Mixed fuel system

Abstract

The present invention provides a novel combination of devices to measure and transmit to an electronic controller data pertaining to differential pressures, temperatures, regeneration status, exhaust content, accumulated gas consumption and substitute fuel consumption. The electronic controller compares the data to thresholds; when the controller receives signals indicating these thresholds or limits are met, the controller causes the gas substitution rate to be diminished or set to zero until after-treatments elements are fully regenerated thereby facilitating integration of a mixed fuel system with an application internal combustion engine.

Claims

1. A mixed fuel system comprising: a dual fuel controller configured to receive a signal from a user controller, receive at least one signal from an exhaust gas recirculation system, the at least one signal from the exhaust gas recirculation system including one or more of an exhaust gas recirculation valve position, barometric pressure, exhaust gas recirculation differential pressure, intake manifold pressure, and intake manifold temperature, generate and send a first emulated signal based on the signal received from the user controller to an electronic control module (ECM) which uses the first emulated signal to limit a flow of diesel fuel to a diesel engine and allow for a flow of second fuel to the diesel engine to meet user demand, and generate a second emulated signal by manipulating the at least one signal from the exhaust gas recirculating system and send the second emulated signal to the ECM which uses the second emulated signal to control the exhaust gas recirculation system.

2. The mixed fuel system of claim 1, wherein the user controller is at least one of a remote pedal interface, a virtual pedal emulator, a foot pedal and a vehicle cruise control, wherein the ECM limits diesel demand by emulating any one or more of a single analog throttle position sensor (TPS) signal, a dual analog TPS signal, and a single PWM signal or a direct torque/speed command.

3. The system of claim 1, wherein the dual fuel controller interrupts and emulates driver controls to the ECM comprising interruption and emulation of an accelerator pedal input signal or a cruise control activation switch.

4. The system of claim 3, wherein emulation of the accelerator pedal input signal occurs and comprises one of a throttle position sensor, dual analog TPS signal, and a single pulse width modulation signal.

5. The system of claim 4, wherein the pedal input signal is modified to reflect lower diesel demand thereby reducing the pulse width modulation (PWM) and demand for diesel and supplying secondary fuel in order to meet driver demand.

6. The mixed fuel system of claim 1, wherein generating the first emulated signal includes interception and modification by the dual fuel controller of a vehicle cruise control activation switch signal which reduces demand for diesel, allowing substitution of the second fuel to meet driver demand as set through the vehicle cruise control.

7. The system of claim 6, wherein the vehicle cruise control activation switch indicates any one of accelerate, decelerate, and set speed and overall speed governing and other cruise control inputs, are monitored through one of a direct electrical or a serial bus connection to facilitate implementation by the dual fuel controller of overall vehicle speed governing an emulated pedal signal to govern diesel demand limit.

8. A vehicle having a mixed fuel system for substitution of a secondary fuel for diesel in an internal combustion engine, said system comprising: an internal combustion engine; an electronic control module (ECM) configured to control a flow of diesel fuel to the internal combustion engine and control an exhaust gas recirculation system; a user interface; and a mixed-fuel controller configured to receive a signal from the user interface, generate a first emulated signal based on the signal received from the user interface, and send the first emulated signal to the ECM where the ECM uses the first emulated signal to control the flow of diesel fuel to the internal combustion engine, wherein the first emulated signal reduces a demand for diesel allowing substitution of a secondary fuel to meet a driver demand, the mixed-fuel controller being further configured to receive at least one signal from the exhaust gas recirculation system, generate a second emulated signal by manipulating the at least one signal from the exhaust gas recirculation signal, and send the second emulated signal to the ECM where the ECM uses the second emulated signal to control exhaust gas recirculation system.

9. The vehicle having the mixed fuel system of claim 8, further comprising: a plurality of sensors configured to monitor and control EGR emulation, DOC protection, DPF monitoring and SCR after-treatment subsystems.

10. The vehicle having the mixed fuel system of claim 9, wherein at least one of the sensors includes an electrical interface, said interface receiving one or more of a set of signals comprising EGR differential pressure, EGR valve position, barometric pressure, intake manifold pressure, and intake manifold temperature.

11. The vehicle having the mixed fuel system of claim 8, wherein the mixed fuel controller is further configured to generate the second emulated signal based, in part, on a status of a diesel particulate filter.

