EV Fundamentals: Nissan 350Z
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Nissan 350Z
07.04
| 00:00 | Kels is a race car I've had since 2008 and is in a constant state of evolution. |
| 00:04 | Built on a 350z platform, Kels is now running a highly strong naturally aspirated VQ35 along with significant suspension and aero modifications. |
| 00:13 | What was once an endurance racing car turned into a sprint racing car and then later a time attack car with the spirit of a GT car. |
| 00:19 | Once in time attack with a naturally aspirated engine we quickly became power limited. |
| 00:23 | While it would have been fairly straightforward to add a supercharger or some turbos, we really wanted to develop our own hybrid electric system. |
| 00:31 | The goals for the project were to add around 200 horsepower for no more than 200 pounds of additional weight. |
| 00:36 | The secondary goal was to improve the weight distribution of the car with most of the weight being added to the rear of the vehicle. |
| 00:42 | Being able to remove components like the alternator, starter, clutch, and flywheel meant that we could actually add closer to 250 pounds and still achieve our goal. |
| 00:50 | The first item to consider was the system voltage. |
| 00:52 | As I was originally planning to use an OEM based hybrid battery, that forced us to be at 400 volts. |
| 00:58 | We selected an axial flux motor because this would allow us to put the motor in the bell housing between the engine and the gearbox. |
| 01:04 | By removing the clutch and flywheel, the motor directly couples the sequential gearbox with the engine. |
| 01:08 | This means that when the engine is spinning, the gearbox is also spinning. |
| 01:12 | That also means that for the vehicle to start driving, the electric motor has to spin the engine from a stop and power the car forward at the same time. |
| 01:19 | As this is a time attack car only and acceleration from a stop is not important, this was a compromise we made to save weight. |
| 01:25 | Removing the entire clutch and flywheel assembly, including the hydraulics, saved a significant amount of weight. |
| 01:30 | We designed a custom adapter plate for the motor, which also acts as a spacer between the bell housing and the engine. |
| 01:36 | The motor selected has a maximum torque output of 240 newton meters. |
| 01:40 | That means that assuming we have enough voltage to keep the motor operating at peak torque, we can achieve 200 horsepower at 6000 RPM. |
| 01:47 | Initially, the motor was wound with four turns, resulting in a power output of only 100 horsepower with the 400 volt battery, as we were simply running out of voltage. |
| 01:55 | Rewound stators allowed us to get closer to 140 horsepower, but voltage was still the limiting factor. |
| 02:00 | It was at this point that we started developing our own battery, and at the time of this video, we are currently using five of these battery modules, which results in 500 volts. |
| 02:08 | At the same time, we switched to a Cascadia CM200DZ inverter, which has an 800 volt capacity. |
| 02:14 | With this battery setup, we have achieved 175 horsepower, and a sixth module would certainly bring us to our 200 horsepower goal. |
| 02:20 | More about that later. |
| 02:21 | We designed a simple power distribution box that houses the pre-charge resistor, contactors, and isolation module, along with fuses for the DC-DC and charger. |
| 02:30 | One of the contactors actually has an internal current sensor, which communicates over CAN. |
| 02:34 | That allowed us to keep the box smaller and lighter. |
| 02:36 | 50mm squared, or 1 gauge, wire was selected for the high voltage cables connecting the battery modules to the power distribution box, and the power distribution box to the inverter. |
| 02:45 | As the battery never outputs much over 300 amps of current, this was an acceptable wire size. |
| 02:50 | These cables enter the power distribution box using sealed glands and bolted terminals, which removes two connectors from the system. |
| 02:55 | The smaller outputs of the power distribution box are fairly simple, consisting of a connector for the DC-DC converter, and another output for an off-board charger. |
| 03:03 | These connectors use HVIL, so if any of these connections are unplugged, the vehicle automatically shuts down. |
| 03:09 | The DC-DC converter is a tiny little device developed by a company called Brightloop, who supply similar devices into F1. |
| 03:15 | It weighs almost nothing, and is mounted just above the CM200 inverter. |
| 03:18 | Because it tells us how much current it's outputting, and we know from the MoTeC PDM what the total current load of the vehicle is, we're also able to deduce how much charge our 12V battery is absorbing. |
