CA2392112A1

CA2392112A1 - Method for stopping an engine in a parallel hybrid electric vehicle

Info

Publication number: CA2392112A1
Application number: CA002392112A
Authority: CA
Inventors: Anthony Phillips; Michael Degner; Miroslava Jankovic
Original assignee: Ford Global Technologies, Inc.; Anthony Phillips; Michael Degner; Miroslava Jankovic; Ford Motor Company
Current assignee: Ford Global Technologies LLC
Priority date: 2001-06-29
Filing date: 2002-06-28
Publication date: 2002-12-29
Also published as: US20030004031A1; DE10229536A1; JP2003129878A; US6558290B2; JP3862619B2; CA2392120A1

Abstract

The invention provides a strategy to stop a parallel HEV powertrain engine while maintaining smooth vehicle response to driver demand using the motor while simultaneousl y opening an engine disconnect clutch. In the preferred embodiment, the strategy stops an engine (based on, for example, driver demand), disconnects the disconnect clutch to the powertrain, halts fuel to the engine, and predicts a desired motor/generator speed. The prediction of desired motor/generator speed can be: a trajectory comparison based on present and past vehicle velocity and deceleration or on a vehicle accelerator position, or a determination of whether the vehicle is in speed following control mode. The system can also add additional strategies such as accelerate the strategy if a vehicle brake is applied. The gradual takeover by the motor occurs by proportionally decreasing actual engine torque until engine torque is zero while maintaining vehicle velocity using for example a proportional plus integral controller.

Description

SPECIFICATION
Electronic Version 1.2.8 Stylesheet Version 1.0 [STRATEGY FOR STOPPING AN
ENGINE IN A PARALLEL HYBRID
ELECTRIC VEHICLE]
Background of Invention [0001) Feld of tnvenfron