12. The vehicle having the mixed fuel system of claim 11, wherein a status of the diesel particulate filter is based on sensor results from sensors that actively monitor diesel particulate filters differential pressure.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1—Pedal Emulator Interface

(2) FIG. 2—Remote Pedal Emulator Interface

(3) FIG. 3—Torque Speed Command

(4) FIG. 4—Vehicle Cruise Control Emulator

(5) FIG. 5—Emissions Feedback Control

(6) FIG. 6—EGR Emulator

(7) FIG. 7—After-treatment Protection

(8) FIG. 8—EGR Emulator schematic

DETAILED DESCRIPTION

(9) The present invention preserves the most cost effective means for integrating a mixed fuel system 10 with an application internal combustion engine 100. The internal combustion engine 100 includes serial bus 16, diesel fuel control 104, exhaust gas recirculation 200, diesel oxidation catalyst 300, diesel particulate filter 400 and selective catalytic reduction 450 after-treatment subsystems 500. The mixed fuel system 10 includes an electronic controller 600 (also described as a Dual fuel controller, electronic control module), sensors 14, and serial bus 16 communications with the internal combustion engine controller 12, as well as gas regulation components appropriate for fumigation-based control.

(10) The controller 600 may comprise a ruggedized engine control module. The embedded electronic controller is capable of operating in harsh automotive, marine, and off-highway applications. It's hardware features wide-ranging input and output functionality and microprocessor(s) which are pre-programmed and calibrated with a highly customized control strategy. An onboard floating point processor with high clock frequency allows complex control software to run efficiently. Dual and/or fixed-point processors may also be employed for safety, redundancy and/or cost savings. Integrated serial communications data-links ensure interoperability with other system components.

(11) In addition, the present invention also incorporates methods and apparatus necessary for achieving independent diesel fuel control as well as exhaust gas emissions control. The present invention facilitates including monitoring and/or controlling exhaust gas recirculation (EGR) 200 emulation, protecting diesel oxidation catalyst (DOC) 300, monitoring a diesel particulate filter (DPF) 400 and includes a selective catalytic reduction (SCR) 450 after-treatment subsystem 500.

(12) Pedal Signal Emulation:

(13) One preferred approach to diesel demand limiting comprises: accelerator pedal signal 21 emulation. This mechanism limits diesel consumption by stemming driver demand 22 and is shown in FIG. 1.

(14) In diesel only mode, the accelerator pedal signal 21 is passed directly through to the diesel 100 ECM 600. The pedal input 20, 21 is combined with other control signals (e.g. engine speed) as the basis for a diesel fuel map 26 to the engine 100. Particularly in the case of a so-called “min-max” electronic governor, the fuel command is proportional to the magnitude of the pedal input 20, 21 itself. Thus, the driver 28 indirectly commands diesel fuel 18 to the engine 100 via the accelerator pedal 20.

(15) In mixed fuel mode, the accelerator pedal signal 21 is first processed through the mixed fuel control system 10. The system 10 of the present invention intercepts and electrically emulates the accelerator pedal signal 21 to create an emulated pedal signal 40 to reflect a lower level of diesel demand 36 from the driver 28. This allows a secondary fuel 34 (e.g. natural gas) to be mixed with diesel 18, therefore allowing maximum fuel economy without overpowering the engine 100. The emulated pedal signal 40 can also be used to control diesel demand 36 during Vehicle Cruise Control 38 operation as depicted in FIG. 4. (see FIGS. 1 and 4)

(16) Emulation of the pedal signal 40 may involve several different electrical interfaces, including single analog throttle position sensor (TPS) signal; dual analog TPS signal; and a single PWM signal. The pedal signal 21 in any format is intercepted and then modified to reflect a diminished diesel demand 36 during the mixed fuel mode of operation. Modification can be achieved through any of several means. The appropriate selection depends on the signal format.

(17) The modification may be made to employ a simple voltage divider 52. However, this modification changes pedal feel. It also will not work with PWM (Pulse Width Modulation) input and will not allow for VCC 38 (Vehicle Cruise Control) operation. Further, it may not satisfy modern on board diagnostic (OBD) checks. Alternatively, the modification may comprise a Simple Zener diode 52a. Once again, the Simple Zener diode changes pedal 20 feel, effects no Pulse Width Modulation, and does not work with Vehicle cruise control 38. Further, this modification cannot satisfy modern on board diagnostic checks.

(18) Analog input and analog output drivers are also possible modifications, however, they are a relatively expensive solution, and may not handle PWM signal input. As an alternative, analog input combined with Pulse Width Modulation output driver with impedance matching is, generally, the best solution for single/dual analog. This arrangement handles Vehicular cruise control 38 and on board diagnostics checks.

