Patent Application
20070102208
This application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2005-322407 filed on Nov. 7, 2005. The entire disclosure of Japanese Patent Application No. 2005-322407 is hereby incorporated herein by reference.
1. Field of the Invention
The present invention relates to a braking control system for a hybrid vehicle having an electric drive (EV) mode in which a drive wheel is solely driven by a motor/generator and a hybrid drive (HEV) mode in which the drive wheel is driven by an engine and the motor/generator or the engine alone. More specifically, the present invention relates to a braking control system for a hybrid vehicle that is configured to perform a coasting (inertial) motion braking force control.
2. Background Information
Japanese Laid-Open Patent Publication No. 11-082260 discloses one example of a conventional hybrid drive system used in a conventional hybrid vehicle. The hybrid vehicle drive control system presented in Japanese Laid-Open Patent Publication No. 11-082260 has a motor/generator arranged between an engine and a transmission so as to be coupled to a shaft that directs the rotation of the engine to the transmission, with a first clutch disposed between the engine and the motor/generator, and a second clutch disposed between the motor/generator and the output shaft of the transmission.
A hybrid vehicle equipped with such conventional hybrid drive system can be put into an electric drive (EV) mode in which the vehicle travels using power from the motor/generator by releasing the first clutch and engaging the second clutch. Such a hybrid vehicle can also be put into a hybrid drive (HEV) mode in which the vehicle can travel using power from both the engine and the motor/generator by connecting both the first clutch and the second clutch.
When such a hybrid vehicle is coasting in the EV mode and regenerative braking of the motor/generator becomes prohibited because the battery is fully charged, the hybrid vehicle switches to coasting in the HEV mode (in which the engine is connected to the drive wheels) in order to use engine braking force.
When the vehicle switches from coasting in the EV mode to coasting in the HEV mode, there is the possibility that an unpleasant change in the braking force will be transmitted to the drive wheels when the first clutch is engaged and the crankshaft of the engine starts rotating or cranking without fuel supplied to the engine. Such an unpleasant change in braking force can be avoided by temporarily releasing the second clutch, then engaging the first clutch and rotating (driving) the crankshaft of the engine with the motor/generator while suspending the fuel supply to the engine, and finally reengaging the second clutch when the rotational speed difference across the second clutch is substantially zero. In this way, the vehicle can be switched more smoothly to a state of coasting in the HEV mode in which the vehicle can be braked with the engine braking force.
However, during the period when the second clutch is being released, the drive wheels are disengaged from both the motor/generator and the engine and can not be braked by either regenerative braking of the motor/generator or engine braking using the engine. Consequently, the coasting state of the vehicle will be temporarily interrupted by an odd feeling of thrusting forward (freewheeling).
Although it does not solve the problem just described, Japanese Laid-Open Patent Publication No. 11-093724 presents another conventional technology that relates to situations in which the state of charge of the battery of a hybrid vehicle is high and regenerative braking by the motor/generator needs to be limited. In such situations, the conventional technology disclosed in this reference increases the throttle opening degree and adjusts the engine pumping loss as the allowable regenerative braking torque declines even during coasting. As a result, the engine braking force compensates for the decline in regenerative braking torque and the total braking force can be maintained.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved hybrid vehicle control device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
When the throttle opening of the engine is controlled in accordance with the conventional technology described in Japanese Laid-Open Patent Publication No. 11-093724 such that a decrease in regenerative braking torque is compensated with an engine braking force, the response of the engine braking force with respect to adjustment of the throttle opening is poor. Thus, there is the possibility that the throttle control will not be able to increase the engine braking force at an appropriate timing for offsetting the decrease in the regenerative braking torque. Consequently, the control may not be able to achieve the original objective of offsetting (compensating for) the decline in the regenerative braking torque. Furthermore, the braking force acting on the drive wheels may deviate from the target as result of the engine braking force changing at an inappropriate timing.
In addition to the change in braking force that accompanies the temporary release of the second clutch described above, there are other situations in which the braking force acting on the drive wheels changes. For example, when a hybrid vehicle switches from coasting in the EV mode to coasting in the HEV mode in order to compensate for insufficient regenerative braking torque with an engine braking force, a change in braking force will occur if the mode change is accomplished by engaging the first clutch while leaving the second clutch engaged. In such a case, the engine torque will cause the braking force to change during cranking of the engine. This change in braking force cannot be alleviated with the conventional technology described in Japanese Laid-Open Patent Publication No. 11-093724 because of the response speed is poor when the engine braking force is adjusted by controlling the throttle opening degree.
