GB2448671A

GB2448671A - A method of controlling driveline backlash

Info

Publication number: GB2448671A
Application number: GB0701101A
Authority: GB
Inventors: Martin Ranson; Ford Global Technologies Llc
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2007-01-20
Filing date: 2007-01-20
Publication date: 2008-10-29
Also published as: GB0701101D0

Abstract

A method of controlling driveline backlash in a hybrid drive motor vehicle (10) having a primary drive unit (12) and a secondary drive unit comprising an electrical machine (22) arranged downstream of the primary drive unit (12) and which is operable to rotate the driveline. A control unit (32) is controlling the electrical machine (22) and senses electric current flowing to the machine, wherein when the vehicle is stationary, the electrical machine (22) applies a drive torque to the driveline. The electrical current and rotation of said driveline are monitored by the control unit, and when the current reaches a predetermined level, the total rotation is associated with the backlash in the driveline.

Description

* 2448671 AMethod of controlling driveline backlash

Field

This invention relates to a method of controlling drive line backlash in a motor vehicles transmission for vehicles having a hybrid vehicle driveline systems

Background of the Invention

It is well known that the components that make up a vehicle driveline are manufactured to an optimum level of tolerances based around machining accuracy and part costs. The tolerances within the components making up the Jo driveline produces free play within assemblies such as meshed gears. This free play is known as backlash. Within a complex vehicle drive line the tolerances of the components from the engine to the road wheels, for example in the gear box, differential etc., are additive and the overall backlash is relatively large, that is the amount of rotation (degrees) required by the engine to take up all of is the freeplay within the drive line system before turning the road wheels.

Backlash occurs in a vehicle driveline whenever the wheel torque and power unit torque change direction, for example when a vehicle is decelerating under engine braking and the driver then steps on the accelerator pedal and the engine torque is now supplied to the driveline. The backlash take up manifests itself as a loud clunk or bump when the gear teeth impact on each other, and may also be detected as a transitory drop in wheel torque. The phenomenon also occurs when the vehicle driving torque is suddenly removed to apply engine breaking (over-run) and the forces in the driveline reverse direction.

The noise generated by the backlash may be noticeable to the driver especially when the vehicle is in slow speed queuing conditions and there is constant cycling between drive and overrun.

The present invention relates in particular to hybrid vehicles which are provided with an internal combustion engine as its primary drive unit together with a secondary electrical drive unit. An example of a vehicle is described in US2005/054479.

It is know from US2006/0046893 to provide a control for a hybrid vehicle which regulates the application and decay of torque from the engine to hmit the speed with which the backlash is taken up/reversed. Typically these rates are calculated on a series of vehicles to provide an average level of acceptability and engine response and an acceptable level of comfort to the driver. These control systems may be problematic due to the variability of backlash across is different vehicle types and an increase in driveline backlash due to wear.

The present invention provides an control system for a hybrid vehicle which is applicable to any value of driveline backlash and provides active control throughout the life of the vehicle.

Statement of Invention

According to a first aspect of the present invention there is provide a method of controlling driveline backlash in a hybrid drive motor vehicle having a primary drive unit connected to the vehicle wheels by at least one driveline including a change speed transmission and a secondary drive in the form of at least one electrical machine arranged downstream of the primary drive unit, the or each electrical machine being operable to rotate the driveline, and a control unit connected to the electrical machine(s) for controlling operation of the machine(s) and being capable of sensing electric current flowing to the s machine(s) , wherein when the vehicle is stationary the electrical machine is caused to apply a drive torque to the drive line, the electrical current to the machine and the degrees of rotation applied by the machine to said driveline are monitored and when the current reaches a predetermined level the total rotation monitored is associated with the back lash in the driveline and is used by the control unit to control the back lash.

The electrical control unit may form part of the engine control unit or may be separate but programmed to operate in conjunction with the engine control unit.

The transmission-may be an automatic change speed gearbox, Preferably, a first electrical machine is located between the primary drive unit and the transmission and acts on an upper portion of the driveline upstream of the transmission. The first electrical machine may be caused to apply a drive torque to the drive line in first one direction of rotation and then in a second direction of rotation. When the vehicle is moving, the electrical machine is also caused to rotate the driveline during changes in driver demand and/or changes in the primary drive unit torque output..

The secondary drive unit may comprises an electrical machine arranged downstream of the transmission, and preferably the secondary drive unit comprises both the first electrical machine and a further electrical machine arranged downstream of the transmission to act on a rear portion of the driveline.

