Vehicle

Abstract

A vehicle (1) is provided with: a front wheel side device (2) provided corresponding to a pair of left and right front wheels (11, 12); a rear wheel side device (3) provided corresponding to a pair of left and right rear wheels (13, 14); and a control device (6) that controls the front wheel side device (2) and the rear wheel side device (3). The control device (6) controls the front wheel side device (2) and the rear wheel side device (3) in such a manner that a braking force acting on the pair of left and right rear wheels (13, 14) is greater than a braking force acting on the pair of left and right front wheels (11, 12) when the vehicle is decelerating. A differential device (33) in the rear wheel side device (3) that distributes a driving force of an electric motor (31) to the pair of left and right rear wheels (13, 14) has a differential restriction mechanism (70) that generates a differential restriction force for restricting differential rotation of the pair of left and right rear wheels (13, 14).

Description

Technical Field

[0001] This invention relates to vehicles. Background Technology

[0002] Previously, vehicles were known to use separate electric motors to drive the left and right front wheels and the left and right rear wheels. Patent Document 1 describes a front-wheel drive electric vehicle