WO2008118072A1 - Fluid power control system - Google Patents

Fluid power control system Download PDF

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Publication number
WO2008118072A1
WO2008118072A1 PCT/SE2008/050302 SE2008050302W WO2008118072A1 WO 2008118072 A1 WO2008118072 A1 WO 2008118072A1 SE 2008050302 W SE2008050302 W SE 2008050302W WO 2008118072 A1 WO2008118072 A1 WO 2008118072A1
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WO
WIPO (PCT)
Prior art keywords
valve
actuator
port
fluid
pressure
Prior art date
Application number
PCT/SE2008/050302
Other languages
French (fr)
Inventor
Sten Jiewertz
Original Assignee
Scania Cv Ab (Publ)
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Scania Cv Ab (Publ) filed Critical Scania Cv Ab (Publ)
Priority to DE112008000774T priority Critical patent/DE112008000774T5/en
Publication of WO2008118072A1 publication Critical patent/WO2008118072A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B11/00—Servomotor systems without provision for follow-up action; Circuits therefor
    • F15B11/08—Servomotor systems without provision for follow-up action; Circuits therefor with only one servomotor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D9/00—Controlling engines by throttling air or fuel-and-air induction conduits or exhaust conduits
    • F02D9/04—Controlling engines by throttling air or fuel-and-air induction conduits or exhaust conduits concerning exhaust conduits
    • F02D9/06—Exhaust brakes
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B11/00—Servomotor systems without provision for follow-up action; Circuits therefor
    • F15B11/006—Hydraulic "Wheatstone bridge" circuits, i.e. with four nodes, P-A-T-B, and on-off or proportional valves in each link
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B13/00—Details of servomotor systems ; Valves for servomotor systems
    • F15B13/02—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors
    • F15B13/04—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors for use with a single servomotor
    • F15B13/044—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors for use with a single servomotor operated by electrically-controlled means, e.g. solenoids, torque-motors
    • F15B13/0446—Fluid distribution or supply devices characterised by their adaptation to the control of servomotors for use with a single servomotor operated by electrically-controlled means, e.g. solenoids, torque-motors with moving coil, e.g. voice coil
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16D—COUPLINGS FOR TRANSMITTING ROTATION; CLUTCHES; BRAKES
    • F16D48/00—External control of clutches
    • F16D48/06—Control by electric or electronic means, e.g. of fluid pressure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16K—VALVES; TAPS; COCKS; ACTUATING-FLOATS; DEVICES FOR VENTING OR AERATING
    • F16K31/00—Actuating devices; Operating means; Releasing devices
    • F16K31/02—Actuating devices; Operating means; Releasing devices electric; magnetic
    • F16K31/06—Actuating devices; Operating means; Releasing devices electric; magnetic using a magnet, e.g. diaphragm valves, cutting off by means of a liquid
    • F16K31/0603—Multiple-way valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/20—Fluid pressure source, e.g. accumulator or variable axial piston pump
    • F15B2211/205—Systems with pumps
    • F15B2211/2053—Type of pump
    • F15B2211/20538—Type of pump constant capacity
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/305—Directional control characterised by the type of valves
    • F15B2211/3056—Assemblies of multiple valves
    • F15B2211/30565—Assemblies of multiple valves having multiple valves for a single output member, e.g. for creating higher valve function by use of multiple valves like two 2/2-valves replacing a 5/3-valve
    • F15B2211/30575—Assemblies of multiple valves having multiple valves for a single output member, e.g. for creating higher valve function by use of multiple valves like two 2/2-valves replacing a 5/3-valve in a Wheatstone Bridge arrangement (also half bridges)
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/40—Flow control
    • F15B2211/42—Flow control characterised by the type of actuation
    • F15B2211/426—Flow control characterised by the type of actuation electrically or electronically
    • F15B2211/427—Flow control characterised by the type of actuation electrically or electronically with signal modulation, e.g. using pulse width modulation [PWM]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/50—Pressure control
    • F15B2211/52—Pressure control characterised by the type of actuation
    • F15B2211/526—Pressure control characterised by the type of actuation electrically or electronically
    • F15B2211/527—Pressure control characterised by the type of actuation electrically or electronically with signal modulation, e.g. pulse width modulation [PWM]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/70—Output members, e.g. hydraulic motors or cylinders or control therefor
    • F15B2211/705—Output members, e.g. hydraulic motors or cylinders or control therefor characterised by the type of output members or actuators
    • F15B2211/7051—Linear output members
    • F15B2211/7052—Single-acting output members

