Travel driving apparatus of vehicle

In a hybrid vehicle including a front motor for driving front wheels, a rear motor for driving rear wheels, a generator for generating power by being driven by an internal combustion engine, and a step-up converter for stepping up the voltage from a battery and supplying power to the front motor, while stepping-down the generated power of the generator and supplying the power to the rear motor, a hybrid control unit decreases the power supplied from the generator to the rear motor, and increases the power supplied from the battery to the rear motor when input power of the step-up converter is limited based on a temperature condition of the step-up converter.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to control of travel driving of a vehicle.

Description of the Related Art

In hybrid vehicles which have been developed recently, there is known a vehicle which is operable in a travelling mode in which driving wheels for travelling are driven by an electric motor while power is generated by a generator driven by an internal combustion engine (series mode).

Further, there is also proposed a vehicle including a transformer for stepping up voltage, in which voltage outputted from an onboard battery is stepped up by the transformer to drive an electric motor.

For example, Japanese Patent Laid-Open No. 2007-325352 discloses a vehicle including an electrically powered front motor for driving the front wheels and an electrically powered rear motor for driving the rear wheels. In the vehicle of Patent Document 1, the front motor is driven by voltage which is outputted from an on-board battery and stepped up by a transformer. Moreover, power generated by the generator can be supplied to the front motor. Further, by stepping down the voltage of the power generated by the generator with a transformer, it becomes possible to supply power to the rear motor and charge the battery.

Meanwhile, there are upper limits for input and output power for the transformer as described above for protecting components from generated heat or the like. Therefore, in a vehicle which is driven to travel by a rear motor supplied with part of the power generated by the generator as described above and stepped down by the transformer in a series mode, there is possibility that power inputted from the generator to the transformer exceeds an upper limit value when travel driving torque of the vehicle increases.

SUMMARY OF THE INVENTION

Accordingly, it is an objective of the present invention to provide a travel driving apparatus of a vehicle, which satisfies a required torque requested by the driver while protecting a transformer in a hybrid vehicle equipped with a transformer.

In order to achieve the above described objective, the travel driving apparatus of a vehicle of the present invention includes: a first electrical motor for driving either one of front and rear wheels of the vehicle; a generator for generating power by being driven by an internal combustion engine mounted on the vehicle; a transformer for transforming power from a battery mounted on the vehicle and supplying the power to the first electrical motor, while transforming generated power of the generator and supplying the power to the battery, wherein maximum output power is limited based on a temperature condition; a second electrical motor which is supplied with power of the battery not via the transformer while being supplied with power of the generator via the transformer, and drives the other one of the front and rear wheels; and power distribution means for distributing power supplied from the battery and power generated at the generator to the first electrical motor and the second electrical motor when the transformer is not limited, and decreases the power supplied from the generator to the second electrical motor and increases the power supplied from the battery to the second electrical motor when the transformer is limited.

As a result of this, the travel driving apparatus of a vehicle of the present invention can satisfy a required driving force while protecting the transformer when the transformer is limited during power generation operation by the generator.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a schematic configuration diagram of a travel driving apparatus1of a vehicle according to one embodiment of the present invention.

As shown inFIG. 1, a vehicle equipped with a travel driving apparatus1of one embodiment of the present invention is a four-wheel drive hybrid vehicle, which is provided with an electrically driven front motor3(first electrical motor) for driving front wheels2(first travel driving wheels), an electrically driven rear motor5(second electrical motor) for driving rear wheels4(second travel driving wheels), an engine6(internal combustion engine), a generator7, and a battery8.

The engine6can drive the front wheels2via a front trans-axle16and drive the generator7to generate power. Moreover, the engine6and the front wheels2are connected such that power can be transferred therebetween via a clutch11.

Moreover, the vehicle is provided with an inverter12for controlling power supply to the front motor3, an inverter13for controlling power supply to the rear motor5, and an inverter14for controlling output of the generator7.

