Hydraulic Hybrid Powertrains

Hydraulic hybridization would not be my first choice. My first choice would be an ICE/Electric using capacitive storage and applying the Three Fundamental Efficiencies of Hybrid Technology as described in the following link. I ask that you look by the first paragraph and consider the Three Fundamental Efficiencies: Power Averaging, Regenerative Braking, and Peaking Power.

http://www.bestsyndication.com/Articles/2006/c/carter_mark/031206_hybrid_cars.htm

I first wrote about these fundamental efficiencies as a close out to an Individual Studies Project at the University of Northern Iowa in the Fall of 1978 using a regenerative capable locomotive switch engine as the study model. I followed on with an automotive application with an entry in the 1984 Rolex Awards competition.

A couple of years ago I responded to Mr. Okoye's request for assistance in writing a paper on ICE/Hydraulic hybrid power as applied to a bus. Mr Okoye explained that he was cooperating with other people at the Harbin Technical Institute in writing a technical paper in English. I agreed to cooperate with Mr. Okoye but ended up pretty much reconfiguring the process. Once I submitted the completed copy to Mr. Okoye, I never heard from him again. What follows is the editing I did on Mr. Okoye's original paper, which I still have. I have cut most but not all of the original copy; leaving largely the edited and reconfigured portion.

Energy Management and Regenerative Recovery As Applied To Hydraulic Hybrid Vehicle Technology Using an Improved Hydraulic Transformer, Clean Diesel Combustion Technology and Prime Mover Power Averaging.

ABSTRACT

The primary focus of this paper is the integration of Hydraulic Power and Clean Diesel Combustion technologies into a Hybrid Hydraulic Vehicle (HHV). This hybrid power process incorporates four-wheel drive, allows for the regeneration of braking energy, and will include the integration of an improved broad range hydraulic transformer for drive and regenerative braking control. This proposed hybrid power process, when retrofitted to existing body and frame design, will meet or exceed baseline performance of the conventionally configured vehicle while significantly reducing vehicle emissions and radically improving fuel economy.

The motivation for this research is the impact that transportation energy usage has on the economic, political, and environmental stability of the planet.

1. INTRODUCTION

The rapid growth and development of world population has resulted in an exponentially increasing demand for petroleum based transportation fuels. Currently there are over 800 million vehicles consuming 40 million barrels of petroleum per day. This results in about half the urban pollution and 1/10 of anthropogenic green house gasses. (IEA 2000) Energy usage trends inherent to all nations indicate that the transportation sector of world economy will remain the largest user of petroleum based fuels into the future with wheeled vehicles using a disproportionate amount of those supplies. In addition, it is reasonable to assume that energy supply and demand will be a primary driving force in world political interaction. Any incremental increase in the efficiency of wheeled vehicle power processes will have a proportional and positive impact on world economic growth, environmental health and political stability.

1.1 Hydraulic Power Technology

The high power density, cycle rate, and life span of hydraulic accumulators make hydraulic technology very attractive in comparison to electro-chemical batteries for use in the drive and regeneration components of hybrid vehicles(Oko2005)(Buc79). This is particularly true in truck and bus applications where system mass is large and is combined with frequent stop and go cycles. In the proposed process, the enhanced energy management, regenerative braking, and increased efficiency in power supply for steering (Kab93//Shi2003) and other auxiliary systems will further improve overall efficiency with proportional reductions in gas and particulate emissions normally associated with conventional wheeled vehicle power processes.

It is believed that Hydraulic Power is inherently safer than Electro-Chemical Power when applied to Hybrid Wheeled Vehicle Processes. The long life cycle and general composition of the hydraulic components, when compared to equivalent electro-chemical components, should reduce the amount of hazardous materials entering the waste stream, this also is a very important consideration.

A significant challenge being met in the development of an efficient HHV is reducing thermal losses due to piping, valving, and accumulation which require supplemental cooling and treatment of the hydraulic fluids. Other challenges being met include effective program processed control of prime mover power to match averaged demand made possible by temporary storage and regenerative braking.

