WO2018136677A1

WO2018136677A1 - Vehicle transmission electrically-driven secondary oil pump

Info

Publication number: WO2018136677A1
Application number: PCT/US2018/014308
Authority: WO
Inventors: Christopher E. Blair
Original assignee: Borgwarner Inc.
Priority date: 2017-01-20
Filing date: 2018-01-19
Publication date: 2018-07-26

Abstract

A method for operating a vehicle transmission having a transmission hydraulic system, a primary oil pump, a secondary oil pump and an electric motor for driving the secondary oil pump. The method includes: operating the primary oil pump to provide a working fluid at a first pressure to the transmission hydraulic system; halting operation of the primary pump; reducing a pressure of the working fluid in the transmission hydraulic system below a predetermined stall pressure; and operating the electric motor to drive the secondary oil pump such that the secondary oil pump provides the working fluid at a second pressure to the transmission hydraulic system, the second pressure being less than the first pressure but greater than the predetermined stall pressure; wherein the electric motor stalls when a fluid pressure on an outlet of the secondary pump is greater than the predetermined stall pressure.

Description

VEHICLE TRANSMISSION ELECTRICALLY-DRIVEN

SECONDARY OIL PUMP

FIELD

[0001] The present disclosure relates to a vehicle transmission having an electrically-driven secondary oil pump.

BACKGROUND

[0002] This section provides background information related to the present disclosure which is not necessarily prior art.

[0003] Some modern automotive vehicles with start-stop capabilities are equipped with a transmission having a primary (transmission) oil pump, which is driven by rotary power supplied by an internal combustion engine, and a secondary (transmission) oil pump that is driven by rotary power that is supplied by an electric motor. When the vehicle is operated at speed, the primary oil pump is driven by the internal combustion engine and supplies pressurized transmission fluid to operate various clutches within the transmission as well as to lubricate the transmission. When the vehicle is stopped for a predetermined amount of time so that the stop-start function turns the internal combustion engine off, there remains a need in some circumstances to supply pressurized transmission fluid to the various clutches of within the transmission. In such situations, the electric motor can be operated to drive the secondary oil pump.

[0004] It will be appreciated that when the vehicle is stopped, relatively little pressurized transmission fluid is typically required and as such, the secondary oil pump is relatively small, has a relatively lower pressure and lower volumetric flow rate as compared to the primary oil pump. Due to the relatively lower performance requirements for the secondary oil pump, the electric motor can be sized in a commensurate manner. Construction in this manner significantly reduces the size and cost of the secondary oil pump and the motor that drives the secondary oil pump.

[0005] When transitioning between the primary pump and the secondary pump, the pressure of the transmission fluid in the transmission can at times be higher than the maximum output pressure of the secondary oil pump when the secondary oil pump is driven by the electric motor. Operation of the electric motor and secondary oil pump in such cases would cause the electric motor to stall, which is undesirable due to the current drawn by the motor and the amount of heat that is generated by the motor.

SUMMARY

[0006] This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

[0007] In one form, the teachings of the present disclosure provide a vehicle transmission that includes a transmission hydraulic system, a primary oil pump, a first check valve, an electric motor, a secondary oil pump, a pressure- relieving device, and a controller. The transmission hydraulic system has a plurality of valves and a plurality of clutch actuators. The primary oil pump is configured to be driven by an internal combustion engine. The first check valve is disposed between an outlet of the primary oil pump and the transmission hydraulic system. The secondary oil pump is driven by the electric motor. The pressure-relieving device is coupled in fluid communication with the transmission hydraulic system and is selectively operable to limit a working fluid pressure in at least one of the transmission hydraulic system and an outlet of the secondary oil pump to a predetermined maximum working fluid pressure. The controller coupled to the electric motor and the pressure-relieving device. The electric motor stalls when a fluid pressure on an outlet of the secondary pump is greater than a predetermined stall pressure. The predetermined maximum working fluid pressure is less than the predetermined stall pressure.

[0008] In another form, the present teachings provide a method for operating a vehicle transmission having a transmission hydraulic system, a primary oil pump, a secondary oil pump and an electric motor for driving the secondary oil pump. The method includes: operating the primary oil pump to provide a working fluid at a first pressure to the transmission hydraulic system; halting operation of the primary pump; reducing a pressure of the working fluid in the transmission hydraulic system below a predetermined stall pressure; and operating the electric motor to drive the secondary oil pump such that the secondary oil pump provides the working fluid at a second pressure to the transmission hydraulic system, the second pressure being less than the first pressure but greater than the predetermined stall pressure; wherein the electric motor stalls when a fluid pressure on an outlet of the secondary pump is greater than the predetermined stall pressure.