The present embodiment includes a step-up converter15(transformer) which steps up the voltage of the battery8and supplies high voltage power to the front motor3, and at the same time steps down the high voltage power generated by the generator7to supply it to the battery8or the rear motor5.

The front motor3, which can be driven by being supplied with power from the battery8via the step-up converter15and the inverter12, and also can be driven by being supplied with power from the generator7via the inverter14and the inverter12, drives the front wheels2via the front trans-axle16.

The rear motor5, which can be driven by being supplied with power from the battery8via the inverter13, and also by being supplied with power from the generator7via the inverter14, the step-up converter15, and the inverter13, drives the rear wheels4via a rear trans-axle17.

The power generated by the generator7and outputted from the inverter14allows charging of the battery8via the step-up converter15, and can also be supplied to the front motor3via the inverter12and to the rear motor5via the step-up converter15and the inverter13.

Moreover, the generator7, which is driven by being supplied with power from the battery8via the step-up converter15and the inverter14, has a function as a starter motor for starting the engine6.

The battery8, which is made up of a secondary cell battery such as a lithium-ion battery, has a battery module not shown and made up of a plurality of battery cells brought together.

Operation of each of the inverter12, the inverter13, the inverter14, and the step-up converter15is controlled by a control signal from a hybrid control unit20mounted on the vehicle. The hybrid control unit20includes power distribution means for distributing power supplied from the battery and power generated at the generator to the front motor and the rear motor.

The step-up converter15is provided with a temperature sensor21for detecting the temperature of a component (element, etc.) of the step-up converter15.

Further, the vehicle is provided with a front-wheel rotational frequency sensor22for detecting the number of rotation per unit time of the front wheel2, a rear-wheel rotational frequency sensor23for detecting the number of rotation per unit time of the rear wheel4, an accelerator sensor24for detecting an accelerator depression amount, a brake sensor25for detecting a brake depression amount, a G sensor26for detecting longitudinal acceleration and lateral acceleration of the vehicle, a steering angle sensor27for detecting a steering control angle, and an engine control unit30for controlling the driving of the engine6.

The engine control unit30controls the driving of the engine6based on a control signal from the hybrid control unit20.

The hybrid control unit20, which is a control apparatus for performing comprehensive control of the vehicle, is configured to include an input/output apparatus, a storage apparatus (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), and a timer, etc.

The input side of the hybrid control unit20is connected with each of the inverters12to14, the engine control unit30, the temperature sensor21, the front-wheel rotational frequency sensor22, the rear-wheel rotational frequency sensor23, the accelerator sensor24, the brake sensor25, the G sensor26, and the steering angle sensor27, and is inputted with detection and operation information from these equipment.

On the other hand, the output side of the hybrid control unit20is connected with each of the inverters12to14, the engine control unit30, and the clutch11.

Then, the hybrid control unit20transmits a control signal to the engine control unit30, each of the inverters13and14, and the clutch11to control the switching of the travelling mode (EV mode, series mode, and parallel mode) which involves engagement and disengagement of the clutch11, output torques of the engine6, the front motor3and the rear motor5, and generated power of the generator7based on various detection amounts such as accelerator depression amount from the accelerator sensor24of the vehicle, and various operation information.

In the parallel mode, the front wheels2are mechanically driven by the output of the engine6with the clutch11being engaged, and are also driven to travel by the front motor3or the rear motor5.

In the EV mode and the series mode, the clutch11is disengaged. In the EV mode, the engine6is stopped, and the front motor3and the rear motor5are driven by power from the battery8. In the series mode (first travelling mode), the engine6is operated to cause the generator7to generate power, thereby supplying power to and driving the front motor3and the rear motor5.

FIG. 2is a block diagram to show the configuration of a driving control apparatus of the present embodiment.

