Patent Application
20060275137
1. Field of the Invention
The present invention generally relates to a fuel delivery system with improved efficiency.
2. Description of Related Art
Current automotive fuel delivery systems include: mechanical return, mechanical return-less, electronic multiple speed return and electronic return-less fuel systems (ERFS). In each fuel delivery system, pump components have to be sized to provide the maximum flow required by the engine at full load condition. Generally, electric motors are wound for maximum efficiency at an optimal rated voltage for a given load. For mechanical systems the optimal rated voltage is supplied to the motor and the pressure in the fuel system is regulated to provide the desired fuel flow rate. In electronic fuel systems (EFS) the motor is selected such that in a wide open throttle (WOT) condition the motor is supplied the optimal rated voltage. Often fuel flow is controlled electronically by pulse width modulating (PWM) the fuel pump resulting in a signal with a supply voltage equal to the optimal rated voltage modulated by a duty cycle (0 to 100%). The pump speed and fuel flow are reduced to supply only the fuel required for less than WOT or full load conditions. Alternatively, an analog signal may be provided to the motor that is less than the optimized voltage by electronically bucking the signal. Reducing the duty cycle or bucking the drive signal for the motor can result in electrical inefficiencies in the fuel delivery system.
In view of the above, it is apparent that there exists a need for a fuel delivery system with improved efficiency.
In satisfying the above need, as well as overcoming the enumerated drawbacks and other limitations of the related art, the present invention provides a fuel delivery system with improved efficiency.
The fuel delivery system includes a fuel pump, a controller, and a boost circuit. The fuel pump has an electric motor that includes a winding configured to operate with a maximum efficiency at a first voltage for an expected load, such as a flow rate that satisfies the fuel demand for 90% of the drive cycle. The controller includes a pulse width modulator for generating a driving signal for the electric motor. The pulse width modulator is configured to vary the duty cycle of the driving signal based on a fuel demand. Under normal operating conditions, such as a fuel demand within 90% of the drive cycle, the boost circuit acts as a pass-through and the driving signal is modulated at the first voltage to control the pump output. However, when a load greater than the expected load is applied to the electric motor, such as a fuel demand in the remaining 10% of the drive cycle, the boost circuit acts to scale the driving signal to a second voltage that is greater than the first voltage. The second voltage drives the electric motor at a voltage beyond the maximum efficiency, but provides overall improved system efficiency.
In one aspect of the present invention, the fuel pump can be operated for most of the drive cycle without any need for electronics and, therefore, eliminates the electronic losses in conventional PWM systems.
In another aspect of the present invention, the system will be more efficient at nominal operation and under full load conditions because the pump will be designed for low voltage operation. Thus, at higher flow the fuel pump will be operated at a higher and more efficient voltage than a conventional EFS. This strategy allows for improved low voltage start or pressure rise conditions as required. Further, system components may be reduced in some fuel system hardware architectures.
Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification.
Referring now to
The control circuit 14 is configured to generate a driving signal for the electric motor 12. The electric motor 12 is wound to operate with a maximum efficiency at a first voltage for a typical operating load, such as 90 liters per hour which would cover 90% of the vehicle drive cycle. The control circuit 14 includes a controller 18 and a boost circuit 20. A pulse width modulator 22 of the controller 18 provides the driving signal to the boost circuit 20. Under normal operation, the boost circuit 22 passes the driving signal through to the motor 12 without modification. If the fuel demand is lower than the typical demand, for instance less than 90 liters per hour, the pulse width modulator 22 provides a signal with a duty cycle that lowers the output of the motor 12. However, when the fuel demand increases, the load on the motor 12 also increases requiring more motor output. Accordingly, the boost circuit 20 is configured to receive the driving signal from the pulse width modulator 22 and scale the driving signal to a second voltage that is greater than the first voltage. The boost circuit 20 is in communication with a power supply 16, such as the vehicle battery, to provide the second voltage. In one example, the first voltage may be less than the vehicle battery voltage such as 6 volts. In this case, the second voltage could be equal to a vehicle battery voltage, such as 12 volts. In another example, the first voltage could be equal to the battery voltage and the second voltage provided by the power supply 16 could be a stepped up voltage, such as 17 volts. In either case, the motor would be configured to run at maximum efficiency at the first voltage for a typical load, such as a typical fuel demand, and provide an additional voltage overdriving the motor 12 when the load exceeds the expected load for a typical fuel demand.
The architecture illustrated in
Now referring to
The equations provided below can be used to compare the efficiency between the three aforementioned fuel systems. More specifically, equations 1-4 can be used to compare the efficiency of the MRFS to the 2-Speed fuel system. The base efficiency of a mechanical returnless fuel system can be calculated according to equation 1 by substituting in the values from Table 1.
