Background of the invention

[0001] The invention relates to a motor system comprising a pressure medium operated motor and a control valve, the control valve comprising at least one rotating part in order to control a pressure medium flow by means of the control valve.

[0002] The invention further relates to a method in control of a motor system, the motor system comprising a pressure medium operated motor and a control valve, the control valve comprising at least one rotating part in order to control a pressure medium flow by means of the control valve, and the method comprising controlling operation of the pressure medium operated motor by controlling by means of the control valve the flow of the pressure medium flowing to the pressure medium operated motor.

[0003] Pressure medium operated motors may be used in a large number of different applications for the purpose of generating power. Pressure media most commonly used include pressurized air, oil, and water. Oil or water hydraulic motors in particular may be used in applications wherein the motor's shaft is to deliver a large output torque. Pressurized air operated motors, in turn, may be used in applications wherein the output torque required from the motor is smaller. Regardless of the pressure medium used, however, in order to be able to efficiently utilize a pressure medium operated motor the rotation speed of the motor must be controllable.

[0004] The most common way to implement the control of the rotation speed of a pressure medium operated motor is to use a flow control valve. Other possibilities to implement rotation speed control include a displacement control pump and a displacement control motor.

[0005] A flow control valve enables the rotation speed of a motor to be controlled as desired by controlling the pressure medium flow supplied to the motor. In most cases, however, this solution is either inefficient or expen- sive. When the driving power required by the motor is derived from the operating circuit of another actuator, the efficiency of the system is low. In such a case, typically, the operating circuit from which the required driving power is derived is dimensioned to have a higher pressure level than the operating pressure of the motor to be controlled. This means that a pressure difference between the motor and the operating circuit from which the driving power re- quired by the motor is derived directly causes a power loss ^P H = (PI _N ~ PM ) ^{X C} 1 _M ' where P _H is said power loss, p _IN is the pressure of the operating circuit from which the driving power is derived, p _M is the operating pressure of the motor, and q _M is the pressure medium flow supplied to the mo- tor.

[0006] A controllable motor may also be provided with a separate operating circuit of its own, the operating circuit including a pump for feeding a pressure medium to the motor. At its simplest, the pump to be used may be a fixed displacement pump. In such a case, the displacement of the fixed dis- placement pump is always chosen according to the necessary maximum displacement flow. Usually, however, an actuator is used at the maximum displacement flow in special cases only. An extra displacement flow again causes a power loss P _H = (q _MaxM - q _M ) ^X PM - where q _MaxM is the maximum displacement flow to be supplied to the motor.

[0007] A solution with a better efficiency could be achieved by using a variable displacement pump. In such a case, the pump only generates an amount of pressure medium flow necessary for the motor and the the pressure of the pump is determined according to the operating pressure of the motor, whereby in theory it is possible to achieve a 100% efficiency. This solution is, however, expensive since usually the pumps then require electric adjusters and control electronics.

[0008] The rotation speed control of a pressure medium operated motor could also be implemented by using a variable displacement motor, but the problem with the existing variable displacement motors is their failure sus- ceptibility, high price, and large physical size.

[0009] Control valves comprising a rotating part have been used e.g. in gerotor type motors wherein the rotating motion of the motor is generated by an internally-meshing pair of gear teeth. A gerotor type motor has a fixed outer gear and an inner gear, i.e. a gerotor gear, which rotates around the in- ner circle of the fixed outer gear and, simultaneously, around its own axis. While rotating eccentrically along the inner circle of the fixed outer gear and, simultaneously, around its own axis, the gerotor gear forms between itself and the outer gear pressure pockets which have varying volumes. A separate rotating distributing valve arranged in connection with the motor is used for con- necting the motor's expanding pressure pockets to the pressure and the mo- tor's contracting pressure pockets to a tank of the system. The rotation of the distributing valve is synchronized mechanically, via a separate shaft, with the rotation of the motor's gerotor gear in order to enable the connecting of the connections of the system's pressure line and tank line to the expanding and contracting pressure pockets to be timed correctly.

Brief description of the invention

[0010] An object of the present invention is to provide a novel and improved arrangement in a motor system comprising a pressure medium operated motor.

[0011] A motor system according to the invention is characterized in that the motor system further comprises an electric motor connected to the control valve.

[0012] Further, a method according to the invention is characterized by the the motor system further comprising an electric motor connected to the control valve, and controlling, by the electric motor, operation of the control valve in order to control operation of the pressure medium operated motor.

[0013] The motor system comprises a pressure medium operated motor and a control valve, the control valve comprising at least one rotating part in order to control a pressure medium flow by means of the control valve. The motor system further comprises an electric motor connected to the control valve.

[0014] When an electric motor is connected to the control valve, the rotating part in the control valve may be rotated by the electric motor in order to control the flow of the pressure medium to the pressure medium operated mo- tor. Using the electric motor to rotate the control valve and, thus, using the electric motor by means of the control valve to control the rotation of the pressure medium operated motor is advantageous in that it makes the rotation speed of the electric motor simple to control. In such a case, the rotation speed of the pressure medium operated motor may be controlled simply by control- ling the rotation speed of the electric motor.

