Comparison of 4WD Hybrid Systems from 8 Japanese and German OEMs
Automotive World Nagoya 2019: Subaru’s original HEV system, e-BOXER
Automotive World Nagoya 2019 (period: September 18th to September 20th, 2019, venue: Portmesse Nagoya), the second year for the event, saw the participation of many exhibitors from the Chubu region. The exhibition hall is slated for expansion, indicating an increase in expected participation from other regions in the future. During the event, a number of prominent companies delivered keynote speeches, including five domestic OEMs, two foreign OEMs, and four mega-suppliers. The voices of these global corporations echoed throughout the venue, facilitating many connections with companies from the Chubu region, and providing one of the key reasons for the event’s existence.
This report will cover the lecture on Subaru’s original hybrid system, the e-BOXER. Moreover, this report also features a list of 4WD hybrid systems from Japanese and German automakers to highlight the e-BOXER’s unique capabilities.
|Photo of Automotive World Nagoya 2019’s EV・HEV drive system technology exhibition.||Exhibition of xEV components|
(Photographed by reporter, the same hereinafter)
Overview of the 2nd Automotive World Nagoya 2019
Portmesse Nagoya (hereafter referred to as Portmesse) first opened in 1973, with completion of the First Exhibition Hall making it the central trade show venue for the Chubu region. The facilities were later expanded, with the first through third exhibition halls and main hall completed in 1993. The Nagoya Automotive Engineering Exposition, hosted by the JSAE beginning in 2014, and the automotive industry trade show Automotive World, hosted by Reed Exhibitions Japan, launched in 2018.
Roughly 400 exhibitors gathered at Portmesse’s 20,000 square meter venue from September 18th-20th, 2019. The event used the second and third exhibition halls, as well as the event hall and main hall. Compared to the event held in Tokyo (venue: Tokyo Big Sight), which had an area of 98,000 square meters and 1,000 exhibitors, it is clear that the event in Nagoya was smaller and denser in scale.
- Exhibitors: Exhibitors at Automotive World Nagoya were primarily composed of Tier 2 and Tier 3 manufacturers, startups, and production/testing equipment sales companies based in the Chubu region, with few automakers and EV component makers in attendance with the exception of TOP, Subaru’s motor manufacturer. Portmesse is scheduled for further expansion, and the event is expected to grow in size accordingly, with a wider range of exhibitors in attendance.
- Keynotes and Special Lectures: Many lectures by domestic and overseas OEMs and mega-suppliers were held at the event hall and at Takeda Teva Ocean Arena, located adjacent to Portmesse.
German OEM Electrification Strategies, Including EV Product Timelines（Oct. 2019）
Powertrain for Passenger Vehicles in 2030 - For ICE Survival （Jul. 2019）
EV Powertrain Technologies: New powertrain units using Toyota’s THS II electric motor （Jun. 2019）
JSAE 2019 in Yokohama: Displays of six automakers, including PHEV technologies（Jun. 2019）
Automotive Engineering Exposition 2019: Showcase of various xEV drive technologies （Jun. 2019）
Automotive World 2019: Innovations in xEV drive systems（Feb. 2019）
Subaru: 42% operating profit decline forecasted for FY2018 due to sales decline and recall expenses （Jan. 2019）
Automotive World Nagoya 2019 reports:
High-Performance Sensing Technology for Fully Autonomous Driving（Oct. 2019）
4-wheel drive hybrid system (comparison of 8 systems from Japanese and German OEMs)
An explanation of Subaru’s hybrid strategy was featured as part of the special lectures. Before breaking down the major points of the lecture in the next section, this section will summarize the unique qualities of Subaru’s technology in comparison to other companies' systems.
When compared to practical 4WD systems that can be driven in EV mode (see chart below), it becomes clear that Subaru’s e-BOXER has a particularly low motor output. While the system chart appears complex, the only additions to gasoline engine vehicles are MG (motor and generator) and C2 (clutch 2).
