One of the most important environmental issue in the painting process is the reduction in the volume of volatile organic compounds (VOCs) emitted from paint plants.
In 1989, Toyota began developing waterborne paints and introduced the first-generation of waterborne paints at TMUK in the United Kingdom in 1992 and then on Line No. 2 at TMMK in the United States in 1993. In Japan, Toyota commenced use of such paints at its Takaoka Plant in 2000, and subsequently completed introduction at all other plants in Japan in 2005, reaching its VOC emissions-reduction goal.
In the conventional automobile body painting process, baking is required both after a middle coat is applied and after the topcoat is applied. In the 'waterborne 3-wet painting system', a waterborne primer surfacer, waterborne base coat, and solvent clear coat are applied on a wet-on-wet basis, with only one baking process carried out at the end. This system, intended to streamline the painting process and improve its environmental performance, attracted the industry' s attention but did not result in the same level of appearance quality as conventional mass-production painting systems. Therefore, Toyota took the following steps: a) developed a primer surfacer that, by merely being preheated, suppresses layer mixing with a waterborne base coat, b) controlled the curing characteristics of the three layers such that the primer surfacer, the base coat, and the clear coat harden in that order, and c) developed a two-step heating and baking process. Through these accomplishments, Toyota improved the appearance quality of the painted finish, and was able to introduce this improved waterborne 3-wet painting system into the Takaoka Plant.
TMC developed a new self-restoring coat that is highly resistant to car-wash scratches and fingernail scratches around door handles, and adopted it in the Lexus LS.
Scratches on cars are caused when the top clear coat is subjected to a load, causing the coating film to be destroyed or deformed. TMC developed a new clear coat that produces a coating film that is more durable than conventional clear coats and that self-restores even after having being deformed. This clear coat prevents loss of luster caused by scratches and helps preserve the initial color and gloss of the LS well into its life on the road without the need for any special maintenance.
Specifically, special molecules that promote intermolecular bonding are added to the polymer used in this clear coat to enable bonding with multiple molecules, achieving an entirely new, dense molecular structure. The resulting clear coat is highly flexible and elastic, making the coating film durable and more resistant to light and acid, and improving its self-restoring property.
Conceptual Diagram of the Molecular Structure
Toyota developed an intake manifold made of a polyamide resin reinforced with glass fiber accounting for 30% of its weight. This manifold provided many benefits, including light weight, low cost, and high functionality, and its use expanded quickly, replacing cast aluminum products. There are three main manufacturing methods.
An alloy with a low melting point of 130?C is used to form a core, which is set inside an injection mold. A polyamide resin is then molded around it, after which the alloy can be recovered and reused. Although this method provides a relatively high degree of shape freedom, it is complicated.
In this method, the two halves of a product formed through injection molding are vibration welded. Although the process itself is simple, an ample welding flange width must be provided, which limits the direction in which surfaces can be welded and therefore, limits the degree of shape freedom.
After two halves of a product are formed using a rotatable stamping die linked to an injection-molding machine, the die is rotated to position the two halves together inside the mold. A resin is injected into the groove that remains between the two halves to re-melt and fuse their matching surfaces. Because a product can be extracted each time the mold is opened, the process results in high productivity, but limits the degree of shape freedom.
This is a high-performance polypropylene (PP) resin material developed based on Toyota' s unique molecular design theory, which uses an elastomer as a continuous phase and PP resin as micro dispersed crystals. The Super Olefin Polymer has a unique crystal structure in which quadrangular prism-shaped PP crystals are densely oriented, in nano ordering, in the thickness direction during the continuous elastomer phase. This molecular design makes it possible to achieve and improve both high rigidity/flowability and impact resistance, which normally have an inverse relationship.
As a result, Toyota achieved recyclability and material integration, in addition to reductions in wall thickness, weight and cost, and improved productivity, and began using the new material widely in exterior parts such as bumpers, beginning with the Crown series in October 1991.
New material design concept
High-resolution electron microscope photograph of TSOP (Z face)
Classified in line with the characteristics required, interior materials can be classified into two types.
The first is the high-flowability (for forming thin walls) and high-rigidity type required in trim and garnishes, represented by the Toyota Super Olefin Polymer (TSOP) 2. The second is the high-rigidity, high-impact-resistance type required in instrument panels, represented by TSOP-3. Simultaneously achieving the characteristics of both kinds of materials is extremely difficult technically.
