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Reducing vehicle CO2 emissions is an important measure to help address global warming. To reduce CO2 emissions on a global basis, Toyota Motor Corporation is taking a multi-pathway approach that involves the introduction of the optimal powertrains according to the circumstances of each region, including hybrid electric (HEVs) and plug-in hybrid electric vehicles (PHEVs), as well as battery electric vehicles (BEVs). This report describes the development of a new PHEV system for the Toyota Prius. This system features a traction battery pack structure, transaxle, and power control unit (PCU) with boost converter, which were newly developed based on the 2.0-liter HEV system. As a result, the battery capacity was increased by 1.5 times compared to the previous model with almost the same battery pack size. Transmission efficiency was also improved, extending the distance that the Prius can be driven as an EV by 70%.

Driving Automation Systems (DAS) are subject to complex road environments and vehicle behaviors and increasingly rely on sophisticated sensors and Artificial Intelligence (AI). These properties give rise to unique safety faults stemming from specification insufficiencies and technological performance limitations, where sensors and AI introduce errors that vary in magnitude and temporal patterns, posing potential safety risks. The Safety of the Intended Functionality (SOTIF) standard emerges as a promising framework for addressing these concerns, focusing on scenario-based analysis to identify hazardous behaviors and their causes. Although the current standard provides a basic cause-and-effect model and high-level process guidance, it lacks concepts required to identify and evaluate hazardous errors, especially within the context of AI. This paper introduces two key contributions to bridge this gap.

In general, automatic braking uses an electric stability control (ESC) hydraulic unit that can automatically increase the hydraulic pressure in the wheel cylinder (hereinafter called wheel pressure), independent of the driver’s braking operation. The hydraulic unit should have sufficient pressure response to apply autonomous emergency braking (AEB). It was necessary for the hydraulic unit to have a high flow rate for the pressure response. To satisfy the performance requirements of the AEB, a brushless motor, which has a high maximum rotational speed and good response, is adopted for the hydraulic unit. Furthermore, sensorless control, which does not require a rotation angle sensor, has been developed so that the motor size can be small and common to conventional units. The developed sensorless control can switch the driving methods in three states: pre-rotation, low speed, and high speed.

Toyota Motor Corporation has developed a new battery electric vehicle (BEV) on the dedicated e-TNGA platform for BEVs, which was designed to lower the center of gravity of the vehicle and increase body stiffness. In addition to a full-time 4WD system, another feature of this new BEV is its pleasurable driving experience. A new inverter drive unit was developed for this system. Unlike the previous inverter, the advantage of the new inverter is that it is small enough to be mounted inside the transaxle housing, thereby contributing to the availability of interior and luggage space. The temperature rise of the power semiconductors in the inverter was reduced considerably by the development of a new power semiconductor for BEVs. This enables a parallel layout of two power semiconductors instead of three. The components of the inverter were also downsized. A coreless current sensor was adopted, and capacitors were developed with significantly lower capacitance.

Safety assurance is a central concern for the development and societal acceptance of automated driving (AD) systems. Perception is a key aspect of AD that relies heavily on Machine Learning (ML). Despite the known challenges with the safety assurance of ML-based components, proposals have recently emerged for unit-level safety cases addressing these components. Unfortunately, AD safety cases express safety requirements at the system level and these efforts are missing the critical linking argument needed to integrate safety requirements at the system level with component performance requirements at the unit level. In this paper, we propose the Integration Safety Case for Perception (ISCaP), a generic template for such a linking safety argument specifically tailored for perception components. The template takes a deductive and formal approach to define strong traceability between levels.

Increasingly stringent regulations call for the reduction of emissions at engine startup to purify exhaust gas and reduce the amount of CO2 emitted. Air-fuel ratio (A/F) sensors detect the composition of exhaust gas and provide feedback to control the fuel injection quantity in order to ensure the optimal functioning of the catalytic converter. Reducing the time needed to obtain feedback control and enabling the restriction-free installation of A/F sensors can help meet regulations. Conventional sensors do not activate feedback control immediately after engine startup as the combination of high temperatures and splashes of condensed water in the exhaust pipe can cause thermal shock to the sensor element. Moreover, sensors need to be installed near the engine to increase the catalyst reaction efficiency. This increases the possibility of water splash from the condensed water in the catalyst.

