Slide valve, especially hydraulic valve

Abstract

Slide valve (10), in particular hydraulic valve, comprising a housing (12), a main valve spool (16), wherein the main valve spool (16) is arranged in the housing (12), an auxiliary spool (32a; 32b), wherein the auxiliary spool (32a; 32b) is arranged at least partially in the main valve spool (16), wherein the main valve spool (16) and the auxiliary spool (32a; 32b) are axially displaceable by a single common actuator, preferably an electromagnet (54), wherein the auxiliary spool (32a; 32b) is displaceable at least temporarily independently of the main valve spool (16), wherein the slide valve (10) comprises a locking device with which the main valve spool (16) can be locked in a position, and wherein the locking device is controlled by the auxiliary spool (32a;32b) is controlled, characterized in that the locking device comprises a hydraulically effective surface on the main valve spool (16) that defines a locking chamber (62), and that the main valve spool (16) can connect the locking chamber (62) to an inlet port (P) and the auxiliary spool (32a) can connect the locking chamber (62) to an outlet port (T2).

Description

State of the art The invention relates to a slide valve according to the preamble of claim 1. Proportional hydraulic valves of the "slide valve" design generally have only one axially displaceable shut-off element. This shut-off element is usually a cylindrical slide in the form of a piston. Together with laterally arranged inlet and outlet ports in a stationary housing and the longitudinal slots, the valve's intended function, e.g., controlling a flow rate or regulating a pressure according to a setpoint, is achieved by an actuator, usually an electromagnet. The interaction of the magnetic force with a spring force and a fluid force controls the valve. The fluid force is generated either by a step in the valve slide or by a sensing pin. The sensing pin is supplied with hydraulic oil via a channel inside the valve slide. Such a valve design only allows for a stable state without an external energy supply. As soon as the electrical voltage is no longer applied to the electromagnet, the spring force and the hydraulic force move the valve spool towards the electromagnet until it reaches a stop. The valve spool then closes a fixed access opening for the inlet pressure with the aid of a control edge. Currently, there are self-holding valves whose locking mechanism is based on a permanent magnet or on positive-locking mechanisms. From DE 11 2009 000 059 T5, a spool valve is known which comprises a housing, a main valve spool which is arranged in the housing and an auxiliary spool, wherein the main valve spool and the auxiliary spool can be axially displaced by a single common actuator and the auxiliary spool can be displaced at least temporarily independently of the main valve spool and wherein the spool valve comprises a locking device with which the main valve spool can be locked in a position, and wherein the locking device is controlled by the auxiliary spool. Further gate valves are known from US 2009 / 0 224 192 A1, from DE 698 04 426 T2 and from US 2009 / 0 140 192 A1. Disclosure of the invention The problem underlying the invention is solved by a slide valve according to claim 1 or claim 4. Advantageous embodiments are specified in the dependent claims. Further features important to the invention are found in the following description and in the drawings, whereby the features can be important to the invention both individually and in various combinations, without this being explicitly stated again. The invention relates to a spool valve (“valve”), in particular a hydraulic valve, comprising a housing, a main valve spool, wherein the main valve spool is arranged in the housing, and an auxiliary spool (“auxiliary piston”), wherein the auxiliary spool is arranged at least partially within the main valve spool. The main valve spool and the auxiliary spool are axially displaceable by a single common actuator, preferably an electromagnet, wherein the auxiliary spool is displaceable at least temporarily independently of the main valve spool. This enables interaction of two nested pistons (i.e., main valve spool and auxiliary spool) for controlling the spool valve by a common actuator (electromagnet). The main valve spool and the auxiliary spool can therefore be actuated (i.e., moved axially) by the same electromagnet.The slide valve according to the invention has, among other advantages, the fact that it has more than one stable position without an external energy supply. One possible measure is to guide the fluid through channels in the valve slide and in the stationary housing to actuate a locking mechanism. These channels can be opened or closed by the auxiliary slide in the actual main valve slide. The slide valve features a locking device that allows the main valve spool to be locked in a specific position. This locking device is controlled by the auxiliary spool. As a result, the locking device is particularly simple, cost-effective, and does not require a permanent magnet. In a first embodiment of the slide valve according to the invention, the locking device comprises a hydraulically effective surface on the main valve slide that defines a locking chamber. The main valve slide can connect the locking chamber to an inlet port, and the auxiliary slide can connect the locking chamber to an outlet port. This improves the operation of the slide valve and / or the