[0002] The present invenfion relates generally to a hybrid electric vehicle (HEV), and specifically to a strategy to stop an engine a~ an HEV with minimal torque distultiarxe to the poweraain.
[0~3) Discussion of the Pr~r Art [0004] The need to reduce fossil fuel consumption and pollutants from automobiles and other vehicles powered by inflemat combustion engines (ICES) is well lanown. Vehicles powered by electric motors have attempted to address these needs. However, elecMc vehicles have limited range and limited power coupled with the substantial time 'needed to recharge their batteries.
An alternative solution is combine both an ICE and electric traction motor into one vehicle. Such vehicles are typically called hybrid electric vehicles (HEV's). See generally, U.S. Pat. No. 5,343,970 to Severinsky.
[0005] The HEV has been described in a variety of configurations. Some HEV
patents disclose systems where an operator is required to select between electric and internal combustion operation. In other configurations the electric motor drives one set of wheels and the ICE drives a different set.
[0008] Other, more useful, configurations have developed. A series hybrid electric vehicle (SHEV) is a vehicle with an engine (most typically an ICE), which powers a generator. The generator, in turn, provides electricity for a battery and orator coupled ~ the drnre wheels of the vehicle. There is no mechanical connection between the engine and the drive wheels. A parallel hybrid electrical vehicle (PHEV) is a vehicle with an engine (most typically an ICE), battery, and electric motor combined to provide torque to power the wheels of the vehicle.
6/14/01 1 of 14 [0007] A paralleUseries hybrid electric vehicle (PSHEV) has characteristics of both the PHEV and the SHEV. The PSHEV is also known as a tCrque (or power) splitting powertrain configuration. Here, the torque output of the engine is given in part to the drive wheels and in part to an electrical generator.
Ths generator powers a battery and motor that also provides torque output in this configuration, torque output can come from either source or bah simultaneously. The vehicle braking system can even deliver torque to drive the generator to produce charge to the battery (regenerative braking).
[0008] The desirability of combining the ICE with an electric motor is dear.
The ICE's fuel consumption and pollutants are reduced with no appreciable toss of performance orvohide range. A major benefit of parallel HEV configurations is that the engine can be turned off during periods of low or no power demand from the driver ( eg ., wai6rrg for a traffic light). This itrtproves fuel economy by eliminating wasted fuel used during icNe conditions. The motor can then propel the vehicle under conditions of low power demand. In some configurations, the engine can be disconnected from the motor and powertrain when it is not running t?y opening a disconnect clutch. As power demand increases, the engine can be restarted and reconnected bo provide the rrsquested torque.
[0009] Developing a strategy to stop an HEV engine and transfer primary torque production of the powert<ain from the engine to the motor or to set the vehks;ise to idle conditions with minimal torque disturbance is needed for successful implementation: of a parallel HE1J. If the engine is connected to the powertrain, stopping the engine would involve maintaining the vehicle's response to the driver's demand using the motor while simultaneously opening a clutch that connects the engine to the powertrain (disconnect clutch) and stopping the engine. Torque supply to the powertrain should be transferred from the engine to the motor snroo~iy in order to avoid any disturbance to the driver.
[0010] Strategies to turn off an HEV's engine are known in the prior art See generally, U.S. Patent Number 5,788,881 to Egami et al.; U.S: Patent Number 5,993,351 to Deguchi et al., U.S. Patent Number 6,067,801 to Harada et al., and U.S. Patent Number 6,083,139 to Deguchi et al.
Unfortunately, no simple and cost sensitive strategy is known to stop a parallel HEV engine while malntalning a smooth vehicle response to driver demand using the motor while simultaneously opening a chrtch that connects the engine to the povvertrain (disconnect clutch).
Summary of Invention [0011 Accordingly, the present Invention provides a strategy to stop a parallel HEV:engine while maintaining a smooth vehicle r~espa~se to driver demand using the motor while srcrrultaneously 6114!0I 2 of I4 opening a that ~nneds the engine to the powertrain: In the preferred embodiment, the HEV
powertrain has an engine, a motorlgenerator, a power transfer unit (such as an automatic transmission, planetary gear set, or an electronic convertertess transmission), and an engine disconnect Dutch.
[0012] The strategy stops the engine (based on, for example, driver demand) by predicting and commanding a desKed motorlgeneratorspeed, halting fuel to the engine, and opening the disconnect Butch to the powerlrain. Next the strategy calculates a desired mot~lgenerator torque.
[0013] The prediction of a desired motorlgenerator speed can be a trajectory comparison based on, for example, vehicle velocity and deceleration at a present time and at some past time or on a vehicle acceleration controller (such as an accelerator or brake) position. Predicting the desired motorlgenerator speed can also include a determination of whether the vehlGe fs In speed following control mode.
