DE102015111209A1 - Technique for detecting pressure changes in a fuel supply system as a result of pumping - Google Patents

Abstract

The invention relates to a method for detecting and eliminating influences of a pump delivery of a high pressure pump (18) to the pressure signal (Pr) in a high pressure section (HP) of a fuel supply system, in particular in a fuel tank (20) for supply at least one fuel injector (22) of an internal combustion engine (12). The invention further relates to a method for providing a pressure signal (Pr *) adjusted by pumping influences and a method for controlling the injection behavior of the at least one fuel injector (22) based on the adjusted pressure signal (Pr *).

Description

The invention relates to a method for detecting pressure changes in a fuel supply system for an internal combustion engine, which has a high-pressure pump, a fuel reservoir for storing high-pressure fuel and at least one fuel injector supplied by the fuel injector, wherein the pressure change from Pumping the high-pressure pump results. The pressure changes can be recorded and analyzed at least once retrospectively, wherein at least transition parameters for changing a basic vibration behavior are stored. The invention further relates to a method for providing a pressure signal which is adjusted by the pressure changes as a result of a pump delivery. The pressure changes due to a pump delivery are anticipated and eliminated from an actual measured pressure signal in real time.

In practice, methods for controlling the injection quantity of fuel injectors (control methods) in a fuel supply system of the above type are known, which are based on a measurement of the fuel pressure or a detected change in the fuel pressure. In the fuel supply system, due to various causes, pressure waves are spreading, making it difficult to carry out such control methods. In particular, it is necessary in the previously known methods to carry out the execution of fuel injections with a clear time interval to a pump delivery for accurate control or regulation of the injection quantity and / or to detect the fuel pressure at different points in the fuel supply system with multiple sensors ,

It is an object of the present invention to provide a technique with which pressure changes due to a pump delivery can be detected such that control and / or regulation of injection quantities can be carried out with better accuracy, and / or that the control or regulation of fuel injections can be done with a greater temporal flexibility.

In the fuel supply system of the above-mentioned type, high-pressure fuel is supplied to the fuel storage by the high-pressure pump to store it there at a storage pressure of, for example, 1000 bar to 3500 bar or higher (high-pressure area). At least one fuel injector is powered by the fuel storage. When an injection valve of the fuel injector is opened, the high-pressure fuel is injected into a combustion chamber of the internal combustion engine.

In the fuel supply system, starting from the high-pressure pump, via the fuel reservoir, to the at least one fuel injector, a high-pressure section is formed, in which the high-pressure fuel is led through the above-mentioned components through lines. Within this high pressure section, pressure changes and associated pressure waves may propagate.

By a pump delivery additional high pressure fuel from a compression chamber of the high pressure pump is fed to the fuel tank, that is supplied to the high pressure section. By performing a fuel injection high-pressure fuel is removed from the fuel tank, that is discharged from the high-pressure section.

The fuel contained in the high-pressure section has a compressible behavior, which is characterized by the bulk modulus and optionally depends on the temperature. The volume available for the high-pressure fuel in the high-pressure section is generally known very precisely. Elastic changes in the volume as a function of the pressure and / or the temperature of the high-pressure fuel may also be known and taken into account.

From the aforementioned quantities (modulus of elasticity, temperature, volume, instantaneous pressure / base pressure in the high-pressure section) can be calculated according to known physical equations, how much the fuel pressure in the high-pressure section at feeds or withdrawals of a known or determinable amount of fuel will change. Such calculations typically start from a static pressure level before and after the supply or removal of fuel from the high pressure section. In other words, it is possible to calculate an expected change in the pressure signal as a result of a pump delivery on the basis of the aforementioned variables and on the basis of a model for the compressible behavior of the high-pressure fuel.

However, the actual change in the pressure signal is subject to other dynamic influences, which are not or only indirectly related to the pumping promotion. As a result of the compressibility of the fuel For example, pressure changes may undulate in the high pressure section. Several such waves can overlap each other.

In the measured pressure signal, a basic vibration behavior can be detected whose change is not or only indirectly related to the supply of a known or determinable supply of fuel (mass feed) in the high-pressure section. This basic oscillation behavior includes, for example, residual pressure oscillations (not yet fully decayed / damped oscillations) as a result of previous pumping deliveries and / or fuel injections. The basic vibration behavior may also include persistent vibrations, which are caused, for example, as a result of external excitation (structure-borne noise, dynamic forces from the vehicle movement, vibrations from engine operation and / or operation of adjacent components, etc.). The pressure oscillations contained in the basic vibration behavior are changed by or during pumping.

