JPS60252806A - Holding pressure compensating device for hydraulic cyliner carrying load - Google Patents

Abstract

PURPOSE:To prevent the occurrence of scaling-down motion during stop of a hydraulic cylinder and protrusion of the cylinder due to supercharging, by a method wherein an electromagnetic valve, located to a supply circuit for feeding pressure oil to the chamber on the load holding side of the hydraulic cylinder, is controlled by means of the pulse of a timer. CONSTITUTION:A supply circuit B is provided for supplying pressure oil from an oil pressure source P to a pressure oil chamber Ah on the load holding side of a hydraulic cylinder A which sometimes brings a load W into a stop for corresponding time. When expanding and contracting motion of the hydraulic cylinder A is stopped to bring it into a stop state, a pulselike electric signal having preset pulse interval and pulse width begins to be outputted by a timer T, and a proper amount of pressure oil is fed in the pressure oil chamber Ah on each occasion of an electromagnetic valve V repeating switching operation through a solenoid VS for control. When a volume of, for example, the interior of the pressure oil chamber Ah is increased in proportion with an expansion size L of the hydraulic cylinder, a controller C, which outputs a signal for increasing a pulse width or decreasing a pulse interval to the timer T, may be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a holding pressure compensator for a hydraulic cylinder carrying a load.

Hydraulic cylinders are used in hydraulic cranes and aerial work vehicles to extend, retract, and raise and lower booms, and are also used to raise and lower elevators and lifts. These hydraulic cylinders are subjected to large loads through booms and pallets, and during work they may be stopped for a considerable period of time while carrying these loads.

When the hydraulic cylinder stops supplying hydraulic oil and stops moving, the volume of the hydraulic oil in the oil chamber decreases due to leakage of hydraulic oil and a drop in the temperature of the hydraulic oil in the oil chamber, and the holding pressure decreases, causing the hydraulic cylinder to be pushed by the load. may be reduced. This movement occurs when the holding pressure of the hydraulic cylinder decreases beyond the load holding limit due to the packing resistance of the hydraulic cylinder and the frictional resistance of the boom control.
For example, they occur gradually and suddenly, over a period of several minutes.

If this tendency occurs frequently in the hydraulic cylinders used for extending and retracting crane booms and for raising and lowering, it will become impossible to align the suspended load as shown in Figure 8, and reliability of operation will be lost in elevators, lifts, etc. Various inconveniences occur.

Therefore, in hydraulic cylinders that are required to carry a load for a relatively long period of time, a device for compensating the holding pressure has been required.

, 1 (Prior Art) +1 Conventional holding pressure compensators in this field include the following.

The technique disclosed in Japanese Utility Model Application No. 58-64660 uses a limit switch to detect that the hydraulic cylinder has contracted by a certain amount, and replenishes pressure oil until the cylinder returns to its original position. However, this essentially cannot completely eliminate the contraction movement of the hydraulic cylinder since the occurrence of the contraction movement is the activation condition for replenishment. Therefore, there is a problem in that it can only be applied in fields where there is no problem even if there is a slight movement stroke (usually on the order of several cm) between the contraction movement and the restoring movement.

The technique disclosed in Japanese Patent Application No. 57-162689 uses a sensor to detect the pressure in the holding side oil chamber of a hydraulic cylinder, replenishes pressure oil when the pressure drops to a predetermined value or more, and stops replenishing it when the pressure recovers. Although this device allows holding pressure compensation to be performed with a fairly high degree of accuracy, depending on the operating conditions of the hydraulic cylinder, overfilling may sometimes cause the cylinder to pop out. In other words, the extension stroke of the hydraulic cylinder, the inclination, the presence or absence of load,
The pressure in the oil chamber varies greatly depending on the size and outside temperature, and the seal resistance of the hydraulic cylinder and the frictional resistance of the boom inspection also vary within a certain range due to the above reasons and depending on whether the hydraulic cylinder is extended or retracted. fluctuate.

Therefore, the ratio of load sharing between holding pressure and resistance (such as the packing resistance and frictional resistance of the boom inspection mentioned above) may change, and depending on the combination of these conditions, the pressure may not recover to the initial pressure after replenishment starts. In some cases, the extension operation exceeded the initial extension stroke.

As described above, with the conventional technology, it has not been possible to completely stop the boom for a long time.

(Problems to be Solved by the Invention) Therefore, the present invention provides a holding pressure compensator that completely prevents the occurrence of contraction operation when the hydraulic cylinder is stopped, and also prevents the occurrence of jump-out due to supercharging. With the goal.

