EP3526459A1

EP3526459A1 - Method to determine fuel pump phasing

Info

Publication number: EP3526459A1
Application number: EP17784618.5A
Authority: EP
Inventors: Pedro LOQUAIS; Anthony MICHOU
Original assignee: Delphi Technologies IP Ltd
Current assignee: Borgwarner US Technologies LLC
Priority date: 2016-10-14
Filing date: 2017-10-11
Publication date: 2019-08-21
Anticipated expiration: 2037-10-11
Also published as: GB2554917B; EP3526459B1; GB201617450D0; GB2554917A; WO2018069377A1

Abstract

A method of determining the relative phasing between a crankshaft and a crankshaft driven high pressure piston pump via a cam mechanism, said piston pump adapted to provide high pressure fuel to a common rail, comprising: a) measuring the pressure P1 in said common rail at a time before a pumping stroke/event; b) measuring the pressure P2 in said common rail at a time after the pumping stroke/event; c) determining the average pressure of said measured pressure from steps a) and b); d) determining the time point where the measured pressure reaches the average pressure determined form step c) e) correlating said time point with from d) with crankshaft position to determine said relative phasing.

Description

Method to Determine Fuel Pump Phasing

Field of the Invention

The invention relates to fuel pumps for internal combustions engines which are driven by a crankshaft drive. It has particular application to piston (plunger type) fuel pumps, where typically a pump plunger is driven by a pump cam mechanism driven by the crankshaft. The invention relates to a method of accurately and reliably determining the pump phase i.e. in relation to the crankshaft.

Background to the Invention

Modern engines use high pressure pumps to supply fuel to a accumulator volume such as a common rail which supplies fuel in turn to one or more fuel injectors. Typically such pumps are piston or plunger type pumps which reciprocate as a result of an (e.g. offset) cam mechanism driven by the camshaft, to pressurize fuel in a fuel chamber. Typically inlet metering valve and outlet valves are provided adjacent to the fuel chamber.

Pump phasing is defined as the angle (phase offset) between Top Dead Center (TDC) of one (or more) cylinder and pump TDC (i.e. when the pump plunger reaches the top position at the end of the pumping stroke). The pressure control of the common rail by e.g. the use of a digital Inlet valve requires the pump TDC to be accurately known (in relation to the crankshaft position). The digital inlet valve behavior is linked to the pump cycle with an angular timing command.

Typically actual pump TDC scatter (that is the variation in phase the pump in operation) can be up to +/- 20° and DIV control requires a precision of +/-3°.

The usual method to phase the pump is a mechanical indexation by a pin between pump shaft and engine timing pulley. However this phasing method is not enough accurate and other mechanical dispersion are not taken into account (timing belt, crank wheel, sensor location, etc.) It is an object of the invention to provide a method to determine the pump phasing and thus also to control more precisely the pump phase and to reduce the scatter.

Statement of the Invention

In one aspect is provided a method of determining the relative phasing between a crankshaft and a crankshaft driven high pressure piston pump via a cam mechanism, said piston pump adapted to provide high pressure fuel to a common rail, comprising: a) measuring the pressure PI in said common rail at a time before a pumping stroke/event;

b) measuring the pressure P2 in said common rail at a time after the pumping stroke/event; c) determining the average pressure of said measured pressure from steps a) and b); d) determining the time point where the measured pressure reaches the average pressure determined form step c) e) correlating said time point with from d) with crankshaft position to determine said relative phasing.

Said time point in d) may be assumed to be the mid-stroke in a pumping event of said piston pump.

Said correlation may include determining the phase difference between the top dead centre after the pumping stroke from said assumed mid-stroke time point and cam geometry.

Step e) may comprise correlating said time point with a crankshaft signal, said crankshaft signal including a phasing reference point.

Said crankshaft signal may comprise a series of pulses generated as crankshaft teeth pass in proximity to a sensor, and said reference point comprises a tooth having an irregular pitch or gap. Said pressure PI may be that measured during a first plateau phase before a pumping stroke and the pressure P2 is measured during a second higher plateau phase after said pumping stroke. Said pressure PI may be the average pressure Pavl over a timespan in said first plateau phase and said pressure P2 is the average pressure Pav2 over a timespan of said sensor plateau phase.

The term "relative phasing" can mean the phase difference or relative position. In examples it is the phasing between the TDC of the crankshaft (e.g. in relation to one or more cylinders) and TDC of the pumping stroke of the piston/plunder of the high pressure pump.