The present invention is based on the recognition that the basic oscillation behavior changes as a result of a pump delivery to an identifiable extent, at least for a determinable period of time. In particular, there is an increase in the amplitude of identifiable fundamental oscillations and / or a change in the frequency response of fundamental oscillations during and / or after pumping. The said changes can be separately recorded and taken into account for the entirety of the fundamental oscillations and / or for identified individual fundamental oscillations.

The method of detecting pressure changes due to pump delivery in accordance with the present disclosure is capable of metrologically detecting and also identifying these indirect changes in the pressure signal, which are not directly related to the mass feed, as a separate system quantity. As a result, the pressure change behavior of the fuel supply system can be calculated much finer and in particular anticipated, so that the control or regulation of the injection quantity of a fuel injector based on the pressure in the high-pressure section with higher accuracy is feasible. In particular, it is possible to eliminate the (direct and indirect) pressure changes as a result of pump delivery from a detected pressure signal. It is therefore possible to provide a pressure signal which has been cleared of pressure changes as a result of pump delivery. Consequently, the already known methods for controlling the injection quantity of a fuel injector can be carried out on the basis of the adjusted pressure signal and it is not necessary to generally separate the execution of fuel injections from the execution of a pump delivery.

The (direct and indirect) pressure changes as a result of a pump delivery can be determined retrospectively in a test interval, i. by comparing the system behavior before pumping with the system behavior during and / or after pumping.

In the process, transition parameters are determined which describe the change in the system behavior and in particular the pressure changes or changes in the vibration behavior which are only indirectly dependent on the pump delivery. During injection operation, these parameters can be used to calculate appropriate pressure changes during or after pumping. The calculation may be anticipatory, i. expected changes for a planned pumping promotion with a planned mass supply of fuel into the high pressure section are made possible. These changes can be eliminated from a pressure change actually detected, so that a pressure signal adjusted by pressure changes due to the pump delivery is provided. This provision can be done in real time due to anticipation.

Alternatively, of course, a method of providing a pressure signal cleared of pressure changes due to a pump delivery may be carried out retrospectively.

In the claims of the following description and the accompanying drawings further advantageous embodiments of the invention are given.

The invention is illustrated by way of example and schematically in the drawings. Show it:

1 : A schematic of a fuel supply system for an internal combustion engine of a vehicle;

2 FIG. 3: various pressure profiles for explaining a detection method according to the present disclosure; FIG.

3 : different pressure gradients analogous to 2 to explain a method for providing an adjusted pressure signal according to the present disclosure.

A basically known fuel supply system ( 10 ) for an internal combustion engine ( 12 ) is in 1 shown. The internal combustion engine ( 12 ) has at least one combustion chamber ( 32 ), are burned in the intake air and injected fuel to generate a torque. At least one fuel injector ( 22 ) is the combustion chamber ( 32 ). The fuel injector ( 22 ) is using high-pressure fuel from a fuel storage ( 20 ) provided. Between the fuel tank ( 20 ) and the at least one fuel injector ( 22 ) is provided according to at least one fuel line.

A high pressure pump ( 18 ) promotes high-pressure fuel in the fuel storage ( 20 ), for which likewise at least one fuel line is provided.

In the example of 1 is a high pressure pump ( 18 ) with an alternately moving piston ( 25 ). The piston ( 25 ) compresses a fuel that is in a compression chamber ( 24 ) of the high-pressure pump ( 18 ) is contained during a compression phase. This increases the pressure in the compression chamber ( 24 ) at. Once the pressure in the compression chamber ( 24 ) is higher than the pressure in the fuel storage ( 20 ) (plus a differential pressure to overcome a valve closing force of the outlet valve), the outlet valve opens ( 26 ), so that the fuel is introduced into the high-pressure section (HP). The mass of the supplied fuel thus depends on the amount of fuel compressed in the compression chamber.

The piston ( 25 ) is driven by a cam or camshaft ( 27 ) in a lifting and lowering movement. The cam disc ( 27 ) is driving with a crankshaft ( 34 ) of the internal combustion engine ( 12 ) connected.

