This is a U.S. national stage of application No. PCT/EP2016/059159, filed on Apr. 25, 2016. Priority is claimed on German Application No. DE102015207700.4, filed Apr. 27, 2015, the content of which is incorporated here by reference.
The invention relates to a method for controlling a fuel delivery system of an internal combustion engine, having a fuel delivery pump driven by electric motor.
Fuel delivery pumps are used in fuel delivery systems of motor vehicles to meet the fuel requirement of the internal combustion engine. In addition, the operation of additional assemblies, such as suction jet pumps, is made possible by the fuel delivered by way of the fuel delivery pump.
In order to make a precise control of the fuel delivery pump possible, the pressure in the fuel delivery system is required as a relevant variable. The determination of the pressure can take place in a wide variety of ways.
Apparatuses are known in the prior art, which provide a dedicated pressure sensor that detects the pressure in the fuel delivery system. Depending on the configuration of the fuel delivery system, a plurality of pressure sensors can also be installed to determine the pressure at different locations. In the case of gasoline operated motor vehicles, the fuel pressure sensor is typically located in the feed line; it can be mounted there in the vicinity of the fuel delivery pump or in the region of the feed line on the high pressure pump of the internal combustion engine. There is typically a fuel return line only in diesel operated motor vehicles; a fuel pressure sensor can also be provided on the return line there. Therefore, the pressure determination can take place upstream of the fuel delivery pump and/or downstream of the fuel delivery pump.
It is a disadvantage of said apparatuses in the prior art that the sensors are additional structural components that have to be integrated into the fuel delivery system. The fuel delivery system becomes more complex and more expensive as a result. Furthermore, the sensors have to be connected to the vehicle electronics via an additional branch of the wiring harness. This makes the assembly more complex, as a result of which the costs are also increased. Furthermore, dedicated pressure sensors are always associated with a certain risk of failure.
As an alternative, methods are known in the prior art, which permit a control of the fuel delivery system without dedicated pressure sensors. The methods determine an operating mode of the fuel delivery pump which is advantageous for the respective operating situation from characteristic variables detected during the operation of the fuel delivery system, with the aid of characteristic diagrams. To this end, for example, the actuating current of the electric motor of the fuel delivery pump and/or the rotational speed of the fuel delivery pump are/is monitored.
It is a disadvantage of said methods, in particular, that the control of the fuel delivery pump is not optimum, since the determination of the operating mode is often CPU-intensive, and the characteristic variables which are available for the determination are in part not optimum. Furthermore, methods of this type are based on the assumption that the fuel delivery system in the motor vehicle acts like a hydraulic orifice, the consumption quantity of the internal combustion engine being proportional to the orifice opening. This is often not the case in reality, however.
It is therefore an aspect of the present invention is to provide a method that provides an improved control of the fuel delivery system and, in particular, of the fuel delivery pump possible, no pressure sensor being used in the fuel delivery system. Furthermore, an aspect of the invention is to provide a method that can be applied to as great a multiplicity as possible of different fuel delivery systems and to as broad an operating range as possible of fuel delivery systems.
One exemplary embodiment of the invention relates to a method for controlling a fuel delivery system of an internal combustion engine, having a fuel delivery pump that can be driven by an electric motor, the pressure that prevails in the fuel delivery system being determined by way of a volume difference between the fuel quantity delivered by the fuel delivery pump and the fuel requirement of the internal combustion engine and/or of the fuel delivery system.
The fuel delivery pump delivers both the fuel quantity required for the operation of the internal combustion engine and the fuel quantity required for the operation of secondary pumps, such as suction jet pumps. The pressure that prevails in the fuel delivery system can be determined with a knowledge of the fuel delivery system and of the system behavior in the case of different ratios between the fuel delivery quantity and the fuel consumption quantity formed by way of the fuel requirement of the internal combustion engine and the fuel requirement for operating the secondary pumps. In an ideal consideration, merely the fuel requirement of the internal combustion engine is assessed in relation to the delivery quantity of the fuel delivery pump. In a real application, however, the fuel requirement is as a rule, as described above, supplemented by the fuel quantity which is required for operating the suction jet pumps. As a result, the pressure in the fuel delivery system rises somewhat, since an additional pressure loss is produced by way of the suction jet pump and other possibly present consumers. A slightly higher pre-delivery pressure is required as a result.
The pressure loss can be compensated for by way of an increase in the pump rotational speed, since the fuel delivery quantity is increased by way of the increase in the pump rotational speed and the pressure rises slightly at the same time, as a result of which the additional hydraulic losses can be compensated for.
