GB2066912A - Anti-skid sensing means for a vehicle braking system - Google Patents

Abstract

Anti-skid sensing means comprises a shaft (19) driven from a wheel of a vehicle, a flywheel (17) rotatable with respect to the shaft (19), a clutch member (20) through which the flywheel (17) is driven from the shaft (19), a ball and ramp mechanism (21) responsive to relative angular movement between the shaft (19) and the flywheel (17) to produce a skid signal for operating a modulator assembly (4), and a spring (36) acting on the clutch member (20) through a lever (34) to bias the clutch member (20) into engagement with the flywheel (17) and bias the ball and ramp mechanism (21). The spring (36) is constructed and arranged to prevent the skid signal from being produced unless the flywheel (17) has generated sufficient torque to overrun the shaft (19) by a predetermined amount and to maintain the skid signal by permitting the flywheel (17) to overrun the shaft (19) against the clutch member (20). <IMAGE>

Description

SPECIFICATION Anti-skid sensing means for a vehicle braking system This invention relates to anti-skid sensing means for a vehicle braking system of the kind comprising a fluid pressure operable brake for braking a wheel, a supply of fluid under pressure for operating the brake, and a modulator assembly for modulating the supply of fluid to the brake in accordance with a skid signal from the anti-skid sensing means.

In some known anti-skid systems of the kind set forth the sensing means comprises an electronic sensor acting on a solenoid operated valve which controls the application of a control pressure from a power supply to operate the modulator assembly.

These systems generally have separate power supplies to apply the brakes and some incorporate an accumulator to re-apply the brakes when the pressure falls below a certain value. These known systems are all relatively complicated and expensive, and are only practical for use on commercial or luxury vehicles.

According to our invention in anti-skid sensing means for a vehicle braking system of the type comprising a fluid pressure-operable brake for braking a wheel, a supply of fluid under pressure for operating the brake, and a modulator assembly for modulating the supply of fluid to the brake in accordance with a skid signal from the anti-skid sensing means, the anti-skid sensing means comprises a shaft adapted to be driven by the wheel, a flywheel assembly rotatably mounted for rotation with respect to the shaft, drive means including a clutch and through which the flywheel assembly is driven from the shaft, camming means responsive to relative angular movement between the shaft and the flywheel assembly to produce a skid signal for operating the modulator assembly to reduce the pressure of fluid supplied to the brake when the deceleration of the shaft relative to the flywheel assembly exceeds a pre-determined value, the skid signal comprising relative axial movement between said shaft and said flywheel assembly, and biassing means for biassing both the clutch and the camming means, the biassing means being so constructed and arranged to prevent the skid signal from being produced unless the flywheel assembly has generated sufficient torque to overrun the shaft by a predetermined amount and to maintain the skid signal by permitting the flywheel to overrun the shaft against the clutch.

Preferably the clutch comprises the drive means.

Conveniently the flywheel assembly comprises a flywheel member, a thrust member, and means for keying one of the said members against axial movement with respect to the shaft, and the clutch comprises a clutch plate having a frictional engagement with the said other of the said members and of which the magnitude is determined by the magnitude of the biassing means, the said other of the said members being angularly movable with respect to the clutch plate upon the frictional engagement being overcome by overrun of the flywheel member with respect to the shaft, whereby axial movement of the said other member in a direction away from the said one member in response to relative angular movement between the said members produces the skid signal with any additional overrun of the flywheel member with respect to the shaft overcoming the frictional engagement to maintain the skid signal.

The biassing means may comprise a spring, and a lever is incorporated through which the spring acts on the clutch plate and through which the skid signal is adapted to be transmitted to the moduiator assembly.

In one construction the flywheel member is keyed against axial movement with respect to the shaft, the thrust member is both axially and angularly movable, and the clutch plate is urged into frictional engagement with the thrust member by the biassing means.

An embodiment of the invention is illustrated in the accompanying drawings, in which : Figure 1 is an end plan view of an hydraulic anti-skid system; Figure 2 is a section on the line 2-2 of Figure 1; and Figure 3 is a section on the line 3-3 of Figure 1.

In the anti-skid system iliustrated in the drawings a housing 1 is mounted on the frame of a vehicle (not shown) and a reservoir 2 for hydraulic fluid is mounted above the housing 1.

