game (158), wherein the second mating game (158), the second leakage (159) wherein the second mating game (158) is between 2 ym and 4 ym.

13. Piezoinj ector (100) according to one of claims 1 to 11, characterized in that the valve piston (150) between the first control chamber (153) and the spring chamber (154) extending throttle bore (156), wherein the throttle bore (156 ) enables the second leakage (180).

14. Piezoinj ector (100) according to claim 13, characterized

characterized in that the throttle bore (156) through the

Leakage pin (140) is closed when the leakage pin (140) on the valve piston (150) is applied.

15. Piezoinj ector (100) according to any one of the preceding claims, characterized in that in the connecting bore (160) between the first control chamber (153) and the second control chamber (173) is arranged a throttle.

16. Piezoinj ector (100) according to any one of the preceding claims, characterized in that the piezoelectric actuator (130) a

fully active piezo stack is.