Method for operating an electronic pressure regulator

Abstract

Method for operating a pressure regulator for controlling the pressure (p) of a gaseous fuel for an internal combustion engine of a motor vehicle that can be operated with the gaseous fuel, wherein at least one value (w) characterizing a control deviation is determined and a function of the pressure regulator is checked as a function of the detected value (w), wherein a frequency (f) of an oscillation of the pressure (p) is detected, wherein the function of the pressure regulator is checked as a function of the detected value (w) and the detected frequency (f) in order to evaluate a control quality of the pressure regulator.

Description

The invention relates to a method for operating a pressure regulator for controlling the pressure of a gaseous fuel for an internal combustion engine that can be operated with the gaseous fuel. In some countries, there are plans to make functional diagnostics mandatory for electronic pressure regulators in gas-powered vehicles. Currently, electronic pressure regulators in gas-powered vehicles only monitor quasi-static control deviations, meaning deviations that must persist for a certain period of time to detect a malfunction. For example, pressure fluctuations with a frequency of less than 1 Hz, whose average value is at the setpoint, are not detected. However, such pressure fluctuations can still lead to increased emissions. As a representative example of the state of the art, DE 10 2006 019 404 A1 describes a pressure regulator comprising a control unit, a pressure reducer controlled by the control unit, and a throttle connecting the gas outlets of the control unit's working chamber and the pressure reducer. An actuator, which converts electrical signals and acts on the valve of a bypass device, allows for targeted changes to the gas pressure in the control unit's working chamber. Simultaneously, the position of the pressure reducer's bypass valve can be influenced, thereby setting its outlet pressure to a predetermined setpoint. However, the dynamic control behavior of the pressure regulator is insufficiently adjustable with regard to its control deviations. This also applies to two-stage pressure regulators with a first mechanical stage and a second electronically controlled stage. Furthermore, document JP 2001 - 193 571 A describes a method for operating a pressure regulator for controlling the pressure of a gaseous fuel for an internal combustion engine that can be operated with the gaseous fuel, characterized in that at least one value is determined and a function of the pressure regulator is checked as a function of the detected value. Document JP 2011 - 220 821 A discloses a method for diagnosing a “slave controller”, wherein, based on measurement signal values ​​of a sensor representing a pressure or flow rate of a fuel gas, an anomaly of the “slave controller” is diagnosed by means of vibration waves that occur after a predetermined change in the output measurement signal values. It is therefore an object of the present invention to provide a method of the type mentioned at the outset which enables particularly advantageous monitoring of the pressure regulator, regardless of its design. This problem is solved by a method for operating a pressure regulator with the features of claim 1. Advantageous embodiments with expedient and non-trivial further developments of the invention are specified in the dependent claims. According to one aspect, the present invention relates to a method for operating a pressure regulator for controlling the pressure of a gaseous fuel for an internal combustion engine, in particular a motor vehicle, that can be operated with the gaseous fuel. According to the invention, at least one value characterizing a control deviation is determined. Depending on the determined value, the function of the pressure regulator is checked. By monitoring the pressure deviation from a desired setpoint, the control quality of, for example, an electronic pressure regulator can be evaluated. This provides an additional diagnostic function, enabling the reliable detection of malfunctions in the pressure regulator and, consequently, in the internal combustion engine or gas system. The frequency of pressure oscillations is recorded, and the function of the pressure regulator is checked based on the recorded value and frequency to assess its control quality. The pressure in question can be, in particular, a low gas pressure, which prevails in one section of the combustion engine's gas system and is lower than the high pressure of the gaseous fuel in a second section of the system. Monitoring the frequency of the low gas pressure represents another input parameter for evaluating the control performance of the pressure regulator. Including the frequency in this monitoring can lead to particularly high control performance. The method according to the invention makes it possible to detect a malfunction of the pressure regulator that can lead to increased emissions but is not detected by previously used diagnostic systems due to its dynamic nature. This allows emissions from gas-powered combustion engines, particularly in motor vehicles, to be kept low. If a malfunction is detected using the method, this can be communicated to the driver of the vehicle. The driver can then, for example, visit a workshop to have the malfunction rectified. According to another embodiment, the control performance of the pressure regulator is evaluated based on the value characterizing the control deviation. This evaluation of the pressure regulator's control performance allows for a broader consideration of non-static control deviations. This enables the detection of control deviations that only occur for a very short time. Pressure fluctuations with a frequency of less than one hertz (< 1 Hz), which average at the setpoint but nevertheless lead to increased emissions, can also be detected. Pressure regulator deviations refer to deviations between the actual pressure value and a desired setpoint. The pressure regulator's function is to adjust the actual pressure value as closely as possible to the setpoint. According to one embodiment, the value characterizing the control deviation is evaluated with respect to the magnitude and / or frequency of a pressure oscillation relative to a ratio between engine speed, engine load, and / or lambda oscillation in the exhaust gas stream of the internal combustion engine. Intake manifold pressure can be used to characterize the engine load. By considering the engine speed, engine load, and / or lambda oscillation in the exhaust gas stream when determining the value characterizing the control deviation, the value can be evaluated with particular reliability by incorporating the engine characteristics in the respective engine characteristic curve field. Other input variables for determining the value characterizing the control deviation can include, for example, the temperature of the fuel, especially in the first sub-range, and / or the high pressure, and / or an unsteady value characterizing the unsteady behavior of the internal combustion engine. According to another embodiment, the pressure regulator is operated, i.e., controlled and / or regulated, depending on the value characterizing the control deviation. By controlling or regulating the pressure regulator based on the value characterizing the control deviation, an adapted control or regulation of the pressure regulator can be carried out directly, in addition to determining the control deviation or control quality, so that pollutant emissions can be kept particularly low. Further features, advantages and details of the invention will become apparent from the following description of preferred embodiments and from the drawings; these show in: Fig. 1 a flowchart of a method for operating an electronic pressure regulator for controlling the pressure of a gaseous fuel of an internal combustion engine that can be operated with the gaseous fuel according to a first embodiment; Fig. 2 a flowchart of the method according to a second embodiment; and Fig. 3 a flowchart of the method according to a third embodiment. Fig. 1 shows a flowchart of a method for operating an electronic pressure regulator to control the pressure of a gaseous fuel in a combustion engine of a motor vehicle that runs on gaseous fuel. The gaseous fuel is, for example, CNG (Compressed Natural Gas), which is stored under pressure in a tank of the combustion engine's gas system. The gas system serves to supply the internal combustion engine, for example, a reciprocating piston engine, with gaseous fuel. The gas system has a first section, a low-pressure section, in which the gaseous fuel is at a lower pressure. This lower pressure is also referred to as low gas pressure. The gas system also has a second section, the high-pressure section, in which the gaseous fuel is at a higher pressure than the lower pressure. This higher pressure is also referred to as high gas pressure. The pressure regulator serves to regulate at least one of the pressures, particularly the low gas pressure, or both pressures, i.e., to adjust the actual pressure to a desired, predefined setpoint. In the first step S1 of the procedure, a value w characterizing a control deviation is determined, for example, by recording it. This value w thus characterizes a deviation of the pressure actually set by the pressure regulator from the desired setpoint. The value w characterizing a control deviation is then stored in step S2. Finally, the second step S2 is followed by a third step S3, in which the function of the pressure regulator is checked as a function of the recorded or determined value w. By determining the value w characterizing the control deviation and checking the function of the pressure regulator as a function of the recorded value w, the control performance of the electronic pressure regulator can be evaluated.This also makes it possible to detect malfunctions of the pressure regulator that lead to increased pollutant emissions, but which, due to their temporal dynamics, are not detected by conventional diagnostic systems. Through appropriate control and / or regulation measures, the pressure regulator can then be brought into a pollutant-minimizing control state. Fig. 2 shows a flowchart of the method according to the invention. The pressure to be set by means of the pressure regulator is denoted by p in Fig. 2. In this method, the value w, which characterizes the control deviation, is determined. Furthermore, the frequency f of a pressure oscillation p is monitored. The pressure regulator is controlled or regulated taking into account the value w, which characterizes the control deviation, and the detected frequency f of the pressure oscillation p, which is indicated here by a setpoint dp. By including the frequency f, the condition of the pressure regulator can be very accurately assessed. Fig. 3 shows a flowchart of the method according to a further embodiment. In this embodiment, the value w, which characterizes the control deviation, is evaluated in terms of magnitude and frequency relative to a rotational speed n and a motor load v. This allows the motor load v and the rotational speed n to be used as additional parameters in the evaluation and control of the pressure regulator, offering additional possibilities for reliably detecting malfunctions.

Claims

Method for operating a pressure regulator for controlling the pressure (p) of a gaseous fuel for an internal combustion engine of a motor vehicle that can be operated with the gaseous fuel, wherein at least one value (w) characterizing a control deviation is determined and a function of the pressure regulator is checked as a function of the detected value (w), wherein a frequency (f) of an oscillation of the pressure (p) is detected, wherein the function of the pressure regulator is checked as a function of the detected value (w) and the detected frequency (f) in order to evaluate a control quality of the pressure regulator. Method according to claim 1 characterized in that the control quality of the pressure regulator is evaluated on the basis of the value (w) characterizing the control deviation. Method according to one of the preceding claims, characterized in that the value (w) characterizing the control deviation is evaluated with respect to the magnitude and / or frequency (f) of a pressure oscillation (p) in relation to a ratio between a rotational speed (n) and an engine load (v) of the internal combustion engine. Method according to one of the preceding claims, characterized in that the pressure regulator is operated depending on the value (w) characterizing the control deviation.

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