As shown in Figure 3, the housing 1 is provided with a first longitudinally extending stepped bore 3 in which a modulator valve assembly 4 is located for controlling the communication between a first inlet 5 and a first outlet 6, and between a second inlet 7 and a second outlet 8 of the bore. The valve assembly 4 comprises a piston 9 working in a larger diameter portion of the bore to define respective variable volume chambers 10 and 11 at its opposite ends and a ball valve member 12 working in another bore portion and engageable with a seating 13 to cut off communication between the first inlet 5 and an outlet 6 which are connected to a supply of brake operating fluid from a master cylinder assembly and to vehicle wheel brake, respectively.A stem 14 projecting from the one end of the piston 9 acts on the ball valve member 12, and a spring 15 acting on the opposite end of the piston 9 and housed in the chamber 11 urges the ball valve into its open position as shown in Figure 3.

Sensing means 16 for sensing the deceleration of a braked wheel is located in a chamber 17 in the housing 1 as shown in Figure 2 and comprises a flywheel 18 driven by a shaft 19 through a clutch member 20 and a ball and ramp expander mechanism 21. The shaft 19 is itself driven by the vehicle wheel and operates a pump 22 located in another part of the housing 1 and which is arranged to withdraw liquid from the reservoir 2 so that the liquid throughput of the pump 22 will increase with the wheel rotational speed. The pump normally circulates liquid through the modulator valve assembly 4 along the line 23 and back to the reservoir along the line 24 and through a control valve assembly 25 located in a second stepped bore 26 in the housing.

The control valve assembly 25 comprises a spool member 27 working in a bore 28 in a sleeve 29 to control communication between a first radial passage 30 in the sleeve which is connected to the pump output along a line 31 and a second radial passage 32 which is connected to the reservoir 2 via a line 33.

A lever 34 pivotally mounted at 35 acts on the clutch member 20 at its free end and acts on an outer end of the spool member 27 at an intermediate point in its length. A return spring 36 acts on the other end of the spool member 27 to bias the clutch member 20 into operative engagement with the flywheei 18 through the lever 34.

When the vehicle is in motion the shaft 19 is driven by the wheel and rotates and drives the flywheel 18 via the clutch member 20 and the ball and ramp mechanism 21. At the same time the shaft 19 operates the pump 22 and fluid is circulated by the pump through the modulator valve assembly 4.

When the brake is applied fluid from the master cylinder is fed to the brake via the open ball valve 12 and the chamber 10, which is at a minimum volume with the piston 9 in the position shown in Figure 3, and acts on the piston 9 urge it to the right. The end of the piston 9 then defines a restriction 37 in the path between the lines 24 and 23, and this causes the pressure on the pump side of the restriction to rise to balance the pressure applied to the brake.

If the applied brake pressure is too high and the vehicle wheel starts to decelerate rapidly, the flywheel 18 at, say, 1g deceleration provides enough torque to expand the ball and ramp mechanism 21 against the load in the control valve spring 36 acting through the lever 34. The flywheel 18 continues to overrun against the friction of the clutch member 20 at, say 1.2g. Expansion of the ball and ramp mechanism 21 urges the spool member 27 to the left to connect the pump output directly to the reservoir via the radial passage 30, an annular chamber 38 in the spool member and a passageway 39 communicating with the radial passage 32.Release of the pump pressure acting on the modulator valve piston 9 immediately results in the piston shooting to the right, closing the ball valve 12 to cut off the master cylinder from the brakes, and expanding the volume of the chamber 10, which increases the brake volume to reduce the brake pressure and allow wheel acceleration.

When the wheel reaches the speed of the flywheel 18 the ball and ramp mechanism 21 is loaded together by the spring 36 and the spool member 27 moves back into its closed position to cut off the pump outlet from the reservoir and allow the pump pressure to rise. This pressure acting on the piston 9 urges it back to the left to open the ball valve 12 and the restriction 37 is again opened so that the pump pressure increases to balance the brake pressure acting at the opposite end of the piston 9.

When the brakes are applied without rotation of the drive shaft 19, i.e. if the vehicle is stationary; or the pump has failed, the brake pressure forces the piston 9 to the right until the restriction 37 connecting the pump to the reservoir 2 is closed. Fluid in the chamber 11 is then trapped by the closed control valve spool member 27 and prevents further travel of the piston 9 so that the ball valve 12 remains open and the brakes can be applied normally.