However, by making quadrangular prism structures emerge more sharply over the entire surface, minimizing the amount of widely dispersed excess elastomer, and adding a compatibility accelerator, Toyota succeeded in developing the TSOP-5 interior material. TSOP-5 possesses both the ultra-high flowability of TSOP-2 and the high impact resistance of TSOP-3, characteristics that are normally inversely related to each other and previously could not be simultaneously achieved.
TSOP superstructure schematic diagram
Material characteristics of the Interior integrated resin material (TSOP-5)
Toyota developed a thermoplastic polyurethane (TPU) resin made with the powder slush method and used the resin in interior coverings as a replacement for vinyl chloride.
Toyota analyzed the mechanism behind urethane' s problematic lack of alcohol resistance and through designing an optimum resin mixture, was able to keep alcohol-resistant levels similar to that of vinyl chloride. However, this led to a worsening of low-temperature characteristics and meltability, which Toyota addressed by selecting and adding the ideal amount of an optimum plasticizer.
Furthermore, Toyota developed a practical application of an aqueous suspension polymerization method that combines a powderization technology with polymerization reaction speed control, obtaining a powder with excellent flowability and achieving a moldability goal as well.
As the need to reduce vehicle weight has increased, ferrous materials have increasingly been replaced with non-ferrous materials. Among non-ferrous materials, magnesium is expected to contribute greatly to weight reduction due to its particularly small specific gravity and is being used in many commercially available alloys. Some of the issues associated with using magnesium include lack of corrosion resistance and durability in hot environments. There are also issues related to life-cycle assessment and recycling.
Toyota used the general-purpose magnesium metal alloy AM60 in the steering wheel core of the 1989 Lexus, instead of aluminum, for a weight reduction of 15% and in the seat frames of the 2000 Celsior, instead of a steel sheet, for a weight reduction of 30%. Next, Toyota used the general-purpose magnesium metal alloy AZ91 in the cylinder head cover of the 1991 Soarer, instead of aluminum, for a weight reduction of 30%. Toyota has since been using magnesium in these types of parts, which are subject to only small amounts of load.
In the 1980s, metal matrix composites (MMC) were developed as lightweight materials possessing high strength, rigidity, heat resistance, and wear resistance, and the composites began to be used in automobile parts.
In 1982, Toyota, in a first-generation effort, began using a material containing ceramic fiber for the wear-resistant top rings of diesel engine pistons, satisfying the requirements of light weight, high thermal conductivity, and low cost.
In 1988, in response to the need to reduce exhaust emissions and improve performance, Toyota, in a second-generation effort, developed a hybrid material by adding nickel aluminide powder (NiAl3) intermetallic compound particles to conventional ceramic short fibers.
Then in 1997, in response to the emerging need for improved resistance to adhesive wear at high temperatures, Toyota, in a third-generation effort, developed a material reinforced with an iron-based porous sintered body.
In 1996, Toyota used a material containing silicon carbide (SiC) whiskers in the lip of the chamber at the top of the piston in diesel engines, improving resistance to hear cycle fatigue. To reduce cost, Toyota later used alumina-boria whiskers, instead.
In 1992, Toyota reinforced the bolt-securing areas, or boss areas, of the aluminum crankshaft pulley hub with ceramic fibers to prevent the bolts from loosening.
In 1999, Toyota developed a high-rpm, high-output engine by increasing the bore of the base engine and shortening its stroke, utilizing an MMC in a liner-less technology. Toyota added ceramic fibers and particles to the cylinder bore to ensure wear resistance, and also applied ECM(Electro Chemical machining) treatment to the bore surface and Fe-P(Phosohorus) plating to the piston skirt to prevent scuffing.
In 1997, Toyota adopted an aluminum MMC rotor containing SiC particles for the front brakes of the RAV4 EV electric vehicle to reduce weight.
In 1997, Toyota developed an aluminum MMC heat dissipation plate for the IGBT cooling module of the inverter, which became the power device of the Prius. Since this plate must be inserted between a heat-generating silicon board and an aluminum alloy water-cooled heat sink, it must possess high thermal conductivity and a low thermal expansion rate, and therefore contains a large number of SiC particles.
