EP0367038A1 - Système de commande hydraulique et véhicule de terrassement utilisant le même système de commande - Google Patents

Système de commande hydraulique et véhicule de terrassement utilisant le même système de commande Download PDF

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Publication number
EP0367038A1
EP0367038A1 EP89119462A EP89119462A EP0367038A1 EP 0367038 A1 EP0367038 A1 EP 0367038A1 EP 89119462 A EP89119462 A EP 89119462A EP 89119462 A EP89119462 A EP 89119462A EP 0367038 A1 EP0367038 A1 EP 0367038A1
Authority
EP
European Patent Office
Prior art keywords
hydraulic
cylinder
steering system
steering
pressure
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.)
Granted
Application number
EP89119462A
Other languages
German (de)
English (en)
Other versions
EP0367038B2 (fr
EP0367038B1 (fr
Inventor
Douglas Millard Gage
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.)
Deere and Co
Original Assignee
Deere and Co
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
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First worldwide family litigation filed litigation Critical https://patents.darts-ip.com/?family=22997333&utm_source=google_patent&utm_medium=platform_link&utm_campaign=public_patent_search&patent=EP0367038(A1) "Global patent litigation dataset” by Darts-ip is licensed under a Creative Commons Attribution 4.0 International License.
Application filed by Deere and Co filed Critical Deere and Co
Publication of EP0367038A1 publication Critical patent/EP0367038A1/fr
Application granted granted Critical
Publication of EP0367038B1 publication Critical patent/EP0367038B1/fr
Publication of EP0367038B2 publication Critical patent/EP0367038B2/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/225—Control of steering, e.g. for hydraulic motors driving the vehicle tracks
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/08—Superstructures; Supports for superstructures
    • E02F9/0841—Articulated frame, i.e. having at least one pivot point between two travelling gear units
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02F—DREDGING; SOIL-SHIFTING
    • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
    • E02F9/20—Drives; Control devices
    • E02F9/22—Hydraulic or pneumatic drives
    • E02F9/2217—Hydraulic or pneumatic drives with energy recovery arrangements, e.g. using accumulators, flywheels