[0015] Some different embodiments of the solution are disclosed in the dependent claims. Brief description of the figures

[0016] Some embodiments of the invention will be explained in greater detail in the attached drawings, in which

Figure 1 is a schematic side view showing a motor system, Figure 2 is a schematic sectional view showing a motor system according to a basic principle of Figure 1 , as seen from an end of a pressure medium operated motor,

Figure 3 is a schematic sectional end view showing a second motor system according to the basic principle of Figure 1 ,

Figures 4a to 4d schematically show four different use situations in connection with the motor system shown in Figure 3,

Figures 5a and 5b schematically show other two different use situations in connection with the motor system shown in Figure 3,

Figure 6 is a schematic, partially cross-sectional side view showing a third motor system according to the basic principle of Figure 1 ,

Figure 7 schematically shows an embodiment of the motor system of Figure 6, as viewed in a direction of a control valve,

Figure 8 schematically shows a second embodiment of the motor system of Figure 6, as viewed in the direction of the control valve,

Figures 9a and 9b schematically show two different use situations of the motor system of Figure 8, as viewed in the direction of the control valve,

Figure 10 schematically shows a fourth motor system, as viewed in the direction of the control valve,

Figure 1 1a schematically shows a fifth motor system according to the basic principle of Figure 1 ,

Figure 1 1 b schematically shows a control valve to be used in the motor system of Figure 8a,

Figure 12a schematically shows a sixth motor system according to the basic principle of Figure 1 ,

Figure 12b schematically shows a control valve to be used in the motor system of Figure 9a,

Figures 13a, 13b, and 13c are schematic cross-sectional views showing a control valve usable in the motor systems of Figure 11a and 12a,

Figure 14a schematically shows a seventh motor system according to the basic principle of Figure 1 , Figure 14b schematically shows an eighth motor system according to the basic principle of Figure 1 ,

Figures 15a, 15b, and 15c schematically show operation of the motor system of Figure 14b in a use situation thereof, and

Figure 16 is a schematic sectional end view showing a control valve usable in the motor systems of Figures 14a, 14b, 15a, 15b, and 15c.

[0017] For the sake of clarity, the figures show some embodiments of the invention in a simplified manner. In the figures, like reference numerals identify like elements. Detailed description of the invention

[0018] Figure 1 is a schematic side view of a motor system 1. The motor system 1 according to Figure 1 includes a pressure medium operated motor 2, which has a shaft 3, which may be connected to a load (for the sake of clarity not shown in Figure 1 ) intended for the motor 2. As the pressure me- dium, e.g. oil, water or pressurized air may be used, in which case the motor 2 may be e.g. an oil or water operated hydraulic motor or a pressurized air operated motor. The motor system 1 according to Figure 1 further includes a control valve 4. The control valve 4 controls the operation of the motor 2 by controlling the feed of pressurized pressure medium from a pressure medium source 5 along a pressure line PL to the motor 2. A pressure medium flow returning from the motor 2 is controlled to travel along a tank line TL to a pressure medium reservoir 6. The motor 2 is provided with connections or ports schematically shown by arrows A and B in Figure 1. Depending on the operation situation of the motor 2, port A, by means of the control valve 4, may be connected to the pressure line PL and port B to the tank line TL, or vice versa, the optionality being schematically shown by arrows A and B having two heads. The pressure medium source 5 may be e.g. a pump or an accumulator and the pressure medium reservoir 6 may be e.g. a tank and, typically, they belong to the same, larger system or circuit which for the sake of clarity is not shown in Figure 1 and of which the motor system 1 schematically shown in Figure 1 forms only a part. The motor system 1 according to Figure 1 further includes an electric motor 7 whose shaft 8 is connected to the control valve 4 such that the electric motor 7 may rotate the control valve 4 or at least one part thereof, in which case the electric motor 7 may control the operation of the pressure medium operated motor 2 by controlling the operation of the control valve 4, i.e. by controlling, by means of the control valve 4, the pressure medium flow to be supplied to the pressure medium operated motor 2.

[0019] Figure 1 schematically shows, in broken line, a shaft 14 or a connecting shaft 14 which is connected between the control valve 4 and the pressure medium operated motor 2 and which enables the control valve 4 and the pressure medium operated motor 2 to be interconnected, as schematically shown in some embodiments below.

[0020] The motor system 1 shown in Figure 1 may be used in applications of numerous different types wherein a pressure medium operated mo- tor may be used to generate rotational motion necessary in the application. A use object may be e.g. a rock drill provided in a rock drilling rig, wherein the motor system 1 could be used for generating e.g. the rotating motion necessary for rotating a tool of the rock drill.

[0021] Figure 2 is a schematic sectional end view showing a motor system 1 according to a basic principle of Figure 1 while Figure 3 is a schematic sectional end view showing a second motor system 1 according to the basic principle of Figure 1. For the sake of clarity, Figures 2 and 3 show no electric motor 7.

[0022] Figures 2 and 3 schematically show a motor system 1 pro- vided with a gerotor type pressure medium operated motor 2. In gerotor type motors, the rotating motion of the motor is generated by a pair of internally- meshing gear teeth, which includes a fixed outer gear 9 and an inner gear 10, i.e. a gerotor gear 10, which rotates around the inner circle of the fixed outer gear 9 at speed Ω and, simultaneously, around its own axis 10' at speed ω. The rotation speed of the gerotor gear 10 around its own axis 10' is ω = (- 1 /ζ)Ω, where z is the number of teeth of the gerotor gear 10, this number being six in the embodiment shown in Figures 2 and 3. While rotating eccentrically around the inner circle of the fixed outer gear 9 and while simultaneously rotating around its own axis 10', the gerotor gear 10 forms, between itself and the fixed outer gear 9, varying-volume pressure pockets 11 , i.e. expanding pressure pockets and contracting pressure pockets. In the use situation shown in Figures 2 and 3, expanding pressure pockets are indicated by +dV while contracting pressure pockets are indicated by -dV.