There is still another situation in which the braking force acting on the drive wheels will change. The braking force acting on the drive wheels will change (decrease) if the regenerative braking torque generated by the motor/generator is reduced due to the state of charge of the battery gradually becoming higher while the hybrid vehicle is coasting in the EV mode. If the throttle opening control technology described in Japanese Laid-Open Patent Publication No. 11-093724 is used in such a situation to adjust the engine braking force to offset the decrease in regenerative braking torque, it will be necessary to switch from the EV mode to the HEV mode in order to use engine braking. This necessity can become troublesome from a control perspective when the traveling conditions are such that it is better to continue traveling in the EV mode.
The present invention is based on the idea that instead of using engine braking to counterbalance the change in the braking force that occurs in the situations described above, the braking force acting on the drive wheels of a hybrid vehicle can be maintained by automatically operating a service brake that acts on the drive wheels and can be operated with a brake pedal. With this approach, since the control response obtained by automatically operating a service brake is much better than the control response obtained with engine braking and since it is not necessary to change to the HEV mode, the braking force acting on the drive wheels can be stabilized without encountering the various problems described in the preceding paragraphs. The object of the present invention is to provide a hybrid vehicle control device that resolves the aforementioned problems.
In order to achieve the aforementioned object, a hybrid vehicle control system in accordance with the present invention is basically provided with an engine, a motor/generator, a first clutch, a second clutch and a controller. The first clutch is arranged to change a torque transfer capacity between the engine and the motor/generator. The second clutch is arranged to change a torque transfer capacity between the motor/generator and at least one drive wheel. The controller is configured to selectively control the first and second clutches to switch between an electric drive mode in which the engine is stopped, the first clutch is released and the second clutch is engaged and a hybrid drive mode in which both of the first and second clutches are engaged. The controller is further configured to determine whether a power train braking force from a power train of a vehicle that drives the drive wheel is sufficient to achieve a target braking force. The controller is further configured to operate a wheel brake to apply a wheel braking force against a wheel of the vehicle to maintain the target braking force when an accelerator pedal depressing amount is detected as being substantially zero and when the power train braking force is not sufficient to achieve the target braking force.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.
Referring now to the attached drawings which form a part of this original disclosure:
FIGS. 7(A) and 7(B) are a series of flowcharts showing a subroutine of the target automatic drive force computing subroutine shown in
Selected embodiment of the present invention will now be explained with reference to the drawings. It will be apparent to those skilled in the art from this disclosure that the following description of the embodiment of the present invention is provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
Referring initially to
The motor/generator 5 is configured and arranged such that it can be used as a motor or an electric generator. As seen in
The second clutch 7 is provided between the motor/generator 5 and the automatic transmission 3, i.e., more specifically, between the shaft 4 and the transmission input shaft 3a. The second clutch 7 is configured and arranged to selectively engage or disengage the connection between the motor/generator 5 and the automatic transmission 3. Similarly to the first clutch 6, the second clutch 7 is configured and arranged such that the torque transfer capacity thereof can be changed either continuously or in a stepwise manner. For example, the second clutch 7 can be a multi-plate wet clutch configured such that its torque transfer capacity can be changed by controlling the flow rate of a hydraulic clutch fluid (hydraulic oil) and the pressure of the hydraulic clutch fluid (clutch connection hydraulic pressure) continuously or in a stepwise fashion by a proportional solenoid.
In this embodiment of the present invention, the automatic transmission 3 is preferably a conventional automatic transmission such as one presented in pages C-9to C-22 of the “Nissan Skyline New Model (CV35) Handbook” published by Nissan Motor Company, Ltd. More specifically, the automatic transmission 3 is configured and arranged such that a plurality of friction elements (clutches and brakes) can be selectively engaged and disengaged and the power transmission path (e.g., first gear, second gear, etc.) is determined based on the combination of the engaged and disengaged friction elements. The automatic transmission 3 is configured and arranged to transfer the rotation of the input shaft 3a to an output shaft 3b after converting the rotation at a gear ratio corresponding to the selected gear. The rotation of the output shaft 3b is distributed to the left and right rear wheels 2 by a differential gear unit 8 and thereby contributes to moving the vehicle. Of course, it will be apparent to those skilled in the art from this disclosure that the automatic transmission 3 is not limited to a step-type automatic transmission like that just described, and it is also acceptable to use a continuously variable transmission (CTV).
