Rolldynamometer

Details Rolldynamometer Rolldynamometer

2000-01-11

2002-10-01

Fuller, Benjamin R. (Department: 2855)

Measuring and testing

Vehicle chassis

Steering

C073S862000

Reexamination Certificate

active

06457352

ABSTRACT:

The invention relates to a rolldynamometer or drumdynamometer for motor vehicles of the type specified in the preamble of the patent claim 1 as well as a method for controlling a plurality of electric driving motors of rolldynamometers.
For testing dynamic driving parameters as well as exhaust gas values of motor vehicles driven by internal combustion engines complex rolldynamometers or drumdynamometers enabling a simulation of various driving conditions have recently been used. For carrying out tests concerning, for example, the braking functions, the exhaust gas emissions or the likes, the vehicle to be examined is fixed in the rolldynanometer, for example, by means of a rod assembly, while either the two wheels of one axis or the two wheels of a plurality of axes are resting on the crown area of a drum or a pair of rolls, respectively, depending on the design of the dynamometer. The drums or pairs of rolls are coupled with driving/decelerating motors associated with measuring elements for detecting the torques or tensile forces occurring in correspondence with the different test conditions.
In dynamometers used for examining vehicles having a so called four wheel drive, the running rolls or drums for the front wheels and the running rolls or drums for the rear wheels must rotate with equal speeds or circumferential speeds even when the driving speed for the examination changes, since in case of possibly occurring speed differencences between the front and rear pairs of running rolls control actions of the electronics incorporated in the vehicle might be caused. For example, the braking systems of motor vehicles are normally designed so that the braking action applied to the front wheels is stronger than the braking action applied to the rear wheels when the brake pedal is operated. When examining the function of the braking system of the vehicle to be tested, the front wheels with the stronger brake action applied thereto may delay the running rolls of the front test set more, which may cause the anti blocking apparatus of the vehicle to assume an excessive slipping of the wheels and reduce the braking force of the front wheels correspondingly. When, on the contrary, the driven axis and with its wheels the corresponding pair of running rollers becomes faster than the non driven axis during an acceleration operation, this may cause a reaction of the anti slip controller of the vehicle which will then reduce the output of the internal combustion engine. It is plain to see that such control actions will falsify the measurement results.
In a dynamometer designed for function tests for different operation parameters of so called four-wheel-drive vehicles therefore not only the tractive resistances expressed by A, B and C coefficients and the forces and momentums of the moving masses resulting from an acceleration or deceleration have to be detected and controlled, but also the circumferential speeds of the front and rear running rolls or drums must be kept equal, an angularly synchronous rotation of the front and rear running rolls or drums being considered optimal.
From the U.S. Pat. No. 5,452,605 a drumdynamometer for a motor vehicle having a one-axis-drive is known in which a single test set comprises two running drums and a central electrical driving motor borne in a common support frame and driving both running drums directly and synchronously. The stator housing of the driving or deceleration motor is pendulously borne in two vertical posts and additionally supported on the frame via a torque or force sensor. When, for example, during a brake test on the motor vehicle, the braking force transmitted to the running rolls by its braked-down wheels is introduced into the driving motor, the stator housing reacts with a torsion within the limits determined by the torque sensor, the reaction moment of the stator housing being detected by the torque or force sensor. Changes of the torque applied by the stator housing are thus detected as measurement values by the torque sensor. For bearing both sides of the stator housing in the support frame, the stator housing is provided with a hollow tappet on each end face, the rotor shaft connected to the two running drums being borne by internal anti-friction bearings in each hollow tappet. Opposed to the support frame each hollow tappet is borne by another radially outer anti-friction bearing. A drawback of this bearing arrangement is that during a stillstand of the driving motor no lubrication film is present in the anti-friction bearings and that the bearing bodies contact each other directly. This results in extremely high friction values during the start-up of the motor and to a premature damage to the bearing arrangement. This adverse effect is increased by the risk that the roll bodies may sink into the bearing shell due to the structure-borne noise present during the operation of the motor.
For overcoming these adverse effects it is known from the U.S. Pat. No. 5,522,257 to coaxially mount two anti-friction bearings above each other with a central ring interposed between them, the central rings being driven with a predetermined rotational speed via a belt drive before the driving motor is turned on for generating a lubrication film in the two antifriction bearings before the driving motor is activated. There exists, however, a drawback in that a force is introduced duced by the movement of the central rings of these bearings, which force is added to the torque to be measured during the examination. Additionally, the double bearings and the central ring including its rotational drive increase the technical requirements.
From the DE-B-39 20 277 a rolldynamometer for four-wheel-drive motor vehicles is known by which so called yawing moments about the vertical axis of the vehicle may also be simulated and detected. Each front wheel and each rear wheel of the motor vehicle to be examined are supported by a pair of rolls, respectively. To individually drive and brake the wheels, each pair of rolls is driven by an own driving motor, a torque sensor being disposed between each roll and the associated driving motor. The driving motors are preceded by power converters which are each instructed by an associated gain control amplifier. For measuring the rotational speeds of the individual motors, tachometer generators are provided, one tachometer generator, one gain control amplifier, one power converter and one driving motor being the components of one closed loop speed control circuit and all control circuits being connected to a processor formed as a process control computer or programmable control unit. For simulating running through curves the different circumferential speeds of the drums on the inner curve side and the outer curve side corresponding to these curves can be determined with the aid of said processor based on a desired running speed.
It is the object of the invention to provide a rolldynamometer or drumdynamometer providing more accurate measurement results with a less complex construction.
According to the invention, this object is solved by the stator housing of the driving motor being borne in the support frame by bearing arrangements which are virtually friction free even during the activation or start-up operation.
According to a particularly efficacious embodiment of the invention the bearing arrangements are provided with plain bearings of simple design into the bearing parts (bearing shells) of which pocket shaped or groove like cavities are machined to which a largely constant carrying pressure oil flow is applied. Between the sliding surfaces of each bearing a film like cushion of pressure means of high support capacity and negligible friction values with respect to the relatively small pendulum motions of the motor housing in the support frame develops, if required. The torque applied by the motor housing during an examination operation is thus detected by the force meter without errors. One of said bearing arrangements is efficaciously formed as an axially fixed bearing and has an axial pressure bearing with inte

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