WO2023001407A1

WO2023001407A1 - Egr pump pulse synchronization

Info

Publication number: WO2023001407A1
Application number: PCT/EP2022/025341
Authority: WO
Inventors: Douglas Anthony Hughes; Brandon Dennis BILLER
Original assignee: Eaton Intelligent Power Limited
Priority date: 2021-07-21
Filing date: 2022-07-21
Publication date: 2023-01-26

Abstract

An exhaust gas recirculation includes a Roots-type device including a pair of intermeshed rotors and an input shaft, the Roots-type device having an inlet for receiving exhaust gases from an internal combustion engine and having an outlet for discharging the exhaust gases; an electric motor having an output shaft coupled to the Roots-type device input shaft; and an electronic controller for operating the electric motor, wherein the electronic controller is configured to adjust an operating characteristic of the electric motor such that a rotational speed of the rotors is a function of a pulsing rate of the exhaust gas flow received from the internal combustion engine by the Roots-type device.

Description

EGR PUMP PULSE SYNCHRONIZATION

RELATED APPLICATIONS

[0001] This application claims priority to United States Provisional Patent Application Serial Number US 63/224,142, filed on July 21, 2021, the entirety of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] There are many previously known automotive vehicles that utilize internal combustion engines such as diesel, gas, or two stroke engines to propel the vehicle. In some constructions EGR (exhaust gas recirculation) recirculates the exhaust gas into the engine for mixture with the cylinder charge. The EGR that is intermixed with the air and fuel to the engine enhances the overall combustion of the fuel. This, in turn, reduces exhaust gas emissions. Roots pumps, electric motors, and engine exhaust flows include periodic power applications as a function of time. Optimizing the relative phasing of each of these periodic devices may allow peak power from the electric motor to be minimized. [0003] A variety of additional aspects will be set forth in the description that follows.

The aspects relate to individual features and to combinations of features. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad inventive concepts upon which the embodiments disclosed herein are based.

SUMMARY

[0004] An exhaust gas recirculation system can include a Roots-type device including a pair of intermeshed rotors and an input shaft, the Roots-type device having an inlet for receiving exhaust gases from an internal combustion engine and having an outlet for discharging the exhaust gases; an electric motor having an output shaft coupled to the Roots-type device input shaft; and an electronic controller for operating the electric motor, wherein the electronic controller is configured to adjust an operating characteristic of the electric motor such that a rotational speed of the rotors is a function of a pulsing rate of the exhaust gas flow received from the internal combustion engine by the Roots-type device. [0005] In some examples, the electronic controller determines the pulsing rate of the exhaust gas flow from one or both of current sensors and position/speed sensors associated with the electric motor.

[0006] In some examples, the electronic controller uses one or more of the following parameters for adjusting an operating characteristic of the electric motor: a pressure ratio of the Roots-type device; an input shaft torque; an input shaft rotational position; an electric motor voltage and/or current; an electric motor output shaft torque and/or position; an internal combustion engine number of cylinders, combustion cycle type, and/or engine operating speed.

[0007] In some examples, the operating characteristic is a rotational speed of the electric motor.

[0008] In some examples, the electronic controller includes a target operating speed for the electric motor, and wherein the electronic controller deviates from the target operating speed within an allowable range defined within the electronic controller.

[0009] In some examples, the rotors of the Roots-type device each include three or four lobes.

[0010] In some examples, the lobes of the rotors are straight.

[0011] A method for operating an exhaust gas recirculation system including a Roots- type device driven by an electric motor can include determining a pulsing rate of an exhaust gas flow from an internal combustion engine; determining a synchronized operating speed of the electric motor such that a rotational speed of rotors of the Roots-type device is a function of the pulsing rate that minimizes peak power consumption by the electric motor; and operating the electrical motor at the synchronized operating speed.

[0012]

[0013] The method of claim 8, wherein the pulsing rate of the exhaust gas flow is determined from one or both of current sensors and position/speed sensors associated with the electric motor.

