Damping valve

1. A damping valve comprising:

a valve seat member provided with a port;

a valve body that opens or closes the port;

a back-pressure chamber configured to bias the valve body toward the valve seat member using an internal pressure;

a pilot passage configured to reduce a pressure upstream of the port and guide the pressure into the back-pressure chamber; and

a pilot valve provided in the middle of the pilot passage, the pilot valve being configured to control the internal pressure of the back-pressure chamber,

wherein the pilot valve has a pilot valve seat member and a pilot valve body,

the pilot valve seat member having an cylindrical valve container provided with a penetrating hole connecting the inside and the outside, the penetrating hole communicating with the port, and an annular pilot valve seat provided in an end of the valve container, and

the pilot valve body having a large diameter portion, a small diameter portion slidably inserted into the valve container, and a concave portion provided between the large diameter portion and the small diameter portion to face the penetrating hole, and

an end of the large diameter portion is seated on or unseated from the pilot valve seat to open or close the pilot passage.

2. The damping valve according to claim 1 , wherein the valve container has a bottomed cylindrical shape and forms a space along with the pilot valve body,

the pilot valve body has a communicating channel communicating with one end to the other end, and an orifice provided in the middle of the communicating channel, and

the space communicates with the outside via the communicating channel.

3. The damping valve according to claim 1 , further comprising a failsafe channel branching from the pilot passage; and

a failsafe valve provided in the middle of the failsafe channel,

wherein the pilot valve is configured to block a side of the pilot passage downstream from a connection point to the failsafe channel when the pilot valve body is separated from the pilot valve seat at maximum.

4. The damping valve according to claim 1 , wherein the pilot valve further has

a pilot valve body biasing member configured to bias the pilot valve body to recede from the pilot valve seat, and

a solenoid that exerts a thrust force such that the pilot valve body is seated on the pilot valve seat resisting to a biasing force of the pilot valve body biasing member.

5. The damping valve according to claim 1 , wherein the valve seat member has a first valve seat that surrounds the port,

the damping valve further comprising a subsidiary valve body seated on or unseated from the first valve seat, the subsidiary valve body having a second valve seat in a side opposite to the valve seat member,

the valve body is seated on or unseated from the second valve seat and forms a valve-body intermediate chamber between the subsidiary valve body and the valve body in an inner circumferential side of the second valve seat,

the damping valve further comprising a restrictive passage that causes the port and the valve-body intermediate chamber to communicate with each other, the restrictive passage being configured to apply resistance to a passing fluid flow, and

the valve body and the subsidiary valve body are pressed by the internal pressure of the back-pressure chamber toward the valve seat member.

6. The damping valve according to claim 5 , wherein the subsidiary valve body is floatably stacked on the valve seat member.

7. The damping valve according to claim 5 , further comprising a subsidiary valve body biasing means configured to bias the subsidiary valve body toward the valve seat member.

8. The damping valve according to claim 5 , wherein both the first and second valve seats have an annular shape, and

an inner diameter of the second valve seat is set to be larger than that of the first valve seat.

9. The damping valve according to claim 5 , wherein the restrictive passage is formed in the subsidiary valve body.

10. The damping valve according to claim 1 , wherein the valve body is an annular leaf valve having an inner circumference fixed to the valve seat member and an outer circumference that can be flexed.

11. The damping valve according to claim 1 , further comprising a tubular spool that abuts on a side of the valve body opposite to the valve seat member;

a spool holding member having an outer circumference where the spool is mounted movably along an axial direction; and

a ring mounted to the outer circumference of the spool holding member to make sliding contact with an inner circumference of the spool,

wherein the back-pressure chamber is partitioned by the spool and the spool holding member, and

the internal pressure of the back-pressure chamber is applied to an inner circumferential side of the ring.

12. The damping valve according to claim 11 , wherein the ring has a bias cut.