Patent Publication Number: US-2009240414-A1

Title: Brake noise suppression via system pressure modulation

Description:
TECHNICAL FIELD 
     This invention relates generally to vehicle braking systems and, more particularly, to suppression of brake noise via brake system pressure modulation. 
     BACKGROUND OF THE INVENTION 
     Brake noise is a result of the excitation of a brake corner component, e.g. a brake rotor, a brake drum, a caliper bracket, etc., by the friction material. This phenomenon is also known as friction-induced vibration or friction instability, the onset of which is typically attributed to an increase in the friction between a brake pad and a brake rotor under a certain set of conditions, e.g. low ambient temperatures, light brake applies, high humidity, etc. The energy from the friction instability is dissipated through the brake corner component, in the form of a squeal, or through a chassis component, in the form of a groan. 
     One known technique of brake noise suppression includes a brake system that detects an ideal squeal condition and, if certain conditions are met during a brake apply, partially relieves the brake system pressure and then reapplies the brake system pressure as a one-time occurrence. Further, if the ideal squeal conditions are met in an off-brake condition, this known technique lightly activates the brake so as to minimize the possibility of the onset of stick/slip. 
     Other known techniques of brake noise suppression attempt to suppress brake squeal via control of the friction forcing function using piezoelectric stacks, e.g. dither control, or closed-loop hydraulic pressure control to avoid particular conditions that can cause brake squeal. 
     Further, other known techniques of brake noise suppression include physical modifications of the brake system, e.g. the addition of lining chamfers and/or pad shims, or the use of low coefficient friction linings and/or damped iron rotors, which can be costly and represent some measure of additional risk to implement. 
     SUMMARY OF THE INVENTION 
     A method of brake noise suppression via brake system pressure modulation is disclosed including the steps of: detecting a brake apply and modulating a brake system pressure to disrupt formation of a friction instability upon detection of the brake apply. 
     In one example embodiment, the brake system pressure is modulated at each brake apply detected. 
     In another example embodiment, the method further includes the steps of: determining whether the brake apply detected is of a brake apply type that is indicative of brake noise; and modulating the brake system pressure to disrupt formation of the friction instability only when the brake apply type is indicative of brake noise, for example but not limited to, light brake applies, low vehicle speeds and/or low ambient temperature. 
     In yet another example embodiment, the method further includes the steps of: identifying a limit cycle associated with a noise-inducing friction instability; determining whether the brake apply is associated with a noise-inducing friction instability; and modulating the brake system pressure to disrupt formation of the noise-inducing friction instability by hindering development of the limit cycle associated with the noise-inducing friction instability. 
     In yet another example embodiment, the method further includes the steps of: detecting a brake noise; and modulating the brake system pressure only upon detection of the brake noise. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an example hydraulic braking system for a vehicle, including brake noise suppression via pressure modulation according to the present invention; 
         FIG. 2A  is a schematic illustration of an example hybrid electro-hydraulic braking system for a vehicle, including brake noise suppression via pressure modulation according to the present invention; 
         FIG. 2B  is a schematic illustration of an example electric braking system for a vehicle, including brake suppression via pressure modulation according to the present invention; 
         FIG. 3A  is a flowchart illustrating one embodiment of brake noise suppression via system pressure modulation according to the present invention; 
         FIG. 3B  is a flowchart illustrating another embodiment of brake noise suppression via system pressure modulation according to the present invention; 
         FIG. 3C  is a flowchart illustrating yet another embodiment of brake noise suppression via system pressure modulation according to the present invention; and 
         FIG. 3D  is a flowchart illustrating yet another embodiment of brake noise suppression via system pressure modulation according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  is a schematic illustration of an example hydraulic braking system for a vehicle is indicated generally at  10 . The example hydraulic braking system  10  includes a master cylinder  12  in fluid communication with a hydraulic brake unit or anti-lock brake (ABS) modulator  14 . The master cylinder  12  is operable to receive an input from a brake pedal  16 , which is indicative of a brake apply. 
