EP0469056A1 - Systemes de freinage pour vehicules - Google Patents

Systemes de freinage pour vehicules

Info

Publication number
EP0469056A1
EP0469056A1 EP19900907240 EP90907240A EP0469056A1 EP 0469056 A1 EP0469056 A1 EP 0469056A1 EP 19900907240 EP19900907240 EP 19900907240 EP 90907240 A EP90907240 A EP 90907240A EP 0469056 A1 EP0469056 A1 EP 0469056A1
Authority
EP
European Patent Office
Prior art keywords
braking
braking element
override
valve
piston
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.)
Withdrawn
Application number
EP19900907240
Other languages
German (de)
English (en)
Inventor
David Burke
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.)
Group Lotus PLC
Original Assignee
Group Lotus PLC
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 GB898909472A external-priority patent/GB8909472D0/en
Priority claimed from GB898910275A external-priority patent/GB8910275D0/en
Application filed by Group Lotus PLC filed Critical Group Lotus PLC
Publication of EP0469056A1 publication Critical patent/EP0469056A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T7/00—Brake-action initiating means
    • B60T7/02—Brake-action initiating means for personal initiation
    • B60T7/04—Brake-action initiating means for personal initiation foot actuated
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
    • B60T13/58—Combined or convertible systems
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/10—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with fluid assistance, drive, or release
    • B60T13/66—Electrical control in fluid-pressure brake systems
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/74—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with electrical assistance or drive
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T15/00—Construction arrangement, or operation of valves incorporated in power brake systems and not covered by groups B60T11/00 or B60T13/00
    • B60T15/02—Application and release valves
    • B60T15/04—Driver's valves
    • B60T15/14—Driver's valves influencing electric control means