Definitions

  • the invention relates to a hydraulic steering system, in particular for a self-propelled articulated work vehicle, with at least one steering hydraulic motor, which is connected to a hydraulic pressure source via a steering valve, and a self-propelled work vehicle with such a steering system.
  • the object to be achieved with the invention is seen in the provision of a damping device by means of which pressure peaks can be reduced, so that, for example, the hydraulic steering system of a work vehicle works smoothly.
  • a mechanical damping device is arranged between two hydraulic connections of the hydraulic motor or hydraulic motors to compensate for hydraulic pressure peaks.
  • the hydraulic connections are, for example, with the steering control via hydraulic supply lines Connection.
  • the hydraulic motors are preferably hydraulic steering cylinders of a steerable vehicle.
  • the mechanical damping device contains a hydraulic cylinder, the end faces of which are each connected to one of the two hydraulic connections of the hydraulic motors.
  • Two pistons are movably arranged in the cylinder and are held in their rest position by prestressing means, forming three spaces within the cylinder.
  • prestressing means there are also two hydraulic passages through which a one-way liquid flow is possible between the central space between the two pistons and an outer space located on one of the end faces of the cylinder.
  • the adjacent piston moves from its rest position to the center of the cylinder and overcomes the preload of the preloading means.
  • the preloading means absorb the hydraulic pressure peaks.
  • the pressure in the middle room increases. This pressure is discharged through the associated hydraulic passage into the other, opposite outer space.
  • the passages are preferably designed as channels with a limited cross section and act as a throttling point, so that the liquid can slowly flow out of this space at increased pressure in the central space.
  • the hydraulic passages preferably run inside the pistons and each contain a check valve to prevent direct flow between the two outer spaces.
  • the middle space is connected to a check valve, which allows a liquid flow from a reservoir into the middle space.
  • a spring arranged between the two pistons is preferably used as the biasing means. It is a compression spring that pushes the two pistons outwards towards the front of the cylinder.
  • the mechanical damping device contains a hydraulic cylinder, the end faces of which are each connected to one of the two hydraulic connections of the hydraulic motors.
  • a piston is movably arranged in the cylinder, which forms two spaces facing the end faces within the cylinder.
  • Biasing means are also provided which urge the piston into its rest position.
  • Two springs which are each arranged in one of the two spaces, serve as the biasing means. These are compression springs that press the piston into a central position (rest position) within the cylinder.
  • the mechanical damping device contains an exchange check valve and only a pressure accumulator, the two inlet connections of the exchange check valve being connected to the hydraulic motors and the outlet connection of the exchange check valve being connected to the pressure accumulator.
  • Pressure swings in the hydraulic cylinders in the direction of the pressure accumulator can be reduced by the exchange check valve arranged between the hydraulic motors. A flow from one hydraulic cylinder to the other is not possible.
  • the invention further relates to a self-propelled work vehicle which contains a hydraulic steering system.
  • This vehicle preferably contains a hydraulic circuit in which an adjustable displacement pump in an open hydraulic system supplies a priority valve which divides the fluid flow between hydraulic steering circuits and hydraulic working circuits.
  • the steering circuits are given preference.
  • a mechanical damping device is arranged between the hydraulic steering cylinders. This is preferably one of the damping devices according to the invention described above.
  • the loader :
  • the loader 10 shown in Figure 1 is a four wheel driven, articulated loader.
  • the loader 10 comprises a support frame 12 and wheels 14 engaging with the ground.
  • the front part of the loader 10 is provided with a movable boom arrangement 16, at the end of which a pivotable shovel 18 is arranged.
  • the boom is raised by expanding a hydraulic boom lift actuator 20.
  • the blade 18 is pivoted by the hydraulic blade tilt actuation element 22.
  • the loader 10 is articulated on the vertical axes of rotation 24, 26 and can be hydraulic Steer the control circuit, as shown in Figure 2.
  • the supercharger 10 is driven by an internal combustion engine housed in the machine housing 30.
  • the internal combustion engine also drives hydraulic pumps, which in turn supply the working groups of the loader 10 and other hydraulic actuation systems.
  • An operator controls the functions of the loader 10 from the cab 32.
  • FIG. 2 The entire hydraulic steering system is shown schematically in Figure 2. It contains an open and a closed hydraulic system.
  • a hydraulic system according to FIG. 2 has already been disclosed by EP 0 306 988 A 2 or US Pat. No. 4,809,586 by the applicant. Reference is hereby made to this disclosure.
  • the open center hydraulic system is supplied with hydraulic fluid by an non-adjustable positive displacement pump 100, the hydraulic fluid being passed on from the pump through the hydraulic line 102.
  • the closed hydraulic system (closed center hydraulic system) is supplied with hydraulic fluid by a variable pump 104, the variable pump 104 being provided with a pressure-sensing and pressure-compensating arrangement for maintaining a constant pressure in the hydraulic line 106.
  • the pump 104 is also provided with a hydraulic drainage channel 105, through which hydraulic fluid which flows out is led back to a collecting container 108. Both pumps 100, 104 are operatively connected in a piggyback manner and thus form a compact pump unit.
