Measuring and testing – Test stand – For engine
Reexamination Certificate
2000-04-06
2003-04-01
McCall, Eric S. (Department: 2855)
Measuring and testing
Test stand
For engine
C073S862000
Reexamination Certificate
active
06539782
ABSTRACT:
The present invention relates to a load machine for a test bench for the dynamic testing of combustion engines, for example of the diesel or gasoline or gas type.
When a combustion engine is coupled to a load machine on a test bench, the load machine has to be able to brake the rotation of the drive shaft, so as to simulate operation of the engine, as a function of friction with the ground, with the air and as a function of the inertia and speed of the vehicle, under various engine speed/load conditions.
Hydraulic brake machines are already known and have the advantages of low inertia and small size with respect to the braking power that can be supplied, and low cost. However, hydraulic brake machines are in increasingly dwindling use, because they do not allow precise regulation, given that the regulator acts on a fluid with a relatively slow response time. Hence, a hydraulic brake machine is not suited to a combustion engine equipped with an ignition and injection computer requiring high-precision regulation for developing the mapping. Furthermore, it is difficult to manufacture a hydraulic machine which is capable both of braking and of driving the combustion engine.
Eddy-current brakes are the machines most commonly used in test benches for touring-car or competition car engines and truck engines. Eddy-current brakes allow high-precision regulation and have a modest cost for a low or moderate power supplied. By contrast, eddy-current brakes which supply high power are expensive and require a large-diameter rotor in order to be able to operate at low speed and high torque, thus increasing the weight and inertia of the rotor. Furthermore, an eddy-current brake is unable to drive a combustion engine.
In general, an eddy-current brake machine comprises a rotor made up of a toothed ferromagnetic disk rotating in a magnetic field, the teeth of the disk causing a variation in induction and therefore eddy currents at the surfaces of the two metallic parts located on each side of the rotor; these currents move with the rotor in the magnetic field and in return bring about a torque that brakes the rotor, this being the desired effect; a significant amount of energy is dissipated by a Joule effect. The element which generates the magnetic field is an electrically powered coil, for example powered with ac current or chopped dc current, secured to the casing of the machine. The heat dissipated by Joule effect is removed by a bank of heat exchangers, also secured to the casing, which are supplied with coolant by means of appropriate pipe-work.
In order to be able to study the behavior of the combustion engine under engine-braking conditions, it is necessary to add a means of rotating the drive shaft. However, such a drive means does not need to be able to develop 100% of the power of the combustion engine, but simply of the order of 40% of full load, to in fact simply compensate for the kinetic energy of the vehicle. By way of example, if the combustion engine has a power of 200 kW, the eddy-current brake has also to have a power of 200 kW, whereas the drive means need merely have a power of the order of 80 kW.
This is because the brake machine has to be able to compensate for the nominal power of the combustion engine, which depends on the geometric and mass characteristics of the vehicle, with regard to the maximum speed to be achieved, whereas the drive means has simply to be able to simulate the power for driving the combustion engine which depends only on the inertia of the vehicle under phases of deceleration or downhill travel.
Dc electric motors or asynchronous ac motors have already been used by way of drive means, these being coupled in line with the eddy-current brake machine. However, coupling such an electric motor to an eddy-current brake machine has the effect of doubling the length requirement (1.5 m instead of 0.75 m), doubling the inertia and tripling the cost, by comparison with the eddy-current brake machine alone.
Having high inertia in the load machine makes it difficult to raise the speed of the engine quickly. This is a particularly sensitive issue in the case of combustion engine testing for the engines of competition cars, for example, Formula 1 cars, in which the engine has to be able to accelerate from 0 to 15,000 rpm in one second.
It has also been proposed that the eddy-current brake/electric motor machine assembly be replaced by a single dc or asynchronous ac electric motor. The same motor can thus be used to perform dynamic testing, that is to say can operate either as a brake or as a generator. The motor thus allows on-road operation simulation testing to be carried out taking the mass of the simulated vehicle into consideration, including gearshifts. This simulation of the giving-up of the energy stored by the component which absorbs the energy of the combustion engine also finds a few applications outside of cars and trucks. However, the inertia of such an electric motor is about three times greater than that of an eddy-current brake alone, and the cost is about five times higher. This is because when the electric motor is used as a brake, it operates as an alternator or dynamo, that is to say produces electric current which has to be returned to the network. Given the power developed by combustion engines and therefore the strength of the current generated, it is necessary to associate a special cabinet with the electric motor in order to return the current to the electricity network. Furthermore, for example, in the case of a 200 kW brake, the length occupied by this electric motor is of the order of 1.5 m, whereas an eddy-current brake-machine is just 0.75 m long.
Furthermore, the use of dc electric motors in a combustion engine test bench is difficult, because the operation of the wipers or brushes of the electric motor in an oily environment has to be taken into consideration. What is more, asynchronous motors have high inertia and the rotor, which becomes very hot, is difficult to cool because it is a rotating part.
The object of the invention is to eliminate the aforementioned drawbacks and propose a load machine which operates both as a brake or as a generator while at the same time, by virtue of the passive rotor, having low inertia and therefore being highly suited to high speeds, and in which the heating affects the parts external to the rotor, hence making them very easy to cool. Furthermore, the use of a variable-reluctance motor makes it possible to operate either as a brake or as a generator. Finally, the cost of such a machine will be modest. Another object of the invention is to propose such a load machine which occupies only a small amount of space in the lengthwise direction.
To this end, the subject of the invention is a load machine for a combustion engine test bench, comprising at least one eddy-current brake means associated with at least one electric drive means, said brake means comprising a toothed ferromagnetic rotor secured to a shaft mounted so that it can rotate through a casing containing at least one induction coil borne by an internal peripheral region of the casing, so as to generate a magnetic field across which the rotor is intended to pass in order to generate eddy currents so as to brake the rotation of the shaft, said shaft being intended to be coupled to the combustion engine to be tested, characterized in that the electric drive means forms a variable-reluctance electric motor. The eddy currents are not therefore generated in the rotor but in the metal parts located on each side thereof.
In a first embodiment, the variable-reluctance motor is mounted in series with the brake means and comprises a stator secured to two opposed side walls through which the aforementioned shaft rotatably passes, so that one of said walls is adjacent to the casing of the brake means, a ferromagnetic rotor secured to the shaft and spaced axially from the toothed ferromagnetic rotor, and a number of excitation coils arranged on said stator around the periphery of the ferromagnetic rotor, so as to generate a magnetomotive force for dr
Ahmed Hamid Ben
Drecq Daniel
Lesobre Antoine
Prevond Laurent
Borghi Saveri France
McCall Eric S.
Stevens Maurice
LandOfFree
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