DE2411787B2 - FUEL INJECTION DEVICE FOR COMBUSTION MACHINERY - Google Patents

Description

The invention relates to a fuel injection device for internal combustion engines with η injection nozzles, which has / 2 + 2 chambers, namely η chambers upstream of an injection nozzle, upstream of which a second further chamber and upstream of this a first further chamber, and organs which Continuously convey fuel in a controllable quantity under pressure to the first further chamber, each injection nozzle with the chamber upstream of it and all chambers upstream of the injection nozzles successively communicating with the second further chamber by means of a distributor control element driven by the machine.

Such facilities are required for diesel engines and machines for different loads. They are also useful in gasoline engines, especially when there are air pollution regulations make a very precise metering of the fuel necessary.

In a known device of this type (see US-PS 30 77 872) are the first and each one of the Nozzles upstream chambers are constantly connected to each other. Unwanted pressure fluctuations, causing

Due to the movements of the individual parts, they can move in the direction of flow and in the counter-flow direction that interfere with the proper functioning of the facility.

The invention is based on the object of an exact separation of the conveying and metering area from Manifold and injector area.

This object is achieved in that a further chamber between the first and second Control member is provided that releases the connection between these two chambers when the Connection between the second further chamber and one of the chambers upstream of the injection nozzles is interrupted and vice versa.

In this way it is achieved that the first chamber and the chambers upstream of the nozzles always are separate from each other and the conveying and metering elements on the one hand and the distribution and injection elements on the other hand, cannot interfere with one another.

According to the invention, it is of particular importance if all chambers are above predetermined limit pressures have a variable volume against the restoring force.

Details that further develop the subject matter of the invention emerge from the drawing. In this shows

Fig. 1 shows a preferred embodiment for a chamber which is used in the device according to the invention for Application comes,

F i g. 2 is a diagram in which the volume is plotted against the pressure, the pressure-volume ratios for a chamber according to FIG. 1 shows; the diagram also gives the mathematical ones Conditions that must prevail between the chambers,

3 is a block diagram from which the Fuel flow of the device according to the invention results,

4 schematically the device according to the invention,

Fig.5 schematically shows a rotary distributor in the device according to the invention is used,

F i g. 6 a device for forming pulses with the aid of needle valves,

F i g. 6a a section through such a needle valve,

F i g. 7 shows the flow equilibrium behavior of the pulse-shaping device in interaction with the nozzle and the chambers Ch 31 ... Ch 38 and

8 shows a fuel metering system with a device for limiting the maximum pressure is equipped and ensures when it is interconnected with the cascade circuit according to the invention is that the fuel volume per injection pulse does not exceed a certain maximum value can.

A table shows the design requirements and the critical relationships for the different parts.

In Fig. 1 shows a metal tube 1 with holes. This tube sits in a flexible elastic tube 2, e.g. B. a commercially available high pressure nylon hose. This is under strong voltage and is applied to the tube 1 with a corresponding force. The hose 2 is on his The ends are provided with caps 3 and 4 which are connected to the hose in such a way that there is no leakage can be done. The chamber, which is formed by parts 1, 2, 3 and 4, has the property that you Volume is invariable as long as the pressure in it is less than the force generated by the hose 2 will. If the pressure is greater than this force, the hose 2 expands and the chamber volume increases. Will the pressure is reduced, so the elastic tube 2 affects the volume so that the in it the amount in the chamber emerges. The chamber according to FIG. 1 presents a very simple example a spring-loaded collector with mechanical limitation, in which the hose 2 is the expandable Chamber bounded and at the same time forms the spring and the fixed metal tube 1 serves as a delimitation. The collector reacts extremely quickly, can be easily determined using known formulas and has a long shelf life as well as also cheap to manufacture.

The interconnection of 2 + π collectors according to FIG. 1 shows a pressure cascade which can be used with the subject matter of the invention. Each collector has a limit pressure below which the volume is unchanged and which depends on the tension of the elastic hose.

