Diesel engines

Abstract

A Diesel engine comprising a set of starting cylinders and a set of power cylinders, means associated with the starting cylinders, which means make the starting cylinders more suitable for starting the engine than the power cylinders, and means associated with the power cylinders which means makes the power cylinders more suitable for running the engine under full power than the starting cylinders.

Description

The present invention relates to multicylinder Diesel engines.

It is known that, in a Diesel engine, the volumetric compression ratio should be high to ensure the initial firing actions when starting the engine from cold. In normal operation of the engine, when the coolant has reached its stabilized temperature level T.degree., a lower compression ratio is favourable from the point of view of efficiency of operation and durability of the engine. In point of fact, a reduction of the compression ratio results in a reduction of the maximum pressure of the cycle, which leads to a reduction of the mechanical stresses and of the frictional forces, particularly if the engine is supercharged.

By virtue of this fact, Diesel engines commonly have an intermediate compression ratio which provides a compromise between ease of engine starting and the reduction of the maximum cycle pressure within the cylinder or cylinders.

To eliminate this unwieldy compromise moreover, engines have been suggested, wherein the or each cylinder offers a variable compression produced by variation of the unswept volume. Translatory displacement of the precombustion chamber roof or a variable distance between the piston gudgeon pin and the piston crown, render it possible to establish a high compression ratio, for example about 20, for starting purposes, and to cause this ratio to decrease in gradual manner to a minimum value slightly exceeding 10. With such engines which offer the advantage of flexibility of adjustment, the latter remains chancy on occasion, and the cost price of the device is not negligible.

The same description, as a compromise, is applicable to the selection of the time-lag upon closure of the inlet valve.

It is known that the inlet valve is closed several tens of degrees after bottom dead centre (hereinafter referred to as BDC) during the compression stroke of the piston. This renders it possible to assure optimum supply of air at high engine speed at which, taking the inertia of the flow of induction air into account, a delay or overlap increases the charge despite the return of the piston. At low engine speed however, the dynamic action of the air is weak, so that the inlet closure delay (hereinafter referred to as ICD) is useless or even harmful. In point of fact air is returned into the inlet and the true volumetric compression ratio of the cylinder is reduced by a value linked with the loss in the compression stroke between BDC and ICD, which correlatively impairs the ease of starting linked to the intensity of the compression.

A relatively small ICD is adopted, to assist starting, which is sufficient however for charging at maximum speed. The improvement in starting, requiring an ICD equal to nought, operates against the high power output linked to air induction at high engine speed. It was for this purpose that variable distribution mechanisms have been devised, in particular being dynamic devices wherein the ICD increases in continuous manner as the engine speed rises. In this case too, their cost and ticklish adjustment proved to be an obstacle to the development of these mechanisms.

In accordance with the invention there is provided a Diesel engine comprising a set of starting cylinders and a set of power cylinders, means associated with the starting cylinders, which means make the starting cylinders more suitable for starting the engine than the power cylinders, and means associated with the power cylinders which means make the power cylinders more suitable for running the engine under full power than the starting cylinders.

A Diesel engine according to the invention tends to start easily and has a high performance under reduced mechanical stress conditions, particularly if the engine is a supercharged engine.

The starting cylinders may have a higher volumetric compression ratio than the normal compromise assuring normal power in order to provide the means referred to above.

The volumetric compression ratio of the power cylinders may be reduced to a value establishing optimum efficiency. By way of example, for an unitary swept volume of one litre or a bore value taken as approximately 100, the compression ratio of the starting cylinders may exceed 20, the compression ratio of the power cylinders being approximately 13.

A differentiation may be established between the starting cylinders and the power cylinders by a different value of ICD. A smaller ICD than the compromise value assuring optimum charging is adopted for the starting cylinders, to increase their compression. The optimum ICD charging value is adopted for the power cylinders, without any concession to ease of starting.

