CA2120596A1 - Electro-hydraulic brake system - Google Patents
Electro-hydraulic brake systemInfo
- Publication number
- CA2120596A1 CA2120596A1 CA 2120596 CA2120596A CA2120596A1 CA 2120596 A1 CA2120596 A1 CA 2120596A1 CA 2120596 CA2120596 CA 2120596 CA 2120596 A CA2120596 A CA 2120596A CA 2120596 A1 CA2120596 A1 CA 2120596A1
- Authority
- CA
- Canada
- Prior art keywords
- pressure
- pump
- master cylinder
- piston
- brake
- 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.)
- Abandoned
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
- 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
- B60T13/745—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 acting on a hydraulic system, e.g. a master cylinder
Landscapes
- Engineering & Computer Science (AREA)
- Transportation (AREA)
- Mechanical Engineering (AREA)
- Valves And Accessory Devices For Braking Systems (AREA)
- Braking Systems And Boosters (AREA)
- Regulating Braking Force (AREA)
Abstract
An electro-hydraulic brake system (30) comprising: a master cylinder (32); a pump (34) the output being communicated to a pressure regulating valve (50), a motor (36) for rotating the pump; an isolation valve (42) for selectively connecting one of the master cylinder and pump to a brake cylinder(s) (44) and a signal generator (40) to activate the pump. The pressure regulating valve connected between the master cylinder and pump to regulate pump output pressure at a determinable level in proportion to the pressure generated by the master cylinder and for providing a path to drain the brake cylinder(s) to a reservoir during intervals of decreasing master cylinder pressure. The system may also include an excess flow valve(s) (90) to prevent the reservoir from being drained by the pump in the event of a malfunction in the system. Various embodiments of the regulating valve are described which add additional failure mode protection.
Description
,,.,.21?0.59~
r ELECTRO-HYDRAULIC ~RARE SYSTEM
3.~.CKGROU~J~ RY Cr T~r T~E~ITIO~.
J ' The presen~ ~ven~ion relates ;_ 2n ^i~ctr~-hydraulic brakir._ system in wnich the ~rimary ~raking force is sup~Liei t~ brake cyLinders by a ~ump moved 5v ~n electric mot~-.
'~One su~n ei~ o-hyaraulic braki~a syst~m s snown in US Paten~ ~ a_~ 777. ~ sim~ ie~ version o~ an electro-hydraul_^ ~r~king sys~em is sno~n in F-~GURE 1.
The system comDr ses a pump 12 powered ~y a motor 14 ir. -~
~esponse to cer._-~i sianals generated v an ele~rronic _ control unir (~ 16. The pump direc-ly ~ressurizes a brake cilinaer ~ cyiinders generallv s;nown as 18.
The speed ce the mo~or 14/pump 1~ is controile~ so as to modulate brz:~G system pressure in ac~o_danc~ with a commanded brake ~ressure signal. A by-pass orifice 20 2 a is provided acr~ss ;he pump 12 whic-. e~hances the srability of mocc-~pump speea and 2110ws ~5- the rapi~
reiease o_ ora~_ c;linder pressure ~:nen ~e~uire~
-IGURE ~ illus~r__es an improvement ~c .ne sim li~ied system shown ir. r-~U-~E 1 in whicn a mascer cylinder 22 ~5 has been added ;_ provide brake system redundancy in the event that .:~e Dump 12 or electronics fail. In this system the ~otor control signal is generated by comparing master cvlinder pressure as generated by a pressure senso- 2~, co a signal indicative o~ the pressure ln~ the brake cylinder 18 as determined by pressure sensor ~. This technique cou!d also be used in the system of FIGURE 1. An isolation valve 28 is used to communica~e either the master cylinder or the output of the pump to one or more braka cylinders 18.
The isolation valve may be a pressure piloted isolation valve responsive to pump outpuc pressure. The syscem SUBST;TUTE SHEET
2120~.91~
illustr~tea u~ es, in a genera! sense, c flow control d~vic~ ~0 across tne pump ~his flow con~rol devic~ mav be lmpiemented i?. manv differen~ ways, inciuding the fixea orifice snown i-, EIGURE 1 or the solenoid valve shown _n FIGURE 2 Whiie either or the systems showr in FIGUREs 1 and 2 work well, cer~ain time delays will exis~ until the pums OU~pUt pressure builds satisfactorily To reduce an~r time deiay thes-systems require an ex~remely fas. responding mo~or and also require motor speed con~rol elec_ronics whLc;n are useful in re~ulating .he speed or t;~ ~ump suc~; tha~
auring in the s~eadv state the outpu- ?ressure of the pump is eoual tO the commanded G- master c~flinder pressure It is an 02jec~ of the present inven~ion to provide a more rapid responding, less exDensive electro-hydraulic system than that ~!us~rated in the above figures Accordins, the invention comDrises an eLectro-nyaraulic brake syst~m comorising a master cylinder; 2 pump tne ou~put communicated to a ~ressure regulating valve means; a motor for rotating the pump ~5~ at a determinable speed; isolation valve means selectively connecting one of the mas~e~ cylinder and pump to a brake cylinder or group o- brake cvlinders and first means for generating a signal indicative of operator in~tiated brake activity to cause ac~ivation of the pump The valve means, is connected between the master cylinder and pump and reguiates the output pressure of the pump at a decerminable level in proportion to the pressure generaced by the master cylinder and ~or providing a path to ~rain the brake cylinder(s) to a reser~oir during intervals of decreasing master cylinder pressure The system may SU8S~ITUTE SHEET
- 2120~.9fi .
also include an excess flow valve(s) which will pr~ven~
the reservoir from being drained bv the pump in the even.t o a malfunccion such as a derective or leaky brake cyLinder or a hole (leak) in a hydraulic line.
Various embodiments of the valve means are aescribed which add additional failure mode protection to the system.
~.
Many other objects and purposes of the invention will be clear from the foliowing detailed descriptior.
of the drawings.
