GB2044366B - Hydraulic systems for actuators - Google Patents

Hydraulic systems for actuators

Info

Publication number
GB2044366B
GB2044366B GB8009963A GB8009963A GB2044366B GB 2044366 B GB2044366 B GB 2044366B GB 8009963 A GB8009963 A GB 8009963A GB 8009963 A GB8009963 A GB 8009963A GB 2044366 B GB2044366 B GB 2044366B
Authority
GB
United Kingdom
Prior art keywords
actuators
hydraulic systems
hydraulic
systems
Prior art date
Legal status (The legal status 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 status listed.)
Expired
Application number
GB8009963A
Other versions
GB2044366A (en
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Sperry Corp
Original Assignee
Sperry Corp
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
Priority claimed from US06/024,058 external-priority patent/US4201052A/en
Application filed by Sperry Corp filed Critical Sperry Corp
Publication of GB2044366A publication Critical patent/GB2044366A/en
Application granted granted Critical
Publication of GB2044366B publication Critical patent/GB2044366B/en
Expired legal-status Critical Current

Links

Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16HGEARING
    • F16H61/00Control functions within control units of change-speed- or reversing-gearings for conveying rotary motion ; Control of exclusively fluid gearing, friction gearing, gearings with endless flexible members or other particular types of gearing
    • F16H61/38Control of exclusively fluid gearing
    • F16H61/40Control of exclusively fluid gearing hydrostatic
    • F16H61/42Control of exclusively fluid gearing hydrostatic involving adjustment of a pump or motor with adjustable output or capacity
    • F16H61/433Pump capacity control by fluid pressure control means
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B11/00Servomotor systems without provision for follow-up action; Circuits therefor
    • F15B11/02Systems essentially incorporating special features for controlling the speed or actuating force of an output member
    • F15B11/04Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed
    • F15B11/042Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed by means in the feed line, i.e. "meter in"
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B11/00Servomotor systems without provision for follow-up action; Circuits therefor
    • F15B11/02Systems essentially incorporating special features for controlling the speed or actuating force of an output member
    • F15B11/04Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed
    • F15B11/044Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed by means in the return line, i.e. "meter out"
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B13/00Details of servomotor systems ; Valves for servomotor systems
    • F15B13/02Fluid distribution or supply devices characterised by their adaptation to the control of servomotors
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00Circuits for servomotor systems
    • F15B2211/20Fluid pressure source, e.g. accumulator or variable axial piston pump
    • F15B2211/205Systems with pumps
    • F15B2211/2053Type of pump
    • F15B2211/20546Type of pump variable capacity
    • F15B2211/20553Type of pump variable capacity with pilot circuit, e.g. for controlling a swash plate
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00Circuits for servomotor systems
    • F15B2211/30Directional control
    • F15B2211/305Directional control characterised by the type of valves
    • F15B2211/30525Directional control valves, e.g. 4/3-directional control valve
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00Circuits for servomotor systems
    • F15B2211/30Directional control
    • F15B2211/31Directional control characterised by the positions of the valve element
    • F15B2211/3144Directional control characterised by the positions of the valve element the positions being continuously variable, e.g. as realised by proportional valves
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00Circuits for servomotor systems
    • F15B2211/30Directional control
    • F15B2211/32Directional control characterised by the type of actuation
    • F15B2211/329Directional control characterised by the type of actuation actuated by fluid pressure
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00Circuits for servomotor systems
    • F15B2211/30Directional control
    • F15B2211/35Directional control combined with flow control
    • F15B2211/351Flow control by regulating means in feed line, i.e. meter-in control
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00Circuits for servomotor systems
    • F15B2211/40Flow control
    • F15B2211/405Flow control characterised by the type of flow control means or valve
    • F15B2211/40515Flow control characterised by the type of flow control means or valve with variable throttles or orifices
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00Circuits for servomotor systems
    • F15B2211/40Flow control
    • F15B2211/415Flow control characterised by the connections of the flow control means in the circuit
    • F15B2211/41527Flow control characterised by the connections of the flow control means in the circuit being connected to an output member and a directional control valve
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00Circuits for servomotor systems
    • F15B2211/40Flow control
    • F15B2211/42Flow control characterised by the type of actuation
    • F15B2211/428Flow control characterised by the type of actuation actuated by fluid pressure
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00Circuits for servomotor systems
    • F15B2211/40Flow control
    • F15B2211/46Control of flow in the return line, i.e. meter-out control
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00Circuits for servomotor systems
    • F15B2211/50Pressure control
    • F15B2211/505Pressure control characterised by the type of pressure control means
    • F15B2211/50509Pressure control characterised by the type of pressure control means the pressure control means controlling a pressure upstream of the pressure control means
    • F15B2211/50518Pressure control characterised by the type of pressure control means the pressure control means controlling a pressure upstream of the pressure control means using pressure relief valves
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00Circuits for servomotor systems
    • F15B2211/50Pressure control
    • F15B2211/515Pressure control characterised by the connections of the pressure control means in the circuit
    • F15B2211/5156Pressure control characterised by the connections of the pressure control means in the circuit being connected to a return line and a directional control valve
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00Circuits for servomotor systems
    • F15B2211/50Pressure control
    • F15B2211/555Pressure control for assuring a minimum pressure, e.g. by using a back pressure valve
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00Circuits for servomotor systems
    • F15B2211/60Circuit components or control therefor
    • F15B2211/605Load sensing circuits
    • F15B2211/6051Load sensing circuits having valve means between output member and the load sensing circuit
    • F15B2211/6054Load sensing circuits having valve means between output member and the load sensing circuit using shuttle valves
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00Circuits for servomotor systems
    • F15B2211/60Circuit components or control therefor
    • F15B2211/61Secondary circuits
    • F15B2211/613Feeding circuits
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00Circuits for servomotor systems
    • F15B2211/60Circuit components or control therefor
    • F15B2211/635Circuits providing pilot pressure to pilot pressure-controlled fluid circuit elements
    • F15B2211/6355Circuits providing pilot pressure to pilot pressure-controlled fluid circuit elements having valve means
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00Circuits for servomotor systems
    • F15B2211/70Output members, e.g. hydraulic motors or cylinders or control therefor
    • F15B2211/705Output members, e.g. hydraulic motors or cylinders or control therefor characterised by the type of output members or actuators
    • F15B2211/7051Linear output members
    • F15B2211/7053Double-acting output members
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00Circuits for servomotor systems
    • F15B2211/70Output members, e.g. hydraulic motors or cylinders or control therefor
    • F15B2211/75Control of speed of the output member

