The DNA that determines the dynamic sensitivity performance of automobiles is hidden in the numbers in the specification table.

Then, from this time, I will go into each theory.It is a consideration of how the specifications and performance of various components that make up an automobile affect the driver's sensibility.
The basis of the lecture is traditional automobile engineering.First of all, I would like to talk about the reasoning behind what kind of specifications should be used to obtain what kind of performance.I would like to ignore the practical details and try to explain the principle.So to speak, it is an "introduction to automobile engineering".Then, on top of that, I would like to consider the effect of the results on the driver's sensibility, adding my own evaluation.Please understand that is the theme of this seminar, "Dynamic Kansei Engineering".
Of course, the dynamic sensitivity performance of a car is not determined by the specifications of a single component, but various factors work in combination.The evaluation also depends on the sensibility of the evaluator.So you can't just say "this spec is the best" so easily.The aim is to have you understand the relationship between "specifications and performance" and "driver's sensibility" as a concept.By doing so, I would like to use it as a reference for making decisions to determine the direction of your tuning.
So, as for the first theme, from your mood, you may be expecting knowledge such as the damping force of the damper, the spring constant of the spring, etc. that can be used for actual tuning more quickly.Since it is different from a university lecture, there is no need to organize the curriculum systematically (systematically).Rather, I would like to take a random theme that might be of interest to you.However, as a person involved in development among manufacturers, there is something I really want to talk about first.It's about "packaging".


Dynamic sensitivity performance determined by packaging

When a manufacturer develops a car, the concept decided by the product planning department comes down to the development department, and specific vehicle specifications are laid out.This is packaging.Not only the size and shape of the body, but also, for example, the position and posture of the person in the car are determined here.In parallel, the position of the engine, drive system, tread, wheelbase, etc. are determined.Simply put, the qualities of a car that has not yet been born in the world, the basic blueprints for it, and the prototype of the specification table to be published in the catalog are decided at this stage.
In living organisms, packaging is equivalent to DNA (gene).Designs such as engine and suspension, and design such as styling are also directed by this DNA.Of course, the performance of these components can vary, but it may be better to think of them as being acquired through acquired efforts, if compared to the growth of living things.Tuning is also the same.There is a misnomer, but at least when it comes to cars, I think it's impossible to overturn the innate qualities.
Therefore, when considering the dynamic sensibility performance of a car, the most important thing in choosing a car that suits your sensibility is packaging.And the clue to know it is hidden in the numbers in the expressionless "specification table".That is why I chose the most modest "dimensions / weight" in the specification table as the first theme of each theory.Below, I would like to think about that perspective.We hope that you will reconfirm the qualities of your car and use it for future tuning.

See the numbers of dimensions and weight with "division eyes"

Accounting professionals read the business condition from the company's financial statements.That's all you can do with empirical knowledge, but the technique you're using is often a simple division.It seems that the division is done by holding down the key points such as the year-on-year rate and the ratio to sales, not the absolute amount of profit.
Similarly, the car engineer predicts the dynamic sensitivity performance from the specification table.Of course, we also see whether it is heavy or light, large or small, but we also evaluate those numbers by division.As I said last time, these "division eyes" are often useful when thinking analytically.

Then, where is that kimo?For example, in the case of dimensions, total length ÷ total width.More essentially, wheelbase ÷ tread. Since it is a rectangular aspect ratio determined by the positions of the four wheels, it is called the wheel print ratio.If you calculate this, you can compare the shape of the rectangle regardless of the size of the car.So, the more elongated shape has better straight-line stability ... This can be proved by automobile engineering, but it is judged empirically.On the contrary, if it is a zungri rectangle that is close to a square, the reaction when turning the steering wheel seems to be good.

The final steering stability is refined by the suspension specifications and weight distribution, but its basic characteristics can be read by this calculation.
As an aside, traditional Japanese cars have a vertically long package compared to the world standard.The cause was the so-called 2,000 number frame (displacement: 4,700cc, total length: 1,700mm, total width: XNUMXmm).When it exceeded any of them, it became number XNUMX and the taxable amount (excise tax, automobile tax) was high.

Since the taxation system changed in XNUMX and this restriction was lifted, it is not uncommon for cars to have only the full width of the XNUMX number frame.I think this is an epoch that expands the freedom of improving the maneuverability of Japanese cars.
Even by dividing the total height by the total width, you can see the driving characteristics of the car.At Mazda, it was called the Road Hugging Ratio. It means "ratio to grab the way".
More logically, the height of the center of gravity ÷ tread, but since the height of the center of gravity is not listed in the specification table, the total height is used instead.This is related to the mechanism of weight transfer and roll when cornering. If you imagine a triangle formed by two wheels and the position of the center of gravity, you can easily imagine what kind of shape will lead to what kind of performance.
In terms of dimensions, there is also the total length ÷ wheelbase.Of course, the less part of the wheelbase sticks out, the better the car is for you to enjoy driving.In any case, it is within the range of a certain balance except for vehicles for special purposes, but the result of these divisions reveals the DNA related to the steering stability of the vehicle, that is, the dynamic kansei engineering nature. You can do it.
The same is true for weight.Dividing by the maximum torque or maximum output of the engine gives an indication of power performance, but in terms of sensitivity performance, the ratio of the weight applied to the front and rear wheels is calculated.In this case, there is a clear ideal value. 50:50 is the best way to get the most out of the four tires.By how much it deviates from this optimal design, the intention of the car designer and the resulting dynamic sensitivity performance can be compared.So, if you divide the wheelbase by that ratio, you can easily find the position of the center of gravity in the front-back direction.If the catalog doesn't explain it, try this method.However, the load distribution of the front and rear wheels is not listed in most catalogs, but for some reason it is listed in the car verification, so please check it.