In said method, the further electrical machine may brake the rear portion of driveline with the first electrical machine being caused to rotate the upper portion of driveline, the electrical current to the first machine and the degrees of rotation applied by the first machine to said upper portion of the driveline are monitored and when the current reaches a predetermined level, the value for the total monitored rotation of the first machine is associated with the back lash in the upper portion of driveline and is used by the control unit to control the back lash.

When applied to a four wheel drive vehicle, this method can be used to determine the back lash in the driveline to the auxiliary drive wheels, usually the vehicle front wheels.

Alternatively the first electrical machine is caused to rotate the driveline without interference from the further electrical machine, and the electrical current to the first machine and the degrees of rotation applied by the first machine to upper and rear portions of the driveline are monitored separately with the current in said further machine remaining steady, difference between the movement of the upper and lower portions of the driveline provide a phase shift value for control of the electrical machines by the control unit to control the back lash.

Preferably, when the first electrical machine is caused to rotate the driveline, the degrees of rotation applied by the first machine to upper and lower portions of the driveline and the current are monitored separately with the respective currents in the two machines being compared with predetermined values to provide a measured value of the backlash in the rear driveline and which is used by the control unit to control the back lash Preferably with the vehicle moving and the drive line torque being subject to changes from positive to negative or vice versa, the control unit operates the machines to maintain the driveline in a meshed condition so that there is no reversal of the backlash.

Tthe engine control unit may be programmed to take the value for the system backlash when the vehicle is stationary and hold the current engine torque or retain fuel cut-off., and the electrical control unit operates said machines to control wind up of the driveline when the engine fuel supply is cut off or re-commenced. Preferably, the two machines are synchronised to the current driveline state and the electrical control unit blends out torque transfer from the engine whilst maintaining a meshed drive line through the machines or blends out torque transfer from the machines in order maintain the correct rate of deceleration.

Description of the Drawings

The Invention will be described by way of example and with reference to the accompanying drawings in which: Fig. I is a schematic drawing for a vehicle having a transmission control according to the present invention Fig.2A is a schematic drawing of a first embodiment of the Invention, Fig. 2B is a flow chart for a control method for transmission control system of Fig. 2A, Fig. 3A is a schematic drawing of a second embodiment of the Invention, Figs 3B&3C are flow charts for a control method for the transmission control system of Fig. 3A in positive and negative torque applications respectively, Fig. 4A is a schematic drawing of a third embodiment of the Invention, Fig. 4B is a flow chart for a first method of controlling the transmission control system of Fig. 4A, Fig. 4C is a flow chart for a second method of controlling the transmission control system of Fig. 4A, Fig. 4D is a flow chart for a third method of controlling the transmission control system of Fig. 4A, Fig. 5A is a flow chart for a method of controlling the transmission control system of Fig. 4A when the vehicle is moving, and Fig. 56 is a flow chart for a second method of controlling the transmission control system of Fig. 4A when the vehicle is moving.

Detailed Description of the Invention

Fig. I shows a hybrid drive vehicle 10 having an internal combustion engine 12 as its primary drive unit. The internal combustion engine 12 drives a change speed transmission assembly 13 typically mounted to the rear of an engine bell housing 11 and driven through a clutch 20. The transmission assembly 13 is typically an automatic transmission driven via a torque converter and in this example, is arranged with its primary drive connected to the rear wheels 15 which are driven by via a conventional drive shaft 14 and differential unit 16 as is welt known. The transmission assembly 13 may also be provided with a second power takeoff 17 connected to the front wheel 18 via a second transmission shaft 19 and differential 21, in order to provide an all wheel drive facility.

The vehicle is provided a secondary drive operable in parallel with the primary drive unit 12. The secondary drive comprises one or more electrical machines 22 and 23 which are located on the input and/or the output of the majority off the driveline components. The more of the dnveline contained between the or each machine 22, 23 and the road wheels 15,18 the better the backlash control. One electrical machine 22 in the form of a crank integrated starter generator (CISG) 22 is located at the transmission input between the primary drive unit 12 and the transmission assembly 13 thereby encompassing the backlash for both the rear and front wheels 15 & 18. A second electrical drive unit 23 in the form of an electrical rear axle drive (ERAD) 23 is arranged around the drive shaft 14 and encompasses the rear differential 16 its downstream drive to the rear wheels 18.

