ICS 43.040.30  
 
Reference number  
DRS  291: 2021  
© RSB 2021  
1  
 RWANDA 
STANDARD  DRS  
291 
 
Second  edition  
2021-mm-dd 
 
Maximum road speed governors for motor 
vehicles — Requirements  
 
   
  DRS  291: 2021  
©RSB 2021  - All rights reserved    In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB 2021  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized 
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without 
prior written permission from R SB. 
Requests for permission to reproduce this document should be addressed to : 
Rwanda Standards  Board  
P.O Box 7099 Kigali -Rwanda  
KK 15 Rd, 49  
Tel. +250 788303492  
Toll Free: 3250  
E-mail: info@rsb.gov.rw  
Website: www.rsb.gov.rw  
ePortal: www.portal.rsb.gov.rw   
 
   
©RSB 2021  - All rights reserved   Contents  Page 
Foreword  ................................ ................................ ................................ ................................ ....................  3 
1 Scope  ................................ ................................ ................................ ................................ ............  4 
2 Normative references  ................................ ................................ ................................ ..................  4 
3 Terms and definitions  ................................ ................................ ................................ .................  4 
4 Requirements  ................................ ................................ ................................ ...............................  5 
4.1 Requirements for the system  ................................ ................................ ................................ ..... 5 
4.2 Requirements for speed governors  ................................ ................................ ...........................  6 
4.3 Speed recording and storing device  ................................ ................................ .........................  7 
5 Durability and environmental performance  ................................ ................................ ..............  8 
5.1 System durability  ................................ ................................ ................................ .........................  8 
5.2 Time and temperature stability  ................................ ................................ ................................ ... 8 
5.3 Electrical power supply  ................................ ................................ ................................ ...............  8 
5.3.1  Steady state voltage  ................................ ................................ ................................ ....................  8 
5.3.2  Ripple ................................ ................................ ................................ ................................ ............  8 
5.3.3  Reverse polarity  ................................ ................................ ................................ ...........................  8 
5.3.4  Transients  ................................ ................................ ................................ ................................ ..... 8 
5.3.5  Stabilized speed  ................................ ................................ ................................ ...........................  9 
5.3.6  Input/output protection  ................................ ................................ ................................ ...............  9 
5.3.7  Electromagnetic compatibility  ................................ ................................ ................................ .... 9 
5.4 Environmental protection  ................................ ................................ ................................ .........  10 
6 Marking  ................................ ................................ ................................ ................................ ....... 10 
Annex  A (normative)  Sys tem durability test  ................................ ................................ .......................  11 
Annex  B (normative)  Time and temperature stability test  ................................ ................................ . 12 
Annex  C (normative)  Transient voltage test severity levels  ................................ .............................  13 
Annex  D (normative)  Transient voltage test severity levels  ................................ .............................  14 
D.1 Chassis and cab mounted components  ................................ ................................ ..................  14 
D.1.1  General  ................................ ................................ ................................ ................................ ........  14 
D.1.2  Resonance search  ................................ ................................ ................................ .....................  14 
D.1.3  Endurance test at resonance frequency  ................................ ................................ .................  14 
D.2 Engine mounted components  ................................ ................................ ................................ .. 14 
D.2.1  General  ................................ ................................ ................................ ................................ ........  14 
D.2.2  Resonance research  ................................ ................................ ................................ ..................  15 
D.2.3  Endurance test at resonance ranges  ................................ ................................ .......................  15 
   DRS  291: 2021  
©RSB 2021  - All rights reserved    Foreword   
Rwanda Sta ndard s are prepared  by Technical Committees and approved by R wanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task of technical committees is to prepare national standards.  Final Draft Rwanda S tandards adopted 
by Technical committ ees are ratifie d by me mbers of RSB Board of Director s for publication and gazettment as 
Rwanda Standards.  
DRS  291 was prepared by Technical Committee RSB/TC 023, Road Vehicle s. 
In the preparation of this standard, reference was made to the following standard s: 
1) KS 2295 -1: 2011 , Maximum road speed governors for motor vehicles — Part 1: Performance and 
installation requirements   
2) KS 2295 -2:2011 , Maximum road speed governors for motor vehicles — Part 2: Specification for system and 
component requirements   
3) IS 14382:1996 , Automo tive vehicles - Speed limiters — Specification for installed requirements  
The assistance de rived from the above source is hereby acknowledged with thanks.  
This second  edition cancels and replaces the first  edition (RS  291: 2015 ), [clause(s) / subclause(s) /  table(s) / 
figure(s) / annex(es)] of which has been technically revised.  
Committee membership  
The following organizations were represented on the Technical Committee on Title of TC  (RSB/TC 023) in the 
preparation of this standard.  
ATECAR  
KENSRIN COMPANY Ltd 
MOTA ENGIL  
PASCAL Technology Ltd  
PURE PRO Ltd  
Rwanda Polytechnic/ Integrated Polytechnic Regional College Ngoma (IPRC Ngoma)  
Rwanda Polytechnic / Integrated Polytechnic Regional College Kigali (RP/IPRC Kigali)  
University of Rwanda/ College of Science and  Technology (UR -CST)  
VW Rwanda Ltd  
Rwanda  Standards Board  (RSB) – Secretariat  
   
