Vehicle

Abstract

A vehicle 1 comprises: a regenerative braking device 20 (first braking device) that is mounted above a suspension device that suspends left and right wheels with respect to the vehicle body and applies regenerative braking force (first braking force) to the wheels; a friction braking device 30 (second braking device) that is mounted below the suspension device and applies a frictional braking force (second braking force) to the wheels; and a control device 16 that controls the regenerative braking device 20 and the friction braking device 30 so as to cooperatively output a required braking force required for braking. The control device 16 adjusts the distribution ratio of the regenerative braking force and the friction braking force with a tendency such that, at the time of sudden braking of a predetermined degree or more, the amount of load transfer occurring between front and rear wheels changes more gently than when only the regenerative braking force is output, and the maximum value of the amount of transfer of load becomes lesser than when only the friction braking force is output.

Description

vehicle

[0001] The present invention relates to a vehicle that uses multiple braking devices to adjust vehicle behavior.

[0002] Conventionally, there are known techniques for adjusting vehicle behavior using multiple braking devices. For example, Patent Document 1 (JP-A-2005-102626) describes a vehicle equipped with a regenerative brake and a friction brake, and which executes a normal brake control that initiates braking of the vehicle based on the amount of brake pedal operation, and an automatic brake control that initiates braking of the vehicle even when the brake pedal is not operated. In this vehicle, the automatic brake control reduces the proportion of braking force provided by the regenerative brake compared to the normal brake control, thereby shortening the braking distance.

[0003] JP 2015-143073 A

[0004] However, the control described in Patent Document 1 merely aims to shorten the braking distance by reducing the amount of switching from regenerative braking to friction braking, and in order to shorten the braking distance during sudden braking, it is necessary to more appropriately set the distribution ratio of the braking forces output from each braking device.

[0005] The present invention has been made in consideration of these problems, and its purpose is to provide a vehicle that can more appropriately adjust the distribution ratio of braking forces output from each braking device during sudden braking, thereby further shortening the braking distance.

[0006] In order to achieve the above-mentioned object, the vehicle of the present invention comprises a first braking device mounted above a suspension device that suspends the left and right wheels on the vehicle body and applies a first braking force to the wheels, a second braking device mounted below the suspension device and applies a second braking force to the wheels, and a control device that controls the first braking device and the second braking device so that they coordinately output the required braking force required for braking, wherein the control device adjusts the distribution ratio between the first braking force and the second braking force so that, during sudden braking of a predetermined degree or more, the amount of load transfer that occurs between the front and rear wheels changes more slowly than when only the first braking force is output, and the maximum value of the load transfer amount tends to be smaller than when only the second braking force is output.

[0007] According to the vehicle of the present invention, it is possible to more appropriately adjust the distribution ratio of the braking forces output from the braking devices during sudden braking, thereby further shortening the braking distance.

[0008] 10 is a schematic configuration diagram showing a vehicle according to an embodiment. FIG. 10 is an explanatory diagram schematically showing forces acting on a vehicle during braking. FIG. 10 is an explanatory diagram schematically showing a change in pitch of a vehicle when a regenerative braking force is applied. FIG. 10 is an explanatory diagram schematically showing a change in pitch of a vehicle when a frictional braking force is applied. FIG. 10 is an explanatory diagram showing an example of a change over time in load shift amount occurring between a front wheel and a rear wheel during braking. FIG. 10 is an explanatory diagram showing the relationship between a wheel contact patch load and a maximum braking force. FIG. 10 is an explanatory diagram showing a control block for calculating a load shift amount. FIG. 10 is an explanatory diagram showing an example of regenerative braking force and frictional braking force by distribution ratio adjustment control. FIG. 10 is an explanatory diagram showing an example of a calculation result of a load shift amount and a maximum braking force when the braking force shown in FIG. 8 is output.

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] 1 is a schematic diagram showing a vehicle according to an embodiment. The vehicle 1 is a four-wheel drive electric vehicle that travels by transmitting power from a front motor 101 serving as a power source to left and right front wheels 21 and transmitting power from a rear motor 102 serving as a power source to left and right rear wheels 22. The vehicle 1 may be any vehicle that includes an electrified power source, such as a BEV (Battery Electric Vehicle), HEV (Hybrid Electric Vehicle), PHEV / PHV (Plug-in Hybrid Electric Vehicle / Plug-in Hybrid Vehicle), or FCEV / FCV (Fuel Cell Electric Vehicle / Fuel Cell Vehicle).

