Improvements in hydraulic anti-skid braking systems for vehicles

Claim 2

An hydraulic anti-skid braking system for a vehicle in which a supply of operating fluid from a supply (16) to a vehicle brake is modulated by a modulator assembly (2) in accordance with skid signals from skid sensing means (6) and an hydraulic pump (3) incorporating at least one plunger (24; 54, 55) working in a bore (25; 51, 52) has a working chamber (30; 60, 61) which is in communication with the modulator assembly (2) to control brake re-application following skid correction characterised in that the pump (3) is of the double-acting type to provide at least two pump delivery strokes for each pump cycle.

Claim 3

A system as claimed in Claim 1, characterised in that. the pressure of the operating fluid comprises the pressure of the supply (16).

Claim 4

A system as claimed in Claim 1 or Claim 2, characterised in that the pump (3) is provided with at least two separate plungers (54, 55).

Claim 5

A system as claimed in Claim 1 or Claim 2, characterised in that the pump (3) has a single plunger (24) which is urged in one of two opposite directions by the supply (16) of operating fluid and in the other of the said two opposite direction by a drive (23).

Claim 6

A system as claimed in Claim 4, characterised in that the pump plunger (24) is of differential outline working in a stepped bore (25), the end of smaller area of the plunger being exposed to the reservoir (38), the end of greater area being exposed to the working chamber (30), a first one-way valve (31) permitting flow into the working chamber (30) from the reservoir (38) upon movement of the plunger (24) in a first direction towards a drive mechanism (23), a second one-way valve permitting flow into an expansion chamber (18) from the working chamber (30) upon movement of the plunger (24) in a second opposite direction, and a drive piston (26) for urging the plunger in the said first direction.

Claim 7

A system as claimed in Claim 5, characterised in that the drive piston (26) is exposed at one end to the pressure in the working chamber (30) and at the opposite end to the supply (16) of operating fluid.

Claim 8

A system as claimed in Claim 5, characterised in that the drive piston (26) is an extension of the . plunger (24), and the drive piston (26) is only exposed to the supply (16) of operating fluid.

Claim 12

A system as claimed in Claim 10, characterised in that a seal (29) is provided on the pump plunger (24) and the second one-way valve comprises a valve member for engagement with a seating on the opposite side of the seal (24) from the first one-way valve (31).

Claim 13

A system as claimed in Claim 10, characterised in that the second one-way valve comprises a valve seal on the pump plunger (24) for permitting flow past that seal in response to movement of the pump plunger (24) in one direction, a passage (33) leading to the expansion chamber (18) from the stepped bore (25) at a position between the lip seal and a second seal (28) between the bore (25) and the portion (B) of the plunger (24) which is of smaller area and through which fluid is pumped past the valve seal upon movement of the plunger (24) in the said second opposite direction and by the plunger (24) itself upon movement of the plunger (24) in the said first direction, with the second one-way valve in a closed position.

Claim 14

A system as claimed in Claim 12, characterised in that the valve seal comprises a lip seal (29) for controlling flow through ports (32) in the end of the plunger (24) which is of greater area.

Claim 15

A system as claimed in Claim 12, characterised in that the valve seal comprises a sealing ring (40) of an internal diameter greater than the external diameter of a radial groove (41) in the pump plunger (24) in which it is received and of an axial thickness less than the length of the groove (41) itself, and the ring (40) is engagable with spaced opposite faces of the plunger (24) at opposite ends of the groove (41), a clearance being provided between the sealing ring (40) and the face with which the ring engages to permit flow past the sealing ring when the ring engages with that face in response to movement of the plunger (24) in the said opposite direction.

Claim 16

A system as claimed in Claim 12, characterised in that the clearance is defined by at least one flat (44) on the the plunger (24).

Claim 17

A system as claimed in Claim 12, characterised in that the clearance is defined by gaps between castellations (45) on the ring (40) when the castellaions are in engagement with the said face.