A NOZZLE ASSEMBLY ₅ A FUEL INJECTOR AND AN INTERNAL COMBUSTION ENGINE COMPRISING SUCH AN INJECTOR

TECHNICAL FIELD OF THE INVENTION

This invention concerns a nozzle assembly, a fuel injector including such an assembly and an internal combustion engine comprising such an injector.

BACKGROUND OF THE INVENTION

In the field of fuel injection for internal combustion engines, new developments are largely driven by new coming emission regulations, as well as noise and fuel consumption targets. A potential way to improve combustion is to start fuel injection long before the piston reaches its top dead end position (TDC). In some instances, some fuel can be injected up to 180° before TDC. For such an early injection, the spray angle should be small in order to avoid spraying fuel on the cylinder walls, since this would have major drawbacks on emissions, oil dilution and cylinder liners wear. On the contrary, when injection takes place just for TDC, the spray angle should be large in order to suit diesel piston bowls. In order to obtain two spray angles, some nozzles are provided with telescopic needles adapted to feed of two rows of holes or outlets.

In FR-A-2 854 661 , a telescopic needle allows a double stage injection with a first spray having a narrow angle and then a mixture of two sprays. In US-B- 6 557 776, another telescopic needle is used to obtain a first spray through a first row of holes, for small quantities of fuel, and a second spray through two series of holes available, for the main injection. In these systems, the second spray includes a flow corresponding to the first spray. In other words, the second spray is a combination of the first spray and another spray, because prior art systems do not allow the selection of two different rows of holes or orifices. It is only possible to inject fuel either with the first row of holes or with both rows of holes, but not with the second row of holes alone. Moreover, the prior art devices imply complex designs with several actuators, which decreases the reliability of these systems and increases their costs.

US-B-6 769 635 discloses a fuel injector whose nozzle assembly includes two rows of holes which can be fed independently from each other thanks to two

electrical actuators powered and driven according to the needs. This fuel injector is quite complex to manufacture, expensive and difficult to set.

SUMMARY OF THE INVENTION

The invention aims at providing a nozzle assembly which allows to obtain two different spray geometries thanks to two sets of orifices used independently from each other, without needing complex and expensive valves to define which type of orifices is used for spraying fuel within a combustion chamber.

With this respect, the invention concerns a nozzle assembly for injecting fuel into a combustion chamber of an engine, this assembly comprising a first needle and a second needle controlling respectively fuel flow towards a first series of outlets and a second series of outlets. This nozzle includes a passive control valve adapted to select, on the basis of the fuel feeding pressure, the needle to be activated for fuel delivery to the combustion chamber.

Thanks to the invention, the passive control valve enables to select which flow path can be open and which series of outlets can be fed when fuel is to be delivered to the combustion chamber.

According to advantageous aspects of the invention, such a nozzle assembly may incorporate one or several of the following features:

- the passive control valve is driven with fuel coming from a source of fuel under pressure and controls flow of fuel coming from two back-pressure chambers acting on the needles.

- the passive control valve is adapted to selectively connect, depending on the pressure level of the driving fuel coming from the source of fuel under pressure, either of the back-pressure chambers with a discharge line.

- the assembly includes a solenoid valve adapted to pilot one of the needle, depending on the selection made by the passive control valve.

- the solenoid valve controls the connection between the discharge line and a low pressure circuit.

- two fuel paths are defined between a source of fuel under pressure and the passive control valve, each path including a back-pressure chamber acting on one of the needles.

- each fluid path includes at least two throttles located respectively upstream and downstream of the corresponding back-pressure chamber.

- the throttles are made in at least a part mounted on a body of said assembly which surrounds the needles.

- one throttle is located between the source of fuel under pressure and each back-pressure chamber.

- a dedicated throttle is located on the entry line of each back-pressure chamber.

- a throttle is located on a feeding line common to both back-pressure chambers.

- one throttle is located between each back-pressure chamber and the passive control valve.

- one throttle is located downstream of the passive control valve.

