JPH04120323A - Potential energy recovery and utilization device for work machine - Google Patents

Abstract

PURPOSE:To ensure the effective use of potential energy with an accumulator by providing a valve in a hydraulic circuit between the accumulator and an assist cylinder for opening the circuit when a work machine is being operated for elevation. CONSTITUTION:A head side circuit 6 and a bottom side circuit 7 are provided between a hydraulic pump 11 and a work machine elevation cylinder 4. Also, there are provided an assist cylinder bottom side circuit 15 branched from the bottom side circuit 7 to a work machine elevation assist cylinder 5, and an assist cylinder head side circuit 19 led from an oil tank 12 to the assist cylinder 5. Furthermore, a stop valve 16 and an accumulator 17 are arranged in the assist bottom side circuit 15. According to the aforesaid construction, potential energy when a work machine is lifted, can be recovered to a maximum extent in lowering the machine, and utilized in the next elevation process, thereby utilizing the potential energy effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a potential energy recovery/utilization device for a working machine.

[Prior Art] In a construction machine, such as a hydraulic excavator, in which the working machine is moved up and down or back and forth to cut earth and sand, the boom 1 is rotatably mounted on an upper frame 36 as shown in FIG. The boom 1, the arm 2, and the packet 3 are driven to carry out work.

Fig. 11 shows an outline of the hydraulic circuit for driving the boom of a hydraulic excavator. The vertical movement of the boom l is performed by the expansion and contraction of the boom cylinder 4, and the head side and bottom side of the boom cylinder 4 are To the connected hydraulic circuits 6 and 7,
A boom directional control valve 10 is provided, and when the operator operates the boom lever, pilot pressure acts on the boom directional control valve 10 from a pilot pressure control valve (hereinafter referred to as PPC valve) 25, raising the valve spool. Alternatively, switch to lowering and drive boom 1.

A crest 37 is provided on the bottom side return circuit of the boom cylinder 4 to prevent the boom 1 from falling due to its own weight during boom lowering operation, and a crest 37 is provided on the bottom side return circuit of the boom cylinder head side circuit 6 and the bottom side circuit 7 of the boom directional control valve 10. A suction safety valve 8, 9 is provided at each of the suction safety valves 8, 9. When the boom is lowered, pressure oil sent from the hydraulic pump 11 flows into the head side of the boom cylinder 4, and the oil on the bottom side flows into the aperture 37.
and returns to the oil tank 12. With this aperture 37,
Although the boom 1 does not descend rapidly due to its own weight, all of the potential energy is converted to heat, causing an unnecessary rise in oil temperature. Therefore, a large capacity oil cooler 14 is installed to lower the oil temperature. On the other hand, when loading excavated earth and sand onto a dump truck or the like, a working machine weighing more than twice the weight of the earth and sand must be lifted together with the earth and sand to the height of the Hera cell of the dump truck.

In order to solve the above-mentioned problems, there is a hydraulic excavator equipped with a working machine potential energy recovery and utilization device as shown in FIG. In addition to the boom cylinder 4, this hydraulic excavator has an assist cylinder 5 for raising and lowering the boom, and an accumulator 17 is provided in the bottom circuit 15 of the assist cylinder, and the potential energy at the time of lowering the boom is recovered in the accumulator 17, and the boom is raised. I sometimes make use of this energy.

[Problems to be Solved by the Invention] However, the device for recovering and utilizing potential energy for a working machine shown in FIG. 12 has the following problems.

The first problem is that the recovery efficiency of potential energy is low. That is, the arm 2 of the work machine is connected to the upper frame 36.
In the backhoe shown in FIG. 11, when the arm cylinder 38 is extended, in the front loader shown in FIG.
(when retracted), work equipment center of gravity position A around the boom foot
As shown in FIG. 13, approaches the upper frame 36 side from the maximum reach σ to the minimum reach c', the moment M of the work equipment decreases, and the boom cylinder holding pressure also decreases as shown below! '/4.