| 03:28 | This is useful, as I ensure I don't go on the track unless the battery is fully charged, as the DC-DC outputs near its maximum under high electrical load on the track. |
| 03:37 | A high voltage status light is mounted to each side of the vehicle. |
| 03:40 | When the light is green, it means that the high voltage isolation system is online, and the isolation of the vehicle is safe. |
| 03:46 | If the light is red, it means that the system has not yet established an isolation measurement. |
| 03:51 | If the light is flashing red and yellow, it indicates that the isolation system is online, and measuring a dangerously low isolation between one of the high voltage lines and chassis ground. |
| 03:59 | Now, onto the cooling side. |
| 04:01 | The system has two coolant loops, one for the battery, and one for both the inverter and motor. |
| 04:06 | Both heat exchangers are mounted at the rear of the vehicle, as the goal was to keep the weight as far rearwards as possible. |
| 04:11 | The system has worked well, although our current limitation is overheating of the motor's rotor and stators. |
| 04:16 | Despite relatively cool water temperatures, the motor overheats quite quickly, as we're asking a lot of such a small machine. |
| 04:23 | The next upgrade we're planning is a custom oil spray system inside the motor, which will allow us to cool the rotor and more of the stator windings, hopefully meaning that we can maintain peak power for longer. |
| 04:34 | In addition, as we continue to raise the voltage of the battery, less field weakening current will be required. |
| 04:39 | This means that more of the current we inject into the system will be going towards making useful power, rather than field weakening, which just adds heat to the machine. |
| 04:46 | All of the electronics are tied to the main vehicle ECU, and I've written custom software in MoTeC's M1 build environment, as with the Lotus. |
| 04:53 | The ECU is quite busy, managing not only the engine, sequential gearbox, and paddle shifting, but also operates as a full VCU and BMS. |
| 05:01 | If that's not enough, the ECU also handles the four-wheel steering system, and all of the associated software that manages the targeting and control system for those rear wheel steering actuators. |
| 05:11 | Using a torque management system and various different motor and engine maps, a torque request from the engine along with a torque request from the motor are combined. |
| 05:19 | Sometimes opposing torque requests are even made. |
| 05:21 | For example, at partial throttle, I'll command a regen to continue charging the battery, while compensating for that regen by adding more power from the engine. |
| 05:30 | The idea is that the driver always has the same torque output at the pedal, and the torque ramps up linearly with additional pedal application. |
| 05:37 | The control system looks at various inputs such as lap distance, motor and inverter temperature, battery state of charge, requested power map, and of course, pedal position to determine the torque output. |
| 05:47 | Traction control starts cutting the electric motor before the engine's power, so that we never waste energy overheating the motor just to spin the tires. |
| 05:54 | Additionally, the system monitors the rear wheel slip and reduces regen when a certain amount of rear locking is occurring. |
| 05:59 | The degree to which this effect is implemented is part of the driver's regen dial on the steering wheel. |
| 06:04 | This is a very powerful tuning tool that I use to adjust the vehicle's balance on corner entry. |
| 06:08 | In addition, the amount of regen the system commands also varies based on a number of inputs and maps. |
| 06:13 | The system can primarily focus on charging the battery in some maps, while alternatively focusing on preventing battery and motor overheating in alternate maps. |
| 06:21 | This is because when doing all-out time attack laps, it's more likely to overheat the motor and battery before actually running out of energy. |
| 06:27 | The car has been an absolute joy to drive and develop with this system, and I've learned a ton about managing heat and trying to get the most out of relatively small components with this project. |
| 06:35 | With this system, we now have enough additional power to compete with the big boy time attack cars in North America, despite still having just over half the power of some of our competition. |
| 06:44 | In 2023, Kels set a new production car lap record at Laguna Seca, and set a grid life lap record at Lime Rock Park. |
| 06:49 | The beauty is that we get to combine electrification, along with the naturally aspirated whale of this highly strung out, individually throttled VQ engine. |
| 06:56 | It's certainly a car for everyone, and whether you love EVs or hate them, Kels brings everyone together. |