As shown inFIG. 2, the hybrid control unit20includes a maximum step-up input/output limit computing section40, a motor torque limit computing section41, a driving torque computing section42, a motor torque computing section43, a generated power limit computing section44, a generated power computing section45, a generator torque limit computing section47, a rotational speed computing section48, a generator torque computing section49, and power distribution means.

The maximum step-up input/output limit computing section40computes a step-up converter upper-limit power Pvmax, which is the maximum input/output power of the step-up converter15, based on the temperature of the step-up converter15.

The motor torque limit computing section41computes upper limit values of the motor torques (driving torques of the front motor3and the rear motor5)(Tfmax, Trmax), respectively.

The driving torque computing section (required driving force calculation means)42computes driving torque of the entire vehicle (user-requested driving torque Tur).

The motor torque computing section (distributed driving force setting means)43computes motor torques Tmf, Tmr of the front motor3and the rear motor5. Then, based on these motor torques Tmf, Tmr, it controls the operation of the front motor3and the rear motor5via the inverters12,13.

The generated power limit computing section44computes a maximum value of the generated power of the generator7(generator upper-limit generated power Pgmax).

The generated power computing section45computes the generator output Pg, which is generated power by the generator7, which is required corresponding to the user-requested driving torque Tur. Then, the operation of the engine6is controlled via the engine control unit30such that generation of the generator output Pg is possible at the generator7.

The generator torque limit computing section47computes a limiting value of the generator torque.

The rotational speed computing section48computes a rotational speed of the generator7corresponding to the generator output Pg.

The generator torque computing section49computes a generator torque for achieving the rotational speed of the generator7which is computed at the rotational speed computing section48. Based on the generator torque, it controls the generator7via the inverter14.

Next, driving control by the travel driving apparatus1of the present embodiment will be described in detail by usingFIG. 3.

FIG. 3is the flowchart to show the driving control procedure in the travel driving apparatus1.

The hybrid control unit20repeatedly executes routines of driving control shown inFIG. 3in the series mode.

First, in step S10, a temperature of the step-up converter15is inputted from the temperature sensor21. Then the process proceeds to step S20.

In step S20, a step-up converter upper-limit power Pvmax is computed based on the temperature of the step-up converter15which has been inputted in step S10. The step-up converter upper-limit power Pvmax is an upper limit value of the power that can be inputted/outputted in the step-up converter15. The step-up converter upper-limit power Pvmax is computed by using, for example, a pre-stored map, and setting is made such that the step-up converter upper-limit power Pvmax becomes lower as the temperature of the step-up converter15becomes higher. The step-up converter upper-limit power Pvmax is set to be, for example, 50% of maximum rating during a normal condition, and the input/output power of the step-up converter is set to be 30 to 50%. Further, during an abnormal condition of the step-up converter15, the step-up converter upper-limit power Pvmax is set to be 0. Then, the process proceeds to step S30. Note that the control of this step corresponds to the function in the above described maximum step-up input/output limit computing section40.

In step S30, longitudinal acceleration and lateral acceleration of the vehicle are detected by the G sensor26. Moreover, the steering angle of the steering wheel is detected by the steering angle sensor27. Then, these longitudinal acceleration, lateral acceleration, and steering angle are inputted. Then, the process proceeds to step S40.

In step S40, a front-wheel distribution ratio Rdf is computed based on the longitudinal acceleration, lateral acceleration, and steering angle, which are inputted in step S30. For example, when it is judged to be steady travelling based on the lateral acceleration and steering angle, control is performed such that the front-wheel distribution ratio Rdf increases. For example, during other than during a steady operation or straight travelling, or within a predetermined period after the generator is started, the front-wheel distribution ratio Rdf is set to be 50% (0.5), and during a steady operation in straight travelling, etc., the front-wheel distribution ratio Rdf is set to be 90% (0.9). Then, the process proceeds to step S50.

