I met "maneuverability" on a sports track.
And to the first RX-7 who taught me the importance of packaging.

My lecture at the university is quite professional and practical because it aims to train future automobile engineers.That's fine, but on the other hand, for those who enjoy everyday driving as a real user, we don't need an approach that makes it a little easier to imagine only the basics or principles. I think.By understanding the mechanical structure of automobiles, you may be able to love them more deeply, and it may be a hint for tuning to create a car that is more personal to you.That is the aim of my lecture on this site.

So, before going into the specifics of "dynamic Kansei engineering," what kind of car have you been involved with since I joined Mazda?And I would like to talk about how I arrived at the research of dynamic Kansei engineering (generally speaking, a part of steering stability performance) in several parts.From those, I hope you can feel the technical points to drive a car more enjoyably.
Immediately after joining the company, I was assigned to the analysis group for chassis development and assisted in the vibration analysis of the leaf springs of the rear suspension of a light truck called BXNUMX.
It is a truck version of a light passenger car called RXNUMX.The boss at that time was the one who later served as the chief examiner of the first FF Familia, and trained me as an engineer.

For example, I was given the problem of vibration analysis and wanted to formulate and solve the equation of motion. While being told, "You're starting over from elementary school," I worked hard on differential integration.
Eventually, we decided to make a minor change to Titan's predecessor E-track, and moved from the analysis group to the track group.I was involved in the design work and was in charge of measures such as loosening of the U-bolt that holds the leaf spring and axle.After that, I designed various commercial vehicles.Among them was the Proceed Sports Truck with a rotary engine for the United States.
Even though it is a truck, it has a rotary engine, so it can reach speeds of XNUMXkm / h.

The challenge was how to stabilize the high-speed maneuverability of this vehicle, and I learned how to set the suspension and install the leaf springs.
This was my first connection with so-called "sports".

After that, discussions were held on the use of rotary engines, and it was concluded that it would be suitable for sports cars.And it was the development of the first RX-XNUMX of that retractable headlight.However, at that time, after the oil crisis, sports cars were not the atmosphere of the world.The whole company was worried about whether it would be a sports car and whether it could be approved by the Ministry of Transport, such as retractable headlights.Normally, the approval of the Ministry of Transport is given about XNUMX months before the start of production.Therefore, in consideration of the case where the retractable headlight was not approved, we prepared two types of fixed light designs and went to the examination.
Then, some officials of the Ministry of Transport also like sports cars, and on the contrary, they enthusiastically ask various advices and advantages of using retractable headlights in order to obtain approval.
I got approval with a lot of reasons such as that reducing the air resistance by XNUMX% would improve fuel efficiency.The officials also responded cooperatively so that the problem would not be pointed out by others later.

As an aside, when I started developing the RX-XNUMX, I received a request from the passenger car group to come to Kijima, where I was a sports truck.Then my boss at that time said, "I can't get Kijima out of the truck group."I think I had some idea because I was an excellent boss of the elite from the University of Tokyo. He insisted, "If you want Kijima to play a sports car, do a sports car in a truck group."As a result of discussions within the department, we decided to incorporate sports cars into the truck group, and as a result, we decided to design sports cars within the truck group from the first generation of the RX-XNUMX.I don't think it was interesting for the passenger car group, but for me it was a big point for me to turn my career as an engineer toward sports cars.The SAXNUMXC type of the first RX-XNUMX had a strut type front suspension and a rigid type rear suspension.At that time, I had the option of an independent suspension semi-trailing arm type, but I didn't want to have troubles or risks with new technologies because I wanted to get into mass production as soon as possible.Therefore, we adopted a rigid rear suspension.However, in the end, choosing Rigid was the correct answer.With just XNUMX links + lateral rod, there is no trick and the rear axle moves in an arc, so the change in geometry is too large.I just wanted to raise and lower this vertically.