Landscapes

  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Mechanical Engineering (AREA)
  • Fluid-Pressure Circuits (AREA)
  • Valve Device For Special Equipments (AREA)
GB8009963A 1979-03-26 1980-03-25 Hydraulic systems for actuators Expired GB2044366B (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US06/024,058 US4201052A (en) 1979-03-26 1979-03-26 Power transmission
US11793680A 1980-02-04 1980-02-04

Publications (2)

Publication Number Publication Date
GB2044366A GB2044366A (en) 1980-10-15
GB2044366B true GB2044366B (en) 1983-08-03

Family

ID=26697984

Family Applications (1)

Application Number Title Priority Date Filing Date
GB8009963A Expired GB2044366B (en) 1979-03-26 1980-03-25 Hydraulic systems for actuators

Country Status (10)

Country Link
JP (1) JPS6479405A (en)
AU (1) AU536970B2 (en)
CA (1) CA1142057A (en)
DE (1) DE3011088A1 (en)
FR (1) FR2452618A1 (en)
GB (1) GB2044366B (en)
IN (1) IN154913B (en)
IT (2) IT1221037B (en)
NO (1) NO155211C (en)
SE (2) SE443409B (en)

Families Citing this family (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4345435A (en) * 1980-05-05 1982-08-24 Sperry Corporation Power transmission
US4353289A (en) * 1980-05-29 1982-10-12 Sperry Corporation Power transmission
FI72579C (en) * 1981-11-12 1987-06-08 Vickers Inc Transmission.
DE3347000A1 (en) * 1983-12-24 1985-07-04 Robert Bosch Gmbh, 7000 Stuttgart Electrohydraulic arrangement for controlling a double-acting hydraulic motor
CA1234529A (en) * 1984-04-30 1988-03-29 Vinod K. Nanda Power transmission
LU85774A1 (en) * 1985-02-13 1985-07-24 Hydrolux Sarl STEUERBLOCK HYDRAULISCHER
DE3629479A1 (en) * 1985-09-03 1987-07-16 Barmag Barmer Maschf Directional control valve
DE3841507C1 (en) * 1988-01-22 1989-06-29 Danfoss A/S, Nordborg, Dk
US5088384A (en) * 1989-08-30 1992-02-18 Vickers, Incorporated Hydraulic actuator controlled by meter-in valves and variable pressure relief valves
DE4342487B4 (en) * 1993-12-13 2005-03-31 Linde Ag Hydrostatic drive system with after-suction valve
DE10216958B8 (en) * 2002-04-17 2004-07-08 Sauer-Danfoss (Nordborg) A/S Hydraulic control
US20060168955A1 (en) * 2005-02-03 2006-08-03 Schlumberger Technology Corporation Apparatus for hydraulically energizing down hole mechanical systems
US10208456B2 (en) * 2013-10-31 2019-02-19 Volvo Construction Equipment Ab Flow control valve for construction equipment, having floating function

