Patent Description:
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.

Examples of EGR systems are described in <CIT>, <CIT> and <CIT>, respectively.

By including a separate EGR pump an increase in fuel economy may be achieved in comparison to prior art systems that may use a turbocharger to drive an EGR flow with the addition of costly EGR valves. Additionally, a separate EGR pump provides full authority of the EGR flow rate. In a diesel application, a separate EGR pump may allow for removal of an EGR valve and replace a complicated variable geometry turbocharger with a fixed geometry turbocharger optimized for providing a boosted air charge. The separate EGR pump may provide reduced engine pumping work and improved fuel economy.

One disadvantage of intermixing exhaust gas is that the exhaust gas contains particulate matter such as soot. Water vapor may be included in exhaust gases from an engine as a result of the combustion process of fuel supplied to the engine. Generally, the water vapor is expelled to the environment through an exhaust system. However in an EGR application a portion of the exhaust is recirculated to the engine intake manifold. The water vapor may provide a carrier for particulate matter such as soot. Soot deposits may accumulate on various components degrading performance.

It is therefore desirable to provide an EGR pump that resists accumulation of soot deposits. It is also desirable to provide a separate EGR pump that transports EGR gases to prevent degradation of the additional components such as a supercharger or turbocharger.

Various portions of EGR pumps may be exposed to exhaust gases at elevated temperatures. For example the rotors associated with the pump may contact exhaust gases at temperatures such as from <NUM> to <NUM>. In such a scenario, the high temperature may demagnetize the components of the electric motor causing a loss of torque. Additionally, the high temperature may adversely affect the mechanical components of the EGR pump such as varying the heat treatments and properties of the materials.

It is therefore desirable to reduce heat transfer from the EGR pump rotors to the electric motor that drives the EGR pump. There is therefore a need in the art to thermally isolate rotors of an EGR pump from an electric motor that may drive the pump such that the motor does not overheat.

Further, it is desirable to cool and lubricate the various components of the EGR pump for safe and long operation in an EGR environment.

The invention relates to a method of operating exhaust gas recirculation pump for an internal combustion engine as defined in claim <NUM>.

Referring to <FIG>, there is shown an exhaust gas recirculation pump (EGR pump) system <NUM>. The EGR pump system <NUM> includes an electric motor assembly <NUM> including an electric motor <NUM> disposed within an electric motor housing <NUM>. A roots device <NUM> is coupled to the electric motor <NUM>. The Roots device <NUM> includes a housing <NUM> that defines an internal volume <NUM>. Rotors <NUM> are disposed in the internal volume <NUM> and are connected to the electric motor <NUM>. The electric motor <NUM> may be linked with the rotors <NUM> by a transmission assembly <NUM>.

The EGR pump system <NUM> may include a Roots device <NUM> and an electric motor <NUM> that may be utilized for engines to provide higher engine efficiency and improved control of engine emissions.

In one aspect, for diesel applications, the EGR pump system <NUM> 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 system <NUM> provides more accurate EGR flow rate control for better combustion and emissions management. The EGR pump system <NUM> 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.

The function of the EGR pump system <NUM> 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 system <NUM> may use a Roots device <NUM> coupled to an electric motor <NUM> such as a 48V electric motor. The electric motor <NUM> provides control of EGR flow rate by managing the motor speed and in turn the pump speed and flow rate of exhaust gas.

Referring to <FIG>, the exhaust gas recirculation pump system <NUM> includes coolant path <NUM> and an electric motor housing <NUM> having an end plate <NUM> attached thereon. The end plate <NUM> includes end plate inner and outer surfaces <NUM>, <NUM>. The end plate <NUM> includes a coolant inlet slot <NUM> formed therein extending between the end plate inner and outer surfaces <NUM>, <NUM>. The coolant inlet slot <NUM> is linked to a coolant inlet <NUM>. The end plate <NUM> includes a coolant labyrinth <NUM> formed on the end plate outer surface <NUM>. The labyrinth <NUM> extends from the coolant inlet slot <NUM> to at least one coolant outlet slot <NUM>, with two shown in the figures. The electric motor housing <NUM> includes a plurality of coolant passages <NUM> formed therein along a longitudinal axis of the electric motor housing <NUM>. The coolant passages <NUM> including baffle walls <NUM> formed therein directing a flow of coolant.

