BACKGROUND

The invention relates to electro-hydraulic actuators.

Electro-hydraulic actuators, or electro-hydrostatic actuators, (EHA) are apparatuses, in which at least a fluid pressure actuator, a pump driving the actuator and an electric motor rotating the pump are integrated. Electro-hydraulic actuators thus replace hydraulic systems with self-contained actuators operated solely by electrical power. Electro-hydraulic actuators eliminate the need for separate hy draulic pumps and tubing, simplifying system architectures and improving safety and reliability. Electro-hydraulic actuators are used in applications, where it is ben eficial not to have an external hydraulic system with external pumps, tubing and the like. Electro-hydraulic actuators are also used in applications, where simplicity of system architecture and safety and reliability are essential, such as in aerospace industry. An example of such a known EHA is shown in Figure 1 that illustrates schematically an electro-hydraulic actuator 1 comprising a cylinder 2, a piston 3 configured to move within the cylinder and a rod 4 attached to the piston. The cyl inder 2 typically comprises two working chambers 5a, 5b configured to move the piston 3 and the rod 4 as a result of pressure medium provided within the working chamber(s) 5a, 5b to affect in each case an effective area 6a, 6b of the piston 3. The electro-hydraulic actuator 1 of Figure 1 also comprises a hydraulic pump 7 config ured to provide pressure medium to and from the working chambers 5a, 5b, and an electric motor 8 rotating the pump 7.

One of the problems and disadvantages associated with the above ar- rangement is that an external reservoir (not shown in Figure 1) is needed to absorb excess fluid. Additional issues arise from the speed requirements of the hydraulic pump/motor, where cavitation can occur if the inlet pressure is too low and from possible overheating of the electric motor connected to said pump/motor.

BRIEF DESCRIPTION An object of the present invention is to provide a new electro-hydraulic actuator. The object of the invention is achieved by an electro-hydraulic actuator characterized by what is stated in the independent claim. Some embodiments of the electro-hydraulic actuator are disclosed in the dependent claims.

The solution is based on the idea of providing a self-contained electro- hydraulic actuator. An advantage of the apparatus is that it requires no or a minimal num ber of external components.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached [accompanying] drawings, in which

Figure 1 illustrates an embodiment of a known electro-hydraulic actua tor (prior art);

Figure 2 illustrates an example of an embodiment of an electro-hydrau- lie actuator, in which multiple chambers are used to achieve symmetrical areas;

Figure 3 illustrates an example of an embodiment of an electro-hydrau lic actuator, in which a priming pump is integrated, providing an elevated inlet pressure for the main pump, thus preventing cavitation;

Figure 4 illustrates an example an embodiment of an electro-hydraulic actuator, in which the priming pump provides an elevated inlet pressure for the main pump and a cooling flow for the electric motor; and

Figure 5 illustrates an example of a cylinder of an electro-hydraulic ac tuator as a line drawing, where the upper half is shown in cross section.

The figures are schematic and are not shown in scale. DETAILED DESCRIPTION

As mentioned above, one problem associated with known electro-hy draulic actuators is that an external reservoir is needed to absorb excess fluid. The reason for this is that the two areas of the cylinder on opposite sides of the piston are unequal, which necessitates the need for an external reservoir, such as a hy- draulic accumulator, to absorb the differential volume. The differential volume may be caused by the geometrical imbalance. In addition to or instead of the differential volume caused by the geometrical imbalance in the electro-hydraulic actuator, the external reservoir may also be used for compensating the compressibility of the oil volume. Figure 2 illustrates an embodiment of an electro-hydraulic actuator 1, wherein the cylinder 2 comprises at least three chambers and at least two of said chambers comprise working chambers 5a, 5b configured to move the piston 3 and the rod 4 as a result of pressure medium provided within the working chamber(s) 5a, 5b to affect in each case an effective area 6a, 6b of the piston 3. In other words, the cylinder 2 comprises at least three chambers and at least two of said chambers comprise working chambers 5a, 5b configured to move the piston 3 and the rod 4 as a result of pressure medium provided within each of the working chamber(s) 5a, 5b to affect a corresponding effective area 6a, 6b of the piston 3.

In the embodiment of Figure 2, the electro-hydraulic actuator 1 further comprises a hydraulic pump/motor 9 in fluid connection with each of the working chambers 5a, 5b for providing pressure medium to and from the working chambers 5a, 5b, and an electric motor 8 rotating the pump/motor 9. A pump/motor refers to a hydraulic machine operative both as a pump and as a motor. The pump/motor 9 may comprise for instance a fixed displacement hydraulic pump/motor. In the embodiment of Figure 2, at least two of the working chambers 5a,