©RSB 2021  - All rights reserved    
Maximum road speed governors for motor vehicles — Requirements  
1 Scope   
This Draft Rwanda Standard specifies the requirements for the performance and installation of devices designed 
to control the speed and limit the maximum road speed of motor vehicles by control of engine power. It also 
specifies the requirements for the performance of systems and components desig ned to form part of a speed 
governor intended to limit the maximum road speed of motor vehicles by control of engine power  
2 Normative references   
The following documents are referred to in the text in such a way that some or all of their content constitutes  
requirements of this document.  For dated references, only the edition cited applies. For undated references, the 
latest edition of the referenced document (including any amendments) applies.  
IEC 60068 -2-1, Environmental testing – Part 2 -1: Tests – Test A:  Cold stability  
IEC 60068 -2-2, Environmental testing – Part 2 -2: Test – Test B: Dry heat stability  
IEC 60068 -2-38, Environmental testing – Part 2 -38: – Test – Test Z/AD: Composite temperature/humidity cyclic 
test stability   
RS ISO 7637 -1, Road vehicles — Electrical disturbances from conduction and coupling — Part 1: Definitions 
and general considerations   
ISO 7637 -2, Road vehicles — Electrical disturbances from conduction and coupling — Part 2: Electrical 
transient conduction along supply lines onl y 
3 Terms  and definitions   
For the purposes of this standard, the follow ing terms and definitions apply  
3.1  
engine  
source (or sources) of the vehicle’s motive power  
3.2  
qualified agent  
authorized motor vehicle inspector or traffic police officer  
3.3  
inspection device  
piece of equipment that has been designed to test all circuitry and shall be able to detect any interference with 
the system  
3.4  
speed governor  
device designed to limit the maximum speed of an automotive vehicle by controlling the eng ine power of that 
vehicle.    DRS  291: 2021  
©RSB 2021  - All rights reserved    3.5  
set speed  
intended mean vehicle speed when operating in a stabilized condition. It is marked on the vehicle and used for 
calibration purposes  
3.6  
juddering  
action of shaking rapidly during the retardation process  
3.7  
permanent damage  
damage sustained by a component or system which renders it inoperative. For the purpose of this definition the 
rupture of a fuse or the operation of other user serviceable circuit protection devices is not taken to be permanent 
damage  
3.8  
normal function  
functioning in accordance with the requirements of this standard  
3.9  
failure to function  
functioning outside the requirements of this standard but not suffering any permanent damage  
3.10  
nominal voltage  
voltage of 12 V ± 1 V d.c or  24 V ± 2 V d.c  
3.11  
Vmax  
maximum speed declared by the supplier of the speed limiter at which it is set to meet the requirements of this 
standard  
3.12  
Vmin  
minimum  speed declared by the supplier of the speed limiter at which it is set to meet the requirements of this 
standard.  
4 Requirements  
4.1 Requirements for the system  
4.1.1  The systems shall be “failsafe” in such a way that if the plug to the electronic controller is  removed, power 
is disconnected or if the speed signal and/or wire is disconnected the vehicle shall automatically, default to a 
limp mode or the engine shall stall or return to idle and thus shall not be able to be driven in excess of 20 km 
per hour.  
4.1.2 The system shall be able to be verified, authenticated and tested by an authorized agent by means of an 
electronic device, which can be plugged into a receiver installed in a convenient position on the vehicle, whilst 
the vehicle is on the road. This de vice should test all circuitry and shall be able to detect any interference with 
the system.   
©RSB 2021  - All rights reserved   4.1.3  The equipment shall monitor the road speed of the vehicle by being integrated to the electronic 
speedometer signal input, where possible or by the installat ion of an electro -mechanical speed sensor installed 
onto the speedometer cable take off at the gearbox or by use of other speed signal method as may be specified 
by manufacturer.  
4.1.4  All cable or harness connectors in the speedometer circuit shall be wi red and sealed for certification 