A three-way catalytic converter simultaneously oxidizes the hydrocarbons (HC) and carbon monoxide (CO) contained in exhaust emissions and reduces oxides of nitrogen (NOx), converting them into harmless carbon dioxide (CO2), water (H2O), and nitrogen (N2), and is called so because it purifies the three components (HC, CO, and NOx) simultaneously.
The purifying characteristics of a three-way catalytic converter depend greatly on the engine' s air-fuel (A/F) ratio, and are most effective near the stoichiometric A/F ratio, or a catalytic converter' s purification window. Therefore, to utilize these purification characteristics to achieve high purification rates, it is necessary to control the engine' s A/F, maintaining it within the purification window. Toyota achieved this control by developing an oxygen sensor that senses the stoichiometric A/F ratio point and an electronic control system that regulates the fuel injection volume based on the signals from this sensor.
The main catalysts in a three-way catalytic converter are the noble metals platinum (Pt), palladium (Pd), and rhodium (Rh). To enlarge the catalyst' s purification window, an oxygen storage function is added, with solid forms of ceria (CeO2) and zirconia (ZrO2) often used for this purpose.
Cleaning rate relative to the three-way catalytic converter cleaning window
Diesel engines are important in terms of efficient use of energy because of their high fuel efficiency. To make them environmentally friendly, however, it is crucial to reduce the particulate matter (PM) and NOx they emit, especially with exhaust emission regulations being tightened in the U.S., Europe, and Japan.
Because the exhaust emissions from diesel engines are relatively low in temperature and contain sulfur dioxide (SO2) produced from the sulfur contained in the fuel, a pressing need existed to develop a catalytic converter that could purify sulfur in other forms (SOF), hydrocarbons (HC), and carbon monoxide (CO) even at low temperatures, and suppress the generation of sulfate from the oxidation of SO2.
Toyota developed a two-stage oxidation catalytic converter that in its front stage combined an alumina coating and platinum (Pt), which easily adsorb SOF; and in its back stage combined a silica-alumina coating, palladium (Pd), and rhodium (Rh), which do not easily adsorb sulfate. Toyota adopted this oxidation catalytic converter in the 1993 Corolla for Europe ahead of Europe' s Step 2 regulations. Subsequently, Toyota developed an oxidation catalytic converter, in which Pt is carried on a coating consisting of titania with reduced sulfate adsorption and zeolite with high HC adsorption, and which exhibits superior low-temperature characteristics. Toyota adopted this catalytic converter in Japan beginning in 1997, complying with long-term emissions standards.
2-stage oxidation catalyst
The lean burn method is an effective technology for improving the fuel efficiency of gasoline engines and reducing CO2 emissions. However, the conventional three-way catalytic converter has proved unable to sufficiently purify NOx because exhaust emissions contains a large amount of oxygen.
Toyota conducted R&D on catalytic converters that could purify NOx even in a super-oxygenated atmosphere and developed a new-concept catalytic converter called the 'NOx absorption/reduction catalytic converter' and commercialized it in its lean-burn engine vehicles in 1994, as the first time in the world for commercial application of such a catalytic converter.
With the NOx absorption/reduction catalytic converter, when the air-fuel ratio is lean, NO is oxidized by a noble metal (e.g., Pt), reacts with an absorbing material (basic metals such as Ba and K), and is absorbed as nitrate. The absorbed NOx is broken down and desorbed in a reducing atmosphere and is reduced to N2 by noble metals (e.g., Pt, Rh). This catalytic converter has been continuously improved and has been adopted in D-4 engine (stratified lean burn) vehicles, which offer excellent fuel efficiency and output.
Cleaning mechanism of NOx storage-reduction catalyst
In the post-processing of exhaust emissions from a gasoline-powered vehicle, it is important to reduce the emission of HC immediately following cold start of the engine when the three-way catalytic converter is still cold and not yet active.
An HC-adsorbing cylinder, which temporarily traps HC, is effective in addressing this problem. The cylinder is installed in the vehicle' s exhaust system and exhaust emissions are flowed into the HC-adsorbing material inside it to temporarily trap HC until the three-way catalytic converter becomes active. The trapped HC is fed into the three-way catalytic converter at the switching valve once it has become active and is purified.