When the vehicle is traveling under low load/low speed conditions, such as when the vehicle is starting to move from a stopped state, the vehicle requests an electric drive (EV) mode. Under the EV mode, the power train shown in
When the motor/generator 5 is driven under these conditions, the output rotation of the motor/generator 5 alone is transferred to the transmission input shaft 3a and the transmission 3 transfers the rotation of the input shaft 3a to the transmission output shaft 3b at a gear ratio corresponding to the selected gear. The rotation of the transmission output shaft 3b is then transmitted to the rear wheels 2 through the differential gear unit 8 and the vehicle moves in the EV mode using output from only the motor/generator 5.
When the vehicle is traveling at a high speed, under a large load, or under conditions in which the amount of electric power that can be extracted from the battery is small, the vehicle requests a hybrid drive (HEV) mode. Under the HEV mode, the power train is controlled such that the first clutch 6 and the second clutch 7 are both engaged and the automatic transmission 3 is in a power transmitting state. In this state, the output rotation from the engine 1 or the output rotations from both the engine 1 and the motor/generator 5 are transferred to the transmission input shaft 3a and the transmission 3 transfers the rotation of the input shaft 3a to the transmission output shaft 3b at a gear ratio corresponding to the selected gear. The rotation of the transmission output shaft 3b is then transmitted to the rear wheels 2 through the differential gear unit 8 and the vehicle moves in the HEV mode using output from both the engine 1 and the motor/generator 5 or only the engine 1.
When the vehicle is traveling in the HEV mode and the engine 1 is running at optimum fuel efficiency such that a surplus of energy is produced, the surplus energy is used to operate the motor/generator 5 as an electric generator and, thereby, convert the surplus energy into electric energy. The generated electric energy can then be stored and used later to drive the motor/generator 5 as a motor, thereby improving the fuel efficiency of the engine 1.
Although, in
Also, instead of providing a dedicated second clutch 7 in front of the automatic transmission 3 as in
The control system shown in
The integral controller 20 preferably includes a microcomputer with a drive wheel braking force compensation control program that controls the target automatic braking forces as discussed below. The integrated controller 20 can also include other conventional components such as an input interface circuit, an output interface circuit, and storage devices such as a ROM (Read Only Memory) device and a RAM (Random Access Memory) device. The microcomputer of the integrated controller 20 is programmed to control the operating point of the power train. The memory circuit stores processing results and control programs such as ones for the target automatic braking forces calculation operation that are run by the processor circuit. The integrated controller 20 is operatively coupled to the various component of the hybrid vehicle in a conventional manner. The internal RAM of the integrated controller 20 stores statuses of operational flags and various control data. The internal ROM of the integrated controller 20 stores the data used for various operations. The integrated controller 20 is capable of selectively controlling any of the components of the control system in accordance with the control program. It will be apparent to those skilled in the art from this disclosure that the precise structure and algorithms for the integrated controller 20 can be any combination of hardware and software that will carry out the functions of the present invention. In other words, “means plus function” clauses as utilized in the specification and claims should include any structure or hardware and/or algorithm or software that can be utilized to carry out the function of the “means plus function” clause.
The integrated controller 20 is further configured to issue commands indicating a target rear wheel (drive wheel) automatic braking force tTbr and a target front wheel (non-drive wheel) automatic braking force tTbf to a brake-by-wire (electronically controlled) hydraulic brake system 23 in order to achieve the object of the present invention.
The brake-by-wire hydraulic brake system 23 utilizes a conventional technology for electronically controlling a service brake configured to control a braking force imparted to a wheel in response to operation of a brake pedal. More specifically, the brake-by-wire hydraulic brake system 23 has a master cylinder configured to generate a hydraulic pressure corresponding to the force with which the brake pedal is depressed and wheel cylinders constituting a wheel brake unit. The brake-by-wire hydraulic brake system 23 is configured such that the master cylinder and the wheel cylinders are allowed to communicate with each other hydraulically when there is a problem with the electronic control system. Thus, in such case, the brake-by-wire hydraulic brake system 23 can function in the same manner as a regular hydraulic brake system. Meanwhile, when the electronic control system is functioning normally, the hydraulic communication between the master cylinder and the wheel cylinders is shut off and the hydraulic pressures of the wheel cylinders are controlled electronically based on a detected value of the master cylinder pressure. Furthermore, when necessary, the wheel cylinder pressures can be electronically controlled based on control factors other than the detected value of the master cylinder pressure.
