 | The examples and perspective in this article deal primarily with the United Kingdom and do not represent a worldwide view of the subject.(December 2012) |
There are at least three different types of brake tester used to calculate the braking efforts and efficiencies of a motor vehicle:
A roller brake tester is a method of allowing the dynamic assessment of the braking system of a motor vehicle, whilst the vehicle itself is in a static condition. This type of brake tester is normally used in UK garages when used as part of an inspection lane for the MOT test.
Roller brake testers consist of a mechanical floor unit which contains electrical motors, two independent sets of three measuring rollers, brake force transducers and additional safety sensors. [1]
The driving rollers operate at a low (known) speed using a gearbox and motor arrangement and during a test measurements of the maximum braking force are taken by applying the vehicle brakes which induces a reaction force on the electric motor itself. An electric transducer with strain gauges then measures the individual induced forces which are acting during the deceleration phase in order to calculate the individual braking forces for each wheel.
In order to minimize any inaccuracy and variation in the measurement, the roller diameter is sufficiently large to reduce the effects of the mechanical relaxation, or flexing, of the tire itself. A special coating on the rollers is designed to be very wear resistant and provide good friction values, both in wet and dry conditions.
A third smaller roller, on each side between the driving rollers, has two functions: The first is to detect if a vehicle is present in the roller bed (a built in safety device to prevent the motor from starting up unless a vehicle is in the brake tester), the second function is to detect when and if tyre slippage occurs in order to make the measurement before a maximum, predefined value of time passes.
During the test, the computer measures the brake force values and the system will calculate the imbalance between the left and right brake forces of an axle, as well as the brake efficiency of the service brake and the parking brake provided that a vehicle weight is either inputted manually or by using an integrated weighing system. [2]
A plate brake tester is a method of measuring a vehicles braking system in a dynamic test. The unit consists of two moving parallel plates mounted on force transducers. A measurement of the braking force is made when a vehicle passes over the plates and then applies its brakes. The braking action causes the individual plates to ‘slip’ forwards allowing a calculation of braking force to be made. Brake imbalance between the left and right hand side can also be measured by the differences in voltage measured on each of the force transducers under the chassis. Due to the nature of it dynamic operation, plate brake testers are far less common than roller brake testers in UK garages although they are also an extremely accurate method of measurement.
The extremely accurate plate brake method of measuring a vehicle's braking performance in countries such as Australia and New Zealand is increasingly becoming a far more popular alternative to basic decelerometers due to not only accuracy, measurement speed, and the ease of use, but predominately the greatly improved safety offered by removing the need for vehicle inspectors to brake test vehicles on public roads amongst other road users .
A decelerometer is a hand held device for measuring dynamic braking forces during a vehicle road test. [3] A vehicle decelerometer operates as if it were, and it could also be known as, an accelerometer as it calculates braking efficiency by using those forces captured during a vehicle's deceleration. A decelerometer is a basic method by which braking effort can be accessed quickly and easily but it is generally used as an indicator to acceptable brake performance. Low efficiency readings should lead to further investigation on either a plate brake tester or a roller brake tester.
Horsepower (hp) is a unit of measurement of power, or the rate at which work is done, usually in reference to the output of engines or motors. There are many different standards and types of horsepower. Two common definitions used today are the mechanical horsepower, which is about 745.7 watts and the metric horsepower, which is approximately 735.5 watts.
Pressure measurement is the analysis of an applied force by a fluid on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure and display pressure in an integral unit are called pressure meters or pressure gauges or vacuum gauges. A manometer is a good example, as it uses the surface area and weight of a column of liquid to both measure and indicate pressure. Likewise, the widely used Bourdon gauge is a mechanical device, which both measures and indicates and is probably the best known type of gauge.
An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover".
Dynamic braking is the use of an electric traction motor as a generator when slowing a vehicle such as an electric or diesel-electric locomotive. It is termed "rheostatic" if the generated electrical power is dissipated as heat in brake grid resistors, and "regenerative" if the power is returned to the supply line. Dynamic braking reduces wear on friction-based braking components, and regeneration lowers net energy consumption. Dynamic braking may also be used on railcars with multiple units, light rail vehicles, electric trams, trolleybuses, and electric and hybrid electric automobiles.
A dynamometer or "dyno" for short, is a device for simultaneously measuring the torque and rotational speed (RPM) of an engine, motor or other rotating prime mover so that its instantaneous power may be calculated, and usually displayed by the dynamometer itself as kW or bhp.
The MOT test is an annual test of vehicle safety, roadworthiness aspects and exhaust emissions required in the United Kingdom for most vehicles over three years old. In Northern Ireland the equivalent requirement applies after four years. The requirement does not apply to vehicles used only on various small islands with no convenient connection "to a road in any part of Great Britain"; no similar exemption is listed at the beginning of 2014 for Northern Ireland, which has a single inhabited island, Rathlin. The MOT test was first introduced in 1960 as a few basic tests of a vehicle and now covers 20 different parts or systems on or in the car.
