FR3128742A1 - High pressure pump for motor vehicle internal combustion engine - Google Patents

Abstract

A high pressure pump for a liquid fuel direct injection system for a motor vehicle, said high pressure pump comprising a pump body (101) comprising a low pressure liquid fuel inlet, a high pressure liquid fuel outlet and a compression chamber (105) provided with a plunger (108) movable in translation in the pump body (101), said compression chamber (105) connecting the low-pressure liquid fuel inlet to the high-pressure liquid fuel outlet pressure, characterized in that the high pressure pump comprises at least one intermediate piston (121) defining with the plunger (108) an intermediate chamber (120) of variable volume. Figure for abstract: Figure 4

Description

High pressure pump for motor vehicle internal combustion engine

The present invention relates to the field of internal combustion engines, and more particularly to engines comprising a direct injection fuel system comprising a high pressure pump.

Prior techniques

There are different types of fuels used in an internal combustion engine. Conventionally, internal combustion engines use liquid fuels, for example pure gasoline, or a mixture of gasoline and ethanol, or even pure ethanol.

We are familiar with the so-called direct fuel injection technology, acronym "IDE", which allows fuel to be injected directly into the engine cylinders. Direct injection lowers fuel consumption and carbon dioxide emissions, and reduces pollutant emissions.

In a liquid fuel direct injection carburetion system, the injection of fuel (gasoline, gasoline and ethanol or even pure ethanol) is necessarily carried out at high pressure in order to guarantee correct atomization of the fuel into the engine cylinders while maintaining the ability to introduce a sufficient quantity of fuel into the cylinders between each combustion. It is therefore useful to be able to increase the fuel injection pressure in order to obtain better atomization of the fuel which leads to better homogeneity of the fuel - oxidant mixture, improving combustion and thus making it possible to reduce polluting residues. The gasoline direct injection fuel system includes a high pressure fuel pump. The pump is generally driven by an element of the internal combustion engine, in particular a camshaft and an intermediate tappet.

In a high-pressure fuel injection system, the high-pressure pump conventionally uses a single piston, called a plunger, which performs alternating translational movements between two positions known as top dead center (TDC) and bottom dead center ( BMP). In normal operation of the direct injection system, the plunger is driven by an engine cam and through a tappet, typically one pump cycle per engine combustion cycle. The pumping cycle comprises several successive phases.

In the suction phase, the diver goes from TDC to BDC, while the fuel enters the high pressure pump through the fuel inlet, being pushed by a low pressure pump at a supply pressure of the order of three to six bars. During the suction phase, the outlet and safety relief valves are kept closed by springs.

During a phase of checking the quantity of fuel admitted for compression, the plunger partially moves from BDC to TDC with the inlet valve open, which allows a quantity of fuel to be pushed back towards the low pressure chamber. . During the control phase, the outlet and safety relief valves remain closed. When the quantity of fuel remaining in the compression chamber corresponds to the quantity to be injected, the inlet valve is controlled in the closed position.

During the compression phase of the fuel in the compression chamber, the fuel is expelled from the compression chamber through the outlet valve while the plunger finishes moving to TDC.

Conventionally, the lateral dimensions of the plunger are smaller than the internal dimensions of the compression chamber, so that a functional clearance exists between the two. During operation, the fuel heats up during its compression. The heat diffuses inside the pump causing dimensional variations of the pump elements which can cause undesirable friction or even jamming of the plunger. It is therefore useful to keep a functional clearance between the plunger and the compression chamber sleeve, in order to reduce the risk of the high pressure pump seizing.

However, during the fuel compression phase, the presence of said functional clearance makes it possible for fuel to leak from the compression chamber to the outside of it.

This fuel leak is a direct source of loss of volumetric efficiency of the pump, because the leak causes the compressed fuel to expand.

Nevertheless, this fuel leak advantageously forms a thin layer of fuel between the plunger and the liner, which constitutes a useful means of lubrication and which contributes to the cooling of the plunger-liner assembly.

The increase in the fuel injection pressure imposes the increase in the fuel pressure in the compression chamber of the high pressure pump, without requiring an increase in the supply pressure of the high pressure pump. The increase in fuel injection pressure then leads to an increase in the fuel leakage described above, which results in a decrease in the volumetric efficiency of the high pressure pump.