[0011] The front motor 101 outputs driving force to the left and right front wheels 21 via a transaxle 121, which includes a transmission and a differential gear, and left and right front axles 131. The rear motor 102 outputs driving force to the left and right rear wheels 22 via a transaxle 122, which includes a transmission and a differential gear, and left and right rear axles 132. The vehicle 1 is equipped with a battery 14 serving as a power source, which is configured as a secondary battery such as a lithium-ion battery, and power from the battery 14 is supplied to the front motor 101 and the rear motor 102 via a power conversion device such as an inverter (not shown). The front motor 101 and the rear motor 102 are drive-controlled by a control device 16.

[0012] The vehicle 1 also includes a regenerative braking device 20 (first braking device) and a friction braking device 30 (second braking device) as braking devices that apply braking forces to the front wheels 21 and rear wheels 22. The regenerative braking device 20 includes a front motor 101 and a rear motor 102, a battery 14, and a power conversion device such as an inverter (not shown). When the vehicle 1 is decelerating with the accelerator released, the front motor 101 and the rear motor 102 are forcibly driven by the rotational forces of the front wheels 21 and the rear wheels 22 to generate regenerative power. This causes a regenerative braking force F from the front motor 101 to the front wheels 21. ＩＢ１ (first braking force), regenerative braking torque T ＩＢ１, a regenerative braking force F from the rear motor 102 to the rear wheels 22 ＩＢ２ (first braking force), regenerative braking torque T ＩＢ２ The regenerative electric power generated by the front motor 101 and the rear motor 102 is supplied to the battery 14 (FIG. 2).

[0013] The friction braking device 30 is a disc brake device that generates a friction force by pressing brake pads 30P driven by an actuator (not shown) against disc rotors 30D provided corresponding to each front wheel 21 and each rear wheel 22 (each front axle 131 and each rear axle 132). As a result, the friction braking device 30 applies a friction braking force F ＯＢ１ (second braking force), friction braking torque T ＯＢ１ , and a friction braking force F ＯＢ２ (second braking force), friction braking torque T ＯＢ２ is applied (FIG. 2). The actuator may be either a hydraulic or electric type.

[0014] (Control Device) The control device 16 is configured to include input / output devices, storage devices (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), etc., and performs overall control of the vehicle 1. The control device 16 receives inputs of detected amounts detected by various sensors (not shown), such as the accelerator opening, the brake depression amount detected by the brake stroke sensor 15, the vehicle speed, and the wheel speed, as well as various operational information. Based on the input detected amounts and operational information, the control device 16 calculates information necessary for controlling the vehicle 1, such as the required driving force required for running the vehicle 1 and the required braking force required for braking the vehicle 1, and controls various devices of the vehicle 1 based on the calculated information.

[0015] In this embodiment, the control device 16 executes regenerative cooperative control, which outputs a required braking force in cooperation with a regenerative braking force and a frictional braking force. That is, the control device 16 calculates the required braking force according to the amount of brake depression by the driver, and determines the distribution ratio of the regenerative braking force and the frictional braking force so that the total sum of the regenerative braking force and the frictional braking force satisfies the required braking force. The distribution ratio is, for example, such that the regenerative braking force is output within the range of an upper limit of the amount of regenerative power generation, and the shortfall of the regenerative braking force with respect to the required braking force is output as a frictional braking force. The upper limit of the amount of regenerative power generation is set according to the state of charge (SOC) and temperature of the battery 14, etc.

