JP2006180657A - Four-wheel-drive hybrid vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain target fuel consumption as best mileage after driving force redistribution in four-wheel driving of an electric vehicle. <P>SOLUTION: When excess and deficiency in driving force of an engine 1 is regulated for a request driving force by means of a first motor 3 and a second motor 7, a motor torque of lowest power consumption is selected as a motor torque command value among a combination of motor torque within the range of each motor torque limit value. Since power consumption of the motor is reduced effectively, fuel consumption can be reduced during traveling. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hybrid vehicle capable of four-wheel drive, and more particularly to control of driving force distribution thereof.

Japanese Patent Application Laid-Open No. 11-332020 discloses a hybrid vehicle capable of four-wheel drive. In this vehicle, the driving force of the front and rear wheels is set to be uniform, and if slip occurs in one of the driving wheels, the driving force of the slip wheel is reduced to converge the slip, and the non-slip wheel is set. The driving force of the slip wheel is added to keep the driving force of the vehicle constant.
JP-A-11-332020

  In the above-described prior art, the redistribution is performed for the purpose of suppressing the slip and making the driving force constant, and nothing is taken into consideration regarding the fuel consumption after the redistribution. When the driving force is kept constant by suppressing the slip, the driving force distribution is not one way, and there is still room for improvement in the fuel efficiency after the redistribution.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to optimize the fuel efficiency after redistribution when redistributing driving force in a four-wheel drive hybrid vehicle.

  When adjusting the excess or deficiency of the engine driving force with respect to the required driving force with the first and second motors, the combination of motor torques within the range of each motor torque limit value has the least power consumption. Select the motor torque command value.

  According to the present invention, it is possible to effectively reduce the power consumed by the motor after redistribution of the driving force, and as a result, it is possible to reduce the amount of fuel consumed during traveling.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a configuration of a hybrid vehicle to which the present invention is applied. The power train includes a driving force including an engine 1, a clutch 2, a front wheel motor 3 (first motor), a continuously variable transmission 15, a reduction gear 4, a differential device 5, and a front wheel 6 (first driving wheel). It has a transmission path and a driving force transmission path composed of a rear wheel motor 7 (second motor), a reduction gear 8, a differential gear 9, and a rear wheel 10 (second driving wheel), and can drive four wheels. It is a vehicle. The output shaft of the engine 1 and the input shaft of the clutch 2 are connected to each other, and the output shaft of the clutch 2 and the input shaft of the motor 3 are connected.

  When the clutch 2 is engaged, the engine 1 and the motor 3 serve as a vehicle propulsion source, and when the clutch 2 is released, one or both of the front wheel motor 3 and the rear wheel motor 7 serve as a vehicle propulsion source. The driving force of the engine 1 and / or the front wheel motor 3 is transmitted to the front wheels 6 via the continuously variable transmission 15, the reduction gear 4 and the differential 5. Further, the driving force of the rear wheel motor 7 is transmitted to the rear wheel 10 via the speed reduction device 8 and the differential device 9.

  The continuously variable transmission 15 uses a belt type here, but may be a continuously variable transmission of another type such as a toroidal type, or a stepped transmission that performs a stepwise shift instead of a continuously variable transmission. May be used. The continuously variable transmission 15 is supplied with hydraulic pressure from the hydraulic device 17, and is clamped and lubricated. An oil pump (not shown) of the hydraulic device 17 is driven by a DC motor 16 driven at 12V.

  The clutch 2 is a powder clutch and can adjust the transmission torque. As the clutch 2, in addition to a powder clutch, a dry single plate clutch or a wet multi-plate clutch can also be used.

  The motors 3 and 7 are driven by inverters 11 and 13, respectively. The motors 3 and 7 are AC motors here, but DC motors can also be used. In addition, when using a direct current motor for the motors 3 and 7, a DC / DC converter is used instead of an inverter. The inverters 11 and 13 are connected to the power storage device 12 through a common DC link. The inverters 11 and 13 convert the DC charging power of the power storage device 12 into AC power and supply it to the motors 3 and 7. The power generation device 12 is charged by converting the generated power into DC power. As the power storage device 12, various types of batteries such as lithium ion batteries, nickel / hydrogen batteries, lead batteries, and electric double layer capacitors, so-called power capacitors, can be used.

  The controller 14 includes an accelerator pedal operation amount detected by an accelerator operation amount sensor 21, a vehicle speed detected by a vehicle speed sensor 22 including a magnetic or optical encoder, and motors detected by temperature sensors 23 and 24. 3 and 7 are input, and based on these, it is determined what to do with the operating state of the engine 1 and the operating state of the motor 3, and the determination result and the request from the driver via the accelerator operation are to be answered The command values for the engine 1, the clutch 2, the motors 3 and 7, and the continuously variable transmission 15 are generated.

