Incorporating Tesla technology into the DeLorean comes with design and engineering challenges.
The Tesla Model S was designed ground up as an electric vehicle and thus could accommodate design and engineering choices that are not available to a converted car. For example, the Tesla battery pack is attached to the bottom of the passenger cabin - in a flat slab like configuration - which also gives the Model S its excellent handling capability. Using the battery as-configured in the Model S, but in an ICE conversion is essentially impossible with significant deconstruction and rebuilding. The sections below will describe and provide rationale for the design choices selected for the TesLorean. In many cases, the design and engineering selections are compromises seeking to balance space, weight, usability, maintainability, reliability, complexity, cool-factor, and cost (in no particular order).
Table of Contents
- Drive Unit
- Brake Assist
- Power Steering Assist
- Air Conditioning System
- Heating and Cooling
- DC-DC Converter
- Steering Controls
- Drive Computer
After looking at dedicated EV conversion motors (e.g. NetGain Motor's Warp9) and all manner of hybrid and battery electric vehicles from OEMs, and considering the design implications of each in depth, I landed on Tesla as the target motor. There was just one problem - size. The rear motor on the early Tesla Model S cars was approximately 32 inches wide. While the large Tesla motor had very desirable performance characteristics, fitting the motor into the engine bay of the DMC-12 would have meant a complete removal and custom rebuild of the rear frame and rear suspension. This would have been a massive undertaking involving not only safety critical fabrication, but also would be likely to alter the driving characteristics and look of the DMC-12. With the stated goal of keeping the DMC-12 externally unchanged (at least to the casual observer) I needed to find an alternative solution. I briefly considered re-configuring the Tesla drive unit to position the motor length ways in the engine bay, but each change introduced innumerable new complications which detracted significantly from the beauty of using the Tesla motor. Then came along the Tesla 'D' - for dual motor. The front drive unit on the first dual motor cars was significantly smaller than the rear drive unit. It was also less powerful, but still a substantial upgrade to the DMC-12's 105HP at the wheels. When the 70D and 90D were released in mid-2015, the front and rear drive units became identical (the large rear motor preserved for the 'P' performance versions). The new dual motor configuration has two 259HP (*battery limited) drive units on each axle. The 70D drive unit is approximately 12 inches narrower than the prior large rear drive units. The rear motor also positions the single gear transmission just in front of the main drive unit assembly (motor and inverter). The reduced size and transmission output shaft configuration meant that the drive unit could fit in the existing DMC-12 engine cradle and the driveshafts would come from essentially the same position as they do from the stock DeLorean transmission. Using the 70D drive unit meant avoiding a significant redesign of the rear frame and suspension and being able to also remove the stock DMC-12 transmission - saving further weight. Custom driveshafts will connect the output from the Tesla 70D transmission to the DeLorean rear hubs and wheels. To the casual observer the rear arrangement of the car should remain unchanged from stock.
Many cars (actually almost all cars, including early Tesla Model S cars) have a device called the brake booster which enhances the force of the driver pressing on the brake pedal. Even try to press the brake pedal in a car without the engine running, it's hard! The brake booster uses vacuum (energy) generated by the ICE (internal combustion engine) to assist the driver pressing the pedal. An ICE is constantly 'sucking' air in (to combine with fuel in combustion) and this sucking or vacuum can be used in other parts of the car. For example the DeLorean's climate controls use vacuum to operate the various doors and flaps that direct hot and cold air onto the passengers. Electric cars have a problem with electric motors motors do not generate vacuum. So to supply vacuum to the brake booster, they have in the past run a vacuum pump. A simple pump creates vacuum by oscillating a diagram and push, pull air through one-way valves. These pumps can be noisy and consume energy to initially create and maintain a vacuum. The vacuum created is provided to the standard brake booster device. If the driver is doing a lot of braking in a short time, they may consume more vacuum than the pump can provide, so the system in electric cars will include a vacuum reservoir - essentially just a container kept at low pressure (lower than atmospheric pressure). The vacuum pump will run as much as necessary to keep the reservoir at the desired pressure. The TesLorean will be fitted with the iBooster from the Model S 70D with autopilot. Bosch designed the iBooster to solve problems related to electric vehicles and vacuum service. The iBooster does not use vacuum, rather it electrically detects the driver pressing the brake pedal and then uses an electric motor to assist. The iBooster only consumes energy when the driver presses the brake pedal. At all other times the iBooster only consumes a small standby current. The iBooster is also nearly silent drawing on an electric motor to assist. Fitting the iBooster in the TesLorean has some challenges, but the iBooster is smaller than the stock brake booster and master cylinder. The booster will need a spacer to ensure the brake lever interfaces with the DeLorean brake pedal. The DeLorean brake booster is offset by nearly 5 inches from the firewall due to the positioning of the hydraulic clutch. The clutch is no longer required in the TesLorean allowing the iBooster to be easily positioned - once the bolt pattern is accommodated.