The electric motor housing <NUM> includes a coolant barrier cavity <NUM> formed therein on an end of the electric motor housing <NUM> proximate the housing <NUM> and Roots device <NUM>. A gear box housing <NUM> having a cylindrical body extends from a housing flange <NUM> to an electric housing flange <NUM>. The electric housing flange <NUM> is coupled to the electric motor housing <NUM> and the housing flange <NUM> is coupled to the housing <NUM>. The electric motor housing <NUM> and electric housing flange <NUM> define the coolant barrier cavity <NUM>. The coolant barrier cavity <NUM> isolates the electric motor <NUM> from potential heat of the exhaust gas that is contained in the housing <NUM>.

The coolant path <NUM> is linked with an engine cooling path such as coolant from an engine radiator. The coolant enters at the coolant inlet <NUM> and enters the coolant inlet slot <NUM> to first cool an inverter <NUM> associated with the electric motor <NUM>. The coolant is circulated in the coolant labyrinth <NUM> and exits the coolant outlet slots <NUM> to be circulated about the electric motor through the coolant passages <NUM>. The coolant is also captured in the cooling barrier cavity <NUM> and acts to prevent heat being transferring from the housing <NUM>. The coolant then exits at the coolant outlet <NUM> to return to the engine coolant circulation system.

Referring to <FIG>, the exhaust gas recirculation pump system <NUM> includes rotors <NUM> disposed within the housing <NUM>. The rotors <NUM> include a rotor shaft <NUM> having a plurality of lobes <NUM> formed thereon, the lobes <NUM> include a straight profile having a modified cycloidal geometry as disclosed in PCT application <CIT>, 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 <NUM> profile further includes a flattened tip.

Referring to <FIG>, the rotor shaft <NUM> has a plurality of longitudinally spaced groves <NUM> formed on ends of the rotor shaft <NUM>. The grooves <NUM> receive sealing rings <NUM>.

Referring to <FIG>, the exhaust gas recirculation pump system <NUM> includes a housing <NUM> that defines an internal volume <NUM> that receives the rotors <NUM>. The housing includes a generally elliptical shape that accommodates the lobes <NUM> of the rotors <NUM>. The housing <NUM> includes a housing end face <NUM> linked with a housing side wall <NUM>. The portion of the housing <NUM> opposite the end <NUM> face is open. The housing <NUM> includes radial inlet and outlet ports <NUM>, <NUM> formed therein. The inlet port <NUM> and the outlet port <NUM> include an angled geometry <NUM> best shown in <FIG> and <FIG>. In the depicted embodiments, the angled geometry <NUM> 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 <NUM>. This results in reduced pulsations and potential noise, vibration and harshness (NVH).

Referring to <FIG> and <FIG>, the housing <NUM> includes journals <NUM> formed therein receiving bearings <NUM> that support the rotors <NUM>. The housing <NUM> includes an oil slinger <NUM> positioned therein about the rotor shaft <NUM> directing oil away from the sealing rings <NUM>.

The housing <NUM> includes a back flow port <NUM> formed therein facing a rotor end face, as best seen in <FIG>. The back flow port <NUM> includes a curved profile. As the rotors rotate, the lobes <NUM> turn in opposite directions with very tiny clearances between each other and between the rotors <NUM> and the housing <NUM>. As each lobe <NUM> passes air at the inlet port <NUM>, a measured quantity of air is trapped between the lobes <NUM> and the housing <NUM>. As the rotors continue to rotate, this amount of air is transported around the housing <NUM> to the outlet port <NUM>. The back flow port <NUM> connects the trapped quantity of air with the outlet port <NUM> to reduce pulsations and potential noise, vibration and harshness (NVH).

Referring to <FIG> and <FIG>, the housing <NUM> includes an oil cavity <NUM> formed therein. The oil cavity <NUM> is linked with an oil path <NUM> formed in the housing <NUM>. The oil path <NUM> includes oil inlets <NUM> extending to oil outlets <NUM>. The oil inlets <NUM> and outlets <NUM> are coupled to an engine oil circulation system such that the oil path lubricates bearings <NUM> and a transmission assembly <NUM>.

The oil path <NUM> includes selected orifices <NUM> disposed therein providing a selectable amount of oil to the bearings <NUM> and transmission assembly <NUM>. In the depicted embodiment, selectable orifices <NUM> are positioned at each of the bearings <NUM>, at the oil inlet <NUM> and at a selected location of the transmission assembly <NUM>.