purposes.  
4.1.5  The equipment shall pre -warn the driver, by way of a high frequency buzzer, that the set speed is being 
reached. This warning shall occur at 5 % prior to the set speed and shall continue buzzing once the se t speed 
is achieved   
4.1.6  When the set speed is reached, the speed governor shall temporarily cause the engine to lose power. 
Engine power shall be reinstated at a speed not less than the pre -warning switch point, which is 5 % below the 
set speed  
4.1.7  A second (critical) road speed governor set point shall activate a retarder device (where legislated) when 
this set point is reached. This set point shall be no more than 5 % above the standard set point and shall, 
automatically, activate the retarder to ensure that the vehicle cannot exceed the preset limit.  
4.1.8  The speed governor shall be set in such a way that it shall be tamper proof with (adjust speed) and easy 
to detect tampering.  
4.1.9  All road speed governors systems shall be checked for accura cy and functionality, at least once per year, 
at the time of the motor vehicle inspection. The maximum deviation from the set speed limit shall be not more 
than ± 3.3 %.   
4.1.10  Speed shall be sensed to an accuracy of ± 3.3 % of actual vehicle speed, with  the range Vmin to Vmax  
4.1.11  The road speed governor system shall be equipped with a system which shall accept an external device 
for testing the speed governor and verifying its functionality.  
4.1.12  the speed limiting device shall be calibrated to a set speed complying with the regulatory requirements.  
4.1.13  the speed governor shall be type approved by the competent authority. The speed governors that have 
been type approved shall not be permitted to modify or redesign unless the validity of type ap proval has been 
revalidated.  
4.1.14  the manufacturer of the speed governor shall provide manual describing installation, checking and 
calibration procedures. After installation it should be possible to check the set speed while the vehicle is 
stationary.  
4.1.15  The speed governor shall be suitable for installation in the vehicle and shall be installed in accordance 
with the installation procedures of the manufacturer. The installation shall be done by technician s approved by 
competent authority . 
4.2 Requireme nts for speed governors  
4.2.1  The speed governors shall meet the following requirements:  
a) no effect on the normal operation of vehicle  
1) road speed governor shall allow normal acceleration and full engine power up to the set maximum 
speed limit when the limitation function comes to play;  
2) speed limitation function or road speed governor shall not interfere with the brake system of the 
vehic le;    DRS  291: 2021  
©RSB 2021  - All rights reserved    3) speed limiting function shall be performed progressively in such a manner that excessive juddering 
or discomfort is not caused;  
4) speed limiting function shall not cause engine back firing;   
5) speed limitation function or the road speed governor shall no t cause uncontrolled engine power;  
6) no malfunction or tempering shall result in increase in engine power above that demanded by the 
position of the drivers accelerator;  
7) speed limitation function shall be obtained once the vehicle speed reaches the set max imum speed 
regardless of the position action on the accelerator a driver may apply;  
8) speed limitation function shall be independent of the condition or soundness of the speedometer  
b) compatibility with environmental conditions  
1) speed governor shall be so designed, constructed and assembled so as to resist vibrations, corrosion, 
dust, humidity and petrochemical emissions;  
2) speed limitation function, or the speed limitation device shall operate satisfactorily without 
unacceptable electromagnetic disturbance from anything in its environment ; and  
3) road speed governor shall be resistant to reverse polarity connections.  
c) susceptibility to tampering  
1)  limitation threshold shall not, in any case be capable of being increased or removed temporarily on 
vehicles wh ere the speed limitation device has been fitted;  
2) speed limitation function, the road speed governor and the connections necessary for its operation 
shall be capable of being protected from any unauthorized adjustments or the interruptions of its energy 