FIG. 2 shows the characteristics of collectors according to FIG. 1, the functions v (P) _h V (P) ₂ and v (P) a being plotted, where / = 1, 2, 4, ..., η . Below a certain pressure P _ai , P _a2 , P _a y, the collectors or chambers CHI, Ch 2, Ch 3 / (FIG. 4) have a volume that is independent of the pressure. For every collector it is also true that the volume changes with the pressure if the pressure is above the pressure P _a . It is true that dynamic effects can influence the pressure-volume ratios in such a way that in practice the characteristics of the systems shown in FIG. 2 differ slightly. However, as a first approximation, especially at very high speeds, the collectors obey expansion ratios that are shown. It is assumed that the chamber Ch 1 has a volume at a pressure P _t \. Suddenly it comes into liquid contact with the chamber Ch 2, which has an initial pressure which is below the limit pressure P _a2 . As long as the limit volume of the chamber CAl is below Vmax , the entire amount in the chamber Ch 1 is released very quickly to the chamber Ch 2 , where it is stored at a lower pressure Pa- When the chamber Ch 2 with its limit volume (now separated from the chamber CA 1) comes into liquid contact with the chamber Ch 3 /, a complete liquid exchange occurs from the chamber CA 2 to the chamber CA 3 / as long as the pressure in the chamber CA 3 is below P _a2 .

The volume-pressure function in FIG. 2 is of such a nature that with the largest pulp volume that the system can produce, for the highest possible pressure in the chamber CA 3 / the following applies:

P ₃ , MAX <P ₂ MAXk P _x MAX.

In this way it is achieved that a pressure drop always exists between the chambers CA 1 and CA 2 and between the chamber CA 2 and each of the π chambers Ch 3i. This pressure drop ensures complete passage of the desired volume of fuel between the headers towards the nozzles.

The process of transferring a certain volume from a chamber of higher pressure to a Chamber of low pressure occurs completely and very

fast and does not depend on the exact values P _a \, P _a i and P _a 3 / as long as P _a \>Pa> Pai .

The essence of the invention is the described transfer process between chambers via switching elements, in particular a rotary distributor. The chambers Ch 1 and Ch 2 are intermittently in contact with each other, and the chamber Ch 2 is intermittently in contact with the chambers Ch 3 /, which in turn are in contact with the nozzles. If the different injection lines are of different lengths, the pulses arrive at their nozzles at different times, but this phase shift does not affect the measuring process.

From Fig. 3 (reference numerals see FIG. 4) the fuel flow results. The rotary distributors Ll and L 2 rotate synchronously, preferably on a common shaft, so that the chamber Ch 2 is open alternately to the chamber Ch 1 and to a chamber Ch 3 /.

4 shows the injection device. Pressurized fuel from a source P is continuously sent through a control device having a variable orifice V and a bypass system 24,5,6. This system keeps the average pressure drop across valve V constant so that the fuel is properly metered each time valve V is actuated. The system has a bypass line 10, 11 which bypasses fuel at pressures above a maximum pressure. This bypass system has the effect that the measured volume per pulse cannot exceed a certain value.

The metered fuel flows to the chambers Ch 1 and Ch 2: The metered fuel is first collected in the chamber Ch 1 when the chamber Ch 1 is separated from the chamber Ch 2, which is done by part L 1 of the rotary distributor. When the chamber Ch 1 is connected to the chamber Ch 2 , the fuel flows into the chamber Ch 2. The chamber Ch 2 is always open to part L 1 and part L 3 of the rotary distributor via the always open part L 2 of the Rotary distributor. This is designed so that the path between the chambers Ch 1, Ch 2 and Ch 3 / does not change from cycle to cycle. When the chamber Ch 2 is separated from the chamber Ch 1, the chamber Ch 2 is in contact with a chamber Ch 3 / The accumulated volume in it thus reaches the chamber Ch 3i. The chamber Ch 3 / then becomes the assigned one Fuel nozzle supplied. The injection rate is derived from the maximum rate mentioned, namely the desired shape of the fuel pulse is determined by the needle valves Vi ... Vn of the nozzles. Each needle valve is controlled with the other needle valves in the other lines in such a way that an optimal injection is obtained at the corresponding speed (possibly also as a function of other parameters).

