JPH0580975B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a differential pressure gauge for a hydraulic machine, and particularly to a differential pressure gauge suitable for use in an electronic control device of a hydraulic circuit in a hydraulic machine such as a hydraulic excavator.

[Conventional technology]

Today, in hydraulic machines such as hydraulic excavators,
Computerization of control devices for hydraulic circuits is becoming more and more popular. On the other hand, a hydraulic circuit control device installed in a hydraulic machine such as a hydraulic excavator introduces the pressures of two parts within the hydraulic circuit and controls the hydraulic circuit based on the differential pressure. For example, this is a load sensing regulator that maintains the discharge pressure of a hydraulic pump higher than the load pressure of a hydraulic actuator by a predetermined value. Therefore, if such a control device is to be computerized, it is necessary to detect slight pressure differences between high pressures with high precision.

Conventionally, when detecting a pressure difference between two parts, two high-pressure pressure sensors each having a strain gauge attached to a diaphragm were used to measure the difference in output between the two.

[Problem that the invention seeks to solve]

However, the conventional differential pressure gauge described above has the following drawbacks.

High-pressure pressure sensors have thick diaphragms to prevent damage due to high pressure.
There are errors such as hysteresis due to changes in pressure. These errors are about 0.5% of the measured pressure even with high accuracy. Therefore, for example, when measuring a slight differential pressure of about 20 Kg/cm ² under a high pressure of 400 Kg/cm ² , an error of up to ±4 Kg/cm ² will occur, making it difficult to perform accurate calibration and temperature correction. It becomes necessary.
On the other hand, if the thickness of the diaphragm is made thinner, the measurement accuracy will improve, but it will be more likely to be damaged by high pressures, so it cannot be used as a differential pressure gauge for measuring differential pressures between high pressures.

An object of the present invention is to provide a durable and reliable differential pressure gauge for a hydraulic machine that can accurately detect a slight pressure difference between high pressures without causing damage due to high pressure.

[Means for solving problems]

This purpose is to provide a differential pressure gauge for hydraulic machinery that detects the pressure difference between two parts in a hydraulic circuit.
It has a cylinder body having two pressure oil passages through which the pressure of two parts is guided, an outer peripheral piston part with pressure receiving parts of equal area on both sides, and two central piston parts that protrude on both sides of the outer peripheral piston part in the axial direction. and a cylinder chamber in which the outer circumferential piston portion and the central piston portion are accommodated in the cylinder body so as to be able to move in a sealed manner in the axial direction, and the two pressure oil passages are respectively opened between the outer circumferential piston portion and the inner wall of the cylinder body. a stepped piston forming a
a biasing means for biasing the stepped piston against axial movement; and a biasing means disposed on one axial side of the stepped piston to electrically detect displacement of the stepped piston in the axial direction. displacement detecting means, an axial hole formed in the cylinder body to allow axial movement of the central piston portion and opening in an end wall of the cylinder body; a shaft made of a non-magnetic material disposed in the moving axial hole and having an end opposite to the central piston portion protruding from the opening of the axial hole to the outside of the end wall of the cylinder body, the protrusion of the shaft; a magnetic core provided in the portion, a case made of a non-magnetic material that closes the opening of the axial hole outside the end wall of the cylinder body and surrounds the protruding portion of the shaft and the magnetic core, and an outer periphery of the case. A displacement sensor is mounted on the core and detects displacement of the core, and a passage means is provided for communicating the end wall of the central piston portion, the axial hole, and the inside of the case with a tank. Ru.

[Effect]

The present invention employs a cylinder-piston structure consisting of a cylinder body and a stepped piston as two pressure acting parts. In the structure of the present invention, when the pressures of the two pressure oil passages act on the pressure receiving portion of the outer peripheral piston portion of the stepped piston, a force proportional to the difference between the two pressures acts on the stepped piston. This force is transmitted to the biasing means, which displaces the stepped piston in proportion to the force. This displacement is detected by the displacement detection means, and the detected value is output as an electrical signal. Here, the difference between the two pressures is linearly proportional to the displacement of the stepped piston via the biasing means, and this makes it possible to detect the differential pressure with high accuracy.