When the work equipment moment arm reaches the maximum reach (when the arm is extended) M = rlW However, W is when the work equipment weight arm has the minimum reach (when the arm is pulled) M' = G'W When the boom cylinder holding pressure arm reaches the maximum reach (when the arm is extended) However, Q and o are the lengths of perpendicular lines drawn from the fulcrum at the bottom of the boom to the center line of the boom cylinder 4, and d is the length of the perpendicular line drawn from the fulcrum at the bottom of the boom to the center line of the boom cylinder 4, and d is the inner diameter of the boom cylinder 4 when the arm reaches its minimum reach (when the arm is pulled).The boom cylinder holding pressure ratio, therefore, when the arm reaches its maximum reach. Pressure is accumulated in the accumulator 17 while lowering the boom 1, and when the pressure is accumulated to the maximum, the boom cylinder holding pressure becomes 0, and the pressure can no longer be accumulated due to the weight of the work equipment.

This is the state of maximum energy recovery.

As arm 2 is pulled closer from this point, the moment of the work equipment becomes smaller by c'/r. Therefore, the assist cylinder 5 attempts to lift the boom l. At this time, the oil in the oil tank 12 is sucked into the bottom side of the boom cylinder 4 by the suction safety valve 9, so that the boom l is lifted against the operator's intention.

In order to prevent such a problem from occurring, lower the boom 1 with the arm 2 at its minimum reach (the state in which the arm is pulled the most), and with the pressure accumulated in the accumulator 17, the holding pressure of the boom cylinder 4 will be +0. Nearby (actually 10±10kg/cm2 considering various errors)
The capacities of the assist cylinder 5 and accumulator 17 must be set so that the Therefore, the first
4 In the case of an empty packet and arm maximum reach as shown in Figure 4 (a), and in the case of empty packet and arm minimum reach as shown in Figure 4 (b), potential energy can only be recovered in the shaded area. , the recovery efficiency is extremely low at about 7%.

The second problem is that the boom raising operation is performed at a location where the efficiency of the hydraulic pump is low.

In other words, when a packet is loaded with earth and sand, the boom holding pressure increases by the amount of earth and sand, but if the boom is raised with a small amount of recovered potential energy as described above, the boom cylinder holding pressure and the accumulator increase on the way. After that, the internal pressure of the accumulator becomes lower than the holding pressure of the boom cylinder, so that the holding pressure of the boom cylinder further increases.

On the other hand, the theoretical output curve of a hydraulic pump is set so that PXQ is constant, as shown by the solid line in Figure 10, when the discharge pressure is P and the discharge amount is Q, but the actual output curve As shown by the dotted line, as the discharge pressure increases, the actual discharge amount becomes lower than the theoretical discharge amount. Therefore, when the holding pressure of the boom cylinder increases, the boom is lifted at a point where the efficiency of the hydraulic pump is low, and the boom lifting speed inevitably becomes slower.

The present invention focuses on the above-mentioned conventional problems, and makes it possible to recover the potential energy to the maximum extent possible when lowering the work machine when lifting the work machine, and utilize it when raising the work machine next time. It is an object of the present invention to provide a potential energy recovery/utilization device for a working machine that can replenish the insufficient energy to an assist cylinder when lifting the working machine in a state where energy is low.

[Means for Solving the Problems] In order to achieve the above object, the device for recovering and utilizing potential energy of a work machine according to the present invention is provided with a potential energy recovery/utilization device for a work machine according to the present invention. a head side circuit that leads to the bottom side of the work equipment lifting cylinder; a bottom side circuit that branches from the bottom side circuit to the bottom side of the work equipment lifting assist cylinder; and an assist cylinder bottom side circuit that branches from the bottom side circuit to the bottom side of the assist cylinder for lifting and lowering the work equipment; The assist cylinder head side circuit extends to the head side of the assist cylinder, and a stop valve and an accumulator are arranged in the assist cylinder bottom side circuit, and the assist cylinder is connected between the accumulator and the assist cylinder by lowering and raising the work equipment. In addition to providing a valve that intersects the bottom circuit, a stop valve is installed in parallel with the assist cylinder bottom circuit that branches from the bottom circuit of the work equipment lifting cylinder.
A valve that allows flow toward the assist cylinder side is provided.

