Abstract:
Noise produced during a supplemental brake apply is reduced eliminated by reducing the quantity of additional brake fluid supplied to the pump during the apply. The prime valve is opened only at the initiation of the supplemental apply to supply a predetermined small quantity of brake fluid to the accumulator and pump inlet and is then closed for the remainder of the apply. The quantity of extra fluid supplied can be retained by the accumulator and does not need to by blown off back to the master cylinder. The apply valve of the non-regulated wheel brake is controlled to regulate pressure to the regulated wheel brake through the apply valve thereof, which is left open while the release valve of the regulated wheel brake is left closed. The release valve of the non-regulated wheel is controlled to maintain a lower pressure at the non-regulated wheel, preferably equal to the master cylinder pressure whenever possible, while permitting fluid flow back to the accumulator. The more even flow of this arrangement through the circuit permits operation with the smaller quantity of extra brake fluid. The reduction in blow-off events reduces objectionable noise produced by the blow-off valve when the vehicle operator initiates manual brake apply during a supplemental apply.

Description:
TECHNICAL FIELD  
         [0001]    The technical field of this invention is vehicle brake control.  
         BACKGROUND OF THE INVENTION  
         [0002]    Many vehicle brake systems include supplemental apply capability, wherein one or more wheel brakes may be applied by the brake control without initiation by the vehicle operator. An example of such a system includes a brake control with a vehicle stability enhancement (VSE) system, in which a selected wheel brake of the system may be applied to counter an undesired vehicle yawing motion in closed loop control of vehicle yaw rate. Such a system may include an electric motor driven pump for providing braking fluid pressure to the selected wheel and a normally open isolation valve between the master cylinder and the individual brake apply valves that is closed during a supplemental apply to permit braking pressure at the brake apply valves, and thus at the selected brake, to exceed master cylinder pressure as required for the supplemental apply. Such a system further has a normally closed prime valve that is open during the supplemental apply to permit fluid to be supplied as required to the pump inlet from the master cylinder. A blow-off capability is provided at a predetermined high pressure, preferably in the isolation valve but alternatively or additionally in a separate blow-off valve, the blow-off action of the valve being provided when fluid pressure overcomes an electromagnetic force created by an electric current in a coil applied to close the movable valve element and the electric current preferably being controlled by the system controller to establish the predetermined blow-off pressure. The blow-off capability permits excess fluid to escape back to the master cylinder when the pressure of the fluid provided by the pump to the apply valves exceeds the predetermined blow-off pressure. The brake apply and release valves for the regulated wheel brake are operated to regulate the pressure of pump supplied fluid to the regulated wheel brake. Two parallel fluid circulation paths are established through the pump, one through the brake apply and release valves of the regulated wheel brake and another through the isolation or blow-off valve and master cylinder. Each of these circulation paths includes a fluid reservoir open to the pump inlet: an accumulator in the one path through the apply and release valves and the master cylinder itself in the other path supplementing the capacity of the accumulator. Blow-off action, with its undesirable noise, can be common during a supplemental apply, since the pump normally maintains pressure in the brake lines to the apply valves at a high pressure just under the blow-off pressure and a significant amount of fluid, entering the pump from the master cylinder through the opened prime valve, must be returned to the master cylinder.  
           [0003]    If the vehicle operator manually applies the brakes during a supplemental brake apply, pressure in the master cylinder and the brake lines between the master cylinder and the isolation valve is raised. The blow-off action of the isolation or blow-off valve tends to produce audible noise as the moving valve element slams back against the seat after each pulsed release of fluid; and this noise is more easily transmitted to the passenger compartment when the pressure in the master cylinder is high. The noise can be objectionable to vehicle occupants and can occur as long as the brake pedal is depressed during a supplemental brake apply. A reduction in this noise would provide more transparent operation of the supplemental brake apply and greater operator satisfaction with the vehicle in which the brake system is installed.  