  • the pumps are driven by the internal combustion engine via suitable mechanical couplings.
  • the pumps 100 and 104 draw the hydraulic fluid through a common suction line 110 from a common reservoir 108.
  • the line 110 is equipped with a filter 112, which removes large particles from the liquid flow that is fed to the pumps 100 and 104.
  • the hydraulic fluid delivered by pump 100 is directed through line 102 to a priority valve assembly 120 which controls the flow of fluid between a steering assembly 200 and a charger assembly to which line 302 leads.
  • the priority valve assembly 120 gives priority to the steering assembly 200 by closing the hydraulic fluid flow to the loader assembly when there is a fluid request from the steering assembly.
  • the priority valve assembly 120 includes a spring-loaded 2-position spool 122 that selectively directs fluid to the steering and loader assemblies.
  • the slide 122 lies between hydraulic pressure sensing lines 124 and 125, which have constriction points, and is kept in hydraulic balance.
  • valve 210 When the steering valve 210 is set in a middle, neutral position, the hydraulic flow to the supply line 202 through the valve 210 is interrupted, whereby the hydraulic pressure in the line 202 and in the sensing line 124 increases. In its middle position, valve 210 connects sensing line 125 to header return line 140 via line 126a, thereby reducing the hydraulic pressure in sensing line 125. As a result, the increasing hydraulic pressure in line 124 exceeds the hydraulic pressure in line 125 as well as the biasing force of spring 129, causing the spool 122 to be in a position in which hydraulic fluid is delivered to the loader assembly supply line 302.
  • the priority valve assembly 120 is also provided with a filter 126 and a pressure relief valve 128 through which hydraulic fluid can be directed to the reservoir return line 130.
  • the reservoir return line 130 receives hydraulic fluid from the sensing line 125 when a predeterminable pressure is exceeded.
  • Hydraulic fluid flowing out of the steering assembly 200 and the loader assembly is directed through the reservoir return line 140 to the reservoir 108.
  • the collecting container return line 140 is equipped with a return filter arrangement 142, which in turn has a filter 144, a hydraulically balanced pressure relief valve 146 and a hydraulically balanced electrical pressure sensor switch 148.
  • the hydraulic fluid is filtered through filter 144 and then returns to the reservoir 108.
  • the filter 144 collects foreign matter, the hydraulic pressure drop across the filter 144 increases. This leads to the closing of the electrical switch 148.
  • the closing of the electrical switch 148 activates an indicator lamp which is located in the control cabin 32 of the loader 10 and which draws the operator's attention to the fact that the filter 144 should be cleaned or replaced.
  • the pressure relief valve 146 When the pressure drop across the filter 144 continues to increase due to additional substances accumulating on the filter 144, the pressure relief valve 146 also opens and enables a hydraulic flow through a bypass past the filter 144.
  • the hydraulic fluid output of the pump 104 is directed to a hydraulic pressure reduction device via a hydraulic supply line 402 and to a brake arrangement via a hydraulic supply line 502.
  • the steering arrangement 200 receives hydraulic fluid from the priority valve arrangement 120 via the hydraulic supply line 202.
  • the hydraulic fluid is directed to a steplessly adjustable steering control valve 210.
  • Hydraulic fluid is directed through the main fluid passage of the valve to steering hydraulic motors or cylinders 220L and 220R to hydraulically assist the steering of the loader.
  • the control valve 210 includes a metering pump 212 and a valve structure 214 which are coupled together by a mechanical return connection 216.
  • Valve structure 214 includes a main flow opening and may also include a damping flow opening.
  • the vaporization flow opening comprises a number of limited flow channels which serve to dampen pressure peaks in the main flow opening. Damping control valve 210 is described in detail in U.S. Patent No. 4,781,219, which is incorporated herein by reference.
  • the steering arrangement 200 is also equipped with an optionally available additional steering pump 250 which draws hydraulic fluid from the reservoir return line 150 via a hydraulic line 252 and directs the hydraulic fluid to the hydraulic supply line 202 via the hydraulic line 254.
  • the additional pump 250 is electrically powered and alternatively provides hydraulic pressure when the pump 100 is not operating.
  • the valve 256 for the additional steering pump 250 serves to start the pump 250.
  • the tax Valve 256 comprises a hydraulically balanced, spring-loaded piston 258, which is hydraulically balanced between the sensing line 125 and the supply line 202.
  • a hydraulic sensing line 260 of the control valve 256 is fluidly connected to a location of the supply line 202 which is upstream of a check valve 264.
  • a hydraulic sensor line 261 of the control valve 256 is fluidly connected to the sensor line 125.
  • the valve piston 258 is coupled to an electrical switch 270, which in the closed state starts the electrical pump 250.
  • the switch 270 is closed when the hydraulic pressure in the sensing line 125 exceeds or is equal to the hydraulic pressure in the line 260, which indicates that the pump 100 has failed.
  • a mechanical damping device 600 which is the subject of the present invention, is hydraulically arranged between the steering cylinders 220L and 220R.
  • the damping device 600 serves to absorb or dampen hydraulic pressure peaks that occur in the steering cylinders during operation of the vehicle. Such pressure peaks can occur through rapid adjustment of the steering, reversing the steering direction, and / or external impacts on the steering system.
  • FIGS. 3, 4 and 5 show three types of pressure damping devices.
  • the first embodiment of a damping device 670 contains a pressure accumulator 672, which is hydraulically located between the supply line 221 and the return line 223 of the control cylinders 220L and 220R via an exchange check valve 674.