locking device. In a further embodiment of the slide valve, a flow restrictor ("orifice plate") is arranged between the inlet connection and the locking chamber. This advantageously allows the time for the fluid pressure to drop in the locking chamber to be shorter than the time required to refill the locking chamber and the connecting channel with fluid. This can be expressed, for example, using the following equation 3: In a further embodiment of the slide valve, the auxiliary slide is arranged between the actuator and the main valve slide, and a first spring ("main spring") is arranged between the main valve slide and the housing, and a second spring ("auxiliary spring") is arranged between the main valve slide and the auxiliary slide, the second spring being stiffer than the first spring. By using the first and second springs, the main valve slide and the auxiliary slide can be coupled to each other in a particularly simple and defined manner to enable the function of the locking device. In an alternative embodiment of the slide valve according to the invention, the locking device comprises a locking element controlled by pressure in a locking area, which has a locking position and a release position. In the locking position, the locking element interacts with the main valve slide in a frictional engagement, and in the release position, the frictional engagement is released. Furthermore, the main valve slide can connect the locking area to an inlet port, and the auxiliary slide can connect the locking area to an outlet port. The interaction of the described elements and forces enables the locking device to function according to the invention with comparatively little effort. Furthermore, the locking element can be designed to include at least one locking ball or an element that is at least approximately spherical. This allows the slide valve to be manufactured particularly cost-effectively. Additionally, the locking area can include an inclined surface sloping towards the main valve spool, against which the locking ball is pressed by pressure within the locking area. This allows for a particularly simple locking mechanism. Additionally, a spring mechanism can be provided that acts on the locking ball away from the inclined surface. This allows the locking ball to maintain a defined position at all times when the main valve spool is not locked, thereby improving the operation of the spool valve or the locking device. Furthermore, for such designs of the slide valve, in which the locking device has a locking element controlled by pressure in the locking area, it can be provided that the auxiliary slide is arranged between the actuator and the main valve slide, and that a first spring is arranged between the main valve slide and the housing, and a second spring is arranged between the main valve slide and the auxiliary slide, and that the first spring is stiffer than the second spring. By using the first and second springs and the described relative stiffnesses, the main valve slide and the auxiliary slide can be coupled to each other in a particularly simple and defined manner, even when the locking element is present. Exemplary embodiments of the invention are explained below with reference to the drawings. In the drawings: Fig. 1 shows a longitudinal section through a hydraulic slide valve according to a first embodiment of the invention; Fig. 2 shows an enlarged view of an additional slide of the slide valve of Fig. 1; Fig. 3 shows the slide valve of Fig. 1 in a first operating state (“position 1”); Fig. 4 shows the slide valve of Fig. 1 in a second operating state (“position 2”); Fig. 5 shows the slide valve of Fig. 1 in a third operating state (“position 3”); Fig. 6 shows the slide valve of Fig. 1 in a fourth operating state (“position 4”); Fig. 7 shows the slide valve of Fig. 1 in a fifth operating state (“position 5”); Fig. 8 shows the slide valve of Fig. 1 in a sixth operating state (“position 6”); Fig. 9 shows a time diagram with a pressure-flow characteristic curve for the slide valve of Fig. 1. Fig.Fig. 10 a longitudinal section through a hydraulic slide valve according to a second embodiment of the invention; Fig. 11 the slide valve of Fig. 10 in a first operating state (“position 1”); Fig. 12 the slide valve of Fig. 10 in a second operating state (“position 2”); Fig. 13 the slide valve of Fig. 10 in a third operating state (“position 3”); Fig. 14 the slide valve of Fig. 10 in a fourth operating state (“position 4”); Fig. 15 the slide valve of Fig. 10 in a fifth operating state (“position 5”); Fig. 16 the slide valve of Fig. 10 in a sixth operating state (“position 6”); Fig. 17 the slide valve of Fig. 10 in a seventh operating state (“position 7”); Fig. 18 the slide valve of Fig. 10 in an eighth operating state (“position 8”); and Fig. 19 a time diagram with a pressure-flow characteristic curve for the slide valve of Fig. 10 . The same reference symbols are used for functionally equivalent elements and sizes in all figures, even in different embodiments. Fig. 1 shows a first embodiment of a slide valve 10 in a longitudinal section. In the left-hand section of Fig. 1, the slide valve 10 comprises a housing 12 in which a plurality of axial channels and radial channels, bores, recesses, or openings are arranged. As is generally known for slide valves, many of the elements shown in Fig. 1 and in Figs. 2, 3, 4, 5, 6, 7 to 8, described below, are essentially rotationally symmetrical about a longitudinal axis. Four radial