Skip to main content

The Ricardo High Efficiency Excavator (HFX)

This internally funded research programme has looked at the application of energy recovery approaches to construction equipment focussing on electrical, hydraulic and flywheel systems. View the video here

Initial consortium work back in 2009 identified the excavator as a prolific consumer of fuel due to its significant role in most construction sites and its heavy usage. A 24T excavator doing 1500hr/year would use over $49,000 of fuel (corrected to today’s prices). Therefore even single digit fuel savings would make an important impact on the operator’s business. This also simplistically implies a rough budget range for the energy recovery system of between $4,000 and $8,000 if a one to two year payback is to be expected.

Analysis of the energy recovery solutions from a cost/benefit point of view indicated the hydraulic and flywheel approaches were of particular interest to an excavator given the above budget range. Because Ricardo had already invested in flywheel technology and had an innovative solution relevant to the excavator, this was chosen as the technical route forward for this programme.

The main challenges to be studied and overcome in this programme were therefore defined as:

  • Develop the most appropriate flywheel application approach to the excavator for boom and swing energy recovery and re-use to offer at least 10% fuel efficiency saving by the flywheel system alone over typical operator cycles with no other modifications to the machine (total machine energy optimisation targeting much higher savings will be part of a subsequent programme)
  • Develop and validate modelling and analysis tools to allow investigation and optimisation of the hydraulics, flywheel and control systems within an excavator modelling environment
  • Minimise losses throughout the system to maximise fuel efficiency gains
  • Develop a fully automated control system, independent of the driver (no distraction or learning required and only improvements in productivity acceptable)
  • Work within the cost/benefit targets given above.

Programme Structure and Key Inputs

The programme was split into four sections:

  1. Modelling and analysis studying machine-use for operator cycle development, the application of the flywheel and hydraulic systems and the resulting design, bill of materials, (maximising off-the-shelf parts where possible) and parts procurement
  2. Test rig design and development for detailed mapping of the flywheel and application system for data gathering, modelling validation, systems optimisation and control system development
  3. Machine application and development to targets
  4. Data gathering for the validation of all modelling and analysis tools used.

The most significant input to the programme was the Ricardo flywheel system. In the time available to this programme, an existing Ricardo flywheel was utilised, rather than optimising the flywheel exactly to the chosen excavator. The Ricardo flywheel system has a number of innovative features developed by Ricardo over the last four years:

  • Carbon fibre rotor configurable to the application’s energy storage requirements
  • Hermetically sealed so low frictional losses (no need for rotating seals or an onboard vacuum pump)
  • Operation up to 60,000rpm
  • Magnetic gear output drive system with a 5.75:1 ratio and high efficiency
  • In built containment and other safety systems.

Flywheel parameters used in this programme:

  • Inertia: 0.0489kg.m2
  • Total energy stored  960kJ, at 60,000rpm
  • Output ratio and max torque:  5.75:1, 50Nm
  • Total system weight:  32kg

A nearly-new 18 ton wheeled commercial excavator was procured. This was chosen as it offered a manageable size and logistical practicality.

Ricardo’s robust and well proven rapid prototyping control hardware platform tool-chain “R-Cube” was used to embody the flywheel system control logic.


Ricardo used AMESimTM to build models of the flywheel system, the application approach, the necessary elements of the excavator and the control system. This was developed over a period of six months. Flywheel coast down data was available from parallel application programmes.

The excavator was fully instrumented and exercised over a range of operator cycles and the measured data built into the modelling environment.

Test Rig

A test rig was built to house the flywheel system, instrumentation, an electric motor/dyno system to simulate various modes of operation, clutches to switch in and out various systems and the hydraulic integration system. In addition, a hydraulic power pack and valves was configured to simulate the pressures and flows available during the excavator boom ascent and decent (albeit limited in ultimate power capacity). The rapid prototyping control system was also fitted.

This system was therefore able to perform the following tasks:

  • Measure flywheel efficiency and coast down times
  • Map some of the hydraulic application system efficiency operating envelope
  • Test the complete system over simulated excavator cycles automatically
  • Isolate specific elements of the system for more detailed investigations
  • Develop the control system and prove-out before vehicle integration.

The flywheel and hydraulic application system was developed as a module. When the test rig activities were completed, this complete module was then integrated into the excavator. This approach de-risked the practical aspects of the integration considerably.