  • the shuttle valve 674 includes two inlets 676 and 678 which are hydraulically connected to the control cylinders 220L and 220R, respectively.
  • the valve 674 also includes an outlet 680 which is hydraulically connected to the hydraulic pressure accumulator 672.
  • the ball 682 of the shuttle valve 674 can be located anywhere within the valve 674, as shown in FIG. 3a. However, if one of the control cylinders is subjected to a pressure spike, a pressure difference is generated between the control cylinders, by means of which the ball 682 is displaced from the side of the control cylinder with the higher pressure to the side of the control cylinder with the lower pressure. If the hydraulic pressure peak is applied to the steering cylinder 220L, as shown in FIG. 3b, the pressure in the steering cylinder 220L exceeds the pressure in the steering cylinder 220R, as a result of which the ball 682 is moved away from the steering cylinder 220L and in the direction of the steering cylinder 220R .
  • the two-way check valve 674 connects the steering cylinder 220L to the pressure accumulator 672.
  • the hydraulic pressure peak is absorbed by the pressure accumulator 672.
  • Ball 682 prevents direct flow between the two control cylinders.
  • the pressure accumulator 672 drives hydraulic fluid back through the alternating check valve 674 to the steering cylinder 220L and restores the steering cylinder 220L to equilibrium.
  • the damping device 602 contains one Hydraulic cylinder 604, which is hydraulically between the supply line 221 and the return line 223.
  • the second space 626 lies between the first piston 612 and an end wall of the cylinder 604, and the third space 628 lies between the second piston 614 and its adjacent end wall of the cylinder 604.
  • a spring 620 is operably disposed between the two pistons 612, 614 and biases the pistons to bring them into their normal position as shown in Figure 4a. In this normal position, the hydraulic pressure between the steering cylinders 220L and 220R is the same. The pistons 612, 614 are pushed apart from one another by the spring 620.
  • Each of the pistons 612, 614 includes a hydraulic passageway with a throttle 622 and a check valve 624.
  • the check valve 624 allows hydraulic flow from the first space 618 to the second and third spaces 626 and 628, but prevents hydraulic flow from the second or third Rooms 626 and 628 to the first room 618.
  • the first room 618 is refilled with hydraulic fluid via the hydraulic line 630, which is hydraulically connected to the collecting tank return line 140.
  • the line 630 is connected to the hydraulic connection 632 of the hydraulic cylinder 604.
  • a check valve 634 which in a liquid flow Permits direction of the first space 618, but prevents liquid backflow from the space 618 into the line 630.
  • the steering cylinder 220L is subjected to a hydraulic pressure spike, which increases the hydraulic pressure in the second space 626. According to FIG. 4b, this pressure spike displaces the first piston 612 against the spring 620 and compresses it. Hydraulic fluid creeps through the throttle 622 from the first space 618 to the control cylinder 220R.
  • the spring 620 drives the first piston 612 to its previous position, pumping hydraulic fluid back into the cylinder 220L. In order to avoid the formation of bubbles in the space 618 when the first piston 612 moves back, hydraulic fluid is sucked out of the collecting container 108 via the lines 140 and 630 and the check valve 634.
  • cylinder 604 may be provided with stroke limitations to limit the movement of first and second pistons 612 and 614 within cylinder 604.
  • the stroke limits can be formed, for example, in the form of edges attached within the cylinder 604, which limit an outward movement of the pistons 612 and 614 to enlarge the space 618 and thereby define a minimum volume for the second and third spaces 626 and 628.
  • limiting elements can be arranged within the cylinder 604, which limit movement of the pistons 612, 614 towards one another in such a way that the hydraulic connection 632 is prevented from being blocked, as a result of which the flow between the line 630 and the space 618 would be blocked.
  • the throttling points can be replaced by the formation of a sealing arrangement, which extends around each of the pistons and performs the same function as the throttling points 622 and the check valves 624.
  • a sealing arrangement would only have a leak in the area of the seal 616 from the space 618 in Allow outward direction while preventing flow from spaces 626 and 628 to space 618.
  • the pressure damping device 650 has a cylinder 652, which contains a first and a second hydraulic connections 654 and 656, which are arranged on the end faces of the cylinder 652.
  • the damping device 650 is located hydraulically between the hydraulic supply line 221 and the return foot line 223.
  • the cylinder 652 receives a piston 658 with a circumferential seal 660.
  • the piston 658 can be moved in both directions within the cylinder 652.
  • a first and a second spring 662 and 664 are each arranged on one side of the piston 658 and press the piston 658 into a central normal position within the cylinder 652.
  • multiple springs can also be used, which provide a non-linear compression characteristic when the springs compress or expand due to movement of the piston.
  • hydraulic fluid is passed through the hydraulic connection 654 from the cylinder 220L into the first space 666, which is formed by the piston 658.
  • the piston 658 is moved downward and compresses the second spring 664 while the first spring 662 expands.
  • hydraulic fluid is pumped into the steering cylinder 220R.
  • the first and second springs 662 and 664 center the piston 658 and balance the fluid flow between the steering cylinders 220L and 220R.
  • the three mechanical hydraulic damping devices as described here represent a simple and effective means for damping hydraulic pressure peaks in steering systems of large vehicles.
  • the invention is not restricted to the exemplary embodiments described above.

