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A brake control system for a motor vehicle comprising a brake control unit which controls increasing and decreasing of a brake pressure of a wheel cylinder from a pressure source by driving plural solenoid valves without a brake operation by a driver. The system comprises a flow back control unit wh

A brake control system for a motor vehicle comprising a brake control unit which controls increasing and decreasing of a brake pressure of a wheel cylinder from a pressure source by driving plural solenoid valves without a brake operation by a driver. The system comprises a flow back control unit which controls the brake pressure of a wheel cylinder to drive the plural solenoid valves before control by the brake control unit and returns the brake fluid to the pressure source from the wheel cylinder.

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What is claimed is: 1. A brake control apparatus for a motor vehicle comprising: a master cylinder connected via a first hydraulic circuit to a plurality of wheel cylinders, and configured to generate a master cylinder pressure by a driver's braking action; a plurality of pressure control valves di

What is claimed is: 1. A brake control apparatus for a motor vehicle comprising: a master cylinder connected via a first hydraulic circuit to a plurality of wheel cylinders, and configured to generate a master cylinder pressure by a driver's braking action; a plurality of pressure control valves disposed in the first hydraulic circuit for regulating a wheel cylinder pressure of each of the wheel cylinders; a pump having a pump inlet connected via a second hydraulic circuit to the master cylinder and connected via a return circuit to each of the wheel cylinders, and a pump outlet connected via the first hydraulic circuit to each of the wheel cylinders, and configured to generate a hydraulic pressure independently of a driver's braking action; an outflow gate valve disposed in the first hydraulic circuit; an inflow gate valve disposed in the second hydraulic circuit; and a brake control unit configured to be electronically connected to the pressure control valves, the oufflow and inflow gate valves, and the pump, for regulating the wheel cylinder pressure of each of the wheel cylinders by controlling operations of the respective valves and the pump, wherein the brake control unit is configured to execute a pre-charge and flow-back operating mode in which the pump is operated for a pre-charge time duration, before execution of brake control that the pump is operated as a pressure source, or during an initial stage of the brake control, in a specified state where the outflow gate valve, the inflow gate valve, and the pressure control valves are kept open concurrently. 2. The brake control apparatus as claimed in claim 1, wherein: the inflow gate valve is disposed between the master cylinder and the pump and located upstream of the second hydraulic circuit, for enabling pre-charging of brake fluid through a fluid flow path that permits brake fluid flow from the master cylinder to each of the wheel cylinders via the inflow gate valve, the second hydraulic circuit, the pump, and the pressure control valves; and the outflow gate valve is disposed between the master cylinder and the pressure control valves and located upstream of the first hydraulic circuit, for enabling flowing-back of brake fluid through a fluid flow path that permits brake fluid flow from each of the wheel cylinders back to the master cylinder via the pressure control valves, the first hydrauric circuit, and the outflow gate valve, simultaneously with the pre-charging action. 3. The brake control apparatus as claimed in claim 1, wherein: the inflow gate valve comprises a normally-closed solenoid valve configured to open under its energized state for permitting brake fluid flow from the master cylinder via the second hydraulic circuit to the pump inlet; and the outflow gate valve comprises a normally-open solenoid valve configured to open under its de-energized state for permitting brake fluid flow from the master cylinder via the first hydraulic circuit to each of the wheel cylinders. 4. The brake control apparatus as claimed in claim 1, wherein: the brake control unit is configured to determine, based on a comparative check between the wheel cylinder pressure of a road wheel subjected to the brake control and a predetermined pressure value, whether the pre-charge and flow-back operating mode should be executed. 5. The brake control apparatus as claimed in claim 4, wherein: the brake control unit is configured to estimate, based on at least one of an operating time of each of the pressure control valves and a driving characteristic of the pump, the wheel cylinder pressure of the mad wheel subjected to the brake control1 and inhibit the pre-charge and flow-back operating mode when the estimated wheel cylinder pressure is greater than or equal to the predetermined pressure value. 6. The brake control apparatus as claimed in claim 4, wherein: the brake control unit is configured to detect the wheel cylinder pressure of the road wheel subjected to the brake control, and inhibit the pre-charge and flow-back operating mode when the detected wheel cylinder pressure is greater than or equal to the predetermined pressure value. 7. The brake control apparatus as claimed in claim 4, wherein: the predetermined pressure value is defined as a wheel-cylinder-pressure threshold value that is identified when a pad-to-rotor clearance of the road wheel subjected to the brake control has been adjusted to a substantially zero clearance. 8. The brake control apparatus as claimed in claim 4, wherein: the master cylinder comprises a tandem master cylinder; the motor vehicle employs an X-split brake line system in which a first outlet part of the tandem master cylinder is connected via an A-system brake line to the front-left and rear-right wheel cylinders and the second tandem-master-cylinder outlet part is connected via a B-system brake line to the front-right and rear-left wheel cylinders; and the brake control unit is configured to determine, based on a comparative check between an outflow amount of brake fluid flowing out of a noncontrolled wheel cylinder, unsubjected to the brake control at a current brake-control execution cycle and included in the same system brake line as a controlled wheel cylinder subjected to the brake control at the current execution cycle, and a predetermined amount, whether the pre-charge and flow-back operating mode should be executed. 