[Function] According to the above configuration, a valve is provided in the hydraulic circuit between the accumulator and the assist cylinder to open the circuit when the work equipment is lowered or raised, so that the pressure on the bottom side of the assist cylinder is reduced when the work equipment is lowered. Oil can flow into the accumulator and store potential energy. The pressure oil stored in the accumulator then flows into the bottom side of the assist cylinder when the work equipment is raised, thereby pushing up the work equipment. Therefore, the holding pressure of the work equipment lifting cylinder is the sum of the load and the mechanical friction loss associated with the lifting of the work equipment, but since this pressure is significantly lower than in the past, the work equipment can be quickly lifted at the maximum flow rate of the hydraulic pump. can be pushed up.

In addition, a check valve is installed in parallel with the stop valve in the assist cylinder bottom side circuit that branches from the bottom side circuit of the work equipment lifting cylinder, so that when the accumulator oil pressure becomes lower than the work equipment lifting cylinder oil pressure during work equipment lifting operation,
Pressure oil from the hydraulic pump can be supplied to the accumulator and assist cylinder. As a result, the work machine lifting cylinder holding pressure is maintained at a low state, and the hydraulic pump is used at a location where the discharge amount is large, so that the work machine lifting speed can be increased.

[Example] Hereinafter, an example of the potential energy recovery/utilization device for a working machine according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a hydraulic circuit diagram for driving a boom of a front loader type hydraulic excavator, but the hydraulic circuit is the same for a backhoe type.

In Fig. 1, a working machine of a hydraulic excavator consisting of a boom 1, an arm 2, and a packet 3 is shown.
An assist cylinder 5 is provided between the boom cylinders 4, and a boom cylinder head side circuit 6 and a boom cylinder bottom side circuit 7 are connected to a hydraulic pump 11 via a boom directional control valve 10 equipped with suction safety valves 8 and 9, respectively. and the oil tank 12. A small-capacity oil cooler 14 is installed in the drain circuit 13 of the hydraulic circuit.

The assist cylinder bottom side circuit 15 that branches from the boom cylinder bottom side circuit 7 and reaches the bottom side of the assist cylinder 5 is provided with a stop valve 16, an accumulator 17, and a pilot type check valve 18 in order from the branching point. Cylinder head side circuit 19 is check valve 2
0 to the assist cylinder bottom side circuit 15, and also to a tren circuit 22 which runs from the assist cylinder bottom side circuit 15 to the oil tank 12 via a relief valve 21.

A check valve 24 is provided in the bypass circuit 23 of the stop valve 16. Further, a boom lowering pilot circuit 26 is connected to one end of the boom directional switching valve 10 from the PPC valve 25, and a boom raising pilot circuit 27 is connected to the other end of the boom directional switching valve 10. Branch circuit 28 is pilot type check valve 1
8 is connected.

In a hydraulic excavator equipped with a hydraulic circuit as described above,
When the PPC valve 25 is operated to the boom lowering side, the pilot pressure moves the boom directional control valve 10 to the lowering side via the boom lowering pilot circuit 26, and the pressure oil sent from the hydraulic pump 11 is sent to the head side of the boom cylinder 4. The pressure oil on the bottom side flows through the boom cylinder bottom side circuit 7,
The oil is drained into the oil tank 1'2 via the boom directional control valve lO and the oil cooler 14. At this time, the assist cylinder 5 is also compressed, so the pressure oil on the bottom side of the assist cylinder 5 passes through the assist cylinder bottom side circuit 15, passes through the pilot type check valve 18, and flows into the accumulator 17.

