Council Directive of 26 July 1971 on the approximation of the laws of the Member States relating to the braking devices of certain categories of motor vehicles and of their trailers (71/320/EEC) (repealed)

[F1 2. SYMBOLS AND DEFINITIONS U.K.

2.1. Units used U.K.

2.1.1. Masses: kg U.K.

2.1.2. Forces: N U.K.

2.1.3. Torques and moments: Nm U.K.

2.1.4. Areas: cm ² U.K.

2.1.5. Pressures: bar U.K.

2.1.6. Lengths: units specified in each case. U.K.

2.1.7. Acceleration due to gravity: g = 10 m/s ² . U.K.

2.2. Symbols valid for all types of braking systems (see diagram 1 in Appendix 1) U.K.

2.2.1.

G _A

:

‘ maximum mass ’ of the trailer declared to be technically permissible by the manufacturer

2.2.2.

G _A

:

‘ maximum mass ’ of the trailer which, according to the manufacturer's declaration, can be braked by the control device

2.2.3.

G _B

:

‘ maximum mass ’ of the trailer which can be braked by the joint operation of all the trailer brakes

2.2.4.

G _Bo

:

fraction of the permissible ‘ maximum mass ’ which, according to the manufacturer's declaration, can be braked by one brake

2.2.5.

B*

:

braking force required

2.2.6.

B

:

required braking force taking account of rolling resistance

2.2.7.

D*

:

permitted thrust on coupling

2.2.8.

D

:

load on the coupling

2.2.9.

P′

:

control device output force

2.2.10.

K

:

supplementary force of control device by convention; this is defined as the force D corresponding to the point of intersection of the x axes of the extrapolated curve expressing P′ in terms of D, measured with the control system in the mid-travel position (see diagrams 2 and 3 in Appendix 1)

2.2.11.

K _A

:

threshold force of control device — this is the maximum force on the coupling head which can be applied for a short period of time without producing any output force on the control device. By convention, K _A is defined as the force measured when force begins to be exerted on the coupling head at a speed of from 10 to 15 mm/s, the control device transmission being uncoupled

2.2.12.

D ₁

:

this is the maximum force applied to the coupling head when it is forced rearward at a speed of s mm/s ± 10 %, the transmission being uncoupled

2.2.13.

D ₂

:

This is the maximum force applied to the coupling head when this is pulled forward at a speed of s mm/s ± 10 % from its rearmost position, the transmission being uncoupled

2.2.14.

ηH ₀

:

efficiency of the inertia control device

2.2.15.

ηH ₁

:

efficiency of the transmission system

2.2.16.

ηH

:

total efficiency of the control device and of the transmission

2.2.17.

s

:

travel of control (expressed in millimetres)

2.2.18.

s′

:

effective travel of control (expressed in millimetres) fixed in accordance with the requirements of point 9.4.1

2.2.19.

s″

:

spare travel of the master cylinder actuator, measured in millimetres at the coupling head

2.2.20.

s ₀

:

loss of travel, that is to say the travel, measured in millimetres, of the coupling head when it is actuated in such a way as to travel from a point 300 mm above the horizontal plane to a point 300 mm below, the transmission remaining stationary

2.2.21.

2s _B

:

brake-shoe lift measured on the diameter parallel to the operating mechanism and without the brakes being adjusted during the test (expressed in millimetres)

2.2.22.

2s _B*

:

minimum brake shoe centre lift (minimum brake shoe application travel), in millimetres, for wheel brakes with drum brakes:

2r being the diameter of the brake drum expressed in millimetres (see diagram 4 in Appendix 1)

for wheel brakes with disc brakes with hydraulic transmission:

where:

V ₆₀ = fluid volume absorption of one wheel brake at a pressure corresponding to a braking force of 1,2 1,2 B* = 0,6 × G _Bo and a maximum tyre radius,

2r _A = outer diameter of brake disc

(V ₆₀ in cm ³ , F _RZ in cm ² and r _A in mm)

2.2.23.

M

:

braking moment

2.2.24.

R

:

dynamic tyre rolling radius in metres, rounded to the nearest centimetre

2.2.25.

n

:

number of brakes

2.2.26.

D _A

:

application force at input side of the control device, at which the overload protector is activated

2.2.27.

M _A

:

braking torque at which the overload protector is activated

2.3. Symbols for mechanical transmission braking systems (see diagram 5 in Appendix 1) U.K.

2.3.1.

i _{H o}

:

reduction ratio between travel of the coupling head and travel of the lever at the output side of the control device

2.3.2.

i _{H i}

:

reduction ratio between travel of the lever at the output side of the control device and travel of the brake lever (gearing down of transmission)

2.3.3.

i _H

:

reduction ratio between travel of the coupling head and travel of the brake lever

2.3.4.

i _g

:

reduction ratio between travel of the brake lever and the brake-shoe centre lift (see diagram 4 in Appendix 1)

2.3.5.

P

:

force applied to the brake control lever

2.3.6.

P ₀

:

brake retraction force; that is, in the graph M = ƒ (P), the value of the force P at the point of intersection of the extrapolation of this function with the abscissa (see diagram 6 in Appendix 1)

2.3.7.

ρ

:

characteristic of the brake defined by:

2.4. Symbols for hydraulic-transmission braking systems (see diagram 8 in Appendix 1) U.K.

2.4.1.

i _h

:

reduction ratio between travel of the coupling head and travel of the piston in master cylinder

2.4.2.

i _g

:

reduction ratio between travel of the actuation point of the cylinders and the brake-shoe centre lift

2.4.3.

F _{R z}

:

surface area of piston of one wheel cylinder for drum brake(s); for disc brake(s), sum of the surface area of the caliper piston(s) on one side of the disc

2.4.4.

F _{H z}

:

surface area of piston in master cylinder

2.4.5.

p

:

hydraulic pressure in brake cylinder

2.4.6.

p _O

:

retraction pressure in brake cylinder; that is, in the graph M = ƒ (p), the value of the pressure p at the point of intersection of the extrapolation of this function with the abscissa (see diagram 7 in Appendix 1)

2.4.7.

ρ′

:

characteristic of the brake defined by:

]

Textual Amendments

F1 Substituted by Commission Directive 98/12/EC of 27 January 1998 adapting to technical progress Council Directive 71/320/EEC on the approximation of the laws of the Member States relating to the braking devices of certain categories of motor vehicles and their trailers (Text with EEA relevance).