         SUMMARY OF THE INVENTION  
         [0004]    In this invention, the noise produced during a supplemental brake apply is reduced, and possibly eliminated, by reducing the necessity for blow-off of excess brake fluid back to the master cylinder. This is accomplished with no change to the basic fluid conduction apparatus of the brake system (except for the addition of a pressure sensor to measure master cylinder pressure, if it is not already present), by changing the way in which the valves of the apparatus are controlled. Although the prime valve is opened at the beginning of a supplemental apply, it is closed after a predetermined quantity of brake fluid is provided to an accumulator connected to the pump inlet, for example by keeping the prime valve open only for a predetermined time period. This quantity of fluid is sufficient to ensure fill of the brake lines and at least partial fill of the accumulator but is preferably sufficiently small so that all excess fluid likely to be required during a supplemental brake apply can be retained in the accumulator. When the quantity of fluid has been provided, the prime valve is closed and preferably remains closed for the duration of the supplemental apply.  
           [0005]    The method of this invention can operate with a smaller quantity of excess fluid because of the way in which the apply and release valves are operated. With the prime valve closed, a fluid pressure in the master cylinder is sensed, a first wheel brake apply valve is maintained in an open condition and a first wheel brake release valve is maintained in a closed condition. The first wheel brake apply and release valves are those connecting the pump pressure output to the first (regulated) wheel brake of a pair of wheel brakes such as one half of a diagonal split braking system; but, unlike the prior art, these first apply and release valves are not used for regulation of the first wheel brake. Instead, a second wheel brake apply valve, connecting the pump pressure output to the second (non-regulated) wheel brake of the pair and connected on the pump side to the first wheel brake apply valve, is controlled to regulate fluid pressure from the fluid source so as to provide a predetermined regulated fluid pressure to the second wheel brake apply valve and, by the back pressure produced, through the open first wheel brake apply valve to the first wheel brake. A second wheel brake release valve is controlled to maintain the second wheel brake at the sensed fluid pressure in the master cylinder, which pressure will be lower than the predetermined regulated fluid pressure as long as the vehicle operator does not activate the brakes manually to increase the master cylinder pressure above the predetermined regulated pressure.  
           [0006]    In this method, there is no brake fluid circulation through the first brake apply valve of the regulated wheel brake to the accumulator or pump, although the first brake apply valve is fully open, since such circulation is blocked by the closed first brake release valve. And, after the prime valve is closed, there is rarely, if ever, fluid flow through the parallel fluid circulation path of the prior art via the blow-off valve. Essentially, a single fluid circulation path for the pump is established through the second brake apply and release valves of the second (non-regulated) wheel brake and the accumulator. This method provides regulation of the first wheel brake with a more even fluid circulation and thus less need for additional fluid from the accumulator and/or master cylinder. The quantity of excess fluid required is sufficiently small to be stored in the accumulator, and this permits the closure of the prime valve after it has been provided. In addition, brake fluid in the brake lines between the fluid pump and the first and second brake apply valves is maintained at the regulated pressure, which is generally significantly lower, and thus further below the blow-off pressure, than the pressure in these lines using the prior art method. There is thus essentially no need in a supplemental brake apply for blow-off action to release excess fluid to the master cylinder, and objectionable noise is greatly reduced. As an additional benefit, the maintenance of brake pressure at the non-regulated wheel in response to a master cylinder pressure sensor results in at least some braking by the second wheel brake when the vehicle operator manually activates the brakes via the brake pedal and master cylinder during a supplemental brake apply, whereas in the prior art method the second wheel brake apply valve is maintained closed during a supplemental brake apply and the second wheel brake is thus not used. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0008]    [0008]FIG. 1 is a schematic diagram of a brake valve apparatus of the prior art.  
         [0009]    [0009]FIG. 2 is a flow chart illustrating the method of the prior art.  
         [0010]    [0010]FIG. 3 is a schematic diagram of a brake valve apparatus for the method of this invention.  
         [0011]    [0011]FIG. 4 is a flow chart illustrating the method of this invention.  
