JPH0717894Y2 - Relief valve - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a relief valve suitable for controlling the hydraulic pressure of a hydraulic motor for turning a driver's cab or the like in an industrial construction machine such as a power shovel. It is about.

(Prior Art) In a hydraulic circuit of a hydraulic motor, a relief valve is provided in order to suppress a rise in hydraulic pressure during acceleration or braking to a predetermined value. In order to eliminate shock during acceleration or braking, it is common to use a relief valve of the type having a built-in cushioning piston. Relief valves of this type are described, for example, in Japanese Utility Model Publication No. Sho 63-19668 and Japanese Utility Model Publication No. 63-21814, and due to the relationship of the pressure receiving area, the hydraulic pressure at which the piston starts a stroke causes a relief operation. It was well below the starting hydraulic pressure.

(Problems to be solved by the invention) In a hydraulic circuit of a hydraulic motor, a so-called cross connecting two relief valves in antiparallel between a hydraulic fluid supply port and a hydraulic fluid discharge port of the hydraulic motor. There is a circuit and a so-called absolute pressure circuit in which the inflow sides of the relief valves are connected to the pressure fluid supply port and the pressure fluid discharge port of the hydraulic motor, respectively, and the relief sides of these two relief valves are connected to the tank. Since the cross circuit requires an additional overload relief valve and the cost is high, an absolute circuit tends to be adopted.

However, the hydraulic circuit of the hydraulic motor produces a certain amount of hydraulic pressure during normal times other than acceleration and braking, so in the case of an absolute pressure circuit, it is between the inflow side and the relief side of the relief valve. A pressure difference may be generated, and the buffer piston may complete its operation before the relief operation is started. In such a case, there is an inconvenience that a cushioning effect is not obtained at the time of actual relief operation and a large shock is generated.

In order to eliminate such inconvenience, it is conceivable to increase the initial load of the spring that urges the cushioning piston. However, in this case, the starting pressure of the relief operation becomes high, so a sufficient cushioning effect is obtained. However, a shock is generated and the inconvenience cannot be eliminated.

(Means for Solving the Problem) According to the present invention, a tubular casing 1 having an annular sheet 3 forming an inflow hole 2 for inflow side pressure liquid fixed to one end and having the other end closed, and a large one end. A substantially cylindrical plunger 7 formed to have a diameter and slidably fitted to the inner circumference of the one end of the casing 1, and an inner circumference of the other end of the casing 1 and the other end of the plunger 7, which has a small diameter on one end side. A cylindrical stepped piston 10 that slidably fits with the outer circumference of the part and forms a liquid chamber 11 with the other end of the cane sig 1, and a step part on the outer circumference of the stepped piston 10 and An annular high-pressure damping chamber 12 formed by a step on the inner circumference of the casing 1, and a communication passage 10 for communicating the high-pressure damping chamber 12 with the liquid chamber 11.
b is provided, a through hole 8 is formed in the plunger 7 along the axial direction, and an arbitrary portion of the through hole 8 is made into a fine hole to form a narrowed portion 9, and one end of the stepped piston 10 and the A relief valve is characterized in that a spring 13 is interposed between one end of the plunger 7 and the outer diameter d ₃ of one end of the stepped piston 10 and the diameter d ₁ of the inflow hole 2 are substantially equal. Is.

(Operation) Since the outer diameter on the one end side of the stepped piston and the diameter of the inflow hole are made substantially equal, the hydraulic pressure at which the piston starts the stroke and the hydraulic pressure at which the relief operation starts are substantially equal. Damping is applied during the stroke of the stepped piston, and the difference between the pressure to stroke the piston and the relief pressure is small, that is, the pressure difference before and after the throttle of the inflow hole is small.
The buffer time can be set sufficiently long.

