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6. Canada Motor vehicle safety standard - 121 - Parking brake test

Canada Motor vehicle safety standard - 121 - Parking brake test

 

ATTACHMENT B: Summary of legislative requirements for parking brake performance of trailers and converter dollies (TSD No.121):

(Sections not applicable to trailers and converter dollies are omitted. Conversion to imperial units added in brackets)

 

S5.6 Parking brake system

(a) Except as provided in S5.6(b) and S5.6(c), each vehicle other than a trailer converter dolly shall have a parking brake system that under the conditions of S6.1 meets the requirements of:

(1) S5.6.1 or S5.6.2, at the manufacturer's option, and

(2) S5.6.3, S5.6.4, S5.6.5, and S5.6.6.

(b) At the option of the manufacturer, for vehicles equipped with brake systems which incorporate a common diaphragm, the performance requirements specified in S5.6(a), which must be met with any single leakage-type failure in a common diaphragm, may instead be met with the level of leakage-type failure determined in S5.6.7. The election of this option does not affect the performance requirements specified in S5.6(a), which apply with single leakage-type failures other than failures in a common diaphragm.

(c) At the option of the manufacturer, the trailer portion of any agricultural commodity trailer, heavy hauler trailer, or pulpwood trailer may meet the requirements of §393.43 of Title 49 of the Code of Federal Regulations (the most recent edition) instead of the requirements of S5.6(a).

S5.6.1Static retardation force. With all other brakes rendered inoperative, during a static drawbar pull in a forward or rearward direction, the static retardation force produced by the application of the parking brakes shall be:

(a) In the case of a vehicle other than a truck tractor that is equipped with more than two axles, such that the quotient static retardation force/GAWR is not less than 0.28 for any axle other than a steerable front axle; and

(b) -----------

S5.6.2 Grade holding. With all parking brakes applied, the vehicle shall remain stationary facing uphill and facing downhill on a smooth, dry, portland cement concrete roadway with a 20-percent grade, both:

(a) when loaded to its GVWR, and

(b) at its unloaded vehicle mass plus 226.8 kg (500 lb.) (including driver and instrumentation).

S5.6.3 Application and holding. Each parking brake system shall meet the requirements of S5.6.3.1 through S5.6.3.4.

S5.6.3.1 The parking brake system shall be capable of achieving the minimum performance specified either in S5.6.1 or S5.6.2 with any single leakage-type failure, in any other brake system, of a part designed to contain compressed air or brake fluid (excluding failure of a component of a brake chamber housing, but including failure of any brake chamber diaphragm that is part of any other brake system, including a diaphragm which is common to the parking brake system and any other brake system), when the pressures in the vehicle's parking brake chambers are at the levels determined in S5.6.3.4.

S5.6.3.2A mechanical means shall be provided that, after a parking brake application is made with the pressures in the vehicle's parking brake chambers at the levels determined in S5.6.3.4, and all air and fluid pressures in the vehicle's braking systems are then bled down to zero, and without using electrical power, holds the parking brake application with sufficient parking retardation force to meet the minimum performance specified in S5.6.3.1 and in either S5.6.1 or S5.6.2.

S5.6.3.3 --------- For trailers, with the supply line initially pressurized to 689 kPa (100 psi) using the supply line portion of the trailer test rig (Figure 1) and, if designed to tow a vehicle equipped with air brakes, with a 0.819-L (50-cu. in.) test reservoir connected to the rear supply line coupling, no later than three seconds from the time venting to the atmosphere of the front supply line coupling is initiated, the mechanical means referred to in S5.6.3.2 shall be actuated. This requirement shall be met for ------- trailers both with and without any single leakage-type failure, in any other brake system, of a part designed to contain compressed air or brake fluid (consistent with the parenthetical phrase specified in S5.6.3.1).

S5.6.3.4The parking brake chamber pressures for S5.6.3.1 and S5.6.3.2 are determined as follows. ----------- For trailers, with the supply line initially pressurized to 689 kPa (100 psi) using the supply line portion of the trailer test rig (Figure 1) and, if designed to tow a vehicle equipped with air brakes, with a 0.819-L (50-cu. in.) test reservoir connected to the rear supply line coupling, any single leakage-type failure, in any other brake system, of a part designed to contain compressed air or brake fluid (consistent with the parenthetical phrase specified in S5.6.3.1), is introduced in the brake system. The front supply line coupling is vented to the atmosphere and the pressures in the vehicle's parking brake chambers are measured three seconds after that venting is initiated.