  FIG. 2 is a flowchart showing the contents of the driving force distribution process performed in the hybrid vehicle. This process is repeatedly performed in the controller 14 at a predetermined cycle, for example, every 10 [msec].

  First, in step S11, a driving force requested by the driver (hereinafter, required driving force) is calculated from the accelerator operation amount and the vehicle speed.

  In step S12, the operating point of the engine 1 when realizing the required driving force calculated in step S11, the target value of the transmission ratio of the continuously variable transmission 15, and the engagement / disengagement state of the clutch 2 are obtained.

  In step S13, a driving force to be transiently realized (hereinafter referred to as a transient required driving force) is calculated based on the required driving force calculated in step S11.

  In step S14, the torque of the engine 1 with the operating point calculated in step S12 as a target value is estimated, and the driving force being generated by the engine 1 is estimated.

  In step S15, torque limit values of the motors 3 and 7 are calculated. The calculation of the limit value is performed according to the flow shown in FIG. 5 and will be described later.

  In step S16, based on the motor torque limit value calculated in step S15, the motor torque of each wheel that realizes the transient required driving force within the range of the motor torque limit value and with high efficiency (low power consumption). Calculate the command value. The limit value is calculated according to the flow shown in FIG. 7, which will be described later.

  In step S17, each actuator is controlled in order to realize the operating point of the engine 1, the target value of the transmission ratio of the continuously variable transmission 15, and the engagement / disengagement state of the clutch 2 obtained in step S12. The inverters 11 and 13 are controlled so as to realize the torque command values of the motor 3 and the motor 7 obtained in the above.

  Details of each process shown in FIG. 2 will be described below.

  In step S11, the required driving force Fd is obtained by searching the map shown in FIG. 3 based on the vehicle speed [km / h] detected by the vehicle speed sensor 22 and the accelerator operation amount [deg] detected by the accelerator operation amount sensor 21. [N] is calculated. The map shown in FIG. 3 has a tendency to calculate a larger driving force as the vehicle speed is lower, and the value of the map is adjusted in advance so as to follow the driver's feeling from experiments or the like.

  In step S12, the operating points of the engine 1, the clutch 2, and the continuously variable transmission 15 are calculated. For example, each operating point is obtained so as to reduce the amount of fuel consumed during traveling. In this case, taking into account the fuel consumption characteristics of the engine and the loss characteristics of the motor, the amount of charge to the power storage device per fuel consumption (hereinafter referred to as driving efficiency) is the highest in realizing the driver's required driving force. This can be realized by using the operating point. Similarly, when it is desired to change the state of charge of the traveling power storage device 12 to a desired range, it can be realized by associating the state of charge with operating efficiency as disclosed in JP-A-2003-171604.

  In step S13, based on the required driving force calculated in step S11, the transition of the driving force is corrected smoothly to improve the driving performance of the driver, or the rising of the driving force is corrected to produce an acceleration feeling. Thus, the transient required driving force Fdt [N] is calculated. FIG. 4 shows an example of the transient required driving force.

  In step 14, the torque being generated in the engine 1 is estimated. Here, the estimated torque value eTe [Nm] is obtained by experimenting in advance the relationship between the engine torque with respect to the engine rotational speed, the intake pressure and the ignition timing, a map is created, and the basic torque value is calculated by searching the map. . Further, the estimated torque value eTe [Nm] can be calculated by applying a first-order lag process having a torque response time constant to the basic value.

  Then, the driving force eFeng [F] generated by the engine 1 is obtained by the following equation.

  FIG. 5 shows details of the process of calculating the motor torque limit value in step S15 of FIG.

  This will be described. In step S21, the wheel speed of each wheel is read from the vehicle speed sensors provided on the front and rear wheels.

  In step S22, the road surface friction coefficient μ [] is estimated using the wheel speed of each wheel. As an estimation method, for example, as described in JP-A-11-78843, a technique for estimating a road surface friction coefficient gradient, which is a gradient of a friction coefficient between a tire and a road surface, or disclosed in JP-A-10-114263 is disclosed. As described above, as a physical quantity that can be handled equivalently to the road surface friction coefficient gradient, a technique for estimating based on a braking torque gradient or a driving torque gradient with respect to the slip speed is known.