Since exhaust emissions contain roughly 200 types of HC with varying molecular sizes, zeolites having micropores matching molecular sizes of four to eight angstroms are blended and used for the HC-adsorbing material. Toyota was the first automaker in the world to use a HC-adsorbing cylinder and installed it in the Prius for North America, helping it meet California' s SULEV standard, the strictest in the world.
Reducing the amounts of PM and NOx from diesel-engine exhaust had become a globally important issue. Systems utilizing an oxidizing catalytic converter and a diesel particulate filter (DPF) to reduce PM had been commercialized. However, no system that could reduce PM and NOx at the same time had been commercialized. Therefore, Toyota developed its Diesel Particulate-NOx Reduction System (DPNR), a new purification system that combines the NOx adsorption/reduction catalytic converter in use in gasoline engines with the latest engine control technologies, to reduce PM and NOx simultaneously.
In the DPNR catalytic converter, a NOx adsorption/reduction component is supported on the surface of a porous ceramic wall-flow DPF base material. In order to capture PM with minimal pressure loss, Toyota developed for the DPNR catalytic converter a new cordierite DPF base material having a large number of small, uniformly distributed pores. Furthermore, to improve the NOx adsorption/reduction performance, Toyota developed the ideal catalyst for the temperature window of diesel-powered vehicles, as well as a technology that coats the catalyst layer uniformly through slurry atomization, etc. These developments helped realize the DPNR catalytic converter.
In 2003, Toyota installed its DPNR catalytic converter in the Avensis for Europe, as the first such application in the world, achieving a low emissions level of half that specified in Europe' s Euro 4 regulations.
To reduce the size and weight of automatic transmissions, prevent judder and improve reliability, the wet friction materials require a high coefficient of friction, a positive slope of myu-V (coefficient of friction versus sliding speed) and durability.
Toyota developed wet friction material based on an analysis of phenomenon on friction surfaces.
The diatomite is placed on surface intensively. To get soft matrix, new resin is adopted. To improve durability, high-heat-resistance aramid fiber is used.
The developed material offers 30% higher coefficient of friction than conventional material. It also has positive myu-V slope and improved durability.
It was adopted in the B4 multiple brake discs of the 6 speed AT of the Celsior launched in August 2003.
The number of discs and mating steel plates were reduced by half, helping to reduce the weight and cost of the AT.
Structural image of paper friction material
Coefficient of friction
A740: 6-speed automatic transmission for rear-wheel drive vehicles
Slip control of a lock-up clutch system can significantly improve the fuel efficiency of vehicles with an automatic transmission. However, such a system requires a special automatic transmission fluid (ATF) that offers both high anti-judder performance and high torque capacity. By optimizing the friction modifier (FM), which affects judder performance, Toyota developed the T-IV ATF, which achieved both superior anti-judder performance, with a judder prevention lifespan of approximately five times that of a conventional ATF, and high torque capacity.
The T-IV also possessed excellent friction characteristics (according to the SAE No. 2 test), oxidation stability, material compatibility (with nylon, rubber, etc.), and low-temperature followability. Thus, it helped increase the number of vehicle models into which the slip-controlled lock-up clutch system could be installed, greatly contributing to fuel-efficiency improvement in these vehicles.
Toyota developed 5W-20 high-fuel-efficiency gasoline engine oil, which improved a vehicle' s fuel efficiency by at least 1.5% compared to conventional 5W-30 gasoline engine oil. Toyota reduced the viscosity of the oil to reduce the friction in the hydrodynamic lubrication region, and added molybdenum dithiocarbamate, or MoDTC, as the friction modifier to reduce the friction in the boundary lubrication region, achieving low fuel consumption. Furthermore, by using a new sulfur-based additive, Toyota succeeded in maintaining the fuel efficiency improvement effect of the developed oil even after 10,000 km.
For the friction modifier, Toyota analyzed molybdenum and sulfur additives, selecting one that offered low friction and possessed excellent compatibility with other materials. The newly developed 5W-20 oil provides an approximately 1.6% improvement in initial fuel efficiency compared to 5W-30 in Japan' s 10-15 test cycle and the U.S. Federal Test Procedure test cycle, and its fuel efficiency improvement effect was verified up to 10,000 km.