In order to maintain the same fuel flow rate pumped for the same level of overall engine performance, when changing the injection system to a higher injection pressure, it is necessary to increase the theoretical capacity of the pump. at high pressure, for example by increasing its displacement, so as to compensate for the loss of volumetric efficiency of the high pressure pump.

Increasing the displacement of the pump brings several disadvantages.

First, this increase is accompanied by increased friction in the high-pressure pump, with nevertheless negligible consequences thanks to the lubricating effect provided by the fuel leak.

Then, the increase in displacement can be done for example by enlarging the diameter of the displacer, having the effect of increasing the mass and the size of the high pressure pump, or by increasing the stroke of the displacer, which causes the size of the drive cam to increase, in an engine environment that is increasingly constrained by the reduction in the allocated volume and by the proliferation of on-board control systems.

Finally, the increase in the displacement means above all the increase in the drive forces of the high-pressure pump, which implies dimensioning (in size and mass) and greater overall forces on the entire system of driving the high pressure pump and the motor distribution, with consequent amplified energy losses.

Considering the disadvantages brought by the increase in the displacement of the high-pressure pump, it appears necessary to adopt a solution which improves the volumetric efficiency.

In order to overcome the drawbacks associated with the reduction in volumetric efficiency caused by the increase in injection pressure, it is known to reduce the free space between the plunger and the liner of the combustion chamber, either by reducing the clearance functional, or by putting a seal between the two. Nevertheless, each of these two existing solutions has a major drawback.

The decrease in the functional clearance between the plunger and the pump sleeve makes the assembly less robust against temperature variations, while the increase in injection pressure causes the temperature of the compressed fuel to increase, with a increased risk of the high pressure pump seizing.

The addition of a gasket between the plunger and the high pressure pump sleeve does not reduce the functional clearance. However, the use of a gasket prevents the circulation of fuel through the functional clearance, thus reducing the cooling of the plunger-jacket assembly. The risk of the high-pressure pump seizing is nevertheless increased compared to the system before the increase in injection pressure.

In view of the foregoing, the object of the invention is to provide a high-pressure pump for a direct injection carburetion system which avoids the risk of seizing while preserving the volumetric efficiency of the pump.

The subject of the invention is a high-pressure pump for a motor vehicle liquid fuel direct injection system, comprising a pump body comprising a low-pressure liquid fuel inlet, a high-pressure liquid fuel outlet and a chamber compression provided with a movable plunger in translation in the body of the pump, said compression chamber connecting the low pressure liquid fuel inlet to the high pressure liquid fuel outlet.

The high-pressure pump comprises at least one intermediate piston defining with the plunger an intermediate chamber of variable volume.

This intermediate chamber is in compression during the compression phase of the main chamber. The flow of fuel leaving the intermediate compression chamber reduces the leakage of fuel leaving the main compression chamber and thus improves the volumetric efficiency of the pump at high pressure, without increasing the risk of the pump seizing at high pressure. pressure. During the suction phase, a depression is created within the intermediate compression chamber which sucks fresh fuel from the main compression chamber, which helps to cool the high-pressure pump.

Advantageously, the high pressure pump comprises a low pressure chamber located axially under the plunger, said low pressure chamber being connected to the liquid fuel inlet and to the intermediate compression chamber.

Advantageously, the high pressure pump is equipped with at least one and preferably at least three levers.

For example, the proximal ends of the levers are in contact with both the plunger and the intermediate piston.

For example, the proximal ends of the levers have a variable cam-like profile. Thanks to the variable cam-type profile, when the plunger goes up or down, the proximal end automatically imparts a relative movement of the intermediate piston in relation to the plunger.

In one embodiment, the proximal end of the levers is hinged to a bulge in the plunger.

In another embodiment, the proximal end of the levers is articulated on a bulge of the intermediate piston.

The invention also relates to a motor vehicle internal combustion engine comprising a liquid fuel direct injection system comprising a high-pressure pump as defined previously and configured to inject liquid fuel into at least one cylinder of the engine.

Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

very schematically illustrates an example of the general structure of an internal combustion engine comprising a high-pressure pump according to the invention;

very schematically represents an example of a high pressure pump for a gasoline direct injection system of an internal combustion engine according to the prior art;

shows, very schematically, an example of a high pressure pump for a gasoline direct injection system of an internal combustion engine according to one embodiment of the invention;

very schematically illustrates the operation of the high pressure pump during the fuel compression phase, according to one embodiment of the invention; And

very schematically illustrates the operation of the high pressure pump during the fuel suction phase, according to one embodiment of the invention.

Detailed description of at least one embodiment

On the , there is shown, very schematically, the general structure of an internal combustion engine 10, in particular of the spark-ignition type of a motor vehicle.

This architecture is given by way of example and does not limit the invention to the single configuration to which the high-pressure pump according to the invention can be applied.

In the example illustrated, the internal combustion engine 10 comprises, in a non-limiting way, four cylinders 12 in line, a fresh air intake manifold 14, an exhaust manifold 16 and a turbo-compression system 18 .

The cylinders 12 are supplied with air via the intake manifold 14, or intake distributor, itself supplied by a pipe 20 provided with an air filter 22 and the compressor 18b of the turbocharger 18 of the engine 10 .

In known manner, the turbocharger 18 essentially comprises a turbine 18a driven by the exhaust gases and a compressor 18b mounted on the same axis or shaft as the turbine 18a and providing compression of the air distributed by the air filter 22, in order to increase the quantity (mass flow) of air admitted into the cylinders 12 of the engine 10. The turbine 18a can be of the "variable geometry" type, that is to say that the wheel of the turbine is fitted with variable-angle fins in order to modulate the amount of energy taken from the exhaust gases, and thus the boost pressure.

As regards the exhaust manifold 16, the latter recovers the exhaust gases resulting from combustion and evacuates them to the outside, via a gas exhaust duct 24 leading to the turbine 18a of the turbocharger 18 and by an exhaust line 26 mounted downstream of said turbine 18a.

In a non-limiting manner, the engine 10 comprises a partial recirculation circuit 28 of the exhaust gases at the intake, also called “EGR” gases, according to the acronym in Anglo-Saxon terms for Exhaust Gas Recirculation.

The high-pressure exhaust gas recirculation circuit 28, also called the “EGR HP” circuit, originates at a point on the exhaust line 26, upstream of the said turbine 18a and returns the exhaust gases upstream of the intake manifold 14.

By way of non-limiting example, the engine 10 comprises a system 30 for depolluting the combustion gases of the engine. The pollution control system 30 will not be described further.

The engine 10 is associated with a liquid fuel direct injection carburetion system comprising, for example, fuel injectors (not referenced) injecting a liquid fuel, such as for example pure gasoline, or a mixture of gasoline and ethanol, directly into each cylinder 12 from a tank 40 of liquid fuel.

The liquid fuel direct injection fuel system (gasoline, gasoline and ethanol or ethanol) includes a high pressure pump (not shown on the ) configured to guarantee correct spraying of the liquid fuel into the cylinder 12 of the engine 10 while retaining the ability to introduce a sufficient quantity of liquid fuel into the cylinder between each combustion. The high-pressure pump is driven by a component of the internal combustion engine, in particular a camshaft and an intermediate tappet. The pump is therefore fixed to the cylinder head or any other part of the engine.

A well-known example of a high-pressure pump is illustrated in the .

The pump 100A comprises a substantially cylindrical pump body 101A comprising a low-pressure fuel inlet 102A opening into a fuel inlet duct 103A, a high-pressure fuel outlet 104A and a compression chamber 105A placed between the fuel duct. fuel inlet 103A and high pressure fuel outlet 104A.

The pump 100A further comprises a low-pressure chamber 106A connected to the fuel inlet duct 103A by an intermediate duct 107A and a plunger 108A movable in translation in the pump body 101A. The plunger 108A comprises a piston movable in translation in a cylindrical housing 109A of the body 101A opening into the compression chamber 105A and an end rod extending axially from the piston towards the outside of the body 100A.

The pump 100A includes a plug 110A, fixed relative to the body, in which the rod of the plunger 108A slides.

