EP1509432A1

EP1509432A1 - Anti-lock braking for a vehicle with steerable wheels

Info

Publication number: EP1509432A1
Application number: EP03702723A
Authority: EP
Inventors: Colin Ross
Original assignee: Knorr Bremse Systeme fuer Nutzfahrzeuge GmbH; Knorr Bremse Systems for Commercial Vehicles Ltd
Current assignee: Knorr Bremse Systeme fuer Nutzfahrzeuge GmbH; Knorr Bremse Systems for Commercial Vehicles Ltd
Priority date: 2002-02-02
Filing date: 2003-02-03
Publication date: 2005-03-02
Also published as: GB2385645B; AU2003205846A1; WO2003066402A8; GB0202484D0; WO2003066402A1; AU2003205846A8; GB2385645A; WO2003066402A9

Abstract

In an anti-lock braking system for a commercial road vehicle trailer with compressed air brakes and including a self-steer axle with such brakes, an electronic control unit (ECU) (16) selectively controls respective brake pressures to each side of another braking axle according to differential rolling surface adhesion to reduce skidding by way of respective pressure modulators (6L, 6R). The output pressures from these modulators are additionally applied directly via an axle control valve (15) to brake actuators of the wheels of the self-steer axle and the axle control valve has means (Fig 2) which responds to a pressure differential between output pressures of the modulators during anti-lock control to isolate the higher of said modulator outputs from the respective self-steer axle wheel brakes to thereby provide reduced equal brake pressures to the self-steer wheels corresponding to the modulator pressure at the low adhesion side of the other axle.

Description

ANTI-LOCK BRAKING FOR A VEHICLE WITH STEERABLE WHEELS

This invention relates to an anti-lock braking system and an axle control valve for a vehicle with self-steerable wheels, especially but not exclusively a trailer vehicle with compressed air braking. The invention is also applicable to a vehicle with force-steered wheels.

In a multi-axle vehicle with self-steerable wheels, wheels of a self-steerable axle may be provided with means whereby when the vehicle is passing along a curved roadway, pivotal movement of the wheels of the steerable axle out of parallel with other wheels improves lateral stability and reduces tyre scrub. Such steerable wheels may be on a rigid axle or suspended independently. However, if self-steerable wheels are provided with independent anti-lock control of their brakes the self- steer action, especially when being governed by wheel reaction forces with the roadway, can itself result in tyre wear and vehicle instability whilst an anti-lock mode is operating, due to differential braking forces and reactions at opposite wheels of the self-steerable axle.

With an object to reduce the above shortcoming the specification of European Patent No. 0754609 proposes an anti-skid compressed air braking system for a trailer vehicle with a common brake pressure modulator valve which responds to respective wheel-speed sensors at opposite sides of an allotted braked axle having anti-lock control via separate modulators, the common modulator providing the same brake pressure to both wheels of the self-steerable axle.

The present invention seeks to provide an alternative system to the foregoing and having an axle control valve not requiring such a common modulator.

According to the present invention there is provided an anti-lock braking system for a wheeled vehicle having a first axle with speed sensors for braked wheels thereof on opposite sides of the vehicle and a control unit (ECU) which controls fluid pressure modulators to selectively control the respective brake pressures applied to brakes of said wheels in the event of incipient skidding being sensed, the system including means for directly applying output fluid braking pressure from either or both said modulators to brakes of the wheels a further steerable axle of the vehicle and control means whereby at onset of an anti-lock mode accompanied by differential pressures from said modulators the higher of the braking pressures is isolated from the brakes of the steerable axle.

Preferably a said control means is provided by an axle control valve with means to receive the respective output pressures of the brake pressure modulators and communicate them to a delivery port the axle control means including a pressure responsive assembly responsive to a pressure differential between the pressures to isolate the higher said output pressure from the delivery port.