It is particularly advantageous if a calibration is carried out to determine the pressure that prevails in the fuel delivery system, an operating point being set for calibration purposes, at which operating point the fuel requirement of the internal combustion engine is identical to the fuel quantity delivered by way of the fuel delivery pump, a pressure that is known in advance prevailing in the fuel delivery system at the calibration point.
Although a pressure change can be determined by way of the consideration of the difference between the fuel quantity delivered by way of the fuel delivery pump and the fuel requirement produced by way of the internal combustion engine, the absolute pressure value cannot be determined, since an initial pressure level has to be defined to this end. This is advantageously achieved by way of a calibration of the fuel delivery system at a calibration point. The calibration point is advantageously defined by the fact that the fuel quantity delivered by the fuel delivery pump and the fuel requirement of the internal combustion engine are of equal magnitude. In order to make an even more precise calibration possible, the fuel requirement for operating the suction jet pumps in the fuel delivery system can also be added, in addition to the fuel requirement of the internal combustion engine.
An initial value for the pressure in the fuel delivery system can be fixed by way of an operation of the fuel delivery system at said calibration point, starting from which initial value the pressure can be determined at every time and in every operating state. On account of the knowledge of the respective fuel delivery system, the pressure that prevails at the calibration point is in each case known in advance and can preferably be stored in one of the control units. The pressure can be determined empirically, for example, or can be calculated by way of simulations. The pressure might also be determined using an exemplary comparative system having a pressure sensor. Each individual fuel delivery system has, in its respective configuration, a different pressure level at the calibration point.
It is also advantageous if, starting from the calibration point, the change in the pressure is determined in a manner dependent on the fuel quantity delivered by way of the fuel delivery pump. This is possible in a particularly simple way, since the pressure in the fuel delivery system changes predictably. For instance, the pressure increases in the case of an increase in the fuel delivery quantity and a constant consumption quantity. Conversely, the pressure is reduced in the case of a falling fuel delivery quantity and a likewise constant consumption quantity.
There is preferably a calibration point for each consumption quantity and each fuel delivery quantity, which calibration point represents a defined pressure that is known in advance in the fuel delivery system.
One preferred exemplary embodiment is distinguished by the fact that the prevailing pressure in the fuel delivery system is determined within a predefinable operating range of the fuel delivery pump in a manner dependent on a change in the fuel delivery quantity, starting from the fuel delivery quantity at the calibration point.
This is particularly advantageous, since, starting from the pressure level at the calibration point, there is a known dependence that is specific for the respective fuel delivery system between the fuel delivery quantity and the pressure in the fuel delivery system. In addition, the respective consumption quantity of the fuel is to be taken into consideration, which consumption quantity consists of the fuel requirement of the internal combustion engine and the fuel quantity which is possibly required for the operation of suction jet pumps. The fuel delivery quantity which is required for the operation of suction jet pumps is as a rule considerably lower than the fuel requirement of the internal combustion engine, with the result that a very accurate result is achieved in a first approximation, even if the fuel quantity required for the operation of the suction jet pump is disregarded.
It is also to be preferred if a characteristic diagram is used to determine the pressure, the characteristic diagram generating a relationship between the fuel quantity delivered by way of the fuel delivery pump, the fuel requirement of the internal combustion engine and/or of the fuel delivery system, and the pressure that prevails in the fuel delivery system.
A characteristic diagram of this type or a plurality of characteristic diagrams of this type can be determined in a simple way by way of empirical tests or by way of a calculation for a respectively known fuel delivery system. The characteristic diagrams can be stored in the control units used for controlling and regulating the fuel delivery system. In this way, a very accurate determination of the pressure in the fuel delivery system can be achieved using simple means.
Moreover, it is advantageous if the curves of the characteristic diagram which is used to determine the pressure in the fuel delivery system form a straight line with a high ascending gradient for each fuel requirement of the internal combustion engine within a defined pressure range.
In particular, fuel delivery systems that have a wide range of curves which are configured as steeply running straight lines in the relevant characteristic diagrams can advantageously be operated via the method according to the invention. To this end, the characteristic diagrams have the fuel delivery quantity on the X-axis, whereas the pressure which prevails in the fuel delivery system is plotted on the Y-axis. Finally, the fuel consumption quantity is plotted in the characteristic diagram. In the characteristic diagram, the respective curves for the fuel consumption quantities preferably form a straight line with a steep gradient over a broad range, as a result of which in each case one region is generated that allows a precise statement about the respectively prevailing pressure. This is due to the fact that a linear pressure increase and pressure decrease can be assumed along said region configured as a straight line.