Although the power process is modeled as an Internal Combustion Engine/ Hydraulic Hybrid Vehicle the Loading Control Program and Power Flow Process is adaptable any type of prime mover using flywheel, electro-chemical, air pressurization, or other storage and drive methods.

1.2 Clean Diesel Combustion Technology

Diesel Engine emissions contribute to serious human health and environmental hazards. Reducing these emissions through application of CDC technology will help to address one of the most important air quality challenges facing the world. A significant reduction or elimination of nitrogen oxide (NOx), particulate matters (PM), hydrocarbon (HC) and carbon monoxide (CO) from diesel engine exhaust would have a profound impact on human health and environmental quality.

Clean diesel combustion technology is the combination of several innovative improvements in diesel engine technology. The improvements in fuel injection, re-optimization and refinement of air management/turbo charging systems results in cleaner and more efficient combustion of the fuel. (www.epa.gov/otaq/technology/420f04036.pdf) Increasing overall thermal and power process efficiencies reduces the amount of fuel burned for each unit of work performed with catalytic conversion and particulate matter traps in the vehicle exhaust system further reducing emissions. Natural Gas to Liquid Fuel technologies will also serve to support an overall reduction in diesel emissions by presenting a cleaner primary fuel.

Both General Motors and DaimlerChrysler have reported up to a 30% improvement in fuel economy when CDC technologies are used in modern vehicles (www2002 //Mag2003). Utilizing CDC in hybrid vehicles will further optimize CDC technology.

As CDC technology matures it is predicted to drastically reduce if not totally eliminate PM emissions by the end of 2020 as shown in figure 1.

2. PRESSURE COUPLED HHB

2.1 Major Power Production, Drive, and Control Components.

The proposed Pressure Coupled Hydraulic Hybrid Vehicle (HHV) has the following main components: Clean Diesel Combustion Prime Mover, Primary Pressurization Pump, High Efficiency Electronically Controlled Variable Displacement Transformer of radial multi cylinder design, Electronically Controlled Variable Displacement Hydraulic Pump/Motor Unit, Electronically Controlled Variable Displacement Hydraulic Drive Motor, Three Hydro-Pneumatic Accumulators, Electronic Controller, Control Valves, various Sensors, and Processor Based Loading Control Program.

2.1.1 Clean Diesel Combustion Prime Mover. (CDCPM)

A properly sized CDCPM as described in 1.2. CDCPM loading is controlled by the Processor Based Loading Control Program.

2.1.2 Primary Pressurization Pump. (PPP)

A hydraulic pump used to convert the mechanical energy from the prime mover to hydraulic power by pressurizing a common rail to the PPSA and auxiliary power systems.

2.1.3 Three Hydro-Pneumatic Accumulators

1. Primary Power and Storage Accumulator (PPSA) is fed from primary rail and serves as a temporary storage device for power averaging and peaking power supply. It accumulates power when secondary rail pressure is higher than primary rail pressure and feeds secondary rail when secondary rail pressure is below primary rail pressure. A negative pressure check valve prevents hydraulic feed back from the secondary rail during high pressure regeneration.

2. Secondary Regeneration Recovery and Feed Accumulator (SRRFA) receives and stores regenerated energy from the HT during regeneration and delivers energy to the HT during the next acceleration. During acceleration the SRRFA feeds the HT/secondary rail through a pressure differential and check valve when SRRFA pressure exceeds primary rail pressure. SRRFA pressurization will be considerably higher than PPSA pressure during temporary accumulation of regenerated energy. The differential and check valve also reserves capacity on the SRRFA based on LCP input. This insures adequate storage capacity for regenerated kinetic energy based on the velocity of the vehicle and independent of primary rail pressure.

3. Low pressure supply accumulator (LPSA) supplies pressurized hydraulic fluid supply to the HT to prevent cavitation during heavy loading.

2.1.4 Hydraulic Transformer. (HT)

A modified electronically controlled broad range adjustable valve angle plate hydraulic transformer used to transform and direct hydraulic power as demanded by the system. This multi-port transformer handles all power delivered too the drive system during power and all regenerated energy during regenerative braking.

