Product Manager Talks
About Caterpillar’s
Unique Hybrid
In this exclusive Q&A interview,
Caterpillar Large Excavator Global
Product Manager Ken Gray talks
about the new 336E H hybrid and
how it will help customers around
the world dramatically reduce their
owning and operating costs and
their carbon footprint.
Staff Report
Q: Why is Caterpillar introducing a hybrid excavator now?
Gray: We have developed — and more importantly validated— an approach
that will truly lower our customers’ owning and operating costs as well
as contribute significantly toward lowering their carbon footprint. Over
the years, we have developed and tested electric hybrid technologies
because frankly, there has been a significant amount of pressure to follow
the industry. We have tested electric hybrids — our competitors and our
own — but we never found an approach that would actually lower owning
and operating costs without negatively impacting power and productivity
until now. Our technology — developed by a very talented and dedicated
team of people — actually delivers power and productivity with
extraordinary fuel economy and efficiency.
Product Manager Talks About Caterpillar’s Unique Hybrid
Q: How does Caterpillar define “hybrid?”
Gray: Caterpillar defines a hybrid as a machine that collects,
stores, and reuses energy when appropriate. It is not dependent
on any particular technology. In other words, it doesn’t have to
be electric. In fact, our industry has had itself in a box thinking
that hybrids must be electric, but there are many other ways to
store and reuse energy.
Q: How does your hybrid technology work?
Gray: It’s all in the hydraulics. Instead of wasting kinetic energy
during swing braking, we pressurize an accumulator to stop the
machine and use that pressure when needed to accelerate the
machine later. It’s really that simple.
Q: If your system is so simple, why haven’t others done this?
Gray: The concept is simple. Where the intellectual property lies
is in controlling how smoothly we save and reuse that hydraulic
energy or pressure, and our patented Adaptive Control System,
or ACS as we call it, is key as it is unlike any other on the market
with its ability to intelligently manage the restrictions and flows
in the system. That’s where the real customer value comes in.
Q: What’s the benefit of your hydraulic hybrid versus
competitors’ electric hybrids?
Gray: Competitors in our industry who offer an electric hybrid
use an electric swing motor instead of a hydraulic swing motor.
What they do is take the machine’s kinetic swing energy and
convert it into electrical energy using an alternator. During swing
deceleration, the swing motor acts as a generator, which stores
energy in a battery or capacitor that can be used to either
activate swing later or assist the engine with other functions.
There’s nothing wrong with this approach, but our hydraulic
approach is far less complex, less costly, and much more
efficient.
When our machine decelerates for a swing stop, for
example, our hydraulic system pressurizes an accumulator.
When the operator needs energy to swing, our system
releases the pressure stored in the accumulator back into
the hydraulic system. We don’t need an electric motor or
generator. We don’t need a capacitor. Very importantly, we can
use our proven standard hydraulic components. For example,
the swing drive we use in the hybrid is exactly the same as the
one we use in the standard excavator, which means we can
take advantage of the economy of scale across our full product
line to keep costs down for our customers.
Q: What testing has been done to validate your fuel and
productivity claims?
Gray: We have literally thousands of hours on prototype
machines with operators from all over the world, and we have
field follow machines used by actual customers to help us
validate the fuel burn, controllability, reliability, and performance
of the 336E H. In fact, we have had our ACS valve running in a
machine now for several years. One example is in a machine in
a sand and gravel pit just outside Peoria, and it just runs and runs
and runs. Unless we ask, we never hear anything from the owner
operator because it has never failed.
Q: Are there any other competitive advantages?
Gray: Yes. Besides lower cost and complexity and the use of
proven hydraulic components, our hybrid system is offered on a
larger excavator than our competitors offer. A high-production
machine like the 336E is perfect for hybrid technology because
the more an excavator swings or cycles, the more opportunities
there are to store and reuse energy, which leads to more savings
and a quicker payback for customers. Most important, there
is no loss of power and no loss in performance, which is in
stark contrast to competitive hybrid offerings. We are already
beginning to see signs that some competitive excavator
manufacturers may be thinking that hydraulic approaches may
be more beneficial than electric. The challenge for them will be
finding a way to duplicate our smooth controls—and they will
not have the advantage of our proprietary hydraulic components
or system integration.