[0023] Figures 2 and 3 further show a rotating distributing valve, i.e. a rotating control valve 4, which is arranged in connection with the motor 2 and by means of which the expanding pressure pockets +dV of the motor 2 are connected to the system's pressure line PL, i.e. the operating pressure P of the system, and the contracting pressure pockets -dV are connected to the system's tank line TL, i.e. the tank pressure T of the system. In the control valve 4, pressure connections to be connected to the pressure line PL are indicated by P' while tank connections connected to the tank line TL are indicated by T'. In Figure 2, the control valve 4 rotates clockwise at speed ω, i.e. in the same direction and at the same speed as the gerotor gear 10 rotates around its own axis 10', in which case the control valve 4 is provided with a number of pres- sure connections P' to be connected to the operating pressure P and a number of tank connections T' to be connected to the tank pressure T, alternately, where the number corresponds with the number of teeth of the gerotor gear 10. The direction of rotation of the gerotor gear 10 around the inner circle of the fixed outer gear 9 of the motor 2, in turn, is opposite to the direction of rota- tion of the gerotor gear 10 around its own axis 10'. In Figure 3, the control valve 4, in turn, rotates anti-clockwise at speed Ω, i.e. at the same speed and in the same direction as the gerotor gear 10 rotates around the inner circle of the fixed outer gear 9 of the motor 2, the direction of rotation of the gerotor gear 10 around its own axis 10' being the opposite, in which case the pressure connections P' and the tank connections T of the control valve 4 for connecting the control valve 4 to the pressure line PL or to the tank line TL are simpler since the control valve 4 comprises only one pressure connection P" and one tank connection T'.

[0024] Conventionally, a mechanical connection or synchronization has been provided between the gerotor gear 10 and the distributing valve, i.e. the control valve 4, enabling the above-described relations regarding the mutual rotation of the gerotor gear 10 and the control valve 4. According to the solution, the mechanical connection or synchronization between the gerotor gear 10 and the control valve 4 is removed and the rotation of the control valve 4 is controlled by an electric motor 7, i.e. the electric motor 7 is via its shaft 8 connected to the control valve 4 such that the electric motor 7 controls the rotation of the control valve 4. In such a case, the control valve 4 supplies to the pressure pockets 1 1 the operating pressure P from the pressure line PL and the tank pressure T from the tank line TL such that the motor 2 is forced to ro- tate at the same speed as the control valve 4 rotates. Hence, the motor 2 may be considered to be a mere hydraulic booster system wherein the control valve 4 determines the rotation speed of the motor 2 and the motor 2 generates a desired torque.

[0025] Using the electric motor 7 to rotate the control valve 4 and, thus, using the electric motor 7 by means of the control valve 4 to control the rotation of the pressure medium operated motor 2 is advantageous in that the rotation speed of the electric motor 7 is simple to control. For instance, when the electric motor 7 is a direct-current motor, an accuracy of the order of couple of per cent may be achieved in rotation speed control by controlling the rotation speed of the electric motor 7 only by means of its supply voltage, without as much as utilizing feedback from the real speed of the motor 2. When the electric motor 7 is an alternating current motor, for instance a frequency converter may be used for controlling the rotation speed of the electric motor 7.

[0026] When feedback is utilized in controlling the rotation speed of the electric motor 7 and, therethrough, the rotation speed of the control valve 4 and, further, the rotation speed of the pressure medium operated motor 2, a schematically shown measuring member 12 or a measuring arrangement 12 arranged to measure the rotation speed RPMMEAS of the motor 2 by measuring the rotation speed of the shaft 3 of the motor 2 may further be arranged in the motor system 1 shown in Figure 1 , on the shaft 3 of the pressure medium operated motor 2 or in the immediate vicinity of the shaft 3. The different types of measuring members or measuring arrangements suitable for this purpose are known per se to those skilled in the art. The rotation speed RPMMEAS of the motor 2 measured by the measuring member 12 is communicated to a control unit 1 3 which may be e.g. a frequency converter or another control device capable of comparing the measured rotation speed RPMMEAS of the motor 2 with a set or target value RPMSET for the rotation speed of the motor 2 and, on the basis of a difference therebetween, controlling the rotation speed of the electric motor 7 according to a control variable RPM _C TRL- The set or target value RPM- SET for the rotation speed of the motor 2 is set either automatically or manually on the basis of a desired effect the motor 2 is to have on the load connected thereto. The measuring member 12 and the control unit 13 thus form the feedback from the pressure medium operated motor 2 to the electric motor 7.

[0027] Even though the structure of the control valve 4 shown in Figure 2 is more common than the control valve structure shown in Figure 3, the solution will be explained in the following in connection with a gerotor type pressure medium operated motor 2, based on the embodiment shown in Figure 3. The structures of the control valve 4 shown in both Figures 2 and 3, however, enable the solution to be implemented in a similar manner.

[0028] Figures 4a to 4d schematically show four different use situations for the motor system 1 shown in Figure 3. In the use situations shown in Figures 4a to 4d, the control valve 4 is thus rotated anti-clockwise by an electric motor 7 which, for the sake of clarity, is not shown in the figures. Figure 4a shows a theoretical use situation wherein the motor 2 is not loaded at all and no friction occurs in the system. Then, when the control valve 4 rotates, the gerotor gear 10 settles in an angular position with respect to the control valve 4 that a slip or angular slip θ° in relation to the control valve 4 is zero degrees, i.e. Θ = 0°. In such a case, the pressure P of the pressure line PL affects via the pressure connection P' equally strongly both the expanding +dV and con- tracting -dV pressure pockets 11 of the motor 2. The same also applies to the pressure T of the tank line TL acting via the tank connection T. Then, both the displacement of the motor 2 and the pressure medium flow taken by the same are zero. This applies irrespective of the pressure supplied to the motor 2.

[0029] In the use situation shown in Figure 4b, the motor 2 is slightly loaded, in which case the gerotor gear 10 tends to start lagging behind the control valve 4, whereby the angular slip Θ increases and the angular slip Θ is 30°. Owing to the angular slip, the pressure P now affects the expanding +dV more strongly than the contracting -dV pressure pockets 11. Consequently, the motor 2 generates a torque and the rotation speed of the motor 2 achieves the rotation speed of the control valve 4. If the rotation speed of the motor 2 tends to start exceeding the rotation speed of the control valve 4, both the angular slip 0 and the torque decrease and the rotation speed of the motor 2 becomes lower. Along with an increase in the angular slip Θ, the displacement of the motor 2 also increases.

[0030] In the use situation shown in Figure 4c, the motor is loaded even more, in which case the angular slip Θ has increased to a value of 60°. At the same time, the displacement of the motor 2 and the torque generated by the motor 2 have increased.

[0031] In Figure 4d, the motor 2 is further loaded such that the an- gular slip Θ has increased to a value of 90°. In such a case, the displacement of the motor 2 is at its largest and, actually, has a magnitude similar to that of the displacement of a mechanically synchronized motor. At the same time, of course, the torque generated by the motor is also at its largest.

[0032] According to the example shown in Figures 4a to 4d, both the angular slip Θ of the motor 2 and the displacement of the motor increase as the load applied to the motor 2 increases. In such a case, the hydraulic power taken by the motor 2 always adjusts to the load and the theoretical efficiency of the motor is 100%. The angular slip Θ of the motor 2 also depends on the operating pressure supplied to the motor. A high operating pressure enables a necessary torque to be achieved by a smaller angular slip, in which case the displacement flow taken by the motor 2 is smaller.

[0033] If the motor 2 is run by a fixed flow, e.g. by a gear pump, the situation is similar. When a fixed flow is fed to the motor, the angular slip of the motor settles to such a value that a displacement corresponding with the angu- lar slip of the motor as well as the rotation speed of the motor correspond with the flow that has been fed. In such a case, the feed pressure of the motor settles to a value which, at the particular pressure and angular slip, enables the motor to rotate at a speed determined by the valve. In such a case, the theoretical efficiency is also 100%.

[0034] The total efficiency of the motor system 1 is then good since the power taken by the electric motor 7 is determined only on the basis of viscous friction resisting the rotation of the control valve 4 and internal frictions of the electric motor 7, and the power taken by the pressure medium operated motor 2 is determined only on the basis of the shaft power of the motor 2. The power of the electric motor 7 may thus be quite low, i.e. in practice e.g. only about 0.5 to 1 kW.

[0035] According to the solution, the electric motor 7 thus rotates the rotating part in the control valve 4 and, consequently, determines the rotation speed of the control valve 4. The control valve 4, in turn, directs the pres- surized pressure medium to the pressure medium operated motor 2 rotating the load, thus determining the rotation speed of the pressure medium operated motor 2. The electric motor 7 thus, by means of the control valve 4, controls the rotation speed of the pressure medium operated motor 2.

[0036] Figures 5a and 5b schematically show yet two different use situations for the motor system 1 shown in Figure 3. Figures 5a and 5b show use situations wherein the direction of rotation of the control valve 4 has been changed by changing the direction of rotation of the electric motor 7. In such a case, the direction of rotation of the motor 2 also changes and the angular slip Θ of the motor 2 increases in the opposite direction as compared with the use situations shown in Figures 4b to 4d. In Figure 5a, the angular slip Θ is -30° while in Figure 5b the angular slip Θ is -90°. In the embodiments according to Figures 2, 3, 4a to 4d, and 5a and 5b, the direction of rotation of the pressure medium operated motor 2 can thus be changed in a simple manner by only changing the direction of rotation of the control valve 4 by changing the direc- tion of rotation of the electric motor 7. This enables the direction of rotation of the motor 2 to be changed without a separate directional valve.

[0037] Figure 6 is a schematic, partially cross-sectional side view showing a third motor system 1 according to the basic principle of Figure 1. The motor system 1 shown in Figure 6 also comprises a gerotor type pressure medium operated motor 2 of which Figure 6 only shows a gerotor gear 10 in cross-section and in a schematic manner. The motor system 1 according to Figure 1 further shows a connecting shaft 14 which serves as a connecting element between the gerotor gear 10 and the control valve 4 and whose first end 14' is connected to the gerotor gear 10, the connecting shaft 14 being ro- tated by the gerotor gear 10 at speed Ω. A second end 14" of the connecting shaft 14 is arranged inside the control valve 4. For the sake of clarity, Figure 6 shows no electric motor 7 connected to the control valve 4. Hydraulic working surface areas (shown in closer detail in Figure 7) are arranged between the connecting shaft 14 and the control valve 4, the pressure affecting these hy- draulic working surface areas causing a rotating torque between the connecting shaft 14 and the control valve 4, which tries to rotate the control valve 4 in the same direction as in which the connecting shaft 14 rotates. This rotating torque enhances or mitigates the rotation of the control valve 4, in which case the power taken by the electric motor used for rotating the control valve 4 de- creases.

