Hacking Honda’s Insight for Fun and Efficiency
By Bill Moore
When self-taught microprocessor programmer Mike Dabrowski bought his Honda Insight gasoline-electric hybrid he suspected Honda had rushed it into production to beat Toyota to the U.S. Market, which meant they may not have taken the time to fine-tune their control code.
As he approached the end of his 80,0000 miles or 8 year warranty on the Insight's hybrid drive system, he started discussing his ideas with others on the InsightCentral.Net forum how it should be possible to improve the car's performance.
At the urging of a fellow Insight owner in Canada, Dabrowski decided to develop his own circuitry and algorithms that would -- in theory, at least -- allow the driver to pick up where Honda's engineers left off. The result is a prototype kit that includes a LED display, a joystick, circuit board and wiring harness to integrate into the stock Insight electrical system.
Does it work? The winner of the modified hybrid category in the Monte Carlo-style rally at this year's Tour de Sol, Brian Hardegen of Pepperell, MA, demonstrated 93.5 mpg over the 150 mile-long course that wound through the picturesque countryside around Saratoga, New York using one of Dabrowski's early prototypes. And according to the Connecticut-based engineer, the eight people using the early development versions are seeing, on average, a 15 percent improvement in fuel economy. Hardegen -- who is Dabrowski's cousin -- reports that his daily commute performance has gone from 70-80 mpg to 90-100+ mpg.
So, what's the secret?
Dabrowski named his system MIMA, or Manual Integrated Motor Assist, an obvious reference to Honda's own acronym, IMA. And in talking with him, it is obvious that this is a collaborative effort, akin to the Open Source movement where software is created and modified by numerous volunteer contributors, usually via the Internet; a phenomenon that automakers are going to have to account for -- and work with -- as their cars become increasingly electrified and computer controlled.
Unlike the plug-in Priuses developed by EnergyCS and CalCars, MIMA makes use of the Insight's standard 144 volt battery pack. Since the Insight doesn't have the ability to operate in an electric only mode, the driver is dependent on Honda's control codes to determine when to engage the electric drive and when to apply regenerative braking. The gasoline engine runs continuously.
What Dabrowski has done is allow the driver to tell the car when to utilize electric power and for how long. He explained that, typically, Insight drivers can "feather" the throttle while cruising on a flat stretch of road and get 100 mpg, but as soon as they come to a hill, that drops to 45 or so mpg and eventually the electric drive kicks in to help get the car over the hill.
"With MIMA you have no need to step down on the throttle control. You have a manual joystick that can engage the electric drive at will at any level. So, you're cruising along at 100 mpg, you come to a small hill and you've got plenty of battery charge, just push forward on your joystick a little bit, the electric assist comes in, you go over the hill, you never drop from 100 mpg down to 50. You stay at 100 for the whole trip".
Dabrowski noted that there are obvious limitations to this because of the size of the Insight's NiMH battery pack. You won't be able to crest a long series of hills without depleting the pack, but this is where MIMA comes into play again, because it enables the driver to also control the amount of regenerative braking (regen) up to the Insight's maximum of 50 Amps.
|He pointed out that in the typical Insight, you have to apply the brakes to get even a tiny amount of regen, say when coming off a freeway off ramp. The joystick allows the driver to apply regen with the flick of the thumb even while still having your foot on the accelerator.|
While the Insight's engine will continue to run, he said it's possible to drive around a parking lot controlling the vehicle's speed with the joystick alone, a feature roughly analogous to Toyota's Hybrid Synergy Drive "stealth" mode running on electric power only.
Affordable 'Heath Kit'
Dabrowski began work on the circuitry last Spring, finishing just before the Tour de Sol in May, 2005. He is currently redesigning the circuit board so that it can be assembled by the average electronic hobbyist. He calls this the "Heath Kit" approach after the old amateur short-wave radio manufacturer that offered buyers a kit to save money by assembling the finished kit themselves.
He anticipates the kit will sell for $425 instead of the $650 the finished version will cost. Because these are prototypes, users are mounting the joystick in different locations including to the shift lever and parking brake. Ideally, Dabrowski thinks it should be mounted on the steering wheel like cruise control, but that would require some sort of wireless communication between the input device and the control board, an unnecessary complication at the moment, but one that he plans to eventually pursue.
His first couple of customers drove to Connecticut to have their units installed over a weekend, allowing Dabrowski to get more quickly over the top of the learning curve on how to quickly and safely install the unit since it requires opening high voltage panels Honda cautions against doing.
He now has complete, step-by-step instructions on his web site on how to perform the modification and he says that so far the other handful of installations haven't resulted in any major problems.
It starts by removing the rear deck carpet, pulling out the storage well and ignoring the warming sign that says if you open this panel you will be killed. Next you throw the kill switch that turns off all high-power components and wait 5-10 minutes for everything to safely discharge. Then comes, in his words, the "hairy part": unplugging all the connectors and removing all the black electrical tape from around the wiring harness.
Next, you fish the harness that comes with the kit through the shift level and parking brake tunnel into the battery compartment, as well as removing the ECM (engine control module) from under the passenger's side of the dash.