(Means for Solving the Problems) As shown in FIG. 1, the first invention includes a hydraulic cylinder A that lifts, lowers, and carries a load W and its control circuit, and the pressure on the load holding side of the hydraulic cylinder A is The oil chamber Ah is provided with a replenishment circuit B that supplies pressure oil from a hydraulic source P, and is equipped with a solenoid valve (2) for switching between supply and non-supply of pressure oil. The solenoid valve (2) is switched to the supply position when the solenoid v8 is energized, and this energization is performed at preset pulse intervals and pulse widths by the timer T.

As shown in FIG. 2, the second invention uses the detection signal of the sensor S that detects the extension stroke of the hydraulic cylinder A as input information, and increases or decreases the pulse width in proportion to the volume of the oil chamber, or A controller C is added that outputs a signal to the timer T to increase or decrease the pulse interval inversely proportionally.

(Function) In the first invention, when the expansion and contraction operation of the hydraulic cylinder A is stopped and brought into a stopped state, the timer T is simultaneously activated and a pulsed electric signal is output, and in response to this, the solenoid valve ■ repeats the switching operation, An appropriate amount of pressurized oil is supplied into the oil chamber lung each time.

In this state, the pressure inside the oil chamber M pulsates somewhat as shown in Figure 3, but in order for the hydraulic cylinder to start moving, the pressure must fluctuate just enough to go around the packing resistance of the hydraulic cylinder, so there is a limit to this. The amount of replenishment should be determined so that the upper and lower limits of pulsation are within (preferably, the pulse width and pulse interval are set).

As a result, while the hydraulic cylinder A is stopped, an appropriate amount of pressure oil sufficient to compensate for the volume reduction continues to be supplied.

In the second invention, when the hydraulic cylinder A expands greatly and the oil chamber/senior volume becomes large, the pulse width is increased or the pulse interval is narrowed to increase the replenishment amount, and conversely, when the amount of expansion is small and the oil chamber When the internal volume of M is small, the amount of replenishment can be reduced by narrowing the pulse width or increasing the pulse interval.

Therefore, it is possible to supply pressure oil within the pulsation limit even to a hydraulic cylinder with a long extension stroke or to a plurality of hydraulic cylinders.

(Example) An embodiment of the first invention will be described based on FIG.

This example is a cylinder A for extending and retracting the boom of a hydraulic crane.
, applied to A2 and boom hoisting cylinder A3.

The hydraulic cylinders A1 and A2 are telescopically controlled by the directional control valve ■1, and when the switching valve v2 is at the position shown in the figure, the two hydraulic cylinders A1 simultaneously extend and contract to operate the 2nd stage boom and the 3rd stage boom, and the switching valve v2 When the switch is switched, the hydraulic cylinder expands and contracts to operate the four-stage boom. The hydraulic cylinder A3 is expanded and contracted by the directional control valve ■3 to raise and lower the boom.

These hydraulic cylinders A11A2, A3 are provided with supply paths B1, B2, B3, and B4 for supplying pressure oil from the hydraulic source P, and between the hydraulic source P and the supply paths B3 and B4, there are A 4-bottom, 3-position PR connection type solenoid valve v4 for switching non-supply is installed. When this solenoid valve ■4 is in the neutral position, the pressure oil supply is cut off, and when the solenoid V82 is energized, it is switched to the left position, the supply path B3 is connected to the hydraulic pressure source P, and pressure oil is supplied to the hydraulic cylinder A3, and the solenoid V81
When energized, it switches to the right position and the supply path B4 is connected to the hydraulic power source P to supply pressure oil to the hydraulic cylinders A1 and A2. Note that the switching valve v6 switches in synchronization with the right position switching of the solenoid valve v4 in a state after the hydraulic cylinder A1 is fully extended and the hydraulic cylinder A2 has started to extend, and supplies pressure oil to the oil path B2 (that is, the hydraulic cylinder A2). It works like that.

There are four timers: TI, T2, Tl, and T4. When the start switch sW1 is turned on, timers T1 and Tl operate, and turn ON when the 2nd and 3rd stage booms are fully extended.
When the relay contact R1 is closed by the relay R, the timers T4 and T2 also start operating. After startup, the self-holding circuit R2 continues to operate, but when the release switch 8W2 is turned on, all timers TI, T2, Tl, and T4 stop operating. These closing and releasing operations may be performed manually, or may be linked to boom extension/retraction and raising/lowering stopping operations. Note that the pressure switch Ps inserted into the energizing circuit of timer T3 is inserted as a safety measure to prevent supercharging and is not essential.

Next, the operation of this embodiment will be explained.

(b) When the 4th stage boom is fully retracted while the 2nd and 3rd stage booms are in the middle of extension.