The invention also provides an axle control valve comprising means to receive respective output pressures of brake pressure modulators for supply to a delivery port, said valve including means responsive to a pressure difference between said pressures to isolate the higher said pressure from the delivery port. In order that the invention may be more clearly understood, the same will now be further illustrated by way of example with reference to the accompanying drawings of which:-

Fig 1 illustrates in schematic form interconnected components of a compressed air braking system of wheels of a trailer vehicle having three axles, one of which is a self-steered axle;

Fig 2 illustrates diagramatically the example of an axle control valve for the braking system of Fig 1;

Fig 3 illustrates graphically operation of Fig 1 and Fig 2

Referring to Fig 1 , fluid pressure communications are shown by solid lines and electronic communications are shown by broken lines. The compressed air braking system of a two line trailer with electronic braking and anti-lock (EBS/ABS) includes control and supply line couplers 1 and 2 respectively and a relay emergency valve 3 (of known form but which may be optional with EBS) via which a compressed air reservoir 4 is charged from a tractor system (not shown) . The trailer has first, second and third axles with respective pairs of compressed air operable wheel brake actuators 12L, 12R and 13L, 13R and 14L, 14R. The third axle is self-steered. Compressed air pressure graduable according to trailer control line pressure from the reservoir 4 is relayed via valve 3, a load control valve 5 (which again may not be a requirement with EBS) and respective left and right hand anti- lock pressure modulators 6L and 6R to the respective left and right hand brake actuators 12, 13. The actuators 14L and 14R are brake actuators of the steered axle wheels which self-steer according to the reaction between the tyres thereof and the rolling surface to improve stability and minimise tyre wear. In accordance with the invention, 14L and 14R are normally supplied with substantially equal brake pressure via an axle control valve 15. Valve 15 is supplied directly with pressures from both modulators 6L and LR. In the present example these modulator pressures are controlled by an electronic ABS control unit (ECU) 16 which operates in known manner in response to wheel speed signals from transducers 17L and 17R adjacent to the middle pair of wheels which thereby sense the road surface adhesion at each side of the vehicle during braking. In normal braking conditions with no ABS operation the modulators 6L and 6R apply equal load dependent brake pressures to actuators 12L, 13L and 12R, 13R, these equal pressures are also fed to the axle control valve 15 normally emerging at the output of valve 15 to actuators 14R and 14L. However, when the system is operating in ABS mode (and this is a difference of pressures from modulators 6L and 6R,) the axle control valve 15 operates to isolate from actuators 14R and 14L the highest modulator output. These actuators can therefore apply only equal and reduced brake forces to both wheels of the steered axle corresponding to brake pressure at the lowest adhesion side of the first axle.

The brake pressures to actuators 14L and 14R are thereby reduced for as long as the ABS control mode requires, typically until anti-lock control is no longer required or the left to right adhesion is reversed, in which case solenoid control- of the axle control valve is also reversed.

Referring to Fig 2, the axle control valve 15 comprises a housing 31 the interior volume of which is divided by a pressure responsive assembly 32. The assembly 32 is normally in a neutral position to hold spring biased valve members 33, 34 at respective ends of the housing off their respective seats 35, 36. However for the purpose of illustration the assembly is shown so deflected rightwards that valve member 33 is seated with seat 35 whereas valve member 34 is unseated from its seat 36. The pressure responsive assembly comprises a central circular spacer 37 between opposed sides of which and respective circular end mouldings 38, 39 circular flexible diaphragms 40 and 41 of greater diameter are sealingly clamped and the peripheries of the spaced diaphragm are similarly sealingly clamped between opposed sides of a mounting bracket (which provides an annular central part 42 of the housing) and housing end mouldings 43,44. These end mouldings include outwardly extending end regions 45, 46 with end covers which enclose the valve members 34 and 35 and light biasing springs 47 and 48. Castellated ends 49 and 50 of the pressure responsive assembly respectively extend sealingly but axially moveable through interior housing wall portions into regions 45 and 46, to be engageable non-sealingly, for unseating action, with the valve members 33, 34. Regions 45 and 46 are however respectively continually in free connection with respective opposed sides of the assembly via passages 57, 56. The moveable assembly also has an axial bore 51 and radial passages 52 via which bore 51 communicates with a delivery port 53 for the control valve.

In operation of the axle control valve of Fig 2, respective output brake pressures from the ABS modulators 16L, 16R of Fig 1, are applied to- opposite sides of the assembly 32 via input ports 54 and 55 of the housing. Whereas the assembly is shown in its rightward position, it will normally rest in the mid- position with both valve members 33 and 34 unseated from valve seats 35 and 36. In such mid-position air brake pressure can be communicated between input port 54 to the left side of the pressure responsive assembly 32, the region 45, via unseated valve 33, 35, bore 51 and radial passages 52 to the delivery port 53. Similar communication exists between port 55, region 46 via unseated valve 34, 36 to port 531 the pressures at ports 54 and 55 being assumed to be substantially equal.