Additionally, the cylinder/piston structure is basically more resistant to high pressure than a diaphragm and is less susceptible to damage.

In addition, by arranging the displacement detection means on one axial side of the stepped piston, the stepped piston part to which high pressure acts and the displacement detection part to detect its displacement are separated in the axial direction, and the high pressure is applied to the displacement detection part. The structure shall be such that this does not work.

In other words, an axial hole is formed in the end wall of the cylinder body on the side opposite to the central piston to allow movement of the central piston portion in the axial direction within the cylinder body, and one end of the axial hole is formed in the end wall of the cylinder body. A shaft made of a non-magnetic material that moves in the axial direction together with the stepped piston is arranged so as to protrude from the opening to the outside of the end wall of the cylinder body, and a magnetic core is attached to the part of the shaft that protrudes to the outside of the end wall of the cylinder body. will be established. Further, the opening of the axial hole is closed with a case made of a non-magnetic material surrounding the protruding portion of the shaft and the magnetic core, and displacement of the magnetic core is detected by a displacement sensor provided on the outer periphery of the case. Here, the axial hole is
Since the central piston part of the stepped piston and the cylinder body are in a sealed moving relationship, the sealed moving part is hydraulically isolated from the cylinder chamber, and the high pressure in the cylinder chamber does not act, preventing the axial hole and the inside of the case from acting. By communicating with the tank, these parts are held at tank pressure. This prevents high pressure from acting on the inside of the case, preventing damage to the case, and also allows the case to be made thinner, making it possible to detect displacement with high precision.

On the other hand, in the stepped piston part, there is no need to arrange a displacement detection means, and the cylinder and piston do not need to be made of non-magnetic material, and their materials and shapes can be freely designed to obtain sufficient strength. can.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

In Fig. 1, reference numeral 1 is the body of the differential pressure gauge, and the body 1 includes two pressure oil ports 2 and 3 through which two pressures for measuring differential pressure are introduced, and a discharge port 4 connected to a tank. is formed. A cylinder main body 5 is attached to the body 1, and pressure oil passages 5a and 5b are formed in the cylinder main body 5 and communicate with the pressure oil ports 2 and 3, respectively.
The cylinder body 5 also includes an outer piston portion 8a in which pressure receiving portions 6 and 7 having the same area are formed on both sides, and two central piston portions 8b and 8c that protrude on both sides of the outer piston portion 8a in the axial direction. A stepped piston 8 is housed so as to be able to move in a sealed manner in the axial direction. Between the pressure receiving parts 6, 7 of the outer peripheral piston portion 8a and the inner wall of the cylinder body 5,
Cylinder chambers 9 and 10 are formed in which two pressure oil passages 5a and 5b open, respectively. The cylinder chambers 9 and 10 communicate with the pressure oil ports 2 and 3 via pressure oil passages 5a and 5b, respectively, and apply pressure introduced thereto to act on the pressure receiving portions 6 and 7.

Inside the cylinder body 5, there is also a stepped piston 8.
A low pressure chamber 5c is formed that allows the central piston portion 8b on the right side in the figure to move in the axial direction. A low pressure chamber 5d that allows movement is formed. Low pressure chamber 5c
A part of the low pressure chamber 5d is formed by an axial hole 5A formed in the center of the cylinder body, and this axial hole 5A opens at the end wall of the cylinder body 5 on the right side in the drawing. A shaft 11 made of a non-magnetic material is disposed in the low pressure chamber 5c in the cylinder body 5, and the left end of the shaft 11 in the drawing is an enlarged diameter base 12 and comes into contact with the end surface of the central piston portion 8c. One end, that is, the opposite end of the central piston portion 8c, protrudes outward beyond the opening of the axial hole 5A in the end wall of the cylinder body, and a core 13 made of a magnetic material is attached to that end. ing. Further, a case 14 made of a non-magnetic material that closes the opening and surrounds the protruding portion of the shaft 11 and the core 13 is attached to the opening of the axial hole 5A. A chamber 14a is formed that allows axial movement.