When the brake-by-wire hydraulic brake system 23 receives the target rear (drive) wheel automatic braking force tTbr and the target front (non-drive) wheel automatic braking force tTbf, the brake-by-wire hydraulic brake system 23 is configured to supply a hydraulic pressure corresponding to the target automatic braking force tTbr to the wheel cylinders of the rear (drive) wheels 2 and a hydraulic pressure corresponding to the target automatic braking force tTbf to the wheel cylinders of the front (non-drive) wheels independently from the detected value of the master cylinder pressure. As a result, automatic braking can be executed such that the target automatic braking force tTbr is generated at the rear (drive) wheels 2 and the target automatic braking force tTbf is generated at the front (non-drive) wheels.
The integrated controller 20 operatively connected to the following sensors: an engine speed sensor 11, a motor/generator speed sensor 12, a transmission input rotational speed sensor 13, a transmission output rotational speed sensor 14, an accelerator pedal position sensor 15, a state of charge sensor 16 and a master cylinder pressure sensor 24. The engine speed sensor 11, the motor/generator speed sensor 12, the input rotational speed sensor 13, and the output rotational speed sensor 14 are arranged as shown in FIGS. 1 to 3. The engine speed sensor 11 is configured and arranged to detect an engine speed Ne of the engine 1 and produce a signal indicative of the detected engine speed Ne that is inputted to the integrated controller 20. The motor/generator speed sensor 12 is configured and arranged to detect a rotational speed Nm of the motor/generator 5 and produce a signal indicative of the detected rotational speed Nm that is inputted to the integrated controller 20. The transmission input rotational speed sensor 13 is configured and arranged to detect a rotational speed Ni of the input shaft 3a of the automatic transmission 3 and produce a signal indicative of the detected rotational speed Ni that is inputted to the integrated controller 20. The transmission output rotational speed sensor 14 is configured and arranged to detect a rotational speed No of the output shaft 3b of the automatic transmission 3 and produce a signal indicative of the detected rotational speed No that is inputted to the integrated controller 20. The accelerator pedal position sensor 15 is configured and arranged to detect an accelerator pedal depression amount (accelerator position APO) and produce a signal indicative of the detected accelerator pedal depression amount (APO) that is inputted to the integrated controller 20. The detected accelerator pedal depression amount APO expresses the load demand imposed on the engine 1. The state of charge sensor 16 is configured and arranged to detect a state of charge SOC (usable electric power) of a battery 9 in which electric power for the motor/generator 5 is stored and produce a signal indicative of the detected state of charge SOC of the battery 9 that is inputted to the integrated controller 20. The master cylinder pressure sensor 24 is configured and arranged to detect a master cylinder hydraulic pressure Pm and produce a signal indicative of the detected hydraulic pressure Pm of the master cylinder that is inputted to the integrated controller 20. Thus, the integrated controller 20 receives these input signals for determining the operating point of the power train.
The integrated controller 20 is configured to select a drive (operating or traveling) mode (EV mode or HEV mode) that is capable of delivering the drive force desired by the driver based on the accelerator position APO, the state of charge SOC of the battery 9, and the transmission output rotational speed No (vehicle speed VSP). Then the integrated controller 20 is configured to compute the target engine torque tTe, the target motor/generator torque tTm (target motor/generator rotational speed tNm also acceptable), the target first clutch torque transfer capacity tTc1, and the target second clutch torque transfer capacity tTc2. The target engine torque tTe is fed to the engine controller 21 and the target motor/generator torque tTm (or the target motor/generator rotational speed tNm) is fed to the motor/generator controller 22.
The engine controller 21 is configured to control the engine 1 such that the engine torque Te becomes equal to the target engine torque tTe. The motor/generator controller 22 is configured to control the motor/generator 5 through the battery 9 and an inverter 10 such that the torque Tm (or the rotational speed Nm) of the motor/generator 5 becomes equal to the target motor/generator torque tTm (or the target motor/generator rotational speed tNm).
The integrated controller 20 is configured to supply a solenoid current corresponding to the target first clutch torque transfer capacity tTc1 to a connection control solenoid (not shown) of the first clutch 6 and a solenoid current corresponding to the target second clutch torque transfer capacity tTc2 to a connection control solenoid (not shown) of the second clutch 7. In this way, the connection force (holding force) of the first clutch 6 is controlled such that the torque transfer capacity Tc1 of the first clutch 6 becomes equal to the target torque transfer capacity tTc1 and the connection force of the second clutch 7 is controlled such that the torque transfer capacity Tc2 of the second clutch 7 becomes equal to the target torque transfer capacity tTc2.