[0014] The system can also add additional strategies ~ as a termination strategy if the acceleration control is applied aggressively [001 ~ Other objects of the present invention will becon~ more a~arent to persons having ordinary skdi in the art to which the present invention pertains from the following description taken in conjunction with the accompanying figures.
Brief Description of Drawings (0016] The foregoing objects, advantages: and featuees, as well as other objects and advantages, will become apparent with reference to the description and figures below, in which like numerals represent like elements and in which:
[0017] Figure 1 shows a general parallel hybrid electric vehicle configuration with an engine disconnect clutch.
[0018] Figure 2 shows the strategy of the present invention to stop the engine and smoothly disconnect the engage from the vehicle powertrain.
[0019] Figure 3 shows vehicle speed over time for desired and actual vehicle speed.
Detailed Description [0020] The present invention generally relates to hybrid electric vehicles (HEVs). Although the preferred 5114/01 3 of 14 embodiment described is for a parallel HEV, the invent'ron could be applied to any vehicle using a motor and an engine as the drive source having an engine disconnect Butch.
(0021] Figure 1 shows general components of a parallel HEV powertrain with an engine disconnect clutch. An engine 20, is finked to a motorlgenerator 22, via a disconnect clutch 24. The powertrain has a vehicle system controller (VSC) 18, and the motorlgenerator 22 has an additional motor control unit and inverter (MCU} 16. A battery 26 connects to the motarlgenerator 22 to allow the flow of electrical current to and from the two cortrponents. The motor/gers3rator 22 is connoted to a pow~train power transfer unit 28 (such as an automatic transmission, a planetary gear set (power-split}, or an electronic converterless transmission}, that is connected to the vehicle's wheels 30.
Thus, torque and energy flow from the engine 20 and motoNgenerator 22 through the power transfer unit 28 to the wheels 30.
(0022] in this configuration, both the engine 20 and the motor/generator 22 can be directly coupled to the wheels 30, so that both power souroes can independently ~ovide torque to the vehicle povvertrain.
The configuration shown in Figure 1 employs the disconnect clutch 24 between the engine 20 and the motorlgenerator 22 to aNow a t~emponuy disconnection of the engine 20 from the motorlgenerator 22 and the wheels 30. The motor, in addition to propelling the vehicle, can also be operated as a generator for use in charging the battery 26 using the engine 20 or through regenerative braking.
Regenerative braking ups the motorl~enerator 22 to recover vehicle braking energy to charge the battery.
(0023] The pre~nt irnention is a strategy to stop a parallel HEY engine, while maintaining a smith vehicle response to driver demand or other vehicle conditions, using the motorlgenerator Z2 and simultaneously opening the disconnect clutch 24 that connects the engine 20 to the vehicle powertrain. The preferred embodiment of the strategy of the present invention is illustrated in Figure 2.
It is noteworthy at the outset that the strategy can be configured to accelerate completion at any point if a vehicle brake system is applied (such as when a brake pedal is depressed) or abort at any point if vehicle acceleration control is aggressively applied (not shown).
[0024] Figure 2 shows the preferred strategy for stopping the engine 20 in an HEV parallel powertrain confrguration. Initially, the motor/generator 22 ~ commanded to be in speed follow~g control mode. At the same time, a desired angular speed command is also sent to the motorlgenerator 22. If the power transfer unit 28 is engaged, the desired motorlgenerator 22 angular speed ( ~
) is calailated mot des according to:
6!14!01 4 of 14 [0025] w modes ' [v(t o ) + ((v(t 0 ) - v(t Q: T))!T)'kT] ' C.
[0026] In this formula: 'b(t 0 )"is the vehicle speed why an engine stop mode 34 is entered ( i.e. , at time "t o'~; "T' is a sample time between measurements of vehicle speed; "k" is a number of measurement sample int8rvals since t Q ; and "C" is the kinematrc conversion facb~r from vehicle speed to motorlgenerator angular speed and can include wheel radius, final drive ratio, and gear ratio.
The constant "C" converts linear vehicle speed at the wheels to angular motorlgenerator speed. This method effectively uses the vehicle's velocity and acceleration at the beginning of the engine stop event to estimate khe vehicle's velocity'at some future time (t 0 )+ kT.
[0027] Though not shown here, an alternative algorithm for calculating the desired speed trajectory could utilize a map from accelerator or brake position to desired vehicle speed, which could then be translated to desired motorlgenerator speed.
[0028] In general, the strategy compares actual vehicle speed (as translated to motorlgenerator speed) to the desired value once the motorlgenerator 22 is under speed control. When the speed error falls below a calibratable tokerance (Tolerance 1), the controller directs the vehicle system controller (VSC) 18 to halt fuel to the engine 20 and the controller commands the disconnect clutch 24 to open.
Although not showm in the flowchart, the speed error could also be required to stay below the calibratable tolerance for a fixed amount of time in order to guarantee that the speed control has stabilized the system at the desired speed.
