McLaren doesn’t do things like any other car company. For the W1 hypercar, it took a lot of the conventional wisdom around hybrid systems, and threw it out the window. The result is a 1,258-horsepower car that can drive in two different gears at once. Seriously
In a hybrid vehicle with conventional transmission, the electric motor can be directly connected to the internal-combustion engine, or there can be some sort of disconnect device between the two. With the latter, that disconnect device could be a separate clutch, or it could simply be the transmission’s torque converter or clutch pack.
McLaren has used a couple different power-flow layouts in its hybrids. The P1 and Artura have the electric-motor ahead of the transmission’s dual clutches, but with a separate clutch between the engine and e-motor. By disconnecting this clutch, the electric motor can drive the wheels on its own. The Speedtail also had the e-motor ahead of the transmission clutches, but without a disconnect device between it and the engine, and thus no full-electric drive mode.
Photo by: McLaren
With the W1, McLaren has the electric motor positioned after the transmission’s clutches. This isn’t unusual, but what’s novel is that the 342-hp electric motor only runs through the even gears.
How does that work? Richard Jackson, McLaren’s chief engineer for propulsion, fills us in. “This time, what we have is the e-motor mounted on the side, behind the clutches, and [it] feeds through an idler gear into a shaft that runs outside the two input shafts,” he says.
In a dual-clutch transmission, you have two concentric shafts, one for the even gears, one for the odd gears, and each has its own clutch. The two clutches live concentrically in a single clutch pack. With the W1, you have the two input shafts, plus the electric-motor shaft all running concentrically, a shaft inside a shaft inside a shaft. Two synchros at the back of the transmission allow the selection of the odd gears.
“With the e-motor, we’ve got a choice of effectively sharing the gear with the internal-combustion engine, depending on how we engage the synchros,” Jackson explains. “They can both run in 2nd, 4th, 6th, 8th, but with the [internal-combustion engine], if we want to go for 3rd gear, we still have the choice of the e-motor being in 2nd or 4th depending on the synchros.”
When the engine is in an odd gear, the clutch for the even gears disconnects. But because the e-motor feeds in power after the main clutches, it’s still running through those even gears. With the synchros, the car chooses which even gear the motor runs through.
Photo by: McLaren
The McLaren W1’s Transmission with E-Module (motor and power electronics) highlighted in green.
Jackson tells us there are all sorts of benefits to this system. For starters, putting the motor after the clutches allows for a greater torque output, as the limiting factor is the friction material of the clutches. With four ratios for the e-motor to work with, you can get a lot of torque multiplication in the lower ratios if you want lots of electric boost, or use one of the higher ratios for better efficiency and quieter running. There are also scenarios where you might be running up through the gears with the engine, but holding the e-motor in a constant ratio to provide consistent power to the rear wheels.
“It gives us lots of opportunities, but also lots of headaches about what is the best strategy when you’ve got that extra when you’ve got that extra degree of freedom for the e-motor and the ICE,” Jackson says.
McLaren’s engineers are dealing with that now. Some gear combinations aren’t possible because of the way the synchros operate, but Jackson describes scenarios where you run the engine in 3rd gear while the e-motor is in 2nd or 4th, and another where you have the engine in 5th and the e-motor in 8th. And when the engine is an even gear, it’s going to run the same one as the e-motor.
As far as we can tell, no one else does this. Lamborghini does something sort of similar with the Revuelto. It has a unique coupling mechanism that can feed in the power from the e-motor along with the engine through all the forward gears, or use the e-motor to power the rear wheels after the transmission entirely. That has its own unique advantages, but it’s not a solution that allows the engine and e-motor to operate in different forward gear ratios at the same time.
Photo by: McLaren
It represents a very different approach to electric deployment from what McLaren pioneered with the P1. Whereas the P1’s electric motor provided “torque fill,” using its instant torque to plug gaps in the internal-combustion engine’s output, the W1’s hybrid system is all about constant power delivery.
Jackson says it was during the Artura’s development that McLaren realized a downside of the torque-fill approach. It takes a ton of electrical energy. “You soon realize you’re eating into that capability quickly. And obviously, we’ve got a relatively small-capacity battery on the W1, so we really need to make the most of the energy.”
Developing a new, bespoke, 918-hp V-8 allows McLaren to better optimize internal-combustion performance. “By pushing on the turbo suppliers, and the combustion system we’ve got that is so good, we can produce that high-specific output without having such a laggy engine,” Jackson says. That’s the benefit of over a decade of progress in combustion-system design and material science since the P1. It’s also the benefit of designing your own transmission.
All of this reflects McLaren’s pursuit of the lightest, simplest system for providing a ton of extra electric power. That’s why it went with a small battery and eschewed variable-turbine-geometry or electric turbochargers. McLaren claims a dry weight—i.e. without fluids—of 3,084 for the W1. Quite remarkably, that’s only 9 pounds more than the claimed dry weight for the P1.
Let’s put the upshot of all this in very simple terms. The P1 was, and is, a fast car; the W1 will be a very fast car.