BRIEF DESCRTPTION OF THE DRAWINGS
In the drawings:
FIGUREs 1 and 2 illustr.ates simplified versions of an electro-hydraulic braking system.
FIGURE 3 illustrates an improved electro- hydraulic system incorporating features of the present in~ention.
FIGURE 4 illustrates an alternate embodiment or z pressure regulating valve.
FIGURE 5 illustrates another brake system.
FIGURE 6 illustrates another embodiment of a valve.
25 ~
SUBSTITUTE SHEET
W0~3/09012 PCT/US92/08g22 2i20~i!1fi DETAILED DESCRIPTION OF THE DRAWINGS
FIGURE 3 schematically illustrates an electro-hydraulic brake system 30. The system includes a master cylinder 32 and a pump 34 such as a positive-displacement pump rotated by a motor 36.
The motor 36 is activated through a relay 38 by a control signal generated by an ECU 40. As shown the output signal from a brake light switch 80 ~or similar command) is used to activate the relay 38.
While an ECU 40 is shown, this could be eliminated.
The ECU 40 may in its simplest form include electronic filters and a buffer or amplifier circuit for powering the relay 38. The output of the pump 34 and the output of the master cylinder 32 are communicated to an isolation valve generally shown as 42 similar in function to the isolation valve 28 of FIGURE 2. If the pump does not produce adequate pressure, isolation does not oc~ur and conventional manual braking is still available via the master cylinder. In this sense, the failure of the pump is similar to the failure of a vacuum booster found in conventional power brake systems. The system 30 further includes a pressure regulator which is also ~5 referred to as valve 50. As will be seen the valve 50 regulates pump pressure i.e., the pressure supplied to the brake cylinder(s) at a determinable ratio of master cylinder pressure. FIGURE 3 shows one e~mbodiment of the valve 50 which comprises a ,__ first piston 52 exposed to master cyli~der pressure, movable within a piston passage 56. The piston includes a pin or closure element 54. One end 60 of the piston ~assage 56 is communicated to the ~ump 34 as well as to the brake cylinder or cylinders 44.
The piston passage 56 includes a by-pass passage 58 wo 93/0gol2 2 1 2 0 .~ 9 fi PCT/US92/08922 communicated to a reservoir 62. A first orifice 70 is provided in the piston passage 56 and defines a flow area Al which is equal to or less than the area A2 of the first piston 52 that is exposed to master cylinder pressure. As can be seen, the first orifice 70 is located between the by-pass passage 58 and the end 60 of the piston passage 56.
The system 30 additionally includes a means for generating a signal indicative of operator initiated brake acti~ity. As illustrated in FIGURE 3, and as mentioned above, an indication that the operator has stepped on the brake pedal 82 is sensed by the closure of a brake light switch generally shown as 80. The brake light switch is communicated to the ECU 40 which in turn activates relay 38 to cause the motor 36 to rotate at a relati~ely constant speed defined ~y the pump pressure needed to create a force balance across the first piston 52.
Alternatively, an indication of braking activity can be generated by utilizing a force sensor 84 to measure brake pedal force or a pressure sensor 86 to measure developed master cylinder pressure. One ad~antage of using the brake light switch 80 as ~5 opposed to a force transducer 84 or pressure sensor 86 is that the brake li$ht switch 80 will generate a signal slightly before a force sensor or pressure sensor will generate its corresponding signal.
Usin~ the brake light switch as a measure of brake activity reduces time delays permittin~ a more rapid energization of the motor 36/pump 34.
In operation, when the operator depresses the brake pedal 82 pressure in the ma~ter cylinder will increase. The output preqsure of the master WO93~09012 PCT/US92/08922 21 2 O~i '3 ~ -6-cylinder is communicated to the brake cylinder or cylinders 44 through the isolation valve. The nonactivated state of the isolation valve is shown in FIGURE 3. When the brake pedal 82 is depressed, the brake light switch 80 output signal is communicated to the motor relay 38. During the initial moments of operation of the system, the master cylinder pressure will exceed the pressure generated by the pump 34. During this time, the master cylinder pressure acts upon the first piston 52 causing the element 54 to fully close the orifice 70. With the orifice 70 closed the full output flow capacity of the pump 34 is directed to flow to the isolation valve 42.
The isolation valve 42 should typically be designed to change its state at a relatively low output pump pressure such as 30-50 psi. When the isolation valve changes state, it isolates the master cylinder 32 from the brake cylinder 44 and directly communicates the output of the pump to the brake cylinder 44. As the output pressure of the pump builds, this pressure acts upon the lower end of the element 54, moving it from the first orifice 70 in opposition to the forces generated on the first piston 52 by master cylinder pressure. It is desirable to regulate the output pressure of pump 34 to a determinable pressure and as a function of mast~r cylinder pressure. In its equilibrium condition, the valve 50 will regulate pump pressure P to be equal to: P = A2/A~ x P~c where P~c is master cylinder pressure. If A2 is greater than A1 a boosted pump pressure is generated analogous to the output of a conventional power brake.
W093/09012 2 1 2 0 ~ ~ fi PcT/us92/o8922 As can be appreciated, the pressure regulating - action of the valve 50 works on a force balance principle. The master cylinder pressure acts on the working area of its associated piston (piston 52) - 5 and produces a force which is balanced by the pump 34 acting on an associated element (pin or element 54). The pin 54/piston 52 will move until sufficient flow passes through the orifice 70 to produce the required pressure difference.
When using a conventional service brake system the operator modulates the force applied to the brake pedal 82 to vary the pressure applied to the brake cylinder 44. This action also happens in the present invention. The pressure generated by the pump will follow master cylinder pressure which is proportional to brake pedal force.
While FIGURE ~ illustrates a separate master cylinder and valve ~0, it should be appreciated that the valve S0 can be incorporated within a modified master cylinder.
Failure of a portion of the hydraulic system r 25 downstream of the isolation valve 42 such as a broken line or leaking brake cylinder could result in not only a loss of braking to the affected wheel but also allow the pump to completely drain the reservoir so that the pump cannot pressurize other braké cylinders. This undesirable effect can be circumvented by placing an excess flow valve 90 between the pump 34 and isolation valve 44. It should be appreciated that FIGURE 3 9hows a ~ingle brake channel. FIGURE 5 shows a plurality of excess flow valves and a two channel brake system from WO93/09012 PCT/~S92/08922 21205.~6 -8-which the benefit of these valves is more readily apparent. - -Reference is made to FIGURES 4 and 5. FIGURE 4 illustrates an alternate valve 50~. FIGURE 5 illustrates an exemplary braking system 30~ for the control of four brake cylinders 44. The valve 50', also shown schematically in FIGURE 5, is functionally analogous in operation to valve 50. An added feature is that this valve 50' is adapted to communicate to a master cylinder having primary and secondary master cylinder chambers 32a and 32b, respectively providing failure redundancy in operation. The valve 50~ includes a housing 100 defining a plurality of ports 102, 104, 106 and 108, adapted to respectively communicate to the primary master cylinder chamber 32a, pump 34, reservoir 62 and the secondary master cylinder chamber 32b. The valve 50~ includes the first piston 52 (see FIGURE
4) and closure element 54 and a valve seat 110 defining the orifice 70. Port 104 illustrates the use of an inverted SAE fitting which may also be used in any of the various ports of the valve 50~.
The piston 52 is slidably received within a bore 114 which also supports a second piston 116. The valve 50~ includes an additional two ports 120a and 120b which communicate to the isolation valves 42a and 42b shown in FIGURE 5. The exemplary system of FIG~E 5 shows a cross-split brake configuration in which the primary master cylinder 32a is communicated to the left front and to the right rear brake cylinders 44 through a proportioning valve 122a. Secondary master cylinder pressure is u~ed to control the right front and left rear brake cylinders through a second proportioning valve 122b.
W~g3/0901~ 2 1 2 0 5 9 fi PCT/US92/08922 _g_ Returning to FIGURE 4, the passage 114, between the connection points of the primary and secondary master cylinder, is also communicated to the exhaust port through a passage 126. This passage 126 provides a region of atmospheric pressure about piston 116. The purpose of this vent or passage 126 is to insure that if any of the regulator seals such as 128 fail, this failure will be detectable. As an example, if one of the seals 128 fail the secondary master cylinder chamber pressure will decrease as brake fluid will flow to the reservoir. This low pressure will be detected by a low pressure switch in the secondary master cylinder chamber. The pressure switch will typically activate a light on the dashboard informing the driver of the failure.
If such a failure of a component in the valve were not detectable then a subsequent failure of, for example a seal in the primary master cylinder would result in the loss of complete braking control.
Another feature of the valve 50' is that it is operable in the event of a failure of one or the other master cylinder chambers or in the hydraulic lines connecting these chambers to the valve 50'.
~5 The operatipn of the valve 50' is as follows.
As is typically the case, the pressure generated in the primary master cylinder will be approximately 20 to 50 psi (1.38-3.45 bar) greater than the pressure generated in the secondary master cylinder. With the system connected as shown in FIGURE 5, the ~ primary master cylinder pressure is received into chamber 130 of FIGURE 4. This pressure force urges piston 52 downwardly and piston 116 upwardly against stop 132. As can be appreciated, the dynamics of 21 2 0 5 9 6 -lo-valve 50', in this condition, are essentially identical to those of valve 50. In this operating condition, secondary master cylinder pressure does not play an operative role in regulating the output pressure of the pump. The valve 50~ wfill continue to operate even in the face of a failure of the hydraulic system upstream of port 108 i.e. the secondary master cylinder chamber. In the event of ~ failure of the hydraulic system connected to the primary master cylinder chamber, no fluid pressure would be generated within chamber 130, however, secondary master cylinder pressure is communicated to chamber 134 which urges piston 116 downwardly and which in turn will cause piston 52 to close the orifice 70. As before, this action permits full pump output to be communicated to the brake cylinders 44 during pump start-up. In this failure mode, the valve 50' will regulate pump output pressure to be proportional to the pressure in the secondary master cylinder.
Reference is made to FIGURE 6 which illustrates an alternate embodiment of a pressure regulating valve 50~. This valve can be substituted into FIGURE 5. The valve 50 n includes a housing 104 into which are received three pistons 206, 208 and 212.
A pin 214 is secured to one of the pistons 206 or 208. In FIGURE 6 the pin 214 is secured to piston 208 and is slidably received within a bore 216 of piston 206. Pistons 206 and 208 are slidably received within a central bore 220. Pist~n 212 is - received within another bore 222. Various dynamic seals such as 224 and 226 are provided to prevent leakage through the various bores 220 and 222. As illustrated seal 224 can be a GLYD ring while seal ~ ' !
WO93/09012 2 1 2 ~ 5 9 6 pCT/US92/08922 226 is shown as an O-ring.
Piston 212 supports a valve closure element 230 which is spherically shaped and adapted to seat upon a valve seat 232 defining an orifice 2~4.
The valve 50l~ includes a plurality of ports 104, 106, 102 and 108 respectively connected to the pump 34, the reservoir 62, the primary master cylinder chamber 32a, and the secondary master cylinder chamber 32b. The valve ~0" also includes a plurality of vents schematically shown as 242 and 246. As can be appreciated exterior vents are not necessary. Alternately, the bores 220 and 222 can be vented to atmosphere through internal passages (not shown) communicated to the reservoir port which is typically at atmospheric pressure.
The piston 208 has a first working surface 260 of area A3 which is exposed to primary master cylinder pressure. The piston 212 has a second working surface 262 of area Al which is also exposed to atmosphere through the vent 246.
The operation of the system 200 is as follows.
Fluid from the primary chamber 32a will fill the chamber 250 between pistons 206 and 208 and act on the first working surface 260 of piston 208 causing the piston 208 to press down on the working surface 262 of piston 212 causing element 230 to fully close orifice 234. This action enables the full output of - the pump 34 to be communicated to the brake cylinder 44. As the pump pressure builds, it acts upon the piston 212 to move away from the valve seat 232 in opposition to the forces exerted on piston 208. As W093~09012 PCT/US92/08922 2120~ ~ 6 -12-the piston 212 moves out from the orifice 234, the output of the pump 34 will be regulated to a determinable pressure which is a function of master cylinder pressure and more specifically a function of the primary master cylinder pressur~.~~ It can be shown that this determinable pressure equals:
p = [(A3/(A2-A1)] x Ppmc wherein PpmC is primary master cylinder pressure, A3 is the area across piston 208, A2 the area of t~e piston 212 and A~ is the area of the orifice 234. As can be appreciated, the valve S0" shown in FIGURE 6 will permit the pressure generated by the pump to be greater than the pressure generated by the primary master cylinder pressure. If it is desired that the pump pressure be more closely related to master cylinder pressure, that is, that the relationship between pump pressure and primary master cylinder pressure approach unity, then the cross-sectional areas of the various pistons will be made equal.
As can be seen valve 50~ includes failure mode protection similar to that employed in valve 50' and will continue to operate even if primary or secondary master cylinder pressure is not communicated to the various ports. In the event of the failure of the primary master cylinder chamber, the output pressure of the pump 34 will be regulated as a function of the secondary master cylinder. The relationship is as follows:
P = [A4/(A2-AI)l P~c where P,~c is secondary master cylinder pressure and - A4 is the area of the piston 206 expoqed to secondary master cylinder pressure.
W O 93/09012 2 1 2 0 S 9 6 PC~r/US92/08922 ~ ,, Many changes and modifications in the above described embodiment of the invention can, of course, be carried out without departing from the scope thereof. Accordingly, that scope is intended to be limited only by the scope of the~appended claims.
r ELECTRO-HYDRAULIC ~RARE SYSTEM
3.~.CKGROU~J~ RY Cr T~r T~E~ITIO~.
J ' The presen~ ~ven~ion relates ;_ 2n ^i~ctr~-hydraulic brakir._ system in wnich the ~rimary ~raking force is sup~Liei t~ brake cyLinders by a ~ump moved 5v ~n electric mot~-.
'~One su~n ei~ o-hyaraulic braki~a syst~m s snown in US Paten~ ~ a_~ 777. ~ sim~ ie~ version o~ an electro-hydraul_^ ~r~king sys~em is sno~n in F-~GURE 1.
The system comDr ses a pump 12 powered ~y a motor 14 ir. -~
~esponse to cer._-~i sianals generated v an ele~rronic _ control unir (~ 16. The pump direc-ly ~ressurizes a brake cilinaer ~ cyiinders generallv s;nown as 18.
The speed ce the mo~or 14/pump 1~ is controile~ so as to modulate brz:~G system pressure in ac~o_danc~ with a commanded brake ~ressure signal. A by-pass orifice 20 2 a is provided acr~ss ;he pump 12 whic-. e~hances the srability of mocc-~pump speea and 2110ws ~5- the rapi~
reiease o_ ora~_ c;linder pressure ~:nen ~e~uire~
-IGURE ~ illus~r__es an improvement ~c .ne sim li~ied system shown ir. r-~U-~E 1 in whicn a mascer cylinder 22 ~5 has been added ;_ provide brake system redundancy in the event that .:~e Dump 12 or electronics fail. In this system the ~otor control signal is generated by comparing master cvlinder pressure as generated by a pressure senso- 2~, co a signal indicative o~ the pressure ln~ the brake cylinder 18 as determined by pressure sensor ~. This technique cou!d also be used in the system of FIGURE 1. An isolation valve 28 is used to communica~e either the master cylinder or the output of the pump to one or more braka cylinders 18.
The isolation valve may be a pressure piloted isolation valve responsive to pump outpuc pressure. The syscem SUBST;TUTE SHEET
2120~.91~
illustr~tea u~ es, in a genera! sense, c flow control d~vic~ ~0 across tne pump ~his flow con~rol devic~ mav be lmpiemented i?. manv differen~ ways, inciuding the fixea orifice snown i-, EIGURE 1 or the solenoid valve shown _n FIGURE 2 Whiie either or the systems showr in FIGUREs 1 and 2 work well, cer~ain time delays will exis~ until the pums OU~pUt pressure builds satisfactorily To reduce an~r time deiay thes-systems require an ex~remely fas. responding mo~or and also require motor speed con~rol elec_ronics whLc;n are useful in re~ulating .he speed or t;~ ~ump suc~; tha~
auring in the s~eadv state the outpu- ?ressure of the pump is eoual tO the commanded G- master c~flinder pressure It is an 02jec~ of the present inven~ion to provide a more rapid responding, less exDensive electro-hydraulic system than that ~!us~rated in the above figures Accordins, the invention comDrises an eLectro-nyaraulic brake syst~m comorising a master cylinder; 2 pump tne ou~put communicated to a ~ressure regulating valve means; a motor for rotating the pump ~5~ at a determinable speed; isolation valve means selectively connecting one of the mas~e~ cylinder and pump to a brake cylinder or group o- brake cvlinders and first means for generating a signal indicative of operator in~tiated brake activity to cause ac~ivation of the pump The valve means, is connected between the master cylinder and pump and reguiates the output pressure of the pump at a decerminable level in proportion to the pressure generaced by the master cylinder and ~or providing a path to ~rain the brake cylinder(s) to a reser~oir during intervals of decreasing master cylinder pressure The system may SU8S~ITUTE SHEET
- 2120~.9fi .
also include an excess flow valve(s) which will pr~ven~
the reservoir from being drained bv the pump in the even.t o a malfunccion such as a derective or leaky brake cyLinder or a hole (leak) in a hydraulic line.
Various embodiments of the valve means are aescribed which add additional failure mode protection to the system.
~.
Many other objects and purposes of the invention will be clear from the foliowing detailed descriptior.
of the drawings.
BRIEF DESCRTPTION OF THE DRAWINGS
In the drawings:
FIGUREs 1 and 2 illustr.ates simplified versions of an electro-hydraulic braking system.
FIGURE 3 illustrates an improved electro- hydraulic system incorporating features of the present in~ention.
FIGURE 4 illustrates an alternate embodiment or z pressure regulating valve.
FIGURE 5 illustrates another brake system.
FIGURE 6 illustrates another embodiment of a valve.
25 ~
SUBSTITUTE SHEET
W0~3/09012 PCT/US92/08g22 2i20~i!1fi DETAILED DESCRIPTION OF THE DRAWINGS
FIGURE 3 schematically illustrates an electro-hydraulic brake system 30. The system includes a master cylinder 32 and a pump 34 such as a positive-displacement pump rotated by a motor 36.
The motor 36 is activated through a relay 38 by a control signal generated by an ECU 40. As shown the output signal from a brake light switch 80 ~or similar command) is used to activate the relay 38.
While an ECU 40 is shown, this could be eliminated.
The ECU 40 may in its simplest form include electronic filters and a buffer or amplifier circuit for powering the relay 38. The output of the pump 34 and the output of the master cylinder 32 are communicated to an isolation valve generally shown as 42 similar in function to the isolation valve 28 of FIGURE 2. If the pump does not produce adequate pressure, isolation does not oc~ur and conventional manual braking is still available via the master cylinder. In this sense, the failure of the pump is similar to the failure of a vacuum booster found in conventional power brake systems. The system 30 further includes a pressure regulator which is also ~5 referred to as valve 50. As will be seen the valve 50 regulates pump pressure i.e., the pressure supplied to the brake cylinder(s) at a determinable ratio of master cylinder pressure. FIGURE 3 shows one e~mbodiment of the valve 50 which comprises a ,__ first piston 52 exposed to master cyli~der pressure, movable within a piston passage 56. The piston includes a pin or closure element 54. One end 60 of the piston ~assage 56 is communicated to the ~ump 34 as well as to the brake cylinder or cylinders 44.
The piston passage 56 includes a by-pass passage 58 wo 93/0gol2 2 1 2 0 .~ 9 fi PCT/US92/08922 communicated to a reservoir 62. A first orifice 70 is provided in the piston passage 56 and defines a flow area Al which is equal to or less than the area A2 of the first piston 52 that is exposed to master cylinder pressure. As can be seen, the first orifice 70 is located between the by-pass passage 58 and the end 60 of the piston passage 56.
The system 30 additionally includes a means for generating a signal indicative of operator initiated brake acti~ity. As illustrated in FIGURE 3, and as mentioned above, an indication that the operator has stepped on the brake pedal 82 is sensed by the closure of a brake light switch generally shown as 80. The brake light switch is communicated to the ECU 40 which in turn activates relay 38 to cause the motor 36 to rotate at a relati~ely constant speed defined ~y the pump pressure needed to create a force balance across the first piston 52.
Alternatively, an indication of braking activity can be generated by utilizing a force sensor 84 to measure brake pedal force or a pressure sensor 86 to measure developed master cylinder pressure. One ad~antage of using the brake light switch 80 as ~5 opposed to a force transducer 84 or pressure sensor 86 is that the brake li$ht switch 80 will generate a signal slightly before a force sensor or pressure sensor will generate its corresponding signal.
Usin~ the brake light switch as a measure of brake activity reduces time delays permittin~ a more rapid energization of the motor 36/pump 34.
In operation, when the operator depresses the brake pedal 82 pressure in the ma~ter cylinder will increase. The output preqsure of the master WO93~09012 PCT/US92/08922 21 2 O~i '3 ~ -6-cylinder is communicated to the brake cylinder or cylinders 44 through the isolation valve. The nonactivated state of the isolation valve is shown in FIGURE 3. When the brake pedal 82 is depressed, the brake light switch 80 output signal is communicated to the motor relay 38. During the initial moments of operation of the system, the master cylinder pressure will exceed the pressure generated by the pump 34. During this time, the master cylinder pressure acts upon the first piston 52 causing the element 54 to fully close the orifice 70. With the orifice 70 closed the full output flow capacity of the pump 34 is directed to flow to the isolation valve 42.
The isolation valve 42 should typically be designed to change its state at a relatively low output pump pressure such as 30-50 psi. When the isolation valve changes state, it isolates the master cylinder 32 from the brake cylinder 44 and directly communicates the output of the pump to the brake cylinder 44. As the output pressure of the pump builds, this pressure acts upon the lower end of the element 54, moving it from the first orifice 70 in opposition to the forces generated on the first piston 52 by master cylinder pressure. It is desirable to regulate the output pressure of pump 34 to a determinable pressure and as a function of mast~r cylinder pressure. In its equilibrium condition, the valve 50 will regulate pump pressure P to be equal to: P = A2/A~ x P~c where P~c is master cylinder pressure. If A2 is greater than A1 a boosted pump pressure is generated analogous to the output of a conventional power brake.
W093/09012 2 1 2 0 ~ ~ fi PcT/us92/o8922 As can be appreciated, the pressure regulating - action of the valve 50 works on a force balance principle. The master cylinder pressure acts on the working area of its associated piston (piston 52) - 5 and produces a force which is balanced by the pump 34 acting on an associated element (pin or element 54). The pin 54/piston 52 will move until sufficient flow passes through the orifice 70 to produce the required pressure difference.
When using a conventional service brake system the operator modulates the force applied to the brake pedal 82 to vary the pressure applied to the brake cylinder 44. This action also happens in the present invention. The pressure generated by the pump will follow master cylinder pressure which is proportional to brake pedal force.
While FIGURE ~ illustrates a separate master cylinder and valve ~0, it should be appreciated that the valve S0 can be incorporated within a modified master cylinder.
Failure of a portion of the hydraulic system r 25 downstream of the isolation valve 42 such as a broken line or leaking brake cylinder could result in not only a loss of braking to the affected wheel but also allow the pump to completely drain the reservoir so that the pump cannot pressurize other braké cylinders. This undesirable effect can be circumvented by placing an excess flow valve 90 between the pump 34 and isolation valve 44. It should be appreciated that FIGURE 3 9hows a ~ingle brake channel. FIGURE 5 shows a plurality of excess flow valves and a two channel brake system from WO93/09012 PCT/~S92/08922 21205.~6 -8-which the benefit of these valves is more readily apparent. - -Reference is made to FIGURES 4 and 5. FIGURE 4 illustrates an alternate valve 50~. FIGURE 5 illustrates an exemplary braking system 30~ for the control of four brake cylinders 44. The valve 50', also shown schematically in FIGURE 5, is functionally analogous in operation to valve 50. An added feature is that this valve 50' is adapted to communicate to a master cylinder having primary and secondary master cylinder chambers 32a and 32b, respectively providing failure redundancy in operation. The valve 50~ includes a housing 100 defining a plurality of ports 102, 104, 106 and 108, adapted to respectively communicate to the primary master cylinder chamber 32a, pump 34, reservoir 62 and the secondary master cylinder chamber 32b. The valve 50~ includes the first piston 52 (see FIGURE
4) and closure element 54 and a valve seat 110 defining the orifice 70. Port 104 illustrates the use of an inverted SAE fitting which may also be used in any of the various ports of the valve 50~.
The piston 52 is slidably received within a bore 114 which also supports a second piston 116. The valve 50~ includes an additional two ports 120a and 120b which communicate to the isolation valves 42a and 42b shown in FIGURE 5. The exemplary system of FIG~E 5 shows a cross-split brake configuration in which the primary master cylinder 32a is communicated to the left front and to the right rear brake cylinders 44 through a proportioning valve 122a. Secondary master cylinder pressure is u~ed to control the right front and left rear brake cylinders through a second proportioning valve 122b.
W~g3/0901~ 2 1 2 0 5 9 fi PCT/US92/08922 _g_ Returning to FIGURE 4, the passage 114, between the connection points of the primary and secondary master cylinder, is also communicated to the exhaust port through a passage 126. This passage 126 provides a region of atmospheric pressure about piston 116. The purpose of this vent or passage 126 is to insure that if any of the regulator seals such as 128 fail, this failure will be detectable. As an example, if one of the seals 128 fail the secondary master cylinder chamber pressure will decrease as brake fluid will flow to the reservoir. This low pressure will be detected by a low pressure switch in the secondary master cylinder chamber. The pressure switch will typically activate a light on the dashboard informing the driver of the failure.
If such a failure of a component in the valve were not detectable then a subsequent failure of, for example a seal in the primary master cylinder would result in the loss of complete braking control.
Another feature of the valve 50' is that it is operable in the event of a failure of one or the other master cylinder chambers or in the hydraulic lines connecting these chambers to the valve 50'.
~5 The operatipn of the valve 50' is as follows.
As is typically the case, the pressure generated in the primary master cylinder will be approximately 20 to 50 psi (1.38-3.45 bar) greater than the pressure generated in the secondary master cylinder. With the system connected as shown in FIGURE 5, the ~ primary master cylinder pressure is received into chamber 130 of FIGURE 4. This pressure force urges piston 52 downwardly and piston 116 upwardly against stop 132. As can be appreciated, the dynamics of 21 2 0 5 9 6 -lo-valve 50', in this condition, are essentially identical to those of valve 50. In this operating condition, secondary master cylinder pressure does not play an operative role in regulating the output pressure of the pump. The valve 50~ wfill continue to operate even in the face of a failure of the hydraulic system upstream of port 108 i.e. the secondary master cylinder chamber. In the event of ~ failure of the hydraulic system connected to the primary master cylinder chamber, no fluid pressure would be generated within chamber 130, however, secondary master cylinder pressure is communicated to chamber 134 which urges piston 116 downwardly and which in turn will cause piston 52 to close the orifice 70. As before, this action permits full pump output to be communicated to the brake cylinders 44 during pump start-up. In this failure mode, the valve 50' will regulate pump output pressure to be proportional to the pressure in the secondary master cylinder.
Reference is made to FIGURE 6 which illustrates an alternate embodiment of a pressure regulating valve 50~. This valve can be substituted into FIGURE 5. The valve 50 n includes a housing 104 into which are received three pistons 206, 208 and 212.
A pin 214 is secured to one of the pistons 206 or 208. In FIGURE 6 the pin 214 is secured to piston 208 and is slidably received within a bore 216 of piston 206. Pistons 206 and 208 are slidably received within a central bore 220. Pist~n 212 is - received within another bore 222. Various dynamic seals such as 224 and 226 are provided to prevent leakage through the various bores 220 and 222. As illustrated seal 224 can be a GLYD ring while seal ~ ' !
WO93/09012 2 1 2 ~ 5 9 6 pCT/US92/08922 226 is shown as an O-ring.
Piston 212 supports a valve closure element 230 which is spherically shaped and adapted to seat upon a valve seat 232 defining an orifice 2~4.
The valve 50l~ includes a plurality of ports 104, 106, 102 and 108 respectively connected to the pump 34, the reservoir 62, the primary master cylinder chamber 32a, and the secondary master cylinder chamber 32b. The valve ~0" also includes a plurality of vents schematically shown as 242 and 246. As can be appreciated exterior vents are not necessary. Alternately, the bores 220 and 222 can be vented to atmosphere through internal passages (not shown) communicated to the reservoir port which is typically at atmospheric pressure.
