Adhesion utilization curves means curves showing, for specified load conditions, the adhesion utilized by each axle of a vehicle plotted against the braking ratio of the vehicle.
Antilock brake system or ABS means a portion of a service brake system that automatically controls the degree of rotational wheel slip during braking by:
Backup system means a portion of a service brake system, such as a pump, that automatically supplies energy in the event of a primary brake power source failure.
Brake factor means the slope of the linear least squares regression equation best representing the measured torque output of a brake as a function of the measured applied line pressure during a given brake application for which no wheel lockup occurs.
Brake hold-off pressure means the maximum applied line pressure for which no brake torque is developed, as predicted by the pressure axis intercept of the linear least squares regression equation best representing the measured torque output of a brake as a function of the measured applied line pressure during a given brake application.
Brake power assist unit means a device installed in a hydraulic brake system that reduces the amount of muscular force that a driver must apply to actuate the system, and that, if inoperative, does not prevent the driver from braking the vehicle by a continued application of muscular force on the service brake control.
Brake power unit means a device installed in a brake system that provides the energy required to actuate the brakes, either directly or indirectly through an auxiliary device, with driver action consisting only of modulating the energy application level.
Braking ratio means the deceleration of the vehicle divided by the gravitational acceleration constant.
Electric vehicle or EV means a motor vehicle that is powered by an electric motor drawing current from rechargeable storage batteries, fuel cells, or other portable sources of electrical current, and which may include a non-electrical source of power designed to charge batteries and components thereof.
Electrically-actuated service brakes means service brakes that utilize electrical energy to actuate the foundation brakes.
Functional failure means a failure of a component (either electrical or mechanical in nature) which renders the system totally or partially inoperative yet the structural integrity of the system is maintained.
Hydraulic brake system means a system that uses hydraulic fluid as a medium for transmitting force from a service brake control to the service brake and that may incorporate a brake power assist unit, or a brake power unit.
Initial brake temperature or IBT means the average temperature of the service brakes on the hottest axle of the vehicle 0.32 km (0.2 miles) before any brake application.
Lightly loaded vehicle weight or LLVW means unloaded vehicle weight plus the weight of a mass of 180 kg (396 pounds), including driver and instrumentation.
Maximum speed of a vehicle or VMax means the highest speed attainable by accelerating at a maximum rate from a standing start for a distance of 3.2 km (2 miles) on a level surface, with the vehicle at its lightly loaded vehicle weight, and, if an EV, with the propulsion batteries at a state of charge of not less than 95 percent at the beginning of the run.
Objective brake factor means the arithmetic average of all the brake factors measured over the twenty brake applications defined in S7.4, for all wheel positions having a given brake configuration.
Peak friction coefficient or PFC means the ratio of the maximum value of braking test wheel longitudinal force to the simultaneous vertical force occurring prior to wheel lockup, as the braking torque is progressively increased.
Pressure component means a brake system component that contains the brake system fluid and controls or senses the fluid pressure.
Regenerative braking system or RBS means an electrical energy system that is installed in an EV for recovering or dissipating kinetic energy, and which uses the propulsion motor(s) as a retarder for partial braking of the EV while returning electrical energy to the propulsion battery(s) or dissipating electrical energy.
Snub means the braking deceleration of a vehicle from a higher reference speed to a lower reference speed that is greater than zero.
Split service brake system means a brake system consisting of two or more subsystems actuated by a single control, designed so that a single failure in any subsystem (such as a leakage-type failure of a pressure component of a hydraulic subsystem except structural failure of a housing that is common to two or more subsystems, or an electrical failure in an electric subsystem) does not impair the operation of any other subsystem.
Stopping distance means the distance traveled by a vehicle from the point of application of force to the brake control to the point at which the vehicle reaches a full stop.
Variable brake proportioning system means a system that has one or more proportioning devices which automatically change the brake pressure ratio between any two or more wheels to compensate for changes in wheel loading due to static load changes and/or dynamic weight transfer, or due to deceleration.
Wheel lockup means 100 percent wheel slip.
Table 1-Road Test Sequence
Testing order | Section No. |
Vehicle loaded to GVWR: | |
1 Burnish | S7.1 |
2 Wheel lock sequence | S7.2 |
Vehicle loaded to LLVW: | |
3 Wheel lock sequence | S7.2 |
4 ABS performance | S7.3 |
5 Torque wheel | S7.4 |
Vehicle loaded to GVWR: | |
6 Torque wheel | S7.4 |
7 Cold effectiveness | S7.5 |
8 High speed effectiveness | S7.6 |
9 Stops with engine off | S7.7 |
Vehicle loaded to LLVW: | |
10 Cold effectiveness | S7.5 |
11 High speed effectiveness | S7.6 |
12 Failed antilock | S7.8 |
13 Failed proportioning valve | S7.9 |
14 Hydraulic circuit failure | S7.10 |
Vehicle loaded to GVWR: | |
15 Hydraulic circuit failure | S7.10 |
16 Failed antilock | S7.8 |
17 Failed proportioning valve | S7.9 |
18 Power brake unit failure | S7.11 |
19 Parking brake | S7.12 |
20 Heating Snubs | S7.13 |
21 Hot Performance | S7.14 |
22 Brake cooling | S7.15 |
23 Recovery Performance | S7.16 |
24 Final Inspection | S7.17 |
where z = braking ratio at a given front line pressure;
T1, T2 = Braking forces at the front and rear axles, respectively, corresponding to the same front brake line pressure, and
P = total vehicle weight.
where fi = adhesion utilized by axle i
Ti = braking force at axle i (from (e))
Pi = static weight on axle i
i = 1 for the front axle, or 2 for the rear axle
z = braking ratio (from (f))
h = height of center of gravity of the vehicle
P = total vehicle weight
E = wheelbase
Stopping distance: S[LESS THAN EQUAL TO]0.10V + 0.0067V2.
where dc = the average deceleration actually achieved during the shortest cold effectiveness stop at GVWR (m/s2),
Sc = actual stopping distance measured on the shortest cold effectiveness stop at GVWR (m), and
V = cold effectiveness test speed (km/h).
The stopping distance, S, for at least one of the two stops must be within the following limits:
where dc and V are defined in S7.14.4(a).
49 C.F.R. §571.135