Technical Field

The invention relates to an actuator for control of dose of fuel injected by a high- pressure fuel injection pump of a compression-ignition engine, comprising a rotary electromagnet with a rotor on a shaft wherein the shaft is mounted in at least one bearing and carries a lever for controlling the pump.

Background Art

An injection valve and an injection system with such an injection valve is known from the document US2013037622. The injection valve is situated at the very end of the fuel system, i.e. before the combustion chamber of the engine space, into which fuel is injected based on an electric impulse from the control unit. The injection valve of US 2013037622 is in principle a double-acting electromagnet with a core, electromagnet coils and return springs that maintain the electromagnet in the initial position. The control of the quantity of fuel injected by this valve is implemented in such a way that an electric impulse from the control unit, sent to one of the coils, causes an upward or downward movement of the rod. This movement opens one of the conical valves, to which fuel from pressure reservoirs has already been supplied.

Further, an actuator for fuel dose control is known, the fuel being injected by a high-pressure fuel injection pump of a compression-ignition engine. Such an actuator is an electromagnetic device capable of adjusting an exact rotation angle of its shaft. Thus, it is a rotary proportional electromagnet with a position sensor. During the operation of the engine, the entire injection system and thus the actuator is exposed to the effect of intensive vibrations in a wide range of operational temperatures under a possible influence of further environmental impacts and chemicals

Most known designs of rotary electromagnets use permanent magnets that are glued on the rotor. In such a type of structures, the phenomenon is used that the stator coil together with its poles is an electromagnet and depending on the current flow direction through the poles it attracts or repels suitably positioned poles of the permanent magnet. Such types of structures may also have a higher number of poles than two to achieve a better course of the output torque at the required working angle. In such a case, the permanent magnet must be precisely positioned due to a high sensitivity of the position to the output parameters of the actuator.

A further undesired variability of output parameters results from the differences of magnetic fields of individual pieces of permanent magnets.

When permanent magnets are used, a return spring is usually provided to enable return to the zero position. Without this spring, a certain torque must be produced for the return to the zero position that is necessary for the permanent magnet on the rotor to pass over the stator poles that it is attracted to. A return spring positioned in such a way introduces further variability of monitored parameters of individual pieces of actuators with its adjustment and differences of characteristics.

In known designs, the connection of the actuator coil and possibly the position sensor is not implemented in such a way to protect the actuator from undesired effects of external influences. Mainly, there is not a sufficient degree of protection with a cover, i.e. resistance to the action of oil substances, penetration of water and foreign particles.

The rotation angle sensor in the feedback loop is part of the actuator itself and cannot be easily replaced within routine maintenance. Such an integrated sensor itself does not have a sufficient coverage that would protect it from undesired influences that may act inside the actuator body.

The mounting of movable parts of known types of actuators is not suitably designed to ensure long service life under exposure to operational vibrations at demanding conditions of some target applications.

Summary of Invention

The disadvantages of the prior art are eliminated by an actuator for control of dose of fuel injected by a high-pressure fuel injection pump of a compressionignition engine, comprising a rotary electromagnet with a rotor on a shaft wherein the shaft is mounted in at least one bearing and carries a lever for the pump control, according to the invention the principle of which is that the rotor comprises two rectangular arms of magnetically mild steel that are arranged at a distance from each other on a common shaft in the stator. An annular coil that is fixed to the stator protrudes into the space between the arms. The shaft is provided with a return spring and at least one position sensor.

The inventive actuator makes it possible to achieve a significantly lower variability of the output parameters. An advantage is the absence of permanent magnets, which cause a considerable part of such a variability in known designs.

The rotor of the actuator is composed of several parts, so it can be easily assembled into the whole due to the position of the coil in the space between the rotor arms. This enables efficient use of the space and a reduction of the actuator weight.

The actuator may be situated in the pump flange to enhance rigidity of the whole, and thus to increase vibration resistance. This concept also brings a reduction of the overall weight and an improvement of the ability to dissipate waste heat of the actuator coil.

The arms can be advantageously arranged on the common shaft in alignment.

In a preferred embodiment, the return spring is connected to the pump control lever. In another preferred embodiment, both the arms have a rectangular shape with rounded shorter sides that follow the inner surface of the stator.

In still another preferred embodiment, the stator is pressed into a housing that is hermetically closed with a lid.

In another preferred embodiment, the shaft is mounted in a pair of bearings, arranged in the housing.

Brief Description of Drawings

The invention will be described in a more detailed way using a particular example of embodiment of the actuator for fuel dose control according to the invention, shown in drawings wherein individual figures illustrate:

Fig. 1 - a longitudinal cross-section of the actuator;

Fig. 2 - a transversal cross-section of the actuator of Fig. 1.

Description of Embodiments

An embodiment of an actuator for control of dose of fuel injected by a high pressure fuel injection pump of a compression-ignition engine according to Fig. 1 and 2 comprises a housing 8 that can be hermetically closed with a lid 10 against the effect of external influences up to the ingress protection level up to IP69K according to EN 60529.

In the housing 8, a stator 6 is mounted by compression and in a pair of bearings 5 a rotor 1 is mounted, comprising of a shaft 3 carrying two rectangular arms 2 made of magnetically mild steel, arranged in alignment. The shaft 3 further carries a lever 7 for injection pump control. A return spring to return the shaft 3 into the initial position, which is not shown here, is connected to the lever 7. The return spring pushes the lever 7 via a control rod of the pump.

Skilled persons will find it obvious that instead of the two bearings 5, overhung mounting of the shaft 3 in one axial-radial bearing is possible.

In an embodiment, which is not shown here, the arms 2 may not be arranged on the shaft 3 in alignment. In such a case, however, the arrangement of the stator 6 would have to be adapted in the corresponding way.

In the embodiment shown, at each end of the shaft 3, an encapsulated position 9 sensor is arranged to measure the rotation angle of the actuator. The second position sensor 9 is optional and reduces the risk of the engine running in the emergency mode in case of a defect of the primary position sensor 9.

The arms 2 are arranged on the rotor 1 shaft 3 in such a way that they are spaced from each other. In the embodiment shown, both the arms 2 have a rectangular shape with rounded shorter sides that follow the inner surface of the stator 6.

An annular coil 4 that is fixed to the stator 6 protrudes into the space between the arms 2.

When direct current is supplied to the coil 4, a magnetic field is produced in the magnetic circuit to generate torque acting upon the rotor 1 with the arms 2 and causing a partial rotation of the lever 7, which is connected to the control mechanism of the controlled injection pump. Feedback is provided by the position sensors 9.

The rotary movement of the actuator is transformed to the linear movement of the control rod by means of the lever 7. Together with the engine control unit and other components of the system, an injection pump designed in this way is part of the injection system of the engine of a machine or vehicle.

Industrial Applicability The actuator for control of dose of fuel injected by a high-pressure fuel injection pump of a compression-ignition engine is used to ensure precise dosage of fuel of a compression-ignition engine by controlling the position of the control rod of the high-pressure injection pump.

List of reference signs

1 rotor

2 arm 3 shaft

4 coil

5 bearing

6 stator

7 lever 8 housing

9 position sensor

10 lid