Referring to <FIG>, <FIG> and <FIG>, the exhaust gas recirculation pump system <NUM> includes a transmission assembly <NUM> that includes a drive gear <NUM> that is meshed with a driven gear <NUM>. The drive gear <NUM> is coupled to a drive shaft <NUM> of the electric motor <NUM> and to a rotor shaft <NUM>, as will be described in more detail below. The driven gear <NUM> is meshed with the drive gear <NUM> and is coupled to the other rotor shaft <NUM>. The housing <NUM> includes angled transmission oil inlet <NUM> formed therein directing oil to the meshing of the drive gear <NUM> and the driven gear <NUM>.

Referring to <FIG>, the housing <NUM> includes journals <NUM> formed therein receiving bearings <NUM> that support the rotors <NUM>. The journals <NUM> formed on the housing include a plurality of bearing oil outlets <NUM> formed therein, with three shown in the depicted embodiment. The bearing oil outlets <NUM> allow oil to exit the bearings <NUM> to be routed to the oil outlets <NUM> formed in the housing <NUM>.

Referring to <FIG> and <FIG>, the exhaust gas recirculation pump system <NUM> includes a bearing plate <NUM> attached to the housing <NUM>. The bearing plate <NUM> includes bearing plate inner and outer surfaces <NUM>, <NUM>. The bearing plate inner surface <NUM> includes a back flow port <NUM> formed therein as described above with respect to the housing <NUM> and faces a rotor end face. The bearing plate <NUM> outer surface <NUM> includes journals <NUM> formed therein receiving bearings <NUM> as described above with the housing <NUM>. The bearing plate outer surface <NUM> includes an oil cavity <NUM> formed therein.

The bearing plate <NUM> includes journals <NUM> formed therein receiving bearings <NUM> that support the rotors <NUM>. The journals <NUM> formed on the bearing plate include a plurality of bearing oil outlets <NUM> formed therein, as described above. The bearing oil outlets <NUM> allow oil to exit the bearings <NUM> to be routed to the oil outlet <NUM> formed in the bearing plate <NUM> and gear box housing <NUM>.

Referring to <FIG>, the exhaust gas recirculation pump system <NUM> includes an insulated coupling <NUM> joining a rotor shaft <NUM> to an electric motor shaft <NUM>. The insulated coupling <NUM> prevents heat transfer from the housing <NUM> to the electric motor <NUM>. In one aspect, the insulated coupling <NUM> is formed of PEEK or may be formed of other materials such as plastic composites or ceramic insulating type materials.

In one aspect, the insulated coupling <NUM> includes a disk shaped body <NUM> having a plurality of through holes <NUM>. Pins <NUM> formed on the electric motor shaft <NUM> are received in a portion of the through holes <NUM> and pins <NUM> formed on a drive gear <NUM> of the transmission assembly <NUM> are received in another portion of the through holes <NUM>. The insulated coupling <NUM> connects the electric motor <NUM> to the rotors <NUM> and prevents heat transfer.

Alternatively, the insulated coupling <NUM> may include a pentagonal body having an inner bore formed therein. The pentagonal body may include a flange formed on one end. The inner bore may be sized to receive an end of the rotor shaft which has a complementary shape and size. The outer shape of the pentagonal body may be received in a corresponding drive bore formed on the drive shaft of the electric motor. In this manner the drive shaft is thermally isolated and coupled to the rotor shaft.

Referring to <FIG>, there is shown a control structure <NUM> of the EGR pump system <NUM>. The control structure <NUM> includes sensors <NUM> that are in communication with the engine <NUM>. electric motor <NUM>, EGR pump or Roots device <NUM> and an EGR control unit <NUM>. The control structure <NUM> includes sensors <NUM> capable of sensing conditions and of sending signals, such as temperature, pressure, speed, air flow, mass flow or volumetric flow. The control structure <NUM> also includes a control unit <NUM> which includes a computer processor, communication ports, memory, and programming and is linked with the sensors <NUM>. The control unit <NUM> may be a portion of an engine control unit (ECU). The arrows indicate communication between the various components of the control structure.

The control structure <NUM> 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 the engine <NUM>. The EGR control unit <NUM> 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 <NUM> may monitor a current of the electric motor <NUM> for diagnostic and prognostic evaluation.

The mass flow rate may be calculated by the following equations:
<MAT>
<MAT>
<MAT>
<MAT>
<MAT>.

The EGR control unit <NUM> may also detect when a negative torque is being applied to the electric motor <NUM>. This may indicate that the pressure differential across the EGR pump is tending to drive the electric motor <NUM>. 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.