[0029] While the engine 20 is decelerating, it could still impart an undesirable torque on the vehicle [0030]
poHrertrain if the disconnect clutch 24 is even partially closed. Therefore the shutdown strategy does not end until the disconnect clutch 24 is completely open. Since the motorlgenerator 22 is in speed following control mode during the engine stopping strategy, the strategy compensates for any torque disturbances caused by the engine 20 by modifying its torque output in order to maintain the vehicle at the desired speed. In Figure 2, a disconnect clutch position sensor 52 is shown as the measurement signal used for determining whether or not the clutch is still partially closed. Other signals ( lg., clutch apply pressure} could also be used for this purpose.
During the entire engine stopping strategy of the present Invention, a vehicle braking system status (such as brake position) can tie monitored for any changes. At any point when the vehicle brakes are applied, the engine stopping strategy can be accelerated by immediately halting fuel to the engine 20 and commanding the disconnect clutch 24 to open completely: The engine stop strategy is ti/14101 5 of 14 i i then immediately exited to one of several alternative vehicle states, depending on the vehicle operating status. .
[0031] Speafically, Figure 2 illustrates a preferred embodiment of the present invention. The strategy begins with a command from an engine controller such as the vehicle system controller {VSC) 18 to enter the engine stop mode at Step 34. Initially, the motorlgenerator 22 (s commanded to run in speed following control mode in Step 36 (as opposed to torque following mode).
During speed following control mode, the motoNgenerator applies whafever torque is necessary to achieve a desired speed set point. On the other hand, in torque following mode, the moborlgenerator tries to achieve the desired torque set point, allowing the speed to change. The motorlgenerator 22 remains in speed following control mode until the disconnect Butch 24 is fully open. Next, a desired angular speed command is also sent to the motoNgenerator 22 at'Step 38 based on the desired motorlgenerator speed 40 described above.
[0032] After the command for desired motorlgenerator 22 speed is sent in Step 38, an, actual motorlgenerator speed 42 is received by a vehicle sensor and is compand to the desired motoNgenerator speed 40 at Step 44 to pncdu~ an rnotor/generator speed error.
The strategy then determines whether an absolute value of the actual motorlgenerator speed 42 error falls below a calibratable tolerance (Tolerance I) at Step 46: If the speed error is not bel~v Tolerance 1 at Step 46, the strategy mums to Step 38. It the speed error is below Tolerance 1 at Step 46, the strategy directs the VSC 18 to halt fueling the engine 20 at $tep 48 based on its own separate stopping strategy and then commands the disconnect clutch 24 to open at Step 50.
[0033) As the strategy proceeds, the disconnect Butch 24 disengages over a calibratable period of time.
The engine 20 speed will begin to decrease. Since the motorlgenerator 22 is in speed following control mode, it will continue to apply whatever torque is necessary (within its capability) to maintain the desired vehicle speed.
)0034] The prediction of a desired motorlgenerator speed can be a trajectory comparison based on, for example, vehicle velocity and deceleration at a present time and at some past time or on a vehicle acceleration controller (such as an accelerator or brake) position. Predicting the desired motodgenerator 22 speed can also include a determination of whether the vehide is in speed following control mode.
[0035]
The motodgenerator gradually takes over the necessary torque to propel the vehicle by 6/14/01 6 of 14 proportionauy decreasing the aduai engine torque in Step 48 and Step 50 unto engine 20 torque is zero while mainfiaining vehicle velocity using, for example, a proportional plus integral controller.
[0036) At Step 54 the strategy determines whether the disconnect clutch 24 is disengaged from the vehicle powertrain from a disconnect dukch position sensor 52. If the disconnect Butch 24 is disengaged, the strategy continues. When the disconnect clutch position sensor 52 indicate it ~
disengaged from the powertrain the strategy ends.
[0037) Figure 3 shows vehicle speed (velocity) 60 (Y-axis) over time 62 (X-axis) for desired vehicle speed 64 and actual vehicle speed 66. Desired vehicle speed 64 can be calculated using vehicle speed and acceleration at the beginning ~ the engine slap event 68 and vehicle speed and acceleraFron at some past tone 70 to estimate the vehicle's velocity atsome future tkne.
[0038] An attemative strategy for calculating the desired speed trajectory shown in Figure 3 could instead utilize a map from accelerator or brake position to predict desired vehicle speed, wh~h quid then be translated to desired motorlgenerator speed. As stated above for any implemer>tation, ~e vehicle brake system status (such as brake potion) can stilt be monitored for any changes so that the overall strategy can be accelerated if the brake is applied.
[0039] The above-described embodiment of the invention is provided purely for purposes of example.
Many other variafions, modifications, and applications of the invention may be made.
6/14JOI 7 of 14

