4. Verification by full vehicle simulation
4.1 Verification by full vehicle simulation
(1) Vehicle motion model
In order to verify the effectiveness of the KPC concept described in Chapter 2, a full vehicle simulation was performed using the vehicle motion model of previous research”). It is a dynamic model that reproduces the suspension mechanism, and can analyze the roll, pitch, and heave of the sprung body caused by the longitudinal and lateral forces of the tires being transmitted to the body through the suspension.
The vehicle specifications used in the simulation are the same as those in Table 1.
(2) Simulation results
As shown in Fig. 8, the simulation conditions were to enter at a vehicle speed of 54 [km/h], cut the steering angle to 80 [deg], and then turn back. With KPC, the peak value is approx.
of the braking force was applied to the inside rear wheel of the turn.
In order to confirm the transitional changes in the planar motion of the vehicle and the sprung body posture during steering, the vehicle motion parameter changes in the turning-on state relative to the turning-side steering angle of 60 degrees. are shown in Table 2.
The yaw rate increases by 0.08% when the steering angle is 60 degrees, and there is almost no change with KPC ON/OFF. In addition, the roll angle and pitch angle decreased by 0.34% and increased by 0.55%, respectively, and remained almost unchanged with KPC ON/OFF. On the other hand, heave decreased by 3.16%, which is larger than other changes. Looking at the relationship between the yaw rate and heave for steering on the turning side using the Lissajous waveform, there is almost no difference in yaw rate between KPC ON and OFF, but the heave is smaller with KPC ON (Fig.9). In this way, it was confirmed that only the heave can be suppressed without changing the yaw, roll, and pitch movements by generating a braking force on the inside rear wheel within a range in which the yaw rate response to the steering operation during a turn is small.
Table 3 shows the results of an investigation of the yaw, roll, pitch, and heave motion when a braking force similar to that of the KPC was applied to the wheels other than the inner rear wheels to which the braking force was applied by the KPC.
shown in In the case of the front wheels inside and outside the turn, the pitch angle increased by about 3 to 4%, and there was almost no change in heave. but out of turn
For the rear wheels, the heap was reduced by 4.70% and the
Larger than the rear wheels (approximately 1.1 times), and the yaw rate is also reduced by 0.37% (approximately 4.6 times), so while it is possible to suppress heave in the same way as the inner rear wheels, the force that damps yaw motion is also possible. is known to occur easily.
From the above results, when the braking wheel is the inside rear wheel, a certain braking force is applied.
It was confirmed that only the heave can be suppressed without changing the yaw, roll and pitch motion within the power range. As shown in Table 1, the vehicle equipped with KPC this time has a large rear anti-lift angle of 22.2 [deg], so a small amount of braking force generates a large anti-lift force. Therefore, heave of the vehicle body can be suppressed without changing the yaw motion.
4.2 Verification by actual running measurement
(1) Driving mode
As in the desktop simulation in section 4.1, the approach vehicle speed is 54
[km/h], maximum steering angle of about 80 [deg], KPC effect was verified in actual driving in a U-turn. The vehicle speed is adjusted while driving straight before entering the vehicle, and after that, the accelerator opening is kept constant with a dedicated device for measurement, and the driver only operates the steering wheel to turn. After obtaining informed consent, the subjects were instructed to run as much as possible in the same manner as the experiment. Fig. 10 shows the measured running trajectory. KPCON
is indicated by a red line, and KPC OFF is indicated by a black line.
(2) Measurement results
The measurement results are shown in Fig. 11. The heave was obtained from the measured values of height gauges attached to the four corners of the vehicle, and the KPC flag in the PCM was measured in synchronization with other measured values.
As in Fig. 10, KPC ON is indicated by a red line, and KPCOFF is indicated by a black line.
is working. Comparing the heave during KPC operation, the heave is small with KPC ON. After suppressing heave, the operation after 7 seconds is different depending on KPC ON/OFF.
In the case of KPC ON, the return is smooth, but in the case of KPC OFF, the initial return is sharp. As for the yaw rate, the steering angle changes after 7 seconds, but there is almost no difference before the KPC is activated. The left figure of Fig.12 shows the relationship between steering angle and yaw rate.
It can be seen that there is no difference in On the other hand, the heap on the right shows a clear difference between KPCON/OFF, and it can be seen that KPC reduced the heap by about 1 [mm].
As described above, as a result of comparing U-turn turning with KPC ON/OFF, it was confirmed that the yaw rate does not change much with KPC and the heave becomes smaller with KPC, similar to the full vehicle simulation results in section 4.1. In addition, the reduction in heap changes the driver's steering behavior, and the KPC operation also has the effect of smoothing the return steering. We were able to confirm that by suppressing heave during cornering, the driver is able to operate the steering wheel with a sense of leeway without having to steer sharply, including at high frequencies.
4.3 Verification on general road driving
As in Section 4.2, ground height gauges were attached to the four corners of the vehicle.
We ran on a winding road in the suburbs of Europe.
Sprung vehicle during cornering (lateral acceleration = 0.45 [C])
Fig. 13 shows a contour diagram showing the body posture, and Fig. 14 shows the vertical movement of the vehicle center point at that time. It can be seen that the turning posture of the car body is reversed from the floating direction to the sinking direction by KPC. It was confirmed that the heap control effect as intended was achieved even on ordinary roads.
In addition, vehicle speed that reproduces the severe road environment of European general roads,
High lateral turning acceleration and many road undulations
KPC ON/OFF the time-series waveform when driving the Nirburgring
Fig. 15 shows the results of the comparison in . In part A of the figure, when the black line shows the KPC OFF, the driver feels uneasy when the vehicle lifts and pulls off the accelerator pedal. I confirmed that I was able to accelerate toward exiting the corner without correcting the accelerator pedal.
Based on these results, sensory evaluations were conducted by comparing the presence or absence of KPC on a large number of drivers in Japan and overseas, including general drivers. The comments obtained are described below. As the vehicle dynamics concept shown in Fig. 1 was aimed at, it can be confirmed that by suppressing heave during turns, the driver has more leeway to operate the vehicle and is able to operate the vehicle with self-reliance.
KPC evaluation comments)
* From corner turn-in to exit, the roll in the floating direction is suppressed, and you can feel the effect of improving the grounding feeling.
* The feeling of ground contact on the inner wheel side is improved in corners with undulations.
* Good controllability in S-shaped corners.
* Because the rear is stable when exiting the corner, you can step on the accelerator.
5. Conclusion
We have developed a KPC that controls the vehicle body posture according to the difference in left and right wheel speeds at the rear during cornering. DYC gives a yaw moment due to the difference in braking/driving force between the left and right wheels, but KPC produces a significantly smaller braking force due to braking. Therefore, the yaw moment generated in the vehicle is small and the yaw motion hardly changes. On the other hand, for the heap, the amplification effect combined with the suspension geometry
It was confirmed by simulation results and actual vehicle measurements that it was reduced. By suppressing heap, KPC stabilizes the vehicle posture that the driver feels and has the effect of smoothing the steering. As described in previous research (), longitudinal acceleration and
In addition to the pitch, it was confirmed that the heave also affected the driver's operation.
