Steering characteristics omnibus.Consider the relationship between yaw change during accelerated turning and dynamic sensitivity.

In this course, from §11 to 4 times, the theme is steering characteristics during accelerated turning, starting with geometrical content, what is happening at the point of contact between the tire and the road surface, what is the SA (slip angle) of the four wheels? I have talked about how it will change from various perspectives.Steering characteristics are typical steering characteristics that are often taken up in test drive impressions of automobile magazines, but considering the automobile engineering theory of why this happens, you can see that it is quite complicated. ..
But in my own interest, this is just a preliminary knowledge stage.This time, as a omnibus of steering characteristics, I would like to consider how it affects the driver's sensibility ... so to speak, the meaning from the driver's perspective.In other words, it is an approach from the perspective of "dynamic sensitivity," which is the original theme of this lecture.As usual, it's a bit of a hassle, but I'll explain it in the simplest possible way, so please be patient.

■ Differences in steering characteristics from the driver's perspective
In a previous lecture, I explained that "turning a car is a movement that combines rotation and revolution."It is a relationship in which the moon revolves around the earth while rotating.If you watch the car turn a corner from the sky, its trajectory should be similar to the orbit of the moon.If the vehicle accelerates on the way, does the radius of the turning trajectory expand or narrow, or does it change? That is the steering characteristic of the car from the viewpoint of revolution.So to speak, it is the way it looks from the perspective of space.Then, what kind of scenery would you see if you look at the same movement from the perspective of the moon?I'm sure the earth will look like it's spinning around the moon.If so, how would the landscape change if it accelerated at some point?To be precise, it is different from the turning mechanism of the car, but if you think about it, I think it will help you to get an idea of ​​this idea of ​​looking at the steering characteristics of the car from the driver's perspective.
In reality, when a car enters a curve, it always turns the steering as a trigger for the time being.At that time, what will happen to the scenery reflected in the driver's eyes?The scenery that has been approaching in the front-back direction begins to flow sideways.It may be hard to feel because it is moving forward, but it is because the car has begun to rotate.Pseudo, if the car navigation screen is headed up, you can check the situation by rotating the map in the direction opposite to the rotation of the car.This is the rotation movement of the car, the movement called "Yo" that I have often talked about before.
Although it is possible to accurately measure the actual state of this yaw using the latest experimental equipment, it is thought that most human senses judge it from the input to the visual sense.How much yaw appears at what timing with respect to the driver's steering ... This is an important guideline for manipulating the car and is a judgment factor for various design factors, but here the steering characteristics Focus on and proceed with further analysis.

I have already explained many times that yaw angles are always generated in cornering cars even if the steering angle is kept constant.However, the explanation that originates from the yaw moment due to the product of the size of CF generated in the front and rear wheels and the distance from the position of the center of gravity is from a revolutionary point of view.If you trace the source further, it is caused by "centrifugal force due to turning (revolution)".Of course, this understanding is not a mistake.
But it can be explained from a different perspective.It is the generation of yaw moment by "driving force".There is a cycle in which the driver's action of stepping on the accelerator directly promotes the rotation of the car and visually confirms it.This is exactly the theme of dynamic Kansei engineering, but before I explain it, I think that basic knowledge of automobile engineering is also required here.Why does the car intensify the yaw movement when you step on the accelerator?Below, I will focus on the principle part and explain it in a simplified manner.

■ Yaw generation and steering characteristics due to driving force
During cornering, the drive wheels already have SA, so when you step on the accelerator, the resultant force at the center of the driving force works toward the outside of the center of gravity, generating a yaw moment, and that force increases the yaw angle. Let me do it.
In addition, when both FR and FF are in a turning state, the contact load of the outer ring is larger than that of the inner ring due to centrifugal force, so the driving force is generated more in the outer ring where the contact load is large.Therefore, in reality, the yaw moment that tries to rotate the vehicle body around the center of gravity is generated at the position of the tire farther from the center of gravity.This is the reason why "when you step on the accelerator, the yaw (rotation) angle of the car increases".