In the low pressure chamber 5c, the case 14 and the shaft 1
A spring 15 is provided between the expanded diameter base 12 of the stepped piston 8 and the stepped piston 8 to urge the stepped piston 8 against its rightward displacement.
is placed in a pre-compressed state. Further, in the low pressure chamber 5d, between the end of the central piston portion 8c of the stepped piston 8 and the body 1, a spring 16 is also pre-compressed for biasing the stepped piston 8 against its leftward displacement. It is arranged in condition.

With the above configuration, the displacement of the stepped piston 8 is transmitted to the shaft 11 and the core 13, and the core 13 is transferred to the stepped piston 8 in the chamber 14a of the case 14.
has the same displacement. Further, the stepped piston 8 is held at the neutral position when no pressure is introduced into the cylinder chambers 9 and 10 or when the introduced pressures are equal, and when different pressures are introduced into the cylinder chambers 9 and 10. , a force proportional to the differential pressure is transmitted to the spring 15 or 16, and the biasing of this spring causes displacement in proportion to the force.

A displacement sensor 17 is mounted on the outer periphery of the case 14 for sensing the displacement of the core 13 and outputting an electric signal proportional to the displacement.

A cover 18 surrounding the case 14 is attached to the outer end of the cylinder body 5.
An amplifier 20 that amplifies the electrical signal from the displacement sensor 17 and outputs it to the outside via lead wires 19a and 19b is housed inside.

Coaxial central holes 21, 22, and 23 are formed through the stepped piston 8, shaft 11, and core 13 in the axial direction, and the low pressure chamber 5d communicates with the discharge port 4. As a result, the low pressure chamber 5c and the shaft 1
1 and the case 14 and the chamber 14a communicates with the low pressure chamber 5d through central holes 21, 22, 23, and further communicates with the low pressure chamber 5d through the discharge port 4 with the tank. With such a passage configuration, the hydraulic oil leaked into the low pressure chamber 5c and the chamber 14a is discharged to the tank from the discharge port 4 together with the oil leaked into the low pressure chamber 5d via the central holes 21, 22, and 23, and the hydraulic oil leaks into the low pressure chamber 5c and the chamber 14a. , 5d and case 14
The inner chamber 14a is maintained at tank pressure.

As the displacement sensor 17, a differential transformer type or a magnetoresistive element type is used.
For this reason, the shaft 11 and the case 14 are made of a non-magnetic material, and the core 13 is made of a magnetic material.
By using such a non-contact displacement sensor, the displacement of the core 13 can be appropriately detected even if oil is present in the portion of the core 13 that is displaced.

In the differential pressure gauge configured in this way, when pressure is guided to the pressure oil ports 2 and 3, the pressure is transmitted to the cylinder chambers 9 and 10 via the pressure oil passages 5a and 5b, and , the pressure-receiving portions 6 and 7 of the outer peripheral piston portion 8a of the stepped piston 8 are respectively acted on. At this time, the pressure introduced to the pressure oil port 2 is P1, the pressure introduced to the pressure oil port 3 is P2, and the pressure receiving area of the pressure receiving parts 6 and 7 is A.
Then, due to the pressure P1 acting on the pressure receiving part 6, A
The force of ×P1 acts as a force that moves the stepped piston 8 to the right in the drawing, and the pressure that acts on the pressure receiving part 7
Due to P2, the force A×P2 acts as a force that moves the stepped piston 8 to the left in the drawing. On the other hand, since the end faces of the central piston parts 8b and 8c and the end face of the shaft 11 that moves in the axial direction together with the stepped piston 8 are at tank pressure as described above, the force acting on these parts can be ignored. I can do it.

Therefore, if pressure P1>P2, stepped piston 8
A force of A×(P1-P2) acts on the right side of the drawing. As a result, the piston 8 is moved by the spring 15,
16 is now displaced against the spring 15. When the spring constants of the two springs 15 and 16 are K1 and K2, the displacement of the stepped piston 8 is S=A×(P1−P2)/(K1+K2).

This displacement is transmitted to the core 13 via the shaft 11, and the core 13 also undergoes the same displacement as the stepped piston 8.