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  • Engineering & Computer Science (AREA)
  • Mining & Mineral Resources (AREA)
  • Civil Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Structural Engineering (AREA)
  • Power Steering Mechanism (AREA)
  • Fluid-Pressure Circuits (AREA)
EP89119462A 1988-10-25 1989-10-20 Système de commande hydraulique et véhicule de terrassement utilisant le même système de commande Expired - Lifetime EP0367038B2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US262399 1988-10-25
US07/262,399 US4915186A (en) 1988-10-25 1988-10-25 Hydraulic steering systems dampening devices

Publications (3)

Publication Number Publication Date
EP0367038A1 true EP0367038A1 (fr) 1990-05-09
EP0367038B1 EP0367038B1 (fr) 1992-12-30
EP0367038B2 EP0367038B2 (fr) 1995-05-17

Family

ID=22997333

Family Applications (1)

Application Number Title Priority Date Filing Date
EP89119462A Expired - Lifetime EP0367038B2 (fr) 1988-10-25 1989-10-20 Système de commande hydraulique et véhicule de terrassement utilisant le même système de commande

Country Status (5)

Country Link
US (1) US4915186A (fr)
EP (1) EP0367038B2 (fr)
JP (1) JP2937364B2 (fr)
CA (1) CA1320980C (fr)
DE (1) DE58903167D1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0909690A2 (fr) * 1997-10-17 1999-04-21 Deere & Company Système de freinage et véhicule