At this time, relay contact R1 is broken, so the timer is set to T.
Only l and Tl operate. As shown in FIG. 5, the operation is such that a pulse current of O8 for several seconds is passed during one cycle of several ten seconds, and only during that period, the solenoid valve v4 is switched. While the pulse current of the timer T1 is flowing, the solenoid valve 4 is in the right position and supplies pressure oil to the hydraulic cylinder A1 via supply paths B4 and B1. Thereafter, after a short time, when the pulse current of the timer T3 flows, the solenoid valve 4 becomes the left position and supplies pressure oil from the supply path B3 to the hydraulic cylinder A3. While the timers T1 and Tl are operating, this cycle is repeated to continue replenishing the pressure oil.

tO) When the 2nd and 3rd stage booms are fully extended and the 4th stage boom is in the middle of extension.

At this time, relay contact R1 closes and all timers T1 and T
2, Tl and T4 are activated. As shown in Fig. 6, the timer T2 operates after the timer T1 and switches the solenoid valve v4 to the right position, and in response to the pulse current of the timer T4 which operates in synchronization with this, the switching valve v6 shifts to the left position. Can be switched. As a result, pressure oil is supplied to the hydraulic cylinder A2 through the supply path B2. In order to ensure the replenishment operation, the pulse width of the timer T4 is set wider than that of the timer T2 so that the switching of the switching valve 5 is made early and the return is delayed. Timer T
The replenishment of the hydraulic cylinder A3 in step 3 is done in the same manner as in case (a), and this cycle is repeated during operation.

In this embodiment, since the above-described replenishment operation is performed, the boom is completely prevented from falling off or flying out even if the boom is stopped for a long time by stopping its extension/contraction and raising/lowering operations.

(Effects of the Invention) According to the first invention, the holding side oil chamber of the stopped hydraulic cylinder continues to be replenished with pressure oil commensurate with the volume reduction. Further, this replenishment amount can be set to an optimum value within a wide range by adjusting the pulse interval and pulse width of the timer in consideration of the volume of the oil chamber of the hydraulic cylinder and other usage conditions.

Therefore, it is possible to prevent most hydraulic cylinders from suddenly contracting and flying out due to supercharging.

Furthermore, in the case of the second invention, the amount of replenishment can be made variable depending on the size of the extension stroke when the hydraulic cylinder is stopped. Therefore, it is possible to supply an appropriate amount even to a hydraulic cylinder with a long stroke, a ring, or a hydraulic cylinder with a large number of cylinders.

From the above, according to the present invention, it is possible to stop the hydraulic cylinder for a long time.

[Brief explanation of drawings]

FIG. 1 is a principle diagram showing the first invention, FIG. 2 is a principle diagram showing the second invention, FIG. 3 is a diagram showing pressure fluctuations in the holding side oil chamber in the first invention, and FIG. A hydraulic electric circuit diagram of the embodiment of the first invention, FIGS. 5 and 6 are time charts showing the operation of the embodiment, and FIG. 7 shows a state in which the hydraulic cylinder carrying the load suddenly contracts. 8A and 8B are diagrams showing a state in which the boom telescoping cylinder and the boom hoisting cylinder suddenly contract while the crane is performing alignment work, causing the boom to completely fall. A: Hydraulic cylinder B: Supply circuit B1, B2, B3, B4: Supply path ■ = Solenoid valve ■ 4: Solenoid valve T: Timer T1, T2, T3, T4: Timer Figure 5 Figure 6

Claims (2)

[Claims] (1) A replenishment circuit (B) is provided to supply pressure oil from a hydraulic source (P) to a pressure oil chamber (Ah) on the load holding side of a hydraulic cylinder (A) that carries a load, and this replenishment circuit (B) A solenoid valve (V) that switches between supply and non-supply of pressure oil, and a timer (T) that outputs a pulsed electric signal with preset pulse intervals and pulse widths to the solenoid (V8) for operating this solenoid valve (V). A holding pressure compensator for a hydraulic cylinder carrying a load, comprising: (2) A replenishment circuit (B) is provided to supply operating power from the hydraulic source (P) to the pressure oil chamber (Ah) on the load holding side of the hydraulic cylinder (A) that carries the load, and this replenishment circuit (B) A solenoid valve (V) that switches between supply and non-supply of pressure oil, a timer (T) that outputs a pulsed electric signal to the solenoid (Vs) for operating this solenoid valve (V), and a hydraulic cylinder (
A controller (C) that inputs the amount of extension (L) of the hydraulic cylinder and outputs a signal to the timer (T) to increase/decrease the pulse width in proportion to the amount of extension of this hydraulic cylinder, or to increase/decrease the pulse interval in inverse proportion to the amount of extension of the hydraulic cylinder. ), and a holding pressure compensator for a hydraulic cylinder carrying a load.