[0016] (Forces acting on the vehicle during braking) Figure 2 is an explanatory diagram that schematically shows forces acting on the vehicle 1 during braking. Between each front wheel 21 and each rear wheel 22 of the vehicle 1 and the vehicle body, there is provided a suspension device 11 that suspends each front wheel 21 and each rear wheel 22 from the vehicle body. In the following description, the sprung portion of the vehicle 1 above the suspension device 11 is referred to as the "inboard portion," and the unsprung portion below the suspension device 11 is referred to as the "outboard portion." The regenerative braking device 20 described above is mounted on the inboard portion, and the friction braking device 30 is mounted on the outboard portion. Therefore, the front wheels 21 and rear wheels 22 of the vehicle 1 are subjected to a regenerative braking force F output from the inboard portion. ＩＢ１ , F ＩＢ２ and the friction braking force F output from the outboard section ＯＢ１ , F ＯＢ２ The suspension link 11L, which connects the suspension device 11 to the body (inboard portion), has an anti-angle θ 2 determined by the geometry of the suspension device 11. ＩＢ１ , θ ＩＢ２ , θ ＯＢ１ , θ ＯＢ２ Depending on this, the regenerative braking force F ＩＢ１ , F ＩＢ２ Anti-force Z ＩＢ１ , Z ＩＢ２ , friction braking force F ＯＢ１ , F ＯＢ２ Anti-force Z ＯＢ１ , Z ＯＢ２ is effective.

[0017] (Pitch Change and Load Movement Amount During Braking) Next, the pitch change and load movement amount during braking of the vehicle 1 will be described with reference to Figs. 3 to 5. Hereinafter, unless there is no need to distinguish between them, the regenerative braking force F ＩＢ１ , F ＩＢ２ "Regenerative braking force F ＩＢ ”, frictional braking force F ＯＢ１ , F ＯＢ２ is the friction braking force F ＯＢ 3 shows the regenerative braking force F ＩＢ 4 is an explanatory diagram showing a schematic diagram of a pitch change of the vehicle 1 when a friction braking force F ＯＢ 5 is an explanatory diagram showing an example of a change in the pitch of the vehicle 1 when braking is applied. Also, FIG. 5 is an explanatory diagram showing an example of a change in the amount of load shift (amount of shift of the contact patch load) that occurs between the front wheels 21 and the rear wheels 22 during braking.

[0018] As shown in Figures 3 and 4, when the vehicle 1 is braked, the pitch center PC is moved in the inboard portion due to the action of the inertial force Gx. ａ , PC ｂ The pitch angle changes downwards with the fulcrum at "θ" in the figure. However, the regenerative braking force F ＩＢ When only the friction braking force F acts on the vehicle 1, and when the friction braking force F acts on the vehicle 1, the friction braking force F acts on the vehicle 1. ＯＢ The instantaneous center of pitch change (not shown) is different when only the pitch center PC acts. ａ Height h from the wheel contact surface ａ (Figure 3) is the pitch center PC ｂ Height h from the wheel contact surface ｂ (Figure 4)

[0019] As a result, the load shift amount ΔW during braking changes in the manner shown in FIG. 5. In FIG. 5, "h" represents the height of the center of gravity CG (FIG. 2). As shown in the figure, the regenerative braking force F ＩＢ In the case of 100% regeneration where only the frictional braking force F acts on the vehicle 1, the load shift amount ΔW increases quickly up to time t1, and then increases gradually. ＯＢIn the case of 100% friction where only friction acts, the load shift amount ΔW increases quickly until time t2, which is later than time t1, and then increases gradually. In this way, in the initial stage of braking, the load shift amount ΔW changes more gradually with 100% friction than with 100% regeneration. Note that time t3, when the load shift amount ΔW with 100% regeneration and the load shift amount ΔW with 100% friction intersect, is the same as the time t3 when the center of gravity height h and the pitch center height h ａ , h ｂ This is the time when the load shift amount ΔW reaches a maximum value (peak value) P when it is assumed that the loads are the same as the loads of the regenerative braking force and the frictional braking force. Furthermore, when the maximum value Pa of the load shift amount ΔW when regeneration is 100% that occurs after time t3 is compared with the maximum value Pb of the load shift amount ΔW when friction is 100%, the maximum value Pa is smaller than the maximum value Pb.

[0020] 6 is an explanatory diagram showing the relationship between the wheel contact patch load and maximum braking force. For example, assume that the absolute value of the load transfer amount ΔWA between the front wheel 21A and the rear wheel 22A during a certain braking operation is smaller than the absolute value of the load transfer amount ΔWB between the front wheel 21B and the rear wheel 22B during another braking operation. In this case, the maximum braking force FmaxA acting on the front wheel 21A and the rear wheel 22A (the average value of the maximum braking forces Fmax acting on each wheel) is greater than the maximum braking force FmaxB acting on the front wheel 21B and the rear wheel 22B. Thus, the smaller the absolute value of the load transfer amount ΔW, the greater the maximum braking force Fmax acting on the wheel.

