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The cooling performance and the heat resistance performance of commercial vehicle are balanced with aerodynamic performance, output power of powertrain, styling, cost and many other parameters. Therefore, it is desired to predict the cooling performance and the heat resistance performance with high accuracy at the early stage of development. Among the three basic forms of heat transfer (conduction, convection and radiation), solving thermal conduction accurately is difficult, because modeling of “correct shape” and setting of coefficient of thermal conductivity for each material need many of time and efforts at the early stage of development. Correct shape means that each part should be attached correctly to generate the solid mesh with high quality. Therefore, it is more efficient and realistic method to predict the air temperature distribution around the rubber/resin part instead of using the surface temperature at the preliminary design stage.

The dynamic performance of battery electric vehicles (BEV) is affected by battery output power, which depends on state of charge (SOC) and the temperature of battery cells. The temperature of the batteries varies in particular with the environment, in which the user stores the vehicle, and the battery output power. It is therefore necessary to employ thermal management systems that can control the battery temperature within the optimal range under severely hot and cold conditions in BEVs. A highly sophisticated thermal management system and its operation strategy were developed to fulfill the above requirements. The powertrain components to be thermo-controlled were located into two coolant circuits having different temperature range. The compact and efficient front-end heat exchangers were designed to optimally balance the cooling performance of powertrain, cabin comfort, vehicle aerodynamics and the vehicle design.

Gaskets made of joint sheet are widely used for mating surfaces in engines and transmissions. Before the regulation was issued for restrictions of asbestos usage as a hazardous substance, Honda had already developed non-asbestos joint sheets using aramid fibers substituting for asbestos and started applying them to the products sold worldwide. However, aramid fiber is significantly expensive but, on the other hand, the amount of aramid fiber mixed in a joint sheet will largely influence the sealing performance. Thus, when aramid fiber is applied, cost increase becomes a concern. With this background, a gasket material was designed for reducing the cost without sacrificing the required reliability as a joint sheet assuming the actual applications. The cost was reduced mainly by reducing the amount of aramid fibers used.

We had developed Electric Servo Brake System, which can control brake pressure accurately with a DC motor according to brake pedal force. Therefore, the system attains quality brake feeling while reflecting intentions of a driver. By the way, “Build-up” is characteristics that brake effectiveness increases in accordance with the deceleration of the vehicle, which is recognized as brake feeling with a sense of relief as not to elongate an expected braking distance at a downhill road due to large-capacity brake pad such as sports car and large vehicles. Then, we have applied the optical characteristic control to every car with Electric Servo Brake System by means of brake pressure control but not brake pad. Hereby, we confirmed that the control gives a driver the sense of relief and the reduction of pedal load on the further stepping-on of the pedal. In this paper, we describe the development of brake feel based on the control overview.

In our preceding report [1], we showed that the thermal conductivity of a heat pipe dramatically improves during high-speed reciprocation. However, this cooling method has rarely been applied to car engine pistons because the thermal conductivity of commercially available heat pipes does not increase easily even if the pipe is subjected to high-speed reciprocation. In consideration of the data from our preceding report, we decided to investigate heat pipe designs for car engine pistons, propose an optimum design, and conduct thermal analysis of the design. As a result, we found that it is possible to transport heat from the central piston head area, where cooling is most needed, to the piston skirt area, suggesting the possibility of efficient cooling.

Recently, the electronic fuel injection systems have been widely applied to small motorcycles including scooters. In the high pressure fuel lines, plastic hoses have been increasingly used instead of conventional rubber hoses. As the plastic hose is less elastic than the rubber hose, the fuel pressure pulsates more in the plastic hose. To cope with this issue, we have conducted researches on how the fuel pressure pulsation in the plastic hose affects the accuracy of fuel injection. Keeping our eyes on the pulsation damping effects derived from the changes of volume due to the expansion and contraction of hose when the pressure changes, we have established the analysis method for optimization of the inner diameter and the thickness of the hose utilizing CAE analysis. The newly-developed plastic hose is applicable to motorcycles having a single cylinder 250 cm3 engine using an injector of a high static flow rate.

A method was designed to predict the gasket surface pressure in consideration of creep which occurs on the surface of the gasket side of the cylinder head in air-cooled engines. Creep caused by heat can cause major deformation on the gasket side of the cylinder head in air-cooled engines, which may result in combustion gas leaking from between the cylinder and cylinder head. Until now, there have been no reports of methods to accurately predict phenomena relating to this deformation in the initial stage of engine design. This study combined values of strain and temperature occurring on the gasket side of the cylinder head, obtained through FEM analysis of steady heat transfer and thermal stress, with unit test results showing the domains in which the influence of the creep is critical or not. This information was used to design a method to determine whether or not an engine's specifications fell into a domain in which creep would have an effect, and predict surface pressure.

