JP3073845B2 - Swash plate type piston pump or motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a swash plate type piston pump or motor and, more particularly, to a swash plate type piston pump or motor in which a piston used for a cast iron cylinder block whose inner surface remains cast iron without a bushing. Regarding things that are difficult to wake up.

[0002]

2. Description of the Related Art In the case of a swash plate type piston pump or motor manufactured for the first purpose to be inexpensive, its cylinder block is made of cast iron, and a bush made of copper alloy or the like is not used on the inner peripheral surface of the cylinder. In the construction, the cast iron surface was used as it is or subjected to tuftride treatment (nitriding treatment), and the piston was subjected to carburizing and quenching treatment using chromium molybdenum steel.

[0003]

Such a swash plate type piston pump or motor is used, for example, as a traveling motor for construction equipment. However, when it is operated at a certain high speed, a copper alloy bush is used. However, there is a disadvantage that seizure occurs, which is not seen in the burned material. Therefore, usually 25
00r. p. m. When used at a higher rotational speed, there is a problem of burning. As a countermeasure against this seizure, the clearance between the piston and cylinder may be increased to cool the sliding surface better. However, if the clearance is increased, the mechanical efficiency at startup decreases and the amount of external drain increases. There is a problem in what leads to. SUMMARY OF THE INVENTION An object of the present invention is to provide a piston which is hard to cause seizure when used in this kind of swash plate type piston pump or motor, so that it can be used at a higher rotation speed.

[0004]

Means for Solving the Problems The present invention is directed to a cylinder block in which the inner peripheral surface of a cylinder is cast iron material as it is or is nitrided, and a piston used in combination with the cylinder block. It is a steel, which is subjected to nitriding to temper and raise the base hardness,
Removing the high hardness layer reforming tone of hardened surface layer of the peripheral surface
Characterized by comprising the ones left high hardness layer than prime locations hardness after.

[0005]

When a nitriding treatment is performed, for example, a surface hardened layer of about 0.5 mm is formed by a tuftride treatment for 5 hours. The hardness distribution state of the hardened layer is the hardest on the surface, and approaches the base hardness as it moves inward. If the tufted piston is used as it is, the hardened layer is partially peeled off in a short time by about 10 to 20 μm, and the inner peripheral surface of the cylinder block is scraped off by the stepped portion at the peeling boundary. However, when the hardened surface layer is removed from the hardened surface layer, for example, by removing about 20 μm from the surface, the hardened surface layer does not peel off, and seizure does not occur even if the piston speed is increased compared to the conventional case. No longer occurs. That is, the limit speed for burning is increased. As the nitridable steel used in the present invention, in addition to structural steel, chromium molybdenum steel known as nitrided steel, aluminum chromium molybdenum steel, chromium vanadium steel,
Nickel chromium aluminum molybdenum steel and the like.

[0006]

An embodiment of the present invention will be described below. Schematic configuration of the swash plate type piston motor of this embodiment is as shown in FIG. In FIG. 1A, reference numeral 1 denotes a main body, and 2 denotes an inner hole provided in the main body 1. Reference numeral 3 denotes a rotation shaft that penetrates the inner hole 2 and is rotatably supported on the main body 1. 4 is a cylinder block, Yes coupled by a spline to the rotary shaft 3, a plurality of pistons 5a, 5b hole 4a which is fitted slidably, 4 b are are to puncture set. Reference numeral 7 denotes a swash plate with which the pistons 5a and 5b abut via the shoes 6a and 6b. The swash plate 7 is provided in the inner hole of the main body 1 so as to be tiltable to two positions. 8
Is a valve plate which is provided between the left end face of the cylinder block 4 and the lid 9 which closes the inner hole of the main body 1, and is used for supplying and discharging pressure oil to the holes 4 a and 4 b of the cylinder block 4. It has a type (not shown) port.

In the axial type piston motor, the pressure oil flows through the hole 4 of the cylinder block 4 through the valve plate 8.
a and 4b. (Note that the cylinder block 4 has nine holes 4a and 4b, and the hydraulic pressure is set to the nine holes 4a and 4b.
4b, the oil is supplied to four of the four holes and the oil in the other five holes is discharged, and the pressure oil is supplied to the five holes 4a and 4b to discharge the oil in the other four holes. The valve plate 8 controls the supply and discharge of the pressure oil to and from the holes 4a and 4b. Then, the piston slidably fitted into the hole to which the pressure oil is supplied and discharged causes the cylinder block 4 to rotate together with the rotary shaft 3 by the component force received from the slope of the swash plate 7.

In the above operation, as shown in the enlarged view of FIG. 1B, pressure oil is supplied to the hole 4a and the piston 5a
Is pressed against the slope by the pressing force f1, the force of the component force f2 is applied to its tip. In order for the piston 5a to receive the component force f2, a force f2-1 acts on the end (opening end) 4a1 of the hole 4a, and the end 5a of the piston 5a.
The force of f2-2 acts on the portion of -2. Generally this hole 4
Seizure is likely to occur in the part of the piston that comes into contact with the end (opening end) 4a1 of a.