In step S50, a user-requested driving torque Tur is computed based on a vehicle speed V computed based on detection values (Rf, Rr) of the front-wheel rotational frequency sensor22and the rear-wheel rotational frequency sensor23, an accelerator depression amount and a brake depression amount based on detection values of the accelerator sensor24and the brake sensor25. The user-requested driving torque Tur is a travel driving torque of the entire vehicle which is needed when accelerating/decelerating the vehicle from the current vehicle speed V in correspondence with the acceleration/deceleration instruction of the driver based on the acceleration amount and the braking amount. Then, the process proceeds to step S60. Note that the control of this step corresponds to the function of the above described driving torque computing section42.

In step S60, a front-wheel driving required torque Tfur is computed. The front-wheel driving required torque Tfur, which is a driving required torque of the front wheel2, is a value obtained by multiplying the user requested driving torque Tur computed in step S50and the front-wheel distribution ratio Rdf computed in step S40as shown in Formula (1) below.
Tfur=Tur×Rdf(1)

Then, the process proceeds to step S70.

In step S70, a rear-wheel driving required torque Trur is computed. This is a driving required torque at the rear wheel and is a value obtained by subtracting the front-wheel driving required torque Tfur computed in step S60from the user-requested driving torque Tur computed in step S50as shown in Formula (2) below.
Trur=Tur−Tfur(2)

Thereafter, the process proceeds to step S80.

In step S80, a generator upper-limit generated power Pgmax is computed. The generator upper-limit generated power Pgmax, which is a maximum value of generated power by the generator7(generator output Pg), is a value obtained by subtracting the step-up converter upper-limit power Pvmax computed in step S20from the front-wheel driving power Pf as shown by Formula (3) below.
Pgmax=(Pf−Pvmax)  (3)

Note that the front-wheel driving power Pf may be computed based on the front-wheel driving required torque Tfur computed in step S60and, for example, may be obtained by multiplication of the front-wheel driving required torque Tfur, the front wheel speed Vf, an appropriately set coefficient “a”, and an efficiency ηmf of the front motor3as shown in Formula (4) below.
Pf=Tur×Vf×a/ηmf(4)

Thereafter, the process proceeds to step S90.

In step S90, required driving power Pur is computed. The required driving power Pur, which is a total value of required driving power of the front motor3and the rear motor5, is computed by the front-wheel driving required torque Tfur computed in step S60, the rear-wheel driving required torque Trur computed in step S70, a tire radius r of the vehicle, a vehicle speed V, and efficiency ηm of the front motor3and the rear motor5as shown in Formula (5) below.
Pur=(Tfur+Trur)/r×V/3.6×ηm(5)

Thereafter, the process proceeds to step S100.

In step S100, generator output Pg is computed. The generator output Pg is supposed to be a lower value between the required driving power Pur computed in step S90and the generator upper-limit generated power Pgmax computed in step S80as shown in Formula (6) below.
Pg=min(Pur,Pgmax)  (6)

Then, the process proceeds to step S110.

In step S110, a front-wheel driving upper-limit torque Tfmax is computed. The front-wheel driving upper-limit torque Tfmax is an upper limit value of the front-wheel driving torque Tf which is limited based on the step-up converter upper-limit power Pvmax in which a generator output amount is taken into consideration. The front-wheel driving upper-limit torque Tfmax is computed from the step-up converter upper-limit power Pvmax computed in step S20, the generator output Pg computed in step S100, efficiency ηmf of the front motor3, and a front-wheel rotational frequency Rf detected by the front-wheel rotational frequency sensor22as shown in Formula (7) below.
Tfmax=(Pvmax+Pg)×ηmf/Rf/(2π/60)  (7)

Then, the process proceeds to step S120.

In step S120, a rear-wheel driving upper-limit torque Trmax is computed. A rear-wheel driving upper-limit torque Trmax is computed from the front-wheel driving upper-limit torque Tfmax computed in step S110, and the front-wheel distribution ratio Rdf computed in step S40as shown in Formula (8) below.
Trmax=Tfmax×(1−Rdf)/Rdf(8)

Then, the process proceeds to step S130.