Claims

1. A system to stop an engine in a parallel hybrid electric vehicle powertrain comprising:
a vehicle system controller (VSC);
an engine;
a motor/generator;
a power transfer unit;
a vehicle powertrain connecting the engine, motor/generator, and power transfer unit;
a disconnect clutch to disconnect the engine from the vehicle powertrain;
a strategy to stop the engine comprising a system to disconnect the disconnect clutch, a strategy to halt fuel to the engine, and a strategy to predict a desired motor/generator speed;
and a strategy to calculate a desired motor/generator torque.

2.The system of claim 1 wherein the strategy to predict the desired motor/generator speed comprises a trajectory comparison based on vehicle velocity and acceleration at a present time and at some past time.

3.The system of claim 1 wherein the strategy to predict the desired motor/generator speed comprises a prediction based on a vehicle accelerator position.

4.The system of claim 1 wherein the strategy to predict the desired motor/generator speed comprises a prediction based on a vehicle brake position.

5.The system of claim 1 wherein the strategy to predict the desired motor/generator speed further comprises a determination of whether the vehicle is in speed following control mode.

6.The system of claim 1 further comprising a strategy to accelerate the system to stop the engine if a vehicle brake is applied.

7.The system of claim 1 further comprising a strategy to terminate the system if an acceleration control is applied aggressively.

8.The system of claim 1 wherein the power transfer unit is an automatic transmission.

9.The system of claim 1 wherein the power transfer unit is a planetary gear set.

10.The system of claim 1 wherein the power transfer unit is an electronic converterless transmission.

11.A means to stop an engine in a parallel hybrid electric vehicle powertrain comprising:
a vehicle system controller (VSG);
an engine;
a motor/generator;
a power transfer unit;
a vehicle powertrain connecting the engine; motor/generator, and power transfer unit:
a disconnect clutch to disconnect the engine from the vehicle powertrain;
a means to stop the engine comprising a means to disconnect the disconnect clutch,a means to halt fuel to the engine; and a means to predict a desired motor/generator speed; and a means to calculate a desired motor/generator torque.

12.A method of stopping an engine in a parallel hybrid electric vehicle powertrain comprised of a vehicle system control (VSC) an engine, a motor/generator, a power transfer unit, and a vehicle powertrain connecting the engine, motor/generator, power transfer unit, and an engine disconnect clutch comprising the steps of:
stopping the engine comprising the steps of disconnecting the disconnect clutch and halting fuel to the engine;
predicting a desired motor/generator speed;
calculating a desired motor/generator torque.
l3.The method of claim 12 wherein the step of predicting the desired motor/generator speed comprises a trajectory comparison based on vehicle velocity and acceleration at a present time and at some past time.
l4.The method of claim 12 wherein the step of predicting the desired motor/generator speed comprises a prediction based on a vehicle accelerator position.
l5.The method of claim 12 wherein the step of predicting the desired motor/generator speed comprises a prediction based on a vehicle brake position.
l6.The method of claim 12 wherein the step of predicting the desired motor/generator speed further comprises the step of determining whether the vehicle is in speed following control mode.

l7.The method of claim 12 further comprising the step of accelerating the method to stop the engine if a vehicle brake is applied.
l8.The method of claim 12 further comprising the step of terminating the method to stop the engine if an acceleration control is applied aggressively.
19.The method of claim 12 wherein the power transfer unit is an automatic transmission.
20.The method of claim 12 wherein the power transfer unit is a planetary gear set 21.The method of claim 12 wherein the power transfer unit is an electronic converterless transmission