At this point, you begin to strip, splice and solder 15 different connections, each of which is identified on the web site. Once that's done, you mount the LCD display forward of the shift level under the dash. The actual control circuit board mounts under the shift level cover using an existing bolt hole.
The system is tested using two independent diagnostic signals Dabrowski engineered that mimic those generated by the car. If everyone works, you rewrap the harness in electrical tape, seal up the high voltage panel, replace the trunk well and re-lay the carpet.
The obvious next question is, what does this do to the life of the battery? Considering that his system has been installed on less than a dozen cars for less than a year, it's probably premature to say the effect will be, but Mike has taken precautions to make sure the health of the battery is respected.
For example, he noticed while reverse engineering Honda's system that its two battery cooling fans will turn off when the car is stopped even when the battery is hot. He suspects this was a marketing decision so drivers wouldn't hear it running when they were in auto-stop mode. He added two temperature sensors, one for the control electronics and one for the battery, that automatically turns on both fans "full blast" when the temperature gets above 95 F (35C).
Dabrowski told me that the decision as to whether or not to install the kit while the car is under warranty is entirely up to the owner. He waited until his was out of warranty, but he has one unit that an owner in California installed in a brand new Insight. He noted that unless you know what to look for, his modifications to the wiring harness are difficult to spot. And the visible pieces of the system -- the LCD display and joystick -- are easily removed when its time to take the car in for service.
"I think would be smart to look at this very carefully" he observed, "in order to improve their cars and to give them some competitive advantage".
As for installing the kit, he said his qualifier is that if you don't have a roll of black electrical tape in your tool kit, then don't try to do it yourself. Beyond that, he thinks any auto electronics shop that does after-market installations of GPS systems, for example, should be able to follow his instructions and safely install the kit. The main criteria is being able to solder small wires.
"Most people who haven't done any soldering tend to overheat the connections, not apply enough solder, apply too much solder, that type of problem".
He also thinks it's possible to use telephone-type crimp connectors where you put the stripped ends of wires into the connector and squeeze them tight, but he thinks soldering is the more reliable method.
He cautions that its very important to make sure the 20 wires that are part of the install are properly connected and tested before the car is turned on because if they aren't it's possible to do a great deal of expensive damage to the vehicle.
Besides offering to be available by telephone to consult on any installations, he's also planning to offer everyone who buys the "Heath Kit" version the option of sending the completed circuit board back to him to have it tested for an additional $20.
How About Civics?
Owners of Honda Civic Hybrids and the newer Accord Hybrid won't be able to use the kit because these newer versions of the IMA drive use serial communications protocols based a special computer language developed by Honda engineers instead of the logic protocol used in the Insight. The system would be much more difficult to hack into because just looking at the signal doesn't tell you its function without knowing the underlying code.
"It's like trying to understand a foreign language without any reference books", Dabrowski said. He added that if Honda were willing to cooperate and supply him with the necessary support, it would be a "piece ‘a cake" to adapt MIMA to these newer models.
He explained that today's cars rely on the MAP (Manifold Absolute Pressure) signal to manage the emissions and performance of the engine based on the voltage detected by the system. The more power requested, the higher the MAP voltage. The less power needed, the lower the voltage. The typical range might be 2.8 to 0.5 volts respectively. The Insight's MPG indicator is fairly close approximation of the MAP voltage. Knowing this is important because this is how you manually set the operating parameters of the MIMA system.
Dabrowski took pains to explain to me exactly how the programmable version of MIMA, called PIMA, works.
"PIMA uses the engine load sensitive MAP signal to determine when to turn on assist or regeneration. This allows one to drive using only the throttle as the control. The assist activation point is set for say 95 MPG, and the regen is set for say 115 MPG, as long as the engine load is between those two points, the IMA is off, and no charging or assist will happen. If you come to a hill, and step down slightly on the gas making the MPG drop to 95MPG or less, the assist will begin to activate, and help climb the hill, the more you step down, the more the assist helps up to the maximum 13 HP or 100 A, with full assist by the time the MPG is at 80 MPG. Without PIMA, the MPG would have to drop to 40-45MPG before the assist would fully activate. The regeneration works in the same way, as the MPG raises over the regen activation point on a down hill run, the regeneration begins to recharge the battery, the higher above the activation point the MPG goes, the more regeneration you get, up to the limit of 50A of charge. Adjustments to the assist and regeneration activation points are easily made by jogging the joystick while driving".
He doesn't intend to be the sole developer of this system and is willing to share his source code with other engineers and to sell them at a discount the assembly language software that compiles the code.
I should also point out that Dabrowski requires the prospective owners to sign a comprehensive waiver of liability and transfer of ownership before they can buy the system, as controlling the electric motor with add-on circuitry can present some potential risk which the owner must assume.
I still have about 40,000 miles to go on my warranty, so I probably won't be opting to modify my Insight, but Mike assures me that by the time I am, the system will have evolved and improved. Whatever happens, it is exciting to see how collaboration and human ingenuity can take even the best system and improve it.