Definitions

  • the invention relates to vehicle braking systems.
  • the systems generally comprise either drum or disc brakes with a brake pedal connected to a piston in a master cylinder whence the hydraulic operating pressure originates. Depression of the brake pedal forces the hydraulic brake fluid along a network of pipes and hoses to wheel cylinders which urge brake calipers or shoes into contact with a brake disc or drum to provide the braking action.
  • Hydraulic systems have many advantages, such as being self-lubricating (reducing the chance of seizure), having a low rate of wear and low friction, and enabling equal pressures to be exerted on all the brake shoes or calipers, even compensating for unequal wear or adjustment. Further, installation is generally easier than for mechanical systems because of the flexibility of the hoses.
  • both axial brakes would be operated identically. It would also be useful in braking systems to be able to control the feel at the braking, as some drivers prefer sharp braking and others prefer to have to move the brake pedal some distance before maximum braking is achieved.
  • a vehicle fcraking system comprising a braking element operable by a driver; control signal generating means responsive to operation of the braking element; means braking at least one vehicle wheel in response to control signals generated by the control signal generating means; and means for activating an override system to enable direct control of the braking means by operation of the braking element independently of said control signals.
  • the override system can be selectively activated by means of a manual switch, or activated automatically on detection of a system failure on application of a force to the braking element greater than a predetermined force.
  • the means for activating said override system comprises a solenoid valve and a power supply thereto, said override system being activated by de-energisation of the solenoid valve.
  • the solenoid valve is preferably de-energised on failure in the power supply thereto and/or by a control signal from said control signal generating means.
  • the override system preferably comprises means for transmitting a force applied to the braking element to operate the braking means.
  • the transmitting means comprises a hydraulic piston and cylinder arrangement, the arrangement being such that movement of the piston forces hydraulic fluid in the cylinder to operate the braking means.
  • the braking element preferably moves the piston of said arrangement by hydraulic means or by mechanical means.
  • the mechanical means comprises a moveable rod arranged such that operation of the braking element with a force greater than a predetermined force moves said rod which in turn moves said piston.
  • spring means biassing said rod to provide said predetermined force.
  • the braking element is preferably a foot pedal.
  • a preferred embodiment of the invention includes means to make the braking means unresponsive to said control signals, which means may comprise at least one valve the state of which is changeable by the application of pressure thereto.
  • Figure 1 is a schematic representation of the layout of the system
  • Figure 2 is a part sectional front elevation of a brake "feel” actuator assembly which is a part of the system of Figure 1;
  • Figure 3 is a sectional view of Figure 2 on III-III;
  • Figure 4 is a part sectional front elevation of a distribution valve which is a part of the system of Figure 1;
  • Figure 5 is a front elevation of the distribution valve of Figure 3 with parts omitted for clarity.
  • a braking system 10 for use in a motor vehicle such as a motor car, having steerable wheels (not shown) .
  • the motor vehicle has four wheels each fitted with standard hydraulically operated disc or drum brakes. Although the brakes themselves are not shown in the drawings, the operable calipers or shoes or each wheel (hereinafter brake mechanism) are attached to a respective servo valve 11, 12, 13, 14, which independently controls the pressure to the brake mechanism at the associated wheel.
  • brake mechanism the operable calipers or shoes or each wheel
  • the system 10 combines a primary active brake system and a secondary brake override system that provides the braking effort in the event of a system failure or when the active system is turned off.
  • the active system is a fully active "feel" system including a braking element in the form of a brake pedal 15 which is physically decoupled from the braking mechanisms.
  • the brake pedal 15 is mounted to the vehicle body to be pivotal about its point of attachment. Attached to the brake pedal 15 is a "feel" actuator 16.
  • the feel actuator 16 is a double acting hydraulic actuator comprising a moveable piston 17 having a pair of opposed piston faces and contained in a cylinder 18. Mounted on the piston 17 is a piston head 17a which provides the piston faces. One end of the piston 17 is coupled to the brake pedal 15 by means of a linkage element 20 which includes a load cell 21 (or other suitable device) which is preferably a duplex sensor, for sensing the force applied by a driver of the vehicle to the brake pedal 15.
  • the load cell 21 is electrically connected to a control unit 25, such as a mircoprocessor, and sends input signals thereto relating to the force applied to the brake pedal 15.
  • a rod 22 which enters a holder 23 of a linear variable differential transformer (LVDT) 24.
  • the LVDT holder 23 is fixed adjacent to the cylinder 18 on a manifold block 75 housing the feel actuator 16.
  • the LVDT 24 converts the mechanical displacement of the linkage element 20 (and therefore the displacement of the brake pedal 15) into an electrical signal which is transmitted to the microprocessor 25 to which the LVDT 24 is electrically connected.