5b of the electro-hydraulic actuator comprise equal volumes. More particularly, in the embodiments of figures 2 to 5, the cylinder 2 comprises two working chambers 5a, 5b. In other words, the effective areas, or cross-sectional areas, of the two work ing chambers 5a, 5b are equal. Thereby, the volumes of a first working chamber 5a and a second working chamber 5b are equal. Thus, the volumes displaced by a movement of the piston 3 in the first working chamber 5a and the second working chamber 5b are equal but opposite, whereby the volume of one of the working chambers 5a, 5b decreases by an amount equal to that the volume of the other working chamber increases. The effective areas, or cross-sectional areas, of the working chambers 5a, 5b being equal means that the difference of the effec- tive/cross-sectional areas of the first working chamber 5a and the second working chamber 5b is less than or equal to 3 percent. This kind of an electro-hydraulic ac tuator may be referred to as a symmetrical electro-hydraulic actuator. In such an actuator there is no need for a reservoir or the need for a reservoir is minimized. In the embodiment of Figure 2, at least one of the chambers of the cyl inder 2, which is not one of the working chambers 5a, 5b, is a reservoir chamber 11 configured to act as an integrated reservoir. In other words, the reservoir cham ber 11, which is a chamber of the cylinder 2, can be configured to absorb excess fluid in the hydraulic system, whereby it acts as an integrated reservoir. An ad- vantage of such an embodiment is that no external reservoir is needed, for instance for thermal expansion and/or oil compressibility. Although the embodiments of the Figures 2 to 5 each have one reservoir chamber 11, it should be noted that in other embodiments, the electro-hydraulic actuator 1 may comprise more than one reservoir chambers 11. According to an embodiment, in an electro-hydraulic actuator 1, for in stance in an electro-hydraulic actuator of Figure 2 or an electro-hydraulic actuator according to another embodiment described in this description, the leakage pres sure medium from the pump/motor 9 may be configured to be guided to the reser voir chamber 11. Thereby the reservoir chamber 11 may be configured to act as an expansion chamber for the pressure medium leaked from the pump/motor 9. An advantage of such an embodiment is that a reservoir can be provided for pressure medium leaked from the pump/motor 9 without providing the hydraulic system with an external reservoir.

According to an embodiment, such as the embodiment of Figures 2, 3 and 4, a first working chamber 5a may be provided between the rod 4 and the outer tube 17 of the cylinder 2. The cylinder may be provided with at least one first chan nel 15 for providing pressure medium into the first working chamber 5a.

According to an embodiment, the rod 4 may be formed as hollow. In other words, the rod 4 may be configured to determine an internal cavity inside the rod 4. In such an embodiment, a second working chamber 5b may be provided in the cavity inside the rod 4. The cylinder may be provided with at least one second channel 16 for providing pressure medium into the first working chamber 5b.

According to an embodiment, the reservoir chamber 11 may be pro vided inside the cylinder 2, at an opposite side of the piston 3 compared to the first working chamber 5a. In other words, the reservoir chamber 11 may be provided within the outer tube 17 of the cylinder 2 at a side of the piston 3 opposite to that on which the rod 4 is provided.

According to an embodiment, the electric motor 8 may comprise a var iable speed electric motor, preferably a bi-directional variable speed electric mo tor. According to an embodiment, the electric motor 8 may comprise a permanent magnet motor. Such variable speed electric motors and permanent magnet motors as such are known in the art and are, thus, not described in more detail in this de scription.

According to an embodiment, the electro-hydraulic actuator 1 may be configured to act as a four-quadrant electro-hydrostatic actuator. In this descrip- tion, a four-quadrant electro-hydrostatic actuator refers to an electro-hydraulic ac tuator capable of brake and drive the output, such as the linear movement of the rod 4 inwards the cylinder 2 and outwards from the cylinder 2, in both directions of the output, such as in both directions of the movement. For instance, a four-quad- rant electro-hydrostatic actuator may be configured to both drive and to brake the movement of the rod 4 in both positive and negative direction of movement of the rod 4. This means that the pump/motor 9 can rotate in either direction and the electro-hydraulic actuator 1 may be configured to selectively either drive or brake this output regardless of the direction of rotation of the pump/motor. Such an elec tro-hydraulic actuator can be configured to recuperate energy. Preferably, an elec tro-hydraulic actuator configured to act as a four-quadrant electro-hydrostatic ac- tuator can be configured to recuperate energy electrically. Thereby, such electro- hydraulic actuators can be used for energy regeneration. An advantage of such em bodiments is that a variable-speed, bi-directional force generation may be pro vided simultaneously with energy regeneration.

According to an embodiment, the electro-hydraulic actuator 1 com- prises a priming pump 12 arranged in parallel with the pump/motor 9. An example of such an embodiment is shown in Figure 3. Such an electro-hydraulic actuator 1 may otherwise be similar to the electro-hydraulic actuator 1 of the embodiment of Figure 2 and/or comprise a combination of features of other embodiments de scribed in this description. An advantage of such embodiments is that the size of the pump/motor 9 can be decreased, since the priming pump 12 can increase the inlet pressure for the pump/motor 9. Thereby, the cost, size and weight of the pump/motor 9 and, thereby, the electro-hydraulic actuator 1 can be lowered.