channels are provided in a lower section of the housing 12 in Fig. 1, which in this case correspond to an inlet port P, a working port A, a first outlet port T, and a second outlet port T2. The second outlet port T2 is connected in the housing 12 via a second tank channel 66 (see Fig. 6). A main valve spool 16 is arranged to be axially movable in an axial housing bore 14 of the housing 12.The main valve spool 16 has three sections with different outer radii in the axial direction: a first guide section (without reference numeral) in a left-hand area of ​​the main valve spool 16 in the drawing, the outer radius of which corresponds at least approximately to an inner radius of the housing bore 14, whereby the main valve spool 16 is guided radially in the housing bore 14; a channel section (without reference numeral) located approximately axially centrally, the outer radius of which is smaller than the inner radius of the housing bore 14, whereby an outer hydraulic channel 17 is formed between the channel section and the housing bore 14; and a second guide section (without reference numeral) in a right-hand area of ​​the main valve spool 16, which is designed similarly to the first guide section, whereby the main valve spool 16 is also guided radially in the housing bore 14. As can be seen from the drawing, a control edge 16a and 16b are provided between the first guide section and the channel section of the main valve spool 16, as well as between the channel section and the second guide section of the main valve spool 16. The control edges 16a and 16b can interact hydraulically with control edges (without reference numerals) provided in the housing bore 14. Furthermore, the main valve spool 16 has several axial or radial recesses, bores, channels, or openings. In one area of ​​the first guide section, an axial first guide bore 18 extends from an end face on the left in Fig. 1, and in one area of ​​the second guide section, an axial second guide bore 20 extends from an end face on the right in Fig. 1. Both are open at their end faces. The first and second guide bores 18 and 20 are essentially blind holes. The first guide bore 18 opens to the left in the drawing with its full cross-section.At a right-hand end section of the main valve spool 16 in the drawing, there is a circular central opening (without reference numeral) through which the second guide bore 20 in the drawing opens to the right; however, the radius of the central opening is smaller than the inner radius of the second guide bore 20. In an approximately central region of the channel section, a continuous first radial channel 22 is provided, which is thus connected to the outer hydraulic channel 17. An inner channel 24, axially centered in the main valve spool 16, hydraulically connects the first radial channel 22 and the first guide bore 18. The radius of the inner channel 24 is smaller than the inner radius of the first guide bore 18. Likewise, the radius of the inner channel 24 is smaller than the outer radius of the main valve spool 16 in the region of the channel section. A section of the housing 12 on the left side of Fig. 1 comprises a centrally arranged cylindrical feeler pin 26, which is rigidly connected to the housing 12 and projects into the first guide bore 18. An outer radius of the feeler pin 26 corresponds at least approximately to an inner radius of the first guide bore 18, so that the main valve spool 16 is axially movable relative to the feeler pin 26. A first spring 28 ("main spring"), designed as a helical spring, is arranged axially between an annular end face of the main valve spool 16 (left in the drawing) and an inner wall surface of the housing 12 facing the main valve spool 16, and radially outward around an axial section of the feeler pin 26. The first spring 28 exerts an axial force on the main valve spool 16 to the right in the drawing. Furthermore, in a region of the second guide bore 20 (near the right-hand end face of the main valve spool 16 in the drawing), a continuous second radial channel 30 is provided on the main valve spool 16, which is open on both sides towards the second guide bore 20 and towards the housing bore 14, respectively. A piston 34 of an auxiliary spool 32a, forming a guide section, is axially movable ("integrated") in the second guide bore 20 of the main valve spool 16. This is shown enlarged in Fig. 2. The auxiliary slide 32a is essentially rotationally symmetrical and, as shown on the left in the drawing, has the aforementioned guide section 34, by means of which the auxiliary slide 32a is guided radially in the second guide bore 20. A second spring 37 ("auxiliary spring"), also designed as a helical spring, is tensioned between an end face of the guide section 34 (left in the drawing) and the bottom of the second guide bore 20. This spring acts on the main valve slide 16 to the left and on the auxiliary slide 32a to the right. In the drawing to the right of the guide section 34, the auxiliary valve 32a comprises a control section 36, the outer radius of which corresponds at least approximately to the circular central opening at the right end section of the main valve spool 16. The control section 36 is thus guided radially in the circular central opening and is axially movable within it. From left to right in the drawing, the control section 36 comprises: a first transverse channel 38, a central longitudinal channel 40 (the "inner channel" in the auxiliary valve 32a), a second transverse channel 42, and a coupling