This paper describes an exhaust system using a new air-fuel ratio (hereinafter, A/F) sensor that contributes to low emissions and low fuel consumption of gasoline engines. As the first technical feature, the water splash resistance of the A/F sensor has been substantially improved which allows A/F control to be enabled without delay during engine cold start. To realize this capability, it is important that the sensor characteristics are not affected by the condensed water generated in the exhaust pipe. Therefore, a technique that has the effectiveness of a water splash resistance layer with water repellent function is demonstrated. As the second technical feature, the power consumption of the sensor has been substantially reduced. This is achieved by improving thermal efficiency of the sensor that the element can be activated at a low temperature.

Diesel injection equipment is required to be more accurate and higher in pressure to meet the increasingly strict emission, fuel consumption regulations and higher engine performance. It also needs to achieve a number of requirements such as robustness against diversified market fuels, pressure maintenance characteristics in the idle stop system (ISS), easy installation to engine, etc. One of the key component to meet these demands is injector.

Injuries to the lower extremities are one of the major issues in vehicle-to-pedestrian collisions. To evaluate pedestrian lower extremity protection, the Transport Research Laboratory (TRL) legform impact tests have been conducted according to the specifications in the EU directive. The TRL legform impactor consists of a tibia and a femur steel shaft connected by deformable knee bars. A Flexible Pedestrian Leg-form Impactor (Flex-PLI), which has flexible femur and tibia, is examined in the Global Technical Regulation (GTR). Previous studies compared the responses of both impactors; however, the relation between the tibia acceleration in the TRL legform impactor and the maximum bending moment in the Flex-PLI (both injury measures are for the tibia fracture) is not understood sufficiently.

A response surface model of a diesel spray, parameterized by the internal geometries of a nozzle, is established in order to design the nozzle geometries optimally for spray mixing. The explanatory variables are the number of holes, the hole diameter, the inclined angle, the hole length, the hole inlet radius, K-factor and the sac diameter. The model is defined as a full second-order polynomial model including all the first-order interactions of the variables, and a total of 40 sets of numerical simulations based on D-optimal design are carried out to calculate the partial regression coefficients. Partial regression coefficients that deteriorate the estimate accuracy are eliminated by a validation process, so that the estimate accuracy is improved to be ±3% and ±15% for the spray penetration and the spread, respectively. Then, the model is applied to an optimization of the internal geometries for the spray penetration and the spray spread through a multi-objective genetic algorism.

The hybrid vehicle market is growing rapidly recently, while carmakers are planning to expand their lineup of hybrid vehicles from the compact to the full-size. To make this rapid development possible, the Power Control Unit (PCU) that controls traction motors of hybrid vehicles is required both to be smaller in size for the ease of packaging, and higher in output power to fulfill the need for full-size vehicles. To achieve both of these targets, we have developed a PCU for the Lexus LS600h with higher output power per volume through significantly improved cooling design for power semiconductor chips by dissipating heat from both sides of them. The following is an overview of the developed technology.

In automotive air conditioning, balancing comfort and fuel efficiency is very important. Vehicle cooling performance improvements during initial cool down has reached a limit in recent years, especially in very hot regions. We have addressed this issue by developing a unique double-pipe internal heat exchanger. In the main discourse, we first clarify the concept of the internal heat exchanger system (IHE) using the temperature difference between the high and low pressure pipes in the refrigeration cycle, and propose the application of an efficient internal heat exchanger. This unique double-pipe internal heat exchanger can easily be manufactured by inserting the inner pipe into the outer pipe and by fixing the pipes at both ends. The length of the IHE is 400mm. This double-pipe internal heat exchanger can increase cooling performance by 5-12% at the equivalent power consumption levels in the same space as a conventional front air conditioner system.

We have developed a novel capacitive acceleration sensor fabrication process by applying surface MEMS (Micro Electro-Mechanical System) technology and successfully introduced this process for volume production of a new super slim sensor. The new process uses the ICP-RIE(Inductively Coupled Plasma - Reactive Ion Etching) technology to etch single crystal SOI(Si on Insulator wafers. In this technology, vertical Si etching is followed by, lateral etching along the buried oxide to release the movable electrode. Because of a dry process, the new process does not cause the movable structures to stick to each other. Our process uses only three masks and reduces the sensor chip size to a half that of our conventional capacitive acceleration sensors.

