Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
1999-08-23
2001-05-22
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S456000, C123S1980DA
Reexamination Certificate
active
06234148
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and a device for monitoring a pressure sensor which sets the pressure in a pressure accumulator, in particular in a high-pressure accumulator for a fuel supply system.
High-pressure accumulators are used in fuel supply systems, primarily in fuel injection systems for internal combustion engines which operate with very high injection pressures. Such injection systems, which, in diesel engines, are known as common-rail systems, have marked advantages, as compared with conventional injection systems, in terms of flexibility and costs. In these injection systems, a high-pressure pump conveys fuel out of a fuel tank into the pressure accumulator, via which the fuel is then made available at injection valves which are provided in the cylinder heads of the engine. The process of injection into the cylinders is triggered by supplying current to the injection valves. The injection volume depends on the pressure present at the injection valves and on the duration of the current supply.
The pressure in the pressure accumulator is regulated by a pressure actuator which is set by an electronic engine control unit. This engine control unit, via a sensor connected to the pressure accumulator, also detects the pressure level, so that the pressure actuator can be adjusted correctly. The pressure sensor therefore also performs an essential function in setting the pressure in the pressure accumulator. A malfunctioning of the pressure sensor and the resulting error in the pressure control of the pressure accumulator may result in an impaired injection behavior and therefore in an impaired combustion characteristic, and this, in turn, may entail an increased emission of pollutants.
Pressure sensors which are equipped with a function monitoring device and with additional measurement transducers are known. However, these additional measurement transducers result in a considerable increase in the cost of manufacturing the sensors. Furthermore, such function monitoring devices must also be adapted in their construction to the respective circumstances in the internal combustion engine, thus incurring additional costs. Published German patent application DE 195 13 158 A1 discloses a method for detecting a leak in a fuel supply system, in which the gradient of the fuel pressure is evaluated in the system after the fuel pump has been switched off. A fault detection is carried out if the pressure reduction in a part of the fuel supply system takes place more quickly than expected. Furthermore, German Patent DE 41 31 401 C1 discloses a method and a device for monitoring pressure sensors in a medical operating system. The range of fluctuation of the pressure signals for a specific operating pressure, which are delivered by the pressure sensors to be monitored, is compared with a desired range of fluctuations for detecting faults.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and a device for monitoring the functioning of a pressure sensor which overcome the above-mentioned disadvantages of the heretofore-known methods and devices of this general type and which determine the pressure in a pressure accumulator regulated by a pressure actuator and which check the functioning and operability of the pressure sensor in a simple and reliable manner without requiring additional measurement transducers.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for monitoring a pressure sensor determining a pressure in a pressure accumulator regulated by a pressure actuator. The method includes the steps of:
calculating an expected pressure value in a pressure accumulator for a given point in time based on a holding pressure preset at a pressure actuator and based on a detected rate of change in a mass balance of a medium contained in the pressure accumulator;
determining a pressure value in the pressure accumulator with a pressure sensor at the given point in time;
comparing the expected pressure value with the pressure value determined by the pressure sensor for detecting a difference value; and
detecting a malfunction in the pressure sensor if an absolute value of the difference value exceeds a predetermined difference value.
In accordance with another mode of the invention, a gradient of the expected pressure value and a gradient of the pressure value determined by the pressure sensor are calculated, the gradients are compared with each other, and a malfunction in the pressure sensor is detected if an absolute value of the difference between the gradients exceeds a predetermined value.
In accordance with yet another mode of the invention, the holding pressure in the pressure accumulator is calculated from a control value of the pressure actuator, which is delayed by a predetermined time constant, the holding pressure being preset at the pressure actuator for the given point in time.
In accordance with a further mode of the invention, the holding pressure is calculated from the control value in dependence of a rotational speed of an internal combustion engine and/or a cooling temperature of the internal combustion engine.
In accordance with yet a further mode of the invention, the rate of change in the mass balance of the medium contained in the pressure accumulator at the given point in time is calculated from an injection mass flow into an internal combustion engine, from a leakage mass flow of injection valves of the internal combustion engine, and from a feed mass flow supplied to the pressure accumulator, the pressure sensor is monitored during a pressure build-up operating state of the internal combustion engine with the pressure actuator closed.
With the objects of the invention in view there is also provided in an injection system having a pressure sensor determining a pressure in a pressure accumulator regulated by a pressure actuator, a device for monitoring the pressure sensor. The device for monitoring comprises:
an accumulator pressure evaluation unit for calculating an expected pressure value in a pressure accumulator for a given point in time based on a holding pressure preset at a pressure actuator and based on a detected rate of change in a mass balance of a medium contained in the pressure accumulator; and
a comparator unit connected to the accumulator pressure evaluation unit for comparing the expected pressure value calculated for the given point in time with a pressure value determined by a pressure sensor at the given point in time and detecting a malfunction in the pressure sensor if an absolute value of a difference between the expected pressure value and the pressure value determined by the pressure sensor exceeds a predetermined difference value.
In accordance with another feature of the invention, the comparator unit includes a model pressure calculation unit for calculating a gradient of the expected pressure value, a sensor pressure calculation unit for calculating a gradient of the pressure value determined by the pressure sensor, and a gradient difference unit connected to the model pressure calculation unit and to the sensor pressure calculation unit for calculating a gradient difference between the calculated gradients and for detecting a malfunction in the pressure sensor if an absolute value of the gradient difference between the calculated gradients exceeds a predetermined gradient difference value.
In accordance with yet another feature of the invention, a pressure actuator evaluation unit is connected to the accumulator pressure evaluation unit and has a delay element of the first order for calculating the holding pressure preset at the pressure actuator from a control value of the pressure actuator, delayed by a predetermined time constant.
In accordance with a further feature of the invention, the pressure actuator evaluation unit includes a holding pressure mapping unit for calculating the holding pressure from the control value of the pressure actuator in dependence on a rotational speed of an i
Birkner Christian
Hartke Andreas
Gimie Mahmoud M
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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