[0009] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

[0010] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0011] Figures 1 through 3 are schematic illustrations exemplary vehicle transmissions constructed in accordance with the teachings of the present disclosure.

[0012] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

[0013] With reference to Figure 1 , an exemplary vehicle transmission 10 constructed in accordance with the teachings of the present disclosure is schematically illustrated. The vehicle transmission 10 can include a transmission hydraulic system 12, a primary oil pump 14, a first check valve 16, an electric motor 18, a secondary oil pump 20, a second check valve 22, a pressure- relieving device 24, and a controller 26.

[0014] The transmission hydraulic system 12 is conventional in its construction and operation and can include various electronically-controlled hydraulic valves (not specifically shown) that are operable for controlling the engagement and disengagement of various clutches (not shown) within the vehicle transmission 10.

[0015] The primary oil pump 14 is conventional in its construction and operation and is configured to be driven by rotary power supplied by an internal combustion engine 36. The primary oil pump 14 has a first inlet 38, which is coupled via a first conduit 40 to a reservoir 42 that holds a working fluid (i.e., a transmission fluid), and a first outlet 44 that is coupled via a second conduit 46 to an inlet 48 of the first check valve 16. An outlet 50 of the first check valve 16 is coupled in fluid communication to the transmission hydraulic system 12 via a third fluid conduit 52. The first check valve 16 is configured to transmit pressurized working fluid supplied by the primary oil pump 14 to the transmission hydraulic system 12 when the fluid pressure in the second fluid conduit 46 exceeds the fluid pressure in the third fluid conduit 52 by a first predetermined differential, as well as to inhibit fluid flow from the third fluid conduit 52 to the second fluid conduit 46.

[0016] The electric motor 18 is drivingly coupled to the secondary oil pump 20. The secondary oil pump 20 has a second inlet 60, which is coupled via a fourth conduit 62 to the reservoir 42, and a second outlet 64 that is coupled via a fifth conduit 66 to an inlet 68 of the second check valve 22. An outlet 70 of the second check valve 22 is coupled in fluid communication to the transmission hydraulic system 12 via a sixth fluid conduit 72. The second check valve 22 is configured to transmit pressurized working fluid supplied by the secondary oil pump 20 to the transmission hydraulic system 12 when the fluid pressure in the fifth fluid conduit 66 exceeds the fluid pressure in the sixth fluid conduit 72 by a second predetermined differential, as well as to inhibit fluid flow from the sixth fluid conduit 72 to the fifth fluid conduit 66.

[0017] The primary oil pump 14 can be configured to supply pressurized working fluid at a first maximum pressure and at a first maximum flow rate, whereas the secondary oil pump 20 can be configured to supply pressurized working fluid at a second maximum pressure, which is less than the first maximum pressure, and a second maximum flow rate that is less than the first maximum flow rate. It will be appreciated that the electric motor 18 will stall (i.e., be unable to rotate) when a fluid pressure of the working fluid at the second outlet 64 is greater than a predetermined stall pressure. The predetermined stall pressure is less than the first maximum pressure.

[0018] The pressure-relieving device 24 can be coupled in fluid communication with the transmission hydraulic system 12 and can be configured to limit the fluid pressure of at least a portion of the working fluid between the transmission hydraulic system 12 and the second outlet 64 of the secondary oil pump 20. In the example shown, the pressure-relieving device 24 is an electronically-operated valve that is disposed in the sixth fluid conduit 72 between the second check valve 22 and the transmission hydraulic system 12. The pressure-relieving device 24 is operable in a first mode, which does not affect the pressure of the working fluid in any portion of the sixth fluid conduit 72, and a second mode that limits the pressure of the working fluid in at least a portion of the sixth fluid conduit 72 to a predetermined relief pressure that is less than the predetermined stall pressure. In the particular example provided, operation of the pressure-relieving device 24 in the second mode operably limits the pressure of the working fluid in the entirety of the sixth fluid conduit 72 as well as the transmission hydraulic system 12 to a predetermined relief pressure that is less than the pre-determined stall pressure.

