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Large truck accidents sometimes result in severe damages or give large disturbance of traffic and there are demands of improving vehicle safety characteristics. Main types of traffic accidents concerned are rear-end collision and single accident. As countermeasures for rear-end collisions, world-first collision mitigation brake for commercial vehicles; Pre-crash Safety System, was developed. If there is possibility of collision, warning to driver and brake control intervention is carried out in stepwise fashion and collision speed is decreased. To achieve higher effect in collision mitigation, it is necessary to activate warning or brake-force in earlier timing. Inter-vehicle or infrastructure-vehicle communication offer promising prospect. Tractor-trailer combinations show some instable behaviors. “Roll Stability Assist” and “Vehicle Stability Control” were developed to assist drivers to avoid the occurrence of these instable behaviors.

A new model of 4 × 2 semi-trailer tractor was introduced to the Japanese truck market from HINO MOTORS last year, which has improved riding comfort and remarkable features for trailer connecting/disconnecting operations. This new model has two typical methods of comfortable ride, those are full-floating cab mount system and air ride suspension for the rear axle. Since the analysis of tractor vibrations and the vehicle height control system of this model have given satisfactory results, and their outline is described here.

Design work for truck suspension systems requires multi-objective optimization using a large number of parameters that cannot be solved in a simple way. This paper proposes a process-based systematization concept for ride comfort design using a set-based design method. A truck was modeled with a minimum of 13 degrees of freedom, and suspension performance under various vehicle speeds, road surface conditions, and load amounts was calculated. The range of design parameters for the suspension, the range of performance requirements, and the optimal values within these ranges were defined based on the knowledge and know-how of experienced design engineers. The final design of the suspension was installed in a prototype truck and evaluated. The performance of the truck satisfied all the objectives and the effectiveness of the set-based design approach was confirmed.

The sensitivity of steering increases as the vehicle speed rises. It requires a driver to make different steering maneuvers at high speed zone from that at low speed zone. In order to reduce the difference and to have a better steering “feel” for the driver, the characteristics of steering should be studied from both “the vehicle lateral movement corresponding to steering effort” and “the time lag of the vehicle lateral movement to steering effort”. And both should be decreased as vehicle speed rises. This paper explains how the above conclusion was reached through the development of engine/vehicle speed sensing power steering for commercial vehicles.

Diesel particulate trap systems are one of the effective means for the control of particulate emission from diesel vehicles. Hino has been researching and developing various diesel particulate trap systems for city buses. This paper describes two of the systems. One uses a wall flow filter equipped with an electric heater and a sensing device for particulate loading for the purpose of filter regeneration. Another makes use of a special filter named “Cross Flow Filter” with an epoch-making regeneration method called “Reverse Jet Cleaning”, by which it becomes possible to separate the part for particulate burning from the filter. Both systems roughly have come to satisfy the functions of trap systems for city buses, but their durability and reliability for city buses are not yet sufficient.

A historical review of Japanese turbocharged diesel engines for heavy duty vehicles is described, and newly developed turbocharged diesel engines of HINO are introduced. The design features of these engines include new turbocharging technologies such as highly backward curved impeller for compressor blade, variable controlled inertia charging and waste gate. Laboratory and field test results demonstrated better fuel economy and improved low speed and transient torque characteristics than the predecessors. Several operational experiences, technical analysis and reliability problems are discussed.

The friction pattern on the chamfers of sleeves and dog gears is a combination of peeling and adhesive wear caused by the formation and propagation of fine cracks. The effect of additional elements on wear were checked by making a test apparatus capable of performing evaluations on test pieces equivalent to those using actual parts. The results showed that the addition of B, Ti-Nb helped improve wear resistance. This is attributed to enhanced toughness and reduced peeling due to the formation of a texture. A 45% reduction in wear was achieved in actual parts tests on steel with added B, Ti-Nb.

In the '97 Dakar Rally, Hino FT model, 8,000cc engine truck, won 1st, 2nd and 3rd places by defeating upper class trucks having engine of 19,000cc. The average speed of the '97 Hino model was increased more than 15 km/h over the '96 model by improving the riding comfort and handling stability. Larger diameter tires, and softer parabolic leaf springs with long and inclined axle-locus for reducing road impact, gas charged dampers, suspension rods which control compliance-steer-motion and wind-up motion of unsprung masses were adopted for the '97 model.

Vehicle responsiveness to the driver's steering maneuvers and external turbulences caused by irregularities in the road surface and wind gusts are two opposing factors to be studied for better stability and controllability of vehicles. The cruising speeds of vehicles on freeways have been becoming higher, and wider physiological differences in the driving ability of drivers are appearing with the increase in elderly drivers. Therefore, to meet the requirements of higher cruising speeds and the expanding physiological differences between drivers, an electro-hydraulic feedforward control power steering system has been developed for trucks and buses. This is a parallel operating system consisting of a mechanical route and an electronic route, and improves vehicle responsiveness so as to absorb the physiological differences of drivers.

An integrated engine subsystem incorporating Internal Exhaust Gas Recirculation (IEGR) or alternatively referred to as Pulse EGR™ and Compression Release Retarding (CRR) functions has been developed and introduced to production with the new E13C engine from Hino Motors Ltd. This new system provides the nitrous oxide (NOX) reduction benefit of IEGR and the vehicle control and brake saving benefits of CRR in a single integrated package, without the need for increased vehicle cooling capacity or additional components external to the engine. The product is a result of a close cooperation between two companies, Hino Motors Ltd. of Japan and Jacobs Vehicle Systems, Inc. of the U.S.A.

