JPS5965607A - Hydraulic driving device - Google Patents

Abstract

PURPOSE:To improve a coefficient of power utilization in a motor while preventing any stoppage due to its overloading, by making a maximum work in time of operation on total hydraulic pump load smaller than the sum total of the maximum work of individual hydraulic pumps, and thereby limiting the input power to some extent. CONSTITUTION:The discharge pressure of each of fixed displacement hydraulic pumps 2 and 3 being subject to a maximum discharge pressure setting value is led into each of relief valves 10 and 11, which set the maximum discharge pressure of these fixed displacement hydraulic pumps 2 and 3, as a selector pressure through selector pressure lines 12 and 13, while also the discharge pressure of these fixed displacement hydraulic pumps 3 and 2 besides these ones is led into each of selector pressure lines 14 and 15. The selector pressure being led in from these selector pressure lines 14 and 15 energizes those of assistant pistons 16 and 17 of these relief valves 10 and 11 in a valve opening direction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a hydraulic drive device equipped with a plurality of hydraulic pumps driven by one prime mover, and is particularly suitable for hydraulic excavators. Multiple hydraulic pumps are operated by one prime mover,
Each hydraulic pump supplies pressure oil to a plurality of hydraulic cylinders or a hydraulic motor. FIG. 1 shows an example of a conventional hydraulic drive system in which two fixed capacity hydraulic pumps 2.3 are operated by one prime mover 1. The pressure oil of the fixed capacity hydraulic pump 2.3 is supplied via a directional valve 4.5 to a hydraulic motor 6.7, respectively.
rotates to drive the load of the hydraulic motor 6.7, such as the traveling body of a hydraulic excavator. Fixed displacement hydraulic pump2.
The discharge pressure of No. 3 is regulated below the set pressure of the relief valve 8.9.

FIG. 2 is a characteristic diagram showing the relationship between the input horsepower from the prime mover 1 to the fixed capacity hydraulic pump 2.3 and the output of the fixed capacity hydraulic pump 2.3. P is the pressure of the fixed displacement hydraulic pump 2.3, Q is the flow rate, pI is the set pressure of the relief valve 8.9, A is the rated horsepower of the prime mover 1, and B1 is the maximum work done by one fixed displacement hydraulic pump 2 or 3. (corner horsepower), B! is the maximum work done by the two fixed displacement hydraulic pumps 2 and 3.

When only one fixed capacity hydraulic pump 2 or 3 does work, the flow rate is constant at q, and the maximum work B1 is performed at the set pressure p1 of the relief valve 8 or 9. When the two fixed capacity hydraulic pumps 2 and 3 work simultaneously, the total flow rate is q2, which is constant, and the maximum work B is performed at the set pressure p1. As shown in Fig. 2, if the set pressure 1)+ is determined so that the maximum work B2 is done with the rated horsepower A, the two fixed capacity hydraulic pumps 2.3 simultaneously do the maximum work. Since the time is rare, the horsepower utilization rate of the prime mover 1 is small. Therefore, conventionally, B, ≧A) B,
The set pressure p of the relief valve 8.9 is set so as to satisfy the relationship of
It is common to define . However, if the maximum work B is too large compared to the rated horsepower A, the prime mover 1 will stop due to overload, so it is normal to make it slightly larger.

Therefore, conventionally, it has been difficult to increase the horsepower utilization rate of the prime mover 1 while preventing the prime mover 1 from stopping due to overload. In particular, the maximum work B of one fixed capacity hydraulic pump 2 or 3 during load operation is half of the rated horsepower (A/
2), and the prime mover horsepower utilization rate was low.

An object of the present invention is to provide a hydraulic drive system that can solve the above-mentioned problems and increase the horsepower utilization rate of the prime mover while preventing the prime mover from stopping due to overload.

In order to achieve this object, the present invention provides switching pressure adding means for introducing the discharge pressure of other hydraulic pumps as switching pressure in addition to the discharge pressure of the hydraulic pump whose maximum discharge pressure is to be set. It is characterized in that it is provided in the IJ IJ-F valve to limit the input horsepower by making the maximum work during full hydraulic pump load operation smaller than the sum of the maximum work of each individual hydraulic pump.

Hereinafter, the present invention will be explained in detail based on illustrated embodiments.

FIG. 3 shows an embodiment of the invention. Components similar to those in FIG. 1 are designated by the same reference numerals.

Setting the maximum discharge pressure of fixed displacement hydraulic pump 2.3 I
The discharge pressure of the fixed capacity hydraulic pump 2.3 for which the maximum discharge pressure is to be set is introduced into the J IJ valve 10.11 as a switching pressure through a switching pressure line 12.13, and the other fixed capacity hydraulic pressures are The discharge pressure of pump 3.2 is introduced via switched pressure line 14.15. Switching pressure line 14
．． The switching output introduced from 15 is the relief valve 10.1.
1 assisting pistons 16 and 17 are urged in the valve opening direction. That is, each IJ valve 10.11 is connected to the switching pressure line 1.
Opening/closing is controlled by the sum of the switching pressure from 2.13 and a predetermined ratio of the switching pressure from switching pressure line 14.15.

