JSAE Exposition 2016: Electric components for powertrains that raise fuel economy and reduce CO2
IPTT's integrated electric supercharger and starter generator; Schaeffler's electric valve control
At the JSAE Exposition 2016, companies displays included parts and materials that incorporated the latest technologies. This report will focus on two unique electrified powertrain components developed chiefly to improve fuel economy and reduce CO2 emissions.
The first is the SuperGen, an electro-mechanical supercharger that integrates a starter, generator, and drive power assist, which was developed by Integral Powertrain Technology (IPTT), a joint venture formed by Canada-based Magna International Inc and Integral Powertrain Limited, a British company. The second is a continuously variable valve timing control system called Electric Cam Phaser (ECP), which was developed by the German firm Schaeffler. Both exhibitors displayed their prototypes and gave detailed presentations about the components.
IPPT’s SuperGen - integrating the four functions of a starter, generator, power drive assist, and electro-mechanical supercharger
What is SuperGen?
SuperGen is an integral powertrain developed by IPPT that combines an electro-mechanical supercharger with an ISG (Integrated Starter Generator), which is to say it is a single multi-function 12V system that functions as a starter, generator, drive assist motor, and electro-mechanical supercharger. Coupled with the engine start-stop functions, the SuperGen can increase a vehicle’s output by 4 to 6 kW, which contributes to improving engine fuel economy and reducing CO2 emissions.
|Photo 1 SuperGen external view (Source: IPPT)||Photo 2 SuperGen internal view|
What makes SuperGen so unique? How is it different from competitors?
A comparable product is an ISG for hybrid systems that integrates an electric assist motor, starter and generator. Various ISGs have been developed by a number of manufacturers and they all offer the following functions:
- An electric motor that starts the engine
- An alternator function that uses the motor as a generator while the engine is running
- A regenerative brake that uses the motor as a generator to recover electric energy from kinetic energy when the brakes are applied
- A mild hybrid system that uses the motor as a drive power source to assist the engine
The mild hybrid functions mentioned here refers to low-part count, low-cost, low-voltage system rather than 100V or other high-voltage systems. The two groups of mild hybrid systems described below have similar structures but have various differences including how they are controlled:
- A) 48V hybrid systems offer power assist of around 10 kW to the engine
- B) 12V hybrid (micro hybrid) systems offer power assist of up to 2 kW to the engine
European manufacturers are developing 48V systems (group A) a turbocharger booster in downsized turbo engines. Nissan and Suzuki are developing low-cost mild hybrid systems (group B).
SuperGen is a 12V system like those in group B but its power assist level falls between groups A and B. It is unique in that it offers two different types of power assist; engine starting and supercharge boosting while driving.
- ① a mild hybrid like those in group B that use the motor to directly assist the engine rotation when the engine starts
- ② an electro-mechanical supercharger that supplements low engine speed pressure boost, which is lacking in turbochargers
Unlike an ISG, SuperGen has two compact motors that are coupled to each other by a planetary gear mechanism. The two motors are coupled to transmit torque when the engine is started, and decoupled while the vehicle is in motion, which allows them to function independently as a generator and a supercharge booster. The selective use of a planetary gear depending on the engine condition is a unique feature of SuperGen.
SuperGen is designed to replace the alternators in conventional internal combustion engines. This will allow OEMs to easily upgrade existing vehicles to mild hybrids.
Table 1 Comparison of SuperGen and conventional ISG for mild-hybrid use
|No. of drive motors||2||1||1|
|Power coupling with the engine||Belt
|Assist mechanism||Traction boost
|Traction boost||Traction boost|
|Assist range||Acceleration, cruising||Stop ~ start||Acceleration, cruising|
|Engine power assist||+4～6kW||～+2kW||～+10kW|
What are the mechanism and structure like?
As explained above, SuperGen selects power assist or electro-mechanical supercharger function by coupling or decoupling two motors. This coupling is not executed by switching the clutch mechanism on and off, but instead uses the planetary gear mechanism, which changes the supercharger speed continuously. Generally speaking, planetary gear mechanisms are characterized by a large reduction gear ratio, provision of strong torque, and the ability for the input and output shafts to be mounted coaxially. A planetary gear mechanism can control the supercharger-compressor shaft continuously and provide ideal power assist for starting the engine that requires a large torque.
In short, a planetary gear mechanism is mounted between motor E1 and motor E2. Motor E1, which is attached to the belt pulley, is connected directly to the outer gear. Motor E2 is connected to the planetary gear and the compressor shaft is connected directly to the sun gear shaft.
- ✔ when motor E2 is locked, the sun gear shaft no longer rotates and the compressor stops.
- ✔ when the outer gear is locked, the revolution of motor E2 causes the planetary gear to revolve, and the sun gear rotates in the same direction at a lower speed.
