This invention relates to a vehicle brake system for semi trailers, trucks, buses, trains and the like-

It has been found that heavy vehicles eςruipped with compressed air brake systems, especially prime movers when towing trailers, are experiencing premature brake lining wear. Premature brake lining wear results in costly down time. This is particularly relevant to systems conforming to ADR 38 and comparable international standards.

It has been found that 90% of all braking events are relatively gentle. Premature wear of prime mover brakes is due to the fact that gentle braking results in a delay in a low pressure signal being transmitted along a control line from the prime mover to the trailer. Low pressure signals travel slowly, and also the trailer brake system takes longer to actuate to the point of brake shoe to drum contact compared with the response to a higher pressure signal from a more severe braking event. Therefore, there tends to be a significant lag between the onset of gentle braking by the prime mover and the application of the trailer brakes. Thus, the prime mover brakes take most of the braking load initially and therefore wear to a greater extent than the trailer brakes. It is believed that the excessive initial load is important for wear because surfaces of the prime mover brake linings heat up, and then stay hotter than the trailer brake linings for the duration of the braking event, even after the trailer brakes have balanced an application pressure with the prime mover brakes. Since brake lining wear increases exponentially with surface temperature, the fact that the prime mover brakes have attained a higher temperature and remain hotter for the duration of each gentle braking event results in increased wear of the prime mover brakes.

The timing delay whereby the prime mover brakes are applied before the trailer brakes also contributes to the tendency of the vehicle to jackknife.

Some attempts have been made to address the above problem and basically comprise the injection of air into the braking system. However, conventional systems have not met with any commercial success and semi trailers and similar large vehicles still suffer from premature brake lining wear in the prime mover and a tendency to jackknife.

In the conventional systems, the emphasis has been placed on activation of a relay valve in the brake control system by either applying compressed air from a supply line or other source direct to the relay valve, to the relay valve via a three way valve whilst blocking the control line, or by coupling the air in close proximity to the relay valve.

We have found that close proximity coupling makes the trailer brakes prone to momentary lock up which is highly undesirable. This is most likely due to a pressure spike which occurs for about 0.2 seconds as the injected air dissipates down the control line towards the foot valve operated by the brake pedal in the prime mover. With conventional arrangements, the only way to reduce this effect is to reduce the volume of air injected to a point where reduction in application delay of the driver controlled braking force is ineffective and therefore no advantage is obtained.

Furthermore, prior art systems seem to be directed more to initial activation of the relay valve rather than addressing the problem of initial braking imbalance caused by the delay of the driver controlled braking force. That is, the imbalance between braking load taken up by the prime mover brakes and the trailer brakes at the onset of braking.

The present invention may be said to reside in a vehicle brake system which includes: a brake valve associated with the vehicle; a relay valve for supplying fluid to vehicle brakes for activating the vehicle brakes; a fluid supply coupled to the relay valve so that upon actuation of the relay valve, supply fluid is supplied from the fluid supply via the relay valve to the vehicle brakes to actuate the vehicle brakes; a control line connected between the brake valve and the relay valve so that upon movement of a brake mechanism in the vehicle, a control signal is supplied down the control line to the relay valve to activate the relay valve; and fluid supply means for supplying fluid to the control line to prime the control line when the brake mechanism is moved, the fluid supply means supplying fluid to the control line such that the control line is primed to thereby enable rapid transmission of a control signal in the control line from the brake valve to the relay valve without causing the relay valve to activate to cause momentary lock up of the vehicle brakes.

Since the invention primes the control line, the control signal from the brake valve is rapidly transmitted to the relay valve to thereby cause the brakes to be applied without delay thereby ensuring that the initial braking load is shared between all the brakes of the braking system, and in the case of a prime mover and trailer, between the prime mover brakes and the trailer brakes. The application of the fluid to the control line is such that the relay valve is not activated sufficiently to cause momentary lock up thereby ensuring braking is smooth and the braking system operates effectively and safely during gentle braking events.

Preferably the fluid supply means supplies fluid from a

single outlet into the control line.

In a first embodiment of the invention, the fluid supply means comprises a fluid branch conduit interconnecting the supply line with the control line, the fluid branch conduit having a valve member for selectively opening and closing the fluid conduit to allow flow of fluid from the supply line to the control line, the valve member being activated at the start of a braking event and wherein the conduit is coupled to the control line at a point falling within the range, in terms of volume of the control line between the relay valve and the brake valve, of about 10% of the total volume of the control line taken from the relay valve to about 70% of the total volume of the control line taken from the relay valve.