Definitions

  • This invention relates to a fluid power control system
  • a seat valve comprising a first port, a second port, a valve body biased by a spring to a closed valve position and subjected to a force in an opening direction when said first port is pressurized, and an electromagnet capable of moving said valve body to an open valve position when energized.
  • the system also comprises a pressure source, a fluid power actuator, a fluid line for communicating pressurized fluid from the pressure source between the valve and the actuator, and an electronic control unit for energizing the electromagnet by electric current pulses having a varying pulse ratio.
  • a reliable and inexpensive valve is the on-off valve.
  • An on-off valve however, by definition has a very steep control characteristic. It is, nevertheless, at least partially possible to have an on-off valve mimic a proportional valve by giving the input pulse a high resolution. More precisely, the actuator operation, controlled by an on-off valve, is normally monitored by a pressure sensor device or a position sensor device from which the respectively signal is connected to an input stage of the electronic control unit in a closed loop function. By giving the input signal from these sensors a high resolution, before calculating the signal values in the control unit, for example by an A/D converter having a high resolution, the control region of the on-off valve in some way can be "stretched". This approach will still be an expensive solution.
  • An object of the invention is to provide a system of the kind defined above that uses the inexpensive, reliable and rugged on-off valve and still is capable of controlling the actuator in the desired fashion.
  • the seat valve is of the on-off type, and the first port of the on-off valve is exclusively a fluid inlet port and the second port is exclusively a fluid outlet port.
  • the valve will have a substantially proportional control region.
  • "Proportional” in this context is to be understood as a gently sloping, easy controllable input pulse to output pressure characteristic as opposed to the sudden, high gradient characteristic which is otherwise significant for the on-off valve.
  • the on-off valve will unexpectedly have the desired pronounced proportional characteristic, without any extensive adaptation of the control system.
  • the spring is selected to securely seat the valve body against the operational pressure from the pressure source. Such a stiffer spring may also be selected in order to prevent the valve from opening unintentionally due to vibrations influencing the valve, for example vibrations from a truck where the system is installed.
  • the first port is connected to the pressure source for increasing a pressure in the actuator. Thereby, the proportional control region is effective on filling the actuator by the pressurized fluid.
  • the first port may be connected to the actuator input for decreasing a pressure in the actuator.
  • the proportional control region is effective on emptying the actuator from the pressurized fluid.
  • a proportional control region is, of course, effective for both filling and emptying the actuator.
  • the first and second ports of each valve will then be connected accordingly to the system by choosing one of the possible four configurations when the system has two valves. In the scope of the invention, the system may, however, have more on-off valves with correspondingly more combinations of configurations.
  • FIG. 1 is a diagrammatic view of a fluid power control system according to the invention.
  • FIG. 2 is a graph showing pulse ratio to pressure characteristics, respectively of an on-off valve in a conventional system and an on-off valve in a system according to the invention.
  • the fluid power control system has two identical or substantially identical on-off valves of the 2/2 type, a first valve 10 and a second valve 10', for controlling the stroke of a cylinder-piston actuator, such as an automotive clutch actuator, an EGR valve actuator or an exhaust brake actuator, generally designated by 40.
  • a cylinder-piston actuator such as an automotive clutch actuator, an EGR valve actuator or an exhaust brake actuator, generally designated by 40.
  • the system is usually pressurized by an air pressure source 30 as indicated in FIG. 1.
  • the fluid pressure source in a system accord- ing to the invention may as well be a hydraulic pressure source.
  • Fluid inflow from pressure source 30 to actuator 40 is communicated via first valve 10 by an inflow fluid line 32, and fluid outflow from actuator 10 to an outlet 60 is communicated via second valve 10' by an outflow fluid line 34 connected to inflow fluid line 32 between first valve 10 and actuator 40.
  • first valve 10 is responsible exclusively for increasing the pressure in the actuator 40 and the second valve 10' is responsible exclusively for decreasing the pressure in the actuator 40.