The New European Driving Cycle (NEDC) is a driving cycle, last updated in 1997, designed to assess the emission levels of car engines and fuel economy in passenger cars. It is also referred to as MVEG cycle.
Condition monitoring is the process of monitoring a parameter of condition in machinery, in order to identify a significant change which is indicative of a developing fault. It is a major component of predictive maintenance. The use of condition monitoring allows maintenance to be scheduled, or other actions to be taken to prevent consequential damages and avoid its consequences. Condition monitoring has a unique benefit in that conditions that would shorten normal lifespan can be addressed before they develop into a major failure. Condition monitoring techniques are normally used on rotating equipment, auxiliary systems and other machinery, while periodic inspection using non-destructive testing (NDT) techniques and fit for service (FFS) evaluation are used for static plant equipment such as steam boilers, piping and heat exchangers.
In the automotive industry, brake-by-wire technology is the ability to control brakes through electrical means. It can be designed to supplement ordinary service brakes or it can be a standalone brake system.
Force platforms or force plates are measuring instruments that measure the ground reaction forces generated by a body standing on or moving across them, to quantify balance, gait and other parameters of biomechanics. Most common areas of application are medicine and sports.
Road surface textures are deviations from a planar and smooth surface, affecting the vehicle/tyre interaction. Pavement texture is divided into: microtexture with wavelengths from 0 mm to 0.5 millimetres (0.020 in), macrotexture with wavelengths from 0.5 millimetres (0.020 in) to 50 millimetres (2.0 in) and megatexture with wavelengths from 50 millimetres (2.0 in) to 500 millimetres (20 in).
Motorcycle testing and measurement includes a range of more than two dozen statistics giving the specifications of the motorcycle, and the actual performance, expressed by such things as the output of the engine, and the top speed or acceleration of the motorcycle. Most parameters are uncontroversial and claims made by manufacturers are generally accepted without verification. These might include simple measurements like rake, trail, or wheelbase, or basic features, such as the type of brakes or ignition system.
The international roughness index (IRI) is the roughness index most commonly obtained from measured longitudinal road profiles. It is calculated using a quarter-car vehicle math model, whose response is accumulated to yield a roughness index with units of slope. This performance measure has less stochasticity and subjectivity in comparison to other pavement performance indicators, such as PCI, but it is not completely devoid of randomness. The sources of variability in IRI data include the difference among the readings of different runs of the test vehicle and the difference between the readings of the right and left wheel paths. Despite these facts, since its introduction in 1986, the IRI has become the road roughness index most commonly used worldwide for evaluating and managing road systems.
The balancing of rotating bodies is important to avoid vibration. In heavy industrial machines such as gas turbines and electric generators, vibration can cause catastrophic failure, as well as noise and discomfort. In the case of a narrow wheel, balancing simply involves moving the center of gravity to the centre of rotation. For a system to be in complete balance both force and couple polygons should be close in order to prevent the effect of centrifugal force. It is important to design the machine parts wisely so that the unbalance is reduced up to the minimum possible level or eliminated completely.
A duct leakage tester is a diagnostic tool designed to measure the airtightness of forced air heating, ventilating and air-conditioning (HVAC) ductwork. A duct leakage tester consists of a calibrated fan for measuring an air flow rate and a pressure sensing device to measure the pressure created by the fan flow. The combination of pressure and fan flow measurements are used to determine the ductwork airtightness. The airtightness of ductwork is useful knowledge when trying to improve energy conservation.
Test equipment is a general term describing equipment used in many fields. Types of test equipment include:
A headlamp beam tester is a means to check both the orientation and intensity of a vehicle headlamp to ensure that it meets a minimum standard for the country of use of the vehicle. In the United Kingdom, a headlamp beam tester is used to assess the headlight during an MOT test but in order to be used it must be approved as suitable for use in the scheme. A list of acceptable headlight testers for use within the MOT test scheme is listed on the Department of Transport website.
An electric motor (E-motor) test stand is a test stand for reproducible testing of electric motors. In addition to the mechanical design, an electric motor test stand consists of accompanying measurement devices, sensors and application software. The bus systems used to control and monitor the test objects are also included in the test stand. There are a variety of different types of test stands, such as developmental test stands, endurance test stands, end-of-line (EoL) test stands, and hardware-in-the-loop (HiL) test stands.
A chassis dynamometer, informally referred to as a rolling road, is a mechanical device that uses one or more fixed roller assemblies to simulate different road conditions within a controlled environment, and is used for a wide variety of vehicle testing and development purposes.