Compensator assembly in a hydraulic control unit for vehicular brake systems

A hydraulic control unit of an electronically-controlled vehicular brake system comprising:

• a housing including a bore, wherein the bore is in fluid communication with a first fluid passage leading to an outlet of a pump and a second fluid passage leading to a master cylinder, and wherein the bore is only in fluid communication with the first and second fluid passages;
• a retainer cap mounted in the bore;
• a piston slidably received in the retainer cap, the piston including an internal fluid channel providing fluid communication between the first and second fluid passages;
• a spring positioned between the retainer cap and the piston to urge the piston from the retainer cap;
• a check valve assembly mounted in the internal fluid channel of the piston that permits only one-way fluid flow from the first fluid passage to the second fluid passage;
• and
• an annular undercut formed in an outer surface of the piston that cooperates with the bore of the housing to form an annular fluid chamber, wherein the undercut has a predetermined length so that the annular fluid chamber is in fluid communication with the second fluid passage at all positions of the piston.

An electronically-controlled vehicular brake system comprising:

• a master cylinder;
• a wheel brake;
• a hydraulic control unit connected in fluid communication between the master cylinder and the wheel brake, the hydraulic control unit including a housing have a bore and a pump;
• and
• a compensator assembly mounted in the bore and in fluid communication with an outlet of the pump and the master cylinder, the compensator assembly including
• a retainer cap mounted in the bore,
• a piston slidably received in the retainer cap, the piston including an internal fluid channel providing fluid communication between the pump outlet and the master cylinder and an annular undercut formed in an outer surface of the piston that cooperates with the bore of the housing to form an annular fluid chamber, wherein the undercut has a predetermined length so that the annular fluid chamber is in fluid communication with the master cylinder at all positions of the piston,
• a spring positioned between the retainer cap and the piston to urge the piston from the retainer cap, and
• a check valve assembly mounted in the internal fluid channel of the piston that permits only one-way fluid flow from the pump outlet to the master cylinder, wherein the compensator assembly provides means for allowing a controlled amount of additional travel for a piston in the master cylinder when the brake system is operating in an electronically activated mode only.

An electronically-controlled vehicular brake system comprising:

• a master cylinder;
• a wheel brake;
• a hydraulic control unit connected in fluid communication between the master cylinder and the wheel brake, the hydraulic control unit including a housing have a bore and a pump;
• and
• a compensator assembly mounted in the bore and in fluid communication with an outlet of the pump and the master cylinder, the compensator assembly including
• a retainer cap mounted in the bore,
• a piston slidably received in the retainer cap, the piston including a fluid channel providing fluid communication between the pump outlet and the master cylinder and an annular undercut formed in an outer surface of the piston that cooperates with the bore of the housing to form an annular fluid chamber, wherein the undercut has a predetermined length so that the annular fluid chamber is in fluid communication with the master cylinder at all positions of the piston,
• a spring positioned between the retainer cap and the piston to urge the piston from the retainer cap, and
• a check valve assembly mounted in the fluid channel of the piston that permits only one-way fluid flow from the pump outlet to the master cylinder, wherein a volume of brake fluid is temporarily stored in the compensator assembly when an electronically activated mode ends.

An electronically-controlled vehicular brake system comprising:

• a master cylinder;
• a wheel brake;
• a hydraulic control unit connected in fluid communication between the master cylinder and the wheel brake, the hydraulic control unit including a housing have a bore;
• a pump mounted on the hydraulic control unit;
• a compensator assembly mounted in the bore in fluid communication with the pump, the compensator assembly including
• a retainer cap mounted in the bore,
• a piston slidably received in the bore, the piston including an annular undercut formed in an outer surface of the piston that cooperates with the bore of the housing to form an annular fluid chamber, wherein the undercut has a predetermined length so that the annular fluid chamber is in fluid communication with the master cylinder at all positions of the piston, and
• a spring positioned between the retainer cap and the piston to urge the piston from the retainer cap,
• wherein the compensator assembly provides means for allowing a controlled amount of additional travel for a piston in the master cylinder when the brake system is operating in an electronically activated mode only.