GB2073348A - Modulator assemblies for hydraulic anti-skid braking systems for vehicles - Google Patents

Abstract

In a modulator assembly (2) for an hydraulic anti-skid braking system a signal piston (85) which modulates the supply of fluid from a master cylinder (16) to a brake (67) is located in a bore (97) in a housing (1), together with a pump plunger (91) which controls operation of the signal piston (85) to effect re-application of the brake (67) at the termination of a skid signal. <IMAGE>

Description

SPECIFICATION Improvements in modulator assemblies for hydraulic anti-skid braking systems for vehicles This invention relates to modulator assembly for hydraulic anti-skid braking systems for vehicles of the kind in which the supply of operating fluid from a supply to a vehicle brake is modulated by themodulatqr assembly in accordance with skid signals from skid sensing means.

Modulator assemblies for systems of the kind set forth normally hold open a brake valve between the supply and the brake and when a skid signal is received the modulator assembly is operative to permit the brake valve to close and then to relieve the pressure applied to the brake. The modulator assembly may also include means for ensuring that a pump which circulates fluid in the system is operative only when a skid is being corrected and on brake re-application following a skid.

These modulator assemblies may be difficult and expensive to manufacture and assemble, as the various components are located in different parts of the housing.

According to the present invention in a modulator assembly adapted for an hydraulic anti-skid braking system of the kind set forth and incorporating a pump having a piston assembly including a pump plunger adapted for reciprocation by means of a drive mechanism, a signal piston coupled to the pump plunger, and resilient means for urging the pump plunger into a retracted position out of engagement with the drive mechanism, the signal piston having a first area adapted to be exposed to pressure from the supply or the brake when the brake is applied to urge the signal piston in a direction such that the pump plunger can engage with the drive mechanism, the modulator assembly also comprising a dump valve for controlling fluid in a stop chamber to which the piston assembly is exposed at least after the brake has been applied, the dump valve being normally closed to trap fluid in the stop chamber to hold the piston assembly in the retracted position, and the dump valve being movable into an open position in response to an skid signal to allow fluid in the stop chamber to return to a fluid reservoir, whereafter the pump plunger can engage with the drive mechanism, the pump plunger and the signal piston are both located in a single common bore in a housing.

Thus manufacture and assembly of the modulator are simplified.

Preferably, a first one-way valve is located between the stop chamber and a pump chamber, and a second one-way valve is located between the pump chamber and the reservoir.

One embodiment of our invention is illustrated in the accompanying drawings in which Figure 1 is a transverse section through a combined modulator and a skid sensing assembly for an hydraulic anti-skid braking system; and Figure 2 is a longitudinal section through the assembly in a plane normal to the plane of Fig. 1.

The assembly illustrated in Figs. 1 and 2 comprises a housing 1 incorporating a modulator assembly 2, an hydraulic pump 3 and a pressure dump valve 4. A longitudinally extending shaft 5 projecting at opposite ends from the housing 1 is coupled at one end to the wheel and at the other end carries skid sensing means 6 in the form of a flywheel assembly 7 which can be enclosed within a cylindrical guard 8 carried from the adjacent end of the housing 1.

The modulator assembly 2 comprises a signal piston 85 which works in a bore 86 in the housing 1 to control operation of a brake ball valve 87 which, in turn, controls communication between the master cylinder 1 6 and the brakes 67. Normally the piston 85 is biassed by a spring 88 in a direction to hold the ball valve 87 open. The piston 85 carries a piston rod 89 which has an enlarged head 90, and the head 90 is adapted normally to hold a pump plunger 91 away from an eccentric cam 27 on the shaft 5 by means of a sleeve 92 which is a press fit in a bore in the plunger 91. A spring 93 biasses the plunger 91 towards to cam 27.

One-way valves 1 9 and 20 are arranged in interconnected parallel bores in the housing 1 with the one-way valve 1 9 providing communication between a working chamber 30 above the piston 91 and a chamber 94 between the piston 85 and the rod 89, and the one-way valve 20 providing communication between the reservoir 21 and the working chamber 30.

When the brake 67 is applied the pressure applied to the brake 67 acts against the upper surface of the signal piston 85 which is unable to move because fluid in the chamber 94 is trapped between the pressure dump valve 4 and the one-way valve 1 9.