The two electrical machines 22 and 23 are driven by a secondary power source 30, which may be any suitable voltage source such as a battery, capacitor, or fuel cell. As previously described, the primary power source 12 drives the rear wheel 15 through a conventional automatic change speed transmission 13 and drive shaft 14. The automatic transmission 13 is controlled by the driver through a driver operable selector means 36 and an electronic control module 32 (ECU) which may form part of an engine control unit, or may be separate from the engine control unit 37.

The ECU 32 may also monitor and control various aspects of the hybrid vehicle. The control module 32 may be connected to the primary drive unit 12, is to the CISG 22 and to the ERAD 23 to monitor and control their operation and performance. In addition the control module 32 may receive signals from vehicle parameter sensors represented by sensor 33. The sensors 33 may include engine speed sensor, vehicle speed sensor, accelerator position sensor, brake pedal condition sensor, transmission selector sensor, wheel speed sensor, rotational position encoders for the electrical drive units, ignition switch sensor.

and others as is desired. The engine control unit 37 is programmed with torque control software with a suitable interface with the ECU 32 so that the value of rotation may be used so as to regulate the application/decay of torque to prevent bumps and clunks.

The ERAD is adapted to rotate the drive shaft 14 and rotate the transmission assembly 13 via a suitable clutch device 34. The CISG 22 may be selectively coupled to the primary drive unit 13 via the clutch 20. If the clutch 20 is engaged the transmission assembly 13 is driven by the primary drive unit and when the clutch 20 is disengaged the battery 30 may power the CISG 22 to rotate the transmission assembly 13. In addition both the primary drive unit 12 and the battery 30 may simultaneously provide power to the CISG 22.

The secondary power source 30 may be connected to the CISG 22 through a power inverter 35 which converts direct currant (DC) to alternating current (AC) when current flows from the secondary power source 30, and vice versa when AC is generated by the CISG 22 in power conservation mode, for example regenerative braking. The ERAD 23 and CISG may be operated to rotate the transmission assembly 13 and drive shaft 14 drive shaft either in parallel with the primary drive unit 12, or independently of the primary drive unit and in both directions of rotation.

The ECU 32 is programmed to follow a series of steps which are shown in the following schematic drawings and flow charts.

In the first embodiment of the present invention, shown in Fig 2A the vehicle is provided only with the CISG 22 upstream from the transmission 13 and with various sensors 33 including a brake pedal condition sensor 33A, accelerator position sensor 33B, and a vehicle speed sensor 33C. In this case the ECU 32 is separate from the engine control unit 37.

The control operates through a series of steps shown in Fig.2B. The ECU 32 is programmed to sense when the vehicle is stationary (step 221), and the driver demand is zero (step 222). The CISG 22 is caused to apply a driving torque to the transmission assembly 13 such that the driveline components rotate through to the road wheels (step 223). The amount of rotation (degrees of arc) and the applied electric current is monitored in step 224 and 225 and repeated until the current rises. When the electrical current begins to rise it is assumed that the backlash has been eliminated and the measured rotation in step 225 equates with the total free play in the system. The process is then applied in steps 223A-224A, 225A in the opposite direction of rotation. The total value V for the shaft rotation is calculated at step 226 and can be used as a factor within the torque control software in the engine control unit 37.

The scheduling of this backlash measurement may be set to monitor an initial state of free play within the vehicle driveline when new, and then at set intervals to monitor wear over the lifetime of the vehicle, with suitable updates to the ECU when incremental limit(s) have been exceeded.

For complicated drivelines it will be beneficial to quantify the backlash in all combinations of gear ratio, in particular with all wheel drive systems.

In a second embodiment of the invention shown in Fig 3A, similar to the first embodiment, the vehicle sensors further include a gear selection sensor 33D a brake pressure sensor 33E and an engine torque sensor 33F. The backlash data V is used by the ECU as detailed in Fig 3B and with positive driver demand as monitored in step 331 causes the CISC 22 in step 332 to rotate the driveline 13 to remove the backlash prior to the engine delivering torque.

Alternatively the value V from step 226 with engine torque going from positive as determined in step 333 also causes the CISC 22 to rotate the driveline in step 332. Signals V2 and V3 as calculated by the ECU 32 are then passed to the engine control unit 37 for the delivery of torque without shock via steps 334, 335.

In over-run conditions as show in Fig. 3C, with the driver demand going to zero and/or engine torque going negative as monitored in steps 335, 336, the electric machine 22 is caused in step 332A to rotate to unwind the backlash.