The displacement sensor 17 senses this displacement, converts it into an electrical signal, amplifies it with the amplifier 20, and outputs it. Whether the displacement sensor 17 is a differential transformer type or a magnetoresistive element type, the relationship between the electric signal level E and the displacement S is linear and linearly proportional. Therefore, when the proportionality constant is K, the electric signal level E is as follows: E=K.S={K.A/(K1+K2)}(P1-P2). Here, A, K1, and K2 are all constants, so
Electronic signal level E is the differential pressure between two pressures (P1-P2)
The value is proportional to .

If the two pressures are P2>P1, the above explanation applies as is, only the direction of displacement of the stepped piston 8 is reversed.

In this embodiment, in order to simultaneously apply two pressures to the pressure receiving parts 6 and 7 of the stepped piston 8, the respective pressures are guided to separate pressure sensors to obtain respective electric signals, and then their respective electric signals are obtained. Unlike when measuring a difference to obtain an electrical signal corresponding to the differential pressure, errors due to non-linearity of the output with respect to pressure in a pressure sensor and hysteresis with respect to increases and decreases in pressure do not occur, and the differential pressure between high pressures is not generated. can be measured with high precision.

Furthermore, when measuring differential pressure under high pressure, the differential pressure gauge must not be damaged by the high pressure. In this embodiment, two springs 15 and 16 are used to convert the differential pressure into displacement of the stepped piston 8, and the displacement is sensed by a displacement sensor 17. Here, if the piston 8 does not have a central piston portion 8b and the pressure oil passage 5
High-pressure oil flowing from b flows into chamber 1 in case 14.
4a, the high pressure acts on the case 14, causing damage to the case 14a. In order to prevent damage to the case 14a,
When the thickness of the magnetic core 13 is increased, the distance between the magnetic core 13 and the displacement sensor 17 increases, making it impossible to detect displacement with high accuracy.

In this embodiment, the piston 8 is provided with central piston portions 8b and 8c, and the cylinder chamber 10 is isolated from the low pressure chamber 5c and the chamber 14a in the case 14 by a sealed moving portion between the central piston portion 8b and the cylinder body 5. , these chambers are communicated with the tank together with the low pressure chamber 5d. As a result, the chamber 14a inside the case 14 is maintained at tank pressure, the plate thickness of the case 14 is made thinner, the displacement sensor 17 can detect displacement with high sensitivity and precision, and damage to the case 14 is prevented. Ru.

Further, when the displacement of the stepped piston 8 is detected by a displacement sensor, a configuration is usually considered in which a magnetic material is incorporated into the piston part and a displacement sensor such as a differential transformer is set in the cylinder body part around the piston part. However, as mentioned above, in order to increase the detection sensitivity, it is necessary to place the magnetic core and the displacement sensor close to each other.If the magnetic core and the displacement sensor are placed close to the piston and cylinder body parts where high pressure acts, It is difficult to make the cylinder body with high strength.

In addition, when detecting displacement electrically with a displacement sensor such as a differential transformer, the surrounding area other than the magnetic core must be made of non-magnetic material. In this case, the piston and cylinder bodies must be made of non-magnetic material such as resin. However, for example, 400Kg/
When measuring a small differential pressure under a high pressure of ^cm2 , a maximum differential pressure of nearly 400Kg/ ^cm2 may occur.If the piston and cylinder body are made of resin, this large differential pressure will cause the piston to When it collides with the main body, there is a risk that the wall of the cylinder main body or the piston will crack.

In this embodiment, the cylinder/piston part on which hydraulic pressure acts and the part that electrically detects the displacement of the piston are separated in the axial direction, a magnetic core 13 is provided on the shaft 11, and a case 14 is provided on the outside of the cylinder body 5.
A displacement sensor 17 is installed on the outer periphery. Therefore, only the shaft 11 and the case 14 need to be made of non-magnetic material, and the stepped piston 8 and the cylinder body 5 can be made of strong casting suitable for mass production, for example, so that the design can be freely designed in terms of strength. As a result, a high-strength piston-cylinder structure can be obtained.

