Internal-combustion engines – Charge forming device – Fuel flow regulation between the pump and the charge-forming...
Reexamination Certificate
2002-06-19
2004-10-19
Miller, Carl S. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel flow regulation between the pump and the charge-forming...
C123S516000, C123S276000
Reexamination Certificate
active
06805105
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to an improved fuel supply system designed to supply to diesel engines an alternative fuel such as dimethyl ether (DME) which is lower in viscosity and susceptible to vaporization.
2. Background Art
Fuel now being developed as an alternative to diesel fuel such as light oil is showing a tendency to have a lower viscosity and higher evaporability. Typical of such an alternative fuel is dimethly ether which has a cetane number nearly equal to that of the diesel fuel and is lower in concentration of NOx and HC contained in exhaust emissions of the engine. For these reasons, dimethly ether is being expected to become an alternative fuel for diesel engines which produces black smoke in small quantities over the whole of an output range.
Japanese Patent First Publication Nos. 10-281029 and 10-281030 each teach a fuel injection pump for diesel engines employing dimethly ether as a main fuel. The fuel injection pump is designed to have a decreased gap (less than 3 &mgr;m) between a plunger and a plunger barrel in order to reduce a leakage of fuel and to return the fuel leaking out of the gap to an inlet pipe of the engine through a leakage gas return line.
A technical paper IMechE (C517/022/96) describes a fuel injection system designed to supply a dimethly ether fuel through a high-pressure fuel supply pump to a common rail and to injectors for realizing low-emission vehicles.
In a case where the gap between the plunger and the barrel in the structure, as taught in each of the above publication Nos. 10-281029 and 10-281030, is 3 &mgr;m, this value is typical of standard pumps. Further, returning of the fuel under high pressures to the engine is achieved using a single line. It is, thus, difficult to decrease a leakage of the fuel to a desired quantity. Particularly, under high temperature conditions, the viscosity of the fuel is lowered, thus resulting in a overmuch increase in leakage of the fuel. The total of the fuel leaking out of the fuel injection pump returned to the inlet pipe of the engine and the fuel sprayed from the injectors, thus, exceeds an allowable level, which may result in a difficulty in controlling the diesel engine correctly.
The system, as taught in the technical paper IMechE (C517/022/96), is designed to produce a pressure intermediate between an injection pressure and a fuel feed pressure to avoid evaporation of the fuel and returns a leaking fuel to a fuel path kept at the intermediate pressure. The injector is equipped with a solenoid valve. A difference between the intermediate pressure and the injection pressure is used to open the injector. This eliminates a leakage of the fuel from the injector to a lower-pressure side completely, but however, resulting in an overmuch leakage of the fuel from high to intermediate pressure side.
Further, the solenoid valve built in the injector is of a hydraulically servo type and thus complex in structure, which result in a difficulty in ensuring a quick response.
The production of the intermediate pressure requires a large number of control valves and intermediate tanks, thus resulting in a difficulty in using the system with diesel engines.
The system is also designed to relieve the fuel from the feed tank, the intermediate tank, and the common rail to a purge tank using a solenoid valve during standstill of the engine. This, however, requires a supply pump to output a large quantity of fuel when it is required to fill the common rail with the fuel, thus resulting in a time delay in starting the engine.
SUMMARY OF THE INVENTION
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide an alternative fuel supply system which has a simple structure designed to reduce the quantity of fuel leaking out of a high-pressure pump and return it to a fuel tank, thereby ensuring a desired quantity of fuel to be fed to an internal combustion engine, which results in improved fuel economy, engine startability, and engine drivability.
According to one aspect of the invention, there is provided a fuel supply apparatus for supplying fuel such as a dimethly ether used as an alternative to a typical fuel for an internal combustion engine. The fuel supply apparatus comprises: (a) a high-pressure pump working to feed a fuel which is susceptible to vaporization to injectors from a fuel tank through a common rail under a given high pressure; (b) a return line extending from the high-pressure pump to the fuel tank; and (c) a pressurizing mechanism working to add to the return line a back pressure higher than a vapor pressure of the fuel. The addition of the back pressure higher than the vapor pressure of the fuel facilitates liquidizing of the fuel. When the fuel is injected into the injectors, a high-pressure feed pressure and an injection pressure are held within the closed circuit in a fluid-tight fashion without use of an intermediate pressure. The fuel leaking from the high-pressure pump at a lower pressure is introduced into a purge tank or an inlet pipe of the engine, thereby resulting in a decrease in leakage of the fuel, which improves the efficiency of burning of the fuel and ensures the startability and drivability of the engine. In a case where a dimethly ether which is susceptible to vaporization and has a low viscosity is used, exhaust emissions of the engine contains less NOx, HC, and black smoke.
In the preferred mode of the invention, the high-pressure pump includes a pump chamber to which the fuel from the feed pump is inputted through a fuel gallery at a feed pressure, a plunger reciprocating within a plunger chamber formed within a cylinder to pressurize the fuel within the pump chamber and inject the pressurized fuel into the engine through a discharge valve and each of the injectors, a higher-pressure leakage line, and a lower-pressure leakage line. The higher-pressure and lower-pressure leakage lines work to withdraw the fuel leaking out of the pump chamber through a gap between the plunger and the plunger chamber following reciprocating motion of the plunger.
The higher-pressure leakage line communicates with the fuel gallery through a feed line. The lower-pressure leakage line communicates with a sealed chamber formed beneath the plunger.
The fuel flowing through the lower-pressure leakage line is withdrawn through a withdrawing means provided in the cylinder.
The withdrawing means is implemented by a leakage path formed in a side wall of the cylinder.
The apparatus further comprises a solenoid valve which is disposed within an upper end portion of the cylinder and includes a valve member, a valve body, a non-magnetic member, and a plurality of cores. The valve member works to selectively open and close a line connecting between the pump chamber and the fuel gallery to control an amount of the fuel flowing out of the discharge valve. The valve body is disposed within the upper end portion of the cylinder in a fluid-tight fashion. The cores are arranged coaxially with each other through the non-magnetic member and welded rigidly in a fluid-tight fashion inside the solenoid valve.
The discharge valve is opened in response to a pressure which acts thereon and is lower than the feed pressure.
The apparatus further comprises a pressure regulator connected to the fuel gallery. The pressure regulator includes a valve which is urged by a spring into a closed state. The valve of the pressure regulator is moved by a back pressure arising from a vapor pressure of the fuel against a mechanical pressure produced by the spring so that the valve is opened to discharge the fuel flowing from the fuel gallery.
The apparatus further comprises a pressure sensor and a temperature sensor which measure a pressure and a temperature of the fuel whose bulk modulus of elasticity and density are sensitive to changes in pressure and temperature of the fuel and a control circuit which works to correct a discharged amount of the fuel from the high-pressure p
Kato Masaaki
Sasaki Satoru
Takeuchi Hisaharu
Denso Corporation
Miller Carl S.
Nixon & Vanderhye PC
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