AU8102287A

AU8102287A - Anti-lock braking system with failure detection and pressure recovery

Info

Publication number: AU8102287A
Application number: AU81022/87A
Authority: AU
Inventors: G. Emerson Brown; Richard Troy Hendrickson
Original assignee: Allied Corp
Current assignee: Allied Corp
Priority date: 1986-10-14
Filing date: 1987-09-24
Publication date: 1988-05-06
Also published as: ES2005393A6; WO1988002710A1

Description

ANTI-LOCK BRAKING SYSTEM WITH FAILURE DETECTION AND PRESSURE RECOVERY

BACKGROUND OF THE INVENTION The present invention relates to anti-lock braking systems and in particular to such a braking sys¬ tem which includes means for sensing and identifying specific failure modes and utilizing pressurized hydrau- lie fluid from a power booster to improve vehicle braking under specific failure conditions.

Anti-lock braking systems are now well known. In such braking systems, hereinafter denominated ABS, the rotational behavior of the vehicles wheels is monitored during braking. When it is determined that the wheels are approaching a lock or excessive slip condition, the ABS automatically interrupts operator control of the brakes and automatically modulates brake pressure applied to the vehicles wheel cylinders to provide maximum braking without skid or loss of control. Control con¬ tinues until the vehicle has stopped, reached a pre¬ determined minimum speed, or the imminent wheel-lock condition terminates.

In one such type of ABS, the braking system is powered by a closed center hydraulic booster which in¬ cludes a master cylinder having primary and secondary chambers and a power or booster section which includes a fluid reservoir and a control valve supplied with high pressure fluid from an accumulator and pump. Under nor- mal braking, pressurized fluid is modulated to the boost¬ er chamber of the master cylinder. This pressure in turn applies pnwer assist pressure to the primary and second¬ ary pistons. Under ABS operation, the primary and sec¬ ondary pistons are isolated from the wheel cylinders and pressurized braking fluid is applied from the booster, pump, and accumulator to the wheel cylinders by an ABS control through the medium of modulating means which may comprise a plurality of solenoid actuated valves or multi¬ function valves such as disclosed in commonly assigned co-pending United States Patent Application Serial Nos. 789,203 and 789,202. In prior art ABS, it is known to provide redun¬ dancy of components, and a variety of sensors in the braking system to monitor operation thereof. In the event that a system failure is detected, ABS operation is typically terminated- and the system returned to a manual or manually controlled power boost operation.

In accordance with the present invention, the normally closed build valves of the ABS modulating means are energized upon the sensing of specific failures. These valves are connected directly to the boost pressure output of the hydraulic booster. This applies pressur¬ ized braking fluid to the normally closed isolation valve of the modulating means which, because of its physical structure, permits manually modulated pressurized braking fluid to pass therethrough to the wheel cylinder. This produces a system that.provides a flow of pressurized braking fluid to the wheel cylinders to maintain at least partial power boosted braking in the specific failure modes.

It is therefore an object of the invention to provide an improved an anti-lock braking system.

It is another object of the invention to provide such a system which exhibits improved braking performance when the system experiences specific failure modes.

Yet another object of the invention is to pro- vide such a system in which normally closed build valves are energized on the sensing of specific failure modes to enable the application of a flow of pressurized braking fluid to the vehicle's brakes.

Still another object of the invention is to provide such an improved anti-lock braking system wherein energization of normally closed build valves upon sensing of specific failure modes will provide continued partial system performance and, in some cases, alleviation of the failure.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of the invention itself will be best understood in view of the following specification taken in conjunction with the appended drawings:

Figure 1 is a schematic diagram of the anti-lock braking system in accordance with the present invention; and

Figure 2 is a simplified sectional drawing use¬ ful in explaining operation of the flow through valve arrangement. DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, there is shown in Figure 1 a functional block diagram of an adaptive braking system for use in a motor vehicle such as an automobile. The system comprises a dual cylinder, hydraulically boosted displacement type master cylinder 10 having primary and secondary cylinders 12, 14, activated by pressurized fluid in booster chamber 16. The pres¬ surized fluid in booster chamber 16 is modulated by means such as a foot pedal 18 and pressure control valve 20. Pressurized fluid for the system is supplied from a motor driven pump 22 and accumulator 24 through hydraulic line 26. Fluid is provided to the pump 22 and master cylinder 10 from a fluid reservoir 28. Fluid passed through the system is returned to the reservoir by conduits such as ^3π-

Hydraulic fluid is also communicated from the reservoir 28 to cylinders 12, 14 through fluid lines 32, 34, and blocking valves 36, 38. A primary hydraulic circuit is connected to cylinder 12 and includes a modu- lating valve means 50 connected to one or more wheel brake cylinders 52. The modulating valve means, de¬ scribed in more detail below, may comprise a plurality of solenoid actuated valves such as disclosed in co-pending United States Patent Application Serial No. 789,203, or by a multiple function device such as disclosed in co- pending United States Patent Application Serial- No. 789,202, both commonly assigned to the assignee of the present invention.