As mentioned earlier, when arm 2 is fully extended (
When the boom 1 is lowered at the maximum reach in FIG. 13, the maximum pressure is accumulated in the accumulator 17, and the holding pressure of the boom cylinder 4 becomes O. If arm 2 is pulled in this state (minimum reach C' in Fig. 13),
The moment of the work machine decreases to e'/u, but since the assist cylinder bottom side circuit 15 leading from the accumulator 17 to the assist cylinder 5 is closed by the pilot check valve 18, the assist cylinder is activated against the operator's will. 5 will never expand.

When excavation is completed and the boom is raised with the packet 3 fully loaded with earth and sand, the pilot pressure from the PPC valve 25 passes through the boom raising pilot circuit 27 and acts on the boom direction switching valve 10, causing the boom direction to change. Switch the switching valve 10 to the up side.

Pressure oil discharged by the hydraulic pump 11 flows into the bottom side of the boom cylinder 4 via the boom cylinder bottom side circuit 7. At the same time, the pilot pressure acts on the pilot type check valve 18 and opens the assist cylinder bottom side circuit 15, which had been closed until then, so that the pressure oil stored in the accumulator 17 is transferred to the assist cylinder bottom side circuit 15. It flows into the bottom side of the assist cylinder 5 through the cylinder and pushes up the boom 1.

Therefore, during the first excavation and loading operation, an energy key is required to lift the weight of the work equipment + the weight of earth and sand, but from the second time onwards, the potential energy when lifting the work equipment is stored in the accumulator 17.
Loading can be carried out using only a small amount of energy needed to lift the weight of the earth and sand inside the packet.

Next, if the boom is raised while the accumulator 17 does not have sufficient pressure, the accumulator oil pressure may become lower than the bottom side oil pressure of the boom cylinder 4 during the boom's rise. In this case, a part of the pressure oil flowing from the hydraulic pump 11 through the boom cylinder bottom side circuit 7 via the boom directional control valve 10 pushes open the check valve 24 and supplies pressure oil to the bottom side of the accumulator 17 and the assist cylinder 5. do.

When the accumulator oil pressure is higher than the boom cylinder bottom side oil pressure, the check valve 24 cannot be pushed by the boom cylinder bottom side oil pressure, so the pressure oil discharged by the hydraulic pump 11 flows only into the boom cylinder 4.

2 to 6 show second to sixth embodiments of the present invention, in which the pilot type check valve 18 in FIG. 1 is replaced with
Various spool type switching valves are used. In FIG. 2, a boom lowering pilot circuit 26 and a boom raising pilot circuit 27 are connected to a 2-bot 2-position switching valve 3 provided in the assist cylinder bottom side circuit 15 via a shuttle valve 29.
Connected to 0. When the switching valve 30 is activated by the boom lowering operation, the pressure oil on the bottom side of the assist cylinder flows into the accumulator 17 via the switching valve 30. When the switching valve 30 is activated by the boom raising operation, the pressure oil stored in the accumulator 17 flows into the accumulator 17. It flows into the bottom side of the assist cylinder via the switching valve 30.

FIG. 3 shows a configuration in which the switching valve shown in FIG. 2 is replaced with a two-bottom, three-position switching valve 31, and pilot pressure is introduced to both ends of the facing valve.
Figure 4 shows an example in which the switching valve is an electromagnetic proportional control valve 32.
The figure shows a four-bottom, two-position switching valve 33, and FIG. 6 shows a four-bottom, two-position switching valve 33 and a sub-tank 34 dedicated to the assist cylinder.

FIG. 7 shows a second embodiment of claim (2) of the present invention, in which a two-point, two-position switching valve 35 is used in place of the check valve 24 in FIG. When the oil pressure of the accumulator 17 is higher than the boom cylinder bottom side oil pressure, the switching valve 35 is in the position shown in FIG. 7 to close the circuit, and when the oil pressure of the accumulator 17 becomes lower than the boom cylinder bottom side oil pressure, the switching valve is switched to supply the accumulator 17 and the assist cylinder with pressure oil sent from the hydraulic pump through the hydraulic circuit.