(19) Finally, Analog/Digital input combined with Schottky trigger, TPU (Time Processor Unit) and Pulse Width Modulation output driver is considered by the inventors to comprise a preferred solution for Pulse Width Modulation and the combination handles Vehicular Cruise Control 38 and on-board diagnostics. The TPU is a microprocessor which counts/captures digital events such as pulses over a given time period. In the case of a PWM signal, there are on/off digital pulses modulated with a certain duty cycle and frequency. A TPU is required to process the signal

(20) Diesel engine 100 electronic control module 12 self-test and diagnostic criteria for the throttle position sensor (TPS signal) are also satisfied by the emulated signal output 40. For failsafe reasons, the accelerator pedal signal 21 is switched to the emulated signal 40 using a normally-closed (NC) dual-pole single throw (DPST) relay. Any mixed-fuel component failure will pass the accelerator pedal signal 21 through NC contacts to the diesel ECM 600 and fully restore operation to diesel-only mode.

(21) Remote Pedal Interface:

(22) A second preferred approach to diesel demand limiting involves bypass of the primary accelerator pedal 20 input 21 through a remote pedal interface 58 is depicted by FIG. 2. Since some engine ECMs 12 are designed to allow for remote pedal 57 operation (e.g. for work-truck applications), activated by a separate switch or jumper input, diesel demand limiting can be achieved without interrupting and processing the primary pedal input 21.

(23) In diesel-only mode, the driver commands diesel fuel 22 to the engine 100 via the accelerator pedal 20. In mixed fuel mode, the remote accelerator pedal signal 64 instead originates from the mixed fuel control system 10. The mixed fuel control system 10 may comprise controller 600, sensors 14, serial bus 16, communications with the engine controller 12.

(24) The present invention monitors the primary pedal input 21 level through the ECM 12 serial bus 16 connection and electrically emulates the accelerator pedal signal 21 to reflect a lower level of diesel demand 36 sent from the remote pedal 55 input 64. As with the first approach, this allows secondary fuel 34 (which may comprise natural gas) to be supplied to the engine 100 with diesel 18, therefore allowing maximum fuel economy without overpowering the engine 100.

(25) The remote accelerator pedal 55 signal 58 must accommodate the interface requirements of the diesel ECM 12 in order to satisfy self-test and diagnostic criteria. For failsafe reasons, the accelerator pedal signal 21 is switched to the emulated output signal 40 using a separate digital output from the dual fuel ECM 600. Any component failure in the mixed-fuel system 10 will return the primary accelerator pedal signal 21 to the diesel ECM 12 and fully restore operation to diesel-only mode.

(26) Using the remote pedal input 55, 58 and emulation of VCC operation 38, diesel 18 demand can be directly controlled by the mixed fuel controller 600, allowing significant substitution of a secondary fuel 34. This is the preferred embodiment for engines equipped with a secondary, remote pedal input and networked through J1708/J1587 serial or proprietary CAN busses.

(27) Torque Speed Command:

(28) A third, and most preferred method for diesel demand limiting involves direct control of the engine 1 using the J1939 Torque Speed Command (TSC) interface 70. The TSC interface 70 allows the engine torque and/or speed to be limited and/or controlled by an externally networked device, in particular the mixed fuel controller 600. For J1939 capable engines, this method allows the mixed fuel ECM 600 to substitute the secondary fuel 34 in place of diesel 18 in a highly controlled manner and manage engine torque and/or speed during all modes of engine operation. A similar command interface is also available and may be utilized for certain proprietary CAN busses. FIG. 3

(29) During diesel only operation, the mixed-fuel system 10 does not send any torque speed command 70 over the CAN bus 16, and therefore does not limit or control engine torque. Once mixed-fuel mode is active, the controller 600 sends the torque speed command 70 in accordance with the J1939 specification, thereby enabling control over engine torque and/or speed. This, in turn, gives the mixed-fuel ECM 600 independent control over diesel fuel consumption, irrespective of whether the driver or VCC 38 is governing engine speed and/or acceleration.

(30) If an automatic transmission shift or traction control event (etc.) occurs during mixed fuel operation, the engine ECM 12 itself will arbitrate any transient conflict in TSC 70 commands. In either case, the mixed fuel system 10 will revert to diesel-only mode for any remaining duration of the event.