For example, with only the switching pressure (hereinafter referred to as self-pressure) from the switching pressure line 12.13, the relief valve 10.11 is 20.
When relief is set to 0 to 9/-, the pressure receiving area of the assisting piston 15.16 is determined so that the addition ratio of switching pressure (hereinafter referred to as partner pressure) from the switching pressure line 14.15 is 10%. If so, two fixed displacement hydraulic pumps2.3
When both loads become large, the relief valve 10.1
1 becomes relieved at about 180 noodles/crl.

Also, when the partner pressure is 100 to 9/d, the self pressure is 19
Relief with 0 Kf/ad, opponent pressure is ax, chest/-
At the time of , the self-pressure relieves at 5 Kv/d per 12 minutes, and in this way, the self-pressure at the time of relief changes continuously according to the partner pressure.

FIG. 4 is a characteristic diagram showing the relationship between input horsepower and output in one embodiment of the present invention. Two fixed displacement hydraulic pumps2.
The self-pressure p2 at the time of relief is set so that the maximum work B2 due to No. 3 is equal to the rated horsepower A. l] The self-pressure p at the time of IJ-F corresponds to 180 kg/- in the above-mentioned specific example. As the partner pressure decreases, the self pressure increases during relief, and one fixed capacity hydraulic pump 2 or 3
The pressure during load operation increases to pl during relief, and the maximum work becomes B:. The self-pressure p at the time of relief corresponds to 200 odor/crl in the above-mentioned specific example.

As can be seen from FIG. 4, the maximum work B'1 is considerably larger than the input horsepower A/2 in the conventional case, so that the horsepower utilization rate during one pump load operation can be increased. The shaded area in FIG. 4 is the horsepower that can be used more than before.

Even during 2-pump load operation, when the opposing pressure is less than p1, the self pressure at relief is p! Since it is larger, the maximum work by the two fixed displacement hydraulic pumps 2 and 3 is larger than before, and the 10 horsepower of the prime mover can be used effectively over a wide pressure range.

When both the self pressure and the opposing pressure reach p, the maximum work B is limited to be equal to the rated horsepower A, so
The maximum work will not exceed the rated horsepower A and become Bt,
It is possible to prevent overload from being applied to the prime mover 1.

In this embodiment, the assisting pistons 16, 17 correspond to the switching pressure adding means of the present invention.

Although the present invention is very effective for a hydraulic drive system equipped with a fixed displacement hydraulic pump as shown in FIG. 3, it can also be applied to a hydraulic drive system equipped with a variable displacement hydraulic pump. Further, the present invention can be applied not only to open circuits but also to closed circuits. In the case of a closed circuit, the crossover relief valve is provided with switching pressure adding means.

The switching pressure adding means is not limited to the one shown in FIG.
It is possible to create a structure that weakens the spring pressure.

Further, the number of hydraulic pumps is not limited to two, but can be three or more. In this case, the relief valve is controlled to open and close by a switching pressure obtained by adding a predetermined ratio of two or more partner pressures to the self pressure.

As explained above, according to the present invention, in each IJ IJ, switching pressure adding means for introducing the discharge pressure of other hydraulic pumps as a switching pressure in addition to the discharge pressure of the hydraulic pump whose maximum discharge pressure is to be set is provided. - It is installed in the valve to limit the input horsepower by making the maximum work during full hydraulic pump load operation smaller than the sum of the maximum work of each individual hydraulic pump, thereby preventing the prime mover from stopping due to overload. The horsepower utilization rate of the prime mover can be increased.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a conventional hydraulic drive device, Fig. 2 is an input horsepower-output characteristic diagram of the fixed capacity oil field pump in Fig. 1, and Fig. 3 is a circuit diagram showing an embodiment of the present invention. FIG. 4 is an input horsepower-output characteristic diagram of the fixed capacity hydraulic pump of FIG. 3. 1... Prime mover, 2.3... Fixed capacity hydraulic pump, 4.5... Directional switching valve, 6', 7.
... Hydraulic motor, 10.11 ... Relief valve, 12.13.14.15 ... Switching pressure pipe, 16.17 ... Assisting piston, A...
... Rated horsepower of the prime mover, B: ...Maximum work when operating with 1 pump load, B: ...Maximum work when operating with 2 pumps load. ] Figure 1 Figure 9 Figure 4

Claims (1)

[Claims] 1. Multiple hydraulic pumps operated by one prime mover and a relief that sets the maximum discharge pressure of each hydraulic pump,
In a hydraulic drive device equipped with a valve, each relief valve is provided with switching pressure adding means for introducing the discharge pressure of other hydraulic pumps as switching pressure in addition to the discharge pressure of the hydraulic pump whose maximum discharge pressure is to be set. A hydraulic drive device characterized by: