Abstract:
A hydraulic brake system wherein a portion of a volume of a first fluid supplied to a steering system by a pump is selectively diverted to an actuator assembly for a master cylinder to develop an force for actuating a master cylinder to pressurize fluid which is supplied to wheel brakes. An electronic control unit (ECU) for the brake system receives a first input signal indicative of the flow of fluid from the pump in the steering system, a second input signal indicative of the input force applied by the operator and a third input signal indicative of the speed of the wheels of the vehicle for developing a pulse modulated operational signal. The electronic control develops an operational signal which is supplied as the pulse modulated operational signal to a magnetic responsive valve. The pulse modulated operational signal creates a variable orifice in the magnetic responsive valve to restrict the flow of the first fluid to the steering gear and increases the fluid pressure of the first fluid. This increase in the fluid pressure of the first fluid is develops an operational force for actuating the master cylinder to effect a brake application. The electronic control unit supplies the pulse modulated operational signal to the magnetic responsive valve until a desired braking of the vehicle is achieved.

Description:
This invention relates to a hydraulic braking system for a vehicle wherein operational pressurized fluid is supplied to a remote actuator assembly to operate a master cylinder that pressurizes fluid that is supplied to wheel brakes to effect a brake application. An operator applies an input force to a force sensor, which supplies an electronic control unit with an input signal indicating a desired braking for the vehicle. The electronic control unit develops an operational signal as a function of the input signal, deceleration of the vehicle and the flow of the pressurized fluid of a source. The operational signal is supplied from the electronic control unit to a magnetic responsive valve as a pulse modulated operational signal such the flow of pressurized fluid from the source to a steering gear is restricted to correspondingly increase in the fluid pressure therein to an operational pressure to activate the remote actuation assembly. 
     BACKGROUND OF THE INVENTION 
     Hydraulic brake boosters have been designed to provide an assist in the actuation of a master cylinder to pressurize fluid to developed a force to effect a brake application. In order to reduce the cost of a hydraulic brake booster, often the same hydraulic power source used to supply a steering gear is used to power a hydraulic brake booster. The controls for such hydraulic brake boosters are designed such that a minimum amount of hydraulic fluid is always available for operation of either the hydraulic brake booster or the steering gear. In certain brake boosters, of a type disclosed in U.S. Pat. Nos. 3,967,536; 4,131,055; 4,179,980; 4,514,981; 4,724,674 and 5,442,916, the booster operates by restricting flow from one side of a power piston to the other side of the power piston to create a fluid pressure differential which causes the power piston to move and provide power assisted displacement of the pistons in a master cylinder. In this type of brake booster, the master cylinder and booster are joined together and as a result the overall length occupies considerable under hood space of a vehicle. Because of the efficiency of such brake boosters they have found application in many vehicles and in particular van and certain mid-sized trucks. However, in some models of recently manufactured vehicle, the physical design of the under hood space is often restricted or reduced, and as a consequently locating a brake booster and other components is often a difficult task. To better utilize under hood space, it has been disclosed in U S. Pat. Nos. 5,329,769, 5,313,796 and U.S. patent application Ser. No. 09/097,778, now U.S. Pat. No. 6,038,857 that certain brake systems components could be located remotely from under the hood. These brake systems functioning in an adequate manner but require a considerable number of components in the control apparatus to provide a stable and smooth application of the wheel brakes. 
     U.S. Pat. No. 4,865,399 discloses an anti-lock brake system wherein pressurized fluid developed by a pump system is supplied to wheel brakes to effect a brake application. The time the pressurized fluid is supplied to any individual wheel brake is alternately increased and decreased through the actuation of a solenoid valve by a pulse-width-modulated signal to produce a desired braking deceleration for a vehicle. 
     SUMMARY OF THE INVENTION 
     A primary object of the present invention is to provide a hydraulic brake system wherein pressurized fluid is supplied to wheel brakes to effect a brake application in response to braking signals generated through an electronic control unit (ecu) which supplies a magnetic responsive valve with a pulse modulated operational signal to create a variable orifice. The creation of the variable orifice in the magnetic responsive valve restricts the flow of pressurized fluid from a source to a steering gear and increases the fluid pressure of the fluid therein from a source, a portion of the fluid with the increased fluid pressure is thereafter supplied to activate an actuator assembly and operate a master cylinder that produces pressurize fluid that is supplied to wheel brakes to effect a desired brake application. 
     In more particular detail, in the present invention of a hydraulic brake system for the vehicle, a portion of a volume of a first fluid from a first source supplied to a steering system is selectively diverted to an actuator assembly for a master cylinder as a function of the a braking operational signal developed by an ecu including a pulse width modulation signal for operating a magnetic responsive valve in the fluid circuit of the steering system. The ecu for the hydraulic brake system develops the operational braking signal from various inputs including a first input signal indicative of the flow of the first fluid in the steering circuit, a second input signal indicative of an input force applied by the operator to a brake pedal and a third input signal indicative of the movement of the wheels of the vehicle. The ecu supplies the pulse modulated operational signal to the magnetic responsive valve to restrict the flow of the first fluid to the steering by creating a variable orifice in the magnetic responsive valve. Restriction of the flow of the first fluid to the steering circuit causes an increase in the fluid pressure of the first fluid. This increase in the fluid pressure of the first fluid is communicated to the actuator assembly to develop an operational force in a second fluid that is supplied to wheel brakes to effect a brake application in response to an operator input force applied to a input member. The ecu continues to supplies a pulse modulated operational signal to the magnetic responsive valve until a desired rate of braking occurs in the vehicle corresponding to the operator input as indicated by the second input signal. In the absence of the first signal, the ecu supplies a back-up pump with an actuation signal which supplies the actuator assembly with a secondary pressurized fluid to create an operational force to effect a brake application. In the absence of the first signal and actuation of the back-up pump, the input assembly acts through a reaction assembly to pressurized fluid which is supplied to the wheel brakes to effect a brake application. 
     An advantage of this hydraulic brake system of this invention resides in the actuation of a magnetic responsive valve by a pulse modulated operational signal developed by an ecu as a function of an input force from an operator, motion or movement of a vehicle and fluid pressure developed by the restriction of flow through a variable orifice to produce an actuation force. 
     A further advantage of this brake system of this invention is by providing by a hydraulic brake system with a primarily braking circuit through the activation of a pulse modulated magnetic responsive valve to create a first operational force for a master as a function of an operator input force, movement of the vehicle, and the availability of fluid pressure from a first source, secondarily braking circuit through the activated by an electric pump to create a second operational force as a function of an operator input force, movement of the vehicle and fluid pressure developed in a fluid by the electric pump and a manual or back up circuit through wherein fluid pressure is developed by the operator input moving a piston in a reaction assembly to provide pressurized fluid to effect a brake application. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of a hydraulic brake system according to the present invention having a primarily mode of operation through actuation of a magnetic valve by a pulse modulated signal developed by an electronic control unit, a secondary mode of operation through the operation of an electric pump developed by the electronic control unit and a back-up mode of operation through manually moving a piston by an operator input to develop pressurized fluid to effect a brake application; 
     FIG. 2 is a sectional view of a magnetic valve for use in the hydraulic brake system illustrated in FIG. 1; 
     FIG. 3 is a sectional view of a reaction assembly and linkage-force sensor associated with a brake pedal for use in the hydraulic brake system illustrated in FIG. 1; 
     FIG. 4 is a partial sectional view of an actuator assembly and master cylinder for use in the hydraulic brake system illustrated in FIG. 1; and 
     FIG. 5 is a graph illustrating the operation of the brake system of FIG.  1  through the operation of the magnetic valve of FIG.  2 . 
    
    
     DETAILED DESCRIPTION 
     The brake system  10  shown in FIG. 1 is a schematic illustration of the present invention and includes a first or primary source of pressurized fluid which is developed in a pump  12  for use in a steering system  11 , a second or secondary source of pressurized fluid which is developed by electric motor  210  connected to a pump  212  for use in the brake system  10  and a back-up source of pressurized fluid which is developed through movement of pistons  60 , 62  in a reaction mechanism  50  by a manual input applied to brake pedal  26  to effect a brake application. The selected source of pressurized fluid is dependent on a plurality of inputs supplied to ecu  30  which develops an operational brake signal to either activate a magnetic responsive valve  32  located in conduit  16  or electric motor  210  connected to pump  212 . In the absence of inputs supplied to the ecu  30 , the manually activated development of pressurizing fluid by brake pedal  26  moving pistons  60 , 62  is always available to effect a brake application. 
     When a vehicle is operating, pump  12  is continually circulating fluid through conduit  16  to steering gear  18  and back to a reservoir  20 . A flow switch  34  located in conduit  16  provides ecu  30  with a first signal that indicates that the first source of pressurizing fluid is flowing in conduit  16 . 
     A magnetic responsive solenoid valve  32  of a type disclosed n U.S. Pat. No. 4,765,587 and illustrated in FIG. 2 is located in conduit  16 . Valve  32  has an inlet port  36  separated from an outlet port  38  by an annular seat  40  and an adjustable plunger or poppet assembly  42  connected with armature  44  which responds to the electrical energy or current supplied to coil  46 . Coil  46  is connected to receive an operating signal from the ecu  30 . Coil  46  is normally inactivated such that fluid freely flows through valve  32  from pump  12  to steering gear  18 . 
     A check valve  49  is located in conduit  16  down steam from the solenoid valve  32  such that when the steering gear  18  is operated, any change in the pressure of the fluid during the operation of the steering gear  18  is not communicated through conduit  24  which connects conduit  16  to the actuator assembly  400  of the brake system  10 . 
     The brake system  10  is responsive to input applied to brake pedal  26 . Pedal  26  is connected by linkage  54  to a reaction assembly  50 . The linkage  54  includes an adjustable push rod  56  that is connected to a central pivot pin  61  on arm  58 . Arm  58  provides a linear input for moving pistons  60  and  62  respectively located in bores  64  and  66  of housings  68 , 68 ′ of the reaction assembly  50 . Piston  60  separates bore  64  into a reaction chamber  65  and a reservoir chamber  67  while piston  62  separates bore  66  into a reaction chamber  65 ′ and reservoir chamber  67 ′. Piston  60  has a passage  61  with an orifice  63  located therein to connected reaction chamber  65  with reservoir chamber  67  while piston  62  has a passage  61 ′ with an orifice  63 ′ located therein to connected reaction chamber  65 ′ with reservoir chamber  67 ′. Housing  68  includes a first reservoir  75  which is connected to reservoir chamber  67  through first compensation port  77  while housing  68 ′ includes a second reservoir  75 ′ which is connected to reservoir chamber  67 ′ through a second compensation port  77 ′. Communication between reservoir  75  and reservoir chamber  67  is controlled by a first tilt valve  79  which is located in the first compensation port  77 . Similarly, communication between reservoir  75 ′ and reservoir chamber  67 ′ is controlled by a second tilt valve  79 ′ which located in the second compensation port  77 ′. In the rest position as shown, piston  60  engages stem  81  of tilt valve  79  to provide a flow path from reservoir  75  to a first chamber  512  in master cylinder  500  by way of conduit  23  while piston  62  engages stem  81 ′ of tilt valve  79 ′ to provide a flow path from reservoir  75 ′ to a second chamber  514  in master cylinder  500  by conduit  23 ′. Linkage  54  also includes a force sensor  52 , which receives any input force applied to pedal  26 . Force sensor  52  supplies ecu  30  with a signal indicative of the force associated with the desired braking application. 
     Piston  60  and piston  62  are identical with reaction chamber  65  being connected by conduit  85  to a first set of wheel brakes  80  and reaction chamber  65 ′ being connected by conduit  87  to a second set of wheel brakes  82  in the brake system  10 . Communication between chamber  65  and the first set of wheel brakes  80  is controlled by a first shuttle valve  180  while communication between chamber  65 ′ and the second set of wheel brakes is controlled by a second shuttle valve  180 ′. 
     The first shuttle valve  180  which is located in conduit  85  between the master cylinder  500  and the first set of wheel brakes  80  directs fluid to and from chamber  65  of the reaction assembly  50  as a function of operating conditions present in the brake system at any particular time. The first shuttle valve  180  components of which are not shown includes a piston which is positioned in a bore by a spring such that fluid is freely communicated between chamber  512  of the master cylinder  500 , the first set of wheel brakes  80  and chamber  65  in a rest position, as illustrated in FIG.  1  and when pressurized fluid is developed in chamber  512  through movement of piston  504  to effect a brake application. Shuttle valve  180  is designed to operate and prevent communication to chamber  512  of the master cylinder  500  when the fluid pressure in chamber  65  is greater than the pressure of the fluid in chamber  512 . In this condition, the piston moves against spring to close communication between the bore therein and direct the fluid pressure from chamber  65  to operated the first set of wheel brakes  80 . 
     A second shuttle valve  180 ′ is located in conduit  87  between the master cylinder  500  and the second set of wheel brakes  82  to direct fluid to and from chamber  65 ′ of the reaction assembly  50  as a function of operating conditions present in the brake system at any particular time. The second shuttle valve  180 ′ in identical to the first shuttle valve  180  and also includes a piston which is positioned in a bore by a spring such that fluid is freely communicated between chamber  514  of the master cylinder  500 , the second set of wheel brakes  82  and chamber  65 ′ in a rest position as illustrated in FIG.  1  and when pressurized fluid is developed in chamber  514  through movement of piston  506  to effect a brake application. Shuttle valve  180 ′ is designed to operate and to prevent communication to chamber  514  of the master cylinder  500  when the fluid pressure in chamber  65 ′ is greater than the pressure of the fluid in chamber  514 . In this condition, piston moves against spring to close communication between bore therein and chamber  514  such that the fluid pressure is directed from chamber  65 ′ to operated the second set of wheel brakes  82 . 
     The first and second set of wheel brakes  80  and  82  each have wheel speed sensors  84 , 86  which function to provide the ecu  30  with a signal indicative of the speed or rotative movement of an individual wheel of the vehicle at any given period of time. The wheel speed sensors  84 , 86  are generally associated with an anti-lock brake function for a vehicle but in this brake system the output is used to provide an indication of the speed and/or rate of deceleration of an individual wheel during a brake application. 
     The master cylinder  500  for brake system  10  is remotely located with respect to brake pedal  26  and is operated by an input force supplied by actuator assembly  400 . The actuation of the actuator assembly  400  by achieved by a change in the fluid pressure of the fluid supplied by pump  12  to the steering system  11 . Actuator assembly  400  has a housing  402  with a bore  404  therein. Bore  404  has a first port  406  connected to supply conduit  16  of pump  12  by conduit  24 , a second port  408  connected to an outlet of pump  212  by passage  407  to conduit  208 , a third port  410  connected to reservoir  20  by return conduit  25  and a fourth port  412  connected by conduit  214  to an inlet of pump  212 . A piston  414  separates the interior of bore  404  into an actuation chamber  416  and a reservoir chamber  418 . Seal  420  located in groove  422  of piston  414  prevents communication from actuation chamber  416  to reservoir chamber  418  while bearing seal  421  surrounding shaft  424  of piston  414  prevents communication of fluid from reservoir chamber  418  to bore  502  associated with master cylinder  500 . It being understood that steering fluid associated with pump  12  has different properties than the brake fluid associated with the brake system  10  and it is desirable to prevent mixture of such fluids. In order to assure such mixture is avoided, a passage  403  is provided in housing  402  to allow communication of fluid to the surrounding area rather than into bores  404  and  502  should leakage occur through the seals associated with actuator assembly  400  or master cylinder  500 . 
     A check valve  430  associated with the second port  408  is located down stream from the communication tee  409  for conduit  208  of pump  212 . Check valve  430  includes a ball  432  that is urged against seat  434  by a spring  436 . Spring  436  has a high value and is designed to prevent damage to the actuator assembly  400  should the fluid pressure developed by pump  212  exceed a predetermined valve but will always main seated when fluid pressure is provided to actuator assembly  400  by the pump  12  of the steering system. Check valve  430  is also connected to reservoir  20  by way of conduit  214  of the inlet of pump  212  to define a closed circuit. 