2.1.5 Variable Displacement Hydraulic Pump/Motor (HP/M)

This device is integral with, or mechanically coupled to the front drive axel. It is used in the motor mode during initial acceleration and is switched to pump mode for regeneration of the linear kinetic energy of the vehicle during braking. This device is isolated during cruising and coasting.

2.1.6 Hydraulic Variable Displacement Hydraulic Drive Motor (HDM)

This device is mechanically coupled to the rear drive axel through a two speed forward and single speed reverse automatic transmission. It is used in conjunction with the front motor/pump during high pressure acceleration and serves as the single driving motor during cruising.

2.1.7 Control Valves, and various Sensors.

The Control Valves check and direct fluid power supply. Chop Valves interrupt hydraulic supply to secondary rail drive components during emergency braking. Various sensors feed input to the LCP and fail safe critical valves.

2.1.8 Loading Control Program (LCP)

The Loading Control Program receives input from, CDCPM RPM, vehicle velocity and cycle displacement, PPSA pressure, SRRFA pressure, and Reference Memory Files to maintain near constant loading of the prime mover by controlling the CDCPM fuel supply.

2.1.9 Power Component Control Unit.

The control unit receives input from conventional controls and converts that input to electronic control signals fed to the various power components.

3. Power Flow Control in Hydraulic Hybrid Vehicle

3.1 Initial Prime Mover Start Up and System Preconditioning.

After the prime mover has stabilized at idle, the operator will enter a choice of control programs at the dash mounted key pad. The Loading Control Program (LCP) will control prime mover loading from that point on. If needed, time is allowed for preconditioning of the PPSA to the initial operating pressure as called for by the LCP. The choice of control programs can be changed at any time in the transportation cycle.

After preconditioning, the prime mover begins to supply hydraulic energy to primary rail at the Loading Control Program averaged power.

3.2 Acceleration

During acceleration the HT is powered off secondary rail. Secondary rail is fed first from the SRRFA when SRRA pressure exceeds primary rail pressure. As SRRFA pressure drops to primary rail pressure, the primary rail outlet check valve opens allowing power to begin flowing from PPP/PPSA/primary rail and SRRFA. As velocity increases pressure decay on the HM/P line triggers the isolation of the HM/P for cruising with the HT then delivering all power to the HDM.

The prime mover continues to supply hydraulic energy to primary rail at the Loading Control Program averaged power.

3.3 Cruising

The HM/P has been conditioned for cruising by incremental isolation via a spring valve with all hydraulic power being directed to the HDM. Above a base line velocity, HDM line pressure triggers the gear set shift to reduce fluid flow rates and associated losses for increased efficiency.

The prime mover continues to supply hydraulic energy to primary rail at the Loading Control Program averaged power.

3.4 Coasting

The HT incrementally reduces hydraulic pressure to neutral at the HDM rear axel drive unit.

The prime mover continues to supply hydraulic energy to primary rail at the LCP averaged power.

3.5 Non-Emergency Regenerative Braking

In non-emergency braking the front axel HM/P unit is switched to the pump mode, reverse pressurizing the HM/P line, and driving the HT. The HT then feeds hydraulic energy to the SRRFA. The inherent properties of hydraulic power prevent axel lock and wheel slide during regenerative braking. Conventional Braking is incrementally blended based on demand.

The prime mover continues to supply hydraulic energy to primary rail at the LCP averaged power.

3.6 Emergency Braking

If the control unit receives input from the conventional controls indicating emergency braking the LCP and Control Unit chops prime mover power to idle, triggers chopping valves on both sides of the HT, and uses conventional friction braking to supply braking force.

4.0 Power Flow Diagram for this Proposed Hydraulic Hybrid Vehicle Configuration.

A. Clean Diesel Combustion Prime Mover B. Primary Pressurization Pump C. Primary Power and Storage Accumulator D. Secondary Regeneration Recovery and Feed Accumulator E. Hydraulic Transformer F. Front Drive Train G. Rear Drive Train

5.0 Basic configuration of (HHV)

5.1 Hydraulic Hybrid Vehicle Configuration

Figure 2 shows the proposed Hydraulic Hybrid Vehicle (HHV)

Needs Diagram

Figure 2: Hydraulic Hybrid Vehicle Configurations

In this configuration, the engine is mechanically coupled to the Primary Pressurization Pump which pressurizes primary rail powering auxiliary systems, charging the PPSA, and feeding secondary rail. A check valve blocks reverse hydraulic flow from secondary to primary rail when the SRRFA is above PPSA/primary rail pressure.

