TECHNICAL FIELD

The present invention concerns a method and a device for a freely controllable electrically activated valve actuator for controlling the gas flow in 2- or 4-stroke engines.

BACKGROUND

Freely controllable valves allow improved efficiency and substantially reduced emissions, i.e. cleaner exhaust gases. Valve actuators for such freely controllable valves may be pneumatically or hydraulically activated.

Today's valve actuators for freely controllable engine valves often have high energy consumption and/or complex construction and/or have difficulties in quickly closing and opening the valve, i.e. to achieve a short duration.

SUMMARY

The purpose of the invention is to achieve a new actuator technology in the form of an electrically controlled electromechanical valve actuator which is principally simple in its construction, energy efficient and which is capable of quickly opening and closing an engine valve in a cylinder head of an engine. This purpose is achieved by providing the invention with the features described in the patent claims.

According to a first aspect of the invention, there is provided a method for electrically controlling a valve actuator in a 2-stroke or 4-stroke combustion engine, where the actuator comprises a first solenoid with a first plunger and a second solenoid with a second plunger. The engine has at least one cylinder with at least one freely controllable engine valve comprising a valve disc with associated valve stem and a valve spring and where air is introduced, or exhaust gases are evacuated from, a combustion chamber past a lower part of the valve stem with the valve disc via at least one channel in the cylinder, wherein the valve actuator is activatable to open the engine valve. The method is characterized in that both the first and the second solenoid are activated during opening of the engine valve.

In embodiments, the first and second plungers together act on the valve stem during initial opening movement of the engine valve.

In embodiments, the first and second solenoids are arranged in series, preferably such that the first plunger, during the initial opening movement of the engine valve, acts on the second plunger, which in turn acts on the valve stem. The valve spring is preferably arranged to keep the engine valve closed, i.e. to apply a force on the engine valve in such a direction that the valve disc is pressed in the direction of the valve seat. In such an embodiment, the solenoids together act on the valve during opening to overcome the force of the valve spring.

The technology involves using at least two solenoids and an engine valve spring which in a traditional manner keeps an engine valve closed and using a here-called “soft hammer effect” when the engine valve is to be opened.

The first and second plungers are each provided with a stop defined as the position at which respective solenoid exerts maximum force on the plunger.

In embodiments, the for instance two solenoids are arranged in series with each other, wherein the first solenoid has a short stroke and a high strength already at activation compared with the second solenoid which has a long stroke and is weak at activation. In other words, the first solenoid has a shorter stroke and higher strength that the second solenoid. The strengths of both solenoids, i.e. the force with which respective plunger may act, increases as the respective plunger is moved further into the magnetic field until they are completely surrounded in their respective magnetic field. The at least two solenoids are activated together. The plunger of the first solenoid pushes on the plunger of the second solenoid with a strong and even stronger force during its relatively short stroke, which thereby leads to the mentioned soft hammer effect. The plunger of the second solenoid is coupled to, or rests on, the valve stem of an engine valve and acts with pushing force thereon together with the plunger of the first solenoid. When the plunger of the first solenoid has reached its stop, the plunger of the second solenoid has reached sufficiently long into its magnetic field such that the plunger with strong and increasing force acts on the valve stem during further movement of the plunger towards the stop until the stop is reached when the engine valve is fully open.

A problem with using solenoids for opening engine valves is that they need to be strong to overcome the force of the mechanical spring, the engine valve spring, which keeps the valve closed. A disadvantage is that with high strength comes with great size and weight of the moving iron core, the plunger, whose force is to overcome the closing force of the engine valve spring. The weight of the iron core and the valve spring together with the force of the valve spring contravenes the possibility for a short duration, i.e. a short time from that the valve is closed until it is fully open and once again closed. In embodiments, the method comprises that, when the plunger of the first solenoid has reached its stop in the first solenoid, the plunger of the second solenoid continues to act on the valve stem until the plunger of the second solenoid has reached its stop in the second solenoid. In this embodiment, the mass of the iron core in the first solenoid will not be involved during a substantial part of the duration. By means of this method, a significantly short duration is made possible.

The invention is not departed from by placing another solenoid in series with the above described two solenoids. For example, an additional solenoid may be placed before the above mentioned first solenoid. Preferably, this solenoid has a substantially shorter stroke and is substantially stronger than the above mentioned first solenoid.

In embodiments, the first and/or the second solenoid is/are activated just before the engine valve reaches the valve seat, such that the closing movement is retarded. The activation is preferably of short duration, i.e. during a predetermined time period. The activation is preferably started at a predetermined time before the engine valve reaches the valve seat.

According to a second aspect of the invention, there is provided a device for electrically controlling a valve actuator in a 2-stroke or 4-stroke combustion engine, where the actuator comprises a first solenoid with a first plunger and a second solenoid with a second plunger, wherein the engine has at least one cylinder with at least one freely controllable engine valve comprising a valve disc with associated valve stem and a valve spring and where air is introduced, or exhaust gases are evacuated from, a combustion chamber past a lower part of the valve stem with the valve disc via at least one channel in the cylinder, wherein the valve actuator is arranged activatable to open the engine valve. The device is characterized in that both the first and second solenoid are activated during opening of the engine valve. In embodiments, the device is formed as an engine control system.

According to a third aspect of the invention, there is provided a valve actuator for a 2-stroke or 4-stroke combustion engine, where the valve actuator comprises a first solenoid with a first plunger and a second solenoid with a second plunger, wherein the combustion engine has at least one cylinder with at least one freely controllable engine valve comprising a valve disc with associated valve stem and a valve spring, wherein air is introduced, or exhaust gases are evacuated from, a combustion chamber past a lower part of the valve stem with the valve disc via at least one channel in the cylinder, wherein the valve actuator is arranged activatable to open the engine valve. The valve actuator is characterized in that the first and second solenoids are arranged to both be activated during opening of the engine valve.

According to a fourth aspect of the invention, there is provided a valve arrangement for a 2-stroke or 4-stroke combustion engine having at least one cylinder with at least one freely controllable engine valve comprising a valve disc with associated valve stem and a valve spring, wherein air is introduced, or exhaust gases are evacuated from, a combustion chamber past a lower part of the valve stem with the valve disc via at least one channel in the cylinder, wherein the valve arrangement comprises a valve actuator according to the third aspect of the invention and said freely controllable engine valve. In embodiments, the valve arrangement also comprises a device according to the second aspect of the invention.

According to a fifth aspect of the invention, there is provided a 2-stroke or 4-stroke combustion engine comprising at least one cylinder with at least one freely controllable engine valve comprising a valve disc with associated valve stem and a valve spring, wherein air is introduced, or exhaust gases are evacuated from, a combustion space past a lower part of the valve stem with the valve disc via at least one channel in the cylinder. The combustion engine further comprises a valve actuator according to the third aspect of the invention. In embodiments, the combustion engine also comprises a device according to the second aspect of the invention.

Above described embodiments of the method are applicable also as corresponding embodiments of the second, third, fourth and fifth aspects of the invention.

