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Thomas Ford 85-16
Top Member
USA
4177 Posts |
 Posted - 11/23/2010 : 5:15:23 PM
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Is anyone using service brake interlocks on air brakes, where a full pressure application is automatically made on the service brake when the red flashing lights are activated, thus avoiding the use of the spring applied parking brakes? I would like to hear of your experiences with them. I have become interested in these lately because of the following reasons:
I apply my parking brake (via the dash push/pull valve) at every bus stop (as required by state policy). Toward the middle of the year, my hand starts to get tingly and then becomes somewhat numb an hour or so after the run each day.
I am well aware of the wear this frequent application puts on the spring brakes. I am the only person in my fleet to use my park brake so religiously, and it's always my buses that need new dash valves, that are blowing diaphragms, and are breaking their springs inside the chambers.
The bus stop could be a quieter experience for the waiting students. The percussive "whoosh" typical of Blue Bird transits and almost all conventionals tends to startle some of the youngest students.
I was sure I read about automatic service brake interlock systems before on the SBF forums, but a search has revealed nothing. The following link is the only place I can find info online anymore.
http://www.loadingzonesafety.com/products/pedlok.html
I have a feeling that since the product didn't take off, that most companies no longer offer it.
Here are the advantages of the system that I could see:
Less wear! Parking brake is now just used for PARKING.
More effective way to hold the vehicle stationary in the event of a crash. Ie: 6 tires now have braking force, rather than the previous 4.
If a bus is hit and starts to slide while a service brake interlock is applied, I would think the ABS could start to do its thing and bring the bus to a stop sooner, compared to a parking brake where the rear axle would just keep skidding.
One less step for the driver. I can spend more time looking at my mirrors now.
Quieter bus stops.
One thing that might be handy with these sytems is an exterior "beep" when it is applied. That way students (who used to listen for an air brake) know that the bus is secured. I've heard IC CE's beep ever so breifly when they are moved in and out of their park position (because they pass through reverse) and I think using that sort of sound would be effective.
So anyway, I'd like to hear of your thoughts on these systems! |
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bus724
Top Member
USA
1609 Posts |
Posted - 11/23/2010 : 5:47:14 PM
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I have a problem with telling drivers not to apply the spring brake when an interlock is present unless the interlock is mandatory on every bus and buses are placed out of service for any failure of the system. I work with drivers who have enough trouble finding the switches on different buses and remembering to do all the pick-up steps in the proper sequence. If you add an optional interlock to the mix, it would be very easy to forget if the bus has one or not and either set the brake with the interlock applied (causing that extra wear on the system) or not set the brake on a bus without the interlock (potentially running someone over).
I've heard mechanics say that setting the brake at every stop adds extra wear to the components, but I would argue that a brake system designed for a school bus application should be able to withstand that much us, and any resulting maintenance is a cost of business for a school bus operation. It would be the same as saying that stop-and-go driving is excessive wear on a transmission.
As for your hand, you should try one of those rubber covers for the brake knob, I had some wrist pain until I got one for my bus.
http://commerce1.cera.net/tacbusparts/sections/catalog/catalog.asp?cat_id=1415 |
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bwest
Administrator
United States
3820 Posts |
Posted - 11/24/2010 : 07:41:55 AM
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| Thanks for the information on the rubber covers. I ordered one to try today. I am thankful we don't have many air brake systems because we have the same law in Illinois. Now, I don't know if the drivers follow procedure or not but I do not have trouble with my drive line park brake systems like you are having trouble with your air system. I have all kinds of opinions on this law but sufice to say I won't be getting any more air systems if I have any say at all. |
Bryan |
Edited by - bwest on 05/06/2011 1:42:00 PM |
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Fastback
Top Member
1500 Posts |
Posted - 11/24/2010 : 09:04:35 AM
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"More effective way to hold the vehicle stationary in the event of a crash. Ie: 6 tires now have braking force, rather than the previous 4."
Of course the spring applied air parking brake 4 tire braking force is far more secure than any driveline parking brake could accomplish on a hydraulic brake bus.
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Why yes, the ORIGinal CHARGER is a Fastback |
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08 Thomas EF
Top Member
533 Posts |
Posted - 11/24/2010 : 4:32:18 PM
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^ I think that would be better than not setting the brake at all. I've known drivers who set their air parking brakes religiously but never set hydraulic parking brakes... either because the hydraulic buses are AmTran FEs and the parking brake lever is on the floor to the right of the driver's seat (making it very inefficient to engage the brake, put it into neutral, and open the door with one hand)... not to mention how painful it must get to bend to the floor at every stop. My former driver who was T-boned in her personal vehicle by a motorcycle had hip injuries. She returned to drive almost a year later, and we had switched from an '01 TC with air brakes to a '97 TC with hydraulic brakes because the '01 didn't have enough seats for our growing load count. Operating that foot-controlled hydraulic parking brake in the '97 TC was not a good thing for her. She still did it at stops with many people or on hills, but that's it. She applies air parking brakes at every stop, along with another driver who doesn't apply the AmTran FE brakes at stops.
So, the moral of the story is that, since drivers around here don't tend to use hydraulic parking brakes anyway, I'd like to see this kind of system on them if it could be done. |
Edited by - 08 Thomas EF on 11/24/2010 4:33:29 PM |
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JustinB
Advanced Member
United States
490 Posts |
Posted - 11/25/2010 : 08:31:57 AM
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A device I've seen that works well on air brake systems:
Many refuse trucks have a "Work brake". It's a detented "Johnny bar" lever on the column.