The high pressure pump ( 18 ) according to the example of 1 has a control valve ( 28 ), with which the discharge behavior of the high-pressure pump ( 18 ) is controllable or controllable. This is a self-opening solenoid valve which is activated during a lifting movement of the piston ( 25 ) can be closed at a definable time. Once the control valve ( 28 ) is closed, is in the compression chamber ( 24 ), which is compressed by the further lifting movement of the piston. The earlier the control valve ( 28 ) during the lifting movement of the piston ( 25 ) is closed, the more fuel is contained in the compression chamber and the more fuel is pumped to the fuel storage during pumping ( 20 ), and vice versa.

Alternatively, any other high-pressure pump with a controllable or controllable Pumpförderverhalten be provided, in particular a high-pressure pump with a suction control valve (suction control valve).

In practice, various methods are known to determine the amount of fuel (feed mass) added to the high pressure section (HP) during pumping. Accordingly, an expected pressure signal (Pex) may be calculated during and / or after the pumping based on the amount of fuel supplied to the high pressure section (HP), in particular based on the compression modulus, the fuel pressure (Pr) before pumping, possibly the fuel temperature, and the effective volume of the high-pressure section (HP) and possibly the control parameters for the high-pressure pump ( 18 ).

In the example of 1 obtains the high-pressure pump ( 18 ) Fuel from a fuel tank ( 14 ), optionally via an additional low-pressure pump ( 16 ).

The control of the high-pressure pump ( 28 ) and the at least one fuel injector ( 22 ) is preferably carried out by a common electronic control unit ( 30 ) (ECU) which senses the fuel pressure (Pr) in the high-pressure section (HP) at at least one location. For this purpose, preferably a pressure sensor ( 36 ) on or in the fuel storage ( 20 ) and / or a pressure sensor (not shown) on or in the fuel injector ( 22 ) be provided. Alternatively or additionally, the fuel pressure (Pr) can be detected at any other point in the high-pressure section (HP), for example at the outlet of the high-pressure pump (FIG. 18 ) or on a fuel line.

The following is based on 2 a method for detecting (direct and indirect) pressure changes in the fuel supply system ( 10 ) as a result of a pumping subsidy ( Detection method). The detection method is preferably performed during a test interval in which no fuel injections are made. For example, during the initial deployment of the high pressure level in the fuel supply system ( 10 ) at the beginning of a driving operation, during a shifting operation or during a coasting operation of the vehicle. Within the test interval, the detection method can be executed one or more times and the parameters determined thereby can be stored, for example, for different pressure levels of the fuel pressure (Pr) and stored in an ordered data structure, preferably in a characteristic field.

Alternatively, the detection method may also be performed while performing fuel injections, for example, when the pressure changes in the high pressure section (HP) due to fuel injection are very small or calculable based on accurate models.

In 2 are a time interval (Tpre) before a pumping promotion, a time interval (Ttr) during a pumping promotion and a time interval (Tpost) after a pumping promotion. The sensed pressure signal (Pr), a model-based calculated expected pressure signal (Pex) due to mass promotion, and two examples of a calculated differential pressure signal (Pd, Pd ') are related to each other with respect to the aforementioned time intervals (Tpre, Ttr, Tpost) compared.

In the time interval (Tpre) before pumping, the basic vibration behavior (Pb) of the actual pressure signal (Pr) is detected and, if necessary, analyzed with respect to one or more contained vibrations. For example, the n (n = 1, 2, 3,...) Strongest vibration components in the measured pressure signal (Pr) can be identified on the basis of a Fourier analysis. Subsequently, a pumping promotion takes place during the time interval (Ttr).

The pressure signal (Pr) is detected in the time interval (Ttr) during the pumping promotion and / or in the time interval (Tpost) after pumping. Further, during and / or after pumping, the expected pressure signal (Pex) is calculated as a result of the amount of fuel supplied in the above manner. For this calculation, it is preferably assumed that there is a static outlet pressure prior to pumping, which is, for example, an averaged value from the pressure signal (Pr) in the time interval (Tpre) before pumping.