In the event of a skid the dump valve 4 is opened by the flywheel assembly 7 so that fluid from the chamber 94 can escape to the tank thus allowing the signal piston 85 to retract under the effect of the pressure applied to the brake 67. The piston 85 moves towards the cam 27 until it abuts against a stop 95 defined by a shoulder in the bore 86 at the lower end of the chamber 94. During this movement the ball valve 87 is permitted to close thus isolating the master cylinder 1 6 from the brake 67. Further movement of the piston 85 in the same direction and beyond the point at which the valve 67 closes serves to reduce the pressure in the line to the brake 67-by expansion in the effective volume of an expansion chamber 96 above the piston and leading to the brake 67.

As the signal position 85 moves towards the eccentric cam 27, the pump plunger 91 is allowed to engage the eccentric cam 27 and starts to pump fluid from the reservoir 21, through the valve 20, into the working chamber 30 and thence out through the valve 1 9 and back to the tank 21 by way of the pressure dump valve 4.

When the skid has been corrected the pressure dump valve 4 closes, and fluid from the working chamber 30 pressurises the chamber 94. This urges the signal piston 85 back towards its original position, thus re-pressurising the brake line by reducing the effective volume of the chamber 96, and subsequently re-opening the ball valve 87.

In the construction described above the signal piston besides acting as a modulator piston to modulate the supply of fluid to the brake 61 also serves to isolate the master cylinder 1 6 from the pulsations of the pump 3. Also the signal piston 85, the pump plunger 91, and the valve 87 are housed within a common bore 97 of stepped outline in the housing 1. In particular the signal piston 85 works in the bore of a sleeve 98 which is sealingly received in a portion 99 of the bore 97, which is of greater diameter, and the plunger 91 works in a portion 100 of the bore, which is of smaller diameter. This facilitates construction since the modulator assembly 2 can be assembled by inserting the plunger 91, and the sleeve 98 as a subassembly embodying the piston 85 and the valve 87, into the outer end of the bore 97 which is of greater diameter and which is subsequently closed by a plug 101.

The flywheel assembly 7 is described in detail in our GB Application No. 7928209 out of which this application is divided.

Claims (6)

1. A modulator assembly adapted for an hydraulic anti-skid braking system of the kind set forth and incorporating a pump having a piston assembly including a pump plunger for reciprocation by means of a drive mechanism, a signal piston coupled to the pump plunger, and resilient means for urging the pump plunger into a retracted position out of engagement with the drive mechanism, the signal piston having a first area adapted to be exposed to pressure from the supply or the brake when the brake is applied to urge the signal piston in a direction such that the pump plunger can engage with the drive mechanism, the modulator assembly also comprising a dump valve for controlling fluid in a stop chamber to which the piston assembly is exposed at least after the brake has been applied, the dump valve being normally closed to trap fluid in the stop chamber to hold the piston assembly in the retracted position, and the dump valve being movable into an open position in response to a skid signal to allow fluid in the stop chamber to return to a fluid reservoir, whereafter the pump plunger can engage with the drive mechanism, in which the pump plunger and the signal piston are both located in a single common bore in a housing.

2. A modulator assembly as claimed in Claim 1, in which the piston and the plunger work in different bore portions.

3. A modulator assembly as claimed in Claim 1 or Claim 2, in which the bore is of stepped outline having a first bore portion of greater area and a second bore portion of smaller area, the piston working in the bore of a sleeve which is sealingly received in the first bore portion and the plunger working in the second bore portion.

4. A modulator assembly as claimed in any preceding claim, in which the signal piston acts as a modulator piston to modulate the supply of fluid under pressure from a source to a brake by controlling operation of a one-way brake and valve disposed in the bore between the master cylinder and the brake and, following closure of the one-way valve, by altering the effective volume of an expansion chamber defined between the one-way brake valve and the piston.

5. A modulator assembly as claimed in Claim 4, in which a first one-way valve is located between the stop chamber and a pump chamber, and a second one-way valve is located between the pump chamber and the reservoir.

6. A modulator assembly substantially as described herein with reference to and as illustrated in the accompanying drawings.