supply by the attachment of sealing devices and/or the need to use special tools;   
3) all components necessary for the full function of the limiter shall be energized whenever the vehicle is 
being driven ; and  
4) road speed governor shall be designed and construc ted in such a way that it can be fitted in a place 
not easily accessible to  unauthorized people.  
d) functionality inspection devices (policing units)  
4.2.2  The road speed governor shall have in built features that allow functionality checks and shall ha ve 
special inspection devices for this purpose to facilitate the checking when the vehicle is not in motion  or the 
speed governor is disconnected .  
NOTE An example of such features is the Global Positioning System GPS . 
4.3 Speed recording and storing device  
4.3.1  The speed limiting system shall incorporate a mechanism for recording the speed of the vehicle which 
speed shall be date (day, month and year) and time related, which shall store the data in a non erasable memory 
and when power supply disconnected sh all remain.   
4.3.2  The speed shall be recorded in km/h at not more than 5 sec interval  
4.3.3  The stored data shall be retrievable and easy to export in a format which is acceptable and type approved 
by the competent authority.   
©RSB 2021  - All rights reserved   4.3.4  The file of at least within past 72 h driving time data shall be read only and stored in accordance with 4.3.3.  
5 Durability and environmental performance   
5.1 System durability  
The system, in condition equivalent to new, shall be tested in accordance with Annex A and, after complet ion 
of test, shall comply with the manufacturer’s specification.  
5.2 Time and temperature stability  
The system, in condition equivalent to new, shall be tested in accordance with Annex B. During the procedures 
in clause B.1 to B.7 and B.9 the sensed speed shal l not differ from the set speed by more than 3.3 %.  
5.3 Electrical power supply  
5.3.1  Steady state voltage  
The system shall function normally when connected to a power supply in the range (12/24 V) d.c.  
5.3.2  Ripple  
Normal operation of the system shall not be affected by regular or irregular variations in voltage about the 
prevailing supply level (excluding transients) not exceeding 3 V (± 2 V d.c.) peak to peak in the range 10 Hz to 
10 000 Hz  
5.3.3  Reverse polarity  
The system shall be reverse polarity protector.  
5.3.4  Transients  
5.3.4.1 After the set speed is achieved (see fig 1), the following conditions shall be fulfilled:  
a) the sensed speed shall not exceed t he set speed by more than 5 %;  
b) the rate of change of sensed speed shall not exceed 0.5 m/s2; and  
c) the stabilized speed  conditions specified in 5.3.5 shall be attained within 10 sec of first reaching the set speed .   DRS  291: 2021  
©RSB 2021  - All rights reserved     
Figure 1 — Allowed tolerances of governor response characteristic  
5.3.4.2  Tests for immunity to transients shall be conducted  in accordance with ISO 7637 -1 for 12 V systems 
and ISO 7637 -2 for 24 V systems. Transient voltage test severity levels are given in Annex C.  
5.3.5  Stabilized speed  
When stable speed control has been achieved (see fig 1), the following conditions shall be fulfil led:  
a) the sensed speed shall not differ from the set speed by more than 3.3 % ; and   
b) the rate of change of sensed speed shall not exceed 0.2 m/s2.  
5.3.6  Input/output protection  
Each output/input in turn shall withstand connection to earth for 1 min duration, wi thout permanent damage, 
with the system operating and shall return to normal function when the connection is removed.  
5.3.7  Electromagnetic compatibility  
5.3.7.1  Supply line interface  
When tested in accordance with relevant approved standards, the system shall operate correctly with 3 V r.m.s. 
interference, at any frequency in the range 1 MHz to 150 MHz, superimposed on either battery supply line with 
respect to a reference ground plane . 
5.3.7.2  Electromagnetic emissions  
When tested in accordance with relevant approved standard s and with the values of electromagnetic emissions 
measured on the output port of a 50 -W line impedance stabilizing network, the system under test shall not cause 
interference in the supply line exceeding the value shown in Table 1.  
 
