2003 Honda Civic Hybrid -- Powertrain - IMA - Transmissions

2/6/2002 2:36:52 PM

System Overview
The new, more advanced version of Honda's patented Integrated Motor Assist (IMA) system represents the second generation of IMA technology from Honda. The new IMA system uses technology that delivers increased performance and provides enhanced packaging flexibility within the vehicle.

Primary motive power for the Civic Hybrid is provided by the system's 1.3-liter i-DSI gasoline engine. Although the engine alone provides sufficient driving performance, even in sustained uphill driving, the electric motor mounted between the engine and transmission provides power assistance under a broad range of conditions, such as initial acceleration from a stop. And since the electric motor is used only for power assistance and not for primary motive power, it too can be made smaller and lighter (along with the batteries) compared to the full-size traction motors in other hybrid systems.

As the IMA gasoline engine enters its cruising operating range, the electric motor assist has a minimal role and the engine supplies the power required. Power for the electric motor is mainly generated by capturing energy from the forward momentum of the vehicle rather than from the gasoline engine. When the Civic Hybrid is coasting or its brakes are applied when the engine is in gear, its electric-assist motor becomes a generator, converting forward momentum (kinetic energy) into electrical energy, instead of wasting it as heat during conventional braking. Energy is stored in the system's NiMH battery pack located behind the rear seat in the trunk. If the charge state of the IMA battery is low, the motor generator will also recharge while the Civic Hybrid is cruising.

Engineering Goals
The engineering goals for using the second generation IMA system on the Civic platform included increasing total power output of the system, increasing the regenerative braking capability and making the overall package smaller. The end result of the IMA development process is performance similar to a Civic LX sedan with the 1.7-liter engine, yet the Civic Hybrid has a 1.3-liter engine. Additionally, the IMA batteries and related components utilize minimal cargo space in the trunk, leaving room for items such as two large pieces of luggage or a baby stroller.

IMA Technology Highlights

  • Ultra thin DC brushless motor provides 30 percent more efficiency.
  • The volume of the Intelligent Power Unit (IPU) has been reduced by 42 percent compared to the system used in the Insight.

Technological Advancements
Several key technology advancements have occurred to enable engineers to extract more power out of a smaller IMA package. Compared to the Insight, the major areas of improvement to the IMA system involve the decreased size of fundamental components such as the IPU, PCU, motor electronic control unit, energy storing system, IPU cooling system and the merging of major components into a centralized Intelligent Power Unit (IPU).

  • New winding methods for the electric motor wire result in greater wire density within same space.
  • Within the IPU, the combination of the inverter and pre-driver results in a 28 percent weight savings and a 39 percent volume savings.
  • Used in the inverter, new high-density silicone wafers contribute to 25 percent less heat loss.
  • A new cooling system combines two fans into one while consuming 85 percent less energy to cool both the battery and the PCU, resulting in a 32 percent weight reduction and a 20 percent volume reduction for the cooling system.
  • Battery module has reduced resistance and reduced energy losses, which has improved output density by 23 percent. More welding points between the pole plates and current collector plates contribute to this improvement.

Electric Motor
The 13-horsepower, 144-volt ultra thin DC brushless electric motor's function is to boost the output of the ultra efficient gasoline engine in order to provide powerful acceleration. The electric motor does not provide primary motivation, and in fact, the Civic Hybrid will continue to operate with reasonably good performance on the gasoline engine alone.

The performance characteristics of the electric motor, which has a width of 2.55 inches (65 mm), results in high amounts of torque across a wide rpm range with peak torque available at 1000 rpm (46-lb.-ft @ 1000 rpm). It produces a peak of 13 horsepower at mid range engine rpms. The gasoline engine excels at providing horsepower at higher rpms, and in the case of the i-DSI engine, it supplies reasonably good torque, too. The most significant contribution the electric motor makes to the overall performance of the vehicle is it adds significant amounts of torque at lower rpms.

The electric motor is positioned between the gasoline engine and the transmission. The output shaft of the engine connects directly to the electric motor and the output shaft of the electric motor attaches directly to the transmission. The electric motor and the gasoline engine always turn in tandem since they are connected together.

Intelligent Processing Unit (IPU)
The Intelligent Processing Unit (IPU) is the nerve center that controls the power of the IMA system. The IPU houses the Power Control Unit (PCU), motor Electric Control Unit (ECU), energy storage module (battery), and a compact cooling system.

The battery box is located inside the IPU. The battery box's dimensions measure 495mm x 372 mm x174 mm for a volume of 26.8 liters (a volume reduction of approximately 30 percent compared to the Insight) and it weighs 63 pounds (a reduction of approximately 6 percent compared to the Insight). The battery system is comprised of 120 individual 1.2 volt cells for a total battery system output of 144 volts and a capacity of 6.0 AH. The warranty for the battery is 8years/80,000 miles.

Automatic Idle Stop
The Civic Hybrid automatically turns off the gasoline engine during complete stops under most circumstances. This feature allows the Hybrid to use even less fuel and emit fewer emissions than an ordinary car at stop lights and other traffic conditions where the car is not moving. The system uses the electric motor to re-start the engine. The Idle Stop feature is not activated during the first few minutes of engine startup or if the automatic climate control system is being used in air conditioning mode and "Economy Mode" is not selected.

5-Speed Manual Transmission
One model of the Honda Civic Hybrid is available with a 5-speed manual transmission. Special features unique to the Hybrid manual transmission compared to other Civic sedan and coupe models include a specially developed clutch to accommodate the IMA system regeneration capabilities, a double cone synchronizer in both first and second gears and optimal gear ratios that maximize performance and economy.

This 5-speed manual transmission was originally designed for the 2000 Honda Insight. In order to accommodate the Honda Civic Hybrid, the clutch size, gear ratios, case housings and shift lever were redesigned to offer the refined gear change feel of Civic sedan and coupe models.

Automatic Continuously Variable Transmission (CVT)
First introduced on Honda products in 1996, the automatic Continuously Variable Transmission has been in use on Civic HX coupes for two model generations, plus it became available on the natural gas-powered Civic GX and the Insight for the 2001 model year. The CVT's unique stepless shifting system is smoother than a normal automatic transmission with a torque converter, and there is less torque loss - meaning the engine's output characteristics can be fully transmitted. There is no gear shift shock (it provides a seamless feel) and the acceleration is smooth while fuel consumption is reduced. The CVT can change the "gear" ratio from 2.367:1 to an overdrive level of 0.407.

The CVT transmission used in the Civic Hybrid (derived from the Insight) has been enhanced with the addition of increased torque capacity and increased overall efficiency.

CVT Improvements:

  • Improved torque capacity (5 percent improvement).
  • Compact design (20 mm less width).
  • Improved hydraulic controls on clamp and pulley systems.
  • New deceleration feedback control for increased regeneration.
  • Facilitates seamless integration of cruise control.
  • New lining material incorporates carbon fiber for the starting clutch.
  • Overall changes result in improved start feel and more precise movement within the transmission.
  • Creeping Aid System minimizes the car from rolling backwards from a stop on steep hills.

How it works…
The CVT system works by varying the position of a high-strength steel belt between two metal cones under high pressure - one cone connects to the power input of the transmission and one cone connects to the power output side of the transmission. Through various guides within the transmission, the belt can occupy any position between the two cones to create the most suitable gear ratio for any vehicle speed and throttle input.