This testing work was completed successfully with the learning fed into the modelling activities and pointers to future research and development activities understood.

This rig work demonstrated:

  • Successful energy recovery and reuse at conditions of flow and pressure emulating typical excavator operation
  • Areas of development within the complete system to optimise global system efficiency
  • Robust control system developed with the following functions proven on the rig:
    o    Flywheel idle speed hold (if required)
    o    Energy recovery
    o    Energy re-use
    o    Torque and speed control plus limits handling
    o    Automatic pressure and flow matching
    o    Safety systems
    o    Other strategies required for integration such as automatic mode switching and flywheel management
    o    Information exchange

Machine Application and Development to Targets

The rig module was transferred to a vibration isolating framework, external to the excavator for ease of integration appropriate for research and development. Six new manifolds for high and low pressure with the system control valves integrated within were procured and fitted, and the Ricardo R-Cube control system and electrical wiring, connected to the new systems and the original machine. The machine controls and structures were already instrumented. The final two parts added to the machine were an external, high visibility light tower, to indicate mode of operation and flywheel energy, and a wireless data link to an iPad to allow on-lookers the ability to understand the functions and status of the various systems. The system was commissioned over a period of a week and the control functions checked whilst exercising the system over the chosen operator cycles.

The development activities focused on:

  • Mapping energy recovery to boom and slew motion, bucket load and extension whilst recording base machine pressures and flows at strategic places
  • Energy re-use options
  • Energy flow efficiency optimisation to maximise fuel savings
  • Operator and machine feel analysis
  • Understanding areas for future development
  • General data collection for modelling validation.

Data Collection and Modelling Validation

The machine and control system was instrumented, including the machine CAN network, and the data was logged at 1HZ frequency. Base machine pressure, flow and losses data was the most valuable, being very hard to estimate or simulate accurately prior to machine measurements, taking account of all the interactions within the Main Control Valve of the base machine and the operator control inputs. This data has allowed the simulation accuracy to be improved and a better understanding of the system integration interactions. Flywheel speed comparisons in simulation and on the machine show a very good correlation over the chosen cycles. At the time of writing, the data collection and validation exercise is on-going.

Findings to date

The HFX programme is targeting >10% fuel energy savings and <2 year payback from the application of a Ricardo designed and developed flywheel energy recovery and re-use system and is well on track to deliver that. A subsequent programme will look at the optimisation of the complete machine looking at engine and

The main findings so far can be summarised thus:

  • The application approach chosen offers a wide range of energy recovery and reuse options and is highly configurable through electronic control
  • The complete functionality of the Ricardo flywheel system and automatic operation has been demonstrated safely
  • Energy recovery and re-use is highly cycle and machine configuration sensitive, not matter what the energy recovery approach used is, so the flexibility offered by this system is beneficial
  • Hydraulic work savings locally at the boom, before the main control valve can approach 30%. Realising a proportion of this in practice as a fuel saving requires careful system optimisation and minimising of energy losses within the recovery system
  • Combination of boom and slewing recovery and re-use important to realise targets.
  • The simulation approach has been extremely useful in choice of system components, control system development and machine testing guidance. On-going validation has improved this further.
  • The Ricardo flywheel and this application approach has been shown to be a good match to a cyclical hydraulic machine. Other construction applications are also being considered.


The Ricardo HFX programme to develop and apply a flywheel energy recovery system has so far yielded significant information and learning on a highly promising, cost effective fuel efficiency improvement system of hydraulic cyclical construction equipment such as excavators. This is currently being developed to achieve a less than two year payback, targeting a large excavator.

The programme has:

  • Developed and validated modelling and simulation tools for flywheel application
  • Demonstrated a practical and effective flywheel integration approach
  • Developed a control system with full authority over the recovery and re-use system
  • Formed the basis for on-going development to achieve the programme targets.

The Ricardo team is continuing to develop the machine and will publish further, more detailed information at a later date.

Ricardo has also developed the flywheel for on highway and rail applications.

For more information on HFX and to discuss the modelling and application of the Ricardo flywheel system to your machine, please contact:

Simon Mall
Senior Business Development Manager
Direct Dial:  +44(0)1273 794191
Mobile:       +44(0)7880 746 212 

Contact Us

Name *
Email *
Location *
Query *