Development of "idling stop system" for small-size motorcycles

An advanced system aimed to reduce fuel consumption and exhaust emissions by means of an automatic engine stop, while the vehicle is stopped due to a traffic signal, traffic jam, etc.

Ever since its inception, Honda has been conscious of environmental protection, as evidenced by the challenges for application of 4-stroke engines in Honda products. Shifting to 4-stroke engines for all Honda motorcycles, including scooters, to reduce fuel consumption while assuring clean exhaust gases, Honda introduced the new-generation 4-stroke scooter in 1999. While maintaining fundamental performance, this scooter became the benchmark in terms of environmental protection by reducing CO and HC emissions approximately 50% below the 1998 Domestic Exhaust Emission Regulations. Also fuel consumption was decreased by approximately 30% from the previous models. All this was achieved by applying the latest 4-stroke engine technologies. Additionally, the newly developed "idling stop system" was employed to minimize idling, further decreasing fuel consumption, exhaust emissions, vibration, and noise. When compared to models without the "idling stop system", fuel economy improved by 5.1%. In 2001, the "Crea Scoopy-i" was introduced as the first 50cc scooter equipped with a water-cooled 4-stroke engine, which is lightweight and has an outer-rotor-type ACG starter. Coupled with the use of the "idling stop system", the fuel economy improved by 5.5%* while reducing CO2 emissions by 5.2%, CO by 8%, and HC by 2% without an additional emission control system.

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*Tested using domestic exhaust emission measurement mode (city-driving) designated by Ministry of Transport

Stops the engine automatically, starts the engine by only opening the throttle.

Incorporating an ECU (Electronic Control Unit) that centrally controls engine operations on the basis of inputs from various sensors, the "idling stop system" automatically stops idling when the vehicle stops for a traffic signal or traffic jam, and restarts the vehicle when the throttle is opened.

Key points of development

In the "idling stop system", the ECU centrally controls engine operations on the basis of inputs from various sensors. By precisely controlling revolutions of the ACG starter, which is directly mounted on the end of the crankshaft and serves as an ACG (alternator), as well as a starter motor, the system permits jolt-free restarting. The speed sensor, thermo-sensor, throttle sensor, pulse generator, and seat sensor detect conditions such as stopping of the vehicle, engine temperature, throttle opening, engine revolutions, seating of the rider, etc. During cold starts, the ECU automatically stops the engine when warm, and restarts the engine when the throttle is opened. It also controls the stand-by indicator lamp that notifies the rider of the condition of the "idling stop system".

Operations of "idling stop system"

1.When starting the engine (initial starting)

Initially, the rider starts the engine by pushing the starter button in the same manner as an ordinary scooter because it sometimes takes several seconds to start a cold engine after long-term storage or when the ambient temperature is low. Under these conditions, the engine continues to idle eventhough the vehicle is not moving for more than 3 seconds.

2.When engine is warm and/or during vehicle movement (shifts to the "idling stop" mode)

After initial engine start, vehicle speed has exceeded 10km/h, and the water temperature sensor detects a temperature above 50?, by which the ECU judges that the engine has been warmed up, the system shifts to the "idling stop" mode from the next stop of the vehicle.

3.When the vehicle stops moving ("idling stop" ready)

As the vehicle stops with the throttle fully closed and the rider seated, the ignition is turned off to stop the engine. The ignition turns off 3 seconds after the vehicle stops moving. The delayed engine shut-off allows the rider the ability to make a U turn or a momentary stop at a stop sign.

4.When restarting ( engine restart and vehicle movement )

When restarting, the throttle sensor attached to the carburetor detects an opening of the throttle, and the system turns on the starter motor as well as allowing ignition. As the engine starts and the engine speed increases, the centrifugal clutch engages, thus starting the vehicle movement.

0.9 second from the opening of throttle to the start of vehicle

The time period from the opening of throttle to the start of vehicle is 0.5sec when the engine is idling, and it is 0.9sec when not idling. Although there is a delay of 0.4sec, practically the delay in the starting of vehicle is almost unnoticeable.

Starts the engine quiet and jolt-free, scooter starts moving smoothly

In the "idling stop system", it is important to have a quiet starting charging system that keeps the battery adequately charged to assure starter motor operations. Also, it is important to have a fuel supply system that ensures restarting of the engine even after the throttle has been opened. The key component for engine starting and battery charging is the newly developed ACG starter having a combination of alternator and starter functions.