     Check valve  48  is an off-on solenoid valve and in conduit  24  at a position adjacent inlet port  406 . Solenoid valve  48  is designed to receive an operational signal from ecu  30 . As long as a first signal is supplied to ecu  30  by switch  34  indicating fluid flow in conduit, solenoid valve remains in the off position, however in the absence of flow in conduit  16 , ecu  30  supplies solenoid valve  48  with a signal to move to an on position to block fluid communication from chamber  416  to conduit  24 . 
     The master cylinder  500  is conventional in that first and second pistons  504 ,  506  are located in bore  502  of housing  499  by spring  508  and  510  to define a first chamber  512  and a second chamber  514 . The first chamber  512  is connected to the first wheel brakes  80  and chamber  65  by conduit  85  while the second chamber  514  is connected to the second wheel brakes  82  and chamber  65 ′ by conduit  87 . Springs  508  and  510  act on the first piston  504  to urges the second piston  506  into a rest position where the second piston  506  engages and urges piston  414  of the actuator assembly  400  into engagement with housing  402  to define a rest position and size for actuation chamber  416 . In the rest position, chamber  512  is also connected reservoir  75  by way of conduit  23  and chamber  67  while chamber  514  is connected to reservoir  75 ′ by way of conduit  23 ′ and chamber  67 ′. In the rest position, the first and second set of wheel brakes  80  and  82  are also connected to reservoirs  75 , 75 ′ such that any fluid displaced during a brake application can be replaced on the termination of an input force on brake pedal  26 . 
     Mode of Operation 
     When an operator desires to effect a brake application an input force is applied to pedal  26 . Sensor  52  is responsive to the input force and communicates a corresponding input signal to the ecu  30 . If pump  12  is operating, flow switch  34  supplies the ecu  30  with an operational signal indicating that fluid having a predetermined fluid pressure is circulating in the steering system  11  and a portion thereof is available for use in the operation of the brake system  10 . Further, wheel speed sensors  84 , 86  providing the ecu  30  with signals to indicate movement of the vehicle at any given time period. The ecu  30  evaluates various input signals including the input signal from the switch  34  indicating the flow of fluid from pump  12 , movement of the vehicle by wheel speed sensors  84 , 86  and the intensity of the input force on brake pedal  26  as sensed by force sensor  52  to develop a corresponding operational braking signal which includes a pulse width modulation signal for activating coil  46  in solenoid valve  32 . The pulse width modulation signal causes armature  44  to oscillate within a magnetic field developed in coil  46 . Plunger  42  is connected to armature  44  and as a result face  41  moves toward and away from seat  40  to define a variable orifice which restricts the flow of fluid between the inlet port  36  and outlet port  38  to cause a resulting increase in the fluid pressure at the inlet port  36 . This increase in fluid pressure is freely communicated to actuation chamber  416  of actuator assembly  400  by way of conduit  24  since off-on valve  440  is in an off state in the absence of a signal from the ecu  30 . The fluid pressure presented to chamber  416  acts on piston  414  and provides an operational force which moves pistons  506 , 504  within the master cylinder  500  to produce pressurized fluid which is supplied to the first  80  and second  82  set of wheel brakes to effect a brake application. 
     The pressurized fluid developed in master cylinder  500  is simultaneously supplied to the wheel brakes  80 , 82  and reaction chambers  65 , 65 ′ of the reaction assembly  50 . The pressurized fluid acts on pistons  60  and  62  to oppose the input force applied by the operator to push rod  56  by brake pedal  26 . The pressurized fluid acts on pistons  60  and  62  to develop a reaction force which eventually nullifies the input force applied to brake pedal  26  to initiate a brake application. The reaction force is received by sensor  52  and continually up dates the input signal communicated to the ecu  30  such that a pulse width modulation signal supplied to coil  46  of solenoid valve  32  is continually changed to reflect the current braking operation. When the desired rate of braking of the vehicle is achieved, as indicated by sensor  52 , the pulse width modulation signal from the ecu  30  to coil  46  is terminated and plunger  42  returns to a rest position to allow free flow from the inlet port  36  to the outlet port  38  of valve  32 . 
