High-pressure pump for motor vehicle internal combustion engine

Description

Technical field

[0001] The present invention relates to the field of internal combustion engines, and more particularly to engines comprising a direct injection carburetion system comprising a high pressure pump. Previous techniques

[0002] There are different types of fuels used in an internal combustion engine. Typically, internal combustion engines use liquid fuels, such as pure gasoline, a blend of gasoline and ethanol, or even pure ethanol.

[0003] We know of the so-called direct gasoline injection technology, abbreviated as "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.

[0004] In a liquid fuel direct injection carburetion system, the injection of fuel (petrol, petrol 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 capacity to introduce a sufficient quantity of fuel into the cylinders between each combustion. It is thus useful to be able to increase the fuel injection pressure to obtain a better atomization of the fuel which results in a better homogeneity of the fuel - oxidant mixture, improving combustion and thus reducing polluting residues. The gasoline direct injection carburetion system includes a high pressure fuel pump, as indicated, for example, in DE102005054451A1.

[0005] The pump is usually driven by a component of the internal combustion engine, notably a camshaft and an intermediate tappet.

[0006] In a high-pressure fuel injection system, the high-pressure pump typically uses a single piston, called a plunger, which performs reciprocating translational movements between two positions called top dead center (TDC) and bottom dead center (BDC). In normal operation of the direct injection system, the plunger is driven by an engine cam and via a pusher element, generally at a rate of one pumping cycle per engine combustion cycle. The pumping cycle comprises several successive phases.

[0007] In the suction phase, the plunger moves 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 around three to six bars. During the suction phase, the outlet and safety relief valves are held closed by springs.

[0008] During a control phase of the quantity of fuel admitted for compression, the plunger moves partially from BDC to TDC with the inlet valve open, which allows a quantity of fuel to be discharged into 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 piloted to the closed position.

[0009] During the fuel compression phase in the compression chamber, the fuel is expelled from the compression chamber through the outlet valve as the plunger finishes moving to TDC.

[0010] Typically, 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 in the pump components that can cause unwanted friction or even blockage of the plunger. It is therefore useful to maintain a functional clearance between the plunger and the compression chamber sleeve to reduce the risk of the pump seizing at high pressure.

[0011] 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 thereof.

[0012] This fuel leak is a direct source of loss of volumetric efficiency of the pump, because the leak causes the compressed fuel to expand.

[0013] However, 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.

[0014] Increasing the fuel injection pressure requires increasing 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 results in an increase in the fuel leakage described above, which results in a decrease in the volumetric efficiency of the high-pressure pump.

[0015] In order to maintain the same pumped fuel flow rate for the same overall engine performance level, when upgrading the injection system to a higher injection pressure, it is necessary to increase the theoretical capacity of the high-pressure pump, for example by increasing its displacement, so as to compensate for the loss of volumetric efficiency of the high-pressure pump.

[0016] Increasing the pump displacement brings several disadvantages.

[0017] First, this increase is accompanied by increased friction in the high-pressure pump, although the consequences are negligible due to the lubrication effect provided by the fuel leak.

[0018] Then, the increase in displacement can be done for example by enlarging the diameter of the plunger, having the effect of increasing the mass and size of the high pressure pump, or by increasing the stroke of the plunger, which causes the increase in the size of the drive cam, in an engine environment increasingly constrained by the reduction in the allocated volume and by the multiplication of on-board control systems.

[0019] Finally, the increase in displacement means above all an increase in the drive forces of the high-pressure pump, which implies a dimensioning (in size and mass) and greater overall forces on the entire drive system of the high-pressure pump and the engine distribution, with consequently amplified energy losses.

[0020] Considering the disadvantages brought by the increase in the displacement of the high pressure pump, it appears necessary to adopt a solution that improves the volumetric efficiency.

[0021] In order to overcome the disadvantages associated with the decrease in volumetric efficiency caused by the increase in injection pressure, it is known to reduce the free space between the plunger and the combustion chamber liner, either by reducing the functional clearance or by placing a seal between the two. However, each of these two existing solutions has a major drawback.