Base efficiency of MRFS=(195×500)/12×9.99×3600=22.6% (1)
Equation 2 provides the average effective current for a 2-speed fuel system over the drive cycle. Accordingly, current savings of the 2-speed fuel system over the mechanical returnless fuel system is illustrated in
2-Speed current=9.99×(10%)+6.14×(90%)=6.52 A (2)
Accordingly, current savings of the 2-speed fuel system over the mechanical returnless fuel system is illustrated by equation 3.
Savings of 2-Speed over base MRFS=9.99−6.52=3.47 A (3)
Further, the average effective efficiency of the 2-speed fuel system over the drive cycle can be calculated according to equation 4 by substituting in the values from Table 1.
Effective efficiency of 2-Speed=(195×500)/12×6.52×3600=34.62% (4)
Equations 5-7 can be used to compare the efficiency of the MRFS to the boost architecture of
Boost current=13.6×(10%)+4.5=(90%)=5.41 A (5)
Equation 6 provides a current savings of the boost architecture over the mechanical return fuel system.
Savings of Boost over MRFS=9.99−4.5=5.49 A (6)
Lastly, the average effective efficiency of the boost architecture over the drive cycle can be calculated according to equation 7 by substituting in the values from Table 1.
Effective efficiency of Boost =(195×500)/12×5.41×3600=41.74% (7)
For the boost system illustrated in the graph, system consumption is calculated using 90 liters per hour at a 12 volt system voltage to the pump. This system consumption would cover 90% of the vehicle drive cycle, if the maximum fuel demand were 195 liters per hour. To provide a fuel demand of 195 liters per hour would require the 12 volts system voltage plus an additional boost voltage to provide 17 volts for the remaining 10% of the drive cycle.
Bars 30, 32, and 34 relate to a mechanical return fuel system. Bar 30 illustrates the power required to provide 90 liters per hour (covering 90% of the drive cycle). Bar 32 illustrates the power required to provide fuel at 195 liters per hour (typical of WOT and required in less than 10% of the drive cycle). The resulting system efficiency is 22.6% as illustrated by bar 34.
Bars 36, 38, and 40 relate to a system with a 2-speed fuel pump. Bar 36 illustrates the power required to provide 90 liters per hour (covering 90% of the drive cycle). Bar 38 illustrates the power required to provide fuel at 195 liters per hour (required in less than 10% of the drive cycle). The resulting system efficiency for the 2-speed fuel pump is 34.62% as illustrated by bar 40.
Bars 42, 44, and 46 relate to the boost architecture described above. Bar 42 illustrates the power required to provide 90 liters per hour (covering 90% of the drive cycle). Bar 44 illustrates the power required to provide fuel at 195 liters per hour (required in less than 10% of the drive cycle). The resulting system efficiency for the boost architecture is 41.74% as illustrated by bar 46. Accordingly, the improvement system efficiency is significantly improved for the system with the boost architecture.
Now referring to
Now referring to
A fuel pressure sensor 80 is provided to measure the fuel pressure within the fuel delivery system 70 and generate a feedback signal that is provided to the controller 82. The controller 82 generates a drive signa, that may be pulse width modulated, based on the fuel demand and provided to the boost circuit 74. The boost circuit 74 can then be enabled based on the pressure feedback signal to scale the drive signal 76 generating a boost voltage 76.
In addition the fuel pump should provide flow and pressure at cold temperature and at 6 volts or less. The described boost architecture can provide superior performance under these conditions by boosting voltage to a pre-determined higher voltage.
For example, consider three drive modes (cold start, highway, tip-in/W.O.T) using the boost architecture. At cold start, initially the RPM of the fuel pump motor is low. The boost strategy is applied to the fuel pump, allowing the required fuel pressure and RPM while operating with boost voltage. In cruise mode, the fuel pump operates at the nominal system voltage, with the boost circuit operating as a pass thru only function. During “Tip-in” or WOT mode, the controller recognizes the increased engine fuel requirement and the boost circuit will operate to boost the drive signal to a pre-determined voltage based on specific pump and vehicle requirements.
Pressure response is also addressed with the boost architecture. Pressure response time is improved with a higher voltage applied to the fuel pump. In systems where additional pressure response is needed, an additional boost voltage can be supplied.
In addition, the electronic control module can be designed to pass thru system voltage during nominal drive cycle, thereby reducing EMC induced noise and electronic losses associated with more typical EFS systems during normal drive cycle.
As a person skilled in the art will readily appreciate, the above description is meant as an illustration of implementation of the principles this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from spirit of this invention, as defined in the following claims.