In this example, it was decided to recover the potential energy as much as possible when lifting the work equipment when lowering the work equipment, and then utilize that energy when lifting the work equipment, so the energy used to lift the work equipment itself is It is only necessary for the first time, and in the second and subsequent work cycles, only the total energy of the amount of earth and sand scooped into the packet and the amount of mechanical friction loss needs to be applied.

In addition, in this example, since the weight of the work equipment is supported by the assist cylinder, the holding pressure of the boom cylinder is 75 to 135 kg/cm2 (Figure 8) when loaded with a packet and the arm has maximum reach, and when the arm is unloaded and has the maximum reach. 0~60k
g/cm” (Figure 9), and the energy in the shaded areas in Figures 8 and 9 can be recovered.The energy recovery efficiency is approximately 78%, which is higher than conventional technology. Furthermore, as shown in Figure 10, the maximum discharge amount of the hydraulic pump (2000 IJ
/m1n) to raise the boom, making it possible to improve fuel consumption by approximately 20% over the entire work cycle.

When the present invention is not applied, the boom cylinder holding pressure is 22
Since it is 5 kg/cm2, the hydraulic pump discharge amount is 1400
(The boom is raised at 1!/min. Therefore, by applying the present invention, the boom raising speed is 2!/min.
000/1400; 1.4 times faster. This reduces work cycle time by approximately 20% and reduces work volume by approximately 20%.
increase In order to simplify the explanation, the values calculated using the theoretical output curve shown in FIG. 10 are used in the above, but in reality, as the discharge pressure of the hydraulic bomb increases, the efficiency decreases, so the effect becomes even greater.

Also, the relief set pressure in the boom cylinder (32
The margin up to 0kg/crn2) is conventional: 320
-225= 95kg/crn2 Invention: 320-
135=185kg/cm2 Therefore, the actual bending force ratio by the boom is 185 -. It was twice that.

In conventional technology, in order to control the speed due to the falling weight of the work equipment when the boom is lowered, a ridge is inserted into the oil return circuit for lowering the boom, and the ridge causes a large amount of heat to be generated in the hydraulic oil. This is a cause of early deterioration of the hydraulic oil, and a large-capacity oil cooler is used to cool the hydraulic oil. However, in this example, an oil cooler with a capacity that is approximately 0% smaller than the conventional one is used. I found out that I can use it.

In addition, a check valve is installed in parallel with the stop valve, so even if the boom is raised without sufficient pressure accumulated in the accumulator, pressure oil from the hydraulic pump is sent to the assist cylinder to maintain the boom cylinder's holding pressure. It can remain low and the boom lifting force is ensured. Furthermore, by keeping the holding pressure of the boom cylinder low, the boom raising speed was ensured.

This example describes the recovery and utilization of potential energy from the boom of a hydraulic excavator, but is not limited to this. The present invention can also be applied to machines that move loads.

[Effects of the Invention] As explained above, according to the present invention, the following effects can be obtained.

(1) We decided to recover the maximum amount of potential energy when lifting the work equipment when lowering the work equipment, and then utilize that energy when lifting the work equipment, so the energy recovery efficiency is higher than that of conventional technology. This increases fuel efficiency by more than 10 times, resulting in an approximately 20% improvement in fuel consumption over the entire work cycle.

(2) Since the weight of the work machine is supported by the assist cylinder, the holding pressure of the work machine lifting cylinder is significantly reduced, and the load on the hydraulic pump is reduced.

Therefore, the working machine can be raised with the maximum discharge amount of the hydraulic pump, making it possible to shorten the work cycle time by about 20% and increase the amount of work by about 20%.

(3) When raising the work equipment without sufficient pressure accumulated in the accumulator, the pressure oil from the hydraulic pump is supplied to the accumulator and assist cylinder, so the holding pressure of the work equipment lifting cylinder should remain low. is possible,
The lifting force of the work equipment can be increased compared to the conventional technology.

Furthermore, by keeping the holding pressure of the work machine lifting cylinder low, the work machine lifting speed can be increased compared to the conventional technology.

