Internal-combustion engines – Poppet valve operating mechanism – Electrical system
Reexamination Certificate
2001-12-26
2004-01-27
Gimie, Mahmoud (Department: 3747)
Internal-combustion engines
Poppet valve operating mechanism
Electrical system
C123S404000
Reexamination Certificate
active
06681729
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and a device for controlling a gas fill of a plurality of cylinders in an internal combustion engine having variable valve timing.
BACKGROUND INFORMATION
Conventional internal combustion engines have one or more camshafts for controlling the engine valves with a predefined lifting curve. The lifting curve of valve actuators of the engine valves is defined by the design of the camshaft. However, a defined lifting curve does not permit optimal operation of the internal combustion engine in each operating state, since in general, different operating states of the internal combustion engine require different lifting curves.
Because of the fixed lifting curve, control of a gas exchange, i.e. filling a gas into a cylinder and letting gas out, is possible only to a limited extent in a conventional internal combustion engine having cam-actuated valves, and cannot be optimized for all operating states. A gas fill denotes the charge of a combustion chamber of the cylinder with air, added fuel and, depending on the operating state and the type of internal combustion engine, a recirculated exhaust gas from the combustion.
The control of the gas exchange (also known as charge cycle) in a camless internal combustion engine differs in principle from this. In an internal combustion engine having an electrohydraulic, camless valve drive, the engine valve operations are flexible. The quantities of intake air and of residual exhaust gas in each cylinder can be controlled by varying the instant of the opening and/or closing of the intake and exhaust valves. While an electrohydraulic, camless valve drive offers more flexibility, on the other hand, disadvantages exist which do not occur in arrangements having mechanical camshafts.
In systems with fully variable valve timing, the lifting curve of the valve actuators exhibits certain tolerances from actuator to actuator. These deviations of the lifting curves are caused by tolerances of mechanical, hydraulic, magnetic or electrical components of the valve actuators. Furthermore, the lifting curves change due to different wear over time in an unequal manner.
However, different lifting curves produce filling differences between the individual cylinders. This leads to a deterioration in the smooth-running performance of the internal combustion engine, elevated noise emission, increased fuel consumption, and a greater stress on the moving parts of the internal combustion engine, which results in greater wear.
German Patent No.195 11 320 proposes the formation of cylinder-individual correction values for the solenoid-valve control of an electrohydraulic valve actuator. The fresh-gas and residual-exhaust-gas charge is ascertained from a fresh air measured individually for each cylinder and a combustion chamber pressure measured individually for each cylinder, as well as from a temperature, and is compared to pre-determined setpoint values. Thus, a balance of different lifting curves is achieved by suitable determination of the correction values.
To measure these quantities, German Patent No. 195 11 320 proposes using a single air-mass flow sensor in the intake flow and/or a single oxygen sensor in the exhaust-gas flow which is operated on a time-resolving basis. With the detected air quantity, the residual exhaust-gas portion can then be ascertained by offsetting against a combustion chamber pressure measured in a cylinder-individual manner, given a specific piston reference position and the temperature.
However, in the device disclosed in German Patent No. 195 11 320, it is necessary to ascertain the above-indicated measured quantities individually for each cylinder. Thus, it is necessary to arrange at least one combustion-chamber pressure sensor per cylinder. This is very costly, since a pressure sensor must be arranged with access to the combustion chamber of the cylinder. Moreover, the customary pressure sensors are temperature-sensitive, and output inaccurate measured values in response to changing temperatures.
German Published Patent Application No. 42 36 008 describes a cylinder-individual lambda closed-loop control for a system having variable valve timing. There, a lambda probe is used indirectly as filling sensor, in that the fresh-air charge of the cylinder is calculated back with the aid of the injection quantity. However, this device supplies inaccurate calculation values for the fresh-air charge, since because of the necessary rapid calculation, many influence factors such as a temperature of the internal combustion engine, a load status of the internal combustion engine, a combustion-chamber pressure and an ambient temperature cannot be sufficiently taken into account in the calculation. In addition, this device assumes injection valves with a very small tolerance in order to be able to calculate usable results for the fresh-air charge at all.
SUMMARY OF THE INVENTION
An object of the present invention is to specify a method and a device, which are simple and accurate, for controlling a gas fill of a plurality of cylinders in an internal combustion engine having variable valve timing.
In the method for controlling a gas fill of a plurality of cylinders in an internal combustion engine having variable valve timing, a multitude of sampling values of a detection signal of a filling sensor are ascertained by sampling the detection signal with a sampling rate. Furthermore, a first detection interval is determined for a first cylinder. In the following, those sampling values which are within the first detection interval for the first cylinder are summed up. This sum is designated as first sampling-value sum. In addition, the number of sampling values within the first detection interval is counted. This yields a first count value. A first air mass filled into the first cylinder is then ascertained by forming a quotient from the first sampling sum and the first count value.
The advantages attained with the invention are, in particular, that the first air mass filled into the first cylinder is ascertained in a simple manner based on one detection signal. This detection signal is the output signal of a filling sensor. Beyond the detection signal of the filling sensor, it is preferably not necessary in the method of the present invention to acquire further measured quantities such as a combustion-chamber pressure or a temperature. Furthermore, the method according to the invention supplies a precise gas fill, i.e. the first air mass filled into the first cylinder, even when inexact injection valves having great tolerances are used.
In one advantageous refinement of the invention, the first detection interval is variable.
Due to a change in the first detection interval, a selection may advantageously be made as to whether, for example, the detection signal of a filling sensor is evaluated upon opening of the valve or upon closing of the valve. It is thereby possible to determine whether the valve or the valve actuator exhibits more deviations or tolerances during opening or during closing, and whether the valve or the valve actuator has a defect.
In a further advantageous development of the invention, a second detection interval for a second cylinder of the plurality of cylinders of the internal combustion engine is determined. The sampling values within the second detection interval are then summed up for ascertaining a second sampling-value sum. Furthermore, the number of sampling values within the second detection interval are counted. The count value is designated as the second count value. An air mass filled into the second cylinder is then ascertained by forming a quotient from the second sampling-value sum and the second count value. In the following, a gas-fill difference between the first and the second cylinder is then ascertained by comparing the first air mass filled into the first cylinder to the second air mass filled into the second cylinder. A first gas-exchange actuator for actuating the intake valve of the first cylinder and a second gas-exchange actuator for actuating
Beuche Volker
Diehl Udo
Gaessler Hermann
Grosse Christian
Mallebrein Georg
Gimie Mahmoud
Kenyon & Kenyon
Robert & Bosch GmbH
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