Pilot-operated switching valve and shock absorber

Abstract

A pilot-operated switching valve (20) comprises an actuator unit (30) driven by an electrical current, a first valve body (53) which opens a flow path (R) when the actuator unit (30) is driven, and a second valve body (61) which opens and closes the flow path (R) together with the first valve body (53). The second valve body further opens the flow path (R) by means of a pressure differential between an upstream and a downstream side of the first valve body (53) when the first valve body (53) opens the flow path (R). The actuator unit (30) allows the second valve body (61) to remain in contact with the flow path (R) when it is open.

Description

TECHNICAL AREA

[0001] The present invention relates to a pilot-operated switching valve and a shock absorber. State of the art

[0002] It is known, for example, that a pilot-operated switching valve is provided within a shock absorber of a straddle-seat vehicle to open and close a flow path through which oil flows. Patent literature 1 discloses a prior art technology in which a pilot-operated switching valve is mounted.

[0003] A shock absorber as disclosed in patent literature 1 comprises a drive unit which is operated by electrical current, a first valve body which opens a flow path when the drive unit is operated, and a second valve body which further opens the flow path due to a pressure difference when the first valve body opens the flow path.

[0004] By first opening the first valve body, which is smaller than the second valve body, the second valve body is opened using a pressure differential. Since the force required to open the small first valve body can be small, the force required to open the flow path can also be small. CITATION LIST PATENT LITERATURE

[0005] Patent Literature 1: JP2016-176552A SUMMARY OF THE INVENTIONAL PROBLEM

[0006] As a result of studies on the pilot-operated switching valve disclosed in patent literature 1, the inventors discovered that the second valve body can oscillate in a state where the flow path is open. This is attributed to the fact that the degree of opening of the second valve body depends on the flow rate passing through the first and second valve bodies, and the flow rate, in turn, is mutually dependent on the degree of opening of the second valve body, resulting in an oscillatory motion of a non-convergent system. It was found that when such a pilot-operated switching valve is used in a shock absorber, the damping force generated in the shock absorber can be influenced.

[0007] One object of the present invention is to provide a pilot-operated switching valve that is able to prevent vibrations of a second valve body. SOLUTION TO THE PROBLEM

[0008] As a result of intensive studies, the inventors discovered that vibrations of a second valve body are prevented by applying pressure from a drive unit to press a first valve body against the second valve body in a state where a flow path is open. The present invention was further developed based on these findings.

[0009] The following describes the present revelation.

[0010] According to the present disclosure, a pilot-operated switching valve is provided, comprising a drive unit configured to be operated by electrical current, a first valve body which is a valve body which opens a flow path when the drive unit is operated, and a second valve body configured to open and close the flow path together with the first valve body, and which is a valve body which further opens the flow path by means of a pressure difference between an upstream side and a downstream side of the first valve body when the first valve body opens the flow path, wherein the drive unit can also hold the second valve body which opens the flow path in an open state. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0011] According to the present invention, it is possible to provide the pilot-operated switching valve which is able to prevent vibrations of the second valve body. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a front view of a shock absorber equipped with a pilot-operated switching valve according to an example. Fig. 2 is an enlarged view of part 2 in Fig. 1. Fig. 3 is a cross-sectional view along a line 3-3 in Fig. 2. Fig. 4A is a front view of a second press section and Fig. 4B is a side view of the second pressing section. Fig. 5A is a view illustrating the pilot-operated switching valve before a drive unit is operated. Fig. Figure 5B is a view illustrating the operation of the pilot-operated switching valve when the actuator unit presses a first valve body, and Fig. 5C is an enlarged view of section 5C of Fig. 5B. Fig. Figure 6A is a view illustrating operation when a second valve body is pressed downwards, and Fig. 6B is an enlarged view of part 6B in Fig. 6A. Fig. Figure 7 is a diagram illustrating a relationship between time and the position of the second valve body. DESCRIPTION OF EXECUTION FORMS

[0012] One embodiment of the present invention is described below with reference to the accompanying drawings. The embodiment shown in the accompanying drawings is an example of the present invention, and the present invention is not limited to this embodiment. <beispiel>

[0013] It will be on Fig. 1 referenced. Fig. Figure 1 illustrates a telescopic shock absorber 10 that forms a major part of a front fork. The front fork is located in the front section of a straddle-seat vehicle, such as a two-wheeled vehicle, and prevents vibrations received from a road surface from being transmitted to one side of the vehicle body.