(31) Vehicle Cruise Control:

(32) The apparatus required for emulation of vehicle cruise control 38 functionality within the mixed fuel system 10 is shown and described by FIG. 4. During VCC operation and in mixed-fuel mode, the diesel fuel 18 is controlled by the electrically emulated pedal signal 40 while natural gas 34 is controlled by a variable flow control valve such as an electronic throttle body (ETB) 75. The overall fuel demand is controlled by the emulated VCC function 38, 40 while the resulting gas substitution ratio (GSR) is defined by fuel tables which are optimized for fuel economy, engine performance, emissions, etc. Details are described below.

(33) The VCC 38 is operated by on/off switch 39 which is electrically interrupted and monitored by the mixed fuel controller 10. During diesel-only operation, the state of that switch 39 is passed through to the diesel ECM 12, allowing for normal VCC 38 operation. In mixed-fuel mode, the state of the switch 39 is emulated by the dual fuel controller 600 and passed through in an “off” state, preventing the diesel ECM 12 from activating the internal VCC 38 function.

(34) Instead, with the physical VCC on/off switch 39 in the “on” state, the dual fuel controller 600 emulates the VCC 38 function for effective mixed fuel operation. To accomplish this, the dual fuel ECM 600 must also monitor the state of all other VCC 38 control inputs (e.g. “set 602,” “accel,” 604 “decel,” 606 etc.) as well as driver inputs (e.g. brake 608, clutch 610) and vehicle speed using the serial bus 16 (e.g. J1587) connection.

(35) Thus, when the driver presses the VCC 38 switch 39 to “set” 602, the current vehicle speed is captured as a VCC control set-point. Any deviation from that set-point results in a speed error signal. Based on the sign and magnitude of that error over time, a dual-fuel VCC 38 feedback controller 612 generates an increasing, decreasing or constant overall fuel demand. Note that the dual-fuel VCC controller 612 responds similarly to an “accel” or “decel” input from the driver.

(36) The resulting, overall fuel demand is then satisfied by a fuel mixture 18/34 employing a gas substitution ratio which is defined through a fuel map 26 in the dual-fuel ECM 600. In turn, this gas substitution ratio (GSR) is optimized for fuel economy, engine performance and exhaust gas emissions. The diesel portion of the fuel demand is processed by the emulated pedal signal 40. See FIGS. 1 and 2 for related details. The natural gas (secondary fuel 34) demand is controlled by the variable flow valve which may comprise the ETB 75. The exhaust gas emissions, E.g. NOx, are monitored using existing sensors and the CAN bus or sensors specific to this task, thereby providing means for real time control and adjustment of gas, secondary fuel, and air to adjust and manage emissions via the ECM 600 and EGR 200.

(37) Should the driver cancel or otherwise interrupt VCC 38 operation by tapping the brake, depressing the clutch, etc., the dual fuel ECM 600 will revert to pedal operation but remain in mixed-fuel mode. Any mixed-fuel component failure will pass the VCC 38 on/off signal through digital output to the diesel ECM 12 and fully restore operation to diesel-only mode.

(38) By monitoring all VCC 38 control inputs and assimilating all control outputs, the present invention allows the dual fuel ECM 12 to emulate entirely the VCC function 40 through use of an optimal fuel mixture 22, 34. Status lamps on the instrument panel may also be controlled through the applicable serial bus 16. Without this invention, gas substitution, and therefore fuel economy, emissions performance, etc. are completely constrained by the diesel ECM 12 speed governor.

(39) Feedback Control of Combustion, Exhaust Gas Recirculation:

(40) For feedback control of the combustion process, with improved fuel economy and emissions performance as control objectives, the present invention monitors the diesel engine, gas train and after-treatment system 500. Engine data 82 is acquired through the diesel ECM serial bus 16 as depicted in FIG. 5 or through direct engine sensing of at least some of the following parameters: Engine speed; Engine load (e.g. manifold air pressure, external load sensor, etc.); Pedal position 20, 21 or governor demand input; and Diesel fuel consumption. Though not all depicted in FIG. 5, gas train sensing measurement and devices may also include: Tank pressure as applicable; Regulator pressure; Gas temperature; Gas fuel consumption either directly or indirectly through: gas-compatible hot-wire anemometer; differential pressure sensor; Coriolis flow meter; gas flow estimation.

(41) The dual fuel system 10 also monitors exhaust gas emissions 90, either through the diesel ECM 12 and/or after-treatment (AT) 500 control module serial bus connection, or through direct sensing of one or more of the following: NO.sub.X/O.sub.2 concentration level via CAN-based Smart Sensor or Standalone O.sub.2 sensor along with Exhaust Gas Temperatures (EGTs) and pressure.