Furthermore, it is advantageous if, starting from the pressure at the calibration point, the pressure in the fuel delivery system rises in the case of an increase in the fuel quantity delivered by way of the fuel delivery pump, at a constant fuel requirement of the internal combustion engine. This is due to the fact that a fuel quantity is delivered that cannot be consumed completely by the internal combustion engine, as a result of which ultimately the pressure in the fuel delivery system rises. Fuel delivery systems which do not have any pressure relief valves or other apparatuses for pressure reduction exhibit a behavior of this type.
It is also expedient if, starting from the pressure at the calibration point, the pressure in the fuel delivery system drops in the case of a reduction in the fuel quantity delivered by way of the fuel delivery pump, at a constant fuel requirement of the internal combustion engine. This is due to the fact that the fuel requirement is in practice higher than the fuel quantity delivered by the fuel delivery pump.
Moreover, it is advantageous if a value for the fuel requirement of the internal combustion engine is provided by a control unit of the internal combustion engine. In modern fuel injection systems and internal combustion engines, the respectively required fuel and the consumed fuel are as a rule known very accurately on account of the complexity of the combustion. The value for the fuel requirement can therefore be provided at a high quality without additional complexity by one of the control units that controls the combustion in the internal combustion engine.
Furthermore, it is expedient if the fuel quantity, which is delivered by the fuel delivery pump, is determined via a flow meter, or is determined computationally from the rotational speed of the fuel delivery pump, or is determined from the current, with which the fuel delivery pump is actuated. It is particularly advantageous if no additional physical apparatus is required for determining the fuel quantity, which is delivered by the fuel pump, in order for the fuel delivery system to be of as simple configuration as possible.
Advantageous developments of the present invention are described in the subclaims and in the following description of the figures.
In the following text, the invention will be described in detail using exemplary embodiments, with reference to the drawings, in which:
It can be seen from the curves 4 to 8 that a pressure, which is constant across the fuel requirements 4 to 8, prevails in the fuel delivery system in each case in the case of a match of the fuel requirement 4 to 8 and the fuel delivery quantity on the X-axis 2. The pressure is set when, for example, 20 liters per hour are delivered by the fuel delivery pump and the fuel requirement of the internal combustion engine is likewise 20 s per hour. The substantially constant pressure is dependent on the respective fuel delivery system and can correspondingly be somewhat higher or lower. In the example of
In the case of a fuel requirement that lies considerably above the fuel delivery quantity, the pressure in the fuel delivery system drops greatly. This can be seen in the region 9 of
The curves 4 to 8 result from a simulation and show values for a defined fuel delivery system. Here, this is, in particular, a fuel delivery system that does not act as a hydraulic orifice. Therefore, the fuel consumption quantity of the internal combustion engine is not proportional to the hydraulic orifice formed by way of the fuel delivery system. Depending on the operating mode, the high pressure pump connected downstream of the fuel delivery system and delivers the fuel to the internal combustion engine can contribute to a different appearance of the characteristic diagrams. The basic statement that a constant pressure is set in the fuel delivery system if the fuel consumption quantity coincides with the fuel quantity delivered by way of the fuel delivery system remains unaffected by this, however.
It can be derived from the graphs 1 and 11 of
A substantially constant pressure value can be determined for every fuel delivery system by way of a calibration, which pressure value is used as a starting basis for the pressure determination. Furthermore, the pressure can also be calculated using what is known as a gradient function in the case of a defined consumption quantity in the fuel delivery system. This can take place, for example, by way of a consideration of the different gradients in the case of different fuel volumes that are delivered. The calibrated base value can be stored in a control unit of the fuel delivery system, with the result that a precise determination of the pressure which prevails in the fuel delivery system is possible at every operating time.
A reliable starting basis for volume-based calculations, such as the throughflow control or the throughflow monitoring, is obtained as a by-product of the setting of an operating point, at which the fuel consumption by way of the internal combustion engine and the fuel delivery quantity of the fuel delivery pump coincide. Furthermore, the aging of the fuel delivery pump and the therefore slowly dropping fuel delivery volume can also be compensated for in this way.
The exemplary embodiments of
Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.
Number | Date | Country | Kind |
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10 2015 207 700 | Apr 2015 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2016/059159 | 4/25/2016 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2016/173979 | 11/3/2016 | WO | A |
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20180087458 A1 | Mar 2018 | US |