[0019] The controller 26 is coupled to the electric motor 18, the pressure- relieving device 24 and the electronically-controlled hydraulic valves in the transmission hydraulic system 12. When rotary power is supplied to the vehicle transmission 10 by the internal combustion engine 36 (e.g., to propel a vehicle in which the vehicle transmission 10 is operatively connected), the primary oil pump 14 is operated and provides pressurized working fluid to the transmission hydraulic system 12, including the electronically-controlled hydraulic valves of the transmission hydraulic system 12. The controller 26 operates the electronically- controlled hydraulic valves of the transmission hydraulic system 12 to selectively engage and disengage various clutches (not shown) in the vehicle transmission 10 to obtain a desired overall gear reduction between the internal combustion engine 36 and an output (not shown) of the vehicle transmission 10. The controller 26 does not operate the electric motor 18 at this time and maintains the pressure-relieving device 24 in the first mode.

[0020] When the internal combustion engine 36 is not providing rotary power to drive the primary oil pump 14 but pressurized working fluid is nevertheless desired, the controller 26 can operate the pressure-relieving device 24 in its second mode and can operate the electric motor 18 to drive the secondary oil pump 20. Depending on the configuration of the pressure-relieving device 24 and the placement of the pressure-relieving device 24 within the hydraulic circuitry of the vehicle transmission 10, the controller 26 can operate the pressure-relieving device 24 in various different ways. For example, if the pressure-relieving device 24 depicted in Figure 1 operates in a normally open manner (i.e., permitting fluid communication between the secondary oil pump 20 and the transmission hydraulic system 12) when in the first mode, the controller 26 can briefly operate the pressure-relieving device 24 in the second mode (to thereby relive the pressure of the working fluid in the sixth fluid conduit 72 and the transmission hydraulic system 12 to a pressure that is below the predetermined relief pressure. If the pressure-relieving device 24 depicted in Figure 1 operates in a normally closed manner (i.e., inhibiting fluid communication between the secondary oil pump 20 and the transmission hydraulic system 12) when in the first mode, the controller 26 can maintain operation of the pressure-relieving device 24 in the second mode while the electric motor 18 is operated. It will also be appreciated that if the pressure- relieving device 24 depicted in Figure 1 operates in a normally closed manner when in the first mode, the second check valve 22 could be omitted. Preferably, the pressure-relieving device 24 is operated in the second mode prior to the start of the operation of the electric motor 18.

[0021] While the pressure-relieving device 24 has been depicted as a two- mode relief valve that is disposed in the third fluid conduit 72, it should be appreciated that the pressure-relieving device 24 could be configured somewhat differently.

[0022] In the example of Figure 2, the pressure-relieving device 24a is identical to the pressure-relieving device 24 of Figure 1 except that it is placed in fluid communication with the fifth fluid conduit 66. In this example, the second check valve 22 inhibits pressurized working fluid from flowing from sixth fluid conduit 72 toward the second outlet 64 of the secondary oil pump 20 (i.e., so that working fluid having a pressure that exceeds the predetermined stall pressure cannot be applied to the second outlet 64) and the pressure-relieving device 24a permits fluid to be discharged from the fifth fluid conduit 66 to the reservoir 42 to limit the pressure of the working fluid in the second outlet 64 to a pressure that is less than or equal to the predetermined relief pressure. Consequently, the electric motor 18 can be operated to drive the secondary oil pump 20 without stalling the electric motor 18 even at times where the pressure of the working fluid in the transmission hydraulic system 12 is greater than the predetermined stall pressure. [0023] In the example of Figure 3, the pressure-relieving device 24b is a line pressure regulator that is coupled to the transmission hydraulic system 12 at a location that is in fluid communication with both the third and sixth fluid conduits 52 and 72, as well as coupled to the controller 26. The line pressure regulator is configured to control the pressure of the working fluid in the transmission hydraulic system 12 to a control pressure that can be varied by the controller 26. When the internal combustion engine 36 is not providing rotary power to drive the primary oil pump 14 but pressurized working fluid is nevertheless desired, the controller 26 can operate the line pressure regulator (i.e., the pressure-relieving device 24b) so that the maximum pressure of the working fluid in the transmission hydraulic system 12 is equal to the predetermined relief pressure.

