Flywheel Hybrid System Field of the Invention

The invention relates to a flywheel hybrid system, and more particularly, to a flywheel hybrid system comprising a flywheel selectively clutched to an internal combustion engine accessory belt drive system.

Background of the Invention

Flywheels are a well known means of storing energy and regulating speed. On vehicles including automobiles a large flywheel is typically mounted to the crankshaft. The flywheel inertia acts to smooth out the pulsating nature of the internal combustion process and prevents speed fluctuations from being transmitted to the transmission and the rest of the drivetrain.

Other uses of flywheels are known as well. For example, a flywheel is used to regulate the grid frequency. When the demand for electricity is high, the generator speed slows reducing the frequency of the supplied AC power as shown in Figure 1A. At peak demand a flywheel system could provide power, reducing the load on the generator. This keeps the speed of the generator up and maintains the frequency of the AC power. Further, flywheel based auxiliary power units (APU) can be used in power critical applications. In hospitals, if grid power is lost, a flywheel based APU can be used to provide instant power to bridge the gap between grid power loss and diesel generator start up. Similarly, critical computer systems could be kept powered up in the face of power outages. Figure IB demonstrates the use of the flywheel in manufacturing. _. Machines such as presses use flywheels A to maintain a constant speed under varying loads.

Further, flywheel systems called kinetic energy recovery system (KERS) are being used in certain racing applications including open wheel racing. For example, by recovering energy what would otherwise be wasted in braking the KERS can provide an extra 80Hp over 6.67 seconds .

Another known system is provided by Flybrid System _. , Northamptonshire, England as shown in Fig. 2. The system generally comprises a flywheel module A, a CVT module B, a gear train C, and output drive shafts D. The system provides 60 kW and can store 400kJ of energy in the flywheel with a top speed of 60000RPM.

Representative of the art is US patent number 3,672,244 which discloses an automotive system employing a high velocity, moderate mass flywheel capable of storing and rapidly dissipating large supplies of kinetic energy coupled with a transmission adapted to permit the smooth release of stored kinetic energy from the flywheel to the vehicle wheels, and a charging means for supplying kinetic energy to the flywheel at relatively low energy levels. The system provides substantial fuel economy and pollution relief through an efficient energy-conversion system.

What is needed is a flywheel hybrid system comprising a flywheel selectively clutched to an internal combustion engine accessory belt drive system. The present invention meets this need. Summary of the Invention

The primary aspect of the invention is to provide a flywheel hybrid system comprising a flywheel selectively clutched to an internal combustion engine accessory belt drive system.

Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings.

The invention comprises a kinetic energy recovery system for a belt driven accessory system comprising a kinetic energy storage device, a driver having a driver output, a transmission having a gear ratio connected to the driver output, a belt driven accessory system connected to the transmission through a first clutch, the kinetic energy storage device connected to the belt driven accessory system through a second clutch, and the kinetic energy storage device and the transmission connectable through the first clutch and second clutch. Brief Description of the Drawings

The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention.

Figure 1A is prior art showing a schematic showing regulation of a power system.

Figure IB is prior art showing a piece of industrial equipment using a flywheel.

Figure 2 is prior art showing a drivetrain KERS system.

Figure 3A is a table of pulley ratios for the system in Figure 3B. Figure 3B is a schematic of the inventive KERS system.

Figure 4 is a prespective view of a flywheel.

Figure 5A is a table of pulley ratios for the system in Figure 5B.

Figure 5B is a schematic of the inventive KERS system showing flywheel drive.

Figure 6 is a chart showing system characteristics. Figure 7 is a chart showing system characteristics. Figure 8Ά is a table of pulley ratios for the system in Figure 8B.

Figure 8B is a schematic of the inventive KERS system showing flywheel recharge during a braking event.

Figure 9 is a chart showing flywheel speed characterisitcs during flywheel recharging.

Figure 10A is a chart showing fuel savings with air conditioning operation.

Figure 10B is a chart showing fuel savings with no air conditioning.

Detailed Description of the Preferred Embodiment The ensuing description provides embodiments only, and is not intended to limit the scope, applicability, or configuration of the claims. Rather, the ensuing description will provide those skilled in the art with an enabling description for implementing the described embodiments. It being understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the appended claims .

The inventive system comprises a kinetic energy recovery system (KERS) system used to drive an internal combustion engine belt driven accessory system (ABDS) . The dual clutch configuration allows either the internal combustion engine or the flywheel to drive the accessories .

Significant fuel savings can be realized if the energy, otherwise wasted when the vehicle brakes are applied, is recovered and stored to be used later to propel the accessories. Usually, regenerative braking energy is used to propel the vehicle which is less efficient. In the inventive system, the recovered energy will be used to drive the engine accessories by use of a flywheel.