  • a housing 1 1 of each on-off valve 10, 10' has a first port 12 used as an inlet port, and a second port 14 used as an outlet port.
  • ports 12 and 14 are thereby reversed as compared to the common manufacturer specification: first port 12 is often marked “A” for "Actuator” and second port 14 is often marked “P” for "Pressure”.
  • a valve body in the shape of a plunger or piston 16 is seated to a valve seat 18 by a force from a spring 20.
  • the valve body 16 closes a fluid passage in the valve between the inlet port 12 and the outlet port 14.
  • the valve body 16 is also subjected to an opening force by pressure in inlet port 12, and to a closing force by pressure in outlet port 14.
  • the force from spring 20 may be selected so as to always keep valve body 16 securely seated against any operational pressure difference between inlet port 12 and outlet port 14 that strives to unseat the valve body 16.
  • valves 10, 10' are influenced by vibrations that might be in resonance with the frequency of electric current pulses of an electronic control unit 50 yet to be described, for example vibrations from a truck where the system is installed, the force from spring 20 may be se- lected to keep valve body 16 securely seated also against that influence.
  • the above-mentioned electronic control unit 50 is provided for controlling the respective valves 10, 10'.
  • Control unit 50 is capable of selectively energizing an electromagnet 22 in each valve 10, 10' by electric current pulses via respective electric lines 52, 52'.
  • the electromagnet 22 of each valve 10, 10' is capable of opening the valve by unseating the valve body 16 against the combined force from spring 20 and the above-mentioned pressure difference.
  • the electric current to the electromagnet 22 is pulsed by a constant frequency, and the pulse ratio, i.e. the ratio of the duration of the electric current in each period to the full duration of each period, is varied.
  • the pulse ratio i.e. the ratio of the duration of the electric current in each period to the full duration of each period.
  • a short current pulse low pulse ratio
  • an extended current pulse high pulse ratio
  • a control region at a certain frequency is as large as possible in order to have the clutch engage smoothly.
  • the control region is usually defined as the difference in pulse ratio when the valve starts to open and when it is regarded as fully open.
  • the graph in FIG. 2 shows an example of tests A and B made by the inventor using in test A a conventional on-off valve in a conventional configuration (dotted line), and in test B the reversed configuration (full line) in accordance with the invention.
  • the electronic control unit had a conventional inexpensive pulse generator.
  • the helical spring 20 (FIG. 1 ) of the on-off valve was replaced by a stiffer spring than in test A as discussed in the foregoing.
  • the different characteristics are readily distinguishable: The expected narrow control region of the on-off valve in test A is confirmed, as well as the near proportional control region of the on- off valve in test B according to the invention.
  • the different characteristics in test A and B can be explained as follows in a valve opening operation. A valve closing operation will behave in a corresponding reversed manner.
  • test A the force of the static pressure in outlet port 14 striving to close the valve comes to an end at a certain low flow through the valve, and the resulting force from the electric current on the valve body 16 (the weak spring force subtracted from the force of the electromagnet 22) suddenly gets way too high, whereby the valve will open to a large flow without any increase of the electric current. Accordingly, the valve will be difficult to control.
  • test B the force of the static pressure in inlet port 12 striving to open the valve comes to an end at a certain low flow through the valve and the electric current (the pulse ratio) through the electromagnet 22 has to be successively increased to further open the valve. Accordingly, an increasing electric current (pulse ratio) results in a correspondingly increasing flow through the valve over the control region.
  • a system according to the invention it may be convenient to combine the inventive valve configuration with the conventional configuration in order to have ON and OFF actuator strokes exhibiting different characteristics.
  • an engaging ON actuator stroke has the smooth, low gradient proportional behaviour in FIG. 2
  • a disengaging OFF actuator stroke has the rapid, high gradient sudden behaviour in FIG. 2.
  • the ports 12, 14 of valve 10' in the system of FIG. 1 need only be reversed, and the on-off valve 10' can be selected directly from the shelf, i.e. without having the possibly modified, stiffer spring 20.