  In step S23, the load applied to the front and rear wheels is multiplied by the road surface friction coefficient estimated in step S22, whereby the maximum value of the driving force that can be generated in each wheel without causing overspeed slip (hereinafter referred to as front and rear wheel limits). Driving force). Here, the limit driving force of the front wheels is Ffmax [N], and the limit driving force of the rear wheels is Frmax [N].

  In step S24, a motor torque limit value is obtained from the engine drive force estimated value eFeng obtained in step S14 and the front and rear wheel limit drive forces Ffmax and Frmax using the following equation.

  Here, Tfmmax [Nm] indicates the torque of the front wheel motor 3 when generating the front wheel limit driving force, and Trmmax [Nm] indicates the torque of the rear wheel motor 7 when generating the rear wheel limit driving force. Gff [] is the front final gear ratio, Gfr [] is the rear final gear ratio, Rtire [m] is the effective tire radius, Ncvtin [rpm] is the input rotational speed of the continuously variable transmission 15, and Ncvtout [rpm] is the The output rotation speed is shown.

  Note that it is not always necessary to estimate the road surface friction coefficient μ. For example, a driving force in which slip converges may be used as a limit driving force that can be generated by the driving wheel. In this case, the driving force that can be generated by the other driving wheel that has not slipped is substituted by correcting the convergence value of the slip wheel by wheel load distribution.

  In this case, the motor torque limit value is set from the estimated engine drive force value and the front and rear wheel limit drive force. In addition to this setting method or instead of this setting method, the motor torque limit value is set. Thus, the motor torque may be limited. This is done in order to prevent motor performance degradation due to high temperatures. Specifically, the motor cooling water temperature representing the motor temperature is detected by the temperature sensors 23 and 24, and the torque of the motors 3 and 7 is limited accordingly. FIG. 6 shows an example of the map used at this time. It can be obtained by limiting the motor output in a stepwise manner according to the coolant temperature and searching for a torque limit value in accordance with the motor rotation speed.

  FIG. 7 shows the processing in step S16 of FIG. In step S16, a motor torque command value for each wheel that realizes the transient required driving force with high efficiency within the range of the motor torque limit value is calculated.

  Explaining this, in steps S31 to S33, the transient required driving force Fdt [N], the engine generated driving force eFeng [N], and the front and rear wheel motor limit values Tfmmax [Nm] and Trmmax [Nm] are read.

  In step S34, the output possible power Pout [kw] of the power storage device 12 is calculated. Here, the output power Pout [kW] can be obtained by using the following equation. Vmin [V] is a lower limit voltage that can be used by the power storage device 12, Vo [V] is a current open-circuit voltage of the power storage device 12, and R [Ω] is an internal resistance of the power storage device 12.

  In step S35, a combination of front and rear motor torques that achieves the transient required drive torque within the range of the motor torque limit value obtained in the previous steps is calculated. In the vehicle configuration shown in the embodiment, when the front wheel motor torque is set to Tfm [Nm], the rear wheel motor torque Trm [Nm] for realizing the transient required driving force can be obtained by the following equation.

  Here, eTe [N] is the engine torque [Nm] estimated in step S14 (engine driving force estimation step). Using this relationship, a combination of motor torques that realize the transient required driving force is calculated within the range of the motor torque limit value.

  FIG. 8 shows an example of a combination of motor torques. The motor torque of the front and rear wheels indicates a combination of motor torques that realize the transient required driving force using the relationship shown in Expression (6), and the points indicated by the circles on the vertical broken lines show an example. The torque limit value indicated by the horizontal broken line indicates the limit value obtained in step S15. In the case where a plurality of torque limit values are set, the motor torque that is more limited (the one with a smaller absolute value) may be used. This limit value is based on the premise that at least the rated output and the maximum torque of the motor are protected. The range in which the transient required driving force is realized within the range of the torque limit value is a range indicated by an arrow in the figure.

  In step S36, the power consumption when the combination of the motor torque obtained in step S35 is realized is calculated. The power consumption can be obtained by the following equation.

  Nfm [rpm] represents the rotational speed of the front wheel motor, and Nrm [rpm] represents the rotational speed of the rear wheel motor. MAPpfloss (Tfm, Nfm) and MAPprloss (Trm, Nrm) are the results of searching a map for calculating the motor power loss for each of the front and rear wheels. 9 can be obtained by creating a map as shown in FIG. 9 and retrieving it.

  If the power consumption is obtained by calculation for each combination and plotted with the driving force distribution on the horizontal axis, a graph as shown in the third row of FIG. 8 is obtained. This graph is a graph at a certain vehicle speed and required driving force, and the shape of the graph will differ if the vehicle speed and required driving force are different. Depending on the driving conditions, it is better to generate driving force with only one of the motors. There may be less consumption. By searching this graph, it is possible to obtain a combination of motor torques that realizes the transient required driving force with the minimum power consumption within the range of the torque limit value.