Referring to the graphical illustration of Fig 3, curves (a) and (b) represent right and left side wheel speeds for the non-steered middle axle of the trailer vehicle following onset of braking at a point in time A. Following some speed reduction, a tendency to skid is observed at point B. At this point, the adhesion is assumed to be equal on both sides of the vehicle and the axle control valve therefore transmits similar co on pressures to the brake actuators as shown in the broken line curve (c) . Following wheel speed recovery at point C a further tendency for the middle axle wheels to skid again occurs at point D but with predominantly lower adhesion on the right hand side of the vehicle. The resultant difference of output from the modulators 6L and 6R then causes the left hand modulator pressure to be isolated by the axle control valve from the direct delivery to both the actuators of the steerable axle, the brake pressure thereto being reduced towards that applied to the right side of the middle axle. The steerable axle wheel speeds resulting from this are illustrated by the part of curve (d) which follows point in time D but it may be observed that the speed fluctuation here may be somewhat less for higher adhesion.

Referring to operation of the ABS to deal with the mentioned reduced braking adhesion on the right side of the vehicle as sensed by the wheel speed sensors, the modulator valve 6R of Fig 1 provides reduced pressure to the brake actuators 12R and 13R of the right hand wheels of the middle axle and first axle. The reduction of pressure from modulator applied via port 55 results in movement of the assembly 32 towards the position shown in the Fig 2, resulting in the valve 33, 35 being seated to isolate the higher pressure (from modulator 6L) at port 54 from the delivery port. Only the pressure at port 55 is therefore communicated via chamber 46 via passage 51 to the delivery port 53 and to both actuators 14L andl4R." The reverse action occurs in the case of the pressure t port 55 being higher -than that at -port 54, to seat valve-34 and isolate port 55 from the delivery port 53.

In order to enhance the speed of reduction of the common brake pressure from the actuators of the self-steer axle the actuators may be provided with actuator pressure through a common delivery port and via a common quick release valve. Indeed, such quick- release valve may be integrated with an axle control valve unit according to the invention if so required.

When installing an axle control valve arrangement such as described in the foregoing for a self-steer axle of a vehicle it is to be appreciated that the air ways are sufficiently large and hysteresis is not such as to result in unintended depletion of brake pressure through unsynchronised cycling in ABS mode.

Whilst the axle control valve described in the foregoing with reference to Fig 2 of the accompanying drawings is described more especially in relation to anti-lock control of brakes of self-steerable axle brakes during anti-lock braking of a vehicle, such an axle control valve may be employed in force steerable arrangements. Moreover, such an axle control valve may be provided to afford a simplified anti-lock control of brake pressure of wheels of a lifting axle the tyres of wheels of which contact the rolling surface only when the vehicle is heavy-laden. By such means the size of actuators to one or more other axles may be less than otherwise required, whilst providing extended distribution of braking of the vehicle.

Claims

1. An anti-lock braking system for a wheeled vehicle having a first axle with speed sensors (171,17R) for braked wheels thereof on opposite sides of the vehicle and a control unit (ECU) (16) which controls fluid pressure modulators (6L,6R)to selectively control the respective brake pressures applied to brakes of said wheels in the event of incipient skidding being sensed, characterised in that the system includes brake pressure application means adapted to directly apply output fluid braking pressure from either or both said modulators (6L,6R) to brakes of the wheels of a further steerable axle of the vehicle and control means whereby at onset of an anti-lock mode accompanied by differential pressures from said modulators the higher of the braking pressures is isolated from the brakes of the steerable axle. ^~

2. An anti-lock braking system as claimed in Claim 1, wherein said control means comprises an axle control valve (15) having means to receive the respective output pressures of the brake pressure modulators (6L,6R) for supply to a delivery port, the control means including a pressure responsive assembly (32) responsive to a pressure differential between said pressures to isolate the higher said pressure from the delivery port.

3. An anti-lock braking system as claimed in Claim 2, wherein said pressure responsive assembly is axially sealingly moveable in a housing (31) , the housing (31) being thereby divided into respective regions (45,46) which communicate with respective valves which are held open in a mid-position of the assembly, movement one way or the other causing closure of a respective said valve each said valve when open providing a communication to the delivery port (53) via an axial passage (51) of the assembly.

4. An anti-lock brake system as claimed in Claim 3, said axial passage (51) communicating with said delivery port (53) via a space between a pair of diaphragms (40,41) within the housing and which separates said regions.