In step S0, the integrated controller 20 is configured to use a prescribed final target driving/braking force map such as one shown in
In step S1, the integrated controller 20 is configured to compute the target automatic braking force tTbr for the rear wheels 2 and the target automatic braking force tTbf for the front wheels. The target automatic braking forces tTbr and tTbf will be used to control the brake-by-wire hydraulic brake system 23 shown in
The control programs (subroutines) shown in FIGS. 6, 7(A) and 7(B) are executed in order to accomplish the calculation of the target automatic braking forces tTbr and tTbf in step S1. The method of calculating the target automatic braking forces tTbr and tTbf will now be explained with reference to FIGS. 6, 7(A) and 7(B).
In step S11 of
In step S21 of
In step S22, the integrated controller 20 is configured to find the efficiency of the automatic transmission 3 based on the transmission input rotational speed Ni and the currently selected gear using a prescribed map such as one shown in
In step S23, the integrated controller 20 is configured to calculate the braking force that the motor/generator 5 can produce under the currently selected gear of the automatic transmission 3. The calculation is accomplished by first finding the product of the amount of output torque that can be obtained from the motor/generator 5 at the current state of charge SOC of the battery 9 (calculated in step S21), the gear ratio corresponding to the currently selected gear, and the gear ratio of the differential gear unit 8. The resulting product value is then divided successively by the dynamic radius of the tires of the drive wheels 2 and the efficiency of the automatic transmission 3 (determined in step S22).
In step S24, the integrated controller 20 is configured to calculate the braking force that the motor/generator 5 will be able to produce under the gear that the automatic transmission 3 will enter if the automatic transmission 3 is changing gears. The calculation is accomplished by first finding the product of the amount of output torque that can be obtained from the motor/generator 5 at the current state of charge SOC of the battery (calculated in step S21), the gear ratio corresponding to the gear the automatic transmission 3 will enter, and the gear ratio of the differential gear unit 8. The resulting product value is then divided successively by the dynamic radius of the tires of the drive wheels 2 and the efficiency of the automatic transmission 3 (determined in step S22).
In step S25, the integrated controller 20 is configured to calculate the engine braking force that can be obtained if the crankshaft 1a of the engine 1 is rotated without supplying fuel to the engine 1 under the currently selected gear of the automatic transmission 3. The calculation is accomplished by first finding the engine friction torque based on the engine speed Ne using a map such as one shown in
In step S26, the integrated controller 20 is configured to calculate the engine braking force that can be obtained if the crankshaft 1a of the engine 1 is rotated without supplying fuel to the engine 1 under the gear that the automatic transmission 3 will enter if the automatic transmission 3 is changing gears. The calculation is accomplished by first finding the engine friction torque based on the engine speed Ne using the map such as one shown in
In step S27, the integrated controller 20 is configured to calculate the clutch connection braking force that the first clutch 6 can produce by rotating the crankshaft 1a of the engine 1 under the currently selected gear of the automatic transmission 3. The calculation is accomplished by first finding the product of the target torque transfer capacity tTc1 of the first clutch 6, the gear ratio corresponding to the currently selected gear, and the gear ratio of the differential gear unit 8. The resulting product value is then divided successively by the dynamic radius of the tires of the drive wheels 2 and the efficiency of the automatic transmission 3 (determined in step S22).
In step S28, the integrated controller 20 is configured to calculate the clutch connection braking force that the first clutch 6 can produce by rotating the crankshaft of the engine 1 under the gear that the automatic transmission 3 will enter if the automatic transmission 3 is changing gears. The calculation is accomplished by first finding the product of the target torque transfer capacity tTc1 of the first clutch 6, the gear ratio corresponding to the gear the automatic transmission 3 will enter, and the gear ratio of the differential gear unit 8. The resulting product value is then divided successively by the dynamic radius of the tires of the drive wheels 2 and the efficiency of the automatic transmission 3 (determined in step S22).
Next, in step S29 in
If the integrated controller 20 determines that the second clutch 7 is in a released state in step S29, the integrated controller 20 is configured to substitute 0 for the power train deliverable braking force Tbp in step S30 because the release of the second clutch 7 causes the braking force from the power train drop to zero.
On the other hand, if the integrated controller 20 determines that the second clutch 7 is engaged in step S29, the integrated controller 20 is configured to proceed to step S31 and to check if the automatic transmission 3 is in the process of changing gears. If the automatic transmission 3 is not in the process of changing gears (No in step S31), then the integrated controller 20 is configured to proceed to step S32 and to determine if the first clutch 6 is slipping i.e., between the engaged state and the released state.