section 44. The longitudinal channel 40 hydraulically connects the first transverse channel 38 to the second transverse channel 42. The function of the longitudinal channel 40 is particularly evident from Fig. 7. Furthermore, in Fig. 1, the housing 12 includes an axial connecting channel 46, which is arranged above the housing bore 14 and extends parallel to it. A left-hand end section of the connecting channel 46 can be hydraulically connected to the outer hydraulic channel 17 via a flow restrictor 48 ("orifice") and a first radial housing channel 50. This connection depends on the axial position of the main valve spool 16 or the control edge 16a. In Fig. 1, however, due to the maximum right-hand position of the main valve spool 16 shown there, an opening of the first radial housing channel 50 facing the housing bore 14 is completely covered by the first guide section of the main valve spool 16. If the main valve spool 16 is in a more left-hand position, the flow restrictor 48 is hydraulically arranged between the inlet port P and the connecting channel 46 via the channel 17.In the present case, the flow throttle 48 is designed by means of an "orifice", that is, as a comparatively short radial channel which has a smaller cross-section than the first radial housing channel 50 and the connecting channel 46. In the drawing, a right-hand end section of the connecting channel 46 leads radially inward via a second radial housing channel 52 to the housing bore 14. A control edge 60 is formed on the housing 12 at an opening of the second radial housing channel 52 (see Figs. 4 and 8). Depending on the axial position of the main valve spool 16, the second radial housing channel 52 and the second radial channel 30 in the main valve spool 16 can be hydraulically connected or separated. In Fig. 1, an opening of the second radial housing channel 52 facing the housing bore 14 is almost completely covered by the second guide section of the main valve spool 16. Furthermore, the slide valve 10 has an actuator in the form of an electromagnet 54 in a right-hand area of ​​the drawing. This actuator comprises a housing (without reference numeral), a solenoid coil 56, and a magnetic armature 58. When the solenoid coil 56 is energized, the magnetic armature 58 can be moved to the left by magnetic force in the drawing, thereby applying an axially acting pressure force to the auxiliary slide valve 32a at a right-hand end section in the drawing. Figures 1, 2, 3, 4, 5, 6, 7, 8 to 9, and Figures 10, 11, 12, 13, 14, 15, 16, 17, 18 to 19, described below, depict a spool valve 10, in particular a hydraulic valve, comprising a housing 12, a main valve spool 16, wherein the main valve spool 16 is arranged in the housing 12, and an auxiliary spool 32a or 32b, wherein the auxiliary spool 32a or 32b is arranged at least partially in the main valve spool 16. The main valve spool 16 and the auxiliary spool 32a or 32b can be axially displaced, at least temporarily, independently of each other by a single common actuator, in this case the electromagnet 54. As will be explained below, the spool valve 10 includes a locking device with which the main valve spool 16 can be locked in a position – in this case, the leftmost position.The locking device can be controlled by the additional slide 32a or 32b. In the first embodiment according to Figs. 1, 2, 3, 4, 5, 6, 7, 8 to 9, the locking device comprises different elements than in the second embodiment according to Figs. 10, 11, 12, 13, 14, 15, 16, 17, 18 to 19, as already explained or as will be explained below. In Figures 1, 2, 3, 4, 5, 6, 7, 8 to 9, the locking device comprises a hydraulically effective surface on the main valve spool 16 that defines a locking chamber 62, which only forms when the main valve spool 16 moves to the left. The main valve spool 16 can connect the locking chamber 62 to the inlet port P, and the auxiliary spool 32a can connect the locking chamber 62 to the outlet port T2. Furthermore, the auxiliary spool 32a is arranged between the actuator (electromagnet 54) and the main valve spool 16, and the first spring 28 is arranged between the main valve spool 16 and the housing 12, and the second spring 37 is arranged between the main valve spool 16 and the auxiliary spool 32a. The second spring 37 is stiffer than the first spring 28. The operation of the first embodiment of the slide valve 10 is explained in more detail below using Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8 to Fig. 9. The invention is based on the idea that the main valve spool 16 and the auxiliary spool 32a are actuated (i.e., axially moved) by the same electromagnet 54, as can be seen from Figs. 1, 2, 3, 4, 5, 6, 7, 8 to 9, and also from Figs. 10, 11, 12, 13, 14, 15, 16, 17, 18 to 19 described below. The main valve spool 16 controls the spool valve 10 with respect to the hydraulic ports P, A, and T in a manner comparable to a known spool valve, by actuating the electromagnet 54 with a normal control current. This means that a control edge (without reference mark) at the far right end of the main valve slide 16 does not release channel 52.As soon as the main valve spool 16 reaches its maximum left end position (maximum opening of the spool valve 10) by energizing the electromagnet 54 with a higher current than the normal control current, the piston chamber between the main valve spool 16 and the electromagnet 54 is filled with fluid via the connecting channel 46 located in the housing 12. The same pressure as in the working