Signals V2A and V3A as calculated by the ECU 32 in step 332A are then passed to the engine control unit 37 allowing for over-run torque without shock via steps 338, 339.

This gives additional benefits in that the engine can deliver greater amounts of torque without the propagation of noise. In the overrun condition, the CISG 22 can control the unwinding of the driveline components allowing the engine to enter fuel reduction modes more quickly thereby giving enhanced fuel economy.

In a third embodiment shown in Fig 4A, the vehicle is also provide with similar sensors 33 as shown in Fig. 3A together with the second electrical machine (ERAD) 23 downstream of the transmission 13.

The control steps for the embodiment shown in Fig. 4A are detailed in Figs 4B and 4C. Referring to Fig 4B, when the vehicle is stationary as previously determined in steps 221,222, the ERAD 23 is braked to hold the drive shaft 14 stationary in step 441. Steps 223, 224,225 and 223A, 224A, 225A are then applied as per Fig 2B. The ECU 32 determines at step 446 a value V4 for the backlash in the driveline to the front wheels 18. This information may be used by the engine control unit 37..

The control can be further enhanced by monitoring the current of the CISG 22 in addition to the current the ERAD 23. This will determine the potential backlash between the ERAD 23 and road wheels 15 and allow the take up of the back lash of the remaining driveline as part of the torque phasing control between the two machines 22,23 and the engine 12.

is In a second operation, the steps of which are shown in Fig 4C, the steps 221,222 are repeated and the CISC 22 rotates the transmission assembly with no braking effect from the ERAD 23 in step 442, and the rotational position of the shaft 14 and the transmission 13 is monitored separately in step 443 to detect the degree of rotation of the transmission assembly 13 prior to rotational movement of the shaft 14. This monitored at step 444 through the current to the ERAD 23 remaining steady. This is then repeated in steps 442A, 443A, and 444A in the opposite direction of rotation. This provides a phase shift value V5 at step 447 that can be applied to the driving torque of the two electric machines 22,23 during launch and slow speed torque fluctuations so that backlash is removed prior to the engine delivering or removing torque.

The speed and accuracy of the response using the CISG 22 and ERAD 23 allows the primary power unit 12 to work with no additional lag to the normal air charge delays.

s The control can be further enhanced as is shown in Fig. 4 D by also monitoring the current of the CISG 22 and the current of the ERAD 23 in step 443B and comparing the measured current with predetermined values in step 444B for the two machines, that is a predetermined maximum for the CISG and a current greater than zero for the ERAD. This is repeated in the opposite direction of to rotation in steps 442A, 443D and 444D. This will determine the potential backlash value V5at step 448 between the ERAD 23 and road wheels 15 and allow the take up of the back lash of the remaining driveline as part of the torque phasing control between the two machines 22,23 and the engine 12.

In a fourth embodiment, with the driveline as shown in Fig 4A and the vehicle in motion, when the driveline undergoes a condition change from coasting to traction, or vice versa, the electric machines 22,23 are operated to eliminate backlash in a series of steps as shown in Figs 5A and 5B. Using the value data V4 obtained from static calibration, the ECU 32 is able to calculate the combination of operations for the CISG 22 and ERAD 23. When the vehicle changes from traction to coasting or over-run as determined in steps 551 and 552, that is driver demand goes from >0 to <0 then the engine control unit 37 in step 553 uses the value V4 and holds the current engine torque. The rear machine (ERAD 23) in step 554 and the front machine (CISG) 22 in step 555 should lead the engine so that a controlled unwinding of the driveline in occurs to prevent a bump when the engine fuel supply is cut at step 556, and the ERAD 23 should lead the CISG 22, as shown.

When the vehicle changes from overrun to traction as determined in steps 551 and 552, that is driver demand goes from <0 to> 0, then the engine control unit 37 in step 553A uses the value V4 and holds the current engine torque or retains fuel cut-off. The front machine (CISG) 22 in step 554 A and the rear machine (ERAD) 23 in step 555A should lead the engine so that a controlled wind up of the driveline occurs to prevent a bump when the engine fuel supply re-commences at step 556A, and the CSIG 22 should lead the ERAD 23, as shown.