[Brief explanation of the drawing]

Figure 1 shows a hydraulic bending machine (front loader type) equipped with a device for recovering and utilizing potential energy of a working machine according to an embodiment.
2 is a hydraulic circuit diagram for driving the boom, and FIG. 2 shows a partially omitted assist cylinder bottom when a 2-bottom 2-position switching valve is used in place of the pilot type check valve, as a second embodiment of claim (1). The side circuit diagram, FIG. 3, also shows the third embodiment.
The partially omitted assist cylinder bottom side circuit diagram when using the bottom 3-position switching valve, FIG. 4, is also the fourth embodiment,
Partially omitted assist cylinder bottom when using electromagnetic proportional control valve 5th embodiment, partially omitted assist cylinder bottom side circuit diagram when using 4-bottom 2-position switching valve, FIG. FIG. 7 is a partially omitted assist cylinder bottom side circuit diagram in the case where the 4-bottom 2-position switching valve and the assist cylinder dedicated sub-tank are provided in the sixth embodiment, and FIG.
In the example, a partial circuit diagram when a 2-point, 2-position switching valve is used in parallel with the stop valve. Figure 8 shows the relationship between the boom cylinder holding pressure and the boom cylinder stroke when the arm is at its maximum reach with a packet load. Figure 9 is a diagram showing the relationship between boom cylinder holding pressure and boom cylinder stroke when the arm is at maximum reach with no packet loaded.
Fig. 10 is a diagram showing the relationship between the discharge pressure and the discharge amount of a hydraulic pump, Fig. 11 is a hydraulic circuit diagram for driving a boom of a hydraulic excavator according to the conventional technology, and Fig. 12 is a diagram showing a hydraulic circuit diagram for driving a boom of a hydraulic excavator equipped with an assist cylinder for raising and lowering the boom. Fig. 13 is an explanatory diagram showing the position of the center of gravity of the work machine at maximum reach and minimum reach, and Fig. 14 is a hydraulic circuit diagram for driving the boom of a conventional hydraulic excavator.
This figure shows the relationship between boom cylinder holding pressure and boom cylinder stroke of a hydraulic excavator equipped with the boom drive hydraulic circuit shown in Figure 2. (a) is when the packet is empty and the arm is at maximum reach, (b) ) indicates when the packet is empty and the arm has minimum reach. 4...Work equipment lifting cylinder (boom cylinder) 5...Assist cylinder 6...Boom cylinder head side circuit 7...
...Boom cylinder bottom side circuit 0... Directional switching valve for lifting and lowering work equipment (boom directional switching valve) 1... Hydraulic pump 2... Oil tank 5... ...Assist cylinder bottom side circuit 6...
... Stop valve 7 ... Accumulator 8 ... Pilot check valve 9 ...
Assist cylinder head side circuit 0.24...Check valve

Claims (2)

[Claims] (1) From the hydraulic pump 11 to the directional control valve 10 for lifting and lowering the work equipment
A head side circuit 6 that connects to the head side of the work equipment lifting cylinder 4 via the bottom side circuit 7 that connects to the bottom side of the work equipment lifting cylinder 4, and a bottom side circuit 7 that branches off from the bottom side circuit 7 and connects to the work equipment lifting assist cylinder 5. It has an assist cylinder bottom side circuit 15 leading to the bottom side, and an assist cylinder head side circuit 19 leading from the oil tank 12 to the head side of the assist cylinder 5, and the assist cylinder bottom side circuit 15 has a stop valve 16 and an accumulator 17. A device for recovering and utilizing potential energy of a work machine, characterized in that a valve 18 is provided between the accumulator 17 and the assist cylinder 5 to open the assist cylinder bottom side circuit 15 by lowering and raising the work machine. . (2) A valve 24 that can flow toward the assist cylinder 5 side is provided in parallel with the stop valve 16 provided in the assist cylinder bottom side circuit 15 branching from the bottom side circuit 7 of the work equipment lifting cylinder. The potential energy recovery/utilization device for a working machine according to claim (1).