So I considered using Wattlink (developed by James Watt, who invented the steam engine).At the beginning of the design, it was installed in the center directly behind the differential case, which is the best in terms of mechanism.However, there is a possibility that it will break through the fuel tank in the event of a rear collision, so we changed the design and decided to install it on the front side of the axle casing.Since there is a differential carrier and a propeller shaft here, you have to shift it from the center, and then you will draw a slight S-shape instead of moving straight up and down.In addition, the toe-out geometry is required, so the bush must be hardened.Since it was attached in front of the axle, the bush of the entire treasuring link including the watt link had to be made harder, which made it difficult to assemble.

Then, when I made a prototype and brought it to the factory, I was asked, "Can I assemble this kind of thing?"That's right, because it is a part that determines the left-right direction with pitch, it will not move as soon as the watt link is assembled, and the next installation will not be possible.Therefore, we devised a taper-shaped mounting point on the axle casing side so that it can be mounted properly in the center by tightening it even if the position is slightly off.Wattlink itself was not a new mechanism in particular, but at that time, only the first RX-XNUMX was adopted for the rear axle.

The first RX-XNUMX was a big hit, but there was such an episode before it was commercialized.It was decided that the first prototype car would be exhibited at the management's new product conference, but the day before the conference, a boss took a test drive on the Ujina test course.
The original RX-XNUMX was made sharp with neutral steer to enjoy driving, so it can not be handled if an amateur makes a sudden lane change at high speed.Therefore, it spins tightly at high speed and collides with the guardrail.I had to repair it by the next day's new product meeting and worked all night.

And from this first RX-XNUMX, I became involved in motor sports.I also designed the suspension for the GT-U Daytona race car of IMSA in the United States.I investigated the regulation to see how much the pivot of the suspension could be changed, and designed it as a parallel link up to the point where the rear seat was punched out.It ran for XNUMX hours and was able to win the class championship.I remember that I was in a good position overall.It was my first full-scale racing car, so I forgot to ship it to the port of Ujina.We all know the success of the RX-XNUMX GT race in the United States after that.

Also, at that time, I was doing the Acropolis Rally in Europe.This is a rally famous for the special stage on rough roads, and there were frequent problems with the axle bending due to harsh conditions.After driving on the special stage, the axle had to be replaced with an assembly by the next stage.In such a situation, I was asked to visit the Acropolis, and I went there for the time being without knowing what kind of load would be applied.And when I actually run on a hard mountain road in the field, it jumps about XNUMXm.When I calculated it, it took more than XNUMXG.I thought that this was not possible in mass production, and after returning to Japan, I sent a part with a V-shaped reinforcing stepner to the underside of the casing, and I was thankful that it did not break.I was able to finish in XNUMXrd place in the Acropolis Rally against competitors such as Audi Quattro, Peugeot XNUMX and Lancia.

By the way, the first RX-XNUMX had Paul Frere ride at the Nürburgring in the early stages of development.However, as soon as he came down, he was angry with "Too Neverous". He said, "Such a sensitive car can't run in Europe."The front and rear weight of the front midship was distributed at XNUMX: XNUMX, and the suspension setting was sharp and sensitive so that it could move quickly.Therefore, it was different from the solid feeling like Porsche.It was a "Tail Happy" car, good or bad.

In the end, the original RX-XNUMX could be said to have depended entirely on the rotary engine.For this car, the engine was more than just a power unit.The initial catalog proudly claims to be "Designed by Rotary."Taking advantage of its compactness compared to power, the position of the engine mounted behind the front axle makes it possible to minimize the yaw moment of inertia by the basic packaging brought about by it. It taught us the joy of driving a car as it is.
It was a machine that stimulated the sensibility.But conversely, non-engine components, such as suspensions, may have been too conventional.

Eventually, the turbocharger was attached and the power increased, so I set it in the bump-under direction in the stable direction.However, I had a hard time at the test drive event.Not all journalists are good drivers, so I was hit by many.Therefore, driven by the need to further improve the maneuvering performance, it will lead to the second generation RX-XNUMX, but in a word, the development of "undercarriage that is comparable to the rotary engine" It was a theme.Next time, I would like to talk about the packaging, the four-wheel independent suspension, and the toe control of the rear hub, which was the biggest feature.