(Embodiment) An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a cross-sectional view of a relief valve according to an embodiment of the present invention, in which 1 is a substantially cylindrical casing main body, and one end of the casing main body 1 has a substantially annular shape which forms an inflow hole 2 for an inflow side pressure liquid. The sheet 3 is fixed in a concentric manner. One end of a substantially cylindrical pressure adjusting plug 4 is screwed into a female screw threaded on the inner circumference of the other end of the casing body 1. A substantially cylindrical lid 5 is screwed onto the female screw threaded on the inner circumference of the pressure adjustment plug 4 on the other end side, and the male thread screwed on the outer circumference of the pressure adjustment plug 4 is fitted to the casing body 1 of the casing body 1. A lock nut 6 that contacts the other end is screwed.

On the inner circumference of one end of the casing body 1, one end of a substantially cylindrical plunger 7 having one end formed in a large diameter and one end formed in a tapered truncated cone surface is slidably fitted. A through hole 8 is formed in the center of the plunger 7 along the axial direction. The through hole 8 is formed as a fine hole in the vicinity of the other end over a predetermined length, and the fine hole constitutes a narrowed portion 9. A stepped piston 10 having a large diameter at the other end is formed on the inner circumference of one end of the pressure adjusting plug 4.
Is slidably fitted, and the inner circumference of this stepped piston 10 is slidably fitted to the outer circumference of the other end of the plunger 7. A plurality of grooves 10a are radially formed on the other end surface of the stepped piston 10, and a liquid chamber 11 including the groove 10a is formed between the stepped piston 10 and the lid 5. Stepped piston 10
An annular high pressure damping chamber 12 is formed by the step portion on the outer circumference of the pressure adjusting plug 4 and the step portion on the inner circumference of the pressure adjusting plug 4, and the high pressure damping chamber 12 is formed in the stepped piston 10 as shown in FIG. It communicates with the liquid chamber 11 through the communication hole 10b.

An annular spring seat 10c is fixed to one end of the stepped piston 10, and a spring 13 composed of a coil spring is contracted between the spring seat 10c and one end of the plunger 7. A plurality of radial holes 1a are radially formed at one end of the casing body 1, and the space between the casing body 1 and the plunger 7 communicates with a tank (not shown) through the holes 1a. ing. A plurality of radial escape holes 1b are radially formed on one end side of the hole 1a of the casing body 1, and the inflow hole 2 and a tank (not shown) can communicate with each other through the escape holes 1b. is there. An O-ring 14 is interposed between the inner circumference of the casing body 1 and the outer circumference of the pressure adjusting plug 4, and the O ring is provided between the inner circumference of the other end of the pressure adjusting plug 4 and the outer circumference of the lid 5. 15 are installed.

If the diameter of the inflow hole 2 of the seat 3 is d1, the inner diameter of the stepped piston 10 is d2, the outer diameter of one end of the stepped piston 10 is d3, and the outer diameter of the other end of the stepped piston 10 is d4, then d3 The value of
It is set to a value close to d1. That is, in this embodiment, the thickness d3-d2 on the one end side of the stepped piston 10 is designed to be as thin as possible in terms of strength.