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7597168B2 (en) * 2005-09-23 2009-10-06 Deere & Company Low engine speed steering performance
DE102009032212A1 (de) * 2009-07-03 2011-01-05 Dr. Ing. H.C. F. Porsche Aktiengesellschaft Hydraulischer Schwenkmotor
DE102020113739A1 (de) * 2020-05-20 2021-11-25 Universität Paderborn Lastsimulationsprüfstand und Kapazitätselement für einen Lastsimulationsprüfstand

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3260325A (en) * 1963-08-19 1966-07-12 Caterpillar Tractor Co Hydraulic steering system
US3360925A (en) * 1966-02-03 1968-01-02 Int Harvester Co Multiple speed hydraulic control system
US4097060A (en) * 1977-03-30 1978-06-27 Caterpillar Tractor Co. Roll stiffening and dampening in articulated vehicles
EP0266785A1 (fr) * 1986-11-05 1988-05-11 Ahlmann Baumaschinen GmbH Véhicule automobile polyvalent
US4781219A (en) * 1986-10-10 1988-11-01 Eaton Corporation Fluid controller and dampening fluid path
EP0306988A2 (fr) * 1987-09-11 1989-03-15 Deere & Company Système hydraulique de freins pour véhicule de travail

Family Cites Families (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
USRE17508E (en) * 1926-01-23 1929-11-26 Power steering apparatus
US3333415A (en) * 1965-11-23 1967-08-01 Abex Corp Hydraulic transmission and speed and direction control valve therefor
DE1915102A1 (de) * 1969-03-25 1970-10-01 Vogel Ignaz Kg Hydropneumatische Druckfeder
DE2742688A1 (de) * 1977-09-22 1979-04-05 Zahnradfabrik Friedrichshafen Hydraulische hilfskraftlenkung mit energieversorgungseinrichtung mit druckspeicher
US4310062A (en) * 1980-01-22 1982-01-12 International Harvester Company Hydrostatic steering arrangement
DE3006509C2 (de) * 1980-02-21 1984-10-25 Danfoss A/S, Nordborg Hydrostatische Lenkeinrichtung
US4405030A (en) * 1981-03-16 1983-09-20 Deere & Company Steering system and compensating valve
US4382483A (en) * 1981-04-09 1983-05-10 Deere & Company Load-responsive steering control valve
US4509409A (en) * 1983-02-07 1985-04-09 Towmotor Corporation Pump arrangement for a linear fluid operated device
JPS6335030U (fr) * 1986-08-25 1988-03-07
US4825748A (en) * 1987-07-02 1989-05-02 Parker-Hannifin Corporation Hydraulic actuator synchronization apparatus and system

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3260325A (en) * 1963-08-19 1966-07-12 Caterpillar Tractor Co Hydraulic steering system
US3360925A (en) * 1966-02-03 1968-01-02 Int Harvester Co Multiple speed hydraulic control system
US4097060A (en) * 1977-03-30 1978-06-27 Caterpillar Tractor Co. Roll stiffening and dampening in articulated vehicles
US4781219A (en) * 1986-10-10 1988-11-01 Eaton Corporation Fluid controller and dampening fluid path
EP0266785A1 (fr) * 1986-11-05 1988-05-11 Ahlmann Baumaschinen GmbH Véhicule automobile polyvalent
EP0306988A2 (fr) * 1987-09-11 1989-03-15 Deere & Company Système hydraulique de freins pour véhicule de travail

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0909690A2 (fr) * 1997-10-17 1999-04-21 Deere & Company Système de freinage et véhicule
EP0909690A3 (fr) * 1997-10-17 2000-04-12 Deere & Company Système de freinage et véhicule

Also Published As

Publication number Publication date
EP0367038B2 (fr) 1995-05-17
EP0367038B1 (fr) 1992-12-30
US4915186A (en) 1990-04-10
CA1320980C (fr) 1993-08-03
JP2937364B2 (ja) 1999-08-23
JPH02171387A (ja) 1990-07-03
DE58903167D1 (de) 1993-02-11

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