channel builds up very quickly. Due to the balance of forces between the main compression spring force generated by the first spring 28, the fluid force generated by a sensing surface on the sensing pin 26, and the right annular end face of the main valve spool 16 (due to the coupling section 44), the main valve spool 16 remains in a stable position (maximum opening of the spool valve 10), because the right annular end face is larger than the sensing surface.The electromagnet 54 no longer needs to be controlled with an electrical voltage. To unlock the slide valve 10 (“hydraulic valve”), the electromagnet 54 is energized with the maximum electrical voltage (compare position 5 in Fig. 9). The auxiliary slide valve 32a opens the control edge 64 (“D-T2”, see Fig. 6), whereupon the fluid flows into the tank and the locking mechanism is released. The main advantage of this valve is the saving of electrical energy. This electrical energy must normally be applied continuously to operate a hydraulic valve with a rising characteristic curve in the steady state of "fully open". The process is explained in detail below: In the embodiment shown in Figures 1, 2, 3, 4, 5, 6, 7, 8 to 9, the fully open end position of the main valve slide 16 (left in each figure) is locked. First, however, the main valve slide 16 releases the connecting channel 46 by means of the control edge 16a and connects it to the working channel A. Before the control edge 60 (see Figure 4) connects the locking chamber 62 (see Figure 4) to the connecting channel 46, the slide valve 10 is fully controllable by maintaining the force equilibrium (see Equation 1 and Figures 3 and 4). As soon as the solenoid coil 56 is energized with a current higher than the control current (Iactuated current > Icontrolled current), the main valve spool 16 moves towards the first spring 28 (“main spring”), and the control edge 60 opens the locking chamber 62. The annular right end face of the main valve spool 16 is larger than the sensing surface, resulting in a force imbalance and compressing the first spring 28 to its limit (see Fig. 5). Due to the force imbalance, the main valve spool 16 remains in its position (i.e., is locked), and the coil current can be reduced to zero (see Equation 2 and Fig. 6). To unlock the main valve spool 16, the solenoid coil 56 is energized with a higher coil current (Iunlock > Icontrol) (see Fig. 9). The second spring 37 ("auxiliary spring") is stiffer than the first spring 28. The second spring 37 is compressed, and the auxiliary spool 32a opens a connection from the locking chamber 62, via the channels 42, 40, 38, and 30, to the tank channel 66 or the tank connection T2 (Fig. 7) by means of the control edge 64. The fluid can thus flow out of the locking chamber 62 via the second tank channel 66. The large connecting channel 46 in combination with the small orifice (flow restrictor 48) and the large cross-section of the second tank channel 66 results in the time to reduce the fluid pressure in the locking chamber 62 being shorter than the time to refill the locking chamber 62 and the connecting channel 46 with the fluid (see equation 3).The control edge 60 can thus be closed in time as a result of a reduction in the coil current to the control current. This allows the main valve spool 16 to retract unimpeded to the left in the figure (see Fig. 8). From this point on, the slide valve 10 (“valve”) can again be controlled by the balance of forces between the counterforce (spring 28 and left sensing surface) and the magnetic force (see Fig. 8). When the coil current drops to zero, the first spring 28 and the fluid pressure at the sensing surface push the main valve slide 16 back into its initial position (see Fig. 3). Figure 9 shows a pressure-flow characteristic curve corresponding to the first embodiment of the slide valve 10. The abscissa of the depicted coordinate system corresponds to a time t. The solid curve and the solid ordinate correspond to a hydraulic pressure at the working port A. The dashed curve and the dashed ordinate correspond to a flow rate. Reference numerals 1 to 6 characterize six positions during operation of the slide valve 10, corresponding to Figures 3, 4, 5, 6, 7 to 8. Several options are available for the design of such an internal auxiliary slide 32a. As an alternative to the embodiment shown in Figs. 1, 2, 3, 4, 5, 6, 7 to 8, a longer auxiliary piston with significantly more connecting channels and control edges can also be used (see Fig. 10). Fig. 10 shows a longitudinal section through the slide valve 10 in a second embodiment, in which the auxiliary slide 32b is integrated into the main valve slide 16. The main valve slide 16 and the auxiliary slide 32b are axially moved ("actuated") by the same magnetic armature 58 of the electromagnet 54. In a region on the left side of the drawing, the slide valve 10 comprises the housing 12, in which a plurality of axial or radial channels, bores, recesses, or openings are arranged. As is generally known for slide valves, in Fig. 10 and in Figs. 11, 12, 13, 14, 15, 16, 17 to 18 described below, many of the elements shown are essentially rotationally symmetrical about a longitudinal axis. Similar to Fig. 1, Fig. 10 also shows the inlet port P, the working port A, the first outlet port T1, and the second outlet port T2 arranged in a lower section of the housing 12. Additionally, the embodiment of Fig. 10 includes a third outlet port T3, which is located to the left of the inlet port P in the drawing. The