It is preferable that power steering permits “static park” and has a good “road Feel” when running. In order to permit “static park”, a large bore actuation cylinder with high flow pump is required. Such a method, however, has two defects, a loss power for driving a large volume pump and a poor “road feel”. Resolving these problems and achieving the above matters. Hino has developed a load sensing power steering system. This system, which employes two actuation cylinders controlled by means of a unique load sensing valve arrangement, is designed to permit use of only one cylinder for highway speeds and both cylinders during a static park maneuver. When the system is combined with the preceding speed sensing power steering, “static park” is further facilitated and a tasty “road feel” is available in accordance with vehicle speed.

In order to reduce particulate and NOx emission from the direct injection diesel engine, most researchers have been expecting the utilization of higher injection pressure and injection rate for improvement of diesel combustion. In the case of pump-line-nozzle system, the injection pipe line is very important with regard to the high injection pressure. Namely, the pipe line must be able to resist not only high pressure but also cavitation erosion. In this paper, the effect of high injection pressure, injection rate and sharp cutting at the end of fuel injection are discussed along with cavitation phenomena on the injection pipe line. And durability tests on the pipe line system under high injection pressure using a test rig are also described. Regarding durability tests, several measures have been taken for the injection pipe. As a result, the authors have found that the best solution for the injection pipe is a composite pipe made with SUS and steel.

The toe-change of road-wheel, so-called compliance-steer(CS), caused by suspension compliance is proved to occur around a steady instantaneous center under steady run at constant speed. The adverse/proverse CS, that increases/decreases the side-slip angle versus the velocity vector of vehicle, is realized by locating the center rearward/forward of the axle. By designing the front/rear wheel CS as a proverse/adverse CS with nonlinear compliance that is large at on-center but small at off-center, vehicle characteristics to reduce lateral deviation caused by disturbance and to improve tracking performance are possible.

Ultra-low energy consumption and ultra-low emission vehicle technologies have been developed by combining petroleum-alternative clean energy with a hybrid electric vehicle (HEV) system. Their component technologies cover a wide range of vehicle types, such as passenger cars, delivery trucks, and city buses, adsorbed natural gas (ANG), compressed natural gas (CNG), and dimethyl ether (DME) as fuels, series (S-HEV) and series/parallel (SP-HEV) for hybrid types, and as energy storage systems (ESSs), flywheel batteries (FWBs), capacitors, and lithium-ion (Li-ion) batteries. Evaluation tests confirmed that the energy consumption of the developed vehicles is 1/2 of that of conventional diesel vehicles, and the exhaust emission levels are comparable to Japan's ultra-low emission vehicle (J-ULEV) level.

An on board burner that enables DPF regeneration even when an engine is at standstill has been researched. By employing pre evaporative combustion with a wick burner, miniaturization of the burner system was successfully accomplished as well as stable ignition and combustion. Total heat necessary for DPF regeneration was reduced in comparison to the active DPF regeneration by means of engine control and an oxidation catalyst. Uneven temperature distribution in DPF and excessive temperature rise, which had been recognized as issues in the regeneration of a DPF while engine is at standstill, were solved by increase of combustion air amount and multi-step control of regeneration temperature and reliable regeneration was accomplished.

A driving simulator system for developing steering road feel has been developed. A new steering gear box or an electronic steering system is installed on the simulator and its road feel and control algorithm are developed according to the characteristics of any vehicle which has been programed into the engineering work-station. The vehicle model programed into the engineering work station runs according to the driver's operations, which are fed through the new steering system to be tested. The steer-restoring torque of the vehicle programed into the engineering work-station is produced by an actuator, and gives the impression through the new system of having been fed back from an actual road.

A newly developed viscous-rubber damper, which employed an innovative structure and a new heat resistant rubber, solved some tough problems. This paper dealt more closely with the features of the new viscous-rubber damper and the new calculation method for the viscous-rubber damper. This damper has been employed for Hino new K13C (K-II) higher boost turbocharged and air to air charge-cooled diesel engine, which has extreme severity on the torsional vibration.

The running direction of a vehicle can be controlled by not only wheel steer but also torque steer. This paper introduces the tractive torque steer effect produced by a newly developed electropneumatic control system, the limited-slip differential for large-sized vehicles. This system enhances the vehicle's running stability and controllability by controlling the tractive force of the drive axle. The tractive force maintains a stable running course against disturbances such as road roughness and wind gusts, thereby enhancing the steering response and providing a better feeling of handling to the driver. The system also improves mobility. especially on low-μ roads. It is expected that a single axle equipped with this system will exhibit good performance comparable to that of tandem axle.

This paper introduces the Japanese standards and regulations of automobiles with brakes as the central subject and clarifies the difference from those of Europe and USA by comparison. Further, this paper describes not only the application status of the standards and regulations in Japan but also the features of structure and performance of Japanese trucks that are designed and produced under such standards and regulations. It can be said that the Japanese trucks are comparatively simple in structure but are in a level equal to or higher than European and USA automobiles in respect of performance. Also in respect of the international harmonization, the internationalization of standards is being conducted in Japan on the basis of ISO and the internationalization for regulations is considered to be under preparation.