Low pressure chamber 106A is located axially below plunger piston 108A.

As shown, the pump 100A comprises an inlet valve 111A for the compression chamber 105A, an outlet valve 112A for the compression chamber 105A and a high pressure circuit discharge valve 113A mounted in a conduit 114A connecting the high pressure chamber 105A and fuel outlet 104A.

In normal operation of the gasoline direct injection system, the plunger 108A is driven by a cam (not shown) and via a tappet (not shown), generally at the rate of one pump cycle per cycle. engine combustion.

The fuel is pushed into the high pressure pump 100A at a supply pressure of the order of 3 bars to 6 bars by a low pressure pump (not shown) through the fuel inlet 102A.

During the fuel suction phase in the compression chamber 105A by the plunger 108A, the uncontrolled inlet valve 111A is open and the fuel arrives from the fuel inlet 102A and the low pressure chamber 106A while the plunger 108A descends from its top dead center to its bottom dead center. The outlet 112A and discharge 113A valves are held closed by the force of their respective springs (not referenced).

During the phase of controlling the quantity of fuel pumped, that is to say when the plunger 108A begins to rise from its bottom dead center, a volume of fuel is expelled from the compression chamber 105A through the valve 111A inlet open to inlet 102A and low pressure chamber 106A. The outlet and relief valves 112A and 113A are held closed by the force of their respective spring (not referenced) and by the fuel pressure present at the outlet 104A.

When the volume remaining in the compression chamber 105A corresponds to the quantity to be pumped, the inlet valve 111A is driven into the closed position.

During the fuel compression phase in the compression chamber 105A and in the outlet 104A, the fuel is expelled from the compression chamber 105A by the outlet valve 112A while the plunger 108A continues its rise to its neutral point. high.

There illustrates a high pressure pump 100 according to one embodiment of the invention.

The pump 100 comprises a substantially cylindrical pump body 101 comprising a low-pressure fuel inlet 102 opening into a fuel inlet duct 103, a high-pressure fuel outlet 104 and a compression chamber 105 connecting the fuel inlet 103 to fuel outlet 104 at high pressure.

The pump 100 further comprises a low-pressure chamber 106 connected to the fuel inlet pipe 103 by an intermediate pipe 107 and a plunger 108 movable in translation in the pump body 101. The plunger 108 comprises a piston movable in translation in a cylindrical housing 109 of the body 101 opening into the compression chamber 105 and an end rod extending axially from the piston towards the outside of the body 101.

The pump 100 includes a plug 110, fixed relative to the body, in which the plunger rod 108 slides.

Low pressure chamber 106 is located axially below plunger piston 108.

As illustrated, the pump 100 comprises a valve 111 for the inlet of the compression chamber 105, a valve 112 for the outlet of the compression chamber 105 and a valve 113 for the discharge of the high pressure circuit mounted in a conduit 114 connecting the high pressure chamber 105 and the fuel outlet 104.

As illustrated, the pump 100 comprises an intermediate piston 121, of generally cylindrical shape and concentric with the plunger 108, which is guided in translation on the plunger 108 and actuated by one or, preferably, a plurality of levers 122. The piston intermediate 121 and the plunger 108 define an intermediate compression chamber 120 of variable volume during the pumping cycle.

In the embodiment described, three levers are arranged radially around the plunger 108, at angular distances equal to 120°.

Other non-uniform radial arrangements of the levers are possible and fall within the scope of the present invention.

As illustrated in the , the levers 122 have a proximal end 123 which is hinged to a bulge of the plunger 108 and a distal end 124 which is hinged to a bulge of the pump body 101. The proximal end 123 has a variable cam-like profile which is in contact with the intermediate piston 121. When the plunger goes up or down, the proximal end 123 automatically imparts a relative movement of the intermediate piston 121 with respect to the plunger 108, thanks to the variable profile of the cam type. One or a plurality of springs 125 force the full stroke of the intermediate piston 121 despite the mechanical play in the joints of the system, in order to take advantage of the maximum depression during the expansion to suck the adequate quantity of fuel from the compression chamber 105 Thus the compression in the intermediate compression chamber 120 is all the more effective in limiting fuel leakage in the compression phase of the high-pressure pump. Ideally, the functional clearance between the intermediate piston 121 and the sleeve 109 is smaller than the functional clearance between the plunger 108 and the sleeve 109, in order to promote the circulation of fuel between the main chamber 105 and the intermediate chamber 120. Indeed , the fuel leak naturally flows globally towards the zone having the lowest pressure on average, in other words towards the low pressure chamber 106.