[0038] Figure 7 schematically shows an embodiment of the motor system 1 of Figure 6, as viewed in a direction of the control valve 4. In the embodiment according to Figure 7, in between the control valve 4 and the connecting shaft 14 are provided a first chamber 18 or a first space 18 which has a first surface area 18', and a second chamber 19 or a second space 19 which has a second surface area 19'. The arrangement further includes a first pressure medium channel 15 to be connected to the first chamber 18 and a second pressure medium channel 16 to be connected to the second chamber 19. When in the use situation according to Figure 7 pressure is connected to the motor 2, the control valve 4 controls the pressure medium to affect also via the first pressure medium channel 15 the first chamber 18 and the first surface area 18' therein. In such a case, the pressure medium supplied to the first chamber 18 causes a force F affecting the first surface area 18' in the first chamber 18 , the force F being proportional to the pressure of the pressure medium and the surface area of the first surface area 18'. The force F causes a torque between the connecting shaft 14 and the control valve 4, and this torque tries to rotate the control valve 4 in the same direction as a desired direction of rotation R of the motor 2 and the control valve 4, thus enhancing or assisting rotation of the control valve 4, which enables the power taken by the electric motor 7 for rotating the control valve 4 to be reduced. If in the embodiment according to Figure 7 the direction of rotation of the motor 2 is to be changed, the direction of rotation of the electric motor 7 is reversed and the order of the pressure connection P' and the tank connection T is changed by a hydraulic directional valve, in which case the operating pressure P of the sys- tern is directed to influence the second chamber 19.

[0039] The first chamber 18 and the second chamber 19 may be provided e.g. on the connecting shaft 14. The connecting shaft 14 may further be provided with one or more projections 17 to be connected to the control valve 4, whereby it is possible to direct the torque generated by the force caused by the pressure of the pressure medium affecting the chamber 18 or 19 of the connecting shaft 14 from the connecting shaft 14 to the control valve 4 via the projections 17. Alternatively, such an arrangement may be achieved by one or more parts provided between the connecting shaft 14 and the control valve 4.

[0040] Figure 8 schematically shows a second embodiment of the motor system 1 of Figure 6, as viewed in the direction of the control valve 4. The embodiment of Figure 8 may be used in a situation wherein the direction of rotation of the motor 2 is to be changed by changing the direction of rotation of the electric motor 7 only. In the motor system 1 according to Figure 8, be- tween the control valve 4 and the connecting shaft 14 are provided, as in Fig- ure 7, a first chamber 18 provided with a first surface area 18' and a second chamber 19 provided with a second surface area 19' as well as a first pressure medium channel 15 to be connected to the first chamber 18 and a second pressure medium channel 16 to be connected to the second chamber 19. The embodiment according to Figure 8 further includes channels 30 and 30' which, when the control valve starts to rotate, automatically connect, depending on the direction of rotation of the control valve 4, either the first chamber 18 or the second chamber 19 via the second pressure medium channel 16 to the tank connection T' in the manner schematically shown in connection with Figures 9a and 9b.

[0041] Figures 9a and 9b schematically show two different use situations of the motor system 1 of Figure 8, as viewed in the direction of the control valve 4. In the use situation according to Figure 9a, the control valve 4 is by an electric motor 7 (which, for the sake of clarity, is not shown in the figure) controlled to rotate anti-clockwise in order to rotate the pressure medium operated motor 2 anti-clockwise. In the use situation according to Figure 9b, the control valve 4 is controlled by the electric motor 7 to rotate clockwise in order to rotate the pressure medium operated motor 2 clockwise.

[0042] In the use situation according to Figure 9a, the electric motor 7 has controlled the control valve 4 into such a position that the operating pressure P is allowed to affect via the first pressure medium channel 15 the first chamber 18 and the first surface area 18' therein, whereby the pressure medium supplied to the first chamber 18 causes a force F which affects the first surface area 18' in the first chamber 18 and which is proportional to the pressure of the pressure medium and the surface area of the first surface area 18'. The force F causes a torque between the connecting shaft 14 and the control valve 4, and this torque tries to rotate the control valve 4 anti-clockwise, i.e. in the same direction as the desired direction of rotation R of the motor 2 and the control valve 4, thus enhancing or assisting the rotation of the control valve 4. The channel 30', in turn, has connected the second chamber 19 to the system's tank line via the second pressure medium channel 16.

[0043] In the use situation according to Figure 9b, the electric motor 7 has controlled the control valve 4 into such a position that the operating pressure P is allowed to affect via the first pressure medium channel 15 the second chamber 19 and the second surface area 19' therein, whereby the pressure medium supplied to the second chamber 19 causes a force F which affects the second surface area 19' in the second chamber 19 and which is proportional to the pressure of the pressure medium and the surface area of the second surface area 19'. The force F causes a torque between the con- necting shaft 14 and the control valve 4 which tries to rotate the control valve 4 clockwise, i.e. in the same direction as the desired direction of rotation R of the motor 2 and the control valve 4, thus enhancing or assisting the rotation of the control valve 4. The channel 30, in turn, has connected the first chamber 18 to the system's tank line via the second pressure medium channel 16.

[0044] The torque or mitigating torque to be generated via the connecting shaft 14 assists the rotation of the control valve 4, which enables the power of the electric motor necessary for rotating the control valve 4 and thus the physical size of the electrical motor to be reduced. By choosing the surface areas 18', 19' in the chambers 18, 19 appropriately, the electric motor may in terms of both its input power and physical size be quite small. The magnitude of the torque to be generated for alleviating or mitigating the rotation of the control valve 4 directly depends on the supply pressure of the motor 2 since in practice the surface area of the surface areas 18', 19' is constant. In addition, since in practice the sealing of the control valve 4 also takes place by means of the very same supply pressure of the motor 2, a torque resisting the rotation of the control valve 4 and caused by the viscous friction of the control valve 4 also depends on the supply pressure of the motor 2.