Carbon brushes for automotive starters are used under severe conditions of high electric current density, high contact pressure and high sliding velocity. Therefore lead has traditionally been added to brushes to improve performance and durability. Lead is an environmental hazardous substance. In the EU, the law prohibits adding lead to brushes for electric motors which is installed on new automobiles in and after January 2005. In order to develop the lead free carbon brush for starters, we analyzed the effect and selected substitutive substance of lead. Adding lead to the brush reduces the electric resistance increase of the brush in high-temperature and high-humidity atmosphere and in high-temperature atmosphere. Furthermore lead reduces the wear amount of brush. We developed the lead free brush surpassing the lead addition brush in performance and durability by addition of lead alternatives silver and zinc.

A recent trend in the making of automotive engines, where high efficiency and low emissions need to be considered, is to mount multiple parts around the motor in order to improve overall engine efficiency. As a result of modern technology, the engine head and surrounding space have an excessive amount of parts. To accommodate the congested engine compartment, it is desirable to reduce the size of the spark plug. Small size spark plugs have the problem of poor resistance to carbon fouling and are subject to side sparks if carbon fouling occurs. This results from a reduced insulating gap between the center electrode and the housing achieved by reducing the size of the spark plug. By using visualization of flame growth and electric field strength analysis, we have conducted studies on insulator temperatures and spark behaviors in search of the optimal specifications.

Through the years, aluminum automotive heat exchangers have been developed in order to have a high performance and a light weight. Therefore, the thickness of the aluminum sheets for the application has been reduced. As the brazeability declines with the reduction in thickness, fins having a thickness under 80μm may be difficult to secure a good brazeability. Therefore, we studied the brazeability to determine the limit of thickness using clad fins from 40 to 80μm. The fillet volume formed at the joints of the fin and tube decreased with the decreasing fin thickness and the Si content in both the filler metals and the core alloys. The suitable range of Si content in the filler metals and the core alloys to obtain a good brazeability decreased with the decreasing fin thickness. When the fins were thinner than the critical values, it was impossible to have a good brazeability.

Recently there has been a market trend requiring End of Life Vehicles to be recycled to satisfy current legislation; therefore, we are approaching the recyclability of automotive parts based upon these environmental requirements. At this time, we have demonstrated a new recycle technology for polyamide using one of the largest automotive applications, the radiator end tank which has been previously viewed as degraded material due to hydrolysis and deemed as shredder residue. This technology [1] allows for the recovery of the base resin that is then recycled into a radiator end tank with performance equivalent to one made of virgin resin. The process for this technology includes collection of post consumer radiator end tanks that are then reground, dissolved, filtered for glass fiber removal, precipitated, recovered, and compounded into a usable resin. This technology is referred to as “Nylon Composite Recycle”.

Spark plugs with higher ignitability are continuously in great demand to realize high fuel efficiency and low emissions. To meet this demand, DENSO launched the Iridium Spark Plug in 1997, which realized the two characteristics that had been conventionally difficult to achieve concurrently-high ignitability and long life. The development of this product was enabled by miniaturizing the center electrode, produced using DENSO's original, highly wear-resistant iridium alloy (featuring a high melting point and excellent oxidation resistance). While spark plugs are now required to have a longer service life, they are also required to be higher in ignitability, as exhaust gas regulations have been tightened recently. However, the effort to miniaturize the center electrode is reaching a limit.

We have achieved significant weight reduction for the MS (Multi-Tank Super Slim Structure) Evaporator (1)currently in production at DENSO CORPORATION. The evaporator of HVAC unit, located in the instrument panel, is a component of the aluminum heat exchanger used in automotive air conditioners. The new evaporator uses thinner quad-layer sheet material, thanks to optimization of the electrical potential among its outer filler metal, intermediate anodic layer and core. The evaporator is thus lighter than conventional evaporators, but retains equivalent corrosion resistance.

In conventional automobile designs, a radiator and a condenser are typically configured and mounted independently of each other. We have developed a smaller and more powerful cooling module by integrating these two products into one piece. The new cooling module has been designed to share the fin material and to have an insulating slit and other means for effective prevention of heat loss that occurs due to thermal conduction between the radiator and the condenser1). In addition, as one of the key techniques for integrating fins, we studied thermal spraying of brazing filler to the tube material and were able to achieve a practical-level cooling module through use of high-performance fins, contributing largely to the efforts to create a more compact, higher performance cooling module.