     FIG. 5 illustrates a trace  700  produced in the development of a brake application using the above-described structural components. As can be seen braking is achieved in a uniform and smooth manner to bring a vehicle to a stop. 
     When the fluid pressure in conduit  24  returns to the fluid pressure of pump  12 , return springs  508  and  510  act on and move pistons  504  and  506  to a rest position as defined by the engagement of face  405  on piston  414  with wall  401  of housing  402  as piston  506  forms a solid link with shaft  424  of piston  414 . As cup seal  503  on piston  504  moves past port  505  and cup seal  507  on piston  506  moves past port  509  of housing  499 , compensatory fluid present in reservoirs  75 , 75 ′ is available, if necessary, for insertion in the brake system  10  by way of conduits  23 , 23 ′. 
     If the ecu  30  receives an input signal from force sensor  52  indicating a desired a brake application but no input signal is presented from flow switch  34 , the ecu develops a secondary braking signal based on inputs from force sensor  52  and the wheel speed sensors  84 , 86 . This secondary braking signal includes a first signal that is initially sent to on-off switch  48  to activate and move a plunger of a solenoid to interrupt flow communication from conduit  24  to port  406  and a second signal which is thereafter supplied to activates motor  210  connected to pump  212 . Pump  212  draws fluid from reservoir  20  by way of conduit  25 , chamber  418  and conduit  214  and supplies conduit  208  with pressurized fluid which is communicated to chamber  416  by way of passage  407  connected to inlet port  408 . This pressurized fluid acts on piston  414  to provide a force which moves pistons  504  and  506  in master cylinder to pressurized fluid which is supplied to the wheel brakes to effect a brake application. This pressurized fluid is communicated through conduits  85 , 87  to reaction chambers  65 , 65 ′ to act on pistons  60  and  62  and oppose the input force applied to sensor  52  by brake pedal  26 . The sensor  52  communicates a current input signal to the ecu  30  which modifies the secondary operational signal to motor  210  and either continues to operated motor  210  or terminates the operation thereof depending on a desired rate of braking of the vehicle. When the desired braking is achieved, the input signal from sensor  52  to the ecu  30  terminates and the ecu  30  correspondingly terminates the secondary operational signal to motor  210  and to check valve  48  to open communication between chamber  416  and reservoir  20  by way conduit  25 . As the fluid pressure in chamber  416  decreases to the pressure of the fluid in reservoir  20 , return springs  508  and  510  in the master cylinder  500  act on pistons  504  and  506  to move to a rest position as defined by the engagement of face  405  on piston  414  with wall  401  of housing  402 . As cup seal  503  on piston  504  moves past port  505  and cup seal  507  on piston  506  moves past port  509  of housing  499 , compensatory fluid present in reservoirs  75 , 75 ′ is available through conduits  23 , 23 ′, if necessary, to add fluid to the brake system  10 . 
     If an operator desires to make a brake application and neither an input signal from relay switch  34  nor a force signal from sensor  52  is supplied to the ecu  30 , a manual brake application is achieved in the following manner. The input force applied to brake pedal  26 , after overcoming return springs  160 ,  162 , respectively moves pistons  60  and  62  in bores  64  and  66  to close tilt valves  79 , 79 ′ from reservoirs  75 , 75 ′ to chambers  67 , 67 . Thereafter, further movement of pistons  60 ,  62  pressurizes fluid in reaction chambers  65 , 65 ′ which after passing through shuttle valves  180 , 180 ′ is directly supplied the first set of wheel brakes  80  and second set of wheel brakes  82  to effect a brake application. While the level of the fluid pressure manually developed is less than through the actuation of either solenoid valve  32  in the primary circuit or pump  212  in the secondary circuit by the ecu  30 , it does provide an emergency braking for a vehicle.