Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
1999-01-11
2001-02-20
Miller, Carl S. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S541000
Reexamination Certificate
active
06189508
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of fuel injection in multicylinder engines. A fuel pre-pressure is generated in order to convey the fuel inside an inertia pipe via electromagnetically or mechanically controlled valves in the acceleration pipes. This occurs by recirculating the fuel to the reservoir via a return line, and subsequently shutting off the valve, in order to provoke a steep pressure rise by water hammer effect. Each injection nozzle associated with a shutoff valve is supplied with a high-pressure wave. The invention also pertains to a device for carrying out the method. Such technical solutions are required mainly for injecting fuel in internal combustion engines. Preferred fields of application are multicylinder gas engines with Diesel pilot injection, multicylinder compression ignition engines, multicylinder spark ignition engines, and multicylinder engines for the use of alternative fuels.
2. The Prior Art
Multicylinder engines are predominantly equipped with fuel pumps, which are driven by camshafts. The injection rate supplied to the operating cylinders has, in this connection, a marked dependence upon the engine speed with respect to droplet size and spray penetration length. On the other hand, in common rail systems, a constant fuel pressure at maximum value is always prevailing in the rail or overall system up to the injection nozzles. The maximum pressure, however, is only required temporarily during injection of the fuel due to the opening of one or a plurality of electromagnetically controlled injection nozzles.
In this case, the droplet size as well as the properties of the fuel jet remain the same irrespective of the engine speed. However, the fuel high-pressure realized by the pump or pumps is exploited only to a minor extent, leading to a disadvantageous energy balance. For example, in a four-cylinder four-stroke engine with a speed of 3000 revolutions per minute, the cycle period for consecutive injections is 40 ms. The duration of injection per injection period, however, maximally comes to only 2 ms, which corresponds with an energetic utilization of 5% at the most.
Proposals for technical solutions are known according to which provision is made for utilizing the water hammer principle for supplying the high-pressure wave required in one-cylinder engines for injecting the fuel into the operating cylinder. In this context, the pre-pressure required from the fuel pump is limited to a fraction of the fuel pressure needed on the respective injection nozzle. For exploiting this principle in multicylinder engines, the number of fuel pump drives, fuel pumps, as well as fuel pre-pressure lines and fuel return lines correspond to the number of engine cylinders.
In the case of cam- or camshaft-operated fuel pumps of the customary type, the drawbacks of the known solution for fuel injection substantially consist of the dependence of droplet size and spray characteristics on the engine speed. On the other hand, in the case of common rail systems, the dependence of the spray characteristics on the engine speed is avoided, but at the expense of unacceptable energetic efficiency because the high-pressure made available over the entire cycle period instead of the only-injection-duration.
If the water hammer principle, which is known for one-cylinder engines, is applied for multicylinder engines, the requirements with respect to machine and control engineering would multiply because of the required multitude of fuel pumps to be used, implicating as well the same number of fuel feed and fuel return lines to the high-pressure units. This leads to increased cost as well as to impairment of the size/performance ratio.
Therefore, it is an object of the invention to overcome the drawbacks of the known state of art. The goal is a technical solution which, with high energetic efficiency and low machine engineering expenditure, offers the possibilities for improving the size/performance ratio and the price/performance ratio in the manufacture of multicylinder engines.
SUMMARY OF THE INVENTION
According to the invention, the problem is substantially solved by a method of fuel injection in multicylinder engines in which substantially one single fuel pump conveys the fuel with pre-pressure into a pre-pressure rail, which is common to several engine cylinders. The pre-pressure corresponds to only a fraction of the required injection pressure. When the adjusted pre-pressure is exceeded, the fuel is fed from the pre-pressure common rail via pre-pressure limiting valves into the return rail, which is also common to a plurality of engine cylinders.
The pre-pressure common rail is connected to the return common rail by acceleration pipes, one pipe being provided with a shutoff valve. The fuel accelerating through a pipe when a shutoff valve is open is conveyed into the return rail, which is common to several engine cylinders. The pressure conditions in the pre-pressure common rail and in the return common rail are maintained constant with simple means, so that optimal flow conditions can be assured in any acceleration pipe over the entire speed range. In any circuit consisting of acceleration pipe and shutoff valve—between pre-pressure and return rail—at least one injection nozzle is provided. The pressure rise generated based on the water hammer effect when a shutoff valve is closed is used for the fuel injection via the respective injection nozzle.
In a preferred method, the energy of the fuel stored in the return common rail is exploited for the fuel-conveying system. The energy expenditure for supplying the fuel pre-pressure required in the pre-pressure common rail is additionally reduced.
The acceleration pipes can be connected to wave dampers as a measure to prevent undesirable impairment of the system injecting the fuel.
For generating the pre-pressure in the pre-pressure common rail, it is possible to employ a plurality of fuel pumps. The number of fuel pumps to be operated can be selected depending on the given requirements with respect to engine load.
In another embodiment of the invention, the acceleration pipe, the shutoff valve, the wave damper and the injection nozzle for every cylinder can be combined in one compact high-pressure unit per operating cylinder. If necessary, the high-pressure unit can be operated with thermal isolation by means of isolator materials and/or cooling by a cooling medium integrated in the unit.
Furthermore, it is possible to actuate the shutoff valves in the acceleration pipes of the injection system for multicylinder engines by means of solenoids.
The invention also comprises a device consisting of fuel pumps, acceleration pipes with shutoff valves, and return pipes to the fuel supply system. In the device, a pre-pressure rail common to a group of cylinders or to all cylinders of the multicylinder engine is arranged between at least one fuel pump and at least one acceleration pipe. A return rail common to a group of cylinders or to all cylinders of the multicylinder engine is arranged between the acceleration pipe and the fuel supply system. Furthermore, one or a plurality of pressure-limiting valves are arranged between the pre-pressure common rail and the return common rail.
In a special embodiment of the device, the acceleration pipe, the shutoff valve, the injection nozzle and, if need be, the wave damper corresponding to one cylinder of the engine are arranged in a common high-pressure module.
In each high-pressure module, one or several injection nozzles can be arranged between the pre-pressure rail and the return rail.
The shutoff valve and the injection nozzles of a high-pressure unit can be designed as a common structural component or in several structural components connected by lines.
Furthermore, in another embodiment of the device, there are one or several fuel pumps arranged on the pre-pressure common rail.
It is also possible to arrange one or several high-pressure modules on each operating cylinder.
In another embodiment of the device, the pre-pressure rail is designed
Collard & Roe P.C.
Forschungs- und Transferzentrum e.V. an der westsächsischen Hoch
Miller Carl S.
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