Next, the operation will be described. When the hydraulic pressure to be regulated by the relief valve exceeds a predetermined pressure, the stepped piston 10 starts to move to the one end side against the biasing force of the spring 13. At this time, the pressure acting on the area of the diameter d1 of the plunger 7 is equal to the pressure acting on the area of the diameter d2 of the opposite end surface (this is because the stepped piston 10 starts to be pushed) and the elastic force of the spring 13. Due to the balance pressure, the plunger 7 moves to the other end side against the urging force of the spring 13, and a gap is created between the one end face of the plunger 7 and the abutting face of the sheet 3, so that the inflow hole 2 The pressure fluid that has flowed into the
It is escaped to the tank through 1b. That is, the relief operation has started. This relief pressure is a pressure or a plunger that pushes the stepped piston 10 by the damping force generated in the stepped piston 10 by moving the stepped piston 10 to one end side and compressing the spring 13 to gradually increase the spring load. Due to both actions of gradually increasing the pressure on the opposite side of the seat 3 side of No. 7, the stepped piston 10 gradually increases until it reaches the stroke limit, and reaches a predetermined set pressure. The moving time of the stepped piston 10 increases the hydraulic pressure in the high-pressure damping chamber 12 due to the movement of the stepped piston 10, and therefore the pressure pressing the stepped piston 10 also increases. Stepped piston
The flow rate for making 10 stroke can be reduced, and the pressurization time can be made sufficiently long. Also, stepped piston
Since the outer diameter d3 on one end side of 10 and the diameter d1 of the inflow hole 2 are made substantially equal, the difference between the hydraulic pressure at which the stepped piston 10 starts the stroke and the hydraulic pressure at which the relief operation starts is reduced. Therefore, it is possible to set the stroke start pressure of the stepped piston 10 higher than the conventional one and set the relief operation start pressure, that is, the low pressure buffer pressure lower. Further, if the casing is composed of the casing body 1, the pressure adjusting plug 4 and the lid 5 as in this embodiment, the initial load of the spring 13 is changed by adjusting the position of the pressure adjusting plug 4 and the final set pressure is set. And at the same time the low pressure buffer pressure can be adjusted.

Here, the above-mentioned action will be considered by using mathematical expressions. If the initial load of the spring 13 is WO, the stroke end load of the spring 13 is w, and the pressure of the liquid chamber 11 at which the stepped piston 10 starts the stroke is P _B , then (π / 4) (d3 ² −d2 ² ) P _B = WO Therefore P _B = 4WO / {π (d3 ² −d2 ² )} At this time, the hydraulic pressure of the inflow hole 2, that is, the low pressure relief pressure,
When _{P A (π / 4) d1} 2 P A = WO + (π / 4) d2 2 P B therefore ^{_{P A = 4WOd3 2 / {πd1}} 2 (d3 2 -d2 2)} Now close the d3 to d1 P _A approaches P _B. The value of d3 is d3
-Depending on the thickness limit of d2, etc.
It is possible to set P _B ≧ 0.12Ps P _A = 0.15 to 0.2Ps by approaching. Note that Ps is the final relief pressure.

Next, the state of the step-up buffering process will be described using mathematical expressions. The plunger 7 and the seat 3 of the seat area of S1, the cross-sectional area of S2 of the piston inside diameter, the large diameter portion sectional area of S3 of the stepped piston 10, when and S4 diameter portion sectional area ^{S1 = πd1 2/4 S2 =} πd2 ^{2/4 S4 = πd3 2/} 4 S3 = πd4 2/4 also, the upstream portion pressure of the plunger 7 (i.e., the relief pressure) P _a, the pressure in the liquid chamber 11 (the differential chamber pressure) P _B, of the spring 13 The initial load is WO and the load when the stepped piston 10 reaches the stroke end is W.

First, consider a case where the hydraulic pressure supplied to the inflow hole 2 is increased from the tank pressure. Since the inflow hole 2 is initially tank pressure and the through hole 8 and the liquid chamber 11 are also tank pressure, the stepped piston 10 is in a state of being pressed against the lid body 5 by the spring 13.

Now, when the damping force does not act on the stepped piston 10, the pressure P _B1 of the liquid chamber 11 is P _B1 (S4-S2) = due to the mechanical equilibrium of the stepped piston 10 with respect to the initial load WO of the spring 13. F1 P _B1 = F1 / (S4-S2) The relief pressure P _{A1 at} this time is P _A1 S1 = WO + P _B1 S2 P _A1 = (WO + P _B1 S2) / S1 This P _A1 is the pressure rising start pressure. If no damping force is applied to the stepped piston 10, pressure oil flows into the through hole 8 and the liquid chamber 11 through the throttle portion 9 due to the pressure difference of ΔP = P _A −P _B , whereby the stepped step is performed. The piston 10 is moved downward. If the pressure P _B of the liquid chamber 11 immediately before the stepped piston 10 reaches the stroke end is P _B2 , then P _B2 (S4-S2) = W P _B2 = W / (S4-S2) The relief pressure at this time is P _A2 = F2 + P _B2 S2 / S1 However, at the moment when the stepped piston 10 reaches the stroke end, the pressure P _{B in} the liquid chamber 11 and the relief pressure P _A become the same pressure, so the relief pressure P _A rapidly increases.