Furthermore, various additives and metal particles such as iron powder and chips are mixed into the hydraulic fluid for hydraulic machines, making it easier to conduct electricity. Therefore, when electrically detecting the pressure difference in the hydraulic oil, the electrical system must be cut off from the hydraulic oil. In this embodiment, since the shaft 11 is used and the magnetic core 13 is attached to it as described above, the displacement sensor 17 can be installed outside the cylinder body 5, which prevents leakage into the chamber 14a, for example. Even if the hydraulic oil is conductive, the displacement of the magnetic core 13 can be detected with high accuracy without being affected by it, and the reliability of the differential pressure gauge can be improved.

Furthermore, in this embodiment, since the amplifier 20 is built-in, zero point adjustment and gain adjustment can be easily performed, and by adding a temperature compensation circuit, errors due to temperature changes are corrected, and the differential pressure can be further increased. It becomes possible to measure accurately.

Further, in this embodiment, the cylinder 5 is attached to the body 1, and the main body portion is of a removable cartridge type, so that maintenance can be easily performed.

As described above, according to this embodiment, even when used under high pressure, the displacement sensor part and the piston/cylinder part will not be damaged, and the slight pressure difference between high pressures can be detected with high accuracy. I can do it. Furthermore, maintenance can be easily performed. Therefore, it is very useful for computerizing control devices that use differential pressure signals.

Note that the above embodiment is an example in which the magnitude relationship between the two pressures P1 and P2 is not constant.
If the relationship P1≧P2 is always maintained, it is only necessary to consider the displacement of the stepped piston 8 in the right direction in the drawing, so the spring 16 may be omitted, and in this case, the structure becomes simpler. The relationship between the differential pressure and the output electrical signal level E at this time is E={K·A/K2}(P1−P2).

Further, in the above embodiment, the amplifier 20 is provided in the cartridge 18, but if necessary, the amplifier 20 may be provided in the cartridge 18.
0 can also be placed externally, in which case the structure becomes more compact.

〔Effect of the invention〕

According to the present invention, even when used under high pressure, the displacement sensor part, piston, etc. will not be damaged, and a slight pressure difference between high pressures can be detected with high accuracy, and therefore the differential pressure signal This will be of great help in the electronicization of control devices that use

[Brief explanation of drawings]

FIG. 1 is a sectional view of a differential pressure gauge according to an embodiment of the present invention. In the figure, code 5... cylinder body, 5a, 5b...
...Two pressure oil passages, 5c, 5d...chamber, 5A...
Axial hole, 6, 7...Pressure receiving part, 8...Stepped piston, 8a...Outer peripheral piston part, 8b, 8c...
Central piston part, 9, 10...Cylinder chamber, 1
1... Shaft, 13... Core, 14... Case, 14a... Chamber, 15, 16... Spring (biasing means), 17... Displacement sensor.

Claims (1)

[Scope of Claims] 1. A differential pressure gauge for a hydraulic machine that detects a pressure difference between two parts in a hydraulic circuit, comprising: a cylinder body having two pressure oil passages through which the pressures of the two parts are guided; It has an outer circumferential piston portion forming a pressure-receiving portion with an equal area and two central piston portions protruding on both sides of the outer circumferential piston portion in the axial direction, and these outer circumferential and central piston portions are capable of sealing movement in the axial direction within the cylinder body. a stepped piston that is housed in the cylinder body and forms a cylinder chamber in which the two pressure oil passages open between the outer peripheral piston portion and the inner wall of the cylinder body; and a displacement detection means disposed on one axial side of the stepped piston to electrically detect the displacement of the stepped piston in the axial direction, the displacement detection means being disposed within the cylinder body. an axial hole formed to permit axial movement of the central piston portion and opening in an end wall of the cylinder body; an axial hole configured to allow axial movement of the central piston portion; a shaft made of a non-magnetic material whose end opposite to the central piston portion protrudes from the opening of the axial hole to the outside of the end wall of the cylinder body; a magnetic core provided in the protruding portion of the shaft; and the cylinder. A case made of a non-magnetic material that closes the opening of the axial hole outside the end wall of the main body and surrounds the protruding portion of the shaft and the magnetic core, and a displacement device that is attached to the outer periphery of the case and detects the displacement of the core. A differential pressure gauge for a hydraulic machine, comprising: a sensor; and passage means for communicating the end face of the central piston portion, the axial hole, and the inside of the case with a tank.