[0045] The connecting shaft 14 makes it also possible to ensure that the pressure medium operated motor 2 and the control valve 4 keep the same pace under all conditions. If the motor 2 is overloaded, the motor 2 is unable to rotate even at a full angular slip. In such a case, the angular slip would tend to increase above 90 degrees and this would result in the motor's running being disturbed. By arranging, as shown, the connecting shaft 14 between the control valve 4 and the motor 2, the angular slip of the motor 2 may be limited mechanically by means of the projections 17 provided in the connecting shaft 14, in which case in an overload situation of the motor 2 the rotation speed of the control valve 4 and the electric motor 7 would also become lower or even come to a halt altogether.

[0046] According to an embodiment, in connection with the connect- ing shaft 14 e.g. a spring or another flexible member may be arranged to affect the surface area 18' or 19' in the chamber 18 or 19, at least partly cancelling out the hydraulic resistance affecting the control valve 4. The spring or some such flexible member and the connecting shaft 14 are thus connecting elements assisting the rotation of the control valve 4. When a spring is used, the spring force of the spring and, therethrough, the magnitude of the effect assisting the rotation of the control valve 4 and being directed to the control valve 4 by the spring, depend on a slip between the motor 2 and the control valve 4.

[0047] It is also possible to dimension the surface areas 18' and 19' in the chambers 18 and 19 large enough for the connecting shaft 14 to try to rotate the control valve 4 without being assisted by the electric motor 7. In such a case, the pressure medium operated motor 2 tends to drift to the full at the angular slip and race. Then, instead of the electric motor 7, an electric brake is to be used. In other words, instead of the motor, the electric motor 7 may then be used as a generator, in which case by loading the electric motor 7 in gener- ator use the rotation speed of the control valve 4 may be controlled. The electric power generated by such a generator use may be utilized e.g. for power feed of control electronics, sensors, and wireless data communications connections possibly included in the system.

[0048] The solutions described above in connection with the gerotor type pressure medium operated motor 2 are suitable for all motors whose operation is controlled by a rotating valve. One such pressure medium operated motor 2 is e.g. a radial piston motor schematically described in Figure 10, which is provided with cylinder-piston units 31 placed in a direction of a radius of the motor, the reciprocating motion of pistons 32 thereof being controlled via operating arms 33 connected to the motor's shaft 3. The general structure and operation principle of various radial piston motors are known per se to those skilled in the art, so they will not be discussed in any further detail herein.

[0049] Figure 1 1 a schematically shows a fifth motor system 1 according to the basic principle of Figure 1 . The motor system 1 according to Figure 1 1a includes an electric motor 7, a control valve 4 serving as a synchronizing valve, and a pressure medium operated motor 2. Figure 1 1 b schematically shows a control valve 4 for use in the motor system 1 according to Figure 1 1 a, the figure also schematically showing a frame structure 4' of the control valve 4. The control valve 4 is connected to the pressure line PL, be- tween the pressure medium source 5 and connection A or port A of the motor 2. Connection B or port B of the motor 2 is connected to the tank line TL leading to the pressure medium reservoir 6. The shaft 8 of the electric motor 7 is connected to a first rotating connecting member 20 provided in the control valve 4, i.e. to a first rotating part provided in the control valve 4, in which case the electric motor 7 may be used for rotating the first connecting member 20. The first rotating connecting member 20 includes first flow channels 21 for enabling a pressure medium flow to flow through the first rotating connecting member 20. The control valve 4 further includes a second rotating connecting member 22, i.e. a second rotating part, connected to the shaft 3 of the pres- sure medium operated motor 2 such that the second rotating connecting member 22 rotates along with the motor 2. The second rotating connecting member 22 includes second flow channels 23 for enabling a pressure medium flow to flow through the second rotating connecting member 22. The rotation speed and direction of the first rotating connecting member 20 are indicated by Q _s while the rotation speed and direction of the second rotating connecting member 22 are indicated by Ω _Η .

[0050] The first rotating connecting member 20 is provided with a projection 24 placed in a groove 25 provided in the second rotating connecting member 22, whereby the projection 24 and the groove 25 limit the mutual an- gular position of the connecting members 20 and 22 to lie within a particular range. In the motor system 1 according to Figure 1 1 a, the control valve 4 is thus placed in the pressure line PL coming from the pressure medium source 5, in which case the control valve 4 is used to directly control the pressure medium flow flowing through the pressure medium operated motor 2. The pres- sure medium flow to flow through the control valve 4 is determined by the mutual angular position of the connecting members 20 and 22 as well as by the pressure difference over the control valve 4. The control valve 4 controls the pressure medium flow flowing to the motor 2 in order to achieve a desired rotation speed of the motor 2. The desired rotation speed is set at the rotation speed of the electric motor 7, the electric motor 7 thus being connected via its shaft 8 to rotate the first rotating connecting member 20 of the control valve 4, in which case the rotation speed of the first rotating connecting member 20 is controlled by the electric motor 7. If the motor 2 rotates at a lower speed, an angular slip is formed between the first rotating connecting member 20 and the second rotating connecting member 22, and owing to the influence of this an- gular slip, a larger flow connection is connected by means of the control valve 4 to connection A of the motor 2. On account of the larger flow connection, the motor 2 accelerates and achieves the desired rotation speed RPM _S ET- Correspondingly, when the motor 2 tries to race, the flow connection settles to be smaller, slowing down the rotation of the motor 2. In the control valve 4, the flow connection is thus formed between the first flow channels 21 in the first rotating connecting member 20 and the second flow channels 23 in the second rotating connecting member 22.

