hydraulic trucks

How Hydraulic Hybrid Trucks Helped Clean Up Waste Management

November 16, 2022 - Emily Newton

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You probably don’t spend much time thinking about garbage trucks. In fact, once the trash is in the dumpster, most people give little thought to who picks it up unless the truck arrives late. But trash trucks use fuel — and emit greenhouse gases — just like any other traditional vehicle on the road. To save power and lower their carbon footprint, some companies adopted hydraulic hybrid trucks in the mid-2000s.

Although the technology is largely being outshined by electric vehicles today, it played an important role in sustainable waste management.

How Efficient Are Traditional Garbage Trucks?

To put it simply: not very. A refuse truck lurching from dumpster to dumpster gets a paltry three miles per gallon on average, making it the least fuel-efficient vehicle on the road. This is partly due to their sheer weight and time spent idling. Clearly, they’re a prime target for an alternative energy overhaul. 

How Does a Hydraulic Hybrid Truck Work?

When people refer to hybrid vehicles, they’re usually talking about electric hybrids that store excess energy in a battery. But a hybrid hydraulic vehicle (HHV) has a very different source of power. Rather than charging up overnight and using a battery to run the motor, an HHV employs a series of fluid-filled tubes at different pressures to power its engine. 

Here’s how the process works:

  1. The driver presses down on the gas pedal. 
  2. Pressurized nitrogen stored in a high-pressure tank, also called an accumulator, forces hydraulic fluid through the pump motor.
  3. The pump motor uses the pressure to turn the vehicle’s wheels. 
  4. The fluid depressurizes and flows into the low-pressure tank, also called a reservoir. 
  5. If the vehicle has been cruising and the fluid in the high-pressure tank drops below a certain level, the engine turns on. 
  6. A hydraulic pump connected to the engine repressurizes the low-pressure fluid so the pump motor can keep turning the wheels. The accumulator stores excess high–pressure fluid. 
  7. When the driver hits the brakes, the engine shuts off.
  8. The pump motor slows the vehicle down. It uses the vehicle’s kinetic energy to pressurize fluid and pump it back into the accumulator. 
  9. When the driver accelerates again, only the saved energy turns the wheels. 

The Introduction of HHVs

Although the EPA created and patented the technology in the 1990s, it wasn’t until 2006 that the first HHV hit the road. The brown UPS delivery van proved to be much more efficient than a traditional diesel-only vehicle, getting 60-70% more miles per gallon in laboratory tests. Soon after, HHVs started popping up in the form of UPS trucks, city buses and garbage trucks. 

People even began talking about creating hybrid hydraulic passenger vehicles. One factor prohibiting this was the fact that hydraulic systems work best in very heavy machines, like bulldozers and dump trucks, whereas passenger cars are much lighter. With the electric car industry already making great strides in the passenger vehicle market, the concept of hybrid hydraulic cars never took off. 

Advantages of Hydraulic Hybrid Trucks

What can hydraulic trucks do that other vehicles can’t? Here are a few advantages of HHVs:

  1. Regen Braking

Like electric vehicles, hydraulic hybrid trucks recapture energy that would ordinarily be lost when braking, a feature known as regenerative braking. This protects the brakes against wear and tear, and is part of what makes HHVs more energy efficient than traditional gas guzzlers. 

  1. No Battery Mining

Additionally, people don’t have to mine metals such as lithium and cobalt to make HHVs, like they do to make electric car batteries. This prevents a lot of environmental damage. There are no toxic lithium-ion batteries, which can be dangerous to handle, to dispose of or recycle at the end of the vehicle’s life. This means hybrid hydraulic vehicles have a lower ecological impact. 

  1. Weather-Resistance

Electric vehicle batteries can run into problems in extreme weather conditions. In contrast, hydraulic systems are less sensitive to heat, cold and moisture. 

  1. Safety Features

Hybrid hydraulic systems aren’t at risk of exploding or catching fire like EV batteries. And, when the driver turns the vehicle off, it automatically discharges any built-up pressure. This feature makes it much safer to operate. 

In the Shadow of Electric

These days, with electric vehicles becoming more efficient, accessible and powerful, some cities are starting to adopt electric garbage trucks. A quick Google News search shows that most of the excitement around hydraulic hybrid trucks appears to have taken place between 2006 and 2015, after which the technology slowly faded from the radar. What happened?

  1. Reliance on Fossil Fuels

One reason is that hydraulic hybrids still rely partly on diesel. Given the choice, most people will opt for a full-electric vehicle that doesn’t use unsustainable fuel, so electric vehicles are exploding in popularity. 

  1. No Battery Storage

Additionally, HHVs can’t power the radio or air conditioner like a battery can. To use the AC, for example, the driver either has to keep the diesel-powered engine running or forego the cooling system while the vehicle is at rest. In states like Texas or California where temperatures routinely reach triple digits, this is a major disadvantage. 

  1. Annoying Noise Levels

They’re also very loud. Hydraulic hybrid trucks emit an angry hissing sound, while electric vehicles are famously quiet. This gave them another leg up over HHVs. 

But during those few awkward years — in the transition between having only internal combustion engine vehicles and the electric revolution — hydraulic hybrid trucks provided a stopgap measure for cities looking for alternatives to diesel. They served as a kind of stand-in for full-electric vehicles, getting people excited about the future of sustainability. 

And they did their job well. 

Under Pressure: The Future of Waste Disposal 

Any amount of fossil fuel reduction is a success, especially in an industry like waste management where the goal is to clean the planet. Technology is ever-evolving, becoming more efficient and sustainable, and new inventions will supersede once-promising ideas. That doesn’t mean they were a failure. 

It seems like electric garbage trucks are the next big thing in the refuse management industry. Then again, we said that about hydraulic hybrid trucks ten years ago. 

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Emily Newton

Emily Newton is a technology and industrial journalist and the Editor in Chief of Revolutionized. She enjoys reading and writing about how technology is changing the world around us.

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