There is another benefit our dealers and “do-it-myself”
customers will appreciate. Since the 336E H uses standard
hydraulic components, service technicians will require very little,
if any, specialized training to care for these machines compared
to a standard excavator. Excavator technicians will not have
to be retrained to add high-voltage service and maintenance
practices to their skill set. If a technician can fix an excavator
today, he can fix the 336E H.
“Where the intellectual
property lies is in
controlling how
smoothly we save
and reuse hydraulic
energy...”
Q: What are the fuel benefits?
Gray: Customers who purchase a 336E H can expect up to 50
percent greater fuel efficiency compared to our 336D and up to
a 33 percent reduction in fuel consumption in a truck loading
application. Even compared with our industry-leading 336E, the
336E H’s fuel savings are substantial—up to 25 percent less fuel
consumed in the same application.
Q: What performance did you give up to get the fuel savings?
Gray: Absolutely none. The hybrid will deliver the same power
and industry-leading level of productivity as the standard 336E.
The 336E H just gets the job done with far less fuel.
Q: Is frequent cycling the key to efficiency?
Gray: Yes. That’s why the excavator, especially in a highproduction application, makes sense because it swings so often.
When the machine stops in a swing cycle, energy is stored;
when it accelerates, the stored energy is reused. Considering an
excavator stops and swings twice every 15 seconds in a typical
high-production application, that’s a significant opportunity for
energy savings.
An analogy for those who are familiar is the effectiveness of a
hybrid automobile in an urban versus highway environment. City
driving offers numerous opportunities to store energy when the
car comes to a stop at a traffic signal and reuse that energy
when the light turns green. Highway driving just does not have
as many opportunities to save and reuse energy because there
are so few stops and starts. An excavator in a utility operation
might have far fewer opportunities to swing stop and start, so
the benefit would be less than in a high-cycling application.
Q: Is there any company outside the industry that does
something similar with their products?
Gray: Conceptually, UPS does something similar with its inner
city trucks. The trucks capture energy with their braking systems.
When the truck accelerates, the first source of energy it pulls
on is the pressure stored in the accumulator. How we differ is in
the control needed because we have a much greater challenge
in keeping dirt in the bucket and loading trucks or in carefully
moving and placing a load than they do in simply stopping and
starting trucks.
Q: How many patents do you have on this hybrid machine?
Gray: We have applied for approximately 300 patents
domestically in the U.S. and internationally in countries such
as Germany, Japan, and China, just to name a few. We anticipate
we’ll have more than that number before it is all said and done.
In a nutshell, ACS directs energy to be where it is needed
precisely when it is needed. Any application—even a utility
application— will benefit from the optimization capabilities of
ACS. ACS also delivers superior multi-function control and
improves the machine’s ability to track while operating the front
structure or a tool. This really has our operators who have tested
the machine excited.
Q: What are the differences an operator will experience
working with the hybrid?
Gray: There will be no noticeable differences even to the most
experienced operator. No special training is required to be
productive since it works like a standard excavator model. Like
any machine, though, there are operator techniques that will
help a customer get the most out of a 336E H, and our dealers
will be well prepared to deliver professional operator training
Cat ® owners have come to expect.
Q: Do they have to “manage” the hybrid technology?
Gray: No. It is completely automatic. The operator can simply
focus on the work at hand. The monitor will provide guidance to
operators so they can see the effect of their operating technique
on fuel usage and savings.
“You are going to
burn less fuel and
produce fewer
emissions owning
a 336E H.”
Q: What type of customer would benefit most from this machine?
Gray: Customers who trench or truck load all day will benefit
more from this machine than a utility customer who uses it to set
pipe or hammer concrete. The reason is that production-oriented
customers have lots of opportunities to collect, store, and reuse
energy over and over again.
Q: Will customers in utility applications or jobs that are not
swing intensive benefit from this machine?
Gray: Our 336E H hybrid implementation really has three pieces
that you can think of as “conserve, optimize, and reuse.”
A hybrid stores and reuses energy, and the hybrid portion of our
336E H system stores and reuses swing energy. Customers in
high-production applications will benefit most from this reuse
aspect of the system. But customers in any application—
including utility applications — will benefit from the conserve and
optimize elements of the system.
One of the important findings of our hybrid development was that
we can conserve fuel with a combination of lower engine speed,
a larger displacement pump, and electronically controlling the
pump to actually anticipate load or demand on the system. This
approach reduces fuel consumption, regardless of application.
ACS, our Adaptive Control System I mentioned earlier, is a valve
system our engineers refer to as “restriction management.”