(42) Importantly, the present invention not only monitors the combustion process, but also independently controls both primary 18 and secondary 34 fuel sources as well as oxygen content through exhaust gas recirculation (EGR) 200. Control over diesel demand is described through FIGS. 1-4 with the CAN-based TSC command 70 implicit within FIG. 5. Gas flow control is achieved through a variable flow valve (not shown) while EGR 200 emulation is depicted in FIG. 6.

(43) While prior art systems do claim to improve exhaust gas emissions through the combustion of natural gas in the fuel mixture, these systems do not actively monitor or control emissions content. Instead, the present invention controls diesel demand, gas flow and exhaust gas recirculation, all while monitoring exhaust gas conditions, for the purpose of optimizing both fuel economy and emissions performance. In summary, this basic responsiveness to emissions performance in addition to lifecycle cost savings is at the core of the novel control system.

(44) Exhaust emission 90 in general, and PM (particulate matter) 95 in particular is further impacted by the use of exhaust gas recirculation (EGR) 200 valves, which are intended to reduce NOR. Most diesel engines ECMs 12 control the EGR 200 in an open-loop manner based on a combination of diesel fuel injection pulse width, engine load and engine speed. However, since the combustion of natural gas 34 reduces the need for diesel fuel 18, the engine ECM 100 perceives reduced engine load and therefore increases EGR 200 as described above to reduce NO.sub.x. This increase in exhaust gas 90 to reduce NOx leads to limited supply of fresh oxygen for complete combustion of the total fuel mixture, a related loss in overall fuel efficiency and a marked increase in soot production.

(45) The elevated soot levels increase service demand for regeneration of the diesel particulate filter (DPF) 400 and also lead to possible DPF 400 failure. These problems are exacerbated by the introduction of SCR after-treatment systems 500, which are inherently more responsive to NOx production and concentration. The contemplated invention solves this problem by actively controlling the EGR 200 during dual fuel operation. Referring now to FIG. 6, EGR 200 control is achieved through manipulation of one or more of five signals to the diesel engine ECM 12: EGR valve position 101, barometric pressure, EGR differential pressure, intake Manifold pressure, and intake Manifold temperature.

(46) Any or all of these signals is intercepted by the ECM 12 and then emulated as depicted in FIG. 6 to reflect the expected, diesel-only EGR level. Modification can be achieved through the following means which may include analog input and analog output drivers; and analog input and PWM output driver with impedance matching.

(47) Diesel ECM self-test and diagnostic criteria for the EGR sensor signal 103 itself are also satisfied by the emulated signal output. For failsafe reasons, the EGR signal 103 is switched to the emulated signal using a normally-closed (NC) dual-pole single throw (DPST) relay. Any mixed-fuel component failure will pass the EGR sensor signal 103 through NC contacts to the diesel ECM 12 and fully restore operation to diesel-only mode.

(48) Through active EGR 200 control, NO.sub.x concentration is maintained at or below diesel-only levels while soot production may be reduced by a factor of five or more. Less soot reduces the need for DPF 400 regeneration and therefore fuel consumed for after-treatment. Less soot also extends the useful life of the DPF 400 itself.

(49) But, even with active EGR 200 control, the diesel oxidation catalyst (DOC) 300 and diesel particulate filter (DPF) 400 should be protected during dual fuel operation. In addition to the potential soot load increase from dual fuel operation, most after-treatment systems regenerate the DPF 400 in part based on diesel fuel 18 consumption over time. Since the diesel fuel 18 consumption rate is reduced even though overall fuel consumption is not, the DPF 400 may not be adequately protected from soot build-up. Therefore, the present invention employs a strategy to protect the DPF 400 by actively monitoring DPF 400 differential pressure 402, temperature and regeneration status, either through direct sensing 14 as shown in FIG. 7 or through serial bus communications as is known in the art.

(50) Protective measures to guard the DPF 400 include the following methods: Monitoring excess soot accumulation through DPF differential pressure 402, differential rate of change and/or the DPF status indicator; restoring diesel-only operation when the DPF status indicates regeneration is required or if differential pressure is deemed excessive for gas operation; upon indication of excess soot load on the DPF 400, prevention of gas operation until regeneration process is complete; Significantly reducing combustion of gas at elevated DOC 300 temperatures indicative of passive regeneration; and preventing combustion of gas during any DPF 400 active regeneration process.

(51) All of these protective measures serve to extend the life of the after-treatment components and reduce lifecycle costs associated with dual-fuel operation.