[0014] In some examples, the step of determining a synchronized operating speed of the electric motor is a function of one or more of: a pressure ratio of the Roots-type device; an input shaft torque; an input shaft rotational position; an electric motor voltage and/or current; an electric motor output shaft torque and/or position; an internal combustion engine number of cylinders, combustion cycle type, and/or engine operating speed. [0015] In some examples, the electric motor has a target operating speed, and wherein the speed of the electric motor deviates from the target operating speed only within an allowable range.

[0016] In some examples, the rotors of the Roots-type device each include three or four lobes.

[0017] In some examples, the lobes of the rotors are straight.

[0018] In some examples, the exhaust gas flow pulses oscillate between upper and lower pressure half cycles, and wherein the step of determining the synchronized operating speed of the electric motor results in a carry volume defined by the Roots-type device is open to an inlet port of the Roots-type device being open for a majority of a time period over which the exhaust gas flow pulses are in the upper pressure half cycle.

BRIEF DESCRIPTION OF THE DRAWINGS [0019] Figure 1 is a schematic view of an EGR system including an engine and an EGR pump. [0020] Figure 2 is a partial sectional view of an EGR pump and transmission assembly usable with the system of Figure 1.

[0021] Figure 3 is a partial sectional view of the EGR pump and transmission assembly shown in Figure 2.

[0022] Figure 4 is a partial perspective view of the EGR pump and transmission assembly shown in Figure 2, detailing rotor profiles.

[0023] Figure 5 is a schematic diagram of an engine and the EGR pump of Figures 1 to 4.

[0024] Figure 6 is a plot of the exhaust pressure and EGR pump port overlay as a function of the engine crank angle for a worst phase condition, for the EGR pump and transmission assembly and engine shown in Figures 1 to 5.

[0025] Figure 7 is a plot of the exhaust pressure and EGR pump port overlay as a function of the engine crank angle for an optimum phase condition, for the EGR pump and transmission assembly and engine shown in Figures 1 to 5.

[0026] Figure 8 is a plot of the motor torque as a function of the electric motor rotation angle for worst and best case phasing, for the EGR pump and transmission assembly and engine shown in Figures 1 to 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Various examples will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. Reference to various examples does not limit the scope of the claims attached hereto. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible examples for the appended claims. Referring to the drawings wherein like reference numbers correspond to like or similar components throughout the several figures.

EGR System 1

[0028] Referring to Figure 1, an EGR system 1 including an EGR pump assembly 30 is presented. In the disclosed example, the EGR pump assembly 30 includes a Roots- type device 38 coupled to an electric motor 38. The EGR system includes an engine 12 having an intake manifold 14 and an exhaust manifold 16. A portion of exhaust gases 17 from the exhaust manifold 16 are routed to an EGR cooler 18 to adjust a temperature of the EGR stream 17. The stream 19 exiting the EGR cooler 18 is next routed to an inlet of the EGR pump assembly 30. The gas stream is then routed to the intake manifold 14 of the engine 12 and combined with fresh air. It should be realized that a turbo charger may also be used and a portion of the exhaust gases may be used to drive the compressor of the turbo charger and the boost air from the turbo charger may be routed to the intake manifold 14. An EGR system suitable for use with the present disclosure is further shown and described in PCT International Application Publication WO2019141767, published on July 25, 2019, the entirety of which is incorporated by reference herein.

Exhaust Gas Recirculation Pump Assembly 30

[0029] Referring to Figures 2 and 3, an exemplary exhaust gas recirculation pump (EGR pump) assembly 30 usable with the system 1 is presented. The EGR pump assembly 30 includes an electric motor assembly 32 including an electric motor 34 disposed within an electric motor housing 36. A roots device 38 is coupled to the electric motor assembly 32. The Roots device 38 includes a housing 40 that defines an internal volume 42. Rotors 44 are disposed in the internal volume 42 and are connected to the electric motor 34. The electric motor 34 may be linked with the rotors 44 by a transmission assembly 46.

[0030] The EGR pump assembly 30 may include a Roots device 38 and an electric motor 34 that may be utilized for engines to provide higher engine efficiency and improved control of engine emissions.