The Hydraulic Transformer is placed between the Hydraulic Pump/Motor, Hydraulic Drive Motor, and Secondary Rail.

7. THE SIMULATION OF HYDRAULIC HYBRID VEHICLE

7.1 Comparison of HHB with traditional vehicles

The research model compares acceleration/deceleration performance between the traditional and hydraulic hybrid vehicle. It also compares the level of energy recovery with and without hydraulic transformer. The base vehicle selected is ??????? Its parameters are presented in Table 1.

Table 1 Baseline Vehicle Specification

Body:

Mode:

Mass:

Engine:

Type: Transmission

Maximum Torque: Differential

Maximum Engine RPM: Accessories

Maximum Power: Power Steer

Figure 4: Acceleration Curve

Insert Acceleration Curve Here

Figure 4: The curve of acceleration performance

The modeling shows that integration of the hydraulic transformer with the hydraulic pump/motor and HDM allows for greater accelerative performance with smaller CDCPM peak horsepower.

Figure 5: Deceleration Curve and

Figure 6: Accumulator Pressurization Curve.

The deceleration performance of hydraulic hybrid vehicle is shown in Figure 5 and the SRRFA pressurization curve is shown in Figure 6. When the vehicle is driven at the speed of XX m/s, the deceleration performance of the HT equipped hydraulic hybrid bus is better than one not equipped with a HT.

Insert Deceleration Curve Here

Figure 5: The curve of deceleration performance

Insert SRRA Pressurization Curve Here

Figure 6: The SRRA Pressurization Curve.

The high pressure hydraulic fluid is used by hydraulic pump/motor unit to generate negative torque, braking the vehicle, and recovering the deceleration energy in a shorter time. Figure 6 shows clearly that with the help of a hydraulic transformer, the accumulator can recovery more energy.

8.0 General Efficiencies:

Summing CDCPM energy output and pressure variation of the hydraulic accumulators and following the high performance LCP the system puts XX Joules of energy into the process in X seconds giving the HHV a velocity of XX m/s. This translates to XX Joules of kinetic energy for a conversion efficiency of XX percent. This includes efficiency losses due to aerodynamic and road drag.

The HHV attains a maximum peaking velocity of XX m/s in XX seconds from stop when both accumulators are fully charged and the LCP is set to real time demand.

The CDCPM operates at XX Watts when operating at the designed cruising velocity of XXm/s.

The CDCPM operates at XX Watts when operating at the maximum sustained velocity of XX m/s.

9.0 CONCLUSION AND FUTURE WORK

The use of hydraulic power technology can enhance both the safety and efficiency of hybrid wheeled vehicles. Hydraulic Hybridization can optimize evolving Prime Mover technologies of all types by increasing overall process efficiencies through efficient mechanical to kinetic conversion and regeneration. The integration of Hydraulic Transformers will play a key role in continuing the evolution of this exciting technology with continued research further refining and enhancing the inherent efficiencies found in hydraulic power. HHV technology is expected to be capable of capturing and reusing a large percentage of braking energy normally lost during conventional friction braking as well as optimizing prime mover power at near peak efficiency. Power Averaging and Regeneration will substantially increase overall fuel efficiency with proportionately positive environmental, economic, and political effects driving this technology into the future.

Future work will focus on reducing thermal losses and reducing if not totally eliminating the need for hydraulic coolers.

The coming evolution of HHV technology will integrate flywheel storage, to efficient prime mover and evolved hydraulic power processes allowing for super high performance with independent 4 wheel traction controlled drive.

Power Averaging techniques will have wide spread application outside wheeled vehicles to include small unit electrical power production and industrial processes.