         [0012]    [0012]FIG. 5 is a block diagram of apparatus providing control of brake pressure at a wheel brake responsive to sensed master cylinder pressure. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    [0013]FIG. 1 shows a brake apparatus including a master cylinder  20  and wheel brakes  22  and  24 . Wheel brakes  22  and  24  are typically diagonally opposed wheel brakes forming one half of a split diagonal vehicle braking system. It is understood that the other two diagonally opposed wheel brakes, not shown, will have a similar control apparatus that is a duplicate of that described herein. Because this description will be describing the regulation of brake fluid pressure to one of wheel brakes  22  and  24 , the wheel brakes are labelled regulated wheel brake  22  and non-regulated wheel brake  24 ; but each of wheel brakes  22  and  24  are equally capable of being regulated as described. Both the brake valve apparatus itself, as shown in FIG. 1, and the description of its operation with reference to FIG. 1 are known in the prior art but are produced here as context for the description of this invention with reference to FIGS.  3 - 5 .  
         [0014]    Master cylinder  20  is connected through a normally open isolation valve  26  and a normally open apply valve  28  in series to regulated wheel brake  22  and is also connected through isolation valve  26  and a normally open apply valve  30  to non-regulated wheel brake  24 . As stated above, non-regulated wheel brake  24  is not regulated in the particular brake apply described herein, but is capable of being regulated in a similar manner. Isolation valve  26  is an electromagnetically controlled blow-off valve having an open state allowing free communication of brake fluid pressure therethrough in either direction and a closed state, as shown, in which the valve can blow off excess brake pressure and fluid back to the master cylinder at pressures above a blow-off pressure which is electromagnetically controllable. An example of such a valve is shown in U.S. Pat. No. 6,247,766, issued Jun. 19, 2001, the disclosure of which is incorporated by reference. In its open state, isolation valve  26  provides direct communication between master cylinder  20  and apply valves  28  and  30  and thus permits base brake operation of wheel brakes  22  and  24  by master cylinder pressure, assuming apply valves  28  and  30  are also open and release valves  40  and  44 , to be described below, are closed. In its closed state, isolation valve  26  permits the brake fluid pressure at apply valves  28  and  30  to exceed the master cylinder pressure and thereby permits system generated brake pressure control of wheel brakes  22  and  24  through apply valves  28  and  30  from a positive displacement pump  32 . But the closed state is only maintained at brake fluid pressures up to a predetermined maximum or blow-off pressure (e.g. 1700 psi). Brake fluid at the apply valves greater than that predetermined maximum will overcome the electromagnetic force of the coil in the valve and permit opening of the valve to permit escape of some fluid back to the master cylinder and thus blow off the excess pressure. The predetermined maximum or blow-off pressure is maintained by providing a predetermined coil current in the valve under control of the system controller, not shown. Isolation valve  26  is bypassed by a one-way valve  34  permitting flow from master cylinder  20  around isolation valve  28  but not in the opposite direction; and each of apply valves  28  and  30  is also bypassed by a one-way valve,  36  and  38  respectively, permitting flow back toward isolation valve  26  but not toward wheel brakes  22  and  24 .  
         [0015]    Regulated wheel brake  22  is connected through normally closed release valve  40  to an accumulator  42 , and non-regulated wheel brake  24  is connected through normally closed release valve  44  to accumulator  42 . Accumulator  42  is connected through a one-way valve to the input of pump  32 , the one-way valve permitting flow only from accumulator  42  toward pump  32 . The pressure output of pump  32  is connected through a damper  48  and orifice  50  in series to the line  51  connecting isolation valve  26  to apply valves  28  and  30 . Pump  32  is electrical motor driven and may be controllably activated to supply brake fluid pressure to the line connecting isolation valve  26  to apply valves  28  and  30  for system generated supplemental brake applies with isolation valve  26  closed. A normally closed prime valve  52  connects master cylinder  20  directly to the inlet of pump  32  and may be opened to allow pump  32  to draw additional fluid from master cylinder  20  as required.  