S6.1 Road test conditions

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S6.1.2The inflation pressure is as specified by the vehicle manufacturer for the GVWR.

S6.1.3Unless otherwise specified, the transmission selector control is in "neutral" or the clutch is disengaged during all decelerations and during static parking brake tests.

S6.1.4All vehicle openings (doors, windows, hood, trunk, cargo doors, etc.) are in a closed position, except as required for instrumentation purposes.

S6.1.5The ambient temperature is between 0ºC and 37.8ºC (32ºF and 100ºF).

S6.1.6The wind velocity is zero.

-----------

S6.1.8For vehicles with parking brake systems not utilizing the service brake friction elements, burnish the friction elements of such systems prior to the parking brake test according to the manufacturer's recommendations. For vehicles with parking brake systems utilizing the service brake friction elements, burnish the brakes as follows. With the transmission in the highest gear appropriate for a speed of 64.4 km/h (40 mph), make 500 snubs between 64.4 km/h and 32.2 km/h (40 mph and 20 mph) at a deceleration rate of 3.05 m/s2 (10 fpsps), or at the vehicle's maximum deceleration rate if less than 3.05 m/s2 (10 fpsps). Except where an adjustment is specified, after each brake application accelerate to 64.4 km/h (40 mph) and maintain that speed until making the next brake application at a point 1.6 km (1 mi.) from the initial point of the previous brake application. If the vehicle cannot attain a speed of 64.4 km/h (40 mph) in 1.6 km (1 mi. mph), continue to accelerate until the vehicle reaches 64.4 km/h (40 mph) or until the vehicle has traveled 2.4 km (1.5 mi.) from the initial point of the previous brake application, whichever occurs first. Any automatic pressure limiting valve is in use to limit pressure as designed. The brakes may be adjusted up to three times during the burnish procedure, at intervals specified by the vehicle manufacturer, and may be adjusted at the conclusion of the burnishing, in accordance with the vehicle manufacturer's recommendation.

S6.1.9Static parking brake tests for a semi-trailer are conducted with the front end supported by an unbraked dolly. The mass of the dolly is included as part of the trailer load.

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S6.1.11 Special drive conditions.A vehicle equipped with an interlocking axle system or a front-wheel drive system that is engaged and disengaged by the driver is tested with the system disengaged.

S6.1.12 Liftable axles. A vehicle with a liftable axle is tested at GVWR with the liftable axle down and at unloaded vehicle mass with the liftable axle up.

ATTACHMENT C: TEST PROCEDURE

Include a step by step description of how the test was performed. The test procedure should include the following steps as a minimum. Document additional steps as necessary.

Note: Several of the procedures below are not explicitly addressed in TSD 121. These are indicated with an asterisk (*) and are intended to clarify the test conditions of the standard.

Step 1-Load and weigh the vehicle and each axle. Attach weight slip and complete chart 1 below.

*For the burnishing procedure, load the semi-trailer so that :

(i) (a) the combined weight of the tow vehicle, the semi-trailer and necessary ballast equals the sum of the GAWR(s) of the semi-trailer's axle(s) and

(b) the tow vehicle's brakes are disabled.

Chart 1 : Vehicle Weights

Unladen trailer weight.:

Unladen tractor weight.:

Rated GAWR(s): Fr. ___________Int. ___________Rear ___________

Trailer ballast (GAWR(s) minus unladen trailer weight minus unladen tractor weight) =

Loaded axle weights of test vehicle: Fr. ___________ Int. ___________ Rear ___________

(ii) Where a weight compatible tow vehicle cannot be obtained, (i.e. the ballast required to load the trailer so that the combined weight is equal to the sum of the GAWR(s) is not sufficient to prevent the trailer wheels from locking during the burnish procedure) additional ballast can be added to the trailer using the formulas below to calculate the corrected deceleration rate and the final velocity from which the snubs are to be performed:

Where: D1 = corrected deceleration D = deceleration specified in TSD 121 GAWR = the axle weight capacity Actual wt. = is the combined weight of the tractor plus the trailer plus the additional ballast req'd to prevent lock up V3 = corrected final velocity of brake snub (Initial velocity of the brake application remains the same) V1 = the initial snub velocity specified in TSD 121-S6.1.8 V2 = the final snub velocity specified in TSD 121-S6.1.8 Step 2- Record the following info (for burnish procedure): Ambient temperature range: _________________to ____________________________ Tire inflation pressure: __________________________________________ Road surface description: ________________________________________ Step 3- Adjust brakes. CHECK *Step 4- Install single plug-type thermocouple in the center of the lining surface of the most heavily loaded shoe or pad(see figure 2 in the TSD 121 for thermocouple installation instructions). Note: Although thermocouples are not required for the burnish procedure in TSD 121, it is beneficial to monitor brake temperatures for indications of brake problems. Thermocouples are also used to measure initial brake temperatures prior to testing. . CHECK IF INSTALLED Step 5 - Perform burnish procedure (ref. S6 Record burnish procedure (complete chart 2). The brakes may be adjusted not more than three times during the burnish procedure, at intervals specified by the vehicle manufacturer, and may be adjusted at the conclusion of the burnishing, in accordance with the vehicle manufacturer's recommendations. Perform snubs consecutively without regard to lining temperature. Draw-bar pull method (see Figure 1) The standard allows for two options to demonstrate parking brake capability after the burnishing procedure is performed. One is the draw-bar pull method the other is the grade holding test. The draw-bar pull test is where the pull force required to move a loaded vehicle is measured in the forward and rearward direction with only the parking brakes on. Since this test gives actual values of the vehicle's parking brake capability, it is considered as a more useful test and is recommended over the grade holding test. Include the following steps when performing the draw-bar pull test. Step 6- Support front end of trailer with an unbraked trailer converter dolly, and include its weight as part of the semi-trailer's load. *Note: An unbraked tractor can be used to support the trailer during the static parking tests provided the rolling resistance of the tractor is subtracted from the retardation force developed by the parking brakes. To measure the tractor's rolling resistance, pull the tractor as a single unit and measure the force required to keep the vehicle moving. Include this result in the test report. Step 7- Align vehicle with pull cable device. Step 8- Connect pull cable and force measuring device. Cable should be horizontal within ± 5 degrees. *Step 9- For the draw-bar pull test the initial brake temperature of the hottest axle shall not be less than 66°C (150ºF) and not more than 93ºC (200ºF). If the brakes need to be re-heated, do so by making additional burnish snubs as required to bring the hottest brake up to 107-121ºC (225-250ºF). Step 10 - With an initial air supply line pressure of 689.5 kPa (100 psi), vent the air supply line to atmosphere. (If the vehicle is designed to draw a vehicle equipped with an air brake system, its air supply line output coupling shall be connected to an 819.35 cm3 (50 in³) test reservoir.) Note: The parking brake test shall be performed without a simultaneous or compounded service brake application. Test retardation force for each non-steerable axle individually (i.e., cage spring brake chambers fully on axles not being tested). *Step 11 - Place marks on circumference at tire-ground contact point, and at 90, 180, 270 degrees from that point. *Step 12 - Pull vehicle forward at a maximum pull rate of 1.25 m/min (4 ft/min). Note: Surface should be smooth and flat. Protrusions and slopes on the surface effect draw-bar results. *Step 13 - Record peak draw-bar force in 90 degrees of wheel rotation. *Step 14 - Record this value in Chart 1 Attachment D. *Step 15 - Release parking brakes and re-apply as per step10. *Step 16 - Repeat steps 9 to 15 until wheels have rotated 360 degrees. *Step 17 - Repeat steps 5 to 16 in a rearward direction and record in Chart 1 Attachment D. Note: Tests supplied by a manufacturer to the government for certification purposes should be performed at levels more severe than specified to allow for a margin of error. Keep this in mind when performing the tests.. Figure 1: Typical set-up for forward draw-bar pull

Chart 2: Burnishing Procedure recording

Reminder: The transmission selector control shall be in the neutral position or the clutch shall be disengaged during all decelerations. Rappel : Au cours de tous les essais de décélération, la commande de transmission doit être en position neutre ou l'embrayage doit être relâché.

 

Snub #	Decel rate	Lining Temp (optional)				Driver	Remarks
		LF	RF	LR	RR
1
25
50
75
100
125
150
175
200
225
250
275
300
325
350
375
400
425
450
475
500

   Comments: _______________________________________________________________________

ATTACHMENT D: RESULTS

 

 

Date modified:

2012-02-06