Preferably the range is from about 15% to about 60% and most preferably, the fluid branch is coupled to the control line at a volumetric point of about 30% of the control line from the relay valve.

In a second embodiment of the invention, the fluid supply means comprises a branch conduit extending from the supply line to the control line, the branch conduit having a valve member which is operated upon commencement of a braking event to supply fluid from the supply line to the control line, the branch conduit joining the control line at a point falling within the range, in terms of volume of the control line between the relay valve and the brake valve, of about 0% of the total volume of the control line taken from the relay valve to about 30% of the total volume of the control line taken from the relay valve, and a blocking member for blocking the supply of air from the branch conduit to the relay valve until the air has primed the control line, thereby preventing a pressure spike from reaching the relay valve and causing momentary lock up of the brakes.

Preferably the point is in proximity to the relay valve.

In a third embodiment of the invention, the fluid supply means comprises a branch conduit extending between the supply line and the control line, the branch conduit having a valve member which is operated upon commencement of a braking event to allow supply of fluid from the supply line to the control line, the branch conduit being connected to the control line at a position in the range, in terms of total volume of the control line between the relay valve and brake valve, of about 30% to 100% of the total volume of the control line taken from the relay valve, and a blocking member arranged to prevent air from the branch conduit from exhausting out of the control line via the brake valve to ensure that the fluid primes the control line.

The blocking member can comprise a check valve or an alternative embodiment can comprise a directional nozzle which simply directs fluid in the control line away from the relay valve or brake valve respectively when the branch conduit is in close proximity to the relay valve and brake valve.

Preferred embodiments of the invention will be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a view of a prime mover and trailer including the braking system of the preferred embodiment of the invention;

Figure 2 is a schematic diagram of the braking system according to a second embodiment of the invention; Figure 3 is a schematic diagram of a braking system according to a third embodiment of the invention;

Figure 4 is a diagram showing a blocking member according to the preferred embodiment of the invention; and

Figure 5 shows the branch conduit arrangement

according to the first embodiment of the invention.

With reference to figure 1, a prime mover 10 is shown which tows a trailer 12. The prime mover has a brake valve, which in the embodiment shown, comprises a foot valve 14 which includes a brake pedal which is depressed by a driver to apply the vehicle brakes.

A control line 18 extends from the foot valve 14 to a relay valve 20. The relay valve 20 supplies fluid to the brakes (not shown) of the trailer 12. A fluid supply line 22 is provided for supplying pressurised fluid to the relay valve which, upon actuation of the relay valve, is supplied to the vehicle brakes to apply the vehicle brakes. The supply line 22 includes a compressor/compressed fluid reservoir 24. As is conventional, the control line 18 includes a part 18b associated with the prime mover and which has a coiled hose 26. The hose 26 is connected to suitable connectors on the trailer 12 to join the hose 26 to the part 18a of the control line 18 associated with the trailer 12. Similarly, the supply line 22 includes a part 22b associated with the prime mover and which has a coiled hose 28 which is connected to the part 22a of the control line 22 associated with the trailer 12 by conventional connectors. An electric cable 32 is also provided for supplying an electric signal to vehicle brake lights 34 upon application of the foot valve 14. Conventionally, the signal is generated by a pressure sensitive switch located in the control line near the brake valve so for all intents and purposes the reaction of the pressure switch can be said to be coincident with the depression of the pedal of the brake valve.

An electrically operated fluid supply means 50 is arranged between the supply line 22 and the control line 18 and includes a branch conduit 52 and a solenoid valve 5 . The solenoid valve 54 is electrically connected to the cable 32

- 1 - by electrical wiring 34 so that upon depression of the brake pedal 14, an electrical signal is provided by the lead 34 to the solenoid valve 54 to activate the solenoid valve 54. Activation of the solenoid valve 54 allows fluid to flow from the supply line 22, through the branch conduit 52 to the control line 18 to prime the control line. Activation of the foot valve 14 by the driver of the prime mover also causes a control signal to be supplied down the control line 18 from the foot valve to the relay valve 20 to activate the relay valve 20 and thereby cause the trailer brakes to be applied.

Priming of the control line 18 with fluid from the supply line 22 substantially immediately upon application of the brake pedal by the driver enables the control signal to be transmitted from the brake valve 14 to the relay valve 20 with reduced delay to thereby cause the trailer brakes to be applied with reduced delay so that in a gentle braking operation the braking load is shared between the prime mover brakes and the trailer brakes.