  In step S37, the output possible power Pout [kW] and the minimum value of power consumption (hereinafter referred to as the minimum power consumption) when the combination of the motor torque that realizes the transient required driving force within the range of the torque limit value is realized. Compare magnitude relationships. If it is determined that the outputtable power Pout [kW] is equal to or greater than the minimum power consumption, the process proceeds to step S39, and the front and rear wheel motor torques that result in the minimum power consumption are directly used as torque command values.

  On the other hand, if it is determined that the output possible power Pout [kW] is less than the minimum power consumption, the process proceeds to step S38, the transient required driving force is corrected to decrease by a predetermined amount, and the process returns to step S35 to return to the sum of power consumption. Search again for a combination of motor torques that minimizes. This process is continued until the condition of step S37 is satisfied.

  An example of the motor torque command value selected when the minimum power consumption exceeds the output power is shown in FIG. The combination of motor torques indicated by the circles shown in gray does not satisfy the output possible power.Therefore, the combination of motor torques that realize the output possible power when the transient required driving force is set low in steps and the power consumption is minimized. Search for the motor torque command value.

  In step S35, each motor torque is estimated from the current values of the inverters 11 and 13 that control the motors 3 and 7, and the sum of power consumption is minimized from the torque within a predetermined range centered on the current motor torque. You may make it add the process which calculates the combination of the motor torque to make. That is, a torque limit value for limiting the fluctuation range of the motor torque is added. As a result, it is possible to suppress a deterioration in drivability associated with a significant change in motor torque.

  In step S17, the fuel injection amount control actuator, the throttle control actuator, and the ignition timing control actuator are controlled so as to realize the engine operating point obtained in step S12. For the continuously variable transmission 15, a gear ratio control hydraulic actuator is controlled to achieve a desired gear ratio. For the clutch 2, the current is controlled to realize the engagement / release command. For the front and rear wheel motors 3 and 7, the inverters 11 and 13 are controlled to realize the torque obtained in step S16.

  Next, the effect of the present invention by performing the above control will be described.

  According to the present invention, when the excess and deficiency of the engine driving force relative to the required driving force is adjusted by the first and second motors (motors 3 and 7), the motor torque that falls within the range of each motor torque limit value. From the combinations, select the one that consumes the least amount of power and use it as the motor torque command value. For this reason, the electric power consumed by the motors 3 and 7 can be effectively reduced, and as a result, the amount of fuel consumed during traveling can be reduced.

  FIG. 11 shows an example of torque change in a comparative example to which the present invention is not applied. The amount obtained by subtracting the driving force obtained by the output of the engine 1 from the driving force required by the driver is calculated as the front wheel motor 3 and the rear The case where it distributes to the wheel motor 7 is shown. The torques of the motors 3 and 7 arranged vertically are combinations that achieve the required driving force, and the third stage shows the total power consumption of both the motors 3 and 7 in the combination. If the output is not limited, the torque combination that minimizes the power consumption is selected, but if the output is limited in this state, the output of the other motor is reduced by the amount that the output of one motor decreases due to the limitation. increase. In FIG. 11, the output of the torque of the rear wheel motor 7 is increased by the amount by which the torque of the front wheel motor 3 is limited, and the power consumption at this time is significantly larger than before the limit. As described above, the operating points of the motors 3 and 7 selected after redistribution of the driving force are not necessarily highly efficient, increasing the power consumption and deteriorating the fuel consumption of the vehicle.

  On the other hand, FIG. 12 shows a case where the present invention is applied, and shows a combination of motor torques selected after redistributing the driving force in the same situation. Since the torque combination that minimizes the power consumption within the range of the torque limit value is selected, an increase in the power consumption after the driving force redistribution is suppressed, and the power consumption is lower than that in the comparative example shown in FIG. It turns out that it decreases.

  Further, as a result of obtaining the motor torque in the motors 3 and 7 so that the power consumption after the redistribution of the driving force is minimized, if the power consumption exceeds the outputable power of the power storage device 12, the required driving force is corrected to decrease. Above, search again for a combination of motor torques that minimizes power consumption. As a result, the power consumption is always kept below the power that can be output, so that the power storage device 12 can be prevented from being overdischarged, and the maximum driving force can be realized within the limit range.

  In addition, the front and rear wheel limit driving force that can be output by each driving shaft is obtained by, for example, estimating the road surface friction coefficient, and the motor torque is limited based on this. While suppressing slip, the power consumed by the motors 3 and 7 can be effectively reduced, and as a result, the amount of fuel consumed during traveling can be reduced.