     As a driver (not shown) exerts pressure on the brake pedal  16 , hydraulic pressure within the master cylinder  12  increases. The hydraulic brake unit or ABS modulator  14  sends the hydraulic pressure through brake lines  18  to wheels RF, LF, RR, and LR located at each of the four corners of the vehicle. 
     Each of the two front wheels, RF and LF, of the vehicle are equipped with disk brake systems  20 . Each of the two rear wheels, RR and LR, of the vehicle are equipped with drum brake systems  22 . 
     Each of the two front disk brake systems  20  includes a brake rotor or disk  24  mounted to a hub  26 . A caliper  28  includes brake pads  30 , which interact with the brake rotor  24  to cause the rotation of wheels RF and LF to slow and/or eventually stop. Each of the calipers  28  engages and/or disengages their respective brake pads  30 , exerting and/or relieving an applied braking force, based on a change in the hydraulic pressure received through brake lines  18 . 
     Each of the two rear drum brake systems  22  includes a brake drum  40  and a pair of brake shoes  42 . A brake pad  44  is mounted to each of the brake shoes  42  and the brake pads  44  interact with an inner surface  46  of each of the brake drums  40  to cause the rotation of wheels RR and LR to slow and/or eventually stop. A hydraulic brake cylinder  48  is operable to receive the hydraulic pressure from the brake lines  18  and to deliver hydraulic pressure to each of the brake shoes  42 . 
     In response, each of the brake shoes  42  engages and/or disengages their respective brake pads  44 , exerting and/or relieving an applied brake force, based on a change in the hydraulic pressure received through the brake lines  18 . 
     The hydraulic brake unit  14  includes a controller, shown generally as  50 , which is operable to detect the brake apply received from the brake pedal  16  and to modulate the hydraulic pressure delivered through the brake lines  18  to each of the wheels RF, LF, RR and LR, to modulate the applied brake force. 
       FIG. 2A  is a schematic illustration of an example hybrid electro-hydraulic vehicle braking system, indicated generally at  1   10 . The example hybrid electro-hydraulic braking system  110  includes a pedal emulator  112  in electronic communication with an electronic controller  150 . The pedal emulator  112  is operable to receive an electronic input from a brake pedal  116 , which is indicative of a brake apply, and to transfer the electronic input to the electronic controller  150 . 
     As a driver (not shown) exerts pressure on the brake pedal  116 , the electronic controller  150  is operable to transmit the electronic input to wheels RF, LF, RR, and LR located at each of the four corners of the vehicle. 
     Each of the two front wheels, RF and LF, of the vehicle are equipped with disk brake systems  120 . Each of the two rear wheels, RR and LR, of the vehicle are equipped with drum brake systems  122 . 
     Each of the two front disk brake systems  120  includes a brake rotor or disk  124  mounted to a hub  126 . A caliper  128  includes brake pads  130 , which interact with the brake rotor  124  to cause the rotation of wheels RF and LF to slow and/or eventually stop. Each of the calipers  128  engages and/or disengages their respective brake pads  130 , exerting and/or relieving an applied braking force, based on the electronic input received from the electronic controller  150 . 
     Each of the two rear drum brake systems  122  includes a brake drum  140  and a pair of brake shoes  142 . A brake pad  144  is mounted to each of the brake shoes  142  and the brake pads  144  interact with an inner surface  146  of each of the brake drums  140  to cause the rotation of wheels RR and LR to slow and/or eventually stop. A hydraulic brake cylinder  148  is operable to receive the electronic input from the electronic controller  150  and to exert hydraulic pressure to each of the brake shoes  142 . 
     In response, each of the brake shoes  142  engages and/or disengages their respective brake pads  144 , exerting and/or relieving an applied brake force, based on the electronic input received from the electronic controller  150 . 
     The electronic controller  150  is operable to detect the brake apply received from the brake pedal  116  and to modulate a hydraulic pressure at each of the wheels RF, LF, RR and LR, to modulate the applied brake force. 
     At each applied brake force interface, i.e. between the brake pads  30 ,  130  and the brake rotor  24 ,  124  and between the brake pads  44 ,  144  and the brake drums  40 ,  140 , there exists an opportunity for brake noise, which is the excitation of a brake corner component, for example but not limited to, a brake rotor, a brake drum, a brake caliper bracket or the like, by the friction material, i.e. the brake pad. This phenomenon is known as friction-induced vibration or friction instability. The energy from the friction instability is dissipated through the brake rotor or the caliper bracket as brake noise, in the form of a groan. 
