[Federal Register Volume 60, Number 145 (Friday, July 28, 1995)]
[Rules and Regulations]
[Pages 38762-38765]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-18381]
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DEPARTMENT OF TRANSPORTATION
49 CFR Part 571
[Docket No. 85-07; Notice 10]
RIN 2127-AF23
Federal Motor Vehicle Safety Standards; Air Brake Systems Control
Line Pressure Balance
AGENCY: National Highway Traffic Safety Administration (NHTSA),
Department of Transportation.
ACTION: Final rule.
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SUMMARY: In response to a petition for rulemaking submitted by Sealco
Air Controls, this document amends the control line pressure
differential requirements in Standard No. 121, Air Brake Systems, for
converter dollies and trailers designed to tow other air braked
vehicles. The agency has concluded that the amendments will improve the
braking compatibility of such vehicles by allowing the use of a relay
valve known as a spool-type low opening valve.
DATES: Effective date. The amendments in this document become effective
August 28, 1995.
Petitions for reconsideration. Any petitions for reconsideration of
this rule must be received by NHTSA no later than August 28, 1995.
ADDRESSES: Petitions for reconsideration of this rule should refer to
Docket No. 85-07; Notice 10 and should be submitted to: Administrator,
National Highway Traffic Safety Administration, 400 Seventh Street,
S.W., Washington, D.C. 20590.
FOR FURTHER INFORMATION CONTACT: Mr. Richard Carter, Office of Vehicle
Safety Standards, National Highway Traffic Safety Administration, 400
Seventh Street, S.W., Washington, D.C. 20590 (202-366-5274).
SUPPLEMENTARY INFORMATION:
I. Background
Standard No. 121, Air Brake Systems, establishes performance and
equipment requirements for braking systems on vehicles equipped with
air brakes, including requirements for pneumatic timing. NHTSA recently
amended the control signal pressure differential requirements of
Standard No. 121, with respect to converter dollies and towing
trailers. (57 FR 37902; August 21, 1992) The amendment specifically
requires that, for trailers and converter dollies manufactured after
August 23, 1993, the pressure differential between the control line
input coupling and a 50 cubic inch test reservoir connected to the rear
control line output coupling shall not exceed 1 psi at all input
pressures between 5 psi and 20 psi and 2 psi at all input pressures
greater than 20 psi. Input pressures below 20 psi represent routine
braking applications, while input pressures between 20 psi and 40 psi
represent moderate to heavy braking applications, and input pressures
above 40 psi represent severe braking applications.1
\1\ In today's final rule, NHTSA has decided to modify the limit
above 40 psi to allow a 5 percent differential (which at higher
pressures exceeds the current limit of 2 psi) based on, among other
things, the Society of Automotive Engineer's (SAE's) Recommended
Practice SAE J1505, Brake Force Distribution Test Code Commercial
Vehicles.
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The August 1992 amendment was intended to ensure that the control
signal ``passes'' through a towing trailer or dolly without being
altered along the way. Since the control signal passes through
unaltered, each vehicle in a combination unit receives the same brake
control signal. This serves to increase the braking compatibility of
combination vehicles, since each vehicle in a combination has
comparable braking performance. By specifying the maximum permissible
differential between the input and output control line pressures, this
requirement addresses problems of heat buildup and brake fade during
long, gradual downhill runs at relatively low
[[Page 38763]]
pressure brake applications, caused by relatively large brake pressure
differentials between the trailers and converter dollies in multiple
trailer combinations.
II. Sealco Petition
On June 18, 1993, Sealco Air Controls (Sealco), a valve
manufacturer, submitted to NHTSA a rulemaking petition to amend
Standard No. 121 with respect to the control line pressure differential
requirements in S5.3.5. Specifically, Sealco requested that NHTSA amend
these requirements to eliminate the need to modify the original design
of its low opening valves (LOVs) that resulted from the August 1992
amendment. Sealco stated that these modifications degraded the ability
of its LOVs to maintain minimal air pressure differentials between the
input and output of these valves. These valves are used as control line
relay valves and service line relay valves in trailers and converter
dollies. The petitioner stated that unlike other relay valves that use
a common poppet, 2 the low opening valves have a balanced spool
technology 3 that allows the valve to initially open at a
relatively low pressure of 1.5 psi. The pressure at which a valve
initially opens is referred to as the crack pressure. According to
Sealco, the spool technology enables the output pressure delivered by
the valve to closely follow (i.e., track) the input control air
pressure. As a result, it claimed that hysteresis 4 is not so
prevalent with low operating valves as with high crack pressures. This
amendment will not significantly affect small businesses, small
organizations, and small governmental units that purchase vehicles
since this amendment will have no significant cost impact on vehicles.