SuperGen planetary gear mechanism (prepared by MarkLines based on IPPT documentation)
How does SuperGen perform in an actual vehicle?
SuperGen was fitted on a test vehicle and its effect was compared with vehicles that don’t have it equipped.
- Vehicle: D-segment car fitted with a 2.0-liter four-cylinder diesel turbo engine
- Test cycle: 1500 rpm, 6th gear, load increased in steps to full-load
- Test time: 4.0 seconds from starting
- ✔ Fuel economy improvement: Approximately 7%
- ✔Acceleration: About 2x faster in-gear acceleration, reached maximum acceleration in approximately 1 second
- ✔ Speed improvement: Approximately 8km/h (5mph) faster
Fig. 1 Comparison of vehicle speed and acceleration of powertrains with and without SuperGen
Electric Cam Phaser from Schaeffler - Continuously variable valve timing control with an electric motor that enables operation during cold starts
What is the Electric Cam Phaser (ECP)? How is it different from competitors?
Technology for optimizing valve timing based on engine conditions is one function that has become essential for improving fuel efficiency and C02 reduction, reducing hydrocarbon emissions, and raising drivability and output performance. An air-intake valve timing control mechanism (a cam phaser) is used in most modern engines. The early variable valve timing systems that were introduced in the early 1980s controlled the timing in steps. They were replaced by continuously variable valve timing control systems in the mid-1990s.
The Electric Cam Phaser (ECP) introduced by Schaeffler at the JSAE Exposition 2016 offers electric motor control, of the continuously variable valve timing control system rather than hydraulic control.
|Photo 4 External views of electric (ECP) and hydraulic
(HCP) cam phasers
|Photo 5 ECP and gearbox in place (Source: Schaeffler)|
Why is an electric system necessary?
Most of the variable valve control is regulated electrically, but even today mainstream designs are configured so the timing (phase angle) of the variable valve mechanism is changed by moving the helical spline along the camshaft through hydraulic pressure regulated by a solenoid valve, which is directed by a controller. A major drawback of hydraulic control is that is does not provide the stable hydraulic pressure needed for cold engine start, restart, and low-speed operation. As a result of this achieving optimal valve timing control is difficult. To solve this problem, a continuously variable valve timing control mechanism based on an electromagnetic clutch was introduced in 2001 by Nittan Valve Co., Ltd. It was integrated in the VQ30DD engine in Nissan’s Skyline Sedan V35. However, the electromagnetic clutch had a large part count, which led to high costs, and in recent years Nissan had a need for a new continuously variable valve timing control that used an electric motor that resolved this issue.
The ECP developed by Schaeffler met Nissan’s requirements, and it was announced during the Exposition that the ECP will be used in the new VR30DDTT engine that will be equipped in Nissan’s Infiniti Q50.
Table 2 Electric ECP versus conventional hydraulic HCP
|Electric ECP||Hydraulic HCP|
|Cold start (-30degC)
(low HC emissions)
|Restart from idle-stop
|Retarded intake valve closing
(less pumping loss)
What makes the ECP so unique? How does it differ from the conventional products of competitors?
The ECP developed by Schaeffler is not the first ever electric continuously variable valve timing control mechanism. Denso achieved that milestone in 2006. The component that was developed is used in the Lexus LS, and its adoption is increasing steadily. Denso is pursuing the integration of intelligent and electromechanical systems and its electric variable timing system has an electric driver unit (EDU) that is integrated with an actuator. However, its housing projects from the side of the engine’s cylinder head, which inevitably increases the physical size.
Unlike Denso, Schaeffler chose to separate its controller (electric driver unit) from the ECP to keep the driver circuit from being heated and allow for easier installation. The compact gearbox also makes the electric ECP as easy to install as conventional hydraulic systems. The signal coupler and electric power coupler are separated from each other in consideration of electromagnetic susceptibility, and to protect the signal circuit from short faults in the coupler.
Fig. 2 ECP system diagram (electric driver unit) (Source: Schaeffler)
Are there discernible results from electrification?
The results of cold start tests were not reported at the Exposition. However, the waveform at engine start in figure 3 shows that the valve shifted to the cam phase as dictated by the valve timing control before initial combustion of the engine took place after the ignition key was turned on. Figure 4 shows the relationship between the engine speed and the cam phasing velocity of the electric cam phaser (ECP) and the hydraulic cam phaser (HCP). As the graph shows, the phasing velocity of the HCP drops in low ranges due to decompression, but rises again as the engine speed increases. In contrast, the ECP maintains necessary cam phasing velocities from the idling range (500rpm) through high ranges (over 4000rpm).
Fig. 3 Cam phasing behavior of ECP at engine start(Source: Schaeffler)
Fig. 4 Cam phasing velocity vs. engine speed(Source: Schaeffler)
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