As an aside, I was once told by the engine development staff at the development site that the suspension was the reason why the corners couldn't turn fast, and the chassis was bad.On the chassis side, I argued that the low-speed torque of the rotary engine is small, and the corners are slow because I do not make an engine that produces torque.I wanted to tell you that the yaw moment changes depending on the magnitude of the driving force, but it was difficult to understand.By stepping on the accelerator and applying the driving force, the greater the driving force, the greater the amount of change in yaw.
However, there is, of course, an upper limit to the generation of yaw angles that originate from the driving force.Since the yaw movement is a rotation around the center of gravity, the same amount of SA increases as the yaw angle increases on both the front and rear wheels.The resulting increased CF in the rear wheels acts as a force in the opposite direction that cancels the yaw moment due to the driving force.Therefore, the change in yaw angle due to driving force cannot exceed the SA of the rear wheels.On the other hand, as the speed increases, the centrifugal force also increases, and the SA for generating CF corresponding to it also increases.Therefore, the yaw angle stabilizes when the increase in rear wheel SA due to the driving force and the increase in rear wheel SA required due to the increase in centrifugal force match.The amount of increase in yaw angle = the amount of increase in rear wheel SA.
So, the steering characteristics appear here.Since the same amount of SA as the increase in rear wheel SA increases in the front wheels, the CF generated by that SA will be too much or less than the CF required by the front wheels at that speed. ..In other words, if the SA required by the front and rear wheels is different, the change in yaw will upset the CF balance of the front and rear wheels, and in order to correct it, the steering must be turned up and down. Hmm.In other words, the question is whether "rear wheel SA-front wheel SA" is XNUMX, positive or negative.You have already noticed.This is the same as the definition of steering characteristics explained so far.One fact is that the perspective has changed.

If you review it just in case, even if the SA of the same amount as the yaw angle increases on the front and rear wheels, the NS characteristic car can turn the revolution track before acceleration with the same steering angle.On the other hand, in US characteristic vehicles, the SA of the rear wheels is essentially small, and the front wheels SA need to be larger than the rear wheels SA as the speed increases, so the direction of travel of the vehicle body swells outward and the steering is turned. Furthermore, if you do not attach SA above the yaw angle to the front wheels, you will not be able to maintain the same trajectory as before. In OS characteristic vehicles, the rear wheel SA is originally large, and if the front and rear wheels have yaw angle SA, the front wheel SA will be excessive and will be caught inward.Therefore, if you do not turn the steering back and reduce the front wheel SA, it will turn too much.
When the accelerator is slightly returned from the accelerated state and kept at a constant driving force, the yaw moment becomes a steady circular turning state by balancing the centrifugal force at that time and the CF due to the addition of SA.Of course, if you step on the accelerator to accelerate and increase it by a certain amount, it will be balanced where SA is further attached.The SA of the rear wheels fixed to the vehicle body is regarded as the yaw angle of the vehicle body, and in other words, the steering characteristic can be rephrased as the difference in the SA balance of the front and rear wheels caused by the change in the yaw angle of the vehicle body. I think.


■ Center of gravity position and driver's visual change
Now, let's get back to the original theme.How does the driver feel the change in yaw angle?Some people may have something like an animal intuition, but as mentioned above, I think it basically depends on visual information.Therefore, what is important is the relationship between the center of gravity, which is the axis of yaw rotation, and the seat position.Let's try to see the difference in the field of vision that the driver feels when the same yaw angle occurs in cars with different seating positions in the middle of the wheelbase and different center of gravity.

Of course, if the position of the center of gravity is different, the steering characteristics will be different, so the yaw angle will also change in actual driving, but to simplify the problem, it is assumed that the spin will be done in the stopped state for the time being.In addition, the yaw angle generated by the driving force is extremely small, but it is enlarged to make it easier to see.The figure on the right shows the relationship between the driver's position and the change in viewpoint with respect to the vehicle body, and the lower right figure shows the resulting change in the driver's visual field.Even if the yaw angle is the same, you can see that the range of change in the driver's field of vision differs for each car.
When seated near the center of gravity, the view from the front window rotates by about the same yaw angle as the car.If you sit behind the center of gravity, you will see the center of rotation from behind, so the change in the scenery seen through the front window will be less than the roll angle.On the contrary, in the seated position in front of the center of gravity, the amount of movement of the viewpoint is large, and the visual feeling is that it bends very much. (This is why when you turn the steering wheel on a cab over truck, it feels like you are turning so much.) In this way, the range of change in visibility is not necessarily the same as the change in yaw angle of the actual car, and the driver's Depending on the seating position, it may be amplified or decreased in some cases.

Next, let's apply this change in field of view to a real car.Since the difference in the position of the center of gravity leads to the difference in steering characteristics, these phenomena are the differences in visual information for each steering characteristic.In a US characteristic vehicle that sits behind the center of gravity, the change in the visual field is smaller than the yaw angle in this schematic diagram, but the yaw angle is small when the same driving force is applied, and the direction of travel also swells outward. , The movement of the field of vision is further reduced, and the "feeling of not bending" becomes stronger visually. In the OS characteristic car, all the directions are in the opposite direction to the US characteristic car, so the yaw angle is large, the course is cut inward, the visibility movement is large, and it gives the driver a "feeling of turning too much". In the NS characteristic car, the yaw angle and the change angle of the field of view are the same, and the direction of travel is also kept on the same circumference, so the movement of the car and the change in the field of view match, and it becomes a "feeling of bending obediently". That's why.How is it? You can see that the engineering facts of each steering characteristic and the impression obtained from the driver's field of vision correspond properly.