That is, the pressure increasing process as shown in FIGS. 4 and 5 is taken.

In such a state, it cannot be said that the pressure rise is extremely gentle.
Therefore, by providing the high pressure damping chamber 12 at the stepped portion by the stepped piston 10 and the pressure adjusting plug 4, the back pressure of the high pressure damping chamber 12 acts on the stepped piston 10.

That is, the throttle 17 is configured as shown in FIG. 3 so that a large damping force acts on the stepped piston 10 as the stepped piston 10 travels.

The back pressure of the high-pressure damping chamber 12 at this time is P _C. Then, the equation expressing the time change of each pressure of P _A , P _B and P _C is as follows P _A (t) ・ ・ ・ Time function of relief pressure P _B (t) ・ ・ ・ Time function of liquid chamber pressure P _C (t) ・ ・ ・ Time function of pressure in high-pressure damping chamber 12 W (t) ・ ・ ・ Time function of spring force of spring 13 X ・ ・ ・ Stroke amount of stepped piston 10 Mechanical force acting on plunger 7 Balance formula S1P _A (t) = S2P _B (t) + W (t) …… Mechanical balance formula acting on the stepped piston 10 (S3-S2) P _B (t) = (S3-S4) P _C (t) + W (t) ...
... Q of the time function of the flow rate flowing from the throttle unit 9 into the liquid chamber 11
When (t), Q (t) = (S4-S2) when dx / dt ...... throttle portion 9 is an orifice, from Bernoulli's equation _{P A (t) -P B (} t) = ρ {Q (t )} ² / 2C ² f ² ......, where C is the flow rate coefficient, ρ is the hydraulic oil density, f is the throttle cross-sectional area, and the time function F (t) of the elastic force of the spring 13 is the spring constant k. Then, W (t) = WO + kdx ... From the above formulas, P _A (t), P _B (t), P _C (t), f
Five variables of (t) and Q (t) are obtained. And from the obtained results, we can conclude as follows.

The time required for P _A (t) and P _B (t) to rise to the final set pressure is the time from when the stepped piston 10 starts its stroke to when it reaches the stroke end. Flow rate Q of pressure oil flowing into the liquid chamber 11 through 9
(Equation) governed by (t).

On the other hand, the flow rate Q (t) is governed by the differential pressure between P _A (t) and P _B (t) (equation).

From the formula, P _A (t) -P _B (t) = (S2P _B (t) + F (t)) / S1-P
_B (t) = F (t) / S1− (1-S2 / S1) P _B (t) On the other hand, as is clear from the equation, P _B (t) is when the damping is acting, that is, P _{When C} (t) is acting, the required P _B (t) is larger than when there is no damping. Also, since 1-S2 / S1> 0 in the above equation, when damping is acting, that is, when P _C (t) is acting, P
_{A (t) -P B (t} ) becomes smaller.

Therefore, when damping is applied to the stepped piston 10, the time function Q (t) of the flow rate flowing into the liquid chamber 11 becomes small.

That is, the time required for the stepped piston 10 to reach the stroke end after starting the stroke is longer when the damping is operating. Also, by appropriately selecting the diaphragm 17, P _B (t) and P
_As shown in FIGS. 6 and 7, _A (t) can be smoothly continuous until reaching the final set pressure Pset.

In this way, the boosting time td to reach the final set pressure is td> t0 compared to the boosting time t0 when there is no damping, and the pressure is approximately linear and gentle until the final set pressure is reached. can do.