After the chamber Ch 2 has delivered a quantity of fuel to the chamber Ch 3 , the chamber Ch 2 is separated from the chamber Ch 3 by means of part L 3. Contact is re-established between the chamber Ch 1 and the chamber Ch 2 , namely through part L 1. The cycle is now repeated, although fuel is fed into the next line.

Since the volume of the chamber Ch 2 does not change after the fuel has been delivered to the chamber Ch 3 / with changes in pressure in the injection line of the chamber Ch 3 / (as long as Phmax is less than P & ), the measuring process is not affected by dynamic changes and other changes affected between the different injection lines. However, there is an exception to the fact that the density of the fuel in the chamber Ch 2, when the chamber Ch 2 is separated from the chamber Ch 3, fluctuates slightly with the pressure, because the modulus of elasticity of the fuel is not infinitely large. This effect is however with low pressure systems

ίο insignificant and small in high pressure injection systems. In practice, it can therefore be assumed that the metering device is subject to all changes is independent in the system, in particular do not need the flow characteristics of the pipes and nozzles

■ 5 to be coordinated.

F i g. 5 shows schematically a rotary distributor. A cylindrical rotor 12 rotates in a receptacle 13. There is a perfect seal between the rotor 12 and the receptacle 13. The rotary distributor has three parts: an upper part Li (see FIG. 4), which connects the chamber Ch 1 eight times per revolution with the rotor 12, a middle part L 2 (FIG. 4), which has an annular slot, see above that the chamber Ch 2 is always in communication with the chamber of the part 12. The arrangement is such that the length of the paths between the chamber Ch 2 and each chamber Ch 3 / is the same. At the lower end is a part L 3 (Fig. 4) which brings a chamber 3 / in contact with the conduit in the rotor 12 when liquid is separated from the chamber Ch 1. The three parts in the rotor 12 are over a line in the center of the rotor 12 is connected to one another.

Of course, other distributors can also be used.

In the case of diesel engines and certain machines with different loads, the shape of the Flow pulses on. Ideally, the shape is rectangular, regardless of speed. To the Improvement of the pulse shape is proposed in the device according to the invention, corresponding organs to be provided for pulse shaping.

Such a device is shown in FIG. 6 and 6a. Each of the π injection lines has a variable area needle valve positioned between a chamber Ch 3 / and a nozzle. The η needle valves are connected to one another in such a way that all valves are open at the same time. The needle valves are connected to one another via a cam arrangement 15 (the control mechanism is not shown).

In FIG. 7, the flow through a nozzle is plotted as a function of the pressure. f " increases with the pressure drop across the nozzle, namely

/ "- *, (Pn-PdY ' ² (Pn-Pd-Po) ,

whereby

fn is the instantaneous flow through the nozzle P _{n is} the instantaneous pressure on the upstream side of the nozzle

Pd is the instantaneous pressure on the downstream side of the nozzle

Po is the pressure on opening the nozzle, assuming that the pressure drop on opening is equal to the pressure drop on closing

of the valve is approximately, and

k \ is a constant that takes the geometric relationships into account.

If Pd and P _{0 are} constant, determining the flow through the nozzle is equivalent to determining the pressure P _n .

The pressure in the chamber Ch 3 / is always high enough to achieve the maximum flow through the nozzle. The needle valve reduces this pressure to the pressure P _n , which is then proportional to the flow (which in turn is proportional to the speed).