The normal operation of the gasoline direct injection system is identical to that of the state of the art described with reference to the , with the details provided by Figures 4 and 5 and developed below.

There illustrates the operation of the pump 100 during the fuel compression phase. In this figure, the fuel flows which pass through the various chambers of the pump 100 are represented schematically by arrows, the thickness of which is proportional to the value of the flow represented, in other words, the line of the arrow symbolizing a flow is d stronger than this flow is important. The direction of movement of the plunger 108 and of the intermediate piston 121 are represented by arrows placed directly on the elements.

During the fuel compression phase and its expulsion from the high pressure chamber 105, the plunger 108 rises towards the top dead center. However, under the effect of the pressure, part of the fuel located in the chamber 105 leaks towards the part 106 of the pump located below the plunger 108. However, the rise of the plunger 108 acts on the levers 122 which move at their turn the intermediate piston 121 towards the top dead center, bringing it closer to the plunger 108, which has the effect of reducing the size of the intermediate chamber 120 and of returning to the chamber 105 part of the fuel which had leaked from the chamber 105 Nevertheless, the leak is not completely driven back, because a part falls back towards the chamber 106 located at the bottom of the pump 100. Thus during the compression phase, the flow of fuel leaving the intermediate compression chamber 120 reduces the fuel leakage from the compression chamber 105 and improves the volumetric efficiency of the high pressure pump 100.

There illustrates the operation of the pump 100 during the fuel suction phase. In the , like the , the fuel flows which pass through the various chambers of the pump 100 are represented schematically by arrows, the thickness of which is proportional to the value of the flow represented, in other words, the line of the arrow symbolizing a flow is all the more strong that this flow is important. The direction of movement of the plunger 108 and of the intermediate piston 121 are represented by arrows placed directly on the elements. During the fuel suction phase, the plunger 108 descends towards bottom dead center. The descent of the plunger 108 acts on the levers 122 which in turn move the intermediate piston 121 towards bottom dead center, away from the plunger 108, which has the effect of increasing the size of the intermediate chamber 120 and create a depression within the intermediate compression chamber 120 which draws fresh fuel from the compression chamber 105, which helps to cool the high pressure pump 100.

Claims (8)

High-pressure pump (100) for a motor vehicle liquid fuel direct injection system, comprising a pump body (101) comprising a low-pressure liquid fuel inlet (102), a low-pressure liquid fuel outlet (104), high pressure and a compression chamber (105) provided with a plunger (108) movable in translation in the pump body (101) and connecting the low pressure liquid fuel inlet (102) to the outlet (104) of high-pressure liquid fuel, characterized in that the high-pressure pump (100) comprises at least one intermediate piston (121) defining with the plunger (108) an intermediate chamber (120) of variable volume. A high pressure pump (100) according to claim 1, comprising a low pressure chamber (106) located axially below the plunger (108), said chamber (106) being connected to the liquid fuel inlet (102) and to the intermediate compression chamber (120). High pressure pump (100) according to claim 1 or 2, comprising at least one and preferably at least three levers (122). A high pressure pump (100) according to claim 3, wherein the proximal ends (123) of the levers (122) contact both the plunger (108) and the intermediate piston (121). A high pressure pump (100) according to claim 4, wherein the proximal ends (123) of the levers (122) have a variable cam-like profile. A high pressure pump (100) according to claim 5, wherein the proximal end (123) of the levers (122) is hinged to a bulge of the plunger (108). A high pressure pump (100) according to claim 5, wherein the proximal end (123) of the levers (122) is hinged to a bulge of the intermediate piston (121). Motor vehicle internal combustion engine (10) comprising a liquid fuel direct injection system comprising a high pressure pump (100) according to any one of the preceding claims and configured to inject the liquid fuel into at least one cylinder ( 12) of the motor (10).