Moreover, Subaru’s PHEV differs from Toyota’s THS by having rear wheel drive power distributed after combining engine and motor power. This system allows manufacturers to apply their gasoline engine vehicle expertise to 4WD mechanisms, with German automobiles widely adopting this configuration.
Comparison of 4WD hybrid systems
|OEM||Drive System Diagram (Battery Omitted)||Maximum Motor Output||Feature|
|This model is based on a gasoline engine vehicle (chain CVT) with the addition of a small motor MG, C2, and a small battery. The system minimizes cost while maximizing hybrid efficacy.|
(CROSSTREK, XV for US market)
|Toyota's electric CVT (Pl) is introduced at the core of the system. Driving force is distributed to the four wheels after combining power from En + MG (different from Toyota).|
|Toyota||Front 88 kW
Rear 40 kW
|Gasoline engine vehicles use a unique 4-wheel drive system, but hybrid vehicles use a method that simply adds an MG to the rear wheel.|
|Nissan||Front 80 kW
|With large battery power storage, SHEV:
power transmission via generation→storage→discharge has low efficiency with mechanical transmissions, but allows for the engine to be driven at a standard load, increasing overall efficiency.
|The hybrid effect is small when the amount of electricity stored is small:
The Note has a particularly small battery; when the amount of electricity stored is small, engine output greatly changes depending on drive load. Thermal efficiency decreases as a result.
|Combining SHEV mode (the combination of G and MG) and engine drive mode will be Honda's standard in the future. Under engine drive mode (C1 engagement), G is idle, and when charging is required, it is conducted with MG, which powers the wheels.|
|Mitsubishi||Front 60 kW
Rear 70 kW
|Alternating between stopping the engine and driving under standard torque eliminates the need for an engine transmission.|
|A uniquely BMW approach. Constantly powers the rear wheels while switching from 2/4WD by distributing power to the front wheels (MINI and derivative models incorporate a different method).|
|Daimler's 4-wheel drive system mainly has a front-wheel-drive system (similar to VW) as well as a full-time system that constantly distributes torque to the front and rear wheels. The GLC is equipped with the latter system.|
|While VW has a system similar to BMW's, its system primarily drives the front wheels. Additionally, the automaker uses a unique DCT (known as DSG) in lieu of an automatic transmission.|
(Source: Created by reporter)
Pl: Planetary transmission mechanism
Tc: Torque converter
Re: 1-stage reduction gear (multi-stage gears for AT and DCT)
SHEV: Series Hybrid (hybrid systems that use an engine exclusively for power generation)
The appeal of Subaru’s e-BOXER electrification technology (summary of the lecture given at Automotive World Nagoya 2019)
|The keynote speech, titled "e-BOXER Electric Technology, Borne from a Commitment to Customer Value," introduced the automaker's unique HEV system technology.|
e-BOXER, Subaru’s original hybrid system, is a product built in response to actual customer feedback regarding 4WD vehicles. It is also an example of applying the Subaru Way, based on the company’s “STEP” slogan, to the new mid-term management vision for electric vehicles. The Subaru Way is the automaker’s customer-oriented product development policy aimed at providing safety, spaciousness, and driving pleasure.
Safety: Improving the safety of electric systems
Subaru fixed the system voltage for its EV drive mode (excluding vehicles designed specifically for evacuation purposes) at 118 V, the lowest voltage of all EV systems, aiming to meet the necessities of real-world demands rather than focusing on electric power. Additionally, the area around the battery pack is reinforced to reduce the risk of fires and harmful substance discharge caused by mechanical abuse (impact deformation, etc.) of the battery. In particular, rear automobile collisions with thin poles are a major real-world risk for battery deformation, leading Subaru to carefully design and conduct evaluations under this collision model.