[0022] The reduction in 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 an increased risk of the high-pressure pump seizing.

[0023] Adding a seal between the plunger and the high-pressure pump liner allows the functional clearance to remain unchanged. However, using a seal prevents fuel from circulating through the functional clearance, thus reducing the cooling of the plunger-liner assembly. This increases the risk of the high-pressure pump seizing compared to the system before the injection pressure was increased. Statement of the invention

[0024] In view of the above, the aim of the invention is to propose a high pressure pump for a direct injection fuel system which avoids the risk of seizure while preserving the volumetric efficiency of the pump.

[0025] The invention relates to a high-pressure pump for a direct liquid fuel injection system for a motor vehicle, comprising a pump body comprising a low-pressure liquid fuel inlet, a high-pressure liquid fuel outlet and a compression chamber provided with a plunger movable in translation in the pump body, said compression chamber connecting the low-pressure liquid fuel inlet to the high-pressure liquid fuel outlet.

[0026] The high pressure pump comprises at least one intermediate piston delimiting with the plunger an intermediate chamber of variable volume.

[0027] This intermediate chamber is in compression during the compression phase of the main chamber. The fuel flow from the intermediate compression chamber reduces the fuel leakage from the main compression chamber and thus improves the volumetric efficiency of the high-pressure pump, without increasing the risk of seizing the high-pressure pump. During the suction phase, a vacuum is created within the intermediate compression chamber, which draws fresh fuel from the main compression chamber, which helps to cool the high-pressure pump.

[0028] 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.

[0029] Advantageously, the high pressure pump is equipped with at least one and preferably at least three levers.

[0030] For example, the proximal ends of the levers are in contact with both the plunger and the intermediate piston.

[0031] For example, the proximal ends of the levers have a variable cam-like profile. Thanks to the variable cam-like profile, when the plunger moves up or down, the proximal end automatically imparts a relative movement of the intermediate piston relative to the plunger.

[0032] In one embodiment, the proximal end of the levers is hinged to a bulge of the plunger.

[0033] In another embodiment, the proximal end of the levers is hinged to a bulge of the intermediate piston.

[0034] The invention also relates to a motor vehicle internal combustion engine comprising a direct liquid fuel injection system comprising a high-pressure pump as defined previously and configured to inject the liquid fuel into at least one cylinder of the engine. Brief description of the drawings

[0035] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely as a non-limiting example, and made with reference to the appended drawings in which: [ Fig 1 ] illustrates, in a very schematic manner, an example of the general structure of an internal combustion engine comprising a high pressure pump according to the invention; [ Fig 2 ] represents, in a very schematic manner, an example of a high-pressure pump for a direct gasoline injection system of an internal combustion engine according to the prior art; [ Fig 3] represents, in a very schematic manner, an example of a high-pressure pump for a direct gasoline injection system of an internal combustion engine according to an embodiment of the invention; [ Fig 4 ] illustrates, in a very schematic manner, the operation of the high-pressure pump during the fuel compression phase, according to one embodiment of the invention; and [ Fig 5 ] illustrates, in a very schematic manner, 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

[0036] On the Figure 1 , the general structure of an internal combustion engine 10, in particular of the spark ignition type of a motor vehicle, is shown in a very schematic manner.

[0037] This architecture is given as an example and does not limit the invention to the sole configuration to which the high pressure pump according to the invention can be applied.

[0038] In the illustrated example, the internal combustion engine 10 comprises, in a non-limiting manner, four in-line cylinders 12, a fresh air intake manifold 14, an exhaust manifold 16 and a turbocharging system 18.

[0039] 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.

[0040] In a 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, with the aim of increasing the quantity (mass flow rate) of air admitted into the cylinders 12 of the engine 10. The turbine 18a may be of the “variable geometry” type, that is to say that the turbine wheel is equipped with blades with variable inclination in order to modulate the quantity of energy taken from the exhaust gases, and thus the boost pressure.