■ Simulation assuming a specific driving scene　
Then, to what extent is the difference in steering characteristics during accelerated turning reflected in the driver's visual information?It is extremely difficult to calculate the qualitative problem of dynamic sensibility by the quantitative method of engineering, but for reference, let us consider the change in the field of vision in the actual driving scene. Used in §13InterchangeThe table below compares the elements related to the field of view at point C with point B. * Up to the third decimal place is displayed.
The movement between these two points has time and distance, and it changes continuously and gradually, but for the sake of simplicity, it is ignored.Also, regarding the steering that should be performed during that time, the calculation is complicated, so the effect is omitted.We will only look at the changes in the direction of travel of the vehicle body that occur purely according to the steering characteristics.You cannot get the exact absolute value, but you can imagine the difference in characteristics. (The SA of the left and right wheels is assumed to be the average value, and the seating position is assumed to be the body center.)

Item		Steering characteristics
		NS characteristic car	US characteristic car	OS characteristic car
Amount of change in vehicle body direction (unit = degree) (Rear wheel SA-Front wheel SA)	Location B	－0.015	－0.055	0.005
	Point C	－0.035	－0.095	0.010
	Point C-Point B	－0.020	－0.040	0.005
Amount of change in visual field depending on the seating position		does not change (± 0)	Get smaller (-Α)	growing (+ Β)
Total amount of change in driver's field of vision		－0.020	-0.040-α	-0.005 + β

The "+" in the direction of travel of the vehicle body causes the turning trajectory to face inward unless the steering angle is corrected, so the driver's field of view is moved inward. If it is "-", it is outward, so the movement of the field of view is small.Conceptually, the degree to which the driver's dynamic sensibilities are given a "bent!" I think that it is a numerical value indicating the size of.
Similar to the previous engineering simulation, it is numerically extremely small, but the trend is to clearly show the effect of steering characteristics on human sensibilities. The US characteristic car has a strong "feeling of not bending", the OS characteristic car gives a "feeling of bending too much", and the NS characteristic car gives a "feeling of bending obediently". Was it?For those who are familiar with their arms and want to swing around the car, the OS characteristics that strengthen the inward visibility change as the accelerator is depressed may be welcomed, but there is only one royal road. The COOL judgment that "the best steering characteristic on the street is NS" does not change even with a dynamic Kansei engineering approach.

So far, I have talked about steering characteristics for a long time, but finally I will summarize how to apply that knowledge to practical skills as a so-called drive technique.Let's set the S-shaped course by connecting curves with the same radius in the opposite direction.In this animation, all the elements are exaggerated for easy understanding intuitively, but the yaw and the change in the direction of travel due to acceleration / deceleration differ depending on the steering characteristics, so just steering operation is enough. The timing of stepping on the brake or accelerator also changes.As a result, the driving line according to each characteristic also changes.
This is a theme that is often taken up in automobile magazines such as the Dratech course, but I think that everyone who has followed the lectures so far can easily understand "Why does that happen?"Just like studying at school, the knowledge of just memorizing the results is not very useful.By imagining the reason and process and running while interacting with the car in real time, I think that you will be able to experience the true "human-horse integrated" drive for the first time.


■ Driving technology & automobile technology from the perspective of dynamic Kansei engineering　
So far, I have explained something like the entrance to dynamic Kansei engineering with the theme of yaw angle and visual change, but at the end, I will expand the theme a little more and dynamic Kansei about your driving technology and related automobile technology. From an engineering point of view, I would like to talk about points that may be helpful at random.

For example, yaw is necessary for a car to turn, which is a major instability in terms of car stability.The cause of the car fluttering even when driving on the highway is yaw.If it does not converge well even when changing lanes, the yaw will cause the rear wheels to slip and spin, causing an accident. With 4WS, yaw does not occur and you can change lanes so that you can move in parallel in a stable state.I practiced 2WS on the second generation RX7 (FC3S) in order to incorporate its stability.It was a system that could take a slip angle even with a yaw angle of "4", but when I ran it, I realized that humans want to make a yaw angle when turning, and also want to change lanes after changing direction.Therefore, I think that the function of 4WS was not interesting in terms of sensitivity, and there was a big sense of discomfort.

Also, I think it is better for yaw changes to move swiftly and then stop swiftly.The most important factor in steering stability is to stop this agilely, that is, how quickly and smoothly the generated yaw can be stabilized.It is CF that stabilizes the yaw.If the wheelbase is long, the yaw will be stable, but it will take some time for the yaw to come out.On the other hand, if the wheelbase is short, the yaw will come out quickly, but it will not be stable.Actually, how to design the relationship between the tread, the wheelbase, and the position of the center of gravity is important, and the rigidity and the suspension settings related to CF also have a great influence.