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  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Magnetically Actuated Valves (AREA)

Abstract

A fluid power control system has a seat valve (10, 10') comprising a first port (12), a second port (14), a valve body (16) biased by a spring (20) to a closed valve position and subjected to a fo rce in an opening direction when said first port is pressurized, and an electromagnet (22) capable of moving said valve body to an open valve position when energized. The system has also a pressure source (30), a fluid power actuator (40), a fluid line (32) fo r communicating pressurized fluid from the pressure source between the valve and the actuator, and an electronic control unit (50) for energizing the electromagnet by electric current pulses having a varying pulse ratio. To provide a system that uses a seat valve (10, 10') of the on-off type which is capable of controlling the actuator (40) in a proportional manner, the first port (12) is exclusively a fluid inlet port and the second port (14) is exclusively a fluid outlet port.

Description

Fluid power control system
TECHNICAL FIELD
This invention relates to a fluid power control system comprising a seat valve comprising a first port, a second port, a valve body biased by a spring to a closed valve position and subjected to a force in an opening direction when said first port is pressurized, and an electromagnet capable of moving said valve body to an open valve position when energized. The system also comprises a pressure source, a fluid power actuator, a fluid line for communicating pressurized fluid from the pressure source between the valve and the actuator, and an electronic control unit for energizing the electromagnet by electric current pulses having a varying pulse ratio.
BACKGROUND In many fluid power control applications such as pneumatic clutch operation, EGR (Exhaust Gas Recirculation) control, and exhaust braking in automotive vehicles, it is desired to control the pressure/flow to the actuator in a proportional manner. A straightforward approach would then be to control the actuator by a proportional valve. Proportional valves are, however, expensive and prone to malfunction if the pressurized fluid is not extremely clean, i.e. free of particles, which may not always be the case in fluid power control systems that favor reliability and low cost. It is therefore desirable to find an alternative more reliable valve for these applications.
A reliable and inexpensive valve is the on-off valve. An on-off valve, however, by definition has a very steep control characteristic. It is, nevertheless, at least partially possible to have an on-off valve mimic a proportional valve by giving the input pulse a high resolution. More precisely, the actuator operation, controlled by an on-off valve, is normally monitored by a pressure sensor device or a position sensor device from which the respectively signal is connected to an input stage of the electronic control unit in a closed loop function. By giving the input signal from these sensors a high resolution, before calculating the signal values in the control unit, for example by an A/D converter having a high resolution, the control region of the on-off valve in some way can be "stretched". This approach will still be an expensive solution. DISCLOSURE OF THE INVENTION
An object of the invention is to provide a system of the kind defined above that uses the inexpensive, reliable and rugged on-off valve and still is capable of controlling the actuator in the desired fashion. In an aspect of the invention, in the system, the seat valve is of the on-off type, and the first port of the on-off valve is exclusively a fluid inlet port and the second port is exclusively a fluid outlet port. Thereby the valve will have a substantially proportional control region. "Proportional" in this context is to be understood as a gently sloping, easy controllable input pulse to output pressure characteristic as opposed to the sudden, high gradient characteristic which is otherwise significant for the on-off valve.
Accordingly, by simply reversing the manufacturer-dedicated ports of the on- off valve, i.e. by instead connecting the first port to the high pressure side and connecting the second port to the low pressure side, the on-off valve will unexpectedly have the desired pronounced proportional characteristic, without any extensive adaptation of the control system.
The only modification that may be needed to an on-off valve selected from stock, is to replace the original spring biasing the valve body against the valve seat by a somewhat stiffer spring, since the reversed output port will then be subjected to the higher pressure.
The spring is selected to securely seat the valve body against the operational pressure from the pressure source. Such a stiffer spring may also be selected in order to prevent the valve from opening unintentionally due to vibrations influencing the valve, for example vibrations from a truck where the system is installed. In an embodiment of the invention, the first port is connected to the pressure source for increasing a pressure in the actuator. Thereby, the proportional control region is effective on filling the actuator by the pressurized fluid.
Alternatively, the first port may be connected to the actuator input for decreasing a pressure in the actuator. Thereby, the proportional control region is effective on emptying the actuator from the pressurized fluid.
If one valve according to the invention is exclusively used for filling the actuator while another valve according to the invention is exclusively used for emptying the actuator, then a proportional control region is, of course, effective for both filling and emptying the actuator. In certain applications, there may be desirable to have a slow proportional filling operation and a rapid "OFF" emptying operation or vice versa. The first and second ports of each valve will then be connected accordingly to the system by choosing one of the possible four configurations when the system has two valves. In the scope of the invention, the system may, however, have more on-off valves with correspondingly more combinations of configurations.
Other features and advantages of the invention is apparent from the appended claims and the detailed description.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a diagrammatic view of a fluid power control system according to the invention; and
FIG. 2 is a graph showing pulse ratio to pressure characteristics, respectively of an on-off valve in a conventional system and an on-off valve in a system according to the invention.
DETAILED DESCRIPTION OF EMBODIMENTS