[0014] The shock absorber 10 extends from the vicinity of a two-wheeled vehicle's head tube to a front wheel. When the two-wheeled vehicle is in motion, vibrations are introduced from the front wheel due to the influence of an uneven road surface or the like. At this point, the shock absorber 10 compresses and expands, generating a damping force.

[0015] The shock absorber 10 comprises as its main components a tubular outer tube 11 extending downwards from the head tube of the two-wheeled vehicle towards the front wheel, a tubular inner tube 12 extending upwards from the front wheel towards the head tube and having a front end inserted into the outer tube 11, and a coil spring (not shown) that biases the outer tube 11 and the inner tube 12 away from each other. A space enclosed by the outer tube 11 and the inner tube 12 is filled with oil as the operating fluid.

[0016] The shock absorber 10 includes an outer tube cover section 16, which closes an upper end (terminating end) of the outer tube 11, and an axle holder 17, which closes a lower end (terminating end) of the inner tube 12.

[0017] A pressure accumulator 18, into which excess oil from the inner tube 12 can flow, is provided at a section adjacent to a lower section of the inner tube 12. A pilot-operated switching valve 20, which opens and closes a flow path R of the oil from the inner tube 12 to the pressure accumulator 18, is provided between the inner tube 12 and the pressure accumulator 18. The flow path R is a section that connects an inner section of the pilot-operated switching valve 20, an inner section of the inner tube 12, and the pressure accumulator 18.

[0018] A bladder or a free piston can be used as the pressure accumulator. Furthermore, any other pressure accumulator can be used besides a bladder or a free piston, as long as the accumulator can store excess oil in the inner tube. The pressure accumulator can be positioned on an axis of the inner tube.

[0019] It will be on Fig. 2 and Fig. 3. Referenced. Fig. 2 and Fig. Figure 3 illustrates a main part of the pilot-operated switching valve 20. A housing 21 is shown schematically for understanding the invention.

[0020] The pilot-operated switching valve 20 comprises the tubular housing 21, which is essentially provided with a bottom; an actuator 30, which is operated by electrical current; a separating element 23, which is provided adjacent to a front end of the actuator 30 and separates the flow path R in the housing 21; a first valve 50, which is a valve that opens the flow path R when the actuator 30 is operated; a second valve 60, which is a valve that further opens the flow path R by means of a pressure differential when the first valve 50 opens the flow path R; a valve housing element 26, which accommodates the first valve 50 and the second valve 60; and a valve guide element 27, which is a tubular element that is accommodated in the valve housing element 26 and guides the second valve 60.

[0021] The housing 21, for example, has a tubular inner circumferential section with a base. The housing 21 has a first flow path orifice section 21a, which is open so that the oil can flow from the inner tube 12 (see Fig. 1) can flow in, and a second flow path hole section 21b, which is open, so that the pressure accumulator 18 (see Fig. 1) through which flowing oil can pass.

[0022] The drive unit 30 comprises a tubular drive unit body 31 with a front end attached to the housing 21, a rod 32 designed to move forward and backward along an axis CL of the drive unit body 31, a coil 33 wound to surround an outer circumference of the rod 32 and capable of receiving power, a piston 40 provided at a front end of the rod 32 capable of moving forward and backward along the axis CL with the rod 32, a retraction stop 35 attached to an inner circumferential surface of the drive unit body 31 and defining a retraction limit of the piston 40, and a piston guide section 36 attached to the inner circumferential surface of the drive unit body 31 and guiding the piston 40.

[0023] The front end of the drive unit body 31 rests against a stepped section formed within the housing 21. Thus, the entire drive unit 30 is positioned.

[0024] A preload force in a retraction direction is exerted on the rod 32 by a spring (not illustrated).

[0025] A battery (not illustrated) is connected to coil 33 and can supply it with power. A control unit switches the electrical current to coil 33 on and off. Various sensors are connected to the control unit, and the control unit switches the electrical current to coil 33 on and off based on electrical signals from these sensors.