[0021] 5, the maximum braking force Fmax at the time when maximum values ​​Pa and Pb are generated is greater with 100% regeneration than with 100% friction. On the other hand, as described above, the load transfer amount ΔW changes more gradually with 100% friction than with 100% regeneration up to time t3, so that in the initial stage of braking, a greater braking force can be obtained for a longer period with 100% friction than with 100% regeneration. As described above, the characteristics of the load transfer amount ΔW and the braking force acting on the vehicle change when a braking device mounted on an inboard portion is used and when a braking device mounted on an outboard portion is used.

[0022] (Distribution ratio adjustment control during sudden braking) In the vehicle 1 of this embodiment, in order to obtain a large braking force by utilizing the characteristics of the braking force described above during sudden braking of a predetermined degree or more, the regenerative braking force FＩＢ and friction braking force F ＯＢ In the following description, it is assumed that the sum of all braking forces (i.e., the required braking force F) and the distribution ratio between the braking force acting on the front wheels 21 and the braking force acting on the rear wheels 22 are maintained.

[0023] An example of sudden braking of a predetermined degree or greater is when the brake depression amount detected by the brake stroke sensor 15 is equal to or greater than a preset threshold and the rate of change in the brake depression amount is equal to or greater than a predetermined value. An example of sudden braking of a predetermined degree or greater may be when a driving safety device is activated, such as an antilock brake system (ABS) that inhibits wheel locking, or an autonomous emergency brake system (AEBS) that automatically generates braking force when an obstacle is detected in front of the vehicle.

[0024] 7 is an explanatory diagram showing a control block for calculating the load shift amount ΔW. As shown in the figure, the required braking force F is used as an input value, and the regenerative braking force F ＩＢ and friction braking force F ＯＢ The distribution ratio is the transfer function G ｃ (s), the regenerative braking force F ＩＢ is expressed by the following equation (1), and the friction braking force F ＯＢ is expressed by the following equation (2): The load shift amount ΔW is expressed by the transfer function G ｃ (s), regenerative braking force F ＩＢ and friction braking force F ＯＢ It can be calculated using the following formula (3). ｐ " is the moment of inertia of the sprung mass around the pitch center. "C ｐ " is the pitch damping coefficient, which is the pitch moment required to change the pitching motion of the vehicle by a unit pitch angular velocity. ｐ " is the pitch stiffness, which is the pitch moment required to change the pitching motion of the vehicle by a unit pitch angle. "L" is the wheelbase. Furthermore, by rearranging equation (3), equation (4) can be obtained.

[0025]

[0026]

[0027]

[0028]

[0029] From equation (4), the response characteristic of the load movement amount ΔW over time (s) is expressed as the transfer function G ｃ (s) and the transfer function G ｃ By adjusting (s), it is possible to adjust the time response characteristics of the braking force. For example, when the time response characteristics of the load movement amount ΔW and the braking force are set to be a first-order lag system, the following equation (5) is established (where "τ" is a time constant). Then, from equation (5), the transfer function G ｃ (s) can be expressed by the formula (6). The control device 16 uses the transfer function G ｃ (s) and calculate the regenerative braking force F according to equations (1) and (2). ＩＢ and friction braking force F ＯＢ Set and output.

[0030]

[0031] FIG. 8 shows the regenerative braking force F ＩＢ and friction braking force F ＯＢ 8 and 9 are explanatory diagrams showing an example of the calculation results of the time response of the load movement amount ΔW and the maximum braking force Fmax when the braking force shown in FIG. 8 is output. ｃ In this example, the regenerative braking force F ＩＢ is set to the drive side value.

[0032] At time t10, the regenerative braking force F ＩＢ and friction braking force F ＯＢWhen is output, as shown by the solid line in FIG. 9, it can be seen that the load movement amount ΔW rises more gently than at least the comparative example of 100% regeneration (dashed line). Also, the maximum value P1 of the load movement amount ΔW is smaller than both the 100% regeneration and 100% friction (chain double-dashed line). In other words, the overshoot of the load movement amount ΔW is well suppressed. As a result, the maximum braking force Fmax is also suppressed from decreasing compared to both the 100% regeneration and 100% friction, and converges more quickly. In this way, the transfer function G is set so that the time response characteristic of the load movement amount ΔW becomes, for example, a first-order lag system. ｃ By setting (s), the load shift amount ΔW is changed more gradually compared to 100% regeneration, while the maximum value P1 is made smaller compared to 100% friction, making it possible to obtain a large maximum braking force Fmax for a longer period of time.