Brief Description of Drawings

The invention will now be described by way of example and with reference to the following figures of which:

Figure 1 shows a schematic figure of a high pressure piston pump system to supply pressurized fuel to an accumulator volume such as a common rail;

Figure 2 shows a diagram representing high pressure piston pump phasing dispersion; Figure 3 shows a chart of crankshaft output pulse against common rail pressure and illustrates an example of how the method can be implemented. Detailed Description of Drawings

Figure 1 shows a schematic figure of a piston pump system 1 to supply pressurized fuel to an accumulator volume such as a common rail. The piston pump includes plunger 2 driven by cam mechanism 4 and is adapted to pressurise fuel in a chamber 3. Located between the chamber outlet and the common rail 5 is an outlet valve 10. Located between the fuel supply and the inlet to the pumping chamber, is an inlet metering valve (IMV) 6. The actuator which drives the pump flow can be an IMV or a DIV (DIV drives the inlet valve closure). A further valve /head cap 10 is normally provided integral with the pump. The cam is driven from the camshaft 8 (shown by the dotted line) which comprises a toothed wheel. Typically one of the teeth 9 has a longer tooth pitch or tooth gap and this is used for reference, i.e. for timing purposes. Figure 2 shows a diagram representing pump phasing dispersion. The cylinder top dead centre (Cyl TDC), for a particular cylinder is at a phase difference to the pump TDC; usually this angle is 44°. The figure shows the typically scatter which is about +/- 20° about a nominal ideal phase angle. Again the typically the phase difference between pump (TDC) and crankshaft (TDC) should be e.g. 44°. It should be noted that examples of the invention can be applied to engines having any number of cylinders. In one example, as single revolution of the crank will result in a single full pumping stroke/period. In other words the frequency of a reciprocation of a piston in a cylinder will be the same as the pumping plunger in the high pressure fuel pump. However the cam mechanism used to drive the plunger may comprise various mechanisms; e.g. it having various numbers of lobes. In this case there may be any number of pumping cycles per crank revolution; thus the invention is also applicable to any of these; there may be for example two lobes and two pumping cycles per one crank revolution. In Figure 3, the bottom plot shows the signal 10 obtained from a toothed crank wheel which e.g. has 60 teeth. This signal is derived from e.g. a proximity sensor such as a Hall effect sensor, where a pulse is obtained every time a tooth of the wheel passes. As can be seen the signal is a rectangular (pulsed) waveform. Note that one of the pulses has a larger pitch or period than the others (shown by the arrow A) - this is from/corresponds to the reference tooth 9 of figure 1- the longer tooth or gap machined into the toothed wheel and in the examples is used as a reference. So thus, typically in order to provide a reference, one tooth has a larger pitch or period that the others. In the example of the figure this indexing tooth or tooth gap is located as shown by the arrow A and is considered a reference point. It is assumed that the phase difference (if any) between this and the crankshaft TDC (e.g. in respect of one or more cylinders) is fixed/known.

The top plot 11 shows the pressure in the common rail 9 as a result of pressurisation of fluid therein resulting from a pumping stroke of the high pressure pump via the cam mechanism driven by the correspondingly rotating crankshaft corresponding to signal 11. Thus, as the pump plunger moves to the TDC position, it acts to pressurize fuel in the fuel rail. Before the pumping stroke the pressure of the fluid is generally at first generally pressure level PI (see plateau 12) and after the pumping stroke the pressure is increased to a higher pressure P2 (see plateau 13). Typically a common rail includes a pressure sensor; pressures can be thus be determined by the pressure sensor already present on the common rail. Finding the exact end of the pumping event on the rail pressure signal is difficult because the end of pressure increase is very slow (due to pump cam profile).

According to one example, the pressures before and after the pumping stroke are measured and the average is determined. The mid-point of the pumping stroke is assumed to be at the point where the pressure is at this value. Thus the pressure PI and P2 may be also averaged, or the pressure over the plateau regions 12, 13 are determined and this averaged. In an example the values of averages pressure values Pavl and average pressure value Pav2 over a period in the plateaus may be determined and the averages of these averages pressures determined. This is illustrated by the boxes designated for Pavl and Pav2 where, within the time span in the box, the average value of pressure is determined.