- the outlets series include a first series of outlets distributed around a central axis with a frustroconical configuration having a first angle and a second series of outlets coaxial with the first series, with a frustroconical configuration having a second angle whose value is superior to the value of the first angle.

- the assembly comprises two back-pressure chambers, each back-pressure chamber acting on one needle.

- the back-pressure chambers and the needles are coaxial.

- the passive control valve comprises a valve core movable in translation within a valve body and subject, on one side, to the action of the fuel feeding pressure and, on the other hand, to the action of elastic return means.

The invention also concerns a fuel injector comprising a nozzle assembly as mentioned here-above. Such a nozzle assembly is more flexible to provide fuel to a combustion chamber.

Finally, the invention also concerns an internal combustion engine comprising at least a cylinder provided with a fuel injector as mentioned here-above. Such an engine offers more possibilities for performance development and opens the door to further potential improvements.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood on the basis of the following description which is given in relation to the annexed drawings, as a non-limiting example. In the drawings:

- figure 1 is a schematic view of a nozzle assembly according to a first embodiment of the invention;

- figure 2 is a schematic flow chart of the nozzle assembly of figure 1 ;

- figure 3 is a view similar to figure 1 when the nozzle assembly is in another configuration of work ;

- figure 4A represents the variation of the fuel injection pressure in the nozzle assembly, as a function of time;

- figure 4B represents the lifts of the needles of the nozzle assembly, as a function of time;

- figure 5 is a structural view of the passive control valve of the nozzle assembly in the configuration of figure 1 ;

- figure 6 is a view similar to figure 5 when the nozzle assembly is in the configuration of figure 3;

- figure 7 is a schematic view of a part of an engine incorporating a fuel injector which comprises a nozzle assembly according to figures 1 to 3, 5 and 6;

- figure 8 is a flowchart similar to figure 2 for a nozzle assembly according to a second embodiment of the invention; and

- figure 9 is a flowchart similar to figure 2 for a nozzle assembly according to a third embodiment of the invention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The nozzle assembly 1 of figures 1 to 3, 5 and 6 is supposed to be fed from a source S ₁ of fuel under pressure which can be an external unit pump, an injector built in pump, an amplification stage of an amplified common rail or a higher stage of any hybrid injector stage providing fuel under pressure at different level during injection. The pressure of the fuel fed to assembly 1 varies as a function of time, as shown on figure 4A. More precisely, this pressure varies between a first value P ₁ , which is lower than a reference value P _ref , and a second value P ₂ which is higher than P _ref . The injection pressure P of fuel in nozzle 1 is higher than P _ref between instant to and instant t' _o .

As an example, P _re f might have a value of 1000 bar, whereas Pi is between 300 and 800 bar and P ₂ is between 1200 and 2000 bar.

Nozzle assembly 1 comprises a main body 2. This body is centered on a longitudinal axis Xi of assembly 1 and includes a first needle 11 which is cylindrical

and centered onto its longitudinal axis Xn which is aligned with axis X ₁ . A second needle 12 is also located within body 2. It has a sleeve like shape and is centered on a longitudinal axis X ₁₂ which is aligned with axes Xi and Xn. Needles 11 and 12 are coaxial and needle 12 surrounds needle 11.

The tip 111 of needle 11 has a conical front surface 112 adapted to lie against a seat formed by a frustroconical surface 211 of body 2 centered on axis X-i. A set of several canals 212 is formed around the central extremity 21 of body 2, these canals being regularly distributed around axis X ₁ and forming all the same angle α with respect to axis X ₁ . One notes 213 the outlets of canals 212.

A distributing chamber 214 is formed in central extremity 21 and all canals 212 depart from this chamber 214.

The annular tip 121 of needle 12 is provided with a front frustroconical external surface 122 adapted to lie against a second frustroconical surface 221 of body 2 which forms a seat for needle 12. A set of canals 222 is distributed around axis Xi, each canal 222 forming with axis Xi and angle β which is larger then α.

One notes 223 the outlets of canals 222 formed on the external surface 23 of extremity 21 , as outlets 213.