The structure of the supply conduit 52 and solenoid valve 54 is fully disclosed in copending international patent application PCT/AU93/00292 and the subject of that application is incorporated herein by this reference. Further details of the solenoid valve 54 and conduit 52 will therefore not be described in detail herein.

The branch conduit 54 is arranged with respect to the control line 18 so that it injects air into the control line at a point falling within the range, in terms of volume of the control line between the relay valve and the brake valve, of 10% of the total volume of the control line taken from the relay valve to 70% of the total volume of the control line taken from the relay valve. It should be noted in some applications prime movers include an intervening relay valve downstream of the foot valve 14 and

in such applications the volume of the control line to determine the location of the branch conduit 52 should be taken between the relay valve 20 and the intervening relay valve (not shown) . Similarly, in multiple trailer units (not shown) a relay valve of one trailer or an intervening relay valve becomes the brake valve for determining the coupling point of the conduit for supplying the fluid to the control line which transmits control signals to the relay valve of the next trailer.

The volumetric range referred to above is determined by starting at the relay valve 20, travelling towards the foot valve 14 or intervening valve (not shown) until a volume of 10/100 X is attained wherein X is the total volume of the control line between the relay valve 20 and the foot valve or intervening valve as the case may be to obtain a first point on the control line. The second point defining the end of the range on the control line is determined by starting at the relay valve 20, travelling towards the foot valve 14 or intervening valve (not shown) until the volume of 70/100 X is attained. The branch conduit 52 interconnects the control line between the first and second points referred to above in the range of 10% to 70% of the total volume of the control line from the relay valve 20. Most preferably the branch conduit 52 interconnects with the control line 18 at a point 30% of the total volume of the control line from the relay valve. The total volume of the control line between the relay valve and brake valve does not include any branch line from the control line to, for example, the prime mover brakes.

In the most preferred example of the invention the reason why the branch conduit 52 interconnects with the control line 18 closer to the relay valve 20 than the brake valve 14, is that when the braking event commences air starts to flow into the control line 18 from the brake valve 14 thereby commencing the priming operation of the control

line 18. Thus, some air is introduced into the control line 18 at the vicinity of the brake valve 14 and therefore in order to prime the control line 18 the branch conduit 52 preferably interconnects closer to the relay valve 20 than the foot valve 14. It is important that the volumetric points along the control line 18 be determined rather than linear points because it is common practice to have lines of different diameter on the prime mover 10 and trailer 12. The purpose of the branch line 52 is to prime the control line without activating the relay valve 20 which would cause momentary lock up of the trailer brakes 12. Priming of the control line 18 enables the control signal from the foot valve 14 to travel from the foot valve 14 to the relay valve 20 with reduced delay thereby causing the trailer brakes to be properly applied at the commencement of the braking event so that in braking events, the braking load is shared between the trailer brakes and the prime mover brakes.

Figure 2 shows a second embodiment of the invention in which the branch conduit 52 is arranged in close proximity to the foot valve 14. Preferably the branch conduit 52 connects to the supply line in the range 30% to 100% of the total volume of the control line and most preferably at the connection of the coiled hoses 26 and 28 with the prime mover 10. In this embodiment, the conduit 52 includes a blocking element and the solenoid valve 54c, and the blocking element typically comprise a three way valve 60 as shown in figure 4. The three way valve 60 includes a solenoid valve 54c which has terminals 55 for connection to the electrical cable 34 described with reference to figure 1 via a timer circuit (not shown) .

The three way valve portion 60a has a passage 62 which has a first opening 64 and a second opening 65 so that fluid can flow through the passage in the direction of arrow A. The control line 18 is cut so that the passage 62 is

located in the control line so that fluid can flow from the control line 18, through the passage 62 and back into the control line 18. The supply line 22 is also connected to an opening 66 via the branch conduit 52 (not shown in figure 4) . The opening 66 communicates with a passage 61a which in turn communicates with a chamber 63. End 61c of the passage 61a is closed by a valve element 64 of the solenoid valve 54c to control the flow of fluid from the branch conduit 52, opening 66 and passage 61a into the chamber 63. The solenoid valve also has an armature 59 which supports the valve element 64 and which is movable in the direction of arrow C upon application of electrical energy to the terminals 55. The armature 59 carries a second valve element 72 at its opposite end. The valve element 72 selectively closes a vent outlet passage 57 when the armature 59 is moved in the direction of arrow C.

The chamber 63 has a passage 61b communicating with it. The passage 61b extends to the valve chamber 67 in the check valve 60. The valve chamber 67 includes a valve element 69 which is spring biased by spring 71 towards the passage 61b. The check valve 60 also has a valve seat 75.