The piston 208 has a first working surface 260 of area A3 which is exposed to primary master cylinder pressure. The piston 212 has a second working surface 262 of area Al which is also exposed to atmosphere through the vent 246.
The operation of the system 200 is as follows.
Fluid from the primary chamber 32a will fill the chamber 250 between pistons 206 and 208 and act on the first working surface 260 of piston 208 causing the piston 208 to press down on the working surface 262 of piston 212 causing element 230 to fully close orifice 234. This action enables the full output of - the pump 34 to be communicated to the brake cylinder 44. As the pump pressure builds, it acts upon the piston 212 to move away from the valve seat 232 in opposition to the forces exerted on piston 208. As W093~09012 PCT/US92/08922 2120~ ~ 6 -12-the piston 212 moves out from the orifice 234, the output of the pump 34 will be regulated to a determinable pressure which is a function of master cylinder pressure and more specifically a function of the primary master cylinder pressur~.~~ It can be shown that this determinable pressure equals:
p = [(A3/(A2-A1)] x Ppmc wherein PpmC is primary master cylinder pressure, A3 is the area across piston 208, A2 the area of t~e piston 212 and A~ is the area of the orifice 234. As can be appreciated, the valve S0" shown in FIGURE 6 will permit the pressure generated by the pump to be greater than the pressure generated by the primary master cylinder pressure. If it is desired that the pump pressure be more closely related to master cylinder pressure, that is, that the relationship between pump pressure and primary master cylinder pressure approach unity, then the cross-sectional areas of the various pistons will be made equal.
As can be seen valve 50~ includes failure mode protection similar to that employed in valve 50' and will continue to operate even if primary or secondary master cylinder pressure is not communicated to the various ports. In the event of the failure of the primary master cylinder chamber, the output pressure of the pump 34 will be regulated as a function of the secondary master cylinder. The relationship is as follows:
P = [A4/(A2-AI)l P~c where P,~c is secondary master cylinder pressure and - A4 is the area of the piston 206 expoqed to secondary master cylinder pressure.
W O 93/09012 2 1 2 0 S 9 6 PC~r/US92/08922 ~ ,, Many changes and modifications in the above described embodiment of the invention can, of course, be carried out without departing from the scope thereof. Accordingly, that scope is intended to be limited only by the scope of the~appended claims.
Claims (12)
1. An electro-hydraulic brake system (30) comprising:
a master cylinder (32);
a pump (34) the output being communicated to a valve means (50);
a motor (36) for rotating the pump (34) at a speed related to the pressure developed by the pump;
isolation valve means (42) for selectively connecting one of the master cylinder (32) and pump (34) to at least one brake cylinder (44);
first means (80,84,86,38,40) for generating a signal indicative of operator initiated brake activity to cause activation of the pump (34); characterized in that the system includes:
the valve means (50,50',50"), connected between the master cylinder (32) and pump (34) for regulating the output pressure generated by the pump (34) at a determinable pressure in proportion to the pressure generated by the master cylinder (32) and for providing a path to drain the at least one brake cylinder (44) to a reservoir (62) during intervals of decreasing master cylinder pressure.
a master cylinder (32);
a pump (34) the output being communicated to a valve means (50);
a motor (36) for rotating the pump (34) at a speed related to the pressure developed by the pump;
isolation valve means (42) for selectively connecting one of the master cylinder (32) and pump (34) to at least one brake cylinder (44);
first means (80,84,86,38,40) for generating a signal indicative of operator initiated brake activity to cause activation of the pump (34); characterized in that the system includes:
the valve means (50,50',50"), connected between the master cylinder (32) and pump (34) for regulating the output pressure generated by the pump (34) at a determinable pressure in proportion to the pressure generated by the master cylinder (32) and for providing a path to drain the at least one brake cylinder (44) to a reservoir (62) during intervals of decreasing master cylinder pressure.
2. The system as defined in Claim 1 wherein the first means (80,84,86) generates a pump activation signal in advance of a substantial increase in master cylinder pressure.
3. The system as defined in Claim 1 wherein the first means includes a brake light switch (80) activated when an operator of the vehicle depresses a brake pedal connected to the master cylinder.
4. The system as defined in Claim 1 wherein the valve means (50) comprises:
a first piston (52;212), having an area A2, exposed to master cylinder pressure, and a closure element (54;230) movable in a piston passage (56;114;220), for controlling flow through a first orifice (70;234) having a flow area Al, the piston passage (56) communicated to the pump (34) and to the reservoir (62), one side of the first orifice (70) communicated to the reservoir, wherein when the pump pressure is less than the determinable pressure, the master cylinder pressure operates to cause the first piston to close the first orifice to enable the full output of the pump (34) to be communicated to the at least one brake cylinder (44), and as the pump pressure builds such pressure acts on the first piston (54) to move same from the first orifice (70) to increase flow thereacross to regulate the output pressure of the pump to the determinable pressure.
a first piston (52;212), having an area A2, exposed to master cylinder pressure, and a closure element (54;230) movable in a piston passage (56;114;220), for controlling flow through a first orifice (70;234) having a flow area Al, the piston passage (56) communicated to the pump (34) and to the reservoir (62), one side of the first orifice (70) communicated to the reservoir, wherein when the pump pressure is less than the determinable pressure, the master cylinder pressure operates to cause the first piston to close the first orifice to enable the full output of the pump (34) to be communicated to the at least one brake cylinder (44), and as the pump pressure builds such pressure acts on the first piston (54) to move same from the first orifice (70) to increase flow thereacross to regulate the output pressure of the pump to the determinable pressure.
5. The system (30) as defined in Claim 4 wherein the determinable pressure P equals P = A2/A1 x Pmc wherein Pmc is master cylinder pressure.
6. The system as defined in Claim 4 wherein the master cylinder includes a primary chamber (32a) and a secondary chamber (32b), and wherein the valve means (50) includes second means (116;206;208), for receiving fluid generally at the pressure levels generated in the primary and secondary chambers (32a, 32b) and for permitting the valve means to regulate pump pressure in the event that only one of primary master cylinder pressure or secondary master cylinder pressure is communicated to the valve means.