All canals 222 depart from a chamber 224 formed between needle 12 and body 2.

When needles 11 and 12 lie against their respective seats formed by surfaces 211 and 221, a chamber 231 is formed between tips 111 and 121 , this chamber being isolated from chambers 214 and 224, thus from canals 212 and 222.

Needle 12 is guided within body 2 thanks to two rings 241 and 242 located around its back extremity 123.

Extremity 123 is provided with an internal recess 124 where a spring 13 is kept compressed by a ring 243 lying against a throttle part 15 connected to a second throttle part 16 fast within ring 242. Since ring 243 lies against part 15 which lies against part 16, spring 13 can exert onto needle 12 a force Fi ₃ pushing tip 121 towards seat 221.

Moreover, a second spring 17 is compressed between the back extremity 113 of needle 11 and part 15, so that it exerts on needle 11 a force Fi ₇ which urges tip 111 towards seat 211.

One can consider that surfaces 112 and 211 form a valve 115 which is either open or closed, depending on the position of tip 111 with respect to surface 211.

Similarly one can consider a second valve 125 formed by surfaces 122 and 221. This valve is either closed or opened, depending on the position of needle 12 with respect to body 2.

These two valves 115 and 125 are represented on figure 2.

If some fuel is provided to assembly 1 by source Si, fuel flows through a first canal 251 defined by body 2 and ring 241 towards a circular chamber 252 where it feeds radial canals 126 provided within needle 12. These canals feed some longitudinal grooves 116 provided on the radial surface of needle 11 , which allows fuel to flow up to chamber 231 where pressure increases as long as needles 11 and 12 remain in the closed position of valves 115 and 125.

Pressure P ₂₃ i of fuel within chamber 231 acts on a frustroconical surface 117 of needle 11 as a lift force Fn which tends to open valve 115. Pressure 231 also acts on a frustroconical surface 127 of needle 12 as a lift force F ₁₂ which tends to open valve 125.

Fuel coming from source Si is also fed by two lines 253 and 254 to two backpressure chambers 261 and 262 whose pressures P ₂₆₁ and P ₂₆₂ act respectively on back extremities 113 and 123. In other words, chambers 261 and 262 act, by their respective pressures, on needles 11 and 12. One notes respectively F261 and F ₂ 62 the forces acting on needles 11 and 12 as the result of pressures P ₂₆₁ and P ₂₆₂ -

A first throttle 151 is defined within part 15 in the entry line 253 of fuel within chamber 261. A second throttle 152 is defined within part 15. This throttle is located on an exit line 255 connecting chamber 261 to a passive control valve 18.

Part 16 is also provided with a first throttle 161 and a second throttle 162 provided respectively on the feeding line 254 of chamber 262 and the exit line 257 of this chamber. The cross section of throttle 162 is larger than the cross section of throttle 161.

Chamber 262 is also connected, by exit line 257, to valve 18.

As shown on figure 5, valve 18 comprises a valve body 181 within which a valve core 182 is movable in translation along a longitudinal axis Xi ₈ of body 181. Valve core 182 is provided with two peripheral grooves 183 and 184. Core 182 is loaded, on a first extremity 185, by a spring 186 whereas its second extremity 187 is subjected to the pressure Pi ₈₈ within a chamber 188 fed by fuel under pressure through a feeding line 258 connected to source Si. In other words, the position of valve core 182 within valve body 181 is controlled thanks to the pressure Pi ₈₈ within

chamber 188. Depending on its value, pressure Piss, which corresponds to pressure P because pressure losses are negligible with respect to the values of fuel pressure, is sufficient or not to push core 182 against the action of spring 186.

The exit or discharge line 259 of valve 18 is connected to a solenoid valve 19 which can either isolate line 259 from a low pressure circuit 20 or connect line 259 to this circuit when it is activated.

Spring 186 is chosen so that when pressure within chamber 188 is lower than Pr _ef , core 182 is in the position of figure 5 so that line 255 is connected to line 259 through groove 183, whereas line 257 is isolated from line 259. On the contrary, when Piss is higher than P _re f, line 255 is isolated from line 259, whereas line 257 is connected to line 259 through groove 184, as shown on figure 6.

