Data processing: structural design – modeling – simulation – and em – Simulating nonelectrical device or system – Mechanical
Reexamination Certificate
2000-03-09
2004-06-22
Broda, Samuel (Department: 2123)
Data processing: structural design, modeling, simulation, and em
Simulating nonelectrical device or system
Mechanical
C703S001000, C703S002000, C702S140000, C701S036000, C073S146000
Reexamination Certificate
active
06754615
ABSTRACT:
The present invention concerns a method of simulating the performance or behavior of a vehicle on a road surface on a power train or drive train test bed.
In addition to the simulation method described below on a power train test bed, German Patent No. 43 25 413 C2 and German Patent Application No. 40 30 653 A1 describe mathematical methods for estimating variables that characterize the actual driving performance but cannot be measured directly. To perform the estimation, the sensor signals that are accessible to measurement are processed with motion equations and take into account a tire model in such a way as to yield the desired variables. To arrive at a set of equations that can be solved to yield the desired variables, German Patent No. 43 25 413 C2, for example, treats the tire forces and the adhesion coefficient between a vehicle wheel and the roadway as quasi-steady-state variables. Signals representing the longitudinal velocity of the vehicle, the longitudinal and lateral acceleration, the yaw rate, the steering angle of the wheels and the angular wheel speed (so called wheel rpm) are entered as measured sensor signals into a computer unit. To make it possible to determine variables characterizing the vehicle attitude or handling in all vehicle driving conditions, the motion equations are supplemented according to German Patent No. 43 25 413 C2 by measurement equations that are based on a vehicle model and can be combined with the motion equations in such a way that the required set of equations for the side slip angle of the vehicle, for example, can be obtained. The measurement equations are derived from a four-wheel model. The side slip angle of the road surface with respect to a plane is used as a state variable. German Patent Application No. 40 30 653 A1 describes an estimation method for the side slip angle of the wheels or the axles of a braked vehicle and for the cornering forces on the wheels and the tire contact or normal forces. A simplified vehicle model which does not take pitching, rolling and up-and-down motion into account is assumed. Cornering force and braking force are calculated from the HSRI (Highway Safety Research Institute of the University of Michigan) tire model using the wheel speed, the yaw rate, the main brake cylinder pressure and the wheel brake pressures as measured quantities.
German Patent Application No. 37 00 409 A1 describes a motion estimation system which represents a simulated vehicle with a set of vehicle motion equations. The system uses a sensor for the measured vehicle velocity which is sent directly to a computer and a sensor for the steering angle which is used in a steering model. The computer should estimate the side slip angle among other variables and it also supplies a lateral acceleration value for use in a roll model. The roll model determines therefrom a vehicle roll angle which is in turn sent to the computer. The digital computer is connected to analog computation circuits for the steering model and the roll model, serving to simulate these parts of the total model used and supply the front wheel steering angle and the roll angle to the digital computer for the computer estimations. Then the digital computer calculates the desired vehicle motion variables from a planar motion model with the help of the measured vehicle velocity. This does not make it possible to implement a slip simulation.
Furthermore, for many years the automotive industry has been using test beds or stands to test the power train or drive train of a vehicle by simulating the running resistance and the acceleration performance of the vehicle and the vehicle wheels by using electric load machines mounted on the drive shafts of the vehicle. One such test bed is described in European Patent No. 338,373 B1, where the actual performance of the main power train, the axle gears, the driving shafts, the clutch, the transmission and the combustion engine enter into the calculations as existing components. The load machines are torque-controlled electric motors with a predetermined torque setpoint value provided by a computer. This value is generated from an angular wheel speed difference which is sent to an integrator with a time constant that is proportional to the tire damping or spring stiffness of the tire and a parallel proportional element with a gain factor that is proportional to the tire damping or elasticity constant. The torque setpoint is obtained from the sum of the elasticity moment and the damping moment supplied by the integrator and the proportional element. The angular speed difference is obtained from the measured angular velocity and the angular wheel speed of the drive shaft at the electric load machine and from an angular velocity that is proportional to the vehicle velocity. The latter is determined by integrating the running resistance moment, reduced by the torque setpoint values for the simulated wheels, in an integrator with a time constant that is proportional to the moment of inertia of the vehicle.
The method described above for obtaining the torque is thus based on a rotational speed regulation which takes into account the elasticity and damping of the tire but essentially disregards the tire slip. To overcome this inadequacy, it is known from European Patent No. 338,373 B1 that in order to take into account a kinematic tire slip, the product of the angular velocity and a slip value which is determined as a function of the torque setpoint, is subtracted from this angular velocity which is proportional to the vehicle velocity before the above angular wheel speed comparison is made on the basis of the angular velocity thus modified. With regard to this method of taking into account the kinematic slip, it has found to be a disadvantage that the moment distribution in the drive train during slip would have to be known to be able to utilize the expected moment balance to calculate the angular wheel speed gradient (rpm gradient), but precisely this moment distribution is not known in particular during dynamic processes or in systems with a variable moment or torque distribution (spinning). Therefore, a spinning or blocked wheel is simulated as an alternative so that the torque setpoint is limited to a corresponding constant slip moment which is calculated from a preselected adhesion value representing the road surface, a tire normal force and a tire radius. The tire is simulated in a slip-free model except torque transmitting conditions where the limiter causes the rotational speed regulator to run to its limit to simulate a locking or spinning wheel.
This known method of taking tire slip into account merely represents a compromise with regard to the realistic simulation of the tire, so that as a rule, a tire simulation is not implemented in today's power train test beds, and the only variables of vehicle performance that are tested are those where the tire and tire slip, respectively, can be disregarded. To avoid inadmissible torque curve values, a torque distribution corresponding only to the theoretical values of the power train but not to the actual curve values is presupposed on the test bed with the help of torque balancing regulators.
Otherwise, the test beds are used to reproduce load collectives whose data in the form of angular wheel speed and torque or moment on the wheels of interest are recorded in a conventional way on vehicles equipped with devices for measuring torque and rotational speed on a representative test route. Then the test object can be tested, for example, with regard to its endurance on the test bed, which is operated as a load test bed, by running the load collectives which have been obtained under realistic conditions on the test route. In the testing equipment described in German Patent Application No. 38 18 661 A1, the previously measured or calculated load collectives are also reproduced on a vehicle test bed. This document does not specify which programs are used in the computer of the testing equipment to specify the desired load collectives and determine the control outputs for the cont
Abler Georg
Brodbeck Peter
Germann Stefan
Kopecky Wolfgang
Nonn Harald
AVL Deutschland GmbH
Broda Samuel
Quarles & Brady LLP
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