[0026] The piston 40 includes a first pressing section 41, which rests against the front end of the rod 32 and has an essentially T-shape, a disc spring 42, through which the first pressing section 41 passes and which rests against a flange-shaped section of the first pressing section 41, and a second pressing section 43, into which a front end of the first pressing section 41 is inserted and which rests against the disc spring 42.

[0027] The first press section 41 includes a bar support section 41a, against which the bar 32 rests, and a first press section body 41b, which extends along the axis CL from a center of the bar support section 41a.

[0028] The disc spring 42 is formed by a ring-shaped section with a multitude of wing-shaped springs extending from the ring section towards the center.

[0029] It will be on Fig. 2, Fig. 4A and Fig. Reference is made to 4B. The second press section 43 includes a tubular disc spring mounting section 43a with a base, which encloses the disc spring 42 together with the retraction stop 35, a tubular coupling section 43b, which extends along the axis CL from the center of the disc spring mounting section 43a and into which the first press section body 41b is pressed, a second shaft section 43c, which is a shaft-shaped section extending along the axis CL from a front end of the coupling section 43b and which can bear against the second valve 60, and a first shaft section 43d, which extends along the axis CL from a front end of the second shaft section 43c and which can bear against the first valve 50.

[0030] The second shaft section 43c has a non-circular cross-section and is specifically formed in a plate shape, the thickness of which gradually decreases from the tubular coupling section 43b towards the first shaft section 43d. Furthermore, a shoulder section 61c (inclined surface) is provided in a lateral direction of the plate-shaped second shaft section 43c, the diameter of which is reduced towards the first shaft section 43d and which can bear against a circumferential edge of a second valve hole section 61a of a second valve body 61. With this configuration, the oil can flow through the second valve hole section 61a in a state in which the shoulder section 61c bears against the circumferential edge of the second valve hole section 61a of the second valve body 61. The front end is formed by a tapered surface whose diameter decreases towards the first shaft section 43d.Shoulder section 61c is not limited to the inclined surface and may have a stepped shape.

[0031] It will be on Fig. 2. Reference is made to the piston guide section 36. The piston guide section 36 has a tapered surface section 36a of a tapered guide section, which is part of an outer circumferential surface and is inclined with respect to the axis CL. The tapered surface section 36a of the guide section is separated from the separating element 23. Therefore, the oil can pass between the tapered surface section 36a of the guide section and the separating element 23.

[0032] A separating element hole section 23a, through which the oil can pass around the axis CL, is open in the separating element 23. The separating element hole section 23a forms part of the flow path R and is opened and closed by the first valve 50 and the second valve 60.

[0033] The first valve 50 comprises a preload element 51, one end of which rests against the valve body element 26 and is implemented by a compression helical spring, a receiving element 52 which receives the other end of the preload element 51, a first valve body 53 which is attached to the receiving element 52 and is able to open and close a part of the flow path R, and a first valve seat section 54 which is formed in the second valve 60 and against which the first valve body 53 rests in a state of closing the flow path R.

[0034] The second valve 60 comprises the second valve body 61, which has a tubular shape with a bottom, and a second valve seat section 62, which is formed in the separating element 23 and against which the second valve body 61 rests in a state of closing the flow path R.

[0035] The preloading element 51 preloads the second valve body 61 in a closing direction over the first valve body 53 and also forms part of the second valve 60. In other words, it can be said that the second valve 60 also includes the preloading element 51.

[0036] The receiving element 52 is displaceable in an axial direction along an inner circumferential surface of the second valve body 61. This means that the direction of movement of the first valve body 53 is guided by the inner circumferential surface of the second valve body 61 via the receiving element 52. An oil passage 52a in the receiving element is open between the receiving element 52 and the inner circumferential surface of the second valve body 61, allowing oil to pass through.

[0037] A front end of the receiving element 52 is designed to have a smaller outer diameter than other sections, and a predetermined space is formed between the front end of it and the second valve body 61.

[0038] The first valve body 53 has a spherical shape. More precisely, a base end of the first valve body 53 is formed in a cylindrical shape, a front end of it is formed in a hemispherical shape, and these are integrally continuous.

[0039] The first valve seat section 54 is inclined with respect to the axis CL in order to increase the contact area with the first valve body 53.

[0040] The second valve body 61 has the second valve hole section 61a, which penetrates the center of a bottom section. The second valve hole section 61a is continuous with the first valve seat section 54.

