1. Field of the Invention
The invention relates to an apparatus for direct gasoline injection in a piston engine. The apparatus is intended in particular for Otto cycle engines but it can also be employed in Diesel engines.
2. Brief Description of the Prior Art
Piston engines that have a hydraulic valve control system are known; the hydraulic valve control system replaces a widely used mechanical valve control by means of camshafts. In the hydraulic valve control system, gas exchange valves of the piston engine are actuated hydraulically. The energy required for actuation is furnished by a high-pressure hydraulic oil pump, which is typically embodied as a piston pump and which puts the hydraulic oil under high pressure and pumps it into a high-pressure hydraulic oil reservoir. The hydraulic oil, under high pressure, from the high-pressure hydraulic oil reservoir is delivered to the gas exchange valves for opening and/or closing, and the delivery is typically controlled by magnet valves, or in other words electrically. In this case, the control system is an electrohydraulic valve control system.
German Patent Disclosure DE 44 07 585 A1 proposes using fuel instead of hydraulic oil for the hydraulic valve control system. Serving as the high-pressure pump is a fuel high-pressure pump of a fuel injection system, to whose high-pressure reservoir the gas exchange valves of the piston engine are connected. This reference considers it an advantage that only one high-pressure pump is needed for both the hydraulic valve control system and for the fuel injection.
In the hydraulic actuation of gas exchange valves with fuel as the hydraulic fluid, it is considered problematic that the fuel for actuating the gas exchange valves is delivered to a cylinder head of the piston engine and is thereby heated, which is intrinsically unwanted. It also appears questionable whether fuel is a suitable hydraulic fluid. Fuel is considerably less viscous than typical hydraulic oils, so leakage problems must be feared. Fuel also lacks lubricating properties, and so if fuel is used as the hydraulic fluid, the hydraulic system is not lubricated by hydraulic fluid; on the contrary, the fuel cleans off any films of lubricant from the surfaces it acts on. The known apparatus is moreover suited only for Diesel engines, because only such engines generated sufficient fuel pressure for hydraulically opening the gas exchange valves. In Otto engines, the gasoline injection is done at low pressure, such as 4 bar of overpressure compared to atmospheric pressure. A pressure of this magnitude is in no way sufficient to actuate the gas exchange valves of a piston engine.
The apparatus according to the invention for direct gasoline injection in a piston engine, in particular an Otto engine, has a pressure booster for two different pressure media. The pressure booster is acted upon by hydraulic oil, at high pressure, from the high-pressure hydraulic oil pump of a hydraulic valve control system of the piston engine. The pressure booster converts the pressure of the hydraulic oil into a higher pressure, with which it acts upon fuel. The pressure booster delivers the fuel, put under high pressure, to a high-pressure fuel reservoir, to which at least one fuel injection valve is connected.
The invention has the advantage that an existing high-pressure hydraulic oil pump of a hydraulic valve control system is used to generate a requisite high pressure for the direct fuel or gasoline injection. Thus an additional high-pressure pump for the fuel is not needed. Another advantage of the invention is that by the use of a pressure booster for two different pressure media, the fuel is separated form the hydraulic fluid for the hydraulic valve control system, and thus a hydraulic oil can be used as the hydraulic fluid. The invention additionally has the advantage that a pressure level of the hydraulic valve control system is approximately of the same order of magnitude as a pressure level in direct gasoline injection; that is, a pumping pressure of the existing high-pressure hydraulic oil pump is approximately of the same order of magnitude required for the direct gasoline injection.
The pressure level of the hydraulic valve control system is between approximately 50 and 250 bar. Modern direct gasoline injection systems have a pressure level of up to about 100 bar; pressure levels of up to 200 bar are expected, while for later development, fuel injection pressures of up to about 400 bar are expected. Since the pressure booster readily makes a pressure boost of up to 1:5 possible, the pressure levels for the direct gasoline injection are readily attainable. If the pressure level of the hydraulic valve control system is sufficient for the direct gasoline injection, the pressure booster can even have a boosting ratio of 1:1 and in that case is a pressure medium converter, which has the task of keeping the fuel separate from the hydraulic oil and acting on it with the pressure of the hydraulic oil. If a lower pressure level than for the hydraulic valve control system is sufficient for the direct gasoline injection, then the pressure booster can even have a boosting ratio of less than 1.
The aforementioned pressure levels for the hydraulic valve control system and the direct gasoline injection should be understood to mean high pressure, in the context of the invention. Pressure levels of conventional (intake-tube) gasoline injection systems, for instance of about 4 bar, should be understood as low pressure.
Another advantage of the invention is that it needs only one pressure booster, even for multi-piston internal combustion engines that have more than one injection valve.