Hybrid & Electric Vehicle Corner
Exploring the Toyota PC60 Hybrid Automatic Transmission (Part 2)
by Curt Ward
As I write this article, we have reached the midpoint of our spring semester, and the temperatures in Chicago have begun to warm. In February, I shared the findings from my initial teardown of a Toyota PC60 hybrid automatic transmission out of a 2023 Crown that Toyota of North American generously donated to our program. This month, I will share what I discovered after completing the teardown and how I plan to incorporate my findings into the curriculum.
As I shared in the last article, this transmission is very different than the THS/HSD two-motor design that Toyota has used in their hybrids since their introduction. It uses a single electric drive motor sandwiched between a 2.4-liter turbocharged engine and an electronically controlled six-speed automatic transmission. The transmission is more compact than previous hybrid models used by Toyota.
Let me begin with an update on the transmission oil pump. After removing the valve body, I discovered the offset oil pump is a combination of mechanical and electronic power. When the internal combustion engine is operating the pump is driven by gear and chain. When the vehicle is operating in hybrid electric mode the pump is driven by an electric motor that is controlled by the transmission control module (See Figure 1 – Oil Pump). The filter is incorporated into the inlet side of the pump and appears to be a non-serviceable component.
The valve body uses an integral valve design that combines the control solenoid and valve into a single unit (See Figure 2 – Integral Valve). There appears to be two valve designs used in the transmission. In their default position, one valve design allows for fluid flow to the hydraulic clutch, and the other blocks flow to clutch assembly. The solenoid/valve assembly is retained to the valve body with a locking pin, and a retainer plate. The transmission case contains 5 external pressure taps that allow for the hydraulic testing of each circuit. This is a welcome diagnostic aid that most manufacturers have eliminated.
The hydraulic clutch assemblies serve as input and holding clutches in a double plan
etary gearset design (See Figure 3 – Planetary Gears).The input clutches are splined to input shaft, and the holding clutches are splined to the case. This design provides for minimal hydraulic change and smoother shifting.
Earlier this month, our program received a Pico Milliohm and Motor Tester (MT03A). This unit connects to all three phases of the motor windings at the same time and provides a temperature compensated resistance reading of each phase after testing them bi-directionally (See Figures 4 & 5 – Tester and Results). This is more of a dynamic test and is considered to be a better measurement of motor state of health than the static tests we have been previously performing. This motor tester will be incorporated into the labs on all the electric machines in our hybrid and electric transmissions.
The hydraulic portion of the transmission was straight forward to disassemble and reassemble. It did not require any special tools outside of the tools we already had in our lab. The pressure taps allowed for the air-check of the unit after clutch units were reassembled in the case. In our lab we plan to leave the electric motor portion of the transmission separate from the more conventional hydraulic portion of the transmission. This will create two work stations. As I mentioned in the last article, Toyota is currently not servicing any internal components in the transmission. The tasks our students will perform on this unit will be focused more on the understanding of its operation and less on the ability to successfully rebuild the unit.
I will finish this article with the same offer I make after each of my presentations. If you are interested in getting started in the process of adding hybrid and electric vehicles to your curriculum or want more information, please feel free to reach out. I am more than willing to sit down in-person or online and share my experiences. Are you looking for a classroom textbook? Reach out to Pearson and ask for a review copy of the all-new Electric and Hybrid Electric Vehicle text that Jim Halderman and I co-authored. It is a comprehensive text covering all the latest information on the subject.