[0041] A hydraulic pressure receiving surface section 61b, inclined in an oblique direction with respect to the oil flowing to the second valve body 61, is formed on an outer circumferential surface of the second valve body 61.

[0042] The second valve seat section 62 is fitted with an O-ring.

[0043] A groove section 26a, formed in a groove shape, is formed in a bottom section of the valve housing element 26 in a radial direction around the axis CL. Furthermore, a housing section through-hole section 26b penetrates the bottom section of the valve housing element 26 along the axis CL from a center point of the groove section 26a. The inner diameter of the housing section through-hole section 26b is smaller than the inner diameter of the preload element 51.

[0044] The valve guide element 27 has a plurality of valve guide hole sections 27a that allow the passage of oil. A central axis of the valve guide hole section 27a is oriented radially. The hydraulic pressure receiving surface section 61b of the second valve body 61 can be said to be inclined with respect to the axis of the valve guide hole section 27a.

[0045] The operation of the pilot-operated switching valve 20, described above, is described below.

[0046] It will be on Fig. 5A is referenced. When the piston 40 is in a retracted position, the first valve body 53 and the second valve body 61 block the flow of oil to the pressure accumulator 18 (see Fig. 1) In this case, the oil flows, for example, to a variable spring rate mechanism. Specifically, the first valve body 53 rests against the first valve seat section 54, and the second valve body 61 rests against the second valve seat section 62 due to the preload force of the preload element 51. Accordingly, the flow path R is closed. At this point, by guiding the oil through a relative movement of the inner and outer tubes to the variable spring rate mechanism, the storage length of the spring of the variable spring rate mechanism is shortened, and a strong spring reaction force is obtained.

[0047] It will be on Fig. 2. Reference is made to. For example, if the variable spring rate mechanism is not operated, the coil 33 is energized. When energized, the rod 32 advances and the piston 40 is pushed out. It is referred to Fig. Reference is made to 5B. The pushed-out piston 40 pushes the first valve body 53 against the preload force of the preload element 51. Accordingly, the blocked flow path R is released, and the oil flows to the pressure accumulator 18. Since the accumulator length of the spring of the variable-rate mechanism does not change, a small spring reaction force is obtained at this time.

[0048] It will be on Fig. Reference is made to section 5C. When the first stem section 43d presses the first valve body 53, the first valve body 53 is separated from the first valve seat section 54. Thus, the oil can pass through the second valve hole section 61a. That is, part of the flow path R is opened.

[0049] It will be on Fig. Reference is made to 6A. When the flow path R is opened, the second valve body 61 is forced downwards by the pressure difference between a hydraulic pressure on an upstream side and a hydraulic pressure on a downstream side of the second valve body 61. As the second valve body 61 is forced downwards, the piston 40 moves further forwards.

[0050] When the second valve body 61 is forced downwards by the hydraulic pressure until it rests against the valve housing element 26, the first valve body 53 is also forced downwards to its retraction limit by the piston 40. Accordingly, the flow path R is fully open. The oil flows from the valve guide hole section 27a through the separating element hole section 23a.

[0051] Since the hydraulic pressure receiving surface section is inclined with respect to both the direction in which the oil flows and the direction in which the second valve body 61 moves, the second valve body 61 can be operated reliably.

[0052] It will be on Fig. Reference is made to Figure 6B. In a state where the second valve body 61 fully opens the flow path R, the first stem section 43d rests against the first valve body 53, and the second stem section 43c rests against the second valve body 61. A section of the second valve body 61 against which the second stem section 43c rests is formed in a tapered shape along an inclined form of the front end of the second stem section 43c.

[0053] In a state where the flow path R is fully open, a condition is maintained in which the drive unit 30 is in contact with the first valve body 53 and the second valve body 61. As a result, the oil is guided to the pressure accumulator 18 due to the relative movement of the inner and outer tubes, so that the oil is not directed to the variable spring rate mechanism, the spring's storage length is not shortened, the spring reaction force is not increased, and the same behavior as that of a normal suspension is maintained.

[0054] On the other hand, if the electrical current is supplied to coil 33 (see Fig. 2) ends, the piston 40 retracts. When the piston 40 retracts, the first valve body 53 and the second valve body 61 close the flow path R by the preload force of the preload element 51.