ACS is essentially a set of hardware and software that
independently controls every function of the machine.
Q: Does the hybrid machine have the same service intervals as
a standard model?
Gray: Yes. The hydraulic oil change interval, for example, is
the same as the standard machine. What is a bit different
is the accumulator, which is precharged with nitrogen, but since
dealer service technicians already charge accumulators on
other Cat products, that’s really nothing new. We expect typical
recharge intervals to be greater than 1,500 hours. The electronic
system will alert the operator if recharging is necessary. That
said, service techs don’t have to change their schedules to
accommodate the hybrid model. They can service it at the same
schedule they follow for their other Cat excavator models.
Q: How much more difficult is the hybrid machine to service
compared to a standard model?
Gray: The hybrid is essentially the same as the standard model
since both operate hydraulically. There is no special training
required since there are no high-voltage components like
competitors have on their electric hybrids. We have also
eliminated many pilot hydraulic lines from this machine to
simplify the design, layout, assembly, and maintenance.
Q: How many models will be equipped with this technology?
Gray: This is the first model with more to come. I will keep the
rest to myself for now.
Q: Is your hybrid built to be rebuilt like your other machine
models?
Gray: There is nothing that would prevent this machine from
being a part of our growing remanufacturing strategy. We have
designed in the same durability Caterpillar customers demand
and expect of all of our large hydraulic excavators.
Q: Do you expect the same results regardless of machine size?
Gray: Regardless of size, the more production oriented the
machine, the more our hybrid technology makes sense for
customers. Again, the more often an excavator swings, the
more money you make. And this is particularly true with our
hybrid technology. While any application will benefit from the
conserve and optimize portions of this design, production
applications will benefit more from the reuse element, which
is central to the definition of hybrid.
Q: What major components have to be replaced? How often and
at what cost?
Gray: It’s really not much different than a standard machine.
Accumulators are expected to have a long service life similar
to our hydraulic cylinders, which can go up to 6,000 hours before
needing a rebuild. Also, accumulators are the same basic
technology as hydraulic cylinders, which make them relatively
easy to service. Plus Cat dealers and our customers have years
of experience servicing these accumulators on other large Cat
machines like wheel loaders and mining trucks.
Q: How are owning and operating costs impacted over time
compared to a standard 336E model?
Gray: Up to a 25 percent reduction in fuel burn is the primary
contributor to lower owning and operating costs for the hybrid
compared to the standard 336E. But it all boils down to fuel cost.
Savings will really add up where diesel prices are high.
“The more often an
excavator swings,
the more money
you make... this is
particularly true
with our hybrid
technology.”
Q: Where will the 336E H and future models be sold?
Gray: This model and others like it will be sold worldwide.
Customers who want to lower their owning and operating costs
and their carbon footprint will want one of our hybrid excavators.
We are starting with the highly regulated markets, so the 336E H
is Stage IIIB andTier 4 Interim emissions compliant. A version for
lesser regulated markets will follow very soon.
Q: How many do you expect to sell in a year?
Gray: I’m expecting a very high percentage of 336E customers
and many new customers will want this machine because it
actually lowers their owning and operating costs. And it’s
environmentally friendly. I do have a good feel for how many
our dealers will sell, but I will not share that publicly.
Q: Are any governmental customer incentives available?
Gray: We did not want to introduce a machine that would need
any form of governmental assistance to gain market acceptance.
We wanted a technology that was so cost effective that
governments around the world would not have to subsidize
construction businesses to reduce their carbon footprint.
This technology actually delivers on that. At the end of the day,
our customers have to make money, and they will make more
money with this machine.
Q: What’s next?
Gray: Caterpillar has an extraordinary team of people working
on hybrid technologies and the next generation of Cat hydraulic
excavators. They are from every corner of the world, are among
the very best and brightest minds, and they are listening very
closely to our customers. It’s exciting for me to see their
enthusiasm for this project and the quality of the product
they have developed. We’re really just getting started.
Q: Should customers have any safety concerns with this
technology compared to your standard model?
Gray: No. Both the standard and hybrid models are built with
similar safety features. One thing different with the hybrid is we
designed it to drain the accumulated oil pressure after key-off
should the hydraulic system need servicing. Also, we took
an extra step to encase the accumulator in the counterweight
because we anticipate that some customers may have
concerns with it. It isn’t necessary from a design standpoint,
but we wanted to make sure our customers have a better
feeling about that part of the hybrid technology.
AEXQ0950
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