Upon application of a brake pedal by a driver, electrical energy is supplied to the terminals 55 which causes the armature 59 to move in the direction of arrow C to move valve element 64 away from end 61c to thereby open the passage 61a. The vent passage 57 is therefore closed by the valve element 72. Supply fluid therefore flows through the passage 61a into the chamber 63 and out through chamber 61b to the valve element 69. The pressurised fluid causes the valve element 69 to move against the bias of spring 71 so that the valve element 69 seats on valve seat 75. Continued supply of pressure in chamber 61b deforms flange portion 69a of the valve element 69 so that air is able to flow about the valve element into the chamber 68. With the valve element 69 seated on valve seat 75, the passage 62 is

shut off and fluid is not able to flow from the chamber 68 towards the opening 64. Fluid is able to flow from the chamber 68, through passage portion 62a, to opening 66 and enter the control line 18 to prime the control line. The seating of the valve element 69 on the seat 75 blocks off the control line to prevent the pressurised air which is priming the control line from simply flowing through the opening 64 and the foot valve 14 and hence to atmosphere.

After a short time interval, the solenoid valve 54c is deactivated thereby causing the armature 59 to move in a direction opposite arrow C to its normal position where the valve element 64 blocks off the opening 61c. This shuts off supply of pressurised fluid to the passage 61b which therefore enables the valve element 69 to be biased by spring 71 to the position shown in figure 4 where the valve element 69 is removed from the valve seat 75 and the passage 62 is effectively opened. The valve element 69, in this position, seals off the passage 61b so that fluid in the passage 62 is not able to pass through the passage 61b. Any pressurised fluid trapped in the passage 61b is able to pass from the chamber 63, around the armature 59, and out through vent passage 57 to atmosphere. The control signal which is generated upon application of the brake valve 14 is thereby able to pass down the control line 18 via the passage 62 to activate the relay valve 20 after priming of the control line 18.

Thus, in this embodiment of the invention the branch conduit 52 can be arranged in proximity to the foot valve 14 without fear of the fluid which is to prime the control line 18 merely exhausting through the foot valve 14 rather than filing the control line 18. In a braking event the foot valve 14 acting as a regulator set to a low pressure, will not hinder the exhausting of the priming air. Because the spring 71 biases the valve element 69 in the open condition, air is also freely able to flow in a direction

opposite arrow A to allow exhausting of the control line at the completion of the braking element .

In the embodiment of the invention shown in figure 3, the branch conduit 52 is located in proximity to the relay valve 20. This embodiment utilises the check valve 60 which is identical to that shown in figure 4 except that valve 60 is arranged so that when the valve element 69 is closed to shut off the passage 62 air is prevented from flowing from the chamber 68 to the relay valve 20 and thereby prevents a pressure spike being supplied to the relay valve 20 which would cause momentary lock up of the vehicle trailer brakes. Once again, after a short period of time, the solenoid valve 54c is deactivated to thereby open the passage 62 to allow normal pressure signals to be transmitted along the control line 18 to the relay valve 20 to activate the relay valve 20 and allow the relay valve brakes to be applied.

Rather than utilise a three way valve as shown in figure 4, the blocking of fluid flow to the foot valve 14 to prevent the fluid from merely venting to atmosphere and the blocking of the fluid flow to the relay 20 to prevent locking up of the vehicle brakes can be achieved by a directional nozzle as shown in figure 2 of previously mentioned international application PCT/AU93/00292. If this arrangement is utilised the fluid is directed down the control line 18 in the desired direction so that it will not flow towards the relay valve 20 or the foot valve 14 as the case may be and will prime the control line 18 without producing a pressure spike which would active the relay valve 20 and cause momentary lock up of the trailer brakes or merely vent into atmosphere through the foot valve 14.

Figure 5 shows an arrangement of the branch conduit 52 on the front of a trailer 12. The branch conduit 52 includes the solenoid valve 54 and leads 34 stemming from a plug 35

included in the electrical line 32 (figure 1) . The branch conduit 52 includes a hose 85 and a hose 86 which interconnect in a T-arrangement with connectors 90 and 92 which in turn receive corresponding connectors of the parts 18b and 22b of the control line 18 and supply line 22 shown in figure 1. The connector 92 includes a directional nozzle (not shown) .

Since modifications within the spirit and scope of the invention may readily be effected by persons skilled within the art, it is to be understood that this invention is not limited to the particular embodiment described by way of example hereinabove.