In step S130, front-wheel driving torque Tf is computed. The front-wheel driving torque Tf is supposed to be a smaller value between the front-wheel driving required torque Tfur computed in step S60and the front-wheel driving upper-limit torque Tfmax computed in step S110as shown in Formula (9) below.
The front-wheel driving torqueTf=min(Tfur,Tfmax)  (9)

Then, the process proceeds to step S140.

In step S140, a rear-wheel driving torque Tr is computed. The rear-wheel driving torque Tr is supposed to be a lower value between the rear-wheel driving required torque Trur computed in step S70and the rear-wheel driving upper-limit torque Trmax computed in step S120as shown in Formula (10) below.
Tr=min(Trur,Trmax)  (10)

Then, this routine is ended.

Through the above described control, the front-wheel driving torque Tf and the rear-wheel driving torque Tr are found. Then, the hybrid control unit20controls the output of the front motor3based on the front-wheel driving torque Tf and controls the output of the rear motor5based on the rear-wheel driving torque Tr. Moreover, the generator output Pg is found and the output of the generator7is controlled based on the generator output Pg.

The vehicle of the present embodiment is a four-wheel drive vehicle in which the front wheel2can be driven by the front motor3and the rear wheel4can be driven by the rear motor5. Further, the vehicle is operable in a series mode in which travel driving is performed by the front motor3and the rear motor5while the engine6is operated to generate power.

The vehicle is mounted with the step-up converter15and is configured such that the front motor3is supplied with and driven by power which is supplied from the battery8and is stepped up in voltage by the step-up converter15. In the series mode, the power generated by the generator7is supplied to the front motor3to drive the front wheels2, and power is supplied from the generator7to the rear motor5via the step-up converter15to drive the rear wheels4.

Thus, in the present embodiment, temperature of the step-up converter15is detected to compute the step-up converter upper-limit power Pvmax, and the generator output Pg, the front-wheel driving torque Tf, and the rear-wheel driving torque Tr are limited based on the step-up converter upper-limit power Pvmax by the driving control shown inFIG. 3above in the series mode so that the power (Pv) which is supplied from the generator7to the rear motor5via the step-up converter15is controlled so as not to exceed the step-up converter upper-limit power Pvmax.

FIG. 4is a graph to illustrate one example of power distribution state between the front and the rear, and driving torque distribution state between the front and the rear during a steady operation in the series mode, particularly when the vehicle is turning or accelerating. InFIG. 4, (a) indicates a driving torque distribution state in which the front-rear wheel distribution ratio of driving torque is 5:5 because the vehicle is turning or accelerating. Where, the front-rear wheel distribution ratio will be 9:1 when the vehicle is neither turning nor accelerating/decelerating. Moreover, (b) indicates a power distribution state before limitation of the generator output Pg of the present embodiment is performed, in which the ratio of the generator output Pg to the output Pb from the battery8at the required driving power Pur is 9:1. Further, (c) indicates a power distribution state when limitation of the generator output Pg of the present embodiment is performed, in which the distribution ratio (output ratio between the generator7and the battery8) of power is 6:4.

When the front-rear wheel distribution ratio of driving torque while the vehicle is turning or accelerating is 5:5 as shown in (a) ofFIG. 4, the required driving power of the rear motor5is relatively large. Thus, if it is arranged that the generator output Pg is at maximum and 90% of the required driving power Pur is supplied by the generator output Pg as shown in (b), the power (Pv inFIG. 4) supplied from the generator7to the rear motor5via the step-up converter15exceeds the step-up converter upper-limit power Pvmax.

In the present embodiment, the generator upper-limit generated power Pgmax according to the step-up converter upper-limit power Pvmax is set such that the generator output Pg is limited and the power supplied from the generator7to the rear motor5via the step-up converter15is not more than the step-up converter upper-limit power Pvmax as shown in (c). This makes it possible to protect the step-up converter15.