Similarly, a secondary brake circuit II includes modulating valve means 56 connected to wheel brake cyl¬ inders 60. The rotational behavior of the wheels is sensed via now well known magnetic sensing devices as at 58. This information is applied to a micro-processor based ABS control 90 wherein signals generated by the sensors 50 indicative of the behavior of the wheels during braking is analyzed and control signals are gener- ated by ABS control 90. These signals control modulating means 50, 56 to automatically control the application of braking pressure when it is determined that the wheels are in an incipient lock or skid condition. Operation of anti-lock braking systems are now well known in the art, one such system being more fully described in my commonly assigned co-pending United States Patent Application Serial No. 903.333 filed September 3_ 198S

Also provided in the ABS are a plurality of switches responsive to operating parameters of the braking system. These include: a fluid level switch 60 operable by means such as a float disposed in the reser¬ voir 28 to sense the level of brake fluid in the reser¬ voir; a differential pressure switch 62 connected between primary master cylinder 12 and boost pressure chamber 16 to respond to a predetermined differential pressure there¬ between; a secondary differential pressure switch 64 con¬ nected between primary cylinder 12 and secondary cylinder 14; and a low pressure switch 66 responsive to a pre¬ determined ^"minimum output pressure from hydraulic pump 22 and accumulator 24.

The switches themselves may be of any form well known in the art and the outputs thereof are also applied to the ABS control 90 the connections not being shown in the drawings for clarity. The control 90 is provided with appropriate software to monitor the operating state of the switches 60, 62, 64, and 66 and to generate appro- priate output signals at output terminals such as 94 in response to the logical combination of the possible operating states of the switches. Operation of this circuitry is more fully described in my co-pending United

States Patent Application Serial No. 903,333 , filed September 3, 198& and commonly assigned with the present invention.

Referring now to Figure 2, there is shown in sim¬ plified form, a cross-sectional view of a modulating means suitable for use in the invention. Modulating means 50 comprises a valve body 52 which incorporates three valve assemblies 100, 102, and 104. Valve assembly 100 is a three-way isolation valve, and assemblies 102, 104 are two-way, normally closed valves which effect control of build and decay of hydraulic pressure, respectively. Assembly 100 includes an inlet port 106 normally in open communication with an outlet port 108 and fluidly connected to master cylinde Ir 10 and a wheel cylinder 60, respectively. A valve element such as a ball valve 110 normally closes a valve seat 112 which communicates with fluid inlet and outlet ports 114, 116. Valve element 110 can be operated by means such as a solenoid 118 to close inlet port 106 and provide fluid communication between inlet and outlet ports 114, 116, and wheel cylinder port 108. The build valve assembly includes an inlet port

120 connected to the boost pressure chamber 16 and an out- . let port 122 in fluid communication with fluid port 114 of the isolation valve assembly 100. The ball valve ele¬ ment 124 normally closes fluid communication between in- let and outlet ports 120, 122 and is operable in response to means such as solenoid 126 to open the valve and to provide fluid communication between the ports 120, 122. Decay valve assembly 104 includes an inlet port 128 and an outlet port 130 connected to the isolation valve assembly outlet port 116 and the reservoir 28, respectively. Assembly 104 includes a ball valve element 132 normally closing communication between ports 128, 130 and operable in response to a solenoid 134 to open the valve and provide communication between the ports 128, 130. It will be seen that the valve assembly can provide the functions of isolation and control of build and decay of fluid pressure to a wheel cylinder in response to operation of solenoids 118, 126, and 134.

Under normal operating conditions, the switches 60 through 64 will be in non-operated states indicating a normal and functional braking system. This will be true both during normal braking and when the system is oper¬ ating in anti-lock mode. With the switches arranged as shown, differential pressure switch 64 will operate in the event that there is a loss of pressure in the second¬ ary brake circuit supplied by cylinder 14 (this assumes that the fluid level switch 60 and low pressure switch 66 have not operated). This loss of pressure can be the result of a leak in the secondary brake circuit or due to the presence of gas in the secondary brake circuit.

In a similar manner, operation of differential pressure switches 62 and 64 will provide an indication of a loss of primary hydraulic circuit pressure, again due to a leak or the presence of gas in the primary braking circuit. Operation of differential pressure switch 62 alone (and again assuming that the low pressure switch 66 - or low fluid level switch 60 have not operated) will indi¬ cate the loss of pressure in both the primary and second¬ ary circuits due to leaks or the presence of gas.