The pistons 5a and 5b and the cylinder block 4 of such a swash plate type piston motor are manufactured as follows. That is, the material of the pistons 5a and 5b is S
CM440, tempered , ie quenched, tempered
And containing Chikata is is Hv 300, after subjecting the Tufftride treatment thereto, the 20μm were removed by grinding as a high hardness layer of the outer peripheral surface, those buffing (surface roughness 0.4
S). The hardness of the surface was Hv650. FIG. 2 shows the hardness distribution of the cross section of the piston subjected to the tuftride treatment. At the stage of tempering, the hardness of the piston base is about HV300, but the surface becomes HV770 by the tuftride treatment, and decreases toward the depth direction and becomes the base hardness at around 0.55 mm. .

[0010] Apart from the pistons 5a and 5b, a piston as a comparative example was prepared. The piston of this comparative example has the same shape, the same dimensions, and the same material (SCM420) as those of the pistons 5a and 5b of the embodiment and is subjected to a conventional carburizing and quenching treatment (the surface hardness is Hv694).
It is.

The cylinder block in each of the embodiment and the comparative example is as follows:
The material is FCD50 and the surface roughness Rmax of the inner surface of the cylinder =
It is about 10 to 30 S, and the gap between the cylinder and the piston is 35 to 50 μm.

Table 1 shows the results of comparison tests between the hydraulic motor of the above embodiment and the hydraulic motor of the comparative example.

[0013]

[Table 1]

Referring to Table 1, when a predetermined load is applied and the number of rotations is 2900 rpm. p. m. , 350kg oil pressure
As a result of continuous operation under conditions of f / cm ² and an oil temperature of 95 ° C., no change was observed in the example of the present invention even after 60 minutes had elapsed, and in the comparative example, burning occurred in 60 minutes. Damaged and stopped. Upon disassembly and observation of the state of the piston, no discoloration was observed on the sliding surface in the example, and the piston surface was widely observed to have adhesive wear on the comparative example, Further, the surface hardness was reduced to about Hv400. In the embodiment, the rotational speed was changed to 3200 r.p.m. by changing the operating conditions. p. m. , Hydraulic pressure is 350kgf /
When the operation was continued for 60 minutes under the conditions of cm ² and an oil temperature of 95 ° C., no abnormality occurred during the operation. However, when the piston was disassembled and the piston was observed, slight discoloration due to heat generation was recognized. However, no decrease in hardness was observed.

From these results, it can be said that the embodiment of the present invention is harder to burn than the conventional carburized and quenched one, and can be operated at a higher speed than the conventional one.

It is considered that the carburized and quenched piston of the comparative example softened beyond the temperature at the transformation point at the local part of the piston surface due to the heat generated by the sliding resistance and adhered to the cylinder block. In the pistons of the examples, it is considered that the compound is formed on the surface of the piston and is hard to soften.
In the piston of the comparative example, no decrease in hardness was observed except at the adhered portion. From this, since the adhesion portion slides the high hardness piston on the high hardness cylinder block,
Since they do not fit each other, it is considered that seizure is caused by high temperature of the partial surface of the piston due to local contact based on cylindricity. Therefore, the type in which the bush made of a copper alloy is press-fitted into the cylinder block has good adaptability, and there is no particular effect even if the piston of the embodiment is applied as it is. Difficult Yaketsuki embodiment, the effect that it is possible faster OPERATION is a unique effect when combined with cast iron cylinder block without using the bush.

In the above embodiment, the tuftride treatment is applied, but other than this, ordinary nitriding, soft nitriding, or the like may be applied.

[0018]

According to the present invention, the surface hardening method utilizes a relatively simple class of nitriding, and a combination of a cast iron cylinder and a nitriding piston improves the seizure limit speed. In this class, a swash plate type pump or motor that can operate at higher speed than before can be provided at low cost.

[Brief description of the drawings]

FIG. 1 shows a schematic configuration of a swash plate type piston motor according to an embodiment of the present invention, wherein FIG. 1 (a) is a longitudinal sectional side view of the whole, and FIG. 1 (b) is a partially enlarged view of FIG.

FIG. 2 is a graph showing a distribution of cross-sectional hardness of a piston subjected to a tuftride process of the embodiment.

[Explanation of symbols]

 4 Cylinder block 4a hole 4a hole 5a piston 5b piston

Claims (1)

(57) [Claims] 1. A cylinder block in which the inner peripheral surface of a cylinder is cast iron material as it is or is nitrided, and a piston used in combination with the cylinder block, the material being a nitridable steel. subjected to nitriding treatment to that raised, characterized by comprising as those leaving the high hardness layer than prime locations hardness after tempered by removing the high hardness layer of the hardened surface layer of the peripheral surface And swash plate type piston pump or motor.