[0031] In one aspect, for diesel applications, the EGR pump assembly 30 enables higher engine efficiency by reducing engine pumping losses by enabling the use of a high-efficiency turbo with a lower exhaust backpressure in comparison to prior designs. The EGR pump assembly 30 provides more accurate EGR flow rate control for better combustion and emissions management. The EGR pump assembly 30 may provide cost benefits in comparison to a traditional EGR system by eliminating structures such as an EGR valve, variable geometry turbocharger, and an intake throttle associated with such designs.

[0032] The function of the EGR pump assembly 30 is to deliver exhaust gas from an engine’s exhaust manifold to its intake manifold at a rate that is variable and that is controlled. In order to pump exhaust gas, the EGR pump assembly 30 may use a Roots device 38 coupled to an electric motor 34 such as a 48V electric motor. The electric motor 34 provides control of EGR flow rate by managing the motor speed and in turn the pump speed and flow rate of exhaust gas.

[0033] Referring to Figure 4, the EGR pump assembly 30 includes rotors 44 disposed within the housing 40. The rotors 44 include a rotor shaft 80 having a plurality of lobes 82 formed thereon, the lobes 82 include a straight profile having a modified cycloidal geometry as disclosed in PCT application PCT/US 16/47225 filed on August 16, 2016, which is herein incorporated by reference. The modified cycloidal geometry includes a cycloid curve modified with at least two interpolated and stitched spline curves. The rotor lobe 82 profile further includes a flattened tip. In the example shown, each rotor 44 is provided with three identically shaped lobes 82. However, other numbers of lobes may be provided, such as two lobes, four lobes, or more lobes. [0034] Referring to Figures 1-2, the EGR pump assembly 30 includes a housing 40 that defines an internal volume 42 that receives the rotors 44. The housing includes a generally elliptical shape that accommodates the lobes 82 of the rotors 44. The housing 40 includes a housing end face 88 linked with a housing side wall 90. The portion of the housing 40 opposite the end 88 face is open. The housing 40 includes radial inlet and outlet ports 92, 94 formed therein. The inlet port 92 and the outlet port 94 include an angled geometry 96 best shown in Figures 4. In the depicted embodiments, the angled geometry 96 is in the shape of a parallelogram. The parallelogram shape provides a gradual or regulated release of the carrier volume of exhaust gas to the outlet port 94. This results in reduced pulsations and potential noise, vibration and harshness (NVH).

[0035] In one aspect, the housing 40 includes journals 98 formed therein receiving bearings 100 that support the rotors 44. The housing 40 can include an oil slinger positioned therein about the rotor shaft 80 directing oil away from sealing rings 86.

[0036] The housing 40 includes a back flow port 104 formed therein facing a rotor end face, as best seen in Figure 4. The back flow port 104 includes a curved profile. As the rotors rotate, the lobes 82 turn in opposite directions with very tiny clearances between each other and between the rotors 44 and the housing 40. As each lobe 82 passes air at the inlet port 92, a measured quantity of air is trapped between the lobes 82 and the housing 40. As the rotors continue to rotate, this amount of air is transported around the housing 40 to the outlet port 94. The back flow port 104 connects the trapped quantity of air within the outlet port 94 to reduce pulsations and potential NVH.

[0037] Referring to Figure 1, the exhaust gas recirculation pump assembly 30 includes a transmission assembly 46 that includes a drive gear 116 that is meshed with a driven gear 118. The drive gear 116 is coupled to a drive shaft 120 of the electric motor 34 and to a rotor shaft 80. The driven gear 118 is meshed with the drive gear 116 and is coupled to the other rotor shaft 80. Referring to Figure 2, the housing 40 includes journals 98 formed therein receiving bearings 100 that support the rotors 44.

[0038] Referring to Figures 1-2, the exhaust gas recirculation pump assembly 30 includes a bearing plate 126 attached to the housing 40. The bearing plate 126 includes bearing plate inner and outer surfaces. The bearing plate inner surface includes a back flow port formed therein as described above with respect to the housing 40 and faces a rotor end face. The bearing plate 126 outer surface includes journals formed therein receiving bearings 100 as described above with the housing 40. The bearing plate outer surface includes an oil cavity formed therein.