\2\ A poppet valve has a valve seat like a typical water faucet
valve. The air flow is increased as the sealing lip is raised higher
off the valve seat by varying the air pressure in the control line.
The valve allows increased or decreased air flow from the supply
line side of the system.
\3\ A spool type valve has a cylinder which slides back and
forth inside of a machined hole called a bore. As the spool slides
past a port or opening on the side of the bore, the exposed side
port then allows the air to flow past the valve spool.
\4\ The phenomenon exhibited by a system in which the reaction
of the system to changes is dependent upon its past reactions to
change. With respect to braking, when the control line input
pressure is increased, the relay valve's output (apply pressure) is
usually a few psi lower than the control line output pressure, and
is usually more than one or two psi above the descending control
line pressure. Complications may arise when a subsequent brake
application is made before the brakes have fully released after a
prior application.
Hysteresis in a valve may cause the output line pressure of the
valve not to track properly the input control line pressure, which may
cause the application pressure of the brakes in the trailer to be
significantly different than the control line pressure signal. In such
situations, the valve's hysteresis may not allow the same pressure to
be applied to the trailer brakes as is signalled by the driver's
application of the brake control. In the case of increasing brake line
pressure, this will cause less braking in the trailer than in the
tractor, causing the trailer to ``push'' the tractor. Similarly, when
the driver decreases the brake application, the hysteresis in the valve
may not allow the brake application in the trailer to decrease to the
same degree, resulting in the trailer brakes still being applied to a
greater degree than those in the tractor. This causes the kingpin to
jerk on the inside of the fifth wheel. Under high speed congested
traffic conditions in which the driver may go through several brake
applications and releases in rapid succession, the jerking and pushing
of the trailer or trailers could be difficult to control. In multiple
trailer combinations, this same phenomenon can be a problem between
successive trailers as well as between tractors and trailers.
Sealco stated that the use of low operating valves would further
NHTSA's goal of ensuring balanced braking in combination vehicles.
However, the petitioner claimed that while its valve meets the
amendment's application requirements, it does not meet the provision
requiring release at high pressure ranges, given the valve's mechanics.
To comply with the amendment, Sealco has drilled a hole in the valves'
piston, thereby allowing pressure to bleed to the supply side. This
action prevents the valves from cracking open when tested according to
S5.3.5. Sealco believes that this modification to allow compliance with
the amendment has reduced the valves' effectiveness.
III. Notice of Proposed Rulemaking
On July 13, 1994, NHTSA published a notice of proposed rulemaking
(NPRM) proposing to amend Standard No. 121 to permit the use of low
opening valves. (59 FR 35672) Specifically, the agency proposed to
amend S5.3.5 to address input pressures over 40 psi. Under the
proposal, the pressure differential would not be permitted to exceed 2
psi at any input pressure between 20 psi and 40 psi and would not be
permitted to exceed 5 percent at any pressure over 40 psi. In other
words, the pressure differential requirements would remain the same as
the current requirements, except for applications resulting in
pressures over 40 psi.
In the NPRM, NHTSA explained that the current requirement may
unnecessarily extend the 2 psi limit into the higher pressure ranges
where it is not necessary for safety. The requirement is intended to
prevent brake fade during relatively low brake applications below 20
psi. The 2 psi limit is relatively more stringent for hard brake
applications, i.e., those exceeding 40 psi. The agency requested
comments about whether the modification to pressure levels over 40 psi
might be detrimental to safety or otherwise inappropriate.
IV. Comments on the NPRM
NHTSA received two comments on the July 1994 proposal to amend the
control line pressure requirements. Mr. Robert Crail, a brake engineer,
stated that ``The adoption of the proposed amendment will not have any
adverse effect on safety.'' He agreed with the agency that the greater
problem area with pressure differentials is at the lower end of the
pressure range and not the upper range, which is being broadened
slightly. Advocates for Highway and Auto Safety (Advocates) criticized
the proposal for several reasons. Advocates was primarily concerned
that there was no real world braking data to support the amendment,
which it believed would degrade heavy vehicle braking.
V. Agency Decision
After reviewing the comments and other available information, NHTSA
has decided to amend Standard No. 121, with respect to the control line
pressure requirements for converter dollies and trailers designed to
tow other air braked vehicles. Specifically, the agency has decided to
amend S5.3.4 to allow pressure differentials of up to 5 percent at
pressures over 40 psi. The current 2 psi allowance is 5 percent of 40
psi, and the agency believes that allowing the same percentage above 40
psi is adequate. Based on its review of the available information, the
agency has concluded that the amendment facilitates the use of an
alternative technology, without being detrimental to safety. As it
explained in the NPRM, NHTSA based the proposed requirement on the
Society of Automotive Engineer's (SAE's) Recommended Practice J1505,
Brake Force Distribution Test Code Commercial Vehicles. In addition,
the agency also contacted all the major valve manufacturers about the
pressure differential requirements. Based on its review, NHTSA believes
that the 2 psi differential in the current requirement is
[[Page 38764]]
unnecessarily stringent for towing trailers and dollies in hard brake
applications over 40 psi. Therefore, the agency has decided to adopt
the petitioner's request to permit pressure differentials of up to 5
percent during hard brake applications.