Then, as for the reduced amount of the generator output Pg, it is possible to fulfill the required driving power Pur and satisfy the user-requested driving torque Tur by increasing the output from the battery8.

Further, setting the generator output Pg to be the generator upper-limit generated power Pgmax makes it possible to increase the generator output Pg as much as possible within a range that the input/output power of the step-up converter15does not exceed the generator upper-limit generated power Pgmax, and thus increase the output torque of the entire vehicle, particularly of the front motor3, thereby improving the travelling performance of the vehicle.

Further,FIG. 5is a graph to illustrate one example of power distribution state between the front and the rear, and driving torque distribution state between the front and the rear in a situation in which generated power by the generator in the series mode is limited, that is, under an environment such as within a predetermined period from the start of the generator, and when atmospheric pressure is low such as at a high altitude. InFIG. 5, (a) indicates a driving torque distribution during a steady operation, that is, in a travelling state in which the vehicle is neither accelerating nor decelerating, in which the front-rear wheel distribution ratio is 9:1. Where, (b) indicates that the distribution ratio between power (output ratio between the generator7and the battery8) becomes 5:5 in a situation in which the generated power by the generator is limited, that is, under an environment such as within a predetermined period from the start of the generator, and when atmospheric pressure is low such as at a high altitude. Further, (c) indicates a driving torque distribution state when the front-wheel driving torque is limited to decrease power passing through the step-up converter, thereby protecting the step-up converter in the situation of (b), in which the front-rear wheel distribution ratio of driving torque is 6:4.

Since the front-rear wheel distribution ratio of driving torque is 9:1 during a steady operation, that is, in a travelling state in which the vehicle is neither accelerating nor decelerating as shown in (a) ofFIG. 5, if the vehicle in such a situation is brought into a situation in which generated power by the generator is limited, that is, under an environment such as within a predetermined period from the start of the generator, and when atmospheric pressure is low such as at a high altitude, the required driving power of the front motor3is relatively large, and power is supplied from the battery8, together with the power of the generator7, to the front motor3via the step-up converter15. In such a case, passing power of the step-up converter15will not be reduced even if the generator output Pg is limited.

Accordingly, in the present embodiment, it is possible to reduce the passing power of the step-up converter15by limiting the front-wheel driving torque Tf as shown in (c). Note that by increasing the supplied power from the battery8to the rear motor5, thereby increasing the rear-wheel driving torque Tr, it is possible to make up for the reduction amount of the front-wheel driving torque Tf, thereby ensuring the driving torque of the entire vehicle.

Note that although the front-rear wheel distribution ratio (front-wheel distribution ratio Rdf) will be changed as a result of the above described control, if for example the step-up converter15fails and the step-up converter upper-limit power Pvmax becomes 0, the front-wheel driving power Pf becomes less than the generator upper-limit generated power Pgmax, and the rear-wheel driving power Pr becomes less than the maximum output power Pbmax of the battery8as shown in Formulas (11) and (12) below.
Pf<Pgmax  (11)
Pr<Pbmax  (12)

Further, when the step-up converter upper-limit power Pvmax becomes 0, the front-wheel maximum distribution ratio Rdfmax and the rear-wheel maximum distribution ratio Rdrmax are determined by the generator upper-limit generated power Pgmax and the maximum output power Pbmax of the battery8as shown in Formulas (13) and (14) below.
Rdfmax=Pgmax/(Pgmax+Pbmax)  (13)
Rdrmax=Pbmax/(Pgmax+Pbmax)  (14)

Thus, a range of selecting the front-rear wheel distribution ratio (front-wheel distribution ratio Rdf) expands in a state in which the step-up converter upper-limit power Pvmax is larger than 0.

Note that the present invention will not be limited to the above described embodiments. The present invention may be widely applicable to a hybrid vehicle, of which operation can be a series mode, and which is equipped with a step-up converter.