Truck & Off-Highway Engineering - October 2024 - 17

POWERTRAIN FEATURE
The HELM X15 has a new DOHC cylinder head that enables
valvetrain technology such as variable valve timing.
how we make the block stiff but light. "
Marsh continued, " If you look at the design, we have
all sorts of patented technology to keep liners straight
in the bores and develop the walls and structure of the
block to integrate the gear housing, which makes the
whole system structurally stiffer. What that's allowed us
to do is reduce the block weight by roughly 50 pounds.
However, the overall system weight is the same due to
an increase in weight for the aftertreatment system. " An
aftertreatment heater was one of the major updates for
the EPA27 X15 engines (see sidebar).
Other significant design changes for the HELM X15
include a new DOHC cylinder head that enables valvetrain
technology such as variable valve timing, the addition
of crankcase ventilation to meet regulatory requirements,
a thermal recirculation valve in the fuel
system to aid in cold starts, and a belt-driven 48-volt
alternator. Maximum output for the HELM X15 is stated
at 605 hp and 2,050 lb-ft.
Cool under pressure
Cummins states that much of the gain in efficiency
for the 2027 X15 came from a thorough revision of
the cooling system. " From a structural design perspective,
we completely redesigned the way we routed
the coolant through the engine, " Marsh said. " One
of the big downsides of the original X15 is that it was
TRUCK & OFF-HIGHWAY ENGINEERING
Tom Marsh, program leader at Cummins, discusses some of the individual
component revisions for the latest X15.
designed without an EGR system. So, when we added EGR, there
were compromises made in the cooling system because the block
wasn't originally designed for it. "
" As a result, we carried more pressure drop in the cooling system
than would be ideal, " he explained. " The new X15 has been designed
with all these future technologies in mind such as cooled alternators.
We really worked on making sure the system was optimized in terms
of pumping coolant in a way that minimized pressure drops because
that's just lost energy. The system also features dual thermostats
with different opening temperatures. This mitigates pressure drops
as each thermostat opens for their individual temperatures. "
Marsh stated that the new X15's cooling system has only 65 kPa of
pressure drop based on Cummins' in-house tests. " If you look at the
new tools that enabled this head design, you can see how much
progress has been made to enable us to design for heat loss, actual
flow interface and cavitation, " he said. " When you look at a totally
optimized system, we've been able to drop the pressure loss to a
third of what it was in the old engine. "
Marsh continued, " When you have areas of stagnant flow, you tend
to get cavitation and you're not taking full advantage of that flow to
remove heat. So now the flow is focused around the top portion of
the cylinder where we can really take a lot of the combustion heat
out of the process. "
Marsh also explained some of the serviceability aspects of the new
system. " One cool aspect about the modular water pump and loop
pump is that the housing, bearings, seals and impeller are completely
serviceable. You can just pull that entire assembly out of the engine
and service those individual components. "
October 2024 17
FROM LEFT: CUMMINS; SAE/MATT WOLFE
Truck & Off-Highway Engineering - October 2024

Table of Contents for the Digital Edition of Truck & Off-Highway Engineering - October 2024