[0051] In the motor system 1 according to Figure 1 a, an alternative location for the control valve 4 is also shown. Instead of being placed in the pressure line PL leading to the motor 2, the control valve 4 (shown in broken line) is placed in the tank line TL coming from the motor 2, between connection B of the motor 2 and the pressure medium reservoir 6. Also in this embodiment, the control valve 4 is used to directly control the pressure medium flow flowing through the pressure medium operated motor 2; only the location of the control valve 4 differs from the above-described one. In this embodiment, the control valve 4 is thus, as indicated by the reference numerals given in brackets in Figure 1 b, connected to connection B of the motor 2 and to the tank line TL.

[0052] Figure 12a schematically shows a sixth motor system 1 according to the basic principle of Figure 1 while Figure 12b schematically shows a control valve 4 for use in the motor system 1 according to Figure 12a. The motor system 1 according to Figure 12a is similar to the motor system 1 according to Figure 1 1 a except, however, that in the motor system 1 according to Figure 12a the control valve 4 is located between the pressure line PL and the tank line TL, in which case the control valve 4 controls the pressure medium flow flowing to the motor 2 by directing a portion of the flow to flow past the motor 2, into the tank line TL. Then, when the motor 2 rotates at a speed lower than the desired one, a flow connection being formed between the flow chan- nels 21 , 23 of the first rotating connecting member 20 and the second rotating connecting member 22 of the control valve 4 decreases, whereby, owing to the greater flow supplied to the motor 2, the motor 2 accelerates and achieves the desired rotation speed. Similarly, when the motor 2 races, this flow connection increases, in which case a larger portion of the pressure medium flow flows past the motor 2, whereby the pressure medium flow flowing to the motor 2 decreases and the rotation speed of the motor 2 becomes lower.

[0053] The embodiments shown in Figures 11a, 11b, 12a, and 12b provide a simple and reliable control for the rotation speed of the motor 2, which is suitable for all motor types. The electric motor 7 is used for rotating the first rotating connecting member 20 of the control valve 4, and the second rotating connecting member 23 connected to the pressure medium operated motor 2 rotates at the same speed, the electric motor 7 thus controlling, by means of the control valve 4, the rotation speed of the pressure medium oper- ated motor 2. As the first connecting member 20 and the second connecting member 22 rotate at the same speed, no kinetic friction is generated between these connecting members 20 and 22. This enables the torque generated by the electric motor 7 to be dimensioned such that it only suffices to offset the angular position between the first connecting member 20 and the second con- necting member 22, i.e. to change the magnitude of a flow connection being formed between the first flow channels 21 of the first rotating connecting member 20 and the second flow channels 23 of the second rotating connecting member 22. Hence, the power taken by the electric motor 7 is extremely low.

[0054] In the control valves 4 according to Figures 11 b and 12b, the first connecting member 20 rotated by the electric motor 7 is placed inside the second connecting member 22 connected to the pressure medium operated motor 2. The first connecting member 20 rotated by the electric motor 7 could, however, alternatively also be placed outside the second connecting member 22, between the second connecting member 22 and the frame structure 4' of the control valve 4. This, however, would result in kinetic friction being generated between the first connecting member 20 and the frame structure 4' of the control valve 4, which means that the input power of the electric motor 7 would have to be increased in order to overcome the kinetic friction, and this, again, would result in both the size and energy consumption of the electric motor 7 being increased. By placing the first connecting member inside the second connecting member 22 as shown in Figures 11 b and 12b, the diameter of the first connecting member 20 may also be decreased, thus decreasing the torque required for rotating the first connecting member 20 and thus the size and input power of the electric motor 7. [0055] It is also possible to apply the solutions disclosed in Figures 7 to 9 between the first connecting member 20 and the second connecting member 22 in order to decrease the power necessary for rotating the first connecting member 20 connected to the electric motor 7.

[0056] Figures 13a, 13b, and 13c schematically show a control valve 4 which may be used in the motor system according to Figure 1 1 a, for example. Figure 13a shows the control valve 4 in a cross-sectional side view, Figure 13b shows the control valve 4 cross-sectioned along cross section line E-E shown in Figure 13a, and Figure 13c shows the control valve 4 cross- sectioned along cross section line F-F shown in Figure 13a. Figure 13a shows the control valve 4 and its frame structure 4'. Figure 13a further shows the shaft 3 of the pressure medium operated motor 2 and the shaft 8 of the electric motor 7. The shaft 8 of the electric motor 7 is connected to the control valve's 4 first rotating connecting member 20 provided with first flow channels 21 , and the shaft 3 of the motor 2 is connected to the control valve's 4 second rotating connecting member 22 provided with second flow channels 23. The flow channels 21 , 23 provided in the connecting members 20 and 22 of the control valve 4 and the connections of the control valve 4 indicated by T' for connecting the control valve 4 to the tank line TL as well as the connections of the control valve 4 indicated by B' for connecting the control valve 4 to connection B of the motor 2 are arranged symmetrically in the control valve 4 such that the control valve is in power balance. The cross-sectional view according to Figure 13c further schematically shows a projection 24 provided e.g. in the form of a stop pin in the first rotating connecting member 20 and arranged in a groove 25 in the second rotating connecting member 22, in which case the projection 24 and the groove 25 prevent the connecting members 20 and 22 from winding up too much with respect to one another.

[0057] The operation of the above-disclosed control valve 4 is thus based on restricting the flow of the pressure medium, so some waste power is generated in the control valve 4.