According to an embodiment, the priming pump 12 may be further in fluid connection with a cooling circuit 13 of the electro-hydraulic actuator 1. The cooling circuit 13 may comprise a cooling element 10. An example of such an em bodiment is shown in Figure 4. Such an electro-hydraulic actuator 1 may otherwise be similar to the electro-hydraulic actuator 1 of the embodiment of Figure 2, Figure 3 and/or comprise a combination of features of other embodiments described in this description. The cooling circuit 13 may be configured to provide a cooling pres- sure medium flow for the electric motor 8. In other words, the priming pump 12 may provide cooling pressure medium to the cooling circuit 13 to cool down the electric motor 8. Preferably, in such an embodiment, the cooling circuit 13 is also in fluid connection with the reservoir chamber 11. An advantage of embodiments provided with such a cooling circuit is that the electric motor requirement may be downsized. Thereby, the size and/or the power requirement of the electric motor can be reduced.

According to a further embodiment, the priming pump 12 may be con nected to the cooling circuit 13 via a valve arrangement configured to provide the pressure medium flow to the cooling circuit in a same direction despite the direc- tion of rotation of the pump/motor 9. This enables advantages explained in con nection with the cooling circuit 13 in a four-quadrant operation and simpler design, because the cooling pressure medium is configured to cool down the electric motor 8 in a similar manner despite the direction of rotation of the pump/motor 9.

The valve arrangement may comprise one or several valves 14, such as non-return valves, configured to provide the pressure medium flow to the cooling circuit in a same direction despite the direction of rotation of the pump/motor 9. Some examples of such valves 14 and valve arrangements are shown in Figures 3 and 4, for example. For the sake of clarity, not all of the valves in Figures 2, 3 and 4 have been provided with reference numbers. It should also be noted that a similar effect of guiding the pressurized fluid can be provided with other kinds of combi- nations of valves besides the embodiment shown in the figures.

The electro-hydraulic actuator 1 according to one of these embodi ments comprising the cooling circuit 13 may otherwise be similar to the electro- hydraulic actuator 1 of the embodiment of Figure 2 and/or comprise a combination of features of other embodiments described in this description. An advantage of such embodiments is that, due to the cooling of the electric motor 8 and thereby lower temperature of the electric motor 8, the electric motor 8 can be configured to run at a higher speed and/or overloaded.

Figure 5 illustrates an example of a cylinder of an electro-hydraulic ac tuator as a line drawing, where the upper half is shown in cross section. The cylin- der 2 of an electro-hydraulic actuator 1 shown in Figure 5 may comprise features of one or several of the embodiments described above, for instance in connection with at least one of Figures 2 to 4, and features similar to those described in con nection with other embodiments are marked with the same reference number.

According to an embodiment, the electro-hydraulic actuator 1 is further configured to supply and/or regenerate power for at least one external component.

The external component refers to a component external to the electro-hydraulic actuator itself. Such an external component may comprise for instance at least one of the following: an accumulator or an actuator, such as a cylinder, a pump, a motor and/or a pump/motor. The electro-hydraulic actuator 1 may be connected hydrau- lically to the at least one external component via a second valve arrangement.

According to an embodiment, the electro-hydraulic actuator 1 may be provided with an integral linear sensor (not shown). An advantage of such an em bodiment is that the position of the piston and/or the rod can be determined.

According to an embodiment, in an electro-hydraulic actuator 1 accord- ing to an embodiment of a combination of embodiments described in this descrip tion, the position of the piston 3 and/or the rod 4 may be configured to be determined on the basis of rotation pulses measured from the electric motor 8. This kind of embodiments of the electro-hydraulic actuator 1 have several advantages, such as eliminating the need for a linear position sensor, since the position of the head of the rod 4 or the position of the piston 3 and/or the rod 4 can be approxi- mated without using a linear sensor. Such embodiments with position integration also enable a use of the electro-hydraulic actuator for a servo-control operation.

An advantage of embodiments, wherein the electro-hydraulic actuator 1 is provided with position determination equipment, such as the integral linear sensor or equipment for transferring information about pulses measured from the electric motor 8, is that such an electro-hydraulic actuator may be configured to work as a standalone, electro-hydraulic servo. Furthermore, such an electro-hy draulic servo does not require any plumbing. Instead such an electro-hydraulic servo can be operated via a CAN message and electric power.

According to an embodiment, the hydraulic pump/motor 9 may com- prise a high-efficiency hydraulic pump/motor, for example. According to another embodiment, a bi-directional hydraulic pump/motor with an efficiency dimen sioned to eliminate the need for reservoir, in other words a pump/motor with lower efficiency, may be used instead of a high-efficiency hydraulic pump-motor. In such embodiments with a lower efficiency hydraulic pump/motor the reservoir chamber 11 may be used solely for cooling fluid. This may be beneficial in applica tions, where the cooling is particularly important.

It is clear for a person skilled in the art that the electro-hydraulic actu ator may comprise other components, such as frames, valves and the like, some of which are also shown in the figures. Electro-hydraulic actuators described in this description may be used in many kinds of applications, but they are particularly useful in applications ena bling electro-mobility, even for heavy-duty and outdoor applications.

It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The inven tion and its embodiments are not limited to the examples described above but may vary within the scope of the claims.