In the exemplary embodiment shown in FIG. 1 , the fluid power control system has two identical or substantially identical on-off valves of the 2/2 type, a first valve 10 and a second valve 10', for controlling the stroke of a cylinder-piston actuator, such as an automotive clutch actuator, an EGR valve actuator or an exhaust brake actuator, generally designated by 40. In case of such an automotive actuator 40, the system is usually pressurized by an air pressure source 30 as indicated in FIG. 1. In these and other applications, however, the fluid pressure source in a system accord- ing to the invention may as well be a hydraulic pressure source.
Fluid inflow from pressure source 30 to actuator 40 is communicated via first valve 10 by an inflow fluid line 32, and fluid outflow from actuator 10 to an outlet 60 is communicated via second valve 10' by an outflow fluid line 34 connected to inflow fluid line 32 between first valve 10 and actuator 40. In other words, the first valve 10 is responsible exclusively for increasing the pressure in the actuator 40 and the second valve 10' is responsible exclusively for decreasing the pressure in the actuator 40.
A housing 1 1 of each on-off valve 10, 10' has a first port 12 used as an inlet port, and a second port 14 used as an outlet port. In the system according to the in- vention, ports 12 and 14 are thereby reversed as compared to the common manufacturer specification: first port 12 is often marked "A" for "Actuator" and second port 14 is often marked "P" for "Pressure".
A valve body in the shape of a plunger or piston 16 is seated to a valve seat 18 by a force from a spring 20. When so seated, the valve body 16 closes a fluid passage in the valve between the inlet port 12 and the outlet port 14. When so seated, and influenced by operational pressure, the valve body 16 is also subjected to an opening force by pressure in inlet port 12, and to a closing force by pressure in outlet port 14. The force from spring 20 may be selected so as to always keep valve body 16 securely seated against any operational pressure difference between inlet port 12 and outlet port 14 that strives to unseat the valve body 16. In case the valves 10, 10' are influenced by vibrations that might be in resonance with the frequency of electric current pulses of an electronic control unit 50 yet to be described, for example vibrations from a truck where the system is installed, the force from spring 20 may be se- lected to keep valve body 16 securely seated also against that influence.
The above-mentioned electronic control unit 50 is provided for controlling the respective valves 10, 10'. Control unit 50 is capable of selectively energizing an electromagnet 22 in each valve 10, 10' by electric current pulses via respective electric lines 52, 52'. When energized, the electromagnet 22 of each valve 10, 10' is capable of opening the valve by unseating the valve body 16 against the combined force from spring 20 and the above-mentioned pressure difference.
The electric current to the electromagnet 22 is pulsed by a constant frequency, and the pulse ratio, i.e. the ratio of the duration of the electric current in each period to the full duration of each period, is varied. For example, when pressurizing actuator 40 by controlling valve 10 via control unit 50, a short current pulse (low pulse ratio) results in a low pressure/flow at the outlet port 14, whereas an extended current pulse (high pulse ratio) results in a high pressure/flow. This also applies to the pressure/flow of air out of valve 10' (and applies to the flow only when the outlet 60 is the ambient atmosphere). The pulse ratio is often expressed as a percentage of the period of time given by a certain frequency. For example, at a frequency of 100 Hz the period is 1/100 s = 10 ms. A pulse ratio of 25 % will then result in an electric current pulse duration of 25/100x10 ms = 2.5 ms. In fluid pressure/flow control of, for example, a clutch actuator 40, it is important that a control region at a certain frequency is as large as possible in order to have the clutch engage smoothly. The control region is usually defined as the difference in pulse ratio when the valve starts to open and when it is regarded as fully open.
The graph in FIG. 2 shows an example of tests A and B made by the inventor using in test A a conventional on-off valve in a conventional configuration (dotted line), and in test B the reversed configuration (full line) in accordance with the invention. In both cases, the electronic control unit had a conventional inexpensive pulse generator. In test B, the helical spring 20 (FIG. 1 ) of the on-off valve was replaced by a stiffer spring than in test A as discussed in the foregoing. The different characteristics are readily distinguishable: The expected narrow control region of the on-off valve in test A is confirmed, as well as the near proportional control region of the on- off valve in test B according to the invention. The different characteristics in test A and B can be explained as follows in a valve opening operation. A valve closing operation will behave in a corresponding reversed manner.
In test A, the force of the static pressure in outlet port 14 striving to close the valve comes to an end at a certain low flow through the valve, and the resulting force from the electric current on the valve body 16 (the weak spring force subtracted from the force of the electromagnet 22) suddenly gets way too high, whereby the valve will open to a large flow without any increase of the electric current. Accordingly, the valve will be difficult to control.
In test B, the force of the static pressure in inlet port 12 striving to open the valve comes to an end at a certain low flow through the valve and the electric current (the pulse ratio) through the electromagnet 22 has to be successively increased to further open the valve. Accordingly, an increasing electric current (pulse ratio) results in a correspondingly increasing flow through the valve over the control region.
As indicated in the foregoing, in a system according to the invention it may be convenient to combine the inventive valve configuration with the conventional configuration in order to have ON and OFF actuator strokes exhibiting different characteristics. For example, it may be desired that an engaging ON actuator stroke has the smooth, low gradient proportional behaviour in FIG. 2, whereas a disengaging OFF actuator stroke has the rapid, high gradient sudden behaviour in FIG. 2. In that case, the ports 12, 14 of valve 10' in the system of FIG. 1 need only be reversed, and the on-off valve 10' can be selected directly from the shelf, i.e. without having the possibly modified, stiffer spring 20.
The foregoing detailed description is given primarily for clearness of understanding and no unnecessary limitations are to be understood therefrom. Modifications will become obvious to those skilled in the art upon reading this disclosure and may be made without departing from the spirit of the invention or the scope of the appended claims.