main valve spool 16 has, viewed axially, five sections with different radii (from left to right in the drawing): a first guide section (without reference numeral), whose outer radius corresponds at least approximately to the inner radius of the housing bore 14, whereby the main valve spool 16 is guided radially in the housing bore 14; furthermore, a first channel section 70, whose outer radius is smaller than the inner radius of the housing bore 14, whereby a first outer hydraulic channel is formed between the first channel section 70 and the housing bore 14; furthermore, a second guide section (without reference numeral) in an approximately central region of the main valve spool 16, which is designed similarly to the first guide section, whereby the main valve spool 16 is additionally guided radially in the housing bore 14;in addition a second channel section 72, the outer radius of which is smaller than the inner radius of the housing bore 14, whereby a second outer hydraulic channel is formed between the second channel section 72 and the housing bore 14; in addition, in the drawing on the far right, an axially very short third guide section (without reference numeral), whereby the main valve spool 16 is additionally guided radially in the housing bore 14. The guide sections of the main valve spool 16 have a plurality of control edges which interact hydraulically with corresponding control edges or with openings on the housing 12. See also the description of Fig. 1 above. Not all of these control edges are described here. Furthermore, the main valve spool 16 has several axial or radial recesses, bores, channels, or openings. In particular, the main valve spool 16 has a centrally located, blind-hole-like guide bore 74 with axial and diameter steps, which is open to the right in the drawing. Accordingly, the main valve spool 16 has a bottom (without reference numeral) on the left side of the drawing. In a left and middle section of the main valve spool 16, the guide bore 74 has a first radius. In an axial section that extends approximately along the second channel section 72 and the third guide section, the guide bore 74 has a second radius that is larger than the first radius. The first radius is smaller than the radius characterizing the first channel section 70, and the second radius is smaller than the radius characterizing the second channel section 72. In the sectional plane of Fig. 10, the main valve spool 16 has a continuous first radial channel (without reference numeral) in an approximately central region of the first guide section. In an approximately central region of the first channel section 70, the main valve spool 16 has a continuous second radial channel (without reference numeral). In a region of the second channel section 72, the main valve spool 16 has a continuous third radial channel (without reference numeral). The first spring 28 ("main spring"), which is designed as a helical spring as shown in Fig. 1, is arranged axially between the base of the main valve spool 16 (on the left in the drawing) and an inner wall surface of the housing 12 facing the base of the main valve spool 16. In the guide bore 74 of the main valve spool 16 of Fig. 10, an auxiliary spool 32b is radially guided and axially movable. The auxiliary spool 32b is essentially rotationally symmetrical and has a first outer radius in a first axial section on the left and center of the drawing, which interacts with the first radius of the main valve spool 16. In a second axial section on the right of the drawing, the auxiliary spool 32b has a second outer radius, which interacts with the second radius of the main valve spool 16. A ring-shaped cavity is formed between the main valve spool 16 and the auxiliary spool 32b due to the step between the aforementioned first and second radii. The volume of this cavity varies depending on the axial position of the auxiliary spool 32b relative to the main valve spool 16. In the first axial section of the auxiliary valve 32b, a first and a second radial through-channel (without reference numerals) are provided, which are axially spaced apart from each other. A central axial first inner channel 33 is provided axially between the first and the second radial through-channel, which hydraulically connects the first and second radial through-channels. This forms a first channel system 35. In the second axial section of the auxiliary valve 32b, a third and a fourth radial passage channel are provided, which are axially spaced apart from each other. A central axial second inner channel 39 is provided axially between the third and the fourth radial passage channel, which hydraulically connects the third and fourth radial passage channels. This forms a second channel system 41. In the guide bore 74 of the main valve spool 16, a second spring 37 (“auxiliary spring”), also designed as a helical spring, is arranged axially between an end face of the auxiliary spool 32b (left in the drawing) and the base of the main valve spool 16. This spring pushes the auxiliary spool 32b and the main valve spool 16 axially away from each other. An end section of the auxiliary spool 32b (right in the drawing) can be subjected to an axially acting pressure force by the magnetic armature 58 (similar to Fig. 1). Furthermore, the housing 12 includes the axial connecting channel 46, which, as in the embodiment of Fig. 1 in the drawing, is arranged above the housing bore 14 and extends parallel to it. The left end section of the connecting