         [0016]    The operation of this apparatus according to the methods of the prior art will now be described with reference to the flow chart of FIG. 2. When a supplemental brake apply is commanded for the regulated wheel brake  22 , for example in response to a vehicle stability enhancement (VSE) system to counteract an undesired yaw moment, at step  60  the non-regulated apply valve  30  is closed and the non-regulated release valve  44  is opened to prevent actuation of non-regulated wheel brake  24 . Prime valve  52  is opened to supply brake fluid from master cylinder  20  to the inlet of pump  32 , and isolation valve  26  is closed to permit pump generated braking pressure in line  51  greater than master cylinder pressure. Blow-off pressure in isolation valve  26  is set to a predetermined value such as 1700 psi via the current level in the valve coil.  
         [0017]    At step  62 , pump  32  is activated. Pump motor current is provided at a predetermined current level to provide an output pressure higher than that required by the wheel brake and also higher than the 1700 psi blowoff pressure of isolation valve  26 ; and apply valve  28  and release valve  40  are controlled to regulate the pressure to wheel brake  22 . A first brake fluid circulation path, shown by arrowheads in the lines in FIG. 1, begins at the pressure output of pump  32 , proceeds through damper  48 , orifice  50 , line  51  and apply valve  28  to regulated wheel brake  22  as permitted by apply valve  28 . It continues away from regulated wheel brake  22  through release valve  40 , one-way valve  46 , as permitted by release valve  40 , to accumulator  42  and the inlet of pump  32 . Since prime valve  52  remains open, plentiful brake fluid is available for pump  32  from the master cylinder as well as from accumulator  42 . When apply valve  28  closes, the fluid from pump  32  dead-heads against isolation valve  26  and, when the blow-off pressure (1700 psi) of isolation valve  26  is exceeded, a second circulation path, also shown by arrowheads in the lines, is established from pump  32  through damper  48 , orifice  50 , line  51  and isolation valve  26  to the master cylinder  20  and from master cylinder  20  through prime valve  52  back to the inlet of pump  32 . When the supplemental brake apply ends, the actions of step  60  are reversed at step  64 . Pump  32  is turned off; both release valves are closed, both apply valves are opened; isolation valve  26  is opened and prime valve  52  is closed.  
         [0018]    Although this prior art method of controlling regulated brake  22  is satisfactory in most respects, it can produce undesirable noise during blow-off conditions while the vehicle operator is applying the brakes with the brake pedal and master cylinder simultaneously with the system generated brake apply. The noise originates in the repeated noise of the valve element in isolation valve  26  as it re-closes after each brief pressure relief opening and the high pressure brake fluid between the isolation valve and master cylinder transmits the noise. Without changing the basic valve apparatus, the method of this operation modifies the operation of the apparatus described above to reduce the amplitude of this noise.  
         [0019]    The undesirable noise described above is reduced by alternative operation of the brake valve apparatus according to the method of this invention. This method will be described with reference to FIG. 3, in which identical elements are given reference numerals greater by 100 than those used in FIG. 1. In a supplemental brake apply of regulated wheel brake  122 , prime valve  152  is initially opened only for a short time at the beginning of the brake apply and then closed to prevent additional brake fluid from entering pump  132  from master cylinder  120  during the apply. Brake pressure to the regulated wheel brake  122  is regulated by apply valve  130  of the nonregulated wheel brake  124 , with the apply and release valves  128 ,  140  of the regulated wheel brake  122  left in their normal positions: open and closed, respectively. Apply valve  130  of non-regulated wheel brake  124  controls the brake fluid pressure at regulated wheel  122  via its back pressure rather than its downstream pressure, and may be designed and operated as a controlled blowoff valve similar to valve  126  but provided with a blow-off pressure equal to the desired regulated pressure. Finally, the non-regulated wheel brake  124  is maintained at master cylinder pressure by its release valve  144  in response to a signal from a master cylinder pressure sensor. As shown in the block diagram of FIG. 5, operator activation of brake pedal  154  causes master cylinder  120  to provide a master cylinder pressure to the apply valves of the wheel brakes of the non-controlled diagonal, not shown (it is blocked from apply valves  128  and  130  by closed isolation valve  126  and closed prime valve  152 ). This pressure is sensed by pressure sensor  156 , which provides a signal thereof to brake system controller  158 . Controller  158  may comprise a programmed digital computer that, for example, controls the coil current of release valve  144 , for example by pulsing the current on and off. The result is a fluid circulation through apply valve  130  and release valve  144  to provide a comparatively even return of brake fluid to accumulator  142 . Thus, the system normally has sufficient brake fluid available in accumulator  142  that it does not need additional brake fluid from master cylinder  120  to maintain the regulated pressure of the supplemental apply. Essentially, the second brake fluid circulation loop of the prior art system is minimal to non-existent in terms of flow volume. With the reduction in blow-off action, isolation valve  126  makes much less noise than does isolation valve  26  in the prior art system of FIGS. 1, 2.  