Advocates criticized several aspects of the proposal to amend the
pressure differential requirements. Specifically, that organization
expressed concern that the amendment (1) was not supported by real
world testing data, (2) would adversely affect safety, (3) was
inappropriate for certain braking techniques, and (4) would allow spool
valves, which it viewed as inferior. As explained below, NHTSA has
concluded that Advocates' concerns are without merit.
Advocates contended that there is no real world safety data to
support the proposed amendment. It stated that it is ``opposed to
safety-related regulatory changes which rely only on a priori
calculations for gauging probable safety consequences.'' It therefore
requested the agency to specify real world braking demonstrations to
establish that spool type valves will not degrade safety.
NHTSA disagrees with Advocates' contention that there are no real
world data to support the amendments to the control line pressure
differential requirements. In fact, the agency has two reports
containing a substantial amount of test data regarding real world
braking.5 These reports cover a substantial amount of real world
braking demonstrations, including actual control line pressures under a
full range of conditions used in a wide range of braking applications.
Supporting data also indicate that the cut off point of 40 psi exceeds
the braking conditions addressed by this rulemaking. All the test data
in the antilock report are real world fleet test data and the down-hill
test data in the Braking Strategy study are also real world and based
on dozens of test runs. These reports illustrate that the cut-off point
of 40 psi is reasonable. They further illustrate that a higher pressure
is not necessary since approximately 99 percent of heavy braking occurs
below that pressure.
\5\ See, (1) ``An In-Service Evaluation of the Performance,
Reliability, Maintainability and Durability of Antilock Braking
Systems (ABSs) for Semitrailers'', DOT HS 806059; October 1993, and
(2) ``The Influence of Strategy on Brake Temperatures in Mountain
Descents'' DTFH61-89-C-00106; March 1992.
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Advocates claimed that the proposed amendments to the control line
pressure requirements would have a deleterious effect on safety under
severe braking conditions. That organization, however, did not state
what it considers to be severe braking conditions.
NHTSA believes that Advocates' concern that the amendment would
adversely affect safety is without merit, since, as mentioned above,
approximately 99 percent of braking occurs at 40 psi or less. At 75
psi, which represents a panic stop on dry pavement that would most
likely lock all the wheels unless the vehicle were fully loaded, the
Sealco valves showed only a 1.5 psi tracking variation 6 in either
the ascending or descending brake line pressures.
6 Tracking variation is a measure of how well matched the
air pressure is between the (control) line side of the air brake
system and the actual (service) air pressure being sent to the brake
chambers. For example, if the driver's foot is placed on the brake
pedal such that a 20 psi signal is sent to the valve that releases
the air from the air reservoir on the trailer and the control valve
releases 20 psi to the brakes, there is ``zero'' tracking error. If
the air pressure at the brake chambers is between 19 to 21 psi, the
tracking error would be within the 1 psi requirement of the
standard.
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With regard to the safety of tracking error variation, the agency
prefers a tracking error of zero as an ideal. However, that would be
unrealistic for a valve manufacturer to achieve. Because of
manufacturing variations in the valves along with hysteresis, 2 psi is
a reasonable pressure limit at the low end.
Advocates commented that the agency mischaracterized braking
practices. It stated that while snubbing (i.e., intermittently exerting
force on the brake pedal) brakes at relatively low pressures is the
preferred braking technique, drivers often ``ride'' (i.e., exert a
constant force on the brake pedal) the brakes at higher pressures in
long downhill descents.
NHTSA believes that Advocates' statement is not accurate, since all
the agency's research data show that ``riding'' the brakes produces
pressures that are approximately 50 percent lower than ``snubbing''
pressures. The agency further notes that Advocates' concern about
snubbing or riding the brakes is not relevant since the air pressure
requirements are being amended for pressures higher than those used in
snubbing or riding the brakes. The air system pressure in either of the
two braking methods is less than the 40 psi cut-off point established
by this amendment. Worst-case conditions produced by snubbing in
mountain grade descents average about 27 psi with peaks to 32 psi.
Riding the brakes results in air pressure that seldom exceeds 10 psi,
even on mountain descents.7
\7\ A report titled ``The Influence of Strategy on Brake
Temperatures in Mountain Descents'' DTFH61-89-C-00106; March 1992,
contains extensive data by both VRTC and The University of Michigan
which relate to the air brake pressure required in ``snubbing' and
``riding'' of the brakes.