Alternatively, as shown in Fig 5B the ECU 32 can be programmed so that the machines 22,23 emulate a solid shaft in the driveline so that when the engine changes state, the two machines 22,23 maintain the driveline in a meshed condition so that there is no reversal of the backlash. The ECU 32 can be programmed such that the deceleration of the driveline is in keeping with the natural coasting inertia of the vehicle necessary to maintain the preload. The steps 551, 552 and 553 are repeated as for the traction to overrun conditions.

The two machines 22,23 are synchronised to the current driveline state (direction and torque) in step 557 and the engine control unit 37 blend out torque transfer from the engine whilst maintaining a meshed drive line through the machines 22,23 in step 558. In step 559, the torque transfer from the machines 22,23 is blended out to maintain the correct rate of deceleration.

Should a gear shift occur, then the ERAD 23 continues to decelerate in line with the above and the CISG 2 alters its torque profile during the shift and then again in the new gear ratio.

Claims

Claims 1. A method of controlling driveline backlash in a hybrid drive

motor vehicle having a primary drive unit connected to the vehicle wheels by at least one driveline including a change speed transmission and a secondary drive S comprising at least one electrical machine arranged downstream of the primary drive unit, the or each electrical machine being operable to rotate the driveline, and a control unit connected to the electrical machine(s) for controlling operation of the machine(s) and being capable of sensing electric current flowing to the machine(s) , wherein when the vehicle is stationary the electrical io machine is caused to apply a drive torque to the drive line and the electrical current to the machine and the degrees of rotation applied by the machine to said driveline are monitored and when the current reaches a predetermined level the total rotation monitored is associated with the back lash in the driveline and is used by the control unit to control the back lash.

IS
2. A method as claimed in Claim 1, wherein a first electrical machine is located between the primary drive unit and the transmission and acts on an upper portion of the driveline.
3. A method as claimed in Claim I or Claim 2 wherein the first electrical machine(s) is caused to apply a drive torque to the drive line in first one direction of rotation and then in a second direction of rotation.
4. A method as claimed in Claim 2 or Claim 3 when dependant upon Claim 2, wherein the electrical machine is also caused to rotate the driveline during changes in driver demand and/or changes in the primary drive unit torque output.
5. A method as claimed in any one of Claims 1 to 4, wherein the secondary drive comprises an electrical machine arranged downstream of the transmission.
6. A method as claimed in Claim 2 or any Claim depending from Claim 2, wherein the secondary drive comprises a further electrical machine arranged downstream of the transmission to act on a rear portion of the driveline.
7. A method as claimed in Claim 6, in which the further electrical machine brakes the rear portion of driveline with the first electrical machine being caused to rotate the upper portion of driveline, the electrical current to the first machine and the degrees of rotation applied by the first machine to said upper portion of the driveline are monitored and when the current reaches a predetermined level, the value for the total monitored rotation is associated with the back lash in the upper portion of driveline and is used by the control unit to control the back lash.
8. A method as claimed in Claim 6 or Claim 7, and wherein the first electrical machine is caused to rotate the driveline without interference from the further electrical machine, and the electrical current to the first machine and the degrees of rotation applied by the first machine to upper and rear portions of the driveline are monitored separately with the current in said further machine remaining steady, differences between the movement of the upper and lower portions of the driveline provide a phase shift value for control of the electrical machines by the control unit to control the back lash.
9. . A method as claimed in any one of Claims 6 to 8, and wherein the first electrical machine is caused to rotate the driveline, the degrees of rotation applied by the first machine to upper and lower portions of the driveline and the current are monitored separately with the respective currents in the two machines being compared with predetermined values to provide a measured value of the backlash in the rear dnveline and which is used by the control unit to control the back lash.
10. A method as claimed in any one of Claims 6 to 9 wherein when the vehicle is moving and the drive line torque changes from positive to negative or vice versa, the control unit operates the machines to maintain the driveline in a meshed condition so that there is no reversal of the backlash.
II. A method as claimed in Claim 10 when dependant upon Claim 7, in which the engine control unit is programmed to take the said value and holds the current engine torque or retains fuel cut-off, and the electrical control unit operates said machines to control wind up of the driveline when the engine fuel supply is cut off or re-commenced.
12. A method as claimed in Claim 10 wherein the two machines are synchronised to the current driveline state and the electrical control unit blends out torque transfer from the engine whilst maintaining a meshed drive line through the machines or blends out torque transfer from the machines in order maintain the correct rate of deceleration.
13. A method of controlling driveline backlash in a hybrid drive motor vehicle substantially as hereinbefore described with reference to the drawings.