[0039] Referring to Figures 1-2, the EGR pump assembly 30 includes an insulated coupling 134 joining a rotor shaft 80 to an electric motor shaft 136. The insulated coupling 134 prevents heat transfer from the housing 40 to the electric motor 34. In one , the insulated coupling 134 is formed of PEEK (polyetheretherketone) or may be formed of other materials such as plastic composites or ceramic insulating type materials. The insulated coupling 134 connects the electric motor 34 to the rotors 44 and prevents heat transfer.

Control Structure 200

[0040] Referring to Figure 5 to 8, there is shown a control structure 200 and related operating states of the EGR pump assembly 30. As shown at Figure 5, the control structure 200 includes sensors 202 that are in communication with the engine 12, electric motor 34, EGR pump or Roots device 38, and an EGR control unit 206. The sensors 202 are capable of sensing conditions and of sending signals, such as temperature, pressure, speed, air flow, mass flow or volumetric flow. The control structure 200 also includes a control unit 206 which includes a computer processor, communication ports, memory, and programming and is linked with the sensors 202. The control unit 206 may be a portion of an engine control unit (ECU). The arrows shown in Figure 5 indicate communication between the various components of the control structure.

[0041] The control structure 200 may be utilized in a method of operating the exhaust gas recirculation pump for an internal combustion engine to provide a desired flow of EGR to an engine 12. The EGR control unit 206 may regulate the motor speed or torque in a feedback loop to control an EGR mass flow rate to the engine. The EGR control unit 206 may monitor a current of the electric motor 34 for diagnostic and prognostic evaluation. The EGR control unit 206 may also detect when a negative torque is being applied to the electric motor 34. This may indicate that the pressure differential across the EGR pump is tending to drive the electric motor 34. In this state, the electric motor may switch to a generator function such that electricity may be stored in a storage device on a vehicle.

[0042] With the control structure 200, various components and characteristics of the components may be controlled or regulated to reduce a peak power of the electric motor 34 that is coupled to the EGR pump 38. Application of the operating parameters of the pump 38, electric motor 34, and the engine 12 characteristics may have an effect on the energy transfer within the system. EGR pump characteristics may include: the torque required to rotate the EGR is a function of the pressure ratio across the pump 38; for a given constant pressure ratio across the EGR pump, the pump shaft torque is a periodic function of the pump rotational position. Motor characteristics may include: for any given constant DC voltage and current, motor shaft torque is a periodic function of motor rotor position. Engine characteristics may include: engine exhaust pulse frequency is a function of engine cylinder count, combustion cycle (2-stroke, 4-stroke), exhaust manifold design, and engine operating speed; engine exhaust pulses vary the pressure ratio across the EGR pump.

[0043] If the above cascaded periodic energy transfer mechanisms can be synchronized to minimize peak torque/power at the motor, then the motor can be downsized and peak electrical power consumption can be minimized.

[0044] In one aspect, the operating system of an EGR pump can include variables that can be optimized including pump rotor lobe count, motor stator pole count, motor rotor pole count, pump displacement, and operating speed range. The pump speed could be varied slightly (within limits consistent with the flow rate target) to synchronize with exhaust pulse frequency. The phase angle between the EGR Pump system’s periodicity and the exhaust flow’ s periodicity may be controlled in order to take maximum advantage of pulse energy capture. Exhaust pulse timing may be detected directly by the motor’s current sensors 28, such as phase current sensors, and appropriate signal processing as the exhaust pulses impart a load onto the electrical motor. Also, as the electric motor 34 is directly coupled to the EGR pump 38, position and speed sensors associated with the electrical motor shaft can also be used to identify the position of the rotors such that it is known by the controller when the rotors are positioned such that the carry volume is open to the inlet port. [0045] Referring to Figures 1-4, the roots based EGR pump 38 transfers exhaust to an intake manifold 14 in discrete pulses, as a function of the number of lobes 82 on the rotors 44 and their rotational speed. Exhaust from the exhaust manifold 16 of the internal combustion engine 12 is drawn into the pump 38 when the rotor lobe 82 opens up a carry volume 21 of the pump to the pump inlet 92. This carry volume 21 between the rotor lobes 82 is then filled with exhaust, which is then sealed between the rotor lobe tips and housing 40 and transported to the outlet 94. By timing the inlet opening with a higher pressure exhaust pulsation, the carry volume 21 will be filled more effectively while using less power, due to the higher torque imparted to the rotor lobe 82 by the higher pressure exhaust.