[0058] A solution with a better efficiency is achieved by utilizing a technique called Pulse Width Modulation (PWM) for controlling a pressure medium flow. The basic idea is to supply the desired power to the pressure medium operated motor 2 in a pulse-like manner by controlling the operation of the control valve 4 by the electric motor 7. [0059] Figure 14a schematically shows a seventh motor system 1 according to the basic principle of Figure 1 while Figure 14b schematically shows an eighth motor system 1 according to the basic principle of Figure 1. In Figure 14a, either the pressure P of the pressure line PL or the pressure T of the tank line TL is supplied in a pulse-like manner to affect connection A of the motor 2. In Figure 14b, either the pressure P of the pressure line PL or the pressure T of the tank line TL is supplied in a pulse-like manner to affect connection B of the motor 2. The control valve 4 implemented as a PWM synchronizing valve is alternately connected to said two different pressure levels, i.e. either to the pressure P of the pressure line PL or the pressure T of the tank line TL, depending on the power demand of the motor 2. Connection times are determined by the angular slip of the control valve 4, in other words by the angular difference between the electric motor 7 and the pressure medium operated motor 2.

[0060] Figures 15a, 15b, and 15c schematically show operation of the motor system 1 according to Figure 14b in a use situation wherein either the pressure P of the pressure line PL or the pressure T of the tank line TL is supplied to affect connection B of the pressure medium operated motor 2. The left-hand side of Figures 15a, 15b, and 15c schematically shows inner opera- tion of the control valve 4. The right-hand side of Figures 15a, 15b, and 15c, in turn, schematically shows time t on the horizontal axis for indicating the time during which either the pressure T of the tank line TL or the pressure P of the pressure line PL is supplied to affect connection B of the motor 2 while the vertical axis shows magnitude E of the effect of either the pressure T of the tank line TL or the pressure P of the pressure line PL.

[0061] In Figure 15a, connection B of the motor 2 is connected in a pulse-like manner only to the pressure T of the tank line TL affecting via connection T of the control valve 4 since the angular slip of the motor 2 with respect to the electric motor 7 is at its greatest. In such a case, a maximum pow- er, i.e. 100% power, is fed to the motor 2. In Figure 15c, the angular slip of the motor 2 with respect to the electric motor 7 has drifted to zero, and connection B of the motor 2 is connected only to the pressure P of the pressure line PL affecting via connection P' of the control valve 4. In such a case, the pressure difference over the motor 2 is zero, and the motor 2 takes no hydraulic power at all. In the situation of Figure 15b, a 50% power is supplied to the motor 2 since connection B of the motor 2 is alternately and for the same duration of time connected both to the pressure P of the pressure line PL affecting via connection P' of the control valve 4 and to the pressure T of the tank line TL affecting via connection T' of the control valve 4. In the solutions shown in Fig- ures 14a, 14b, 5a, 15b, and 15c, the input power of the motor 2 may thus settle steplessly between 0 and 100%. The input power of the motor 2 depends on the magnitude of a torque required to keep the rotation speed of the pressure medium operated motor 2 the same as the rotation speed of the electric motor 7.

[0062] In the embodiments disclosed in Figures 14a, 14b, 15a, 15b, and 15c, it is also possible to apply the solutions disclosed in Figures 7 to 9 between the first connecting member 20 and the second connecting member 22 in order to decrease the power necessary for rotating the first connecting member 20 connected to the electric motor 7.

[0063] Figure 16 shows a control valve 4 usable in the motor systems 1 according to Figures 14a, 14b and 15a, 15b, and 15c. The control valve 4 is shown schematically and sectionally and as seen from an end. The control valve 4 according to Figure 16 has a frame structure 4'. The control valve 4 further includes a non-rotating hub 26 provided with flow channels 27 leading to connection B of the motor 2. Around the hub 26 rotates, controlled by the electric motor 7, the first rotating connecting member 20 around which is provided the second rotating connecting member 22 connected to the pressure medium operated motor 2. The first rotating connecting member 20 is provided with first flow channels 21 while the second rotating connecting member 22 is provided with second flow channels 23. For the sake of clarity, the first flow channels 21 provided in the first rotating connecting member 20 and the second flow channels 23 provided in the second rotating connecting member 22 are shown in their more complete form only in connection with one pair of flow channels formed by the flow channels 21 and 23 while in connection with the rest of the flow channel pairs they are replaced by lines. Depending on the mutual angular slip of the first rotating connecting member 20 and the second rotating connecting member 22, connection B of the motor 2 is connected in a pulse like manner either to the pressure line PL connected to connection P' of the control valve 4 or to the tank line TL connected to connection T of the con- trol valve 4 such that the lengths of the pulses are automatically adjusted to correspond with the power level required by the pressure medium operated motor 2.

[0064] In theory, this solution enables a 100% efficiency to be achieved, but in practice the connecting of the pressure line PL and the tank line TL has to be arranged such that both the pressure line PL and the tank line TL are temporarily simultaneously connected. Otherwise, the pressure medium flows stop completely for a while, which results in high pressure peaks. When the pressure line PL and the tank line TL are temporarily simultaneously connected, the result is a hydraulic breakthrough, in which case the pressure medium temporarily flows directly from the pressure line to the tank line, reducing the efficiency. In order to avoid pressure peaks, it is also possible to use, in accordance with Figure 14b, a pressure accumulator 28 or a check valve 29, in which case the above-described temporary simultaneous connecting of the pressure line PL and the tank line TL is unnecessary.

[0065] In some cases, features disclosed in this application may be used as such, irrespective of other features. On the other hand, when necessary, the features disclosed in this application may be combined in order to provide various combinations.

[0066] The drawings and the related description are only intended to illustrate the idea of the invention. In its details, the invention may vary within the scope of the claims.