9. The brake control apparatus as claimed in claim 8, wherein: the brake control unit is configured to estimate, based on an amount of brake fluid flown out of the noncontrolled wheel cylinder before a predetermined number of execution cycles, the outflow amount of the noncontrolled wheel cylinder, and inhibit the pre-charge and flow-back operating mode when the estimated outflow amount is greater than or equal to the predetemiined amount. 10. The brake control apparatus as claimed in claim 8, wherein: the predetermined amount is defined as an outflow amount enough to adjust a pad-to-rotor clearance of the road wheel subjected to the brake control to a substantially zero clearance by introducing brake fluid, flown out of the noncontrolled wheel cylinder before the predetermined number of execution cycles, into the controlled wheel cylinder subjected to the brake control at the current execution cycle. 11. The brake control apparatus as claimed in claim 1, wherein: the pre-charge time duration is fixed to a time duration. 12. The brake control apparatus as claimed in claim 1, wherein: the pre-charge time duration is a variable determined based on a factor indicative of a dynamic behavior of the vehicle, including at least one of a yaw rate of the vehicle and a lateral acceleration exerted on the vehicle. 13. The brake control apparatus as claimed in claim 12, wherein: the pre-charge time duration becomes longer, as the yaw rate increases. 14. The brake control apparatus as claimed in claim 12, wherein: the pre-charge time duration becomes longer, as the lateral acceleration increases. 15. The brake control apparatus as claimed in claim 1, wherein: only pressure-increase valves of the pressure control valves are kept open during the pre-charge and flow-back operating mode, 16. The brake control apparatus as claimed in claim 1, wherein: pressure-increase and pressure-decrease valves of the pressure control valves are all kept open during the pre-charge and flow-back operating mode. 17. A brake control apparatus for a motor vehicle comprising: first pressure source means connected via a first hydraulic circuit to a plurality of wheel cylinders, for outputting a hydraulic pressure produced by a drivers braking action to each of the wheel cylinders; pressure control valve means disposed in the first hydraulic circuit for regulating a wheel cylinder pressure of each of the wheel cylinders, said pressure control valve means comprising pressure-increase and pressure-decrease valves; second pressure source means having an inlet port connected via a second hydraulic circuit to the first pressure source means and connected via a return circuit to each of the wheel cylinders, and an outlet port connected via the first hydraulic circuit to each of the wheel cylinders, for generating a hydraulic pressure independently of a drivers braking action; outflow gate valve means disposed in the first hydraulic circuit for controlling fluid communication between the first pressure source means and the pressure control valve means; inflow gate valve means disposed in the second hydraulic circuit for controlling fluid communication between the first pressure source means and the second pressure source means; and brake control means configured to be electronically connected to the pressure control valve means, the outflow and inflow gate valve means, and the second pressure source means, for regulating the wheel cylinder pressure of each of the wheel cylinders by controlling operations of the respective valve means and the second pressure source means, wherein the brake control means is configured to execute a pre-charge and flow-back operating mode in which the second pressure source means is operated for a pre-charge time duration, before execution of brake control that the second pressure source means is operated as a pressure source, or during an initial stage of the brake control, in a specified state where the oufflow gate valve means, the inflow gate valve means, and the pressure-increase valves of the pressure control valve means are kept open concurrently. 18. A method of brake control for a motor vehicle employing a master cylinder connected via a first hydraulic circuit to a plurality of wheel cylinders, a plurality of pressure control valves disposed in the first hydraulic circuit, a pump having a pump inlet connected via a second hydraulic circuit to the master cylinder and connected via a return circuit to each of the wheel cylinders and a pump outlet connected via the first hydraulic circuit to each of the wheel cylinders for generating a hydraulic pressure independently of a driver's braking action, an outflow gate valve disposed in the first hydraulic circuit, an inflow gate valve disposed in the second hydraulic circuit, and a brake control unit provided to regulate the wheel cylinder pressure of each of the wheel cylinders by controlling operations of the respective valves and the pump, the method comprising: pre-charging brake fluid through a fluid flow path that permits brake fluid flow from the master cylinder to each of the wheel cylinders via the inflow gate valve, the second hydraulic circuit, the pump, and the pressure control valves, with the inflow gate valve kept open during a pre-charge and flow-back operating mode in which the pump is operated for a pre-charge time duration, before execution of brake control that the pump is operated as a pressure source, or during an initial stage of the brake control, in a specified state where the outflow gate valve, the inflow gate valve, and the pressure control valves are kept open concurrently; and flowing-back brake fluid through a fluid flow path that permits brake fluid flow from each of the wheel cylinders back to the master cylinder via the pressure control valves, the first hydraulic circuit, and the outflow gate valve, with the outflow gate valve kept open during the pre-charge and flow-back operating mode, simultaneously with the pre-charging action.