  • Other suitable devices may of course be used for converting the displacement into an electrical signal.
  • the feel actuator 16 is hydraulically connected to servo valve 28.
  • Hydraulic transfer tubes 9 are provided in the manifold block 75 linking the hydraulic fluid lines from the servo valve 28 to each end of cylinder 18 so that the servo valve 28 may be used to control the movement of the piston 17 by hydraulic pressure to either side of the piston head 17a.
  • a non-return valve 29a is included in the hydraulic fluid line between the servo valve 28 and feel actuator, 16, for reasons described below.
  • the non-return valve 29a is also connected to the pressure supply line 33 via an isolating valve 31 described below.
  • the non ⁇ return valve 29a opens on application of pressure thereto.
  • the servo valve 28 is connected to hydraulic fluid supply pressure and return lines 33, 34 via an isolating valve 31 which is preferably a solenoid valve.
  • an isolating valve 31 which is preferably a solenoid valve.
  • the solenoid valve 31 When the solenoid valve 31 is energised the pressure supply line 33 is connected to the servo valve 28 and when it is de-energised the return line 34 is connected to the servo valve 28.
  • a pressure reducing valve 30 is incorporated in the pressure supply line 33 leading to the isolating valve 31 so that the servo valve 28 uses a pressure lower than the system pressure.
  • An anti-cavitation valve 27 is also included.
  • the microprocessor 25 is connected to control the brake servo valves 11, 12, 13, 14 and signals generated by the micro ⁇ processor 25 control the pressure applied to the four brake mechanisms independently.
  • the servo valves 11, 12, 13, 14 are connected to brake lines 56 which are connected to the brake mechanisms of the front left, rear left, rear right and front brakes respectively, via a distribution valve 35, as shown in Figures 4 and 5.
  • the servo valves 11, 12, 13, 14 are connected to the hydraulic pressure and return lines 33, 34 via connectors 32.
  • One connector 32 connects a branch of the pressure and return lines to one pair of servo valves 11, 14 and the other connector 32 to the second pair of servo valves 12, 13.
  • the distribution valve 35 comprises a valve manifold 36 having four separate chambers 46, 47, 48, 49 therein. Each chamber 46, 47, 48, 49 is connected via a fluid passage 50 to a respective servo valve 11, 12, 13, 14.
  • the manifold 36 has eight ports 37-44 therein such that each chamber 46, 47, 48, 49 has a pair of ports (37, 41), (38, 42), (39, 43), (40, 44) therein.
  • One port 37, 38, 39, 40 of each pair is hydraulically connected to a master cylinder 45 via a pair of fluid lines 58, 59.
  • the master cylinder 45 is preferably a tandem master cylinder and has a hydraulic booster 45a attached thereto, the function of which will be explained later.
  • one pair of ports 37, 38 feeds from one fluid line 58 from the master cylinder whilst the second pair of ports 39, 40 feeds from the second fluid line 59.
  • a balancing valve 60 may be provided in one of the fluid lines 58, 59.
  • the other ports 41, 42, 43, 44 are connected to a brake line 56 leading to a brake mechanism.
  • each chamber 46, 47, 48, 49 is a spool 51 comprising a concave first part 52 which is located in one end of a concave second part 53, the two parts 52 and 53 being secured together by a screw 55. As shown the two parts 52 and 53 are of different materials in view of the possibly different fluids acting on the two parts.
  • the spool 51 is slidable within the chamber 46, 47, 48, 49.
  • a compression spring 54 is also located in each chamber 46, 47, 48, 49, with one end located against an inside face 55 of the second spool part 53 so as to bias the spool 51 outwards to seal off the fluid passage 50 between the chamber 46, 47, 48, 49 and the associated servo valve 11, 12, 13, 14.
  • the length of the spool 51 is such that when it is biased as mentioned above brake fluid from the master cylinder 45 is free to enter/leave the chambers 46, 47, 48, 49 via the ports 37-44.
  • a secondary braking system is also incorporated, the secondary system being isolated when the primary active system is operating and thus providing no braking effort. However, when the primary active system is turned off or fails the secondary system is selectively activated, for example by a positive decision from the driver who operates a manual switch, or by automatic decision from the system in the event of a failure.
  • the second system utilises a secondary hydraulic actuator 65 to operate the booster 45a which in turn operates the master cylinder 45 in a known manner to supply pressurised fluid to fluid lines 58, 59.
  • the actuator 65 comprises a piston 66 having a single head 67 within a cylinder 68.
  • the secondary actuator 65 is hydraulically linked to the feel actuator 16 as follows.
  • a hydraulic fluid line 69 is connected to the cylinder 68 on one side of the piston head 67. After the fluid line 69 leaves the cylinder 68 it divides into two, one branch 69a connecting to the hydraulic fluid return line 34 via a non-return valve 29b, and the second branch 69b leading to a switching valve 70.
  • the switching valve 70 has a fluid line 71 which splits into two branches 71a, 71b; branch 71a leads to the non-return valve 29a and branch 71b to the cylinder 18 of the feel actuator 16.
  • the non-return valves 29a, 29b and the switching valve 70 are connected to the pressure supply line 33 via the isolating valve 31.
  • an override mechanism comes into automatic operation.
  • the brake pedal 15 may be depressed over distance A shown in Figure 2.
