Discussion Paper
ARTSA, April 2008
New technologies that apply electronic control of brakes have now matured into reliable commercial options for single, semi-trailer and B-double vehicles. These are:
- Antilock Brake System (ABS), which limits the friction utilization to pre-slip levels during braking.
- Traction Control (TC), which applies the drive-wheel brakes to prevent wheel slip during traction.
- Electronically Controlled Brake Systems (ECBS), which adjusts the brake balance on a vehicle in response to performance measures.
- Vehicle Stability Systems (VSS), which applies individual brakes to improve directional stability.
Additionally, collision avoidance and lane guidance technologies may become commercially available in the future. Regenerative braking systems are currently being introduced that can apply substantial retardation to the drive wheels.
Australia has baulked at mandating antilock brakes (ABS) on heavy vehicles because of concerns about reliability and cost. There is a respectable argument that mandated ABS provides a protection against the consequence of poor brake balance; which is loss of directional control during heavy braking. Australia’s major trading partners (Europe, USA and China) have mandated ABS on heavy vehicles including trailers.
Whilst new electronic technologies can improve brake performance, there are potential problems. If the brake balance on a vehicle is poor, antilock brakes may increase stopping distances because wheels that have a propensity to lock-up will be routinely modulated (ie the brake is released and then reapplied). The new technologies work best when the brake balance is reasonably good.
In particular antilock brakes may greatly increase stopping distance on gravel roads. Most antilock systems have a second level of control that can be temporarily activated by the driver when driving on a loose surface. This feature should be mandated when antilock brakes are used in Australia.
The case for mandating antilock brakes on trailers is not as strong as on motor vehicles. The greatest benefits come from protection against wheel lock-up on drive axles of motor vehicles. A significant problem is that trailer antilock will not function unless provision is made on the motor vehicle to provide the necessary electrical connections.
Antilock brakes are currently mandated on dangerous-goods hauling B-double trailers as well as B-double prime-movers. It could be that 20% of antilock brake systems on applicable semi-trailers do not function, due mainly to sensor mal-adjustment and wheel bearing slackness. The dangerous-goods haulage sector of the Australian transport industry is accustomed to maintaining antilock brake systems and probably experiences a greater level of reliability.
Manufacturers of electronically controlled braking systems should improve the adjustment performance of wheel speed sensors; which are currently vulnerable to bearing slop and rough-road vibrations. Wheel speed sensors should be ideally located radially and not laterally.
Automatic brake adjusters should be used when antilock brakes are installed. These keep the brakes in tight adjustment and thereby minimise brake air pressure loss when the valves modulate. Furthermore, the cycling modulation performance is improved when the time delays due to brake movement are minimal.
Unreliability with wheel-speed sensor adjustment is a threat to the achievement of the full potential of electronically- controlled brake systems. It is likely that 25% of heavy vehicles on Australian roads that have antilock brakes have some wheel sensors out of adjustment with the consequence that the system does not work on some of the wheels.
On balance, antilock brakes should be mandated on new heavy motor vehicles, but not on heavy trailers. This requirement should apply to new motor vehicles within a two-year time frame. Prime-movers or rigid motor vehicles that are certified for road-train use should be exempt from this requirement.
Electronically Controlled Braking Systems (ECBS) could improve brake balance performance as well as providing antilock brake protection. When used, it is highly desirable that ECBS is on all parts of a combination vehicle. Note that current ECBS systems are usually installed in conjunction with load proportioning brakes.
ECBS in conjunction with vehicle stability systems (VSS) are to be mandated on new heavy vehicles in Europe within a few years. If correctly maintained, these systems should provide greatly improved heavy vehicle braking, directional stability and roll stability. The performance improvements will be lost if new vehicle parts are coupled with old (without electronic technologies) parts.
Governments should find ways to encourage use of the new technologies on all parts of a heavy combination vehicle.
Currently antilock brakes are mandated on B-double prime-movers and on B-double trailers with placarded dangerous goods loads. It is inconsistent that single and semi-trailer vehicles do not also need to have antilock brakes. Despite the recommendation not to mandated antilock brakes in the short-term generally for Australian trailers, there is a good case for requiring all dangerous goods carrying vehicles other than road trails to have antilock brakes. The justification is that the costs of dealing with a crash involving such vehicles are particularly high.
There is also a case for requiring new B-double and B-triple vehicles that haul dangerous goods to have an electronically controlled brake system (ECBS). This requirement would give Australia an extensive experience of the benefits and problems with ECBS. Many dangerous goods B-doubles are currently being specified with ECBS.
Amendments to the Australian Design Rules are needed to set appropriate performance levels, compatibility requirements and warning features for electronic brake control technologies. One important question is whether the type-approval test requirements for antilock brakes that are in UN ECE R13 should be adopted here.
Proposals- Amend ADR 35 to require new motor vehicles, other than road train prime-movers, to have an antilock brake system that controls all wheels.
- Amend the AVSRs to exempt motor vehicles from requiring a functioning antilock brake system when they travel on gravel or unsealed roads.
- Require new vehicles that are fitted with an antilock braking system to not exhibit wheel lock-up (except below 5 km/h) when they are stopped from 60 km/h at full control level.
- Require that antilock brake systems when used on any vehicle other than a steerable trailer axle, to have independent sensing and control between sides on the one axle group. (“Split-mu performance”).
- Require that when a vehicle has both antilock brakes and a tow coupling, that an electrical connection for the trailer of the prescribed type be supplied.
- Require that trucks that are placarded for dangerous goods haulage (other than two or three-trailer road trains) have a functioning antilock brake system on all parts.
- Require in the medium term that B-double trucks that are placarded for dangerous goods haulage have a functioning ECBS system on all parts.
- Require that automatic brake adjusters be installed when a vehicle is fitted with an anti-lock brake system.
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Robert
Suggest add steer axle to "The greatest benefits come from protection against wheel lock-up on drive axles of motor vehicles."
If the proposed dirt road lockout or intelligent equivalent is fitted what is the justification for excluding road train prime movers? The ATA has sought to ensure multi-use prime movers are allowed, and this exclusion undermines this policy intent. The industry should be ensuring that primemovers can be multi-tasked wherever possible.
Can manufacturers confirm that reliable application of ECBS to two trailer plus multicombinations is practical?
The proposals need further work as in some cases they are not discussed within the discussion paper. For example "Split-mu" performance.
David Coonan ATA.
Can I suggest that point 4 needs to be clarified/amended to account for the front dolly on dog trailers. It suggests “any vehicle other than a steerable trailer axle” run an antilock system in ‘split mu’ configuration. However, the front axle group (dolly) on a dog trailer does not technically have steer axles but instead is a steerable group with rigid axles. I believe no current ABS/EBS supplier is able to run split mu on the dolly group on dog trailers.
Tony Ryan (SAF-HOLLAND)