The pressure drop across the needle valve opening is proportional to the square of the flow rate through the opening:

_{/ 1p} _Mf2

'< ^r - "2 J η '

AP is the pressure drop across the needle valve
/ "The current volume of the river

a is the cross-sectional area of the valve opening and
ki a constant

is. Note that the pressure drop across the needle valve for each flow depends on port a.

The interaction between nozzle, chamber and needle valve is such that the flow around a The equilibrium state oscillates, which is given by the following equation:

* 2 fl

where P _{0 is} the instantaneous pressure in the chamber ChSi .
If fl is expanded, we get:

P = P ---

(Pl -3PlP ₀ -:

P ² ρ P ² \

(Let the nozzle be an outwardly opening pen nozzle.) This equilibrium is very stable. The valve opening a is proportional to the flow multiplied by the square root of the pressure drop. If, for example, a constant maximum flow per degree of crankshaft rotation is required over a speed range of 10: 1 (this is equivalent to a / "of 10: 1) and the pressure drop zlP across the needle valve is required to obtain this variation (P ₃ , and Pd are given ), 16: 1, the opening range must vary between 40 and 1. This 40: 1 variation of a causes a 1600: 1 variation for the negative feedback coefficient for the nozzle expression

40

α ² ■

In most practical cases, the required range is less than 40: 1.

For suitably selected values of the parameters k 1, k ₂ and P ₀ and the pressure volume function, the interaction between the chamber, the needle valve and the injection nozzle results in an excellent approximation of the desired square wave for the injection pulses. Above all, the system is stable, even at very high speeds.

F i g. 7 shows the equilibrium relationships for the injection rate f " between the chamber, the needle valve and an outwardly opening needle nozzle, assuming that the pressure Pd on the downstream side of the nozzle and the pressure in the chamber P _{at are} constant.

Shaping the pulse with the aid of the needle valve does not affect the metering because the injection pulse has a duration which is much less than the period between successive injections in the same line. Each chamber Ch 3 / is therefore completely discharged when it is connected to the chamber Ch 2 .

Changes in the pressure-volume characteristics of the π chambers 3 /, the η nozzles and the η needle valves and changes in the line lengths lead to changes in the pulse characteristics of the injection lines. However, if the parameters are sensibly coordinated with one another, the pulses are also coordinated with one another, and each nozzle then emits a pulse with the desired rectangular shape.

With needle valves, the pulse shape can be better adapted to the rectangular shape than with conventional ones Injection pumps because there are no pistons, the inert masses represent, or cam profiles are required, which have a negative impact on the pulse shape.

Fig. 8 shows an apparatus for continuously supplying fuel. The fuel is continuously supplied via a valve V and measured. The pressure dropping in this is kept constant as long as the pressure on the downstream side is below a certain maximum value by means of a branch line in which a membrane is arranged.

The fuel pressurized by the pump P flows into the line 21, where the flow is divided into a flow which flows through the valve V and a flow which flows to the needle valve 24. The needle valve 24 is controlled by a membrane 5. The needle valve 24 is open when the pressure in the chamber la is greater than the pressure in the chamber 16 plus the force of the spring 6. The needle valve 24 closes when the pressure in the chamber la is less than the pressure in the chamber \ b plus the force of the spring 6. In this way it is achieved that the pressure drop to which the valve V responds depends on the spring 6. The spring 6 has such a ratio of spring constant to spring force that its force on the diaphragm 5 is about the same whether the assembly 24 is now open or closed.

The chamber Ab is connected to a line 7 on the downstream side of the valve V via a porous plug 8. As a result, it is difficult for a current to flow through the plug, and even sudden changes in pressure can practically not be transmitted. The mean pressure in the line 7 is thus maintained by means of the plug 8 in the chamber Xb. While the system is unable to maintain a constant instantaneous pressure drop across valve V , it does

709 513/249

Able to maintain a medium pressure drop very well.