The expected pressure signal (Pex) as a result of mass production may include in the time interval (Tpost) after pumping already expected oscillations, according to known laws of hydrodynamics from the propagation of the pressure wave in the high pressure section (HP) and a reflection of the wave and a known damping behavior can be calculated. Such pressure fluctuations also represent direct pressure changes as a result of pump delivery. Alternatively, a static fuel pressure may also be assumed for the expected pressure signal (Pex) for the time interval (Tpost) after pump delivery.

For the time interval (Ttr) during pump delivery and / or for the time interval (Tpost) after pump delivery, a difference signal (Pd, Pd ') is calculated, in particular by taking the instantaneous values of the expected pressure signal (Pex) from the corresponding values of the measured pressure signal (Pr) are subtracted.

The thus obtained difference signal (Pd, Pd ') is compared with the fundamental vibration behavior (Pb) in the time interval (Tpre) before pumping. In this case, in particular one or more vibrations contained in the difference signal (Pd, Pd ') can be identified and compared with the basic vibration behavior (Pb) or the vibrations identified there according to their amplitude and / or their frequency behavior. For example, the n (n = 1, 2, 3,...) Strongest oscillations in the difference signal (Pd, Pd ') can be determined by means of a Fourier analysis and assigned to the n strongest identified vibrations before pumping.

For explanatory purposes, the course (Pb) of the measured pressure signal (Pr) during the time interval (Tpre) is shown again as part of the differential pressure signal (Pd, Pd ').

From the above comparison, at least one transition parameter (XA, XF) is derived, by which the change in the fundamental vibration behavior due to the point promotion is described. According to a preferred embodiment, this is at least one gain factor (dA).

As the first differential pressure signal (Pd) is in 2 an identified pressure oscillation is shown and the amplitude (Apre) in the time interval (Tpre) is compared to the amplitude (Atr) during the pumping and the amplitude (Apost) after the pumping promotion.

An amplification factor (dA) can be determined, for example, as: dA = apost.

If necessary, the amplification factor (dA) can be determined as a function of time. In particular, the time behavior of the decay of an amplitude gain after pumping for an identified oscillation and / or the differential pressure signal (Pd) as a whole can be determined.

As the second differential pressure signal (Pd ') in 2 a second identified oscillation is shown, or the change of the frequency behavior (Fpre) before the pumping over the frequency behavior (Fpost) after the pumping promotion.

A change in the frequency response can be achieved, for example, by an acceleration of traveling pressure waves or by a delay of counter-rotating pressure waves during the delivery of fuel from the high-pressure pump to the fuel storage ( 20 ) respectively. This can lead to a change in the phase position (dPh) and / or to a change in the frequency (dF) or change in the wavelength. Also, such changes in the frequency behavior can go back in time depending on the pumping promotion and they can optionally be determined separately for one or more identified vibrations.

The transition parameters (XA, XF) may be stored in any suitable form, particularly in a map and correlated to a base pressure level prior to pump delivery and / or to a quantity of fuel supplied.

The following is with reference to 3 discloses a method of providing an adjusted pressure signal (Pr *) (delivery method) which eliminates the effects of pump delivery. Moreover, in an adjusted pressure signal (Pr *), the detected fundamental vibration behavior (Pb) can be eliminated.

The representation of 3 is analogous to 2 , The adjusted pressure signal (Pr *) is preferably provided during injection operation, ie, in a period of time overlapping or alternate execution of fuel injections. For reasons of simplified representation are in 3 however, pressure changes due to fuel injections are omitted.

The actual fuel pressure in the high-pressure section (HP) is detected as the pressure signal (Pr), and transition parameters for (planned) pump delivery are determined.

The determination of the transition parameters (XA, XF) can be based on the base pressure level in the period (Tpre) before a planned pumping promotion and / or on the basis of a planned mass production during the pumping promotion, in particular by retrieving the parameter values from the during the Test interval created map.

The fundamental vibration behavior (Pb) in the time interval (Tpre) before the scheduled pumping is detected. The detection can take place, for example, by averaging the currently measured pressure signal (Pr) in the time interval (Tpre). Alternatively or in addition, a previously determined value / data set for the basic vibration behavior (Pb) can be used. This can be particularly useful if in the time interval (Tpre) before the pumping promotion one or more fuel injections are carried out, which could falsify the determination result.

On the basis of the planned pumping, an expected pressure signal (Pex) is calculated for the time interval (Ttr) during the pumping promotion and / or for the time interval (Tpost) after pumping. The calculation may be in the above too 2 explained way.