Two parallel flow paths for fuel extend between source Si and valve 18. The first flow path goes through elements 253, 151 , 261 , 152 and 255. The second flow path goes through elements 254, 161 , 262, 162 and 257.

Assembly 1 works as follows: Between t = 0 and t = to, fuel is provided to assembly 1 at a pressure P lower than P _ref . Under such circumstances, valve 18 is in the configuration of figures 1 and 5. Needle 12 is subject to forces Fi ₂ , F ₁₃ and F ₂₆₂ and spring 13 is chosen so that the sum of these forces pushes needle 12 against surface 221 , so that valve 125 is closed. This situation remains, irrespective of the actuation of valve 19 because line 257 is not connected to valve 19, so that pressure P ₂ 62 remains similar to P-i, with a slight difference due to delay and pressure drop. Since force Fi ₂ is lower than the sum of forces F ₁₃ and F ₂₆₂ , needle 12 remains in its closed position.

Needle 11 is subject to forces Fn, F1 ₇ and F ₂₆ i. Spring 17 is chosen so that, similarly to what happens for needle 12, surface 112 bears against surface 211 as long as force F ₂ 61 is kept constant.

One considers that pressure losses in the different canals and lines are negligible with respect to pressure losses due to throttles 151 , 152 and equivalent equipments.

Throttle 151 has a smaller cross section than throttle 152.

In the configuration of figure 1 , if one activates solenoid valve 19, then line 255 is put into communication with low pressure circuit 20 through valves 18 and 19. In other words, fuel present in chamber 261 flows towards the low pressure circuit and, since throttle 152 is larger than throttle 151 , pressure within chamber 261

decreases. Spring 17 is chosen so that when pressure P ₂₆ i decreases below a prescribed value, force Fn is sufficient to lift needle 11.

If one considers that solenoid valve 19 is activated between instants ti and t'i on figure 4B, the lift Ln of needle 11 takes a first value L ₁ for a period of time δt| depending on the actuation of solenoid valve 19, which allows fuel to flow through canals 212 and to exit assembly 11 through outlets 213. This produces a first fuel spray FSi shown on figure 7, whose geometry is defined by angle α and the number of canals 212.

When fuel injection pressure P becomes larger than P _rβf , at instant t ₀ , passive control valve 18 switches from the position of figures 1 and 5 to the position of figures 3 and 6, so that exit line 255 is isolated from exit line 259, whereas exit line 257 communicates with exit line 259. Under such conditions, if one activates solenoid valve 19 between instant t ₂ and instant t' ₂ , chamber 262 is progressively emptied, so that pressure P ₂₆₂ progressively decreases in such a manner that force F12 is sufficient to lift needle 12 against forces F ₁₃ and F ₂₆₂ -

As shown on figure 4B, the lift L ₁₂ of needle 12 increases progressively up to a predetermined value L ₂ for a period of time δt ₂ which depends on the actuation of valve 19. Then lift L ₁₂ decreases back to zero.

When lift L ₁₂ is non null, fuel can flow from chamber 231 to canals 222 and exit assembly 1 through outlets 223. This produces a second fuel spray FS ₂ whose geometry is defined by angle β and the number of canals 222.

Thanks to the invention, two different types of outlets 213 and 223 can be used successively without obligation to use both series of outlets for a predetermined period of time. Valve 18 allows to automatically switch from the actuation of needle 11 to the actuation of needle 12 depending on the fuel injection pressure P which varies in a known manner, as a characteristic of source S ₁ .

It is therefore possible to use two independent injection spray patterns FS ₁ and FS ₂ defined by angles α and β, the number of canals 212 and 222 and the needle velocity, that is the shape of the lifts Ln and L i ₂ on figure 4B.

Throttles 151 and 152 are made within part 15 and throttle 161 and 162 are made within part 16. These two parts 15 and 16 can be easily changed in order to adapt the geometry of lifts L ₁₁ and L ₁₂ to the desired fuel sprays.