channel 46 in the drawing can be hydraulically connected to a fluid area via the first radial housing channel 50 and an adjoining recess ("ball chamber"). This recess characterizes a locking area 76, in which a plurality of locking balls 78 are present. The sectional view in Fig. 10 shows that the locking area 76 comprises, for example, at least two radially offset sections, or that the locking area 76 is designed as an annular circumferential recess. In the drawing, the left and right (possibly annular) end faces of the locking area 76 are axially inclined, with the locking area 76 opening towards the housing bore 14. The inclination of the end faces forms a conical seat for the locking balls 78, as indicated by arrow 80 in Fig. 10. This means that the locking area 76 comprises an inclined surface inclined towards the main valve spool 16, against which the locking ball 78 is subjected by pressure within the locking area 76. Furthermore, a spring assembly, designated by arrow 82, is provided, which acts on the locking ball 78 away from the inclined surface. The locking area 76, the at least one locking ball 78, the aforementioned conical seat, and the spring assembly are elements of a locking device of the slide valve 10. The right end section of the connecting channel 46 in the drawing can also be hydraulically connected to a fluid area via the second radial housing channel 52, in particular at the second channel section 72 of the main valve spool 16. Figures 10, 11, 12, 13, 14, 15, 16, 17, 18 to 19 describe a slide valve 10, wherein the aforementioned locking device comprises a locking element 78 controlled by pressure in the locking area 76, which has a locked position and a released position. In the locked position, the locking element 78 engages with the main valve slide 16 in a frictional engagement. In the released position, the frictional engagement is released. The main valve slide 16 can connect the locking area 76 to the inlet port P, and the auxiliary slide 32b can connect the locking area 76 to the outlet port T1 or T2. The locking area 76 is permanently connected to the drain connection T3 on the side of the spring assembly indicated by arrow 82, with a small gap. As described above, the locking element comprises at least one locking ball 78.As already described, or as can be seen from Figs. 10, 11, 12, 13, 14, 15, 16, 17 to 18, the auxiliary slide 32b is arranged between the actuator (electromagnet 54) and the main valve slide 16, and the first spring 28 is arranged between the main valve slide 16 and the housing 12, and the second spring 37 is arranged between the main valve slide 16 and the auxiliary slide 32b, wherein the first spring 28 is stiffer than the second spring 37. The operation of the second embodiment of the slide valve 10 is explained in more detail below using Fig. 11, Fig. 12, Fig. 13, Fig. 14, Fig. 15, Fig. 16, Fig. 17, Fig. 18 to Fig. 19. The locking of the main valve spool 16 in the left-hand position shown in Fig. 10 is based on the fact that the fluid enclosed in the locking area 76 exerts pressure on the rotating locking balls 78, pressing them into the conical seat (arrow 80) and generating increased friction between the main valve spool 16 and the stationary housing 12. When the solenoid coil 56 is energized, the solenoid armature 58 and the main valve spool 16 move towards the first spring 28 (see Figs. 11 to 12) until an equilibrium is reached between the magnetic, hydraulic, and main spring forces (Fig. 13). This is the normal operating mode of the spool valve 10. The main spring 28 is stiffer than the auxiliary spring 37. A rapid interruption of the current causes the auxiliary slide 32b to extend, whereupon the first channel system 35 ("inner pressure channel") opens and simultaneously the connection (second channel system 41) between the connecting channel 46 and the second discharge channel T2 closes (see Fig. 14). The locking balls 78 are now pressed into the conical seat (arrow 80) by the fluid pressure in the locking area 76, thereby locking the main valve slide 16 and allowing the coil current to be switched off (see Fig. 15). This applies provided that equation 4 is satisfied. To unlock the main valve spool 16, the solenoid coil 56 is energized with the actuating current (see Fig. 16). The auxiliary spool 32b, through its internal channels, closes the connecting channel 46 from the pressure chamber and connects the connecting channel 46 to the tank. To release the locking balls 78 from their press fit (arrow 80), the solenoid coil 56 is energized with a higher current (see Fig. 19). The locking balls 78 are then released by the movement of the main valve spool 16. A spring element (arrow 82) prevents the locking balls 78 from being drawn into their press fit (arrow 80) when the main valve spool 16 retracts (see Fig. 18). Figure 19, similar to Figure 9, shows a pressure-flow characteristic curve corresponding to the second embodiment of the slide valve 10. The abscissa of the depicted coordinate system corresponds to a time t. The solid curve and the solid ordinate correspond to a hydraulic pressure. The dashed curve and the dashed ordinate correspond to a flow rate. Reference numerals 1 to 8 characterize eight positions during the operation of the slide valve 10, corresponding to Figures 11, 12, 13, 14, 15, 16, 17 to 18. The described nested pistons can be used on all spool valves. This invention is therefore of interest for hydraulic valves in systems requiring self-holding.