As can be seen from FIG. 2, the interaction between the chambers Ch 1 and Ch 2 is such that a certain average cycle pressure in the line 7 corresponds to a certain fuel flow per injection pulse. It is thus the case that a maximum permissible average pressure in the line 7 defines a maximum fuel volume per injection pulse, which is essentially independent of the speed. The parts 10, 11 for the pressure dissipation in the device according to FIG. 8 cause. The plate 10 opens when the average pressure in the chamber \ b A pressure reduction in the chamber \ b is greater causes than the force of the spring 11, opening the valve 24, resulting in a further pressure reduction result. The system cannot therefore maintain an average pressure in the line 7 which is above a certain limit value which is determined by the parts 10, 11. The fuel volume per injection pulse can therefore not exceed the specified volume, which corresponds to the maximum average pressure in the line 7.

The device according to Figure 8 can be modified. This can be necessary, for example, at very high injection pressures. The membrane 5 can be replaced by a piston system. Instead of the porous plug 8, a small opening can be provided. The pump P can be followed by an expansion tank or an elastic hose in order to equalize the pressure. The elastic hose has the advantage that it requires a small volume before it causes pressure changes.

The table shows the essential parts, their functions and the facts to be observed summarized. It is noteworthy that the construction tolerances of most parts are wide. The rotary distributor is the only part of the system that has to be worked very precisely, because it depends on that liquid cannot leak through. The individual parts of the system hardly need to be changed, when the injection pressure is changed, e.g. B. from 3.5 at to 700 at. The production costs for systems with different injection pressures, apart from the pumps, hardly differ from one another.

The individual parts have a very simple geometric shape and are mathematical Precisely defined in terms of their functions. Furthermore, the parts also work simply, and interactions between the parts, which mistake second

Order are eliminated (states of equilibrium between the parts do not occur at the same time, separate one after the other). The distances of pressure wave movements between the dimensional Parts are so small that the desired interrelationships between the dimensional parts always done completely in the time available.

The special feature of the device according to the invention is that pressure changes in the various Lines cannot affect the metering devices.

Function remarks

pump

casing

Bypass system:

1. membrane

2nd spring

3. Needle valve

4. Porous plug

Metering valve

Collectors' chambers

Delivers a certain volume per revolution at a certain pressure. the Changes in pressure should be small. A compensation tank or an elastic hose may have to be connected downstream.

Must be incompressible. No leakage!

Maintains a constant mean pressure drop across the metering valve upright. Negative feedback is stable.

Measures fuel at a constant average pressure drop AP. The fuel supplied to the engine is solely a function of the valve action over a wide range of angular velocities.

The volume νι (Ρ ₍ ) of the chamber i satisfies certain conditions

- ^ = O if P ₁ <P _ai

-Sf- must be sufficiently large, ¹ if P ₁ > P _ai pump only creates pressure, but does not measure. Leak phenomena of a minor nature are not critical.

Volume and surface treatment are not critical.

Stability is important. Porous plug prevents oscillation. The spring should change its force little between open and closed. Errors are entered with the square root of ΔΡ .

Control is easier when the flow through the valve (P = constant) is linear with the control is.

Volume must remain unchanged in the event of pressure variations between the nozzle lines. The volume that results from a pressure above P _ah must be large enough so that a pressure drop can never develop in the opposite direction. The chambers have to fill and empty very quickly.

continuation

11th

function

Remarks

Rotary distributor

Needle valves
to shape the pulses
between
Chambers Ch3i
and the nozzles

Injection lines

Connects and separates the chambers in a certain sequence. The angles between successive distribution lines for opening and closing should be the same. The distributor should open and close positively. Nothing is allowed in closed pipes lick through.

The needle valves cause the same conditions in the injection lines Great importance is attached to tightness. Radial symmetry facilitates compliance with tolerances.