Speaking of the ultimate yaw control, it is still motor sports.The reason is that the positive change of direction by the driving force is directly related to the speed.For example, rally drivers actively control yaw by braking and accelerator work.The inertial force in the direction of the vehicle speed acting on the rear tire that was intentionally drifted and the negative driving force of the strongly locked front tire create a large yaw moment around the center of gravity, and the front tire is used as a fulcrum to turn at once. I will change the run.In addition, racing cars are designed to have oversteer characteristics to make it easier to turn. Whether it's FXNUMX or Le Mans car, it's rear heavy.The point is that I want to turn the car body toward the exit as quickly as possible in the middle of the corner and step on the accelerator.

Even if you are not such a competition driver, for example, in FR cars, the front wheels can change the slip angle by steering operation to change the size of CF.The rear wheels can change the balance between tire CF and driving force by accelerator work.You can do a standing spin by pulling the accelerator while the steering wheel is turned off and engaging the clutch.This is the ultimate turn that only FR can do.This is possible because the elements of controlling the CF by the slip angle and the control of the circle of forces by the driving force are simply separated.
In the case of FF vehicles, when the driving force is applied to the front wheels, the front wheels will go out.On the other hand, if you loosen the accelerator, you can return to the original turning circle (a behavior called tuck-in).There is a way to use it to control the yaw in the corner.However, FF vehicles are complicated because the drive wheels and steering wheels are the same.For example, there are two reasons why the CF of the front wheel decreases = it does not bend.One is overtraction with too much driving force.The other is excessive steering angle.Since they are often done at the same time, it is easy to be confused as to whether the accelerator or the steering angle is the cause, or both.
So what about XNUMXWD is more complicated.Even if the driver tries to change the direction of the car by sliding the rear wheel with the accelerator, the car will distribute the torque arbitrarily and the ratio of the front-rear distribution of the driving force will change regardless of the intention.
It does not fit well as a dynamic sensibility in the sense that it is difficult for humans to grasp a clear effect on their own operations.

In terms of refining your driving skills in Kansei engineering, try driving while being aware of the rise of the body yaw (the car starts to turn).If you can experience it and then quickly converge the yaw and control the yaw, you will have a closer sense of unity between humans and horses.The vehicle body reacts to human operations, and after feeling the reaction properly, perform the next operation.During that exchange, I understand that this car will move like this if I cut this much, and feed it back to the next operation.
If you're happy with the amount of movement, that's it, but if you don't like it, you'll have to operate it again and feel the reaction.This is called a closed loop.The good relationship that the car reacts to the human operation as expected, which requires less repetition, forms the sense of unity between humans and horses.
In contrast to this closed loop, an open loop is a characteristic of a car that cannot be operated by humans.For example, you might suddenly turn the steering wheel (with yaw) while driving and leave it alone to test how the car fits.The yaw angular frequency peculiar to the car (See §11) Is one of them.

In the actual driving scene, there are external stimuli such as input from the road surface and crosswinds.It is not human manipulation.In response to that input, some cars are fluttering and not stable.Up to this point, it is an open loop, but the driver operates it to stabilize it.It's a closed loop.Therefore, it can be said that the relationship between the car and the driver is a semi-open loop.Of course, it is better for the car to have a good personality (characteristic), but if the driver can quickly grasp the character and habit of the car by repeating dialogue (operation, reaction) instead of one-way traffic from either side. , The later reaction should be as expected.Aun's breathing, which can be obtained by enjoying such dialogue, is an important factor of dynamic sensitivity.
The "at will" that the driver feels is that there is an original reaction before the expansion and a reaction that does not deviate from the human senses to the driver's operation even if the performance of the device that expands the physical ability improves. I think that's what it means.
In addition, as the capacity increases and the degree of danger increases, the characteristics related to the driver's operation such as lateral rigidity of the tire, how CF is transmitted to the vehicle body, seat rigidity, front and rear wheel relationship, vehicle body rigidity, etc. The performance of the tire should be improved and the amount of information should be expanded.When I ran with my feet and moss, I rubbed it!However, if you run at 100km / h and moss, there is a danger of life.It is dangerous if the car does not make the driver feel that it is going to be a life-threatening moss.
I may have a bad word, but I think it is dangerous to control a car that is not related to the driver's intention, such as the latest electronically controlled car.With traction control and automatic deceleration system, it is believed that something can be done while driving, and human beings are just being carried, and the consciousness of maneuvering is getting thinner and thinner.Moreover, if it deviates from the logic of the program, do the rest yourself!I cannot deny the half-hearted feeling of being pushed out.I think that such a latest system is a throw-away insurance, and I want you to ride it so that you do not have to use it for the rest of your life.It's just fun while driving, it activates your brain and you'll never fall asleep!I believe that a car with such an attractiveness is much safer.Isn't it a roadster-like car that works the way you want, is fun, and wants to ride again?