Family Cites Families (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
USRE26028E (en) * 1963-05-16 1966-05-17 Pilot operated control valve mechanism
US3411536A (en) * 1966-07-06 1968-11-19 Koehring Co Pilot operated control valve mechanism
GB1302743A (en) * 1969-04-07 1973-01-10
DE1936370A1 (en) * 1969-07-17 1971-02-04 Volkswagenwerk Ag Valve unit for controlling double-acting working cylinders
DE2232857C2 (en) * 1972-07-05 1983-11-24 Robert Bosch Gmbh, 7000 Stuttgart Control device for a hydraulically driven implement
CH563532A5 (en) * 1973-03-14 1975-06-30 Buehler Ag Geb
SE387415B (en) * 1974-03-22 1976-09-06 Tedeco Ag FLUID VALVE DEVICE
DE2500096C3 (en) * 1975-01-03 1984-08-02 Sauer Getriebe KG, 2350 Neumünster Hydraulic circuit device for pressure medium path control with constant control of the pressure medium flow for a double-acting hydraulic motor
US3991571A (en) * 1976-03-15 1976-11-16 Caterpillar Tractor Co. Fluid system of a work vehicle having fluid combining means and signal combining means
JPS5482574A (en) * 1977-12-13 1979-06-30 Kobe Steel Ltd Control circuit of actuator

Also Published As

Publication number Publication date
SE8503569D0 (en) 1985-07-23
IT8048246A0 (en) 1980-03-24
NO800846L (en) 1980-09-29
GB2044366A (en) 1980-10-15
SE443409B (en) 1986-02-24
DE3011088A1 (en) 1980-10-09
SE8002302L (en) 1980-09-27
NO155211C (en) 1987-02-25
CA1142057A (en) 1983-03-01
AU5682480A (en) 1980-10-02
IT1232358B (en) 1992-01-28
FR2452618B1 (en) 1984-02-24
IT1221037B (en) 1990-06-21
IN154913B (en) 1984-12-22
JPS6479405A (en) 1989-03-24
NO155211B (en) 1986-11-17
AU536970B2 (en) 1984-05-31
SE8503569L (en) 1985-07-23
IT8948200A0 (en) 1989-07-18
FR2452618A1 (en) 1980-10-24
SE455637B (en) 1988-07-25

Similar Documents

Publication Publication Date Title
GB2098303B (en) Missile-impact-resistant hydraulic actuator
GB2058225B (en) Control for hydraulic accumulator system
GB2065807B (en) Hydraulic brake system
GB2057580B (en) Hydraulic control circuit system
JPS55132403A (en) Hydraulic servo valve
DE3165029D1 (en) Hydraulic actuator
GB2045177B (en) High pressure hydraulic systems
GB2060798B (en) Hydraulic brake system
GB2045877B (en) Actuators especially for brakes
GB2055490B (en) Electrohydraulic servo arrangement
JPS55114648A (en) Hydraulic pressure actuating antiskiddbrake system
GB2044366B (en) Hydraulic systems for actuators
GB2050646B (en) Hydraulic actuator controls
DE3275653D1 (en) Hydraulic actuator arrangement
GB2008508B (en) Hydraulic systems
GB2068463B (en) Fluid-pressure actuators
GB2065810B (en) Hydraulic brake system
GB2082799B (en) Hydraulic actuator systems
DE3065985D1 (en) Hydraulic braking system
GB2047435B (en) Hydraulic control valve system
DE3365573D1 (en) Actuator system including hydraulically synchronized actuators
JPS55106869A (en) Hydraulic pressure servoosteering system
JPS57111915A (en) Hydraulic actuator
DE3066245D1 (en) Tractor hydraulic control systems
GB2050575B (en) Bleeding device for hydraulic systems

Legal Events

Date Code Title Description
PCNP Patent ceased through non-payment of renewal fee

Effective date: 19930325