[0046] Referring to Figure 6 and 7, there are shown the worst case (Figure 6) and best case (Figure 7) scenarios regarding the relationship between exhaust pressure pulsations and pump inlet port opening events. The pump speed and engine speed are each consistent between these two plots, with the only variable changing being the phasing between the two. As shown at Figures 6 and 7, the exhaust manifold pressure 300 varies in an approximately sinusoidal pattern between a maximum pressure 302 and a minimum pressure 304 about an axis X. As shown at Figure 7, the exhaust manifold pressure 300 thus oscillates between upper pressure half cycle portions A above the axis X and lower pressure half cycle portions B below the axis X. Figures 6 and 7 also show the EGR pump opening state 400 varying between a first position 402 in which the pump inlet port or carry volume is open to the exhaust manifold and a second position 404 in which the inlet port or carry volume is closed to the exhaust manifold. The first position 402, in which the carry volume defined by the rotors is open to the pump inlet port, can be characterized as a pump inlet port opening event.

[0047] The worst case scenario of Figure 6 has two EGR pump inlet port opening events 402 that occur each time on the lower pressure side B of the exhaust pressure curve 300, and only one inlet port opening event 404 occurs when the exhaust pressure is on the higher pressure side A of the exhaust pressure curve 300. Characterized in another way, the scenario of Figure 6 shows a condition in which the inlet port carry volume is closed a majority of the time defined by the upper pressure half cycle portions A. [0048] Meanwhile, for the best-case phasing of Figure 7, two EGR pump inlet port opening events 402 occur each time the exhaust pressure is on the maximum pressure 302 side of the curve 300 (i.e. during the upper pressure half cycle portions A), and only one inlet port opening event occurs when the exhaust pressure is on the minimum pressure 304 side of the curve 300 (i.e. during the lower pressure half cycle portions B). Characterized in another way, the scenario of Figure 7 shows a more optimized condition in which the inlet port carry volume is open a majority of the time defined by the upper pressure half cycle portions A. (e.g. pump inlet is in the open position during times t2 and t3, the sum of which is greater than half of time tl over which the exhaust pressure is in the upper pressure half cycle portion A). Conversely, in this phasing, the pump inlet port opening is closed over a time t4 that is less than half of the time tl associated with the upper pressure half cycle portions A. This condition results in more time that the rotor opening is exposed to the high-pressure pulsation.

[0049] Achieving the best-case phasing may be accomplished by briefly slowing down or speeding up the pump 38 relative to the engine 12 to get to the desired phase relationship, then maintaining the speed which has the same pulsation relationship thereafter.

[0050] Referring to Figure 8, the torque requirements of the electric motor are shown from worst case phasing to best case phasing. As can be seen in the figure, the motor in the worst-case phasing scenario 500 has higher torque peaks, resulting in higher current consumption peaks, and thus more power consumption overall in comparison to the best case phasing scenario 600.

[0051] To determine the optimum phasing, the motor controller or EGR control unit 206 may deviate from the target speed within an allowable range while targeting the lowest current consumption using its internal current sensors 28. In this manner, as the current is directly related to the electric motor torque a reduction of power consumption may be achieved.