  • the braking pedal 15 is subjected to a "panic" force in the event of a failure undetected by the system 10 so that no braking occurs during the normal travel A of the pedal 15, the pedal 15 moves through distance B and operates the override mechanism.
  • the override mechanism comprises a shaft 76 mounted on the piston 66 of the actuator 65 and located within a cylinder 77, extending between the actuators 16 and 65. Under normal conditions the shaft 76 does not contact the cylinder 77.
  • An override compression spring 74 is located between the manifold block 75 which houses the actuator 16 and a fixed support 78 on which the cylinder 77 is mounted on a pivotal arm 79; see Figures 2 and 3.
  • the manifold block 75 is mounted in the system 10 to be moveable, but is held, during normal braking, stationary by the spring 74 acting between the block 75 and the support 78.
  • FIG. 2 shows the system in the condition when the override is operating, although the pedal 15 is shown in solid line in its normal position.
  • a reaction to the driver's demand on the brake pedal 15 is provided by the feel actuator 16.
  • the microprocessor 25 sends control signals to the servo valve 28 which is connected to the feel actuator 16 to apply pressure to either side of the piston head 17a. This is used to provide resistance to movement of the brake pedal 15 and to generally simulate the "feel” of braking. This "feel” may be altered by programming the microprocessor 25 to provide light or heavy braking or whatever the driver prefers.
  • the isolating valve 31 is energised to connect the servo valve 28 with the pressure line 33.
  • pressure is also applied to the non-return valves 29a, 29b This causes the non-return valves 29a, 29b to open and the switching valve 70 to close which allows the feel actuator 16 to be driven directly by the servo valve 28 via the fluid lines to either side of the piston head 17a.
  • Any residual fluid pressure in the master cylinder 45 is vented via fluid line 69 through the open non-return valve 29b to the fluid return line 34.
  • the feel actuator 16 is capable of simulating a wide range of characteristics depending on the 'feel' required.
  • the actual braking is carried out by fluid pressure supplied by the four servo valves 11, 12, 13, 14.
  • the microprocessor 25 sends independent control signals to each of the servo valves 11, 12, 13, 14, according to input signals from the load cell 21.
  • the servo valves 11, 12, 13, 14 are connected to the pressure supply line via the connectors 32.
  • the fluid pressure is controlled by each servo valve 11, 12, 13, 14 to operate each brake mechanism independently.
  • the fluid pressure transmitted from the servo valves 11, 12, 13, 14 via fluid passages 50 is sufficient to overcome the preload on the springs 54 causing the spools 51 to move in the chambers 46, 47, 48, 49 to seal them off from the ports 37-40 from the master cylinder 45.
  • the fluid remaining in the chambers 46-49 is forced out of the chambers 46-49 via the ports 41-44 by movement of the spools 51 to the individual brake mechanisms to operate the brakes independently of each other.
  • the secondary braking system may be activated in two ways; either by means of a manual switch (not shown) operated by the driver to de-energise the isolating valve 31, or as a result of a failure detected in the primary active braking system.
  • the main failures may be in the form of loss of electrical power to the system of a drop in the system pressure below a pre-set safety limit.
  • Various safety control loops may be incorporated in the overall braking system which are monitored by the microprocessor 25.
  • the LVDT, load cell 21 and other sensors in the system are preferably duplex sensors. Their signals are duplicated and the signals combined to give a demand and an error detection signal. Failures in the control loops can be detected by comparing the actual output from the system with a real time model of the system running in parallel. Any detected failures will result in de-energisation of the isolating valve 31.
  • Loss of the electrical supply will automatically result in de-engerisation of the isolating valve 31.
  • the effect of loss of pressure has a similar effect which will be described later.
  • the isolating valve 31 When the isolating valve 31 is de-energised it connects to the fluid return line 34. This results in a drop in pressure to the non-return valves 29a, 29b which close and the and switching valve 70 which opens. This hydraulically disconnects the servo valve 28 from the feel actuator 16 and hydraulically connects the feel actuator 16 to the secondary hydraulic actuator 65 via switching valve 70 which operates the booster 45a and master cylinder 45.
  • brake fluid is forced along the fluid lines 58, 59 from the master cylinder 45, into chambers 46-49 and out of ports 41-44 to the brake mechanism via the brake lines 56.
  • ports 37, 40 are connected to the fluid line 58 and ports 38, 39 are connected to line 59 equal pressures are transferred across each axle pair of brakes.
  • the override mechanism comes into operation. If no braking occurs when the driver depresses pedal 15 through distance A, he will use a panic force and the pedal will move through distance B.
  • the length of the feel actuator cylinder 18 is such that when the brake pedal 15 has reached the end of travel distance A, the piston head 17a reaches the end of the cylinder 18. Further movement of the pedal 15, i.e.
  • the system is thus very versatile, self-monitoring, fail ⁇ safe and may perform to a variety of control laws, such as anti- lock braking, variable balance, deceleration demand and brake performance feed back to pedal.