Alternator/starter motor directly mounted on the end of the crankshaft

In order to start the engine smoothly from the state of idling stop, the brush-less ACG starter has been developed. This is an integrated component mounted directly on the end of the crankshaft serving as a starter motor and an alternator. The new ACG starter technologies permits smooth starting, directly cranks the engine. This eliminates typical noise from the starter gear engagement or meshing.

The brush-less ACG starter is an outer-rotor type having magnets in the flywheel. The stator is a 3-phase winding. The flywheel and the stator serve as a DC brush-less motor when the power is applied through the FET in the ECU. The sensor magnet located in the center part of the rotor, and the Hall-IC-type angle sensor mounted on the stator, detect the rotor position.

When the ACG functions as a starter motor

The rotor core, which serves as an iron core, is located between the magnets in the rotor. A coil is wound around the stator core, which serves as an iron core. By this construction, the single unit serves both purposes as a starter motor and an alternator.

When working as a starter motor

The magnetic flux from the custom-shaped magnet acts on the stator core via the rotor core. When the power is applied to the stator coils, strong magnetic flux occurs in the stator cores, producing adequate torque required to crank the engine.

When working as an ACG (alternator)

If an ordinary starter motor is rotated to a high revolution, an excessive charging current and a large friction from the core loss occur, which does not allow a starter motor to serve as an alternator. In the newly developed ACG starter, laying a rotor core between the magnets has solved the aforementioned problem.

The magnetic flux from the magnets acts on the rotor core and toward the stator core. When a charging current occurs in the coil, the magnetic flux in the reverse direction occurs in the stator core, increasing the magnetic flux toward the rotor core and reducing the magnetic flux toward the stator core. Thus, the friction from the core loss has been successfully reduced while attaining an adequate level of power generation.

Precise control of charging and discharging the battery

When the starter is unable to crank the engine due to a discharged battery, a vehicle equipped with an "idling stop system", will not start. To prevent discharging of the battery, even when operated in traffic, the charging capacity for the "idling stop system" is set higher than usual.

Charging system designed to prevent discharging of the battery

It is necessary to increase charging capacity for an "idling stop" vehicle compared to a vehicle that with idling. This is necessary because the battery is not charging when the vehicle is stopping for a traffic signal etc.
An "idling stop" vehicle cannot restart if the battery is discharged and the starter motor cannot crank the engine. To cope with the aforementioned, the charging output from the ACG starter in the "idling stop" vehicle is designed to such a level that prevents the battery from discharging even when operated on congested roads using the "idling stop system".

Reduced friction from the power generation

When an "idling stop system" is applied, due to lack of power generation during stopping, the electrical loads, such as the headlamp, draw a considerable amount of power from the battery when stopping. Power consumed from the battery during stopping is quickly recovered from the alternator when the engine revolutions increase and the power generation starts. A considerable amount of mechanical energy from the engine must be consumed for the power generation by the alternator, resulting in weak vehicle acceleration.

The charging voltage at the time of start is regulated.

To reduce friction from power generation, and to ensure strong vehicle acceleration when equipped with the "idling stop system", the charging voltage is lowered to 12 volts from the normally regulated voltage of 14.5 volts for a prescribed period of time. In doing so, the battery is not charged during vehicle acceleration, and charged only during constant speed or deceleration. Charging during deceleration is especially effective because it means an efficient use of energy.

Improved fuel economy and reduced exhaust emissions in city-driving mode

The "idling stop system" reduces fuel consumption and exhaust emissions by automatically stopping the engine while the vehicle is stopping due to a traffic signal or traffic jam. The newly developed system allows reduction of fuel consumption and exhaust emissions in the domestic emission measurement mode without an additional emission control system.

Benefits of the "idling stop system"

Compared to the standard type without the "idling stop system", the 50cc, 4-stroke scooter "Crea Scoopy-i" equipped with the "idling stop system" improves fuel economy by 5.5% in the domestic exhaust emission measurement mode that presumes city driving. Also the CO2 emission is reduced by 5.2%, CO by 8% and HC by 2%.

Source: Honda Motor Co., Ltd.

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