RobbertPatrison
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- Joined
- Mar 24, 2022
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- Location
- Silicon Valley, California
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- Ice White Mustang Mach-E
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I decided it was time to check out what is hidden behind the plastic of the frunk. Any maintenance - other than refilling wiper fluid - requires removing the frunk hardware. That adds to the shop cost as it takes time:
Compared to the other EVs and cars I have opened, a few things stand out:
I spent a little time decoding the mess of tubes that cool and heat. First, there is the motor and electronics coolant loop:
This is a single large daisy chain loop that is cooled by the radiator. So large that it needs two push-pull pumps in series. There are two operational modes:
There are four loops that interact in intricate ways.
The MME can switch off the chilling of the battery and only cool the cabin. But it cannot chill the battery without also cooling the cabin. In practice that is probably OK.
All EVs share the AC compressor for both battery and cabin cooling. But the really odd design choice was that Ford decided to share a single PTC heater between the cabin and the battery as well. Most other EVs have a separate PTC heater in the battery loop. After all, PTC heaters are cheap and small.
This PTC heater sharing ik the MME adds a lot of messy plumbing. When heating the battery the diverter valve connects the two loops into one big one like this:
The loop is: cabin pump->PTC heater->cabin heater core->diverter valve->battery pump-> HV battery -> proportional valve -> diverter valve-> heater pump. (!!)
In this heater mode, the refrigerant valve will be off, and the battery proportional valve feeds the fluid into the diverter valve.
It does mean that the cabin heater will always be on in case the battery needs to be heated. If the car is just charging, the cabin fan will be off so little heat energy will be lost there. When driving, some heat will be sent into the cabin by the blower. If this is undesirable, it could fire up the compressor to mix in some cooling.
It is a little odd that the PTC heater is just 6kW while it needs to service the cabin and the battery in parallel. That seems a little weak, but apparently, it works out OK even in cold climates. The small Chevy Bolt had an 8kW cabin heater plus a 2kW battery heater.
Overall, the heating and cooling system still works fine in practice. If you don't take the frunk apart you will be blissfully unaware of its messy complexity. Perhaps that is the reason why the frunk is covered so well.
- Unclip the 3 plastic panels, with quite some force. Clips may fall off and need to be re-attached
- Detach several cover panels to remove 8 screws. Some of the screws did not turn easily due to poor threading: they seem to have been rammed in with oodles of torque on the production line.
- The frunk 'bathtub' is remarkably sturdy and heavy. It has thick metal reinforcements. It feels good, but I don't fully get why Ford did not try to save a little weight here.
Compared to the other EVs and cars I have opened, a few things stand out:
- The plumbing is a royal mess. It seems as if Ford (+ its contractors) designed and placed the components without giving much thought about how they will be hooked up. Piping makes weird detours as a result. Compared to a Tesla MY, the MME has 3X more hoses and 3X more fluid according to Munro. That is a huge difference.
It looks bad, but is it that bad? A large number of connectors increases the chance of leaks and adds a lot of weight. On the other hand, rubber hoses are cheap and off-the-shelf pumps are cheap. They can be repaired much easier. Looking at this, repair seems quite doable. - Given that the front motor is just 50kW, this seems quite large and bulky for what it does. The equipment in my old Chevy Bolt cranked 3X the power out of a hood area that is much smaller. It seems little effort was spent on compact design.
- If you look down in the hole, the frunk could easily have been 3 inches deeper. The clumsy plumbing at the bottom could easily be moved out of the way. I wonder why this was not done.
- The radiator fan blows against the frunk bathtub. This must be a hot place in summer.
- I see 4 electric fluid pumps and a quad valve scattered on the bottom. More on that later.
I spent a little time decoding the mess of tubes that cool and heat. First, there is the motor and electronics coolant loop:
This is a single large daisy chain loop that is cooled by the radiator. So large that it needs two push-pull pumps in series. There are two operational modes:
- L1 or L2 Charging, in which case the onboard AC charger produces up to 800Watts of heat. The heat is pushed through the DC/DC converter, the rear motor, and the front motor. Since the motors are not running, they do add additional heat.
- Driving, in which case most heat comes out of the rear motor and inverter (and the charger is off). The rear motor has an oil heat exchanger with its own oil pump. The front (non-GT) motor is water cooled only.
There are four loops that interact in intricate ways.
- Cabin heater loop: cabin pump->PTC heater->cabin heater core->diverter valve-> cabin pump
- Battery chill fluid loop: battery pump-> HV battery -> proportional valve -> chiller -> battery pump
- Battery refrigerant loop: compressor->condenser->valve->chiller evaporator->compressor
- Cabin cooling loop: compressor->condenser->cabin evaporator core->compressor
The MME can switch off the chilling of the battery and only cool the cabin. But it cannot chill the battery without also cooling the cabin. In practice that is probably OK.
All EVs share the AC compressor for both battery and cabin cooling. But the really odd design choice was that Ford decided to share a single PTC heater between the cabin and the battery as well. Most other EVs have a separate PTC heater in the battery loop. After all, PTC heaters are cheap and small.
This PTC heater sharing ik the MME adds a lot of messy plumbing. When heating the battery the diverter valve connects the two loops into one big one like this:
The loop is: cabin pump->PTC heater->cabin heater core->diverter valve->battery pump-> HV battery -> proportional valve -> diverter valve-> heater pump. (!!)
In this heater mode, the refrigerant valve will be off, and the battery proportional valve feeds the fluid into the diverter valve.
It does mean that the cabin heater will always be on in case the battery needs to be heated. If the car is just charging, the cabin fan will be off so little heat energy will be lost there. When driving, some heat will be sent into the cabin by the blower. If this is undesirable, it could fire up the compressor to mix in some cooling.
It is a little odd that the PTC heater is just 6kW while it needs to service the cabin and the battery in parallel. That seems a little weak, but apparently, it works out OK even in cold climates. The small Chevy Bolt had an 8kW cabin heater plus a 2kW battery heater.
Overall, the heating and cooling system still works fine in practice. If you don't take the frunk apart you will be blissfully unaware of its messy complexity. Perhaps that is the reason why the frunk is covered so well.
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