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Advocates expressed concern that low pressure spool type valves
could adversely affect safety compared to poppet valves. However, NHTSA
notes that each type of valve is used in specific applications to its
own best advantage. The agency is aware of no application in which
either type should be restricted by performance requirements in
Standard No. 121. There are no data available on the performance of air
brake spool valves vs poppet type air brake valves, because the former
type of values have not posed a problem.
Effective date. Each order amending a safety standard is required
to take effect no sooner than 180 days from the date the order is
issued unless ``good cause'' is shown that an earlier effective date is
in the public interest. NHTSA has determined that there is ``good
cause'' not to provide the 180 day lead-in period given that this
amendment will not impose any mandatory requirements on manufacturers.
The public interest in being able to use an alternative technology will
also be served by not delaying the introduction of the requirement.
Based on the above, the agency has further determined that there is
good cause to have an effective date 30 days after publication in the
Federal Register.
VI. Rulemaking Analyses and Notices
1. Executive Order 12866 (Federal Regulatory Planning and Review) and
DOT Regulatory Policies and Procedures
This rulemaking was not reviewed under E.O. 12866. NHTSA has
analyzed this rulemaking and determined that it is not ``significant''
within the meaning of the Department of Transportation's regulatory
policies and procedures. A full regulatory evaluation is not required
because the rule has no mandatory effects and therefore imposes no
costs. Further, it does not make possible cost savings. Instead, the
rulemaking simply permits the use of spool valve technology.
2. Regulatory Flexibility Act
In accordance with the Regulatory Flexibility Act, NHTSA has
evaluated the effects of this action on small entities. Based upon this
evaluation, I certify that the amendment will not have a significant
economic impact on a substantial number of small entities. Vehicle and
brake manufacturers typically do not qualify as small
[[Page 38765]]
entities. For these reasons, no regulatory flexibility analysis has
been prepared.
3. Executive Order 12612 (Federalism)
This action has been analyzed in accordance with the principles and
criteria contained in Executive Order 12612, and it has been determined
that the rule will not have sufficient Federalism implications to
warrant preparation of a Federalism Assessment. No State laws will be
affected.
4. National Environmental Policy Act
The agency has considered the environmental implications of this
rule in accordance with the National Environmental Policy Act of 1969
and determined that the rule will not significantly affect the human
environment.
5. Civil Justice Reform
This rule will not have any retroactive effect. Under section
103(d) of the National Traffic and Motor Vehicle Safety Act (49 U.S.C.
30111), whenever a Federal motor vehicle safety standard is in effect,
a state may not adopt or maintain a safety standard applicable to the
same aspect of performance which is not identical to the Federal
standard. Section 105 of the Act (49 U.S.C. 30161) sets forth a
procedure for judicial review of final rules establishing, amending or
revoking Federal motor vehicle safety standards. That section does not
require submission of a petition for reconsideration or other
administrative proceedings before parties may file suit in court.
List of Subjects in 49 CFR Part 571
Imports, Motor vehicle safety, Motor vehicles, Rubber and rubber
products, Tires.
In consideration of the foregoing, the agency is amending Standard
No. 121, Air Brake Systems, part 571 of Title 49 of the Code of Federal
Regulations as follows:
PART 571--[AMENDED]
1. The authority citation for Part 571 continues to read as
follows:
Authority: 49 U.S.C. 322, 30111, 30115, 30117, and 30166;
delegation of authority at 49 CFR 1.50.
2. In Sec. 571.121, S5.3.5 introductory text and S5.3.5(a) are
revised to read as follows:
Sec. 571.121 Standard No. 121; Air brake systems.
* * * * *
S5.3.5 Control signal pressure differential--converter dollies and
trailers designed to tow another vehicle equipped with air brakes.
(a) For a trailer designed to tow another vehicle equipped with air
brakes, the pressure differential between the control line input
coupling and a 50-cubic-inch test reservoir attached to the control
line output coupling shall not exceed the values specified in
S5.3.5(a)(1), (2), and (3) under the conditions specified in
S5.3.5(b)(1) through (4):
(1) 1 psi at all input pressures equal to or greater than 5 psi,
but not greater than 20 psi; and
(2) 2 psi at all input pressures equal to or greater than 20 psi
but not greater than 40 psi; and
(3) not more than a 5-percent differential at any input pressure
equal to or greater than 40 psi.
* * * * *
Issued on: July 20, 1995.
Ricardo Martinez,
Administrator.
[FR Doc. 95-18381 Filed 7-27-95; 8:45 am]
BILLING CODE 4910-59-P