The inventive KERS system for driving the engine accessories is shown in Figure 3

The system 1000 comprises an internal combustion (IC) engine 100. Engine 100 may comprise an engine used in a vehicle such as a passenger car, truck, bus or any other vehicle using an IC engine. Engine 100 may comprise any number of cylinders as may be appropriate for the particular vehicle application in which the engine is used.

Engine 100 has an engine output 101 such as a crankshaft. A pulley 102 is attached to an end of crankshaft 101. Pulley 102 may comprise a v-belt pulley or a multi-ribbed v-belt pulley.

A belt 105 spans between pulley 102 and a pulley 103. Belt 105 may comprise either a v-belt, a multi- ribbed v-belt, chain or other suitable flexible power transmission member.

Pulley 103 is connected to shaft 104. Pulley 103 may comprise a v-belt pulley or a multi-ribbed v-belt pulley. Shaft 104 is used to redirect the output and may be included or excluded from a system depending on the configuration of the vehicle.

Shaft 104 is connected to a transmission 300. The example transmission comprises three speed ratios, namely, 2.0:1 (gears 301, 304), 1.2:1 (gears 302, 305) and 0.94:1 (gears 303, 306). Transmission 300 may comprise any known in the art suitable for use with a rotating output shaft.

Transmission 300 is connected to a first clutch 400.

Clutch 400 is a friction disk type clutch.

Flywheel 200 is connected to a gear 201 and gear 202. In this embodiment the gear ratio is 8.0:1 for gear 201 and 202. Gear 202 is connected to a second clutch 500. Clutch 500 is a friction disk type clutch.

The output of clutch 400 and the output of clutch 500 are each connected to a pulley 405. Pulley 405 may comprise a v-belt pulley or a multi-ribbed v-belt pulley.

Pulley 405 is connected to pulley 203B of dual pulley 203A, 203B by a belt 204. Dual pulley 203A, 203B may comprise a v-belt pulley or a multi-ribbed v-belt pulleys. Pulley 203A and 203B are fixed together. Belt 204 may comprise either a v-belt or a multi-ribbed v- belt, or other suitable flexible power transmission member.

Accessories comprise an alternator 600, an air conditioning compressor 700 and a power steering pump 800. A pulley 601 is connected to alternator 600. A pulley 701 is connected to air conditioning compressor 700. A pulley 801 is connected to power steering pump 800. A belt 205 is trained between each pulley 601, 701 and 801 and pulley 203A. Each pulley 601, 701, 801 may comprise a v-belt pulley or a multi-ribbed v-belt pulley. However, each pulley must be compatible with the same belt type for a given system. Belt 205 may comprise either a v-belt or a multi-ribbed v-belt.

The arrangement of the system allows the flywheel to make use of the same gearing as used for a three speed accessory drive using only a transmission 300. An example flywheel is shown in Figure 4. In this embodiment flywheel 2000 comprises a carbon cord annulus 2001 wound over a steel hub 2002. The carbon cord annulus is contained within a case 2003 to prevent ingress of debris .

The flywheel system is connected to clutches 400, 5Ό0 through a 8.0:1.0 speed ratio transmission. For example, if the minimum speed of the engine is 800 RPM and the minimum speed of the flywheel is 32,000 RPM, then the flywheel to ABDS ratio will be

_ 32000 _

^^Flywheel/ABDS ~ _QQQ ^— 40.0

At this speed ratio, the flywheel 200 must be disconnected from the engine 100 when the engine speed rises above some threshold to prevent over speeding. For example, if the speed limit of the flywheel is 60,000 RPM, then above and engine speed of

60,000

— = 1500 RPM

40

the flywheel should be disconnected

The pulley ratios for the system are shown in Figure 3A. The legend in Figure 3A shows the gear ratio for the associated gear set.

Flywheel 200 used in the inventive system is shown in Figure 4, which is relatively small and operates at above 30,000 RPM. The example flywheel is a carbon composite installed over a metal hub. The flywheel operates in a vacuum to minimize windage losses. In this embodiment the inertia of the flywheel is approximately 0.035kg. m ² .

In the first mode the kinetic energy stored in the flywheel 200 is used to propel the accessories. In the second mode, the flywheel is charged by the braking energy of the vehicle. In the third mode, the engine drives the accessories while the flywheel idles. As shown in Figure 5, the accessories are connected to the high speed flywheel through a constant speed ratio of:

1.0

— x 0.4 x 0.50 = 0.025

8.0

By using such a large speed ratio, the speed of the accessories is kept low and the speed variations of the accessories are kept re-latively small even though the flywheel speed could vary to a greater extent. This minimizes the power the flywheel has to provide and therefore provides a more efficient system.

To propel the accessories using the flywheel, clutch

400 is disengaged and clutch 500 is engaged. This configuration disconnects the accessories from the engine and utilizes power from the flywheel. The arrows in Figure 5B show the power flow from the flywheel to the accessories.