[0033] As described above, the vehicle 1 of the embodiment is mounted above the suspension device 11 that suspends the left and right wheels on the vehicle body, and the regenerative braking force F ＩＢ a regenerative braking device 20 (first braking device) that applies a friction braking force F (first braking force) to the wheel; ＯＢ The vehicle is equipped with a friction braking device 30 (second braking device) that applies a regenerative braking force F (second braking force), and a control device 16 that controls the regenerative braking device 20 and the friction braking device 30 so that they cooperatively output a required braking force F required for braking. The control device 16 controls the load shift amount ΔW that occurs between the front and rear wheels during sudden braking of a predetermined degree or more to be greater than the regenerative braking force F. ＩＢ The maximum value P1 of the load movement amount ΔW changes more slowly than when only the friction braking force F ＯＢ The regenerative braking force F tends to be smaller than when only ＩＢ and friction braking force F ＯＢ This configuration makes it possible to obtain a large maximum braking force Fmax for a longer period of time, as described above. Therefore, according to the vehicle 1 of the embodiment, it is possible to more appropriately adjust the distribution ratio of the braking forces output from the braking devices during sudden braking, thereby further shortening the braking distance.

[0034] The control device 16 also uses the required braking force F as an input value and the distribution ratio as a transfer function G ｃ (s), the time response characteristic of the load movement amount ΔW becomes the above tendency. ｃ (s) to calculate the regenerative braking force F ＩＢ and friction braking force F ＯＢ With this configuration, the regenerative braking force F is set so that the load shift amount ΔW changes in a desired manner. ＩＢ and friction braking force F ＯＢ This can be easily set.

[0035] Also, the transfer function G ｃ (s) is set so that the time response characteristic of the load shift amount ΔW is a first-order lag system. This configuration makes it easier to change the load shift amount ΔW in the above-mentioned manner. Note that the time response characteristic of the load shift amount ΔW is not limited to a first-order lag system, and may be other characteristics such as a second-order lag system.

[0036] Although the description of the embodiment has been completed, aspects of the present invention are not limited to this embodiment. For example, in the embodiment, the regenerative braking device 20 is used as the first braking device, and the friction braking device 30 is used as the second braking device. However, the first braking device may be, for example, an internal combustion engine capable of applying engine brake torque as the first braking torque. Furthermore, the second braking device may be, for example, an electric in-wheel motor provided corresponding to each front wheel 21 and each rear wheel 22.

[0037] REFERENCE SIGNS LIST 1 vehicle 11 suspension device 16 control device 20 regenerative braking device (first braking device) 21 front wheels (wheels) 22 rear wheels (wheels) 30 friction braking device (second braking device) F required braking force F ＩＢ , F ＩＢ１ , F ＩＢ２ Regenerative braking force (first braking force) F ＯＢ , F ＯＢ１ , F ＯＢ２ Friction braking force (second braking force) Gc Transfer function (distribution ratio) ΔW Load movement amount

Claims

1. A vehicle comprising: a first braking device mounted above a suspension device that suspends left and right wheels on a vehicle body and that applies a first braking force to said wheels; a second braking device mounted below said suspension device and that applies a second braking force to said wheels; and a control device that controls said first braking device and said second braking device so that they coordinate to output the required braking force required for braking, wherein said control device adjusts the distribution ratio of said first braking force and said second braking force so that, during sudden braking of a predetermined degree or more, the amount of load transfer that occurs between the front and rear wheels changes more slowly than when only said first braking force is output, and the maximum value of said load transfer amount tends to be smaller than when only said second braking force is output.

2. The vehicle described in claim 1, characterized in that the control device sets the first braking force and the second braking force using a transfer function that shows the trend in the time response characteristics of the load movement amount when the required braking force is an input value and the distribution ratio is a transfer function.

3. The vehicle according to claim 2, wherein the transfer function is set so that the time response characteristic is a first-order lag system.

4. A vehicle as claimed in any one of claims 1 to 3, characterized in that the first braking device is a regenerative braking device that generates a regenerative braking force, and the second braking device is a friction braking device that generates a friction braking force.

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