  In addition, since the motor torque limit value is limited according to the temperature of the motors 3 and 7, the power consumed by the motors 3 and 7 is effectively reduced within a range that suppresses the decrease in motor performance due to the temperature rise. As a result, the amount of fuel consumed during traveling can be reduced.

  Further, the torques of the motors 3 and 7 may be estimated, and the motor torque command value may be calculated so as to minimize power consumption within a predetermined torque range centered on each estimated motor torque. According to this, it is possible to suppress the deterioration of drivability associated with a significant change in motor torque.

1 is a schematic configuration diagram of a hybrid vehicle to which the present invention is applied. It is the flowchart which showed the content of the driving force distribution process which a controller performs. It is the map which showed the relationship of the required driving force with respect to vehicle speed and the amount of accelerator operation. It is a figure for demonstrating a transient required driving force. It is the flowchart which showed the content of the calculation process of a motor torque limit value. It is the map which showed the relationship between motor temperature and a torque limiting value. It is the flowchart which showed the content of the motor torque command value calculation process. It is the figure which showed an example of the combination of the motor torque which implement | achieves a transient requirement drive force. It is the map which showed the relationship of the loss electric power with respect to motor rotational speed and a motor torque. It is a figure which shows the case where a motor torque is restrict | limited when the power consumption of a motor exceeds the electric power which can be output of an electrical storage apparatus. It is a figure which shows the case where output restriction | limiting is performed and the combination of motor torque is changed when not applying this invention. It is a figure which shows the case where output restriction | limiting is performed in the case of applying this invention, and the combination of the motor torque is changed.

Explanation of symbols

1 Engine 2 Clutch 3 Front wheel motor (first motor)
6 Front wheel (first drive wheel)
7 Rear wheel motor (second motor)
10 Rear wheel (second drive wheel)
REFERENCE SIGNS LIST 11 inverter 13 inverter 14 controller 15 continuously variable transmission 21 accelerator operation amount sensor 22 vehicle speed sensor 23 temperature sensor 24 temperature sensor

Claims (6)

An engine and a first motor for transmitting power to the first drive wheels;
A second motor for transmitting power to the second drive wheel;
A power storage device connected to the first and second motors for transferring power to and from the first and second motors;
Requested driving force calculating means for calculating the driving force requested by the driver;
Motor torque limit value calculating means for calculating torque limit values of the first and second motors;
Engine driving force estimating means for estimating a driving force generated by the power of the engine;
When adjusting the excess or deficiency of the engine driving force relative to the required driving force with the torque of the first and second motors, the sum of the power consumption of the first and second motors within the range of the motor torque limit value. Motor torque command value calculating means for searching for a combination of the first and second motor torques that minimizes the value and calculating the searched combination as command values for the first and second motors;
Motor control means for controlling the first and second motors such that the torques of the first and second motors become the command values, respectively;
A hybrid vehicle characterized by comprising:   The motor torque command value calculating means corrects the required driving force to be decreased when the power consumption due to the calculated combination of motor torques exceeds the power that can be output from the power storage device, and based on the corrected required driving force, 2. The hybrid vehicle according to claim 1, wherein a search is again made for a combination of the first and second motor torques that minimizes the sum of the power consumptions of the first and second motors. Limits for calculating the maximum driving force that can be output from the first and second driving wheels without causing overspeed slip as the limiting driving force of the first driving wheel and the limiting driving force of the second driving wheel, respectively. A driving force calculating means;
For the first motor, the motor torque limit value calculating means obtains a driving force obtained by subtracting a driving force generated by the power of the engine from a limit driving force of the first driving wheel. The torque of the first motor when the motor is generated by the motor, and the second motor when the limit driving force of the second driving wheel is generated by the motor for the second motor. The hybrid vehicle according to claim 1 or 2, wherein each torque is set as a motor torque limit value.   The said limit drive force calculation means estimates the road surface friction coefficient during driving | running | working, and calculates the limit drive force of the said 1st and 2nd drive wheel based on the estimated road surface friction coefficient. The described hybrid vehicle Means for detecting the temperature of the first and second motors;
5. The motor torque limit value calculating means reduces the absolute value of the motor torque limit value as the detected temperature of the first and second motors is higher. 6. The hybrid vehicle described in 1. Motor torque estimating means for estimating the torque of the first and second motors during running,
6. The hybrid vehicle according to claim 1, wherein a motor torque command value that minimizes power consumption is calculated within a predetermined torque range centered on each estimated motor torque.

Images