The differentiation between the starting and power cylinders may be established by means of their injection system. To this end, the cylinders of both categories are equipped with an injection system differing in structure or adjustment. The active injection elements of the two kinds are preferably comprised and actuated within one and the same pump unit, and are preferably in-line. The differentiation between the starting and power cylinders may be established at the point of the injection pump cylinders.

The maximum delivery injected per cycle into the said starting cylinders may be smaller than the maximum feed injected into the power cylinders. This difference may be produced on an in-line injection pump by several means such as variation of the diameter of the pistons, of the cam contours, or of the configuration of the injection headers. To simplify matters, it is preferable to employ identical in-line pump elements with appropriate setting of the pump plungers feeding, respectively, the injectors of the starting and power cylinders with respect to a common rack.

It is also possible to establish a differentiation between the feeds injected into the two kinds of cylinders by choosing different return valves, different injection pipe lengths and diameters, and different calibrations and diameters of the injection holes, which represent parameters affecting the quantity and pressure of the flow injected. This is especially useful in the case in which a rotary pump of the distributor type is employed instead of the conventional pump comprising in-line pistons.

A differentiation between the starting cylinders and the power cylinders may be established by the value of the initial or static injection lead, in order to optimize the operation towards the starting range or towards the range of maximum efficiency and power. It is known that, for the starting cylinders, a reduction of the injection lead improves the initial firing actions and reduces maximum pressure in normal operation.

This differentiation of the injection lead may be produced at the point of the injection piston by displacement of the top edge with respect to the feed opening, by adopting a piston level, an automatic advance injection header or a cam contour, which are different in the case of in-line pumps. To simplify matters, it is preferable to adopt in-line pump elements having identical cam contours, but whereof the setting is different with respect to uniform theoretical distribution, meaning that the cams of the pistons feeding the starting cylinders are dephased to reduce the injection lead with respect to the cams of the power pistons.

In the case of a rotary pump, it is possible to ring the changes by irregular distribution of the distributor passages.

Finally, preferably a small fraction of (d) starting cylinders is selected among the n cylinders of an engine; d and n being such, for example, that d amounts to at most 1/3rd or better yet to 1/4, this last proportion corresponding to the most satisfactory form of embodiment contemplated.

The d starting cylinders will be selected as a function of the evenness of the firing order of the set, of their particular location from the mechanical point of view (torsional vibration, more rigid main bearing at the centre or at the extremities), of their position with respect to the inlet or exhaust ducts, and depending on whether they are combined under one and the same cylinder head or not, in order to concentrate the auxiliary starting means or to establish the corresponding compression changes on a common cylinder head.

The flow of air intended for the starting cylinders may be restricted by shutters calibrating their inlet ports. This results in a greater flow of air towards the power cylinders, into which a greater quantity of fuel is injected.

This arrangement renders it possible to secure a gain in power at full speed without affecting the starting conditions, owing to the fact that the shutters or baffles which do not impede the passage of air at the low rates of starting flow at which they produce a small pressure drop, produce an increasingly substantial pressure drop at "full-bore" speeds, at which the flow is then effectively reduced.

Some engines embodying the invention are described below by way of example, with reference to the accompanying drawings, wherein:

FIG. 1 is a diagrammatic view of a 6-cylinder in-line Diesel engine, the Figure showing the cylinders in plan and the injection pump of the engine;

FIGS. 2A and 2B are alternative diagrammatic longitudinal vertical sectional views through the engine shown in FIG. 1;

FIG. 3 is a view of the injection pump and the non-return valve associated with one of the starting cylinders, of the engine shown in FIG. 1, the non-return valve being shown in section;

FIG. 3A is a sectional view of the non-return valve of one of the power cylinders of the engine shown in FIG. 1;

FIG. 4 is a sectional view of the settings of the injection heads of the injection pumps shown in FIG. 1;

FIGS. 5A to 5C are developed views of injection heads of injection pumps;

FIG. 6 is a diagrammatic plan view of the cylinders of a V-8 cylinder engine;

FIG. 7 is a diagrammatic plan view of the cylinders of a 12-cylinder engine having two opposed lines of 6 cylinders;

FIG. 8 is a longitudinal cross-sectional view of a rotary injection pump;

FIG. 9 is a plan view of the rotary pump shown in FIG. 8 showing the setting of the injection; and

FIG. 10 is a diagrammatic plan view of an engine and its inlet manifold.