About "another Kansei" that a car has

I have sometimes used the term "car's (dynamic) sensibility performance", but this is just a convenience expression, and to be precise, it means "the performance of a car that appeals to human sensibilities."Because sensibility is a human issue, the car does not have sensibility.However, if the reading "Kansei" is converted to "inertia" in Chinese, the situation changes completely.All objects, including cars, have inertia.Unless an external force is applied, the property is that "a stationary object keeps stationary and a moving object keeps moving at a constant velocity."

So, when an external force is applied to the object, it starts accelerating or decelerating, but the acceleration in linear motion is determined by the magnitude of the given force and the division of the mass of the object.The larger the mass, the smaller the acceleration, regardless of the size of the object.Therefore, this "difficulty in accelerating" is called "inertial mass".Strictly speaking, it's the same as what you feel as "weight", and it's easy to understand from the feeling of acceleration and deceleration when driving a car.

The problem is the inertia of the rotational motion.What determines the "difficulty of rotation" when trying to rotate a stationary object?This time, even if the mass is the same, the acceleration changes depending on the distance that the mass is away from the axis of rotation.This "difficulty in rotation" is called the "moment of inertia".The formula is mass x radius of gyration squared.I think that the entrance to why this happens can be roughly imagined by words such as "the principle of the lever" and "rotational moment", but please search on the net for details.Professional commentary will come out around.
So, even in automobile engineering, this "difficulty in rotation" becomes a problem.This is the case when you operate the steering at the entrance of a corner.Do you react swiftly or stubbornly try to go straight?Since the force to rotate is the cornering power of the tire, the mechanism of its generation is also important, but the magnitude of "difficulty in rotation", that is, "moment of inertia" as the DNA peculiar to the car is the sensitivity here. It holds the key to performance.

* Click to open the enlarged image.

Speaking of the rotational movement of a car, you probably imagine a rotation on a certain circumference.This is the locus of circular motion centered on the point where the extension of the front axle intersects with the extension of the rear axle.However, this is, for example, the movement of the earth revolving around the sun, not the rotational movement in question here.The problem is the rotation of the car itself that triggers it.By turning the steering, cornering power is generated in the tires, and the force causes the vehicle body to rotate around the center of gravity, and as a result, the vehicle body turns and revolves.Therefore, the problem is the "difficulty of rotation" of the car itself, that is, the magnitude of the moment of inertia (in this case, the moment of inertia of yaw).So, what is the moment of inertia of your car?How to find out ... Actually, there is an easy way.


The difficult calculation method of integrating dimension x weight 2

In this seminar, I talked about the moment of inertia generated around the center of gravity of the car before (§XNUMX).However, I think it was almost meaningless to everyone because it was only mentioned as a difficult story as a developer.The following is the calculation formula shown at that time.



In short, it is a mathematical formula that shows the logic of "calculating the moment of inertia of each heavy object separately to obtain the sum" of the car.Since the moment of inertia = mass x distance from the center of gravity², the mass and position of each part becomes a problem first, but it is impossible to calculate the specification values ​​of all parts except for the input computer for development. Is possible.
So, I will compromise a little and use an approximate expression that considers only the basic framework of packaging.Ignoring the position of the engine, gasoline tank, battery, etc., we think that the total mass of the car is distributed at all points with uniform density.To simplify the physical formula in this way, the formula for calculating the moment of inertia I of each of the roll, pitch, and yaw motions that occur around the center of gravity of the car on the three axes of X, Y, and Z is as simple as the following. It will be a thing.

If this is the case, I think you can calculate (→ compare between vehicle types) with a calculator while looking at the specification table.Of course, this is a simple approximation and the absolute value is not accurate, but experience has shown that this calculation is not far from the measured value.I've always emphasized that it's important to place heavy objects as close to the center of gravity as possible, so it may seem like something inconsistent, but that's the rest of the story.

The moment of inertia is largely determined by the overall weight and dimensions, and beyond that it is a tiny bit of effort.The result is not a big number in absolute value, but the difference is still important for the driver's dynamic sensitivity.In that sense, please think that the value of the simple calculation using only the numerical value of the specification table is just a barometer to know the "DNA of running".A car that shows excellent numbers at this stage will spare no effort in further improvement in subsequent designs.On the other hand, it is unlikely that a car with a bad number will accumulate subtle improvements after that, and I don't think the effect can be expected to be significant.

This time I mainly talked about the yaw moment of inertia, but the idea is the same for roll and pitch.Their final sensibility performance is not determined solely by the moment of inertia, but is more refined or reversed in relation to the input side mechanism, such as the steering mechanism and suspension layout / specifications, and tire performance. It is also spoiled.But, as I said at the beginning, packaging is the innate DNA that governs the entire car, so it's not surprising that the design of individual components goes along with it.Therefore, I think that knowing the packaging is very important and meaningful in predicting the dynamic sensitivity performance of the entire car.

The word "driving DNA" is used in Mazda's technical public relations and advertising copy, and Auto Exe claims that "the normal evolution of the concept of mass-produced cars" is consistent with this "direction of car making". is what it means.It's not just a mental theory, it's not a matter of image, it's about valuing the technical background for that.In many cases, including catalogs, advertising copy is written by an outside copywriter based on the explanation from the manufacturer, but as a technician, it sometimes feels strange. ..What do you need to do to figure out the design concept of the car yourself, without being confused by the fancy words?If you think in this way, I think that the way you look at the catalog will change.Before thinking about tuning in the future, or when you switch to a new car someday, please analyze the numbers in the specification table and unravel the DNA.The specifications speak for the qualities of the car more honestly than anyone else.