[0052] In another aspect, the motor 34 connection to the EGR pump 38 can be made in such a way to time the phase current pulses of the motor 34 with the pump pulsations in such a way that the energy is utilized most efficiently. The motor 34 can also be selected with characteristics that optimally match those of the EGR pump 38. For example, the electric motor 34 can be selected to have a number of pole pairs that is equal to the number of lobes 82 of the rotors 44, or to have a number of pole pairs that is a multiple of the lobes 82 of the rotors 44. As electrical pulses per revolution of the electric motor 34 are proportional to the number of pole pairs, such a selection can result in a matching of the periodicity of the pulses of the electric motor 34 with the periodicity of the pulses associated with the EGR pump 38, both of which are approximately sinusoidal in nature. After such a matching selection is made, the EGR pump 38 input shaft can be appropriately aligned with the electric motor 34 output shaft before coupling to provide a synchronous coupling that reduces peak or maximum torque at the electric motor 34.

[0053] From the forgoing detailed description, it will be evident that modifications and variations can be made in the aspects of the disclosure without departing from the spirit or scope of the aspects. While the best modes for carrying out the many aspects of the present teachings have been described in detail, those familiar with the art to which these teachings relate will recognize various alternative aspects for practicing the present teachings that are within the scope of the appended claims.

Claims

1. An exhaust gas recirculation system comprising: a) a Roots-type device including a pair of intermeshed rotors and an input shaft, the Roots-type device having an inlet for receiving exhaust gases from an internal combustion engine and having an outlet for discharging the exhaust gases; b) an electric motor having an output shaft coupled to the Roots-type device input shaft; and c) an electronic controller for operating the electric motor, wherein the electronic controller is configured to adjust an operating characteristic of the electric motor such that a rotational speed of the rotors is a function of a pulsing rate of the exhaust gas flow received from the internal combustion engine by the Roots-type device.

2. The exhaust gas recovery system of claim 1, wherein the electronic controller determines the pulsing rate of the exhaust gas flow from one or both of current sensors and position/speed sensors associated with the electric motor.

3. The exhaust gas recovery system of claim 1, wherein the electronic controller uses one or more of the following parameters for adjusting an operating characteristic of the electric motor: a pressure ratio of the Roots-type device; an input shaft torque; an input shaft rotational position; an electric motor voltage and/or current; an electric motor output shaft torque and/or position; an internal combustion engine number of cylinders, combustion cycle type, and/or engine operating speed.

4. The exhaust gas recovery system of claim 1, wherein the operating characteristic is a rotational speed of the electric motor.

5. The exhaust gas recovery system of claim 4, wherein the electronic controller includes a target operating speed for the electric motor, and wherein the electronic controller deviates from the target operating speed within an allowable range defined within the electronic controller.

6. The exhaust gas recovery system of claim 1, wherein the rotors of the Roots-type device each include three or four lobes.

7. The exhaust gas recovery system of claim 6, wherein the lobes of the rotors are straight.

8. A method for operating an exhaust gas recirculation system including a Roots- type device driven by an electric motor, the method including: a) determining a pulsing rate of an exhaust gas flow from an internal combustion engine; b) determining a synchronized operating speed of the electric motor such that a rotational speed of rotors of the Roots-type device is a function of the pulsing rate that minimizes peak power consumption by the electric motor; and c) operating the electrical motor at the synchronized operating speed.

9. The method of claim 8, wherein the pulsing rate of the exhaust gas flow is determined from one or both of current sensors and position/speed sensors associated with the electric motor.

10. The method of claim 8, wherein the step of determining a synchronized operating speed of the electric motor is a function of one or more of: a pressure ratio of the Roots-type device; an input shaft torque; an input shaft rotational position; an electric motor voltage and/or current; an electric motor output shaft torque and/or position; an internal combustion engine number of cylinders, combustion cycle type, and/or engine operating speed.

11. The method of claim 8, wherein the electric motor has a target operating speed, and wherein the speed of the electric motor deviates from the target operating speed only within an allowable range.

12. The method of claim 8, wherein the rotors of the Roots-type device each include three or four lobes.

13. The method of claim 12, wherein the lobes of the rotors are straight.

14. The method of claim 8, wherein the exhaust gas flow pulses oscillate between upper and lower pressure half cycles, and wherein the step of determining the synchronized operating speed of the electric motor results in a carry volume defined by the Roots-type device is open to an inlet port of the Roots-type device being open for a majority of a time period over which the exhaust gas flow pulses are in the upper pressure half cycle.