7. The system as defined in Claim 4 wherein the area Al is equal to or less than the area A2.
8. The system as defined in Claim 4 including excess flow valve means (90), situated downstream of the pump, for terminating pump flow in the event of a loss of pressurization downstream of the pump due to a malfunction.
9. The system as defined in Claim 4 wherein the master cylinder (32) and the valve means (50) are of integral construction.
10. The system as defined in Claim 6 wherein the second means includes a second piston (116) movable into contact with the first piston in response to secondary master cylinder pressure thereby controlling the position of the first piston relative to the first orifice.
11. The system as defined in Claim 6 wherein pump is communicated to the first piston at a location upstream of the first orifice (234) and a downstream side of the first orifice is communicated to atmospheric pressure and wherein the second means comprises:
a second piston (208), having a first working surface (262) of area A3, and an opposite contacting surface movable to contact with the first piston (212) having an area of A2 in response to primary master cylinder pressure applied to the first working surface to move same relative to the first orifice, the contacting surface also being exposed to atmospheric pressure, and a third piston (206), for moving the second piston in response to secondary master cylinder pressure during intervals when the level of secondary master cylinder pressure exceeds the level of primary master cylinder pressure.
a second piston (208), having a first working surface (262) of area A3, and an opposite contacting surface movable to contact with the first piston (212) having an area of A2 in response to primary master cylinder pressure applied to the first working surface to move same relative to the first orifice, the contacting surface also being exposed to atmospheric pressure, and a third piston (206), for moving the second piston in response to secondary master cylinder pressure during intervals when the level of secondary master cylinder pressure exceeds the level of primary master cylinder pressure.
12. The system as defined in Claim 13 wherein the determinable pressure equals p = [A3/(A2-A1)] x Ppmc wherein Pmc is pressure generated in the primary master cylinder chamber, and Al is the area of the orifice.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US78585091A | 1991-10-31 | 1991-10-31 | |
| US785,850 | 1991-10-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2120596A1 true CA2120596A1 (en) | 1993-05-13 |
Family
ID=25136816
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2120596 Abandoned CA2120596A1 (en) | 1991-10-31 | 1992-10-19 | Electro-hydraulic brake system |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0609361A1 (en) |
| JP (1) | JPH07500550A (en) |
| CA (1) | CA2120596A1 (en) |
| MX (1) | MX9206198A (en) |
| WO (1) | WO1993009012A1 (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5364866A (en) | 1989-05-19 | 1994-11-15 | Hoechst-Roussel Pharmaceuticals, Inc. | Heteroarylpiperidines, pyrrolidines and piperazines and their use as antipsychotics and analetics |
| US5776963A (en) * | 1989-05-19 | 1998-07-07 | Hoechst Marion Roussel, Inc. | 3-(heteroaryl)-1- (2,3-dihydro-1h-isoindol-2-yl)alkyl!pyrrolidines and 3-(heteroaryl)-1- (2,3-dihydro-1h-indol-1-yl)alkyl!pyrrolidines and related compounds and their therapeutic untility |
| FR2719678B1 (en) * | 1994-05-06 | 1996-09-06 | Alliedsignal Europ Services | Pressure control system with hybrid structure for a hydraulic brake system of a motor vehicle. |
| US5855417A (en) * | 1994-09-12 | 1999-01-05 | General Motors Corporation | Integral control and isolation valve proportional brake system |
| WO1996026091A1 (en) * | 1995-02-22 | 1996-08-29 | Bosch Braking Systems Corporation | Hydraulic and electric powered parking brake system |
| ES2122919B1 (en) * | 1996-11-19 | 1999-07-16 | Gonzalez Mena Francisco | ACTIVATION SYSTEM OF THE BRAKE SERVO IN AUTOMOBILE VEHICLES. |
| JPH1148955A (en) * | 1997-08-08 | 1999-02-23 | Toyota Motor Corp | Hydraulic pressure braking device |
| DE19949816A1 (en) | 1999-10-15 | 2001-04-19 | Bosch Gmbh Robert | Actuator unit for wheel brakes of road vehicle, has electro-hydraulic valve circuit for anti-lock control, with power provided by motor driven pump, and pressure regulated by controller coupled to brake pedal |
| DE102008021822B3 (en) * | 2008-04-11 | 2009-04-09 | Knorr-Bremse Systeme für Nutzfahrzeuge GmbH | Commercial motor vehicle's pressure medium supply device controlling method, involves separating consumer-side sub-system by storage container from pressure medium supply device to prevent pressure adjustment in sub-system |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3424912A1 (en) * | 1984-07-06 | 1986-01-16 | Alfred Teves Gmbh, 6000 Frankfurt | Electronically controlled brake-actuating system |
| JP2590825B2 (en) * | 1986-07-12 | 1997-03-12 | トヨタ自動車株式会社 | Manual / Electric dual brake system |
| FR2620097B1 (en) * | 1987-09-04 | 1992-02-21 | Renault | PRESSURE GENERATING DEVICE FOR MOTOR VEHICLE BRAKING CIRCUITS |
-
1992
- 1992-10-19 WO PCT/US1992/008922 patent/WO1993009012A1/en not_active Application Discontinuation
- 1992-10-19 CA CA 2120596 patent/CA2120596A1/en not_active Abandoned
- 1992-10-19 JP JP5508451A patent/JPH07500550A/en active Pending
- 1992-10-19 EP EP92922711A patent/EP0609361A1/en not_active Withdrawn
- 1992-10-28 MX MX9206198A patent/MX9206198A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| JPH07500550A (en) | 1995-01-19 |
| WO1993009012A1 (en) | 1993-05-13 |
| MX9206198A (en) | 1993-07-01 |
| EP0609361A1 (en) | 1994-08-10 |
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