         [0020]    [0020]FIG. 4 illustrates the operation of brake system controller  158  when a supplemental brake apply is commanded for the regulated wheel brake  22 , for example in response to a vehicle stability enhancement (VSE) system to counteract an undesired yaw moment, the system proceeds as shown at step  80 . Routine SUPPLEMENTAL BRAKE APPLY 2 begins at step  80 , wherein prime valve  152  is opened; isolation valve  126  is closed; the blow-off pressure in isolation valve  126  is set at a predetermined value (e.g. 1,700 psi) and pump  132  is turned on, as in the prior art system. But apply valve  128  of regulated wheel brake  122  is left open, and release valve  140  of regulated wheel brake  122  is left closed. Thus, the fluid pressure applied to regulated wheel brake  122  is the same as that in line  151 , which is the back pressure generated by apply valve  130 .  
         [0021]    After a short, predetermined time period, at step  82 , prime valve  152  is closed to prevent additional provision of brake fluid from master cylinder  120 . This predetermined time is calibrated to permit the entry of a predetermined volume of brake fluid from master cylinder  120  that is sufficient for operation of the system but does not exceed the capacity of accumulator  142 .  
         [0022]    At step  84 , the brake apply pressure at apply valve  128  of regulated wheel brake  122  is regulated by apply valve  130  of non-regulated wheel brake  124  in the following manner. As pump  132  outputs brake fluid, the brake fluid pressure in line  151  tends to increase. Apply valve  130  is provided with a maximum or blow-off pressure equal to the intended regulated brake pressure and limits the fluid pressure in line  151  to the regulated pressure by releasing fluid when that pressure is exceeded and otherwise closing to permit pressure increase. Alternatively, valve  130  may be provided with a PWM signal to provide the desired pressure with a controlled fluid bleed from line  151 . Since release valve  140  of regulated wheel brake  122  is closed, this regulated back pressure from apply valve  130  of non-regulated wheel brake  124  is applied through the open apply valve  128  to regulated wheel brake  122 . Release valve  144  of non-regulated wheel brake  124  is cycled in a manner to pass the brake fluid released by apply valve  130  back to the accumulator and inlet of pump  132  and to maintain pressure in wheel brake  124  equal or close to the master cylinder pressure. Thus the brake apply pressure at wheel brake  124  is maintained close to the pressure in master cylinder  120  as long as that pressure does not exceed the regulated pressure existing in line  151 .  
         [0023]    The fluid circulation loop from pump  132  proceeds as follows. Fluid exits pump  132  and flows through damper  148 , orifice  150  and line  151  to apply valves  128  and  130 . Fluid flow proceeds as allowed by apply valve  130  to wheel brake  124  and, as permitted by release valve  144 , to accumulator  142  and, through one way valve  146 , to the inlet of pump  132 . The back pressure created in line  151  by apply valve  130  is communicated through open apply valve  128  to regulated wheel brake  122  but is not released by closed release valve  140 . Isolation valve  126  will still limit pressure in line  151  as in the prior art if required, but the necessity for such limiting is much less with this method than with the method of the prior art described above; and, unless prime valve  152  is re-opened, this excess fluid will not find its way back into the fluid circulation loop.