When the lever is pulled into the dentended (or applied) position:
A) primary service brakes (rear axle) are applied
B)the auto neutral function with the Allison transmission is activated.
Transmission is range inhibited until the work brake is released. A truly multi-plexed bus may also include the door proximity switch to show the door as closed.
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I may not know the answer but I can usually find who does. |
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buster133
Top Member
USA
512 Posts |
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57fan
Senior Member
United States
148 Posts |
Posted - 11/28/2010 : 9:08:25 PM
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Thomas- Ford
Here is some thoughts on interlock systems and air brakes from a mechanics view.
Here is Washington state it is a requirement for the drivers to place the bus in neutral and apply the park brake at EVERY stop before loading and un-loading students. Cut and dry. This does cause premature wear on some braking components as well as drivers having issues with the brakes snap of the PP-1 valve when applied. there are a couple of very good alternatives to this. The EZ-Grip as stated above by Bendix is a good start. they are inexpensive and your mechanics should be able to get them from there brake supplier cheaper than finding them here on the internet. They usually cost about $9.00 or so. I'll state the other option later.
I have no knowledge of the interlock systems that are available but if they were good they would be standard on buses. Any thing added to a bus effects the overall cost of a bus. Unless NHTSA requires this addition to a bus you will not see them standard equipment. The technology is there for automatic transmissions to be locked into neutral during loading and un-loading but this is not available in buses by Allison Transmissions to my knowledge. We run mostly Allison World Transmission (push button) which makes it easy to shift in and out of gear (plus they are very durable and will not "do something" that will harm the transmission)
As for the air brake system, When the park brake is applied air is released from the park brake side of the rear brake air cans. This does not happen as fast as you may think. Yes it does cause increased wear on the spring within the air can as well as "S" cam, bushings and slack adjusters. If you have your foot on the brakes and apply the air brake nothing happens to the park brake due to the anti-compounding valve (prevents air brake application while brakes are applied). If you remove your foot from the brake then the park brake will apply as the service brake is released. There is no movement in the drive train at all during this transition.
As far as being in an accident while you have your foot on the brake, the anti lock brakes are useless. The Brake ECU knows the vehicle is not moving fast enough for the ABS to work. The driver could loose there footing on the brake pedal and thus the bus could move. With the park brake applied you are not going to "roll away".
If your bus is needing continued valve and diaphragm replacement you need to look at what is really causing them to go out. Ensure your mechanics are checking for oil in the air system as well as changing the air dryers yearly. Oil in a system is hard on valves and diaphragms as well as dirt getting into the brake cans.
As for quieter stops, Don't worry about it too much. Students need to hear you coming to be aware of whats going on around them. applying the park brake is not much louder that the screeching of brakes in general (some buses sound like garbage trucks when they stop). If it is an issue of just another step for a driver to remember then maybe the driver needs to find another occupation. Safety of the driver and students is priority #1.
Now for another alternative option to pulling the PP-1 knob. There is a manufacturer here in Washington who have come out with a lever to be mounted behind the PP-1 knob to ease in pulling the knob. It does decrease the snapping effect when the brake is applied. This lever comes in 2 types for either small diameter knob, similar to Thomas Buses and the larger diameter knobs like those found in IC's. The jury in still out in our district. We have a few of them in use and some drivers like them and others do not. The lever does not mount well in IC's (05 FE and RE's) due to the location of the ignition switch, but mounts well in the Thomas FE's we run. I suggest people try them and find out for them selves. They go on pretty simple on IC's but a little harder on Thomas. It is not suggested to use the EZ-Grip with this lever due to they will tear the EZ-Grip off in a short period of time.
http://maxiebrakerelease.com/images/MBR_flyer.pdf
Hope this gives you some insiet to the prak brake issue as well as another option for you.. |
Lead, Follow or get out of the way! Thomas Paine |
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tigger2
Advanced Member
USA
470 Posts |
Posted - 11/29/2010 : 06:48:00 AM
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| We have installed the auto brake system by Bendix and have had very good luck with it. It works automatically when the reds are activated and deactivates when the 8 way switch shuts off. The system puts 60# of air to the service side of the brake and the driver must apply the break as well or an alarm sounds, the bus will not roll with the auto brake activated. When testing the system it was found that if the reds were activated under 10 m.p.h. the bus would come to an abrupt halt, thus stopping the drivers from coasting to the stop with the reds on. |
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Frank Williams
New Member
3 Posts |
Posted - 05/06/2011 : 11:41:38 AM
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| Safety Brake Set (Safetybrake.com) manufactures several different systems to assist drivers regarding the parking brake on school buses, including a toggle switch which allows the driver to set and release the parking brake with the flip of the switch thereby eliminating fatigue/pain. |
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Frank Williams
New Member
3 Posts |
Posted - 05/09/2011 : 2:00:25 PM
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Safety Brake Set Inc. (www.safetybrake.com) Designs and manufactures systems to eliminate problems and or injuries associated with setting and releasing the parking brakes. Other SBS systems alert the driver if he or she leaves the seat without setting the parking brake. SBS Systems have been in use in the Transit Industry in the US for the past 15 years. Tri-Met in Portland Oregon is a prime example of installed SBS Systems.
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Service Brake Interlocks (for bus stops)
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