Heretofore, under such circumstances, it has been normal practice to provide an indication of brake system failure and to terminate operation of the anti¬ lock braking system. However, due to the nature of a hydraulically boosted system which includes a pump and an accumulator, there exists a substantial fluid reserve within the braking system. It is therefore recognized that if a sensed loss of pressure is a result of ^"gas in the system the associated displacement loss can be over- come by the introduction of sufficient pressurized fluid, such as exists in the fluid reserve. This fluid will compress the gas and permit braking; and upon release of the brake will circulate "gassed" fluid back to the res¬ ervoir, effectively bleeding the system and eliminating much of the gas. Accordingly, in accordance with the invention, in the event that a failure in the primary or secondary circuits should occur as indicated by operation of one, the other, or both of the differential pressure switches, the ABS control 90 will generate a control signal to energize the build valves of the modulating means 50 and/or 56. It will further be seen that the isolation valve, because of its physical configuration, will permit a flow of hydraulic fluid through the build valve and through- the isolation valve to the wheel cyl- inders even when the isolation valve is in its normal, non-operated state. Thus, this control function will effectively utilize the booster and its reserve source to apply pressurized brake fluid to the wheel cylinders. Under these circumstances, if the failure is a result of a loss of pressure in the primary system, the system will still provide powered secondary brakes. If the pressure failure is in the secondary system, powered primary braking will continue. In the event that both the front and rear systems have failed, the booster will continue to provide braking power to assist in stopping the ve¬ hicle until such time as the consumable supply of reserve braking fluid has been exhausted. In the event that the pressure failure is a result of gas in the system, it may be anticipated that much of the gas will simply be. elimi- nated from the system and normal operation^' of the braking system will be restored. Upon ultimate loss of fluid in the system, as a result of leaks, operation of the low pressure switch 66 or the low reservoir level switch 60 will occur. Under these circumstances, operation of the ABS will be terminated and the system will operate in a manual state only with manual braking being available in either the primary or secondary circuits -assuming that a dual failure has not occurred.

From the above description, it will now be seen that utilization of the build valves and booster source by means of energization of the build valves of the braking system ih the event of specific detected failures ill improve operation of the braking system in these spe¬ cific failure modes by continuing to provide the avail¬ ability of power boosted braking through the nonaffected hydraulic circuit. This mode of operation further effects the alleviation of the failure in the event that the fail¬ ure is a result of gas within one or both of the hydraulic circuits. This operation will normally continue for a sufficient period of time to enable safe stopping of the vehicle arid does not other-wise effect ultimate operation of the system as a dual circuit powered. or manual braking system.

Furthermore, it is contemplated that one skilled in the art could make many modifications and/or changes to the invention as described herein without deviation from the essence thereof. As such these modifications and/or changes are intended to fall within the scope of the appended claims.

Claims

What I Claim Is :

1. In an anti-lock braking system which in¬ cludes a master cylinder having a hydraulic booster con¬ nected to a source of pressurized braking fluid, at least one hydraulic circuit including a wheel cylinder con- nected to said master cylinder and operable to brake the wheels of a vehicle, anti-lock braking means including means for sensing the rotational behavior of said wheel and a computing circuit connected to receive signals from said sensing means and for generating control signals to control a modulating valve means for controlling braking of said wheels in response to an incipient lock con¬ dition, the improvement comprising: an isolation valve normally connecting said master cylinder to said wheel cylinder and operable to isolate said master cylinder from said wheel cylinder and to connect said wheel cylinder to said booster and a re¬ servoir through normally closed build and decay valves, respectively, pressure sensing means for sensing a loss^' of pressure in said hydraulic circuit, said computing circuit being connected to said pressure sensing means and being responsive to said loss of pressure to energize said build valve and apply boost pressure to said isola¬ tion valve, said isolation valve being responsive thereto to apply boost pressure to said wheel cylinder.

2. The system of claim 1 wherein said braking system includes two hydraulic circuits, said pressure sensing means including a first differential switch oper¬ able in response to a predetermined differential pressure between said hydraulic circuits and a second differential pressure switch operable in response to a predetermined differential pressure between one of said hydraulic cir¬ cuits and said booster.

3. The system of Claim 2 wherein said computing circuit generates a signal to energize the build valve in said secondary circuit in response to operation of said second differential pressure switch.

4. The system of Claim 2 wherein said computing circuit generates a signal to energize said boost valves in said primary hydraulic circuit in response to oper¬ ation of said primary and said secondary pressure switches.

5. The system of Claim 2 wherein said computing circuit generates a signal to energize all of the build valves of said system in response to operation of said secondary differential pressure switch and in response to simultaneous operation of said first and said second dif- ferential pressure switches.

6. The system of claim 2 further.including means for sensing a low pressure condition of said booster and means for sensing a low fluid.level in said reservoir, said computing circuit being responsive to operation of said low pressure and responsive to oper¬ ation of said low fluid switches to inhibit operation of said build and said decay valves.