If the integrated controller 20 determines that the automatic transmission 3 is in the process of changing gears (Yes in step S31), the integrated controller 20 is configured to proceed to step S33 and to determine if the first clutch 6 is slipping i.e., between the engaged state and the released state.
If the integrated controller 20 determines in step S31 that the automatic transmission 3 is not changing gears and determines in step S32 that the first clutch 6 is in an engaged state (No in step S32), then the integrated controller 20 is configured to proceed to step S34 and to calculate the power train deliverable braking force Tbp as the sum of the braking force that can be obtained from the motor/generator 5 with the current gear of the automatic transmission 3 (calculated in
If the integrated controller 20 determines in step S31 that the automatic transmission 3 is not changing gears and determines in step S32 that the first clutch 6 is in a slipping state (Yes in step S32), then the integrated controller 20 is configured to proceed to step S35 and to calculate the power train deliverable braking force Tbp as the sum of the braking force that can be obtained from the motor/generator 5 with the current gear of the automatic transmission 3 (calculated in
If the integrated controller 20 determines in step S31 that the automatic transmission 3 is changing gears and determines in step S33 that the first clutch 6 is in an engaged state (No in step S33), then the integrated controller 20 is configured to proceed to step S36 and to calculate the power train deliverable braking force Tbp as the sum of the braking force that can be obtained from the motor/generator 5 with the gear that the automatic transmission 3 will enter (calculated in
If the integrated controller 20 determines in step S31 that the automatic transmission 3 is not changing gears and determines in step S33 that the first clutch 6 is in a slipping state (Yes in step S33), then the integrated controller 20 is configured to proceed to step S37 and to calculate the power train deliverable braking force Tbp as the sum of the braking force that can be obtained from the motor/generator 5 with the gear that the automatic transmission 3 will enter (calculated in
After calculating the power train deliverable braking force Tbp as shown in FIGS. 7(A) and 7(B), the integrated controller 20 is configured to proceed to steps S12 and S13 of
In step S14, the integrated controller 20 is configured to compare the target driving/braking force tFo0 (negative value indicates braking force) calculated in step S0 of
If the integrated controller 20 determines in step S14 that the power train deliverable braking force Tbp is sufficient to produce the target driving/braking force tFo0, then the integrated controller 20 is configured to proceed to step S15 and to set the drive wheel target automatic braking force tTbr to 0 because it is not necessary to generate a compensating braking force with automatic braking. On the other hand, if the integrated controller 20 determines in step S14 that the power train deliverable braking force Tbp is not sufficient to produce the target driving/braking force tFo0, then the integrated controller 20 is configured to proceed to step S16 and to set the drive wheel target automatic braking force tTbr (the amount by which the drive train braking force is insufficient) to the difference between the target drive wheel braking force Tbr (determined in step S13) and the power train deliverable braking force Tbp because it is necessary to generate a compensating braking force with automatic braking.
After determining the target drive wheel automatic braking force tTbr, in step S17, the integrated controller 20 is configured to subtract the target drive wheel braking force Tbr from the vehicle requested braking force Tbw (step S12) and to substitute the resulting difference value as the target automatic braking force tTbf of the non-drive wheels.
Accordingly, the target drive wheel automatic braking force tTbr and the target non-drive wheel automatic braking force tTbf are calculated in step S1 (subroutines illustrated in FIGS. 6, 7(A) and 7(B)) of
In the step S2 of the automatic braking force control shown in
In step S3, the integrated controller 20 is configured to use a prescribed target drive mode map to determine the drive mode to be targeted (EV mode or HEV mode) based on the accelerator position APO and the vehicle speed VSP. The target drive mode region map is normally configured such that the HEV mode is targeted when the vehicle is traveling under high load (large throttle opening)/high vehicle speed conditions and the EV mode is targeted when the vehicle is under a low load/low vehicle speed conditions.
In step S4, the integrated controller 20 is configured to compare the current drive mode to the target drive mode determined in step S3 and to execute a drive mode transition computation. More specifically, if the current drive mode and the target drive mode match, the integrated controller 20 is configured to set commands to hold the drive mode at the current EV mode or HEV mode. If the current drive mode is the EV mode and the target drive mode is the HEV mode, the integrated controller 20 is configured to set commands to change from the EV mode to the HEV mode. If the current mode is the HEV mode and the target mode is the EV mode, the integrated controller 20 is configured to set commands to change from the HEV mode to the EV mode. In step S9, the integrated controller 20 is configured to issue the commands set in step S4 to various parts of the control system to change the drive mode or maintain the drive mode in accordance with the commands.