So, one aspect the point at which the pressure reaches the average value of averages Pavl and Pav2 (or PI and P2) is used to determine phasing and this point is assumed to be the point at which the pump is half way throught he pumping stroke i.e. in the mid-stroke (pressurization) position. This point is illustrated by X in the figure. So in the figure the average of the averages Pavl and Pav2 is determined to be Px equivalent to point X. This point is assumed to be the mid-point of the pumping stroke and can be used to determine pump phasing.

In one example the tooth number corresponding to the time at which the mid-point in terms of pressure is noted and the phase between that and the reference (e.g. crankshaft reference tooth/gap is noted is noted. Thus the phase (difference) between the absolute reference point A and the mid stroke pressurisation point is given by arrow B.

The point of top dead-centre of the pump plunger would be at point CI , effectively and the phase between this point and the absolute reference point is shown by arrow C. This point and thus the phase difference between pump TDC and crank reference (and hence crank TDC) can be determined from the cam profile. From the cam design the difference between the mid-point and the TDC can be easily determined or is already known. So for example with a single lobe cam the point of mid stroke may be 90° ahead of TDC. Of course geometries may vary. There may be more than one lobe e.g. two lobes or more or the geometry may perform two or more pumping operations per cam revolution.

So to recap, the method determines the mid pressure value. At this mid pressure value, the angle in relation to crankshft is determined. With the pump cam profile, the angle between the pump top dead center and the mid lift pump position ("angle2") is known. So we can calculate the position of the pump TDC relative to crankshaft (phase) is Pump TDC angle = angle 1 - angle2

In one example there are 2 pumping events per pump revolution, and so 1 pumping event = 180°. Furthermore the pump cam profile may not be symmetric; the filling phase may cover 85°, pumping phase 95°deg. As the pump may also not be symmetric during pumping, plunger mid point may not be is not 95/2=47.5 but 48.2deg from pump TDC. It is to be noted that in the example the absolute reference point is the nominal TDC of the crankshaft. Of course it may be that there is a known phase difference between crank TDC and the reference point (i.e. that denoted by the larger tooth period/pitch).

Thus according to aspects, a method learns the phasing between the high pressure fuel pump and the engine (crankshaft). As a result, the principle of the pump phasing measurement chosen is to position the middle of the pumping where the pressure increase slope is high in relation to the engine crank wheel. Indeed, the middle of the rail pressure increase during a pumping event corresponds to half of the pumped volume. So in a simple method the end of the pumping event (e.g. the plunger TDC) is identified from the rail pressure and the crank events during the engine starting. As a consequence, examples of the invention allow accurate rail Pressure control by a digital inlet valve (DIV) and then to increase rail pressure control performances and accuracy. The present invention allows to control the rail pressure by a e.g. digital inlet valve (DIV) without adding any manufacturing process constraints (machining tolerance). This method by learning allows diagnosis of a faulty operating pump assembly on engine. This method allow to take into account scatter of chain rattling from pump TDC to software angle reference.

Claims

1. A method of determining the relative phasing between a crankshaft and a crankshaft driven high pressure piston pump via a cam mechanism, said piston pump adapted to provide high pressure fuel to a common rail, comprising:

a) measuring the pressure PI in said common rail at a time before a pumping stroke/event;

b) measuring the pressure P2 in said common rail at a time after the pumping stroke/event;

c) determining the average pressure of said measured pressure from steps a) and b);

d) determining the time point where the measured pressure reaches the average pressure determined form step c)

e) correlating said time point with from d) with crankshaft position to determine said relative phasing.

2. A method as claimed in claim 1 wherein said time point in d) is assumed to be the mid-stroke in a pumping event of said piston pump.

3. A method as claimed in claim 2 wherein said correlation includes determining the phase difference between the top dead centre after the pumping stroke from said assumed mid-stroke time point and cam geometry.

4. A method as claimed in claims 1 to 3 wherein step e) comprises correlating said time point with a crankshaft signal, said crankshaft signal including a phasing reference point.

5. A method as claimed in claims 1 to 4 wherein said crankshaft signal comprises a series of pulses generated as crankshaft teeth pass in proximity to a sensor, and said reference point comprises a tooth having an irregular pitch or gap.

6. A method as claimed in any preceding claim wherein said pressure PI is that measured during a first plateau phase before a pumping stroke and the pressure P2 is measured during a second higher plateau phase after said pumping stroke.

7. A method as claimed in claim 6 wherein said pressure PI is the average pressure Pavl over a timespan in said first plateau phase and said pressure P2 is the average pressure Pav2 over a timespan of said sensor plateau phase.