FIG. 1 shows a Diesel engine having six cylinders 1 to 6, which may or may not be supercharged. The firing order of the cylinders is 1, 5, 3, 6, 2, 4. The engine may be of the precombustion chamber type, as shown in FIG. 2B. As shown in FIG. 2B, each cylinder accommodates a flat-topped piston 7 and communicates with an injection chamber 8. Alternatively as shown in FIG. 2B, the engine may be of the direct injection type. As shown in FIG. 2A each cylinder accommodates a piston 9 having a chamber 10 in its crown.

Each cylinder is associated with a fuel injector 11P or 11D which is connected to a barrel 12P or 12D of an injection pump with in-line barrels. Within each barrel 12P or 12D is accommodated a plunger 13P or 13D (see FIGS. 1 and 3) whereof reciprocating displacement is performed by a rotary cam 14P or 14D and whereof pivoting displacement is performed by a rack 15 which engages with a toothed portion of each plunger. The rack 15 can be longitudinally reciprocated as shown by the double-headed arrow A. Longitudinal movement of the rack 15 causes all the plungers 13P or 13D to pivot.

The cylinders 3 and 4 are for starting the engine under high compression, whether they are under the same cylinder head, if the engine comprises three cylinder heads, or if it would be advantageous for the two starting cylinders having a high compression ratio to act on the central main bearing, whereas the cylinders 1, 2, 5, 6 are for operation of the engine at normal engine power.

As shown in FIGS. 2B and 2A, the differentiation between the compression and starting ratios is established by a variation of the unswept volume 16 and of the topdead centre either by reducing the volume of the chamber 10.sub.4 in the piston 9 in the case of direct injection or by reducing the volume of the chamber 8.sub.3 incorporated in the cylinder head or by combination of these two means.

The cylinders 1, 2, 5, 6 have a greater unswept volume 16 and thus have a lesser volumetric compression ratio. The true compression ratio of the cylinders 3 and 4 is increased further by adopting a smaller inlet closure delay of the order of 16.degree. of crank angle, whereas the power cylinders 1, 2, 5, 6 have an inlet closure delay of the order of 45.degree. of crank angle.

As for induction, the delivery of fuel in mms.sup.3 /cycle to the power cylinders 1, 2, 5, 6 exceeds the delivery injected into the starting cylinders 3 and 4. This result is obtained by separate or simultaneous adjustment of the facilities inherent in the injection device.

To obtain these differences in fuel delivery, in particular into the power cylinder 6 and into the starting cylinder 4 (FIG. 1), the heads of the plungers 13P and 13D developed views of which are shown in FIG. 4, are identical but are differently set, the rack 15 engages them at the same time in the same manner.

On the developed views of the pistons 13P and 13D have been plotted areas 17P, 18P, 19P and 17D, 18D, 19D, which correspond, respectively in operation at idling speeds, at maximum rate of flow and under overload, the extremity 20P or 20D correspond to cut-off of the feed.

The setting of the extremity 20P of the piston 13P with respect to the fuel inlet orifice 21P corresponds to the value .theta.P for the maximum rate of delivery 18P, whereas the setting of the extremity 20D of the piston 13D with respect to the inlet orifice 21D corresponds to the value .theta.D for the maximum rate of delivery 18D.

The settings of the pistons 13P and 13D thus differ by a quantity: .theta.P - .theta.D = .tau.

which corresponds to a difference in the flow of fuel by the action of the profile or helix 22 (FIGS. 3 and 4) whose principle is well known.