[0055] According to the pilot-operated switching valve 20, the actuator unit 30 maintains a state of energization at the second valve body 61 in a state where the second valve body 61 opens the flow path R. The reason for this is described next.

[0056] It will be on Fig. 7 referenced. Fig. Figure 7 illustrates a relationship between time and the position of the second valve body. Line 71 indicates a result when a pilot-operated switching valve is used according to a comparison example, and line 72 indicates a result when the pilot-operated switching valve 20 (see Fig. 2) as shown in the example. A horizontal axis represents time, and a vertical axis represents the position of the second valve body relative to a second valve seat.

[0057] According to the pilot-operated switching valve in the comparative example, as indicated by line 71, the second valve body gradually begins to open when the first valve body begins to open and a predetermined time T1 elapses. Although the second valve body is fully open at time T2, its position is not stable because the second valve body oscillates due to the influence of the oil flow.

[0058] It will also be on Fig. Reference is made to 5C. As indicated by line 72, the second valve body 61, according to the pilot-operated switching valve 20, gradually begins to open as the first valve body 53 begins to open and the predetermined time T1 elapses.

[0059] It will be on Fig. 6B and Fig. 7. The second valve body 61 reaches a fully open position at time T2. Since the second valve body 61 is pressed by the drive unit 30, vibrations are prevented and the position is stabilized.

[0060] The pilot-operated switching valve 20 described above is summarized below.

[0061] It will be on Fig. 2. In the first aspect, the pilot-operated switching valve 20 comprises the actuator unit 30, configured to be operated by electrical current, the first valve body 53, which is a valve body that opens the flow path R when the actuator unit 30 is operated, and the second valve body 61, configured to open and close the flow path R together with the first valve body 53, and which is a valve body that further opens the flow path R by means of the pressure difference between the upstream and downstream sides of the first valve body 53 when the first valve body 53 opens the flow path R. It is referred to Fig. Reference is made to 6B. The drive unit 30 makes it possible to keep the second valve body 61, which opens the flow path R, in an open state as well.

[0062] It will also be on Fig. 7. According to the pilot-operated switching valve 20, the actuator unit 30 is in a state where the second valve body 61 is fully open, in contact with the second valve body 61. Accordingly, it is possible to prevent a change in the position of the second valve body 61 due to vibrations. That is, it is possible to provide the pilot-operated switching valve 20, which is capable of preventing the vibrations of the second valve body 61.

[0063] It will only be on Fig. Reference is made to Section 6B. In the second aspect, the pilot-operated switching valve 20 according to the first aspect further comprises the first valve seat section 54, configured to cause the first valve body 53 to bear against the first valve seat section 54 when the flow path R is closed. The second valve body 61 has the second valve orifice section 61a through which a fluid can flow. The first valve seat section 54 is formed on a circumferential edge of the second valve orifice section 61a of the second valve body 61. Since the first valve seat section 54 is formed in the second valve body 61, the first valve seat section 54 can be formed with a small number of components, which is preferred.

[0064] In the third aspect, the actuator unit 30 in the pilot-operated switching valve 20, as described in the second aspect, comprises the first stem section 43d, configured to pass through the second valve orifice section 61a and depress the first valve body 53. In other words, the second valve orifice section 61a is open on a path along which the first stem section 43d operates, and the first valve body 53 is provided. Accordingly, the actuator unit 30, the first valve body 53, and the second valve body 61 can be provided in a compact form, and the pilot-operated switching valve 20 can be miniaturized.

[0065] In the fourth aspect, the actuator unit 30 in the pilot-operated switching valve 20, as described in the third aspect, comprises the second stem section 43c, configured to abut a circumferential edge of the second valve orifice section 61a. By abutting the circumferential edge of the second valve orifice section 61a, the second stem section 43c can be formed in a position close to the first stem section 43d. The actuator unit 30 can be manufactured compactly, and the pilot-operated switching valve 20 can be miniaturized.

[0066] In the fifth aspect, the second shaft section 43c in the pilot-operated switching valve 20 has a non-circular cross-section according to the fourth aspect, and a fluid can flow through the second valve hole section 61a in a state in which the second shaft section 43c is in contact with the circumferential edge of the second valve hole section 61a.