As shown in <FIG>, the control method includes the steps of :providing an EGR pump assembly including an electric motor coupled to a roots device having rotors, the EGR pump operably connected to an internal combustion engine; providing an EGR control unit linked to the EGR pump assembly; providing sensors linked to the EGR control unit; determining if a motor speed is within a predetermined target in step S1 wherein when motor speed=predetermined target then; determining if a motor torque is within a predetermined target in step S2 wherein when motor torque=predetermined target then; determining if a motor temperature is within a predetermined target in step S3 wherein when motor temperature=predetermined target then; maintaining operation of the exhaust gas recirculation pump.

The method of operating the exhaust gas recirculation pump includes the step of determining the motor speed S1 including determining that the motor speed is not equal to the predetermined target and then including the step S4 of determining whether a motor speed is less than the predetermined target.

The method of operating the exhaust gas recirculation pump includes the step of wherein in step S4 the motor speed is not less than the predetermined target then including the step S5 of indicating an excessive engine delta P.

The method of operating the exhaust gas recirculation pump includes the step of the step S2 includes determining that the motor torque is not equal to the predetermined target and then including the step S6 of determining whether a motor torque is greater than the predetermined target.

The method of operating the exhaust gas recirculation pump includes the step of wherein in step S6 the motor torque is not greater than the predetermined target then including the step S7 of flagging a low torque.

The method of operating the exhaust gas recirculation pump includes the step of wherein in step S6 the motor torque is greater than the predetermined target then including the step S8 of flagging an excessive torque.

The method of operating the exhaust gas recirculation pump includes the step of wherein the step of determining the motor temperature S3 includes determining that the motor temperature is not equal to the predetermined target and then including the step S9 of flagging a motor temperature.

The method of operating the exhaust gas recirculation pump includes the step of wherein in step S4 the motor speed is less than the predetermined target including the step S10 of determining if the motor torque is greater than the predetermined target.

The method of operating the exhaust gas recirculation pump includes the step of wherein in step S10 the torque is not greater than the predetermined target including the step S11 of flagging a low torque and low speed.

The method of operating the exhaust gas recirculation pump includes the step of wherein in step S10 the torque is greater than the predetermined target including the step S12 of determining if the speed is equal to zero.

The method of operating the exhaust gas recirculation pump includes the step of wherein the speed is equal to zero then including the step S13 of indicating pump seizure.

The method of operating the exhaust gas recirculation pump includes the step of wherein the speed is not equal to zero then including the step S8 of flagging an excessive torque.

As shown in <FIG>, the method of operating the exhaust gas recirculation pump includes the step of further including the step of performing an engine shut down S14 and determining if the temperature is less than <NUM> degrees C in step S15.

The method of operating the exhaust gas recirculation pump includes the step of wherein in step S15 the temperature is less than <NUM> degrees C and including the step S16 of moving the rotors.

As shown in <FIG>, the method of operating the exhaust gas recirculation pump includes the step of further including the step of performing an engine start up S17 and the step S18 of determining if the toque is greater than the predetermined target.

The method of operating the exhaust gas recirculation pump includes the step of wherein in step S18 the toque is greater than the predetermined target and including the step S19 of opening an EGR bypass to heat the EGR pump and the step S20 of determining if the temperature is greater than the predetermined target. An additional step of rotating the rotors alternatively clockwise and counter clock wise may be performed to free the rotors from a potential blockage.

The method of operating the exhaust gas recirculation pump includes the step of wherein in step S20 the temperature is greater than the predetermined target and including the step S21 of closing an EGR bypass.

Claim 1:
A method of operating an exhaust gas recirculation pump for an internal combustion engine comprising:
providing an EGR pump assembly (<NUM>) including an electric motor (<NUM>) coupled to a roots device (<NUM>) having rotors (<NUM>), the EGR pump operably connected to an internal combustion engine (<NUM>);
providing an EGR control unit (<NUM>) linked to the EGR pump assembly;
providing sensors (<NUM>) linked to the EGR control unit;
determining if a motor speed is equal to a predetermined target in step S1 wherein when the motor speed is equal to the predetermined target then;
determining if a motor torque is equal to a predetermined target in step S2 wherein when the motor torque is equal to the predetermined target then;
determining if a motor temperature is equal to a predetermined target in step S3 wherein when the motor temperature is equal to the predetermined target then;
maintaining operation of the exhaust gas recirculation pump.