©RSB 2021  - All rights reserved   Table 1 — Maximum suppl y line interference levels  
S/N Frequency band MHz  Measured level relative to 1 microvolt 
in 50 W (+ dB)  
1 0.15 to 0.29  70 level  
2 0.30 to 4.90  60 level  
3 5.00 to 29  50 level  
4 30 to 108  Slope 50 to 30  
 
5.3.7.3  Radio Frequency field susceptibility  
When tested in accordance with relevant approved standards, the system shall function normally when 
subjected to a Radio Frequency field of 140 dB above 1 µV/m (10 V/m) over a frequency range of 1 MHz to 220 
MHz. 
5.4 Environmental protection  
For environmental protection, components of the system shall be subjected to tests in accordance with IEC 
60068 -2-1; IEC 60068 -2-2 and 60068 -2-38, after each of which they shall continue to function normally.  
6 Marking  
Each control unit and actual shall be marked with the fol lowing in one of the official languages used in Rwanda:  
a) name and/or trade mark of the manufacturer;  
b) model number;  
c) serial number;  
d) country of origin ;  
e) set speed, expressed in km/h, at which the vehicle is calibrated; and  
f) calibration da te (day, month and year).  
 
   DRS  291: 2021  
©RSB 2021  - All rights reserved    Annex  A 
(normative)  
 
System durability test  
A.1 Connect the components of a system in accordance with the manufacturer’s instructions and where 
necessary adjust to simulate maximum load/travel conditions (worst case). Connect a 24 V (1 2 V) battery with 
the charge maintained at 28 (14) ± 1 V d.c.  
A.2 Activate the system through the following test cycle:  
a) drive to a full range travel (t1);  
b) reverse to zero output (t2)  
c) drive to mean position (t3)  
d) control at mean output for 5×(t1 + t2 + t3)  and e) reverse to zero out; where t is the time required to complete 
each individual operation.  
A.3 Repeat this test cycle for 250 000 cycles   
©RSB 2021  - All rights reserved   Annex  B 
(normative)  
 