Landscapes

  • Engineering & Computer Science (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Regulating Braking Force (AREA)
  • Braking Systems And Boosters (AREA)
  • Valves And Accessory Devices For Braking Systems (AREA)

Abstract

L'invention concerne un système de freinage pour véhicules qui comprend un élément de freinage (15) actionné par un conducteur, et des moyens de génération de signaux de commande (21) sensibles au fonctionnement de l'élément de freinage (15), ainsi que des moyens qui freinent au moins une roue du véhicule en fonction du signal de commande. Le système comprend aussi des moyens d'actionnement d'un système de priorité permettant, par l'actionnement de l'élément de freinage, le contrôle direct des moyens de freinage, indépendamment des signaux de commande.
EP19900907240 1989-04-26 1990-04-26 Systemes de freinage pour vehicules Withdrawn EP0469056A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB8909472 1989-04-26
GB898909472A GB8909472D0 (en) 1989-04-26 1989-04-26 Vehicle braking system
GB898910275A GB8910275D0 (en) 1989-05-04 1989-05-04 Vehicle braking system
GB8910275 1989-05-04

Publications (1)

Publication Number Publication Date
EP0469056A1 true EP0469056A1 (fr) 1992-02-05

Family

ID=26295272

Family Applications (2)

Application Number Title Priority Date Filing Date
EP19900907240 Withdrawn EP0469056A1 (fr) 1989-04-26 1990-04-26 Systemes de freinage pour vehicules
EP19900907210 Withdrawn EP0469052A1 (fr) 1989-04-26 1990-04-26 Systemes de freinage pour vehicules

Family Applications After (1)

Application Number Title Priority Date Filing Date
EP19900907210 Withdrawn EP0469052A1 (fr) 1989-04-26 1990-04-26 Systemes de freinage pour vehicules

Country Status (4)

Country Link
EP (2) EP0469056A1 (fr)
JP (2) JPH04504698A (fr)
CA (2) CA2053223A1 (fr)
WO (2) WO1990012718A1 (fr)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2762161B2 (ja) * 1990-08-10 1998-06-04 本田技研工業株式会社 車両用制動油圧制御装置
JP2762160B2 (ja) * 1990-08-10 1998-06-04 本田技研工業株式会社 車両用制動油圧制御装置
GB9420957D0 (en) * 1994-10-18 1994-12-07 Lucas Ind Plc Improvements in pedal assemblies for vehicle braking systems
DE29921027U1 (de) † 1999-11-30 2001-06-28 Kober Ag Simulator für ein nichthydraulisches Betätigungssystem
JP2013174767A (ja) 2012-02-27 2013-09-05 Sony Corp レンズ鏡筒及び撮像装置

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2932620A1 (de) * 1979-08-11 1981-02-26 Bosch Gmbh Robert Hydraulische fremdkraftbremsanlage fuer ein zugfahrzeug mit anhaenger
DE3027747A1 (de) * 1980-07-22 1982-02-18 Alfred Teves Gmbh, 6000 Frankfurt Regelsystem fuer eine fahrzeugbremsanlage mit stroemungs- und reibungsbremse
DE3342552A1 (de) * 1983-11-25 1985-06-05 Volkswagenwerk Ag, 3180 Wolfsburg Hydraulisches, mit einer servoeinrichtung versehenes bremssystem fuer kraftfahrzeuge
DE3410006A1 (de) * 1984-03-19 1985-09-19 Alfred Teves Gmbh, 6000 Frankfurt Verfahren zur steuerung einer bremsanlage fuer kraftfahrzeuge und vorrichtung zur durchfuehrung des verfahrens
DE3626751A1 (de) * 1986-03-22 1987-09-24 Bosch Gmbh Robert Elektro-hydraulische bremsanlage

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9012718A1 *

Also Published As

Publication number Publication date
JPH04504698A (ja) 1992-08-20
JPH04504697A (ja) 1992-08-20
CA2053224A1 (fr) 1990-10-27
EP0469052A1 (fr) 1992-02-05
WO1990012717A1 (fr) 1990-11-01
WO1990012718A1 (fr) 1990-11-01
CA2053223A1 (fr) 1990-10-27

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