More compatible Cadillac XTS chassis analysis+test drive
● Track experience
Different from the previous track test drive, this time I didn’t focus on experiencing the dynamic performance of the vehicle, but hoped to get an insight into the design characteristics of the chassis structure, such as the influence of the front of the Hiberstrut structure on steering, whether it can avoid steering, and the control of the MRC magnetorheological shock absorber on the body. I almost forgot that the XTS front brake is also equipped with four fixed-caliper brake calipers, which is a serious sports equipment. The test drive model is a 28T leading model equipped with air and MRC active variable dampers.
◆ Is torque steering avoided?
The data of 269 HP and 355 Nm is presented by this 2.0T engine carried by XTS. This 2.0T engine with LTG model won the title of Top Ten Engine of Ward in 2013, and it is regarded as the exclusive engine in China market. In terms of power performance, its combination with 6AT gearbox can meet most of the use requirements, but in the state of rapid acceleration, the phenomenon of torque steering is always an unavoidable topic. Can the Hiberstrut structure and the middle part of the long side restrain it?
The first experience was a failure, because when the vehicle stability system was turned on, no matter how I stepped on the accelerator pedal, the pointer of the tachometer hovered around 2000rpm like lead, and refused to climb first. In this state, the vehicle started naturally.
The switch of the vehicle stability system is arranged in the touch button on the central control panel. After the finger is lightly touched, the all-liquid crystal instrument panel shows that the vehicle stability system has been turned off, and then the previous actions are repeated. The difference is that the engine has been able to counter the vehicle braking system at a higher speed, and the subsequent state is expected. The vehicle moves forward in the skid of the tires, and at the same time, the direction of the front of the vehicle has also deviated to a certain extent. At this time, it is necessary to give the steering wheel an opposite force to effectively control the vehicle trajectory.
Conclusion Obviously, the structure of the suspension and the universal joint in the middle of the long semi-axle have not completely avoided the torque steering phenomenon, but I believe that the torque steering phenomenon will be more obvious if it is replaced by an ordinary front suspension. In order to prevent this "gaffe" from scaring the driver, it is a very reasonable practice to use the vehicle stability system to limit it.
◆ What is the feedback of the steering wheel?
The U-bend in the track is the best section to feel the steering wheel return to the normal state. In order to fit the driving state of the road better, the speed of entering the bend is controlled at around 40km/h, and the steering force of the steering wheel is not heavy but still very tight. After passing through bending center, I deliberately reduced my grip strength, and the steering wheel naturally completed its proper righting process, and the rhythm of righting basically kept pace with the acceleration of both cars. From the feedback from all sides, this is not the effect simulated by the electric power steering system.
From this point of view, the Hiberstrut suspension structure of XTS adopts a smaller kingpin inclination angle to improve the handling of the vehicle, and at the same time, there is no side effect that affects the driving comfort.
Then I repeatedly passed this U-bend at different speeds (the vehicle stability system was turned off). Under normal circumstances, the front-wheel vehicle with too fast speed will understeer and slide to the outside of the track, while XTS, which is also a front-wheel vehicle, is different. Its rear wheel limit seems to come earlier than the front wheel. Therefore, in the limit state, the rear wheel will be slightly active. If the speed is properly controlled, the front of the vehicle can point to bending center conveniently. If the speed is too fast, the rear wheel will swing too much.
This phenomenon may be related to the body length of XTS. The body length of 5131mm is even longer than that after lengthening. Dragging this rear half will inevitably increase the burden on the rear wheels. In the limit state, it is inevitable that there will be excessive steering.
◆ Is MRC active variable shock absorber effective?
In order to let everyone better experience the effect of MRC active variable shock absorber, the staff specially placed a series of speed bumps on a straight road. When seeing this situation, I subconsciously stepped on the brake pedal, taking into account the passengers’ feelings. However, the instructions from the hand desk can be passed at full speed, so it is natural to look back and forth after getting such a "exemption clause".
After a burst of high-frequency vibration, the vehicle passed the speed bump smoothly. It can only be said that the vehicle did not appear redundant shaking under such continuous bumps, but when dealing with the impact from the speed bump, the vibration was not filtered very cleanly by the suspension.
In contrast, it is easier to feel the existence of MRC active variable damper in continuous corners. Driving into the S-bend at a faster speed, when entering the first bend, with the shift of the center of gravity, the car body appears a certain degree of tilting phenomenon, and the spring supports the tilted car body in this process. In order to make the car body appear a larger tilt to increase the pressure of the suspension, I deliberately cut into the next bend with a larger angle, and the transfer process of the center of gravity to the other side is almost synchronized with the rotation of the steering wheel. After hitting the direction again, it passes through the S-bend smoothly. In the process of shifting the center of gravity, the released spring does not increase the instability of the car body, which ensures the contact area between the tire and the ground to the greatest extent, thus improving the response of the vehicle in corners.
Editor’s summary:
The front suspension of Hiberstrut structure has found its own position between McPherson structure and suspension of structure. The more compact structure makes it not need to occupy a lot of space like the suspension of multi-link structure, but it can control the wheels more delicately than McPherson suspension. The multi-optimized suspension structure has obviously improved the vehicle’s handling ability, but it has not achieved immediate effect in restraining torque steering. Fortunately, the vehicle stability system can fill such "regret". The suspension combination of MRC magnetorheological shock absorber and air spring equipped with two high-profile models makes the vehicle have different chassis characteristics, which is not only suitable for dynamic and static, but also improves the ride comfort to some extent.
It can be seen that Cadillac has put a lot of effort into the chassis of XTS, with accurate steering, quick chassis response and certain comfort. However, in my personal feeling, compared with the benchmark at the same level, Cadillac still owes some time in shaping the driving experience, perhaps because of the excessive pursuit of comfort due to vehicle positioning problems, and the information from the road surface is not directly transmitted to the driver, which also loses some driving pleasure. Fundamentally speaking, the chassis design of XTS still retains certain characteristics of American cars. (Photo/Text Li Boxu)
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