       FIG. 2B  is a schematic illustration of an example electric vehicle braking system, indicated generally at  160 . The example electric braking system  160  includes a pedal emulator  112  in electronic communication with an electronic controller  150  as previously illustrated in the example electro-hydraulic vehicle braking system  110  ( FIG. 2A ). The pedal emulator  112  is operable to receive an electronic input from a brake pedal  116 , which is indicative of a brake apply, and to transfer the electronic input to the electronic controller  150 . 
     As a driver (not shown) exerts pressure on the brake pedal  116 , the electronic controller  150  is operable to transmit the electronic input to wheels RF, LF, RR, and LR located at each of the four corners of the vehicle. 
     Each of the two front wheels, RF and LF, and each of the two rear wheels RR and LR, of the vehicle are equipped with disk brake systems  120 . Each of the disk brake systems  120  includes a brake rotor or disk  124  mounted to a hub  126 . A caliper  128  includes brake pads  130 , which interact with the brake rotor  124  to cause the rotation of wheels RF and LF to slow and/or eventually stop. 
     An electric motor  162  is mounted in electrical communication with each of the calipers  128  and the electronic controller  150 . Each caliper  128  is operable to engage and/or disengage their respective brake pads  130 , exerting and/or relieving an applied braking force, based on the electronic input received from the electronic controller  150 . 
     The electronic controller  150  is operable to detect the brake apply received from the brake pedal  116  and to control each of the electric motors  162  located at each of the wheels RF, LF, RR and LR, to modulate the applied brake force. 
     In one example embodiment, as illustrated in  FIG. 3A , the controller  50 ,  150  is operable to: detect a brake apply  200 ; and modulate a brake system pressure  210  to disrupt formation of a friction instability upon detection of the brake apply, i.e. at each brake apply detected. 
     In another example embodiment, as illustrated in  FIG. 3B , the controller  50 ,  150  is operable to: detect a brake apply  300 ; determine whether the brake apply detected is of a brake apply type that is indicative of brake noise  310 ; and modulate the brake system pressure to disrupt formation of the friction instability only when the brake apply type is indicative of brake noise  320 , for example but not limited to, light brake applies, low vehicle speeds and/or low ambient temperature. 
     In yet another example embodiment, as illustrated in  FIG. 3C , the controller  50 ,  150  is operable to: identify a limit cycle associated with a noise-inducing friction instability  400 ; detect a brake apply  410 ; determine whether the brake apply is associated with a noise-inducing friction instability  420 ; and modulate the brake system pressure to disrupt formation of the noise-inducting friction instability by hindering development of the limit cycle associated with the noise-inducing friction instability  430 . 
     In yet another example embodiment, as illustrated in  FIG. 3D , the controller  50 ,  150  is operable to: detect a brake apply  500 ; detect a brake noise  510 ; and modulate the brake system pressure only upon detection of the brake noise  520 . 
     In each of the disclosed example embodiments discussed above, the brake system pressure modulation results in modulation of a normal force on the brake lining and the friction force, thereby disrupting the formation of friction instabilities. The modulation is of a small enough magnitude that the driver is unaware of any modulation. 
     Further, as discussed above, in the hydraulic braking system illustrated in  FIG. 1 , the brake system pressure is a hydraulic pressure controlled by the controller  50  associated with the hydraulic brake unit or ABS modulator  14 . However, the hydraulic pressure may also be controlled by any other pressure modulating device. 
     Finally, as discussed above, in the electric braking system illustrated in  FIG. 2 , the brake system pressure is a hydraulic pressure controlled by the electronic control unit  150 . However, the brake system pressure could also be an electronic clamping force exerted at each of the wheels RF, LF, RR and LR. As such, the electronic clamping force would be the brake system pressure that would be modulated. Further, the electronic clamping force could be exerted by, for example but not limited to, a motor located at each wheel. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.