Because of the different settings of the injection elements of the plungers 13P and 13D. The useful injection stroke for the maximum delivery rate of the areas 18P, 18D corresponding to the rate of delivery Q for the power cylinder 6 and to the rate of delivery q for the starting cylinder 4, has a profile length differing by the quantity .DELTA..

This simple displacement renders it possible to retain the rate of overload delivery corresponding to the area 19P, 19D and to cause the starting plungers 13D to stop at 20D.

FIG. 3 shows a non-return valve 23D for controlling the delivery of the fuel to the injector 11D of the starting cylinder 4. FIG. 3a shows a valve 23P for controlling the delivery of the fuel to the injector 11P of the power cylinder 6.

A modification of the distances 24D and 24P between the passages 40 and the valve seats may represent a complementary means of establishing a differentiation between the rates of delivery Q and q. The non-return valve 23D, by virtue of the distance 24D corresponds to a considerable rate of flow -Q' subtracted from the quantity delivered by the pump and to a small quantity q injected, whereas by virtue of the smaller distance 24P, the valve 23P corresponds to a small rate of flow -q' subtracted from the quantity delivered by the pump and to a large quantity Q injected.

This expedient is intended more particularly for application of a rotary pump and the action may be intensified by a greater calibration of the injectors 11D installed on the starting cylinders 3 and 4.

As for injection lead, this may be affected by the cams 14P and 14D (FIG. 1) and by the features of the profile at the beginning of the injection (FIGS. 5a to 5c).

It is known that the cams of an in-line injection pump for a 6-cylinder engine are dephased consecutively by an angle of 60.degree. in accordance with the sequence 1, 5, 4, 6, 2, 4, that is to say that the cylinders 6 and 4 taken into account in FIG. 1 are normally displaced by an angle .beta. of 120.degree. on the camshaft.

In this case of the present invention, the cams 14D of the starting cylinders are displaced rearwardly through an angle .alpha. with respect to the direction of rotation of a pump corresponding to the arrow B, in order to reduce the injection lead, which is favourable for starting purposes and for reducing the maximum pressure of the cycle.

In the case of the cylinder 4, the lead is reduced by an angle .alpha., for example having a value of 10.degree., as compared to the injection lead for the cylinder 6.

The same result may be obtained in the case of in-line pumps, by retaining the conventional camshaft of the equal division type, but by employing plungers to feed the starting cylinders 3, 4 whereof the profile 41D illustrated in FIG. 5B offers a reduction in height x as compared to the profile 25P (FIG. 5A) corresponding to the piston feeding the power cylinders 1, 2, 5, 6 in such manner as to reduce the lead and to limit the rate of delivery.

With pistons having a form 26D (FIG. 5C) and comprising a sloping upper profile 27, the same two actions are obtained in increasing manner when the flow rate established increases.

In FIGS. 8 and 9 has been illustrated a rotary injection pump comprising a barrel 28 wherein is rotatably installed a core 29 entrained in rotation by a spindle 30 and having axial bores wherein are slidably installed plungers 31 which co-operate with a cam-shaped ring 32. The fuel which is fed in through the pipe 33 is impelled by the pistons 31 into a passage 34 of a rotary distributor 35, the said passage 34 opening at 36 into a distribution head 37 having outflow passages for each cylinder, such as 38P and 38D, which lead to the corresponding power 6 and starting 4 cylinders.

In FIG. 9 has been illustrated the positioning of the radial passages leading to the different cylinders of the 6-cylinder engine of FIG. 1, and in particular the passage 38P leading to the cylinder 6 normally staggered by the angle .beta. (120.degree.) with respect to the passage 38D and corresponding to the theoretical position 4a. According to the invention however, the injection lead decrease is obtained by an angular displacement of the passage 38D in the direction of rotation, by an angle .alpha..