Claims

Slide valve (10), in particular hydraulic valve, comprising a housing (12), a main valve spool (16), wherein the main valve spool (16) is arranged in the housing (12), an auxiliary spool (32a; 32b), wherein the auxiliary spool (32a; 32b) is arranged at least partially in the main valve spool (16), wherein the main valve spool (16) and the auxiliary spool (32a; 32b) are axially displaceable by a single common actuator, preferably an electromagnet (54), wherein the auxiliary spool (32a; 32b) is displaceable at least temporarily independently of the main valve spool (16), wherein the slide valve (10) comprises a locking device with which the main valve spool (16) can be locked in a position, and wherein the locking device is controlled by the auxiliary spool (32a;32b) is controlled, characterized in that the locking device comprises a hydraulically effective surface on the main valve spool (16) that defines a locking chamber (62), and that the main valve spool (16) can connect the locking chamber (62) to an inlet port (P) and the auxiliary spool (32a) can connect the locking chamber (62) to an outlet port (T2). Slide valve (10) according to claim 1, characterized in that a flow restrictor (48) is arranged between the inlet connection (P) and the locking chamber (62). Slide valve (10) according to one of claims 1 or 2, characterized in that the auxiliary slide (32a) is arranged between the actuator and the main valve slide (16), a first spring (28) is arranged between the main valve slide (16) and the housing (12), and a second spring (37) is arranged between the main valve slide (16) and the auxiliary slide (32a), and that the second spring (37) is stiffer than the first spring (28). Slide valve (10), in particular hydraulic valve, comprising a housing (12), a main valve spool (16), wherein the main valve spool (16) is arranged in the housing (12), an auxiliary spool (32a; 32b), wherein the auxiliary spool (32a; 32b) is arranged at least partially in the main valve spool (16), wherein the main valve spool (16) and the auxiliary spool (32a; 32b) are axially displaceable by a single common actuator, preferably an electromagnet (54), wherein the auxiliary spool (32a; 32b) is displaceable at least temporarily independently of the main valve spool (16), wherein the slide valve (10) comprises a locking device with which the main valve spool (16) can be locked in a position, and wherein the locking device is controlled by the auxiliary spool (32a;32b) is controlled, characterized in that the locking device comprises a locking element controlled by a pressure in a locking area (76), which has a locking position and a release position, wherein the locking element in the locking position interacts with the main valve slide (16) in frictional engagement and in the release position the frictional engagement is released, and wherein the main valve slide (16) can connect the locking area (76) to an inlet port (P) and the auxiliary slide (32b) can connect the locking area (76) to an outlet port (T2). Slide valve (10) according to claim 4, characterized in that the locking element comprises at least one locking ball (78). Slide valve (10) according to claim 5, characterized in that the locking area (76) comprises an inclined surface inclined towards the main valve slide (16), against which the locking ball (78) is acted by a pressure in the locking area (76). Slide valve (10) according to claim 6, characterized in that a spring device is provided which acts on the locking ball (78) away from the inclined surface. Slide valve (10) according to one of claims 4 to 7, characterized in that the auxiliary slide (32b) is arranged between the actuator and the main valve slide (16), a first spring (28) is arranged between the main valve slide (16) and the housing (12), and a second spring (37) is arranged between the main valve slide (16) and the auxiliary slide (32b), and that the first spring (28) is stiffer than the second spring (37).

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