Spaciousness: Securing passenger space with small components
Subaru designed incredibly compact electrical components while still maintaining practical functionality. Specifically, the automaker used a 10 kW motor, which is remarkably small for vehicles capable of EV drive, as well as a low voltage battery (118 V) with around 1/2 to 1/3 the voltage of its competitors, greatly reducing the number of cells. Additionally, Subaru incorporated a variety of ideas into its electric oil pump, an essential component of its EV system. As a result, the motor was built into the transmission, securing foot space in the front seat. By compactly integrating the battery under the floor of the trunk, the automaker was able to secure minimum ground clearance and luggage space.
Driving pleasure: A sense of driving freely with excellent vehicle responsiveness
Subaru carefully considered the placement of heavy electric components, suppressing adverse effects on drivability. The added 110kg of weight was split, with 50 kg going to the front wheel and 60 kg to the rear, lowering the center of gravity by 1% compared to gasoline engine vehicles. Platform rigidity was also improved, with roughly a 100% improvement in bend resistance and 40% improvement in twist resistance.
Meanwhile, the system’s highly responsive motor greatly affected acceleration/deceleration behavior. For example, with gasoline engine vehicles, when accelerating and decelerating alternately while climbing a staircase-like road, delays in output response cause pedal operation overshoots, resulting in intense pitching (forward and rear movements) of the vehicle. By using a responsive motor during climbs, vehicle pitching is minimized.
With its many features, the e-BOXER was positively received by the market. While Subaru originally planned for sales of 70% gasoline engine vehicles and 30% e-BOXER vehicles, sales of the latter have actually reached 42%. e-BOXER separates itself from electric drive systems that focus on complying with regulations. Commitment to customer value and a design aligned with real-world demands may be key reasons for the positive reception.
Features of Subaru's electric drive system
Subaru currently has two hybrid systems: a PHEV system based on technical licensing from Toyota, sold in North America since 2018, and its e-BOXER system, developed and sold since 2013 (the e-BOXER name was coined for the system after 2018). Both systems have unique characteristics that differentiate them from the systems of other automakers (see the chart in the previous section).
While the e-BOXER system is popular among the driving public, the PHEV system is also an indispensable product in Subaru’s strategy to respond to markets with regulations mandating the use of grid power. The characteristics of the various systems are outlined below.
|A compact motor is built into the transmission casing. The protrusion is incredibly small compared to transmission casing in gasoline engine vehicles. The battery is also compact, and the rear end of the battery is retracted from the rear end of the vehicle, improving safety in the event of rear-end collisions. (Source: SUBARU)|
Subaru’s original e-BOXER
The 10kW motor lacks sufficient power for electric driving, and EV start speed is particularly slow. In addition, the regenerative energy of the brake exceeds 20kW at maximum speed reduction during EV mode driving. The motor cannot absorb this energy. However, Subaru decided not to consider infrequent use cases, opting for an extremely small motor and battery. The result was improved vehicle fuel efficiency, mobility, and safety at a reduced price, providing significant merit for domestic users.
The ideas were incorporated into the electric oil pump, as mentioned during the lecture.
- When driving at low speeds, the mechanical oil pump is driven from the wheels even when the engine is stopped, eliminating the need for an electric pump.
- While an electric pump is required at extremely low speeds or when the vehicle is stopped, a 100V drive high-performance electric pump is included in the same space as that of a gasoline engine vehicle.
PHEV system based on technical licensing from Toyota
The PHEV system, based on technology licensed from Toyota, was featured in the North American model Crosstrek (Japanese model name XV). While major components incorporate Toyota technology, Subaru independently decided motor generator placement and 4-wheel drive composition.
|The engine and transmission unit, seen from four angles. Note the boxer engine’s short stature, with negligible height difference compared to the transmission. Subaru also employs unique vehicle packaging in comparison to Toyota vehicles.|
Electric, HEV, PHEV, 4WD, SUBARU, e-BOXER, Battery, Traction Motor, Generator, Reduction Gear, Engine, Transmission, Clutch
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