When the stepped piston 10 starts its stroke under such conditions, the pressure liquid in the inflow hole 2 flows into the liquid chamber 11 through the throttle portion 9. Flow rate Q of the hydraulic fluid flowing into the liquid chamber 11, and the cross-sectional area of the throttle portion 9 and f Q = Cf {2 (P A -P B) / ρ} 1/2 Note Q, P _A, P _B Is a function of time t, and this Q determines the time from the stroke start to the end of the stepped piston 10, that is, the boosting buffer time. Here, since d3 is set to be as close to d1 as possible, it may be possible that the stroke volume of the stepped piston 10 has become smaller and the boost buffer time has become shorter, but in reality, Since P _A -P _{B is} also small, Q becomes small, and therefore the boost buffering time does not become short.

(Another embodiment) In the above embodiment, the casing is the casing body 1
However, the present invention is not limited to such a configuration, and for example, the entire casing may be integrally formed.

(Effect of the Invention) As described above, according to the relief valve of the present invention, the outer diameter d _{3 of} the stepped piston 10 on one end side and the diameter d ₁ of the inflow hole 2 are made substantially equal to each other. Can reduce the difference between the hydraulic pressure at which the stroke starts and the hydraulic pressure at which the relief operation starts, so that the stroke start pressure of the stepped piston 10 is set higher than before, and the relief operation start pressure, that is, the low pressure buffer pressure. Since it can be set low, the stroke of the stepped piston 10 does not end before starting the relief operation even when used in an absolute pressure circuit, and a good shock reduction effect can be obtained. . In the present invention, a high-pressure damping chamber 12 is provided so that damping is applied when the stepped piston 10 is stroked, and the difference between the pressure for making the stepped piston 10 stroke and the relief pressure is small, that is, the inflow hole 2
Since the pressure difference before and after the throttle portion 9 is small, the buffering time can be set sufficiently long.

[Brief description of drawings]

FIG. 1 is a sectional view of a relief valve according to an embodiment of the present invention, and FIG. 2 is a sectional view of essential parts of a damping mechanism of the embodiment,
FIG. 3 is an explanatory view of the operation of the damping mechanism, FIG. 4 is an explanatory view of a variation state of hydraulic pressure acting on the stepped piston at the moment when the stepped piston reaches the stroke end when there is no damping chamber, and FIG. FIG. 6 is an explanatory diagram of a variation state of the relief pressure, FIG. 6 is an explanatory diagram of a relationship between the hydraulic pressure acting on the stepped piston and the time when the relief valve is started when the relief chamber is provided, and FIG. 7 is the relief. It is explanatory drawing of the relationship between pressure and time. 1 ... Casing body, 2 ... Inflow hole, 3 ... Sheet,
7 ... Plunger, 8 ... Through hole, 9 ... Drawing part, 10 ...
… Step piston, 11 …… Liquid chamber, 12 …… High pressure damping chamber, 13 …… Spring

Claims (1)

[Scope of utility model registration request] 1. A tubular casing (1) having an annular sheet (3) forming an inflow hole (2) for an inflow side pressure liquid, fixed at one end and closed at the other end, and one end having a large diameter. A substantially cylindrical plunger (7) formed and slidably fitted to the inner circumference of the one end of the casing (1), and the inner circumference of the other end of the casing (1) and the plunger having a small diameter on one end side A cylindrical stepped piston (10) that slidably fits with the outer circumference of the other end of (7) to form a liquid chamber (11) with the other end of the cane sig (1); This stepped piston (1
An annular high pressure damping chamber (12) formed by a step on the outer circumference of (0) and a step on the inner circumference of the casing (1);
The high pressure damping chamber (12) and the communication passage (10b) for communicating the liquid chamber (11) are provided, and the plunger (7) is provided.
A through hole (8) is formed along the axial direction, and an arbitrary portion of the through hole (8) is made into a fine hole to form a narrowed portion (9), and one end of the stepped piston (10) and the A spring (13) is interposed between one end of the plunger (7) and the outer diameter (d ₃ ) of one end of the stepped piston (10) and the diameter (d ₁ ) of the inflow hole (2). A relief valve characterized in that and are almost equal.