On the basis of the at least one detected transition parameter (XA, XF) and the detected fundamental vibration behavior (Pb) in the time interval (Tpre) before pumping, the expected changed basic vibration behavior (Pb *) in the time interval (Ttr) during the Pumping and / or calculated in the time interval (Tpost) after the pumping promotion.

That is, the changes in amplitude response and / or frequency response (for one or more identified vibrations) observed in the test interval may be translated to one or more vibrations identified in the current fundamental vibration behavior (Pb).

The pressure signal (Pr *) adjusted by pump delivery influences in the time interval (Ttr) during pump delivery and / or in the time interval (Tpost) after pump delivery is calculated by calculating from the sensor-detected pressure signal (Pr) the corresponding values of the expected pressure signal (Pr). Pex) and the expected changed fundamental vibration behavior (Pb *), in particular by subtraction.

The provision of the pressure signal (Pr *), which is adjusted by pump delivery effects, can be done in real time, in particular if the transition parameters (XA, XF) are stored in a map and are retrieved accordingly in real time.

In 3 In the lower part for the time interval (Ttr) and the time interval (Tpost) during and after pumping, the adjusted pressure signal (Pr *) is shown according to the following equation: Pr * = Pr - Pex - Pb *

In the time interval (Tpre), the adjusted pressure signal (Pr *) can be determined by elimination of the determined fundamental vibration behavior (Pb) from the measured pressure signal (Pr), for example according to the following equation: Pr * = Pr - Pb

In a method for controlling or controlling the injection behavior of at least one fuel injector ( 22 ) (Control method), the adjusted pressure signal (Pr *) can be used in any manner. In particular, a known control method for a time interval (Ttr, Tpost) during or after a pump delivery instead of the measured pressure signal (Pr), the adjusted pressure signal (Pr *) are supplied. Alternatively or additionally, a known control method may be adapted to the provision of the adjusted pressure signal (Pr *) during the entire time sequence, in particular by omitting the otherwise double executed steps for averaging in the time interval (Tpre) before pumping.

In the method for controlling the injection behavior, one or more fuel injections may be performed overlapping in time with a pumping feed or directly subsequent to a pump feed, i. within the time intervals (Ttr, Tpost).

Modifications of the invention are possible in various ways. In particular, all claimed, described or shown features can be combined with each other in any manner, replaced with each other, supplemented or omitted.

The internal combustion engine ( 12 ) may preferably be a diesel engine. There may be several fuel tanks ( 20 ), in particular in each case a separate fuel storage ( 20 ) for each fuel injector ( 22 ). The disclosed methods for detecting the pressure change and for purifying the pressure signal may be carried out for a single point or for several points within the high pressure section (HP), in particular in parallel for a pressure change in a fuel tank ( 20 ) and on or in a fuel injector ( 22 ). Accordingly, two or more pressure sensors ( 36 ) may be provided in the high pressure section (HP).

There can be several high-pressure pumps ( 18 ), which perform pumping operations simultaneously, overlapping or alternating. LIST OF REFERENCE NUMBERS 10 A fuel supply system Fuel supply system 12 internal combustion engine Internal combustion engine 14 Fuel Tank Fuel tank 16 Low pressure pump Low-pressure pump 18 High pressure pump High-pressure pump 20 Fuel storage Fuel storage 22 Fuel injector Fuel injector 24 compression chamber Compression chamber 25 Compression means / piston Compression means / piston 26 Outlet valve Outlet valve 27 Compression engine / cam Compression drive / cam plate 28 control valve Control valve 30 Control Unit / Electronic Control Unit - ECU Control device / electronic control unit - ECU 32 combustion chamber Combustion chamber 34 crankshaft Crank shaft 36 pressure sensor Pressure sensor HP High-pressure section High-pressure section LP Low pressure section Low-pressure section pr Actual pressure signal on the sensor Actual pressure signal at sensor Pr * From effects of pump delivery adjusted pressure signal Pressure signal cleared of effects from pump feed pb Basic vibration behavior Basic oscillation behavior Pb * Changed basic vibration behavior Modified basic oscillation behavior Pex Expected pressure signal due to mass production Expected pressure signal due to mass feed Pd Differential pressure signal Differential pressure signal pd ' Differential pressure signal Differential pressure signal apre Amplitude before pumping Amplitude before pump feed atr Amplitude during pumping Amplitude during pump feed Acts Amplitude after pumping Amplitude after pump feed tpre Time interval before pumping Time interval before pump feed Ttr Time interval during pumping Time interval during pump feed tpost Time interval after pumping Time interval after pump feed FPRE Frequency behavior before pumping Frequency behavior before pump feed Fpost Frequency behavior after pumping Frequency behavior after pump feed DPH Change of the phase position Variation of phase position dF Change of frequency Variation of frequency there gain Amplification factor XA Amplitude modification parameters Amplitude modification parameter XF Frequency modification parameter Frequency modification parameter