Claims

1. A fluid power control system comprising: a seat valve (10; 10') comprising: a first port (12); a second port (14); a valve body (16) biased by a spring (20) to a closed valve position and subjected to a force in an opening direction when said first port is pressurized; and an electromagnet (22) capable of moving said valve body to an open valve position when energized; a pressure source (30); a fluid power actuator (40); a fluid line (32; 32, 34) for communicating pressurized fluid from the pressure source between the valve and the actuator; and an electronic control unit (50) for energizing the electromagnet by electric current pulses having a varying pulse ratio; c h a r a c t e r i z e d by said seat valve (10; 10') being of the on-off type; and said first port (12) being exclusively a fluid inlet port and said second port (14) being exclusively a fluid outlet port.
2. The system according to claim 1 , wherein said spring (20) biasing the valve body (16) being selected to securely keep the valve body in the closed position against an operational pressure in said first port (12).
3. The system according to claim 1 or 2, wherein said spring (20) biasing the valve body (16) being selected to securely keep the valve body in the closed position against vibrations influencing the valve.
4. The system according to any of the previous claims, wherein said first port (12) being connected to said pressure source (30) for increasing a pressure in the actuator (40) on valve operation.
5. The system according to any of the previous claims, wherein said first port (12) being connected to said fluid line (32, 34) for decreasing a pressure in the actuator (40) on valve operation.
6. The system according to claims 4 and 5, comprising two on-off seat valves (10, 10'), wherein one valve (10) is responsible exclusively for increasing the pressure in the actuator (40) and the other valve (10') is responsible exclusively for decreasing the pressure in the actuator (40).
7. The system according to any of the previous claims, wherein said actuator is a clutch actuator (40).
8. The system according to any of claims 1 -6, wherein said actuator is an EGR valve actuator (40).
9. The system according to any of claims 1 -6, wherein said actuator is an exhaust brake actuator (40).
PCT/SE2008/050302 2007-03-23 2008-03-18 Fluid power control system WO2008118072A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
DE112008000774T DE112008000774T5 (en) 2007-03-23 2008-03-18 Fluid power control system

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE0700734A SE532097C2 (en) 2007-03-23 2007-03-23 Fluid driven control system
SE0700734-7 2007-03-23

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WO2008118072A1 true WO2008118072A1 (en) 2008-10-02

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SE (1) SE532097C2 (en)
WO (1) WO2008118072A1 (en)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102010054702A1 (en) * 2010-12-16 2012-06-21 Wabco Gmbh Pneumatic air dryer

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4462377A (en) * 1981-12-19 1984-07-31 Nippon Soken, Inc. Exhaust gas recirculation device
US4524948A (en) * 1983-09-09 1985-06-25 Ranco Incorporated Electrically controlled pressure transducer valve
US5020771A (en) * 1989-01-26 1991-06-04 Ranco Japan Ltd. Proportional control valve

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4462377A (en) * 1981-12-19 1984-07-31 Nippon Soken, Inc. Exhaust gas recirculation device
US4524948A (en) * 1983-09-09 1985-06-25 Ranco Incorporated Electrically controlled pressure transducer valve
US5020771A (en) * 1989-01-26 1991-06-04 Ranco Japan Ltd. Proportional control valve

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SE532097C2 (en) 2009-10-20
SE0700734L (en) 2008-09-24
DE112008000774T5 (en) 2010-04-08

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