The properties sought in a multi-layer steel cylinder head gasket include cylinder pressure sealing and fatigue strength in order for there to be no damage while the engine is in operation. Diesel engines, in particular, have high cylinder pressure and a high axial tension by the cylinder head bolt demanding severe environment to the gaskets. As engine performance is enhanced, there are cases when cracks develop in the gasket plate, necessitating countermeasures. The cause of cracking in a flat center plate, in particular, has not yet been explained, and no method for evaluation had previously existed. Three-dimensional non-linear finite element calculation was therefore performed to verify the cause. First, a static pressurization rig test was used and the amount of strain was measured to confirm the validity of the calculations. Then the same method of calculation was used to verify the distribution of strain, with a focus on the plate position.

A compact, low-cost fuel pump module has been developed for use in motorcycles with a small-displacement engine. Various considerations are given to make the module as compact as possible. The pump motor, which is one of the major component parts, is down-sized specifically for applications to small-displacement engines. The pressure regulator uses a simple construction consisting only of a ball and a spring without a diaphragm. Especially noteworthy is that with the volume reduced by approximately 40% from the conventional pressure regulator while using the construction that reduces self-excited vibrations caused by fuel pressure pulsations, the pressure regulator contributes significantly to the down-sizing and cost reduction of the module. Furthermore, the down-sized module remarkably reduces the size of fuel pump mount surface, allowing a modification from the flat-surface sealing to the radial sealing.

A new brake system, able to make efficient use of regenerative braking while maintaining excellent brake feel, has been developed to increase the fuel economy of hybrid vehicles. A hydraulic servo was used as a base to enable mechanical operation of the service brakes; solenoid valves and brake fluid pressure sensors were added to this base to make it possible to control brake line pressure as demanded. The use of a stroke simulator in the hydraulic servo prevents brake feel from being affected by the control of the brake pressure. In addition, high-accuracy brake pressure control that functions cooperatively with the regenerative brakes is enabled, resulting in stable braking effectiveness.

SUS301-EH is widely used as a material for exhaust system gaskets, however, at temperatures in excess of 400°C, it can not be used as gas-seal ability of the material declines due to its reduced hardness. The following methods were found to be effective in controlling the softening of stainless steel at high temperatures: (1) The addition of a nitrogen component; (2) Stabilization of the austenite structure; (3) The addition of a molybdenum component. The addition of 0.5% nitrogen to austenitic stainless steel containing molybdenum has enabled the speed of softening at high temperatures to be significantly reduced, due to strain aging by solid nitrogen below 600°C and the combined effects of precipitation hardening and control of growth of recrystallized grains through the precipitation of fine Cr2N on the dislocations and the grain boundary above 600°C.

In the development of a magnetic-coupling water pump, the pulling-out (disengagement) of a coupling that led to the stopping of an impeller was a concern. Upon analysis of the behavior of the magnetic coupling, presence of two types of the pulling-out was found, that is, the pulling-out resulting from a lack of transfer torque in the high-speed revolutions and the pulling-out due to the resonance of an inner magnet and an outer magnet. Main factors that affect the pulling-out are the angular velocity input to the drive side, the moment of inertia of the driven side, characteristics of the magnetic coupling, and a damping from coolant. Using a measurement and simulation of the behavior of the water pump, factors were analyzed and the process of pulling-out was clarified. As a result, design specifications that prevented the pulling-out were established.

This paper introduces a new type of aluminum radiator that has been developed with the objective of high performance and light weight. Aluminum radiators have recently been replacing copper radiators because of their light weight, but the heat rejection of such conventional alminum radiators does not exceed that of copper radiators. Authors established the aluminum radiator not only being light weight but also having high performance through the following approaches. (1) Optimization of radiator core module. (2) Thickness reduction of tube and fin. (3) Development of aluminum alloys with improved corrosion resistance for tubes and fins. As a result, a new type single-row aluminum radiator has achieved 7% higher rejection at 50% lighter weight than those of copper double-row radiator.

In the consideration of safety to health, many countries have recently been enforsing regulations on the use of asbestos. To keep abreast of this trend, it has become necessary to replace the gasket materials currently used in the cases and the covers of motorcycle engines with non-asbestos materials. The gaskets used in motorcycles are subjected to extremely severe sealing loads and temperature in the small and high performance engines. They are required to have excellent sealability and creep relaxation characteristics at high temperature. Under such conditions, it is extremely difficult to substitute non-asbestos materials for asbestos which has superb material characteristics such as higher heat resistance and greater aspect ratio (length of fiber/dia.).