Analogously, the passage 39D leading to the cylinder 3 is displaced through an angle .alpha. with respect to the theoretical setting 3a.

It is equally possible to act on the positioning of the cam ring 32 to accomplish the same result.

In FIG. 9 has been illustrated another means rendering it possible to establish a differentiation between the rates of flow by making use of non return valves 42D on the passages 38D and 39D of the starting cylinders 3 and 4, which valves have a high rate of flow -Q' corresponding to a rate of flow injected Q.sub.o - Q' = q for the starting cylinders.

On the passages 38P leading to the power cylinders 1, 2, 5, 6 are installed non return valves 42P having a small volume -q', corresponding to a rate of flow injected Q.sub.o - q' = Q for the power cylinders.

In FIG. 6 has been illustrated a V-8 cylinder engine, wherein the starting cylinders 103 and 104 are paired under the same cylinder head 109. It should be noted on this subject that the action of the two cylinders 103 and 104 is not necessarily evenly spread over the mechanical cycle of the engine.

In this embodiment, the cylinders 103 and 104 have a true compression ratio increased by reduction of their unswept volume and/or of the inlet closure delay. These same cylinders have a rate of injection flow which is reduced and delayed by the same combined or coupled means set forth in the case of the 6-cylinder engine.

FIG. 7 is applicable to the case of a flat 12-cylinder engine, wherein three cylinders 210, 211 and 212 are starting cylinders and are evenly spaced apart over two revolutions and grouped in such manner as to concentrate the starting means. Taking the firing sequence 201, 210, 205, 207, 203, 211, 206, 209, 202, 204, 208 into account, this corresponds to a constant spacing of 240.degree. over two revolutions of a four-stroke engine. Operation: the engine is commonly constructed to withstand a given maximum cycle pressure; it is of importance that the starting cylinders having a high compression ratio should receive the same maximum pressure as the power cylinders having a low compression ratio. By comparison to the engine operating in conventional manner, whereof all cylinders work in identical manner with a pressure of the order of 120 kgs/cm.sup.2 for example, endeavours will be made in the case of the engine embodying selective compressions in accordance with the invention, to maintain a maximum pressure of the order of 100kgs/cm.sup.2 in both kinds of cylinders, whilst maintaining performance and improving ease of starting, by an appropriate injection setting of which an example is given hereunder by way of information:

Conventional Selective engine compression engine Starting Power cylinders cylinders __________________________________________________________________________ Volumetric compression ratio 17 20 13 Inlet delay 45.degree.crank 20.degree. 50.degree. angle Maximum rate of delivery per cycle 60 mm.sup.3 /cycle 40 70 Injection lead 20 crank angle 15.degree. 25.degree. Maximum pressure 120 kgs/cm.sup.2 100 100 __________________________________________________________________________

It is considered that the power rating of a given engine making use of selective compression may be improved, as well as the ease of starting, whilst reducing the maximum stresses.

Beyond the advantage of improving durability, it is pointed out that the power cylinders have the benefit of a large unswept volume and of a lower compression ratio allowing of an appreciable reduction of the proportion of nitrogen oxides.

One inventive feature of interest is its ease of adaptation to the engines actually available, which by means of relatively uncomplicated and inexpensive modifications renders it possible to improve their performance and above all their durability.

In FIG. 10 has been illustrated an internal combustion engine comprising power cylinders 301 and 304 and starting cylinders 305 and 306 which are fed through an inlet manifold 307 from a supercharger 308. Constrictors 309 and 310 comprising calibrated orifices 311 and 312 arranged at the inlet ports of the starting cylinders 305 and 306.

These constrictors 309 and 311 consist in particular of a plate equipped with a calibrated orifice and situated at the joint with the flange of the inlet manifold.