[0024] The configuration that is depicted can be advantageous because the controller can be operate the line-pressure regulator to determine an output pressure of the secondary oil pump 20. Configuration in this manner can be advantageous because it eliminate the need to calibrate the combination of the electric motor 18 and the secondary oil pump 20 prior to the integration of these components into the remainder of the vehicle transmission. When conditions are appropriate during operation of the vehicle transmission 10, the controller 26 can enter a learning mode in which the electric motor 18 is operated at a predetermined target speed to drive the secondary oil pump 20. The line- pressure regulator can sense the pressure of the pressurized working fluid provided by the secondary oil pump 20 and can responsively generate a sensor signal that can be transmitted to the controller 26. The controller 26 can determine a calibration of the electric motor 18 and the secondary oil pump 20 that is based on the rotational output speed of the electric motor 18 (or a variable that is related to the rotational speed of the electric motor 18, such as a duty cycle for a pluse-width modulation motor-powering technique), the output pressure of the secondary oil pump 20 and a target output pressure that is to be generated by the secondary oil pump 20. If the difference between the target output pressure output pressure of the secondary oil pump 20 is outside a predetermined range, the controller 26 can execute a corrective control algorithm to adjust the target speed (or other characteristic, such as the duty cycle) so that the output pressure generated by the secondary oil pump 20 is relatively closer to the target output pressure. The new value of the target speed (or other characteristic) can be stored to a memory 200 in the controller 26. The learning algorithm can be terminated and the operation of the electric motor 18 and the secondary oil pump 20 can be based on the new value of the target speed (or other characteristic) when the pressurized working fluid is to be provided to the transmission hydraulic system 12 by the secondary oil pump 20. It will be appreciated that although the controller 26 has been depicted as a single structure in the foregoing embodiments, the controller 26 could be segregated into two or more separate components and that one of these controller components could be coupled to the electric motor 18 and/or the secondary oil pump 20.

[0025] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Claims

CLAIMS What is claimed is:

1 . A vehicle transmission comprising:

a transmission hydraulic system having a plurality of valves and a plurality of clutch actuators;

a primary oil pump that is configured to be driven by an internal combustion engine;

a first check valve disposed between an outlet of the primary oil pump and the transmission hydraulic system;

an electric motor;

a secondary oil pump that is driven by the electric motor;

a pressure-relieving device coupled in fluid communication with the transmission hydraulic system, the pressure-relieving device being selectively operable to limit a working fluid pressure in at least one of the transmission hydraulic system and an outlet of the secondary oil pump to a predetermined maximum working fluid pressure; and

a controller coupled to the electric motor and the pressure-relieving device; wherein the electric motor stalls when a fluid pressure on an outlet of the secondary pump is greater than a predetermined stall pressure and wherein the predetermined maximum working fluid pressure is less than the predetermined stall pressure.

2. The vehicle transmission of Claim 1 , further comprising a line pressure regulator that is coupled in fluid communication with the primary oil pump, the line pressure regulator having an adjustable pressure output that is controlled by the controller.

3. The vehicle transmission of Claim 2, wherein the line pressure regulator is disposed between the primary oil pump and the first check valve.

4. The vehicle transmission of Claim 2, wherein the line pressure regulator is the pressure-relieving device.

5. The vehicle transmission of Claim 1 , further comprising a second check valve disposed between an outlet of the secondary oil pump and the transmission hydraulic system.

6. The vehicle transmission of Claim 5, wherein the pressure-relieving device is disposed in a fluid path between the second check valve and the transmission hydraulic system.

7. The vehicle transmission of Claim 5, wherein the pressure-relieving device is disposed in a fluid path between the secondary oil pump and the second check valve.

8. A method for operating a vehicle transmission having a transmission hydraulic system, a primary oil pump, a secondary oil pump and an electric motor for driving the secondary oil pump, the method comprising:

operating the primary oil pump to provide a working fluid at a first pressure to the transmission hydraulic system;

halting operation of the primary pump;

reducing a pressure of the working fluid in the transmission hydraulic system below a predetermined stall pressure; and

operating the electric motor to drive the secondary oil pump such that the secondary oil pump provides the working fluid at a second pressure to the transmission hydraulic system, the second pressure being less than the first pressure but greater than the predetermined stall pressure;

wherein the electric motor stalls when a fluid pressure on an outlet of the secondary pump is greater than the predetermined stall pressure.