Time and temperature stability test  
B.1 Connect up  the system in a test chamber at 18 0C ± 2 0C to a supply of 28 (14) ±1 V d.c., complete with 
simulation of components of the loop between the throttle actuator and speed (i.e. engine and transmission) 
outside of the test chamber.  
B.2 Set simulated throttle demand to maximum.  
B.3 Adjust the set speed of the system where appropriate.  
B.4 Activate the system and the recorder. Throughout the test, B.5 to B.7, record the maximum deviation from 
the set speed.  
B.5 Allow the system to oper ate for 10 h.  
B.6 Reduce the test chamber temperature to 0 0C ± 2 0C. After the temperature of the test chamber has 
stabilized, operate the systems for further 30 min.  
B.7 Increase the test chamber temperature to 60 0C ± 2 0C. After the temperature of th e test chamber has 
stabilized, operate the system for further 30 min.  
B.8 Increase the test chamber temperature to 80 0C ± 2 0C. After the temperature of the test chamber has 
stabilized, operate the system for a further 30 min. The system shall continue t o function but accuracy may be 
degraded.  
B.9 Reduce the test chamber temperature to 60 0C ± 2 0C. After the temperature of the test chamber has 
stabilized, operate the system for further 30 min. Record the maximum deviation from the set speed.    DRS  291: 2021  
©RSB 2021  - All rights reserved    Annex  C 
(normative ) 
 
Transient voltage test severity levels  
Table C.1 — Transient voltage test severity levels  
Test pulse  Test level  Functional status  Number of pulses or 
test time  Remarks  
1 -150 ( -75) C 5000   
2 +150 (+ 75)  C 5000   
3) a -150 ( -75) A 1h  
3) b +150 (+ 75)  A 1h  
4 -12 (-6) C 5 pulses  1 min between each  
5 +180 (+ 80)  C 1 pulse   
NOTE These values are for use in conjunction with ISO 7637 -1 or ISO 7637 -2  
NOTE A is normal function  and C is fail but recover  
  
©RSB 2021  - All rights reserved   Annex  D 
(normative)  
 
Transient voltage test severity levels  
D.1 Chassis and cab mounted components  
D.1.1  General  
Subject the component to be tested, mounted on its normal mount, complete with its ancillary components, to 
resonance search in all three planes using a sinusoidal wave form under the conditions given in D.1.2 followed 
by an endurance test under the conditions given in D.1.3.  
D.1.2  Resonance search  
  Frequency range   10 Hz to 250 Hz  
  Input      2 gn  
  Sweep time    2 min  
  Duration     Long enough to establish resonant frequency  
D.1.3  Endurance test at resonance f requency  
D.1.3.1  If there is resonance, carry out a broad sweep endurance test under the following conditions:  
 Frequency range   3 dB below peak for each resonance  
  Input                    2 gn  
  Sweep time         1 Hz/s  
  Duration              7.2 h  
D.1.3.2  if there is no resonance, carry out a broad sweep endurance test under the following conditions:  
  Frequency range    10 Hz to 250 Hz  
  Input                       2 gn 
 Sweep rate               4 Hz/s  
  Duration                 30 h/plane  
D.2 Engine mounted components  
D.2.1  General  
Subject the component to be tested, mounted on its normal mount, complete with it ancillary components to a 
resonance search in all three planes using a sinusoidal wave form under the conditions given in D.2.2 followed 
by an en durance test under the conditions given in D.2.3    DRS  291: 2021  
©RSB 2021  - All rights reserved    D.2.2  Resonance research  
  Frequency range   40 Hz to 2 000 Hz  
  Input                     6 gn  
  Sweep time           2 min  
  Duration     Long enough to establish resonant frequencies  
D.2.3  Endurance test at resonan ce ranges  
Frequency range 3 dB below peak for each resonance in the ranges 40 Hz to 200 Hz and 200 Hz to 2 000 Hz  
  Input                       12 gn        6gn  
  Sweep time             2 Hz/s      5 Hz/s  
  Duration  107 reversals at resonant frequency  
  If there is no resonance, carry out a broad sweep endurance test under the following conditions:  
  Frequency range        40 Hz to 200 Hz    200 Hz to 2 000 Hz  
  Input                          12gn                    6 gn  
  Sweep rate                  2 Hz/s              5 Hz/s  
  Duration                      10 h/plane     10 h/plane   
©RSB 2021  - All rights reserved   Bibliography  
RS 291: 2015, Maximum  road speed governors for motor vehicles  — Requirements  
 DRS  291: 2021  
 
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