For purposes of this example it is assumed that the flywheel is maintained at a minimum speed of 32,000 RPM. If the flywheel speed falls below this value, then clutch 400 is engaged and clutch 500 is disengaged. This reconnects the accessories to the engine and disconnects the flywheel. The accessories will then be driven by the engine through the three speed transmission 300 while the flywheel idles until a vehicle braking event occurs to recover energy and charge the flywheel.

In the noted examples, the FTP75 City Cycle is used as the basis of the system analysis. Further, a generic vehicle such as a Toyota Camry® with a 2.4L engine is modeled with two ABDS loading conditions. The base configuration has 25 amperes electrical load, and no air conditioning. The loaded configuration has 50 amperes electrical load and an air conditioning load. The increased electrical load accounts for the AC blower motors .

The example shown in Figure 6 demonstrates that for the base configuration, the energy recovered from the vehicle brakes is enough to propel the accessories for the entire cycle. In the example there are only two brief instances when the flywheel reached the lower speed threshold and the engine propelled the accessories until the flywheel was charged again.

The example system is configured not to propel the accessories when the vehicle is stopped because the engine is shut off at this time. The plot shows that as the vehicle speed goes to zero, the power supplied by the flywheel and engine are zero.

With the AC active, the ABDS requires more power than the base system with AC inactive. The excess power is supplied by the flywheel 200 and engine 100. If we assume that the accessories are suspended from operation during engine idle periods, then the plots of power to propel the accessories is shown in Figure 7. Note the periods in which the engine now has to supply power to the accessories is greater.

When the engine is driving the accessories, it does so through the three speed accessory drive transmission 300. Whenever there is a braking event, the system charges the flywheel which provides the braking torque to the vehicle. For good drivability, a majority of the braking energy can be recovered but not all. This is because the driver has to have control over the length of time the brake is applied and with what pressure. Trying to recover all braking energy could result in an unpleasant driving experience.

The system configuration during a braking event is shown in Figure 8. Figure 8A is a table of pulley ratios for the system in Figure 8B. During a braking event, the engine speed is decreasing and simultaneously it is desired to increase the flywheel speed. This can be achieved with the clutches and the transmission. The arrows show the power flow from the flywheel to the accessories.

During the flywheel charging process, clutch 400 and clutch 500 are engaged and power is transmitted from the engine to the flywheel and accessories through the clutches and the transmission as illustrated in Figure 9. The actual ratio selected during the charging process will depend on the engine speed at that point.

For example, assume the engine speed is 2000 RPM and the flywheel is at 32,000 RPM when the recharging process begins. If transmission 300 having a 0.94 ratio is employed then the speed on one side of the clutch will be

2000RPM x 2.5 X 0.94 =4700 RPM while the speed on the flywheel side of the clutch will be

32000ΛΡ Χ— = 4000 i?P .

8.0

This results in a speed differential of 700 RPM over the clutch 400 and an effective speed ratio of

32000 4000 4700 _

4000 ^X 4700 X ^X 2000 ^{~ 16'} °

between the engine and the flywheel. If it is assumed that the torque transferred through the clutch 400 is limited-, then the speed of the flywheel 200 will increase until the speed on both sides of the clutch 400 are close to being the same and the speed ratio between the engine and the flywheel will be 18.75.

However, if the 18.75 ratio was indefinitely maintained, the speed of the flywheel will start to decrease with the speed of the engine. It is at this moment (speed decrease) that the transmission ratio is switched to 1.2 (gears 302, 305). Utilizing the second ratio will result in one side of the clutch 400 having a higher speed that the other side. Again, as torque is transferred through the clutch 400, the speed of the flywheel will increase even thought the engine speed is decreasing. When the speed on both sides of the clutch 400 is close to being the same, the final ratio of 2.0 (gears 301, 304) can be use to fully charge the flywheel.

As noted previously, for the loading condition with AC loads, it is assumed that during idle periods, the air conditioner 700 will continue to be propelled by the flywheel 200. Whenever the flywheel energy is exhausted, the engine will start up and ramp up speed until the flywheel is fully charged then turn off again. Because of this only a portion of the idle saving with AC load is realized. With no AC load it is assumed that the accessories do not operate during engine idle periods, therefore, all the engine idle savings are realized.

Figure 10A is a chart showing fuel savings with air conditioning operation. Figure 10B is a chart showing fuel savings with no air conditioning.

From the inventive system a 25.7% savings is realized when the air conditioning is operating and a 26.4% savings is realized when there is no air conditioning. Although the savings are similar in value, the absolute savings in terms of volume or weight of fuel is greater with the air conditioning system since the MPG with air conditioning is lower.

The results show that the fuel savings of the inventive system are on par with the hybrid electric vehicles. The advantages of the inventive system is that in production it can be realized for perhaps a third of the cost of a full hybrid electric system according to published reports. Further advantage is realized in terms of not requiring batteries and rare earth magnets used in typical hybrid electric motors.

Although forms of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts without departing from the spirit and scope of the invention described herein.