Not absolutely necessary, but useful. Produce roughly square pulses. Orifice should not change during injection. Needle valves work very fast and are stable. Changes in line lengths only cause phase shifts. The pulse shaping does not influence the metering.

Must be incompressible when printing below the pressure at which open the nozzles.

For this purpose 4 sheets of drawings

Claims (13)

Patent claims: 1. Fuel injection device for internal combustion engines with η injection nozzles, which has / 3 + 2 chambers, namely η chambers upstream of an injection nozzle, upstream of it a second further chamber and upstream of this a first further chamber, and organs that supply fuel in controllable quantities continuously conveying under pressure to the first further chamber, each injection nozzle with the chamber upstream of it and all chambers upstream of the injection nozzles successively connected to the second further chamber by means of a distributor control element driven by the machine, characterized in that between the first and second further Chamber (CA 1, Ch 2) a control member (Li) is provided, which releases the connection between these two chambers (Ch 1, Ch 2) when the connection between the second further chamber (Ch 2) and one of the chambers upstream of the injection nozzles (CA31 ... Ch 38) is interrupted and vice versa. 2. Fuel injection device according to claim 1, characterized in that above predetermined limit pressures all chambers (Ch 1, Ch 2, Ch 31 ... Ch 38) have a variable volume against the restoring force. 3. Fuel injection device according to claim 1 or 2, characterized in that a chamber consists of a tube (1) with holes, which is surrounded by an elastic hose (2), which is closed at both ends by means of tightly fitting caps (3, 4). 4. Fuel injection device according to claim 3, characterized in that the hose (2) is stretched and surrounds the pipe snugly. 5. Fuel injection device according to claims 1 to 4, characterized in that variable openings, especially valves (V), are arranged between the chambers (CA31 ... CA38) and the nozzles, preferably for shaping the injection pulses. 6. Fuel injection device according to claim 5, characterized in that the openings of the rotation of a part of the machine can be controlled so that a maximum discharge over the nozzles takes place. 7. Fuel injection device according to one or more of claims 1 to 6, characterized in that the control elements (Li, L2) are combined to form a rotary switch, which preferably has a third rotary switch, which dte the nozzles upstream chambers (CA31 ... CA38) one after the other with the nozzles. 8. Fuel injection device according to one or more of claims 1 to 7, characterized characterized in that the flow from the first chamber (CA 1) into the second chamber (CA 2) unchangeable within the work phases and that the lines from the second chamber (CA 2) are identical in terms of flow to the chambers (CA 31 ... CA 38) upstream of the nozzles, in particular have the same length. 9. Fuel injection device according to one or more of claims 1 to 8, characterized in that a pump (P) is bypassed by a line with a first valve (24), in particular a needle valve, that in the main line a second valve (V ) sits that a pressure-sensitive organ, in particular a membrane (5), is provided which causes the first valve (24) to open when the difference between the pressure in a connection to an inflow line (7) to the first further chamber ( CA 1) having space (ib) and the pressure in a line (ia) between pump (P) and the first valve (24) or the second valve (V) exceeds a certain value, and the first valve (24 ) causes when this difference falls below the specified value. 10. Fuel injection device according to claim 9, characterized in that a flow-damping member (8), in particular a porous plug, is arranged between the space (ib) and the inflow line (7). 11. Fuel injection device according to claim 9 or 10, characterized in that an element (10, 11) is provided which controls the maximum pressure in the space (ib). 12. Fuel injection device according to claim 11, characterized in that the organ is a spring-loaded valve (10, 11) in a bypass line. 13. Fuel injection device according to one or more of claims 1 to 12, characterized in that the function V (P) for each Chamber is such that ^
dp is when the pressure Pin of the chamber is less than a limit pressure, that ~ is large when P is greater than the limit pressure, and that the limit pressure of the first chamber (CA 1) is greater than the limit pressure of the second chamber (CA 2) and the latter greater than the limit pressure in the chambers upstream of the nozzles (CA31 ... CA 38) is.