Claims

I claim:

1. A diesel engine comprising, a plurality of cylinders arrayed in two predetermined sets consisting of a set of starting cylinders and a set of power cylinders, and means for simultaneously supplying fuel to said two sets of cylinders at differing predetermined flow rates selected to make the set of starting cylinders operative for starting the engine, at a higher volumetric compression ratio than the set of power cylinders, while said set of power cylinders are operative for running the engine under full power at a lower volumetric compression ratio than the set of starting cylinders and with maximum efficiency; said means for supplying fuel to said cylinders including an in-line injection pump and separate injection means associated with each of said cylinders, the injection means for supplying fuel to the starting cylinder supplying fuel thereto at a rate which is less than that at which fuel is simultaneously supplied to the power cylinders from the injection means associated with the power cylinders; said injection means comprising individual simultaneously operated plungers in the pump for supplying fuel to the respective cylinders; said plungers each having fuel control profiles of substantially the same predetermined configuration and being set in predetermined relative positions in said pump for simultaneous movement, the profile setting of the plungers associated with the starting cylinders being different from that of the plungers associated with the power cylinders.

2. An engine according to claim 1 wherein the number of starting cylinders is small compared with the number of power cylinders.

3. An engine according to claim 1, wherein the starting cylinders have an initial or static lead value smaller by a value .alpha. than that of the power cylinders, the phase displacement of the injection lead of the starting cylinders as compared to the power cylinders is established by said in-line injection pump; said pump having cam means of predetermined contour respectively associated with said plungers for reciprocating the plungers, said cam contours being identical and the cams of the plungers feeding the starting cylinders being dephased by the value .alpha., in order to reduce the injection lead as compared to the cams of the power pistons.

4. A diesel engine comprising a plurality of cylinders arrayed in two predetermined sets consisting of a set of starting cylinders and a set of power cylinders, and means for simultaneously supplying fuel to said two sets of cylinders at differing predetermined flow rates selected to make the set of starting cylinders operative for starting the engine, at a higher volumetric compression ratio than the set of power cylinders, while said set of power cylinders are operative for running the engine under full power at a lower volumetric compression ratio than the set of starting cylinders and with maximum efficiency; said means for supplying fuel to the starting cylinders including separate injection means associated with each of said cylinders, the injection means for supplying fuel to the starting cylinder supplying fuel thereto at a rate which is less than that at which fuel is simultaneously supplied to the power cylinders from the injection means associated with the power cylinders; and wherein at the injection outlets leading to the starting cylinders are installed non-return valves having a low rate of flow and at the injection outlets leading to the power cylinders are installed non-return valves having a high rate of flow.

5. A diesel engine comprising a plurality of cylinders arrayed in two predetermined sets consisting of a set of starting cylinders and a set of power cylinders, and means for simultaneously supplying fuel to said two sets of cylinders at differing predetermined flow rates selected to make the set of starting cylinders operative for starting the engine, at a higher volumetric compression ratio than the set of power cylinders, while said set of power cylinders are operative for running the engine at full power at a lower volumetric compression ratio than the set of starting cylinders and with maximum efficiency; and wherein said fuel supply means comprises a rotary pump having distribution passages, for feeding the starting cylinders, staggered in the direction of rotation by an angle .alpha. with respect to the setting of passages for feeding the power cylinders whereby the static injection lead value of the starting cylinders is smaller by a value .alpha. than that of the power cylinders.

6. A supercharged diesel engine comprising a plurality of cylinders arrayed in two predetermined sets consisting of a set of starting cylinders and a set of power cylinders, and means for simultaneously supplying fuel to said two sets of cylinders at differing predetermined flow rates selected to make the set of starting cylinders operative for starting the engine, at a higher volumetric compression ratio than the set of power cylinders, while said set of power cylinders are operative for running the engine under full power at a lower volumetric compression ratio than the set of starting cylinders and with maximum efficiency; wherein constrictors having calibrated orifices are situated at inlet ports of the starting cylinders in such manner that the supply of air to the starting cylinders is reduced at high engine speeds.