The stock DeLorean does not come with power steering. DeLorean fans will tell you that since only 40% of the car's weight is on the front wheels that power steering is not necessary. A more likely explanation is that power steering in a rear engine car would have necessitated a power steering pump at the rear of the car (to use the engine rotation) and high pressure hydraulic lines running to the power steering rack at the front of the car. It would also have consumed additional power in an already under-powered car. Practically speaking driving the DeLorean at low speed feels like arm day at the gym. You have to haul (sometimes with both hands on the same side of the steering wheel) to pull the wheel around and effect a turn. Steering compromises when you can change gears or do other things. The DeLorean needs a power steering solution. There is an electric power steering solution available from DMC-EU (Europe). It replaces the stock steering column, with a new column that includes an electric motor in the driver's foot-well. It draws 12v electric power to assist the driver's steering motions only as needed. The kit currently exceeds $3000 in cost, before including fitting. The TesLorean will have a custom solution created from a readily available GM or Toyota power steering assist motor. At the firewall the DeLorean steering column connects to a linkage (including 2 u-joints) that runs directly to the steering box. The custom solution replaces the link and u-joints with a motor, an anti-vibration u-joint and other u-joints. The multiple u-joints allows the steering column to still adjust up and down, and for the motor to be flexibly bracketed out of the way of the brake lines. This solution keeps the stock steering column and stock steering box and only replaces u-joint linkage between the two. The unit requires a speed sensor (to reduce assistance as speeds increase) which is captured by a sensor installed in place of the lambda counter in the drivers foot-well in-line with the speedometer cable. The Tesla Model S does have an electric assist power steering rack, however the unit is too large to fit into the frame channel that contains the DeLorean steering rack.
TheDeLorean stock AC system used R-12 refrigerant which is now difficult and expensive to get supplies of. R-12 was phased out in the US and in Europe to protect the ozone layer. It was replaced with R-134a, still currently used in the US but being phased out in Europe in favor of R-1234yf due to climate change concerns. The stock DeLorean system had a compressor in the engine bay, with long AC hoses (high and low pressure) running under the body (alongside the frame) to forward of the passenger cabin. The passenger side wheel well contained the AC hub, the accumulator, and links to the condenser and evaporator. The design for the TesLorean maintains the components in the AC system apart from the compressor and the hoses. The AC hoses were replaced due to age with hoses capable of carrying R-134a. The compressor from the Tesla Model S will replace the DeLorean compressor which was belt driven from the engine. The Tesla compressor is an efficient scroll design and is operated by an electric speed controllable motor. The compressor will be relocated to the front of the DeLorean (from the engine bay) to shorten the high and low pressure hoses and bring the system closer to the other AC components.
The stock DeLorean passenger cabin is heated by coolant heated by the engine. Once the engine reaches a given temperature, and the driver selects a heat setting, a vacuum operated value opens and directs hot coolant to the front of the car and into the heat exchanger located in the airbox inside the passenger cabin. A small electric fan blows air over the heat exchanger, warming the air circulating inthe cabin. Coolant is then routed back to the rear of the car to be reheated by the engine. The TesLorean design will use the Tesla PTC Heater. The PTC Heater creates cabin heating electrically using high-voltage (i.e. 400v). From desktop inspection itappears to have 6 heating levels. The Delorean heater core will be removed from the car and the airbox rebuilt to accomodate the Tesla PTC heater (which is larger). The instant heat from the PTC heater will provide for window defrosting - an important safety concern. The TesLorean design will use the coolant system to maintain the battery and drive unit within a suitable temperature operating range. The system includes a coolant heater and a coolant chiller, as well as a radiator. The TesLorean will also use the coolant chiller from the Tesla. The coolant chiller uses compressed R-134a from the air compressor to chill (or reduce the temperature of) the circulating coolantby means of a heat exchanger . This can help prevent the temperature of the coolant from getting too hot, especially if the car is not moving sufficient air over the radiator or the ambient air is not cool enough, for example on a very hot day in the middle of summer, or if the car is charging and the charger and battery require cooling.
