VEHICLE STATE ESTIMATION SYSTEM

Abstract

A vibration model storage unit stores a vibration model which is made up of an unsprung part, a sprung part, a damper, a tire and a suspension spring, an actual relative distance detection unit detects an actual relative distance of the unsprung part to the sprung part, and a deviation calculation unit calculates a deviation between an estimated relative distance of the unsprung part to the sprung part that is estimated by the vibration model and the actual relative distance. An input parameter calculation unit calculates an input parameter that is inputted into the vibration model from a road surface based on the deviation calculated by the deviation calculation unit, and a vehicle state quantity calculation unit calculates a quantity of state of a vehicle by applying the input parameter to the vibration model.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a vehicle state estimation system according to an exemplary embodiment of the present invention.

FIG. 2 is an explanatory diagram which explains an operation of the system when a PID gain is set according to the exemplary embodiment of the present invention.

DETAILED DESCRIPTION

Hereinafter, an exemplary embodiment of the present invention will be described based on the accompanying drawings.

FIGS. 1 and 2 show an exemplary embodiment of the present invention, and FIG. 1 is a block diagram of a vehicle state estimation system, while FIG. 2 is an explanatory diagram which explains an operation of the system when a PID gain is set.

As is shown in FIG. 1, a vehicle state estimation system of the exemplary embodiment includes a vibration model storage unit M1, an actual relative distance detection unit M2, a deviation calculation unit M3, an input parameter calculation unit M4 and a vehicle state quantity calculation unit M5.

The vibration model storage unit M1 stores a vibration model which is made up of an unsprung part 11 which has an unsprung mass m1, a sprung part 12 which has a sprung mass m2, a damper 13 which has a damping coefficient C2, a tire 14 which has a spring constant K1, and a suspension spring 15 which has a spring constant K2. x0, x1, x2 are coordinate systems which are fixed in a space to extend in a perpendicular direction, x0, x1, x2 denoting respectively a displacement of a road surface (irregularities of the road surface), a displacement of the unsprung part 11, and a displacement of the sprung part 12.

The actual relative distance detection unit M2 is such as to calculate an actual relative distance L* which is an actual relative distance of the unsprung part 11 to the sprung part 12 and is specifically made up of a stroke sensor for detecting an extension stroke of the damper 13.

The deviation calculation unit M3 calculates a deviation δ=L*−L between an estimated relative distance L=(x2−x1) which is the relative distance of the unsprung part 11 to the sprung part 12 which is calculated (estimated) by the vehicle state quantity calculation unit M5 based on the vibration model stored in the vibration model storage unit M1 and an actual relative distance L* which is detected by the actual relative distance detection unit M2.

The input parameter calculation unit M4 calculates a road surface displacement x0 which is an input parameter inputted into the vibration model from the road surface by giving a PID gain to the deviation δ calculated by the deviation calculation unit M3. The PID gain is set in a way that will be described below. Namely, as is shown in FIG. 2, an unsprung acceleration sensor 16 for detecting an actual unsprung acceleration is temporarily provided on an actual vehicle, and an estimated unsprung acceleration which is estimated by the vibration model is compared to an actual unsprung acceleration detected by the unsprung acceleration sensor 16. Since the estimated unsprung acceleration changes according to the value of the PID gain, the PID gain is set (tuned) such that the estimated unsprung acceleration coincides with the actual unsprung acceleration. Since, when the setting of the PID gain is completed in this way, it is ensured that the vibration model accurately simulates the road surface displacement x0, unsprung displacement x1 and sprung displacement x2 of the actual vehicle, the unsprung acceleration sensor 16 becomes unnecessary and hence is removed.

Returning to FIG. 1, when the vibration model is vibrated based on, as an input, the road surface displacement x0 which is the input parameter calculated by the input parameter calculation unit M4, the vehicle state quantity calculation unit M5 calculates a plurality of quantities of state of the vehicle based on the vibrating state (road surface displacement x0, unsprung displacement x1 and sprung displacement x2) of the vibration model.

The quantities of state of the vehicle include road surface displacement which is nothing but x0, unsprung displacement which is nothing but x1, unsprung speed which corresponds to dx1/dt, unsprung acceleration which corresponds to d²x1/dt², sprung displacement which is nothing but x2, sprung speed which corresponds to dx2/dt, sprung acceleration which corresponds to d²x2/dt², stroke speed of the damper 13 which corresponds to d(x2−x1)/dt and the like.

Thus, since the PID gain is set such that the estimated unsprung acceleration estimated by the vibration model coincides with the actual unsprung acceleration detected by the unsprung acceleration sensor 16 and the vibration model is vibrated using the input road surface displacement x0 which is calculated based on the PID gain so set, the reliability in coincidence between the vibration model and the actual vehicle is enhanced, thereby making it possible to calculate the quantities of state of the vehicle with good accuracy.

In addition, since the road surface displacement x0 can be calculated, the road surface condition can be determined, which was not possible with the related-art technique described in U.S. Pat. No. 5,987,367 above. Moreover, since the sprung acceleration d²x2/dt² can be calculated, a skyhook control using the sprung acceleration d²x2/dt² can be performed without a need for a special sprung acceleration sensor.

Thus, while the embodiment of the present invention has been described heretofore, various modifications in design can be made to the present invention without departing from the spirit and scope thereof.

For example, the quantities of state of the vehicle which are calculated by the vehicle state quantity calculation unit M5 are not limited to road surface displacement, unsprung displacement, unsprung speed, unsprung acceleration, sprung displacement, sprung speed, sprung acceleration and stroke speed.

Claims

1. A vehicle state estimation system comprising: a vibration model storage unit which stores a vibration model including an unsprung part, a sprung part, a damper, a tire and a suspension spring;an actual relative distance detection unit which detects an actual relative distance of the unsprung part to the sprung part;a deviation calculation unit which calculates a deviation between an estimated relative distance of the unsprung part to the sprung part that is estimated by the vibration model and the actual relative distance detected by the actual relative distance detection unit;an input parameter calculation unit which calculates an input parameter that is inputted into the vibration model from a road surface based on the deviation calculated by the deviation calculation unit; anda vehicle state quantity calculation unit which calculates a quantity of state of a vehicle by applying the input parameter calculated by the input parameter calculation unit to the vibration model.

2. A vehicle state estimation system as set forth in claim 1, wherein the quantity of state of a vehicle that is calculated by the vehicle state quantity unit includes a sprung acceleration.