Claims (7)

Method for detecting pressure changes in a pressure signal (Pr) in the high-pressure section (HP) of a fuel supply system ( 10 ) for an internal combustion engine ( 12 ), the fuel supply system ( 10 ) a high pressure pump ( 18 ), a fuel storage ( 20 ) for storing high-pressure fuel, and at least one of the fuel storage ( 20 ) supplied fuel injector ( 22 ), and wherein the fuel pressure in the high-pressure section (HP) is sensed as the pressure signal (Pr), characterized in that the method comprises the following steps to be carried out in a test interval: Detecting the basic vibration behavior (Pb) of the actual pressure signal (Pr) in a time interval (Tpre) before pumping the high-pressure pump ( 18 ); - Carrying out a pumping subsidy; - Detecting the actual pressure signal (Pr) in a time interval (Ttr, Tpost) during and / or after the pumping promotion; - Calculation of an expected pressure signal (Pex) in a time interval (Ttr, Tpost) during and / or after the pumping promotion on the basis of the amount of fuel supplied to the high-pressure section (HP) during pump delivery; - Determining a difference signal (Pd, Pd ') between the detected actual pressure signal (Pr) and the calculated expected pressure signal (Pex) in the time interval (Ttr, Tpost) during and / or after the pumping promotion; - Comparison of the difference signal (Pd, Pd ') with the basic vibration behavior (Pb) in the time interval (Tpre) before pumping to determine at least one transition parameter (XA, XF) to describe the change in the basic vibration behavior due the pumping promotion, in particular a gain factor (dA). A detection method according to claim 1, wherein a pressure sensor ( 36 ) in or at the fuel storage ( 20 ) is arranged. A detection method according to claim 1 or 2, wherein a pressure sensor on a fuel injector ( 22 ) is arranged. Method for providing a pumping signal (Pr *) adjusted by pumping influences, characterized by the following steps: detecting an actual fuel pressure in the high-pressure section (HP) of a fuel supply system ( 10 ) as a pressure signal (Pr); - Detecting at least one transition parameter (XA, XF) for pressure changes, which are caused by a pump delivery, in particular according to the method of claim 1; - Detecting the fundamental vibration behavior (Pb) of the actual pressure signal (Pr) before pumping; - Calculation of an expected pressure signal (Pex) in a time interval (Ttr, Tpost) during and / or after the pumping promotion on the basis of the amount of fuel supplied to the high-pressure section (HP) during pump delivery; - calculation of an expected changed basic vibration behavior (Pb *) in a time interval (Ttr, Tpost) during and / or after pumping; Calculation of the pressure signal (Pr *) adjusted by pump delivery influences during and / or after pump delivery (Ttr, Tpost) by elimination of the expected pressure signal (Pex) and the expected changed basic vibration behavior (Pb *) from the detected pressure signal (Pr) in the time interval (Ttr, Tpost) during or after pumping. A provisioning method according to claim 4, wherein in a time interval (Tpre) before pumping, an adjusted pressure signal (Pr *) is provided by eliminating the basic vibration behavior (Pb) in said time interval (Tpre) from the detected pressure signal (Pr). Method for controlling the injection behavior of at least one fuel injector ( 22 ) of an internal combustion engine ( 12 ), wherein an injected fuel amount based on a history of the fuel pressure in the high pressure section (HP) of a fuel supply system ( 10 ) of the internal combustion engine ( 12 ) is controlled or regulated, characterized in that the determination of the injection quantity is carried out on the basis of a pump delivery-adjusted pressure signal (Pr *), which is calculated according to one of the preceding claims. Control method according to claim 6, wherein at least one fuel injection is performed overlapping in time with a pumping feed or directly subsequent to a pumping feed.

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