If the master cylinder pressure is released while the ball valve 12 is closed, the ball valve will open to permit brake pressure release once the master cylinder pressure falls below the brake pressure.

Claims (8)

1. Anti-skid sensing means for a vehicle braking system of the type comprising a fluid pressureoperable brake for braking a wheel, a supply of fluid under pressure for operating the brake, a modulator assembly for modulating the supply of fluid to the brake in accordance with a skid signal from the anti-skid sensing means, the anti-skid sensing means comprising a shaft adapted to be driven by the wheel, a flywheel assembly rotatably mounted for rotation with respect to the shaft, drive means including a clutch and through which the flywheel assembly is driven from the shaft, camming means responsive to relative angular movement between the shaft and the flywheel assembly to produce a skid signal for operating the modulator assembly to reduce the pressure of fluid supplied to the brake when the deceleration of the shaft relative to the flywheel assembly exceeds a predetermined value, the skid-signal comprising relative axial movement between the shaft and the flywheel assembly, and biassing means for biassing both the clutch and the camming means, in which the biassing means is so constructed and arranged to prevent the skid signal from being produced unless the flywheel assembly has generated sufficient torque to overrun the shaft by a predetermined amount and to maintain the skid signal by permitting the flywheel to overrun the shaft against the clutch.

2. Anti-skid sensing means as claimed in Claim 1, in which the clutch comprises the drive means.

3. Anti-skid sensing means as claimed in Claim 1 or Claim 2, in which the flywheel assembly comprises a flywheel member, a thrust member, and means for keying one of the said members against axial movement with respect to the shaft, and the clutch comprises a clutch plate having a frictional engagement with the said other of the said members and of which the magnitude is determined by the magnitude of the biassing means, the said other of the said members being angularly movable with respect to the clutch plate upon the frictional engagement being overcome by overrun of the flywheel member with respect to the shaft, whereby axial movement of the said other member in a direction away from the said one member in response to relative angular movement between the said members produces the skid signal with any additional overrun of the flywheel member with respect to the shaft overcoming the frictional engagement to maintain the skid signal.

4. Anti-skid sensing means as claimed in any preceding claim, in which the camming means comprises a ball and ramp mechanism located between the said members to cause axial movement of the other of the said members with respect to the shaft in response to relative angular movement between the said members.

5. Anti-skid sensing means as claimed in Claim 4, in which the biassing means comprises a spring, and a lever is incorporated through which the spring acts on the clutch plate and through which the skid signal is adapted to be transmitted to the modulator assembly.

6. ' Anti-skid sensing means as claimed in Claim 4, in which the flywheel member is keyed against axial movement with respect to the shaft, the thrust member is both axially and angularly movable, and the clutch plate is urged into frictional engagement with the thrust member by the biassing means.

7. Avehicle braking system comprising a fluid pressure-operable brake for braking a wheel, a supply of fluid under pressure for operating the brake, anti-skid sensing means for producing a skid signal, and a modulator assembly for modulating the supply of fluid to the brake in accordance with the skid signal from the anti-skid sensing means, in which the anti-skid sensing means comprises a shaft adapted to be driven by the wheel, a flywheel assembly rotatably mounted for rotation with respecs to the shaft drive means including a clutch and through which the flywheel assembly is driven from the shaft, camming means responsive to relative angular movement between the shaft and the flywheel assembly to produce the skid signal for operating the modulator assembly to reduce the pressure of fluid supplied to the brake when the deceleration of the shaft relative to the flywheel assembly exceeds a predetermined value, the skid signal comprising relative axial movement between the shaft and the flywheei assembly, and biassing means for biassing both the clutch and the camming means, the biasing means being so constructed and arranged to prevent the skid signal from being produced unless the flywheel assembly has generated sufficient torque to overrun the shaft by a predetermined amount and to maintain the skid signal by permitting flywheel to overrun the shaft against the clutch.

8. A braking system as claimed in Claim 7, in which a pump having a liquid throughput adapted to increase with the totational speed of the wheel is arranged to control operation of the modulator assembly, and a control valve adapted to be operated by the anti-skid sensing means is provided to control the supply of operating fluid from the pump output to the modulator valve assembly.