[0041] As regards the exhaust manifold 16, the latter recovers the exhaust gases from the combustion and evacuates them to the outside, via a gas exhaust duct 24 opening onto the turbine 18a of the turbocharger 18 and via an exhaust line 26 mounted downstream of said turbine 18a.

[0042] 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 English terms for Exhaust Gas Recirculation.

[0043] The high-pressure exhaust gas recirculation circuit 28, also called the “HP EGR” circuit, originates at a point in the exhaust line 26, upstream of said turbine 18a, and returns the exhaust gases upstream of the intake manifold 14.

[0044] By way of non-limiting example, the engine 10 comprises a system 30 for depolluting the combustion gases of the engine. The depolluting system 30 will not be described further.

[0045] The engine 10 is associated with a direct liquid fuel 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 reservoir 40 of liquid fuel.

[0046] The liquid fuel direct injection (gasoline, gasoline and ethanol or ethanol) fuel system includes a high pressure pump (not shown in the Figure 1) configured to ensure proper spraying of the liquid fuel into the cylinder 12 of the engine 10 while maintaining 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, including a camshaft and an intermediate tappet. The pump is therefore attached to the cylinder head or any other part of the engine.

[0047] A known example of a high pressure pump is illustrated in the Figure 2 .

[0048] 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 inlet duct 103A and the high pressure fuel outlet 104A.

[0049] The pump 100A further comprises a low-pressure chamber 106A connected to the fuel intake 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.

[0050] The pump 100A includes a plug 110A, fixed relative to the body, in which the rod of the plunger 108A slides.

[0051] The low pressure chamber 106A is located axially below the plunger piston 108A.

[0052] As illustrated, the pump 100A includes an inlet valve 111A for the compression chamber 105A, an outlet valve 112A for the compression chamber 105A and a high pressure circuit relief valve 113A mounted in a conduit 114A connecting the high pressure chamber 105A and the fuel outlet 104A.

[0053] In normal operation of the direct gasoline injection system, the plunger 108A is driven by a cam (not shown) and via a tappet (not shown), generally at the rate of one pumping cycle per combustion cycle of the engine.

[0054] Fuel is forced into the high pressure pump 100A at a supply pressure of the order of 3 bar to 6 bar by a low pressure pump (not shown) through the fuel inlet 102A.

[0055] During the fuel suction phase into the compression chamber 105A by the plunger 108A, the unpiloted inlet valve 111A is opened 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 valves 112A and discharge valves 113A are held closed by the force of their respective springs (not referenced).

[0056] During the control phase of 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 open inlet valve 111A towards the inlet 102A and the low pressure chamber 106A. The outlet and discharge valves 112A and 113A are kept closed by the force of their respective spring (not referenced) and by the fuel pressure present at the outlet 104A.

[0057] When the remaining volume in the compression chamber 105A corresponds to the quantity to be pumped, the inlet valve 111A is controlled in the closed position.

[0058] 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 top dead center.

[0059] There Figure 3 illustrates a high pressure pump 100 according to one embodiment of the invention.

[0060] 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 duct 103 to the high-pressure fuel outlet 104.

[0061] The pump 100 further comprises a low-pressure chamber 106 connected to the fuel intake duct 103 by an intermediate duct 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.

[0062] The pump 100 comprises a plug 110, fixed relative to the body, in which the rod of the plunger 108 slides.

[0063] The low pressure chamber 106 is located axially below the plunger piston 108.

[0064] As illustrated, the pump 100 comprises an inlet valve 111 for the compression chamber 105, an outlet valve 112 for the compression chamber 105 and a relief valve 113 for the high pressure circuit mounted in a conduit 114 connecting the high pressure chamber 105 and the fuel outlet 104.

[0065] 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 intermediate piston 121 and the plunger 108 delimit an intermediate compression chamber 120 of variable volume during the pumping cycle.

[0066] In the described embodiment, three levers are arranged radially around the plunger 108, at angular distances equal to 120°.

[0067] Other non-uniform radial arrangements of the levers are possible and fall within the scope of the present invention.