According to their respective size, throttles 151 and 152 define the speed at which back-pressure chambers 261 and 262 will see their pressure decrease, when

valve 19 opens, or increase again, when valve 19 closes. The variation rate of the pressure will at least partly control the speed at which needles 11 and 12 move with respect to their seats formed by surfaces 211 and 221.

Nozzle assembly 1 is very compact and non sophisticated, insofar as it includes only one electromechanical device, namely solenoid valve 19, the selection of the active needle, 11 or 12, being automatically made by passive valve 18.

As shown on figure 7, nozzle assembly 1 can be part of a fuel injector I mounted on a cylinder head H of an engine E in order to feed a combustion chamber C of this engine. This injector I can be of the amplified type and include an amplifying unit U comprising a source Si of fuel with two pressure levels. Alternatively, injector I can be fed by any of the devices mentioned here-above.

In the embodiment of figure 8, the same elements as in figure 2 bear the same references. Here, throttles 152 and 162 of the first embodiment are replaced by a single throttle 153 placed on exit line 259, which allows to control the discharge of chambers 261 and 262 with the same element.

In the embodiment of figure 9, throttle 151 and 161 of the first embodiment are replaced by a single throttle 154 placed on a common portion 2534 of feeding lines 253 and 254.

The invention has been described with a nozzle assembly whose needles have frustroconical bearing surfaces 112 and 122, which allows a good contact with the corresponding seats 211 and 221. However, other geometries of the tips 111 and 121 can be considered.

The path of fuel between canals 126 and chamber 231 has been described as been made by longitudinal grooves on needle 11. Any kind of other convenient designs is suitable, in particular one or several helicoidal grooves on the first needle 11 or on the internal surface of the second needle 12.

LIST OF REFERENCES

1 nozzle assembly

2 main body

21 central extremity

211 frustroconical surface

212 canals

213 outlets

214 chamber

221 frustroconical surface

222 canals

223 outlets

224 chamber external surface of extremity 21

231 chamber

241 ring

242 ring

243 ring

251 canal

252 chamber

253 inlet line

2534 common portion of 253 and 254

254 inlet line

255 exit line

257 exit line

258 feeding line

259 discharge line of valve 18

261 back-pressure chamber

262 back-pressure chamber needle

111 tip

112 front surface

113 back extremity

115 valve

116 grooves

117 frustroconical surface . needle

121 tip

122 front surface

123 back extremity

124 recess

125 valve

126 radial canals

127 frustroconical surface

13 spring

15 throttle part

151 throttle

152 throttle

153 throttle

154 throttle

16 throttle part

161 throttle

162 throttle

17 spring

18 passive control valve

181 valve body

182 valve core

183 groove

184 groove

185 extremity

186 spring

187 extremity

188 chamber

19 solenoid valve

20 low pressure circuit

S ₁ source

P injection pressure

Pi first value of P

P ₂ second ^ i/alue of P

Pref reference value of P to instant t'o instant ti instant fi instant t'2 instant

t' ₂ instant

δt ₂ period of time

δt ₂ period of time

X ₁ longitudinal axis of assembly 1

Xii longitudinal axis of needle 11

Xi2 longitudinal axis of needle 21

X ₁₈ longitudinal axis of 18 α angle of 212 with respect to Xi β angle of 222 with respect to Xi

Fi ₃ force of spring 13 on needle 12

F- _I7 force of spring 17 on needle 11

F- ₁₁ lift force on needle 11

F- _I 2 lift force on needle 12

F ₂ 61 force acting on needle 11 as a result of pressure P ₂ 61

F262 force acting on needle 11 as a result of pressure P ₂ 62

Ln lift of needle 11

L ₁ value of lift

L ₁₂ lift of needle 12

L ₂ value of lift

P ₂ 3- ₁ fuel pressure within chamber 231

P261 fuel pressure within chamber 261

P262 fuel pressure within chamber 262

P 188 fuel pressure within chamber 188

I fuel injector

H cylinder head

FS-i first fuel spray

FS ₂ second fuel spray