The DeLorean electrical systems are only 12v systems. The battery provides 12v for starting the engine and as a 12v buffer as energy demands vary during driving. The alternator is located in the engine bay, linked to the engine rotation by belt. The TesLorean design will maintain all of the existing 12v DeLorean systems, however the alternator will be replaced by the Tesla DC-DC converter. The converter takes in DC high voltage from the main battery pack (in this case 400v) and outputs 12v for use by the low voltage system. The design will maintain a 12v lead acid battery to continue to act as a buffer for 12v energy demands during driving.The Tesla DC-DC converter will be included in the coolantloops as the unit produces heat as a byproduct.
The steering wheel and steering column sit inside the passenger cabin and comprise the steering controls. Once through the firewall there is the steering linkage, the steering box, and steering rackwhich connectsto the front wheels. The DeLorean steering wheel can be adjusted up/down, and in/out. The up/down movement requires loosening a wheel at the side of the column, adjusting the height and re-tightening the wheel. The in/out adjustment is achieved by lifting a lever at the side of the column. There are no controls (buttons) on the steering column itself. The horn is activated by pressing on the end of the left steering column stalk. The Tesla steering column is adjusted up/down and in/out though a small joystick like control at the side of the column. The column includes 2 electric motors to make the adjustments. The steering wheel includes a horn (by pressing the center pad) and two buttons and a scroll wheel to the left and right hand sides of the wheel. There are left hand control stalks for indicators, light, a stalk for the wipers and wash. On the right hand side the stalk controls the reverse, drive, neutral drive mode of the car. The steering wheel buttons control left and right computer apps displayed in the binnacle display. The TesLorean will include the Tesla steering wheel, column, and controls. The output of the controls will be routed to a dedicated CANbus arduino device that will interpret the commands and interface with the stock DeLorean 12v systems. The commands will also be routed to the custom drive computer which will prepare and control the drive systems accordingly.
Thedrive computer will be the brain of the TesLorean. The drive computer interface will be a 7-in touch screen tablet located in the center console. It will act as the interface between the Tesla and DeLorean systems. The drive computer will take inputs from the steering controls, the pedals, mode switches, etc. and instruct the DeLorean 12v systems and the Tesla systems by CANbus, PWM, or 12v signal to respond accordingly. The drive computer will also monitor the car data, such as road speed, motor rotational speed, coolant and component temperatures, and battery systems information. The drive computer will also interface with the climate control system, taking inputs from thestock DeLorean controls (previously vacuum driven)and activating relays and 12v signals to activate electronic controls within the airbox, the AC system, and coolant loops. I have decided on a Raspberry Pi system as the main computer. The OS (Linux) is robust and it can drive the 7in touch screen display, and has available multiple CANbus extension boards for interfacing with the rest of the car.
The battery for the TesLorean will be the A123 battery pack from the 2014 Chevy Spark EV. After much research and deliberation I decided to not use Tesla modules. The Tesla modules are awkwardly sized, are relatively low voltage per module (~24v), and are expensive. The chemistry, while great for energy density, is more volatile than I'd like for a EV conversion. The #1 challenge was fitting the modules in the DeLorean. Unmodified would have required 16 modules to reach 400v and would have weighed in excess of 1000 lbs. While 8 modified modules would have halved the weight and space requirements, the modifications to the high voltage connections in each module were non-trivial. The modules are also very expensive - currently running $1000 to $1200 per module. 8 modified modules would cost somewhere in the region of $10,000 for the battery pack. The A123 Chevy Spark EV pack contains 4 modules of 92.4v each. So the pack (at nominal voltage) is 370v, weighs 450lbs, and provides 24kWh of capacity. The pack is also configured such that with modest modifications to the pack cover can be made to sit in the DeLorean engine bay area.
Credit: DeLorean DMC-12 Blueprint Engineering and Technology Magazine