[0068] As illustrated in the Figure 3, the levers 122 have a proximal end 123 which is articulated on a bulge of the plunger 108 and a distal end 124 which is articulated on 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 rises or descends, the proximal end 123 automatically prints a relative movement of the intermediate piston 121 with respect to the plunger 108, thanks to the variable cam-like profile. One or a plurality of springs 125 force the complete stroke of the intermediate piston 121 despite the mechanical clearances in the joints of the system, in order to take advantage of the maximum depression during 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 during the compression phase of the high-pressure pump. Ideally, the functional clearance between the intermediate piston 121 and the liner 109 is smaller than the functional clearance between the plunger 108 and the liner 109, in order to promote the circulation of fuel between the main chamber 105 and the intermediate chamber 120. Indeed, the fuel leakage naturally circulates overall towards the zone having the lowest pressure on average, in other words towards the low-pressure chamber 106.

[0069] The normal operation of the direct gasoline injection system is identical to that of the state of the art described with reference to the Figure 2 , with the details provided by the figures 4 And 5 and developed below.

[0070] There Figure 4illustrates the operation of the pump 100 during the fuel compression phase. In this figure, the fuel flow rates which pass through the different chambers of the pump 100 are represented schematically by arrows, the thickness of which is proportional to the value of the flow rate represented, in other words, the line of the arrow symbolizing a flow rate is all the stronger as this flow rate is important. The direction of movement of the plunger 108 and the intermediate piston 121 are represented by arrows placed directly on the elements.

[0071] During the phase of compression of the fuel 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, a 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 in turn move 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 forcing back towards the chamber 105 a part of the fuel which had leaked from the chamber 105. Nevertheless, the leak is not completely forced 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 leakage of fuel leaving the compression chamber 105 and improves the volumetric efficiency of the high-pressure pump 100.

[0072] There Figure 5 illustrates the operation of the pump 100 during the fuel suction phase. In the Figure 5 , like the Figure 4, the fuel flow rates that pass through the different chambers of the pump 100 are represented schematically by arrows, the thickness of which is proportional to the value of the flow rate represented, in other words, the line of the arrow symbolizing a flow rate is all the stronger as this flow rate is important. The direction of movement of the plunger 108 and the intermediate piston 121 are represented by arrows placed directly on the elements. During the fuel suction phase, the plunger 108 descends towards the bottom dead center. The descent of the plunger 108 acts on the levers 122 which in turn move the intermediate piston 121 towards the bottom dead center, moving it away from the plunger 108, which has the effect of increasing the size of the intermediate chamber 120 and creating a depression within the intermediate compression chamber 120 which sucks fresh fuel from the compression chamber 105, which helps to cool the high-pressure pump 100.

Claims

1. High-pressure pump (100) for a direct injection system of liquid fuel for a motor vehicle, comprising a pump body (101) comprising an inlet (102) of liquid fuel at low pressure, an outlet (104) of liquid fuel at high pressure and a compression chamber (105) provided with a plunger (108) movable in translation in the pump body (101) and connecting the inlet (102) of liquid fuel at low pressure to the outlet (104) of liquid fuel at high pressure, characterized in that the high pressure pump (100) comprises at least one intermediate piston (121) delimiting with the plunger (108) an intermediate chamber (120) of variable volume, said intermediate piston (121) being of generally cylindrical shape, concentric with the plunger (108) and guided in translation on the latter (108).

2. 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 the intermediate compression chamber (120).

3. High pressure pump (100) according to claim 1 or 2, comprising at least one and preferably at least three levers (122).

4. High pressure pump (100) according to claim 3, wherein the proximal ends (123) of the levers (122) are in contact with both the plunger (108) and the intermediate piston (121).

5. High pressure pump (100) according to claim 4, wherein the proximal ends (123) of the levers (122) have a variable cam-like profile.

6. 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).

7. 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).

8. Motor vehicle internal combustion engine (10) comprising a direct injection system for liquid fuel 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 engine (10).