[0067] It will be on Fig. Reference is made to Section 5A. In the sixth aspect, the pilot-operated switching valve 20, according to one of the second to fifth aspects, further comprises the preloading element 51, which preloads the first valve body 53 in the direction of the first valve seat section 54, and the second valve seat section 62, configured to cause the second valve body 61 to bear against the second valve seat section 62 when the flow path R is closed. The second valve body 61 receives a preload force in a seat direction on the second valve seat section 62 when the first valve body 53 bears against the first valve seat section 54 by a preload force of the preloading element 51. Since the first valve body 53 and the second valve body 61 are preloaded in the closing direction by a preloading element 51, the number of components can be reduced.

[0068] Although the example described involves applying the shock absorber according to the present invention to an inverted front fork of a two-wheeled vehicle, the shock absorber can also be applied to an upright front fork or a rear cushion. Furthermore, the vehicle to be fitted is not limited to two-wheeled vehicles and can be fitted to a straddle-seat vehicle, such as a tricycle or other vehicles.

[0069] The pilot-operated switching valve can be located between a shock absorber body and the pressure accumulator, or between a shock absorber body and the variable spring rate mechanism. Furthermore, the pilot-operated switching valve can be located in a position other than these sections, and its location is not limited to these sections.

[0070] The present invention is not limited to the example, as long as operations and effects according to the present invention are shown. Commercial applicability

[0071] The pilot-operated switching valve according to the present invention is suitable for opening and closing a flow path of a front fork of a straddle-seat vehicle. Reference symbol list 20 pilot-operated switching valve 30 drive unit 43c second shaft section 43d first shaft section 51 Preload element 53 first valve body 54 first valve seat section 61 second valve body 61a second valve hole section 62 second valve seat section R Flow path QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2016-176552A

[0005] < / beispiel>

Claims

Pilot-operated switching valve (20) comprising: an actuator unit (30) configured to be operated by electrical current; a first valve body (53) which is a valve body that opens a flow path (R) when the actuator unit (30) is operated; and a second valve body (61) configured to open and close the flow path (R) together with the first valve body (53), and which is a valve body that further opens the flow path (R) by means of a pressure differential between an upstream side and a downstream side of the first valve body (53) when the first valve body (53) opens the flow path (R), wherein the actuator unit (30) can also hold the second valve body (61) which opens the flow path (R) in an open state. Pilot-operated switching valve (20) according to claim 1, further comprising a first valve seat section (54) configured to cause the first valve body (53) to bear against the first valve seat section (54) when the flow path (R) is closed, wherein the second valve body (61) has a second valve hole section (61a) through which a fluid can flow, and the first valve seat section (54) is formed on a circumferential edge of the second valve hole section (61a) of the second valve body (61). Pilot-operated switching valve (20) according to claim 2, wherein the actuator unit (30) has a first shaft section (43d) which is configured to pass through the second valve hole section (61a) and to push the first valve body (53). Pilot-operated switching valve (20) according to claim 3, wherein the drive unit (30) has a second shaft section (43c) which is configured to bear against a circumferential edge of the second valve hole section (61a). Pilot-operated switching valve (20) according to claim 4, wherein the second shaft section (43c) has a non-circular cross-section and a fluid can flow through the second valve hole section (61a) in a state in which the second shaft section (43c) is in contact with the circumferential edge of the second valve hole section (61a). Pilot-operated switching valve (20) according to claim 2, further comprising: a preloading element (51) that preloads the first valve body (53) in the direction of the first valve seat section (54); and a second valve seat section (62) configured to cause the second valve body to bear against the second valve seat section (62) when the flow path (R) is closed, wherein the second valve body (61) receives a preload force in a seat direction on the second valve seat section (62) when the first valve body (53) bears against the first valve seat section (54) by a preload force of the preloading element (51). Shock absorber (10) comprising: the pilot-operated switching valve (20) according to claim 1; an outer tube (11) and an inner tube (12) in the form of a telescope; and a pressure accumulator (18) which is provided in the outer tube (11) or the inner tube (12) and is configured to store an oil, wherein the flow path (R) of the pilot-operated switching valve (20) is a section connecting an inner section of the inner tube (12) and the pressure accumulator (18).

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