In step S5, the integrated controller 20 is configured to compute a target transient driving/braking force tFo required in order to move from the current drive force to the final target driving/braking force tFo0 determined in step S1 with a prescribed response characteristic. For example, the target transient driving/braking force tFo can be computed by passing the final target driving/braking force tFo0 through a low pass filter having a prescribed time constant.
The method of calculating the target engine torque tTe in step S6 will now be explained. If the vehicle is in the HEV mode, the integrated controller 20 is first configured to calculate a target input torque tTi of the automatic transmission 3 that will be required in order to attain the target transient driving/braking force tFo calculated in step S5.
tTi=tFo×Rt/if/iG (1)
In the equation (1) above, the value Rt is the effective radius of the tires of the drive wheels 2, the value if is the final gear ratio, the value iG is the gear ratio of the automatic transmission 3 as determined by the currently selected gear.
The target engine torque tTe for HEV mode is calculated using the equation below based on the target input torque tTi, the input rotational speed Ni of the automatic transmission 3, the engine rotational speed Ne, and the target discharge power tP corresponding to the state of charge SOC (extractable electric power) of the battery 9.
tTe=(tTi×Ni−tP)/Ne (2)
If the vehicle will be changed from the EV mode to the HEV mode, then the integrated controller 20 is configured to calculate a target engine torque tTe required to start the engine 1 in connection with the mode change. If the vehicle will be changed from the HEV mode to the EV mode, then the integrated controller 20 is configured to set the target engine torque tTe to 0 for the EV mode transition because engine torque is not required in the EV mode. Similarly, if the vehicle will be held in the EV mode, the target engine torque tTe for the EV mode is set to 0 because the engine torque is not required in the EV mode. In step S9, the target engine torque tTe calculated in step S6 is sent to the engine controller 21 shown in
In step S7 of
After the target first and second clutch target torque transfer capacities tTc1 and tTc2 have been determined, the integrated controller 20 is configured to proceed to step S8 of
With the hybrid vehicle control device of the present invention, when the hybrid vehicle is coasting and the target driving/braking force tFo0 cannot be achieved with the power train deliverable braking force Tbp (step S14 of
During the period directly after the time t1 while the second clutch 7 is released (target torque transfer capacity tTc2=0), the drive wheels 2 are disconnected from both the engine 1 and the motor/generator 5 and the engine braking force remains at 0 as indicated by the solid curve in
Additionally, since the automatic operation of the brake-by-wire hydraulic brake system 23 can exert the drive wheel automatic braking force tTbr against the drive wheels 2 with a high response speed, a compensating drive force (drive wheel automatic braking force tTbr) can be exerted substantially precisely at the time when the braking force Tbp delivered from the power train is lost due to the release of the second clutch 7. As a result, a situation in which the braking force acting on the drive wheels 2 deviates from the target as result of the compensating braking force (drive wheel automatic braking force tTbr) being exerted at an inappropriate timing can be avoided.
As explained above, the second clutch 7 is temporarily released (target torque transfer capacity tTc2=0) in order to avoid an unpleasant change in the braking force from transmitted to the drive wheels when the first clutch 6 is engaged and the crankshaft of the engine 1 starts rotating or cranking without fuel supplied to the engine in the example illustrated in the operation time chart shown in
The drive wheel braking force compensation control in accordance with this embodiment can also be utilized when a hybrid vehicle is changed from a state of coasting in the EV mode to a state of coasting in the HEV mode in order to use an engine braking force to compensate for a deficiency in regenerative braking torque and the mode change is handled by engaging the first clutch 6 while leaving the second clutch 7 engaged as in
In this case, the second clutch 7 remains engaged (torque capacity tTc2>0 as indicated
With the drive wheel braking force compensation control in accordance with this embodiment, starting from the time t1 the braking force of the brake-by-weire hydraulic brake system 23 is adjusted by controlling the target drive wheel automatic braking force tTbr such that the sum of the braking force of the brake-by-wire hydraulic brake system 23, the engine braking force, and the motor braking force is equal to the target drive wheel braking force Tbr. As a result, the excess or deficiency of the braking force is resolved and the target braking force can be maintained.
Additionally, since the automatic operation of the brake-by-wire hydraulic brake system 23 can exert the target drive wheel automatic braking force tTbr against the drive wheels 2 with a high response speed, the compensating braking force (target drive wheel automatic braking force tTbr) can be adjusted substantially precisely at the time when the braking force becomes excessive or insufficient. As a result, a situation in which the braking force acting on the drive wheels 2 deviates from the target as result of the compensating braking force being adjusted at an inappropriate timing can be avoided.
Furthermore, the drive wheel braking force compensation control in accordance with the present invention can also be utilized to effectively compensate for the change (decrease) in the braking force acting on the drive wheels 2 that occurs when the regenerative braking torque generated by the motor/generator 5 is limited so as to gradually decrease due to the state of charge the battery 9 gradually increasing while a hybrid vehicle is coasting in the EV mode as shown in
In the period between the time t1 and the time t2, the torque Tm (Tm<0) of the motor/generator 5 gradually changes as shown in
Since the braking force compensation is accomplished by automatically operating the brake-by-wire hydraulic brake system 23 so as to obtain the target drive wheel automatic braking force tTbr, it is not necessary to change from the EV mode to the HEV mode in order to compensate for a deficiency in regenerative braking torque. Consequently, when the traveling conditions are such that it is better to remain in the EV mode, the change (decrease) in the braking force exerted against the drive wheels can be offset while keeping the vehicle in the more appropriate mode.
As explained previously with reference to FIGS. 7(A) and 7(B), the hybrid vehicle control device of the present invention is configured such that the power train deliverable braking force Tbp is set to the sum value of the motor braking force produced by the motor/generator 5 and the engine braking force (steps S34 and S36) when the second clutch 7 is engaged (step S29) and the first clutch 6 is also engaged (steps S32 and S33). As a result, the power train deliverable braking force Tbp can be calculated accurately when both the first clutch 6 and the second clutch 7 are engaged.
As also explained with reference to FIGS. 7(A) and 7(B), the hybrid vehicle control device of the present invention is configured such that the power train deliverable braking force Tbp is set to the sum value of the motor braking force produced by the motor/generator 5 and the first clutch connection braking force corresponding to the torque transfer capacity tTc1 of the first clutch 6 (steps S35 and S37) when the second clutch 7 is engaged (step S29) and the first clutch 6 is in a slipping state lying between the engaged state and the released state (steps S32 and S33). As a result, the power train deliverable braking force Tbp can be calculated accurately when the first clutch 6 is in a slipping state and the second clutch 7 is engaged.
As also explained with reference to FIGS. 7(A) and 7(B), the hybrid vehicle control device of the present invention is configured such that the motor braking force and the first clutch connection braking force are determined as braking forces that can be obtained with the current gear of the automatic transmission 3 (steps S34 and S35) when the automatic transmission 3 between the motor/generator 5 and the drive wheels 2 is not in the process of changing gears (No in step S31). Meanwhile, the motor braking force and the first clutch connection braking force are determined as braking forces that can be obtained with the gear that the automatic transmission 3 will enter (steps S36 and S37) when the automatic transmission 3 is in the process of changing gears (Yes in step S31). As a result, the power train deliverable braking force Tbp can be calculated accurately both when the automatic transmission 3 is not changing gears and when the automatic transmission 3 is changing gears.
In understanding the scope of the present invention, the term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, “including”, “having” and their derivatives. Also, the terms “part,” “section,” “portion,” “member” or “element” when used in the singular can have the dual meaning of a single part or a plurality of parts. Also as used herein to describe the above embodiment, the following directional terms “forward, rearward, above, downward, vertical, horizontal, below and transverse” as well as any other similar directional terms refer to those directions of a vehicle equipped with the present invention. Accordingly, these terms, as utilized to describe the present invention should be interpreted relative to a vehicle equipped with the present invention.
The term “detect” as used herein to describe an operation or function carried out by a component, a section, a device or the like includes a component, a section, a device or the like that does not require physical detection, but rather includes determining, measuring, modeling, predicting or computing or the like to carry out the operation or function. The term “configured” as used herein to describe a component, section or part of a device includes hardware and/or software that is constructed and/or programmed to carry out the desired function. Moreover, terms that are expressed as “means-plus function” in the claims should include any structure that can be utilized to carry out the function of that part of the present invention. The terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed.
While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. For example, the size, shape, location or orientation of the various components can be changed as needed and/or desired. Components that are shown directly engaged or contacting each other can have intermediate structures disposed between them. The functions of one element can be performed by two, and vice versa. The structures and functions of one embodiment can be adopted in another embodiment. It is not necessary for all advantages to be present in a particular embodiment at the same time. Every feature which is unique from the prior art, alone or in combination with other features, also should be considered a separate description of further inventions by the applicant, including the structural and/or functional concepts embodied by such feature(s). Thus, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-322407 | Nov 2005 | JP | national |
