Method and system for brake control

#The present application relates to methods and system for reducing a hard pedal condition that may occur during brake pedal operation.

#Braking devices for enabling vehicle speed control may be operated using vacuum. The vacuum may be provided by the engine via the engine intake manifold. Alternatively, a vacuum pump may be operated to provide the vacuum. As such, if there is insufficient vacuum to assist in the brake operation, a “hard pedal” condition may occur wherein the vehicle operator has to provide a larger brake pedal force than expected to attain the desired braking. Various approaches have been developed to mitigate such a “hard pedal” condition.

#One such approach is shown by Kamiya et al. in U.S. Pat. No. 6,754,579. Therein, an engine controller automatically starts an engine upon determining that there is insufficient brake booster vacuum. In particular, Kamiya adjusts an automatic engine restart operation based on a brake pedal depression amount and a brake booster vacuum amount.

#FIG. 1 shows a schematic depiction of an engine and an associated brake system;

#FIG. 2 shows a high level flowchart of an example method for improving a brake pedal feel;

#FIG. 3 shows characteristic curves of hydraulic brake line pressure relative to brake booster vacuum that may be used to infer an impending hard pedal condition;

#The present description relates to methods and systems for improving a brake pedal feel so as to reduce the likelihood of a “hard pedal” condition in an engine system, such as the engine system of FIG. 1. An engine controller may be configured to perform a control routine, such as the example routine of FIG. 2, to adjust the operation of one or more brake system components so as to increase a hydraulic brake line pressure in anticipation of an impending hard pedal condition. The controller may be configured to infer an impending change in the pedal feel (that is, the pedal force required to achieve a desired change in brake pedal position) based on the hydraulic brake line pressure relative to the brake boost vacuum level, for example, using the characteristic curves of FIG. 3. As shown in the example of FIG. 4, by making the appropriate adjustments before a hard pedal condition occurs, the brake line pressure may be increased so that a ratio of pedal force applied to brake pedal displacement can be maintained below a threshold amount. That is, a “softer” brake pedal feel can be maintained.

#Referring to FIG. 1, internal combustion engine 10, comprising a plurality of cylinders, one cylinder of which is shown in FIG. 1, is controlled by electronic engine controller 12. Engine 10 includes combustion chamber 30 and cylinder walls 32 with piston 36 positioned therein and connected to crankshaft 40. Combustion chamber 30 is shown communicating with intake manifold 44 and exhaust manifold 48 via respective intake valve 52 and exhaust valve 54. Each intake and exhaust valve may be operated by an intake cam 51 and an exhaust cam 53. Alternatively, one or more of the intake and exhaust valves may be operated by an electromechanically controlled valve coil and armature assembly. The position of intake cam 51 may be determined by intake cam sensor 55. The position of exhaust cam 53 may be determined by exhaust cam sensor 57.

#Fuel injector 66 is shown positioned to inject fuel directly into cylinder 30, which is known to those skilled in the art as direct injection. Alternatively, fuel may be injected to an intake port, which is known to those skilled in the art as port injection. Fuel injector 66 delivers liquid fuel in proportion to the pulse width of signal FPW from controller 12. Fuel is delivered to fuel injector 66 by a fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown). Fuel injector 66 is supplied operating current from driver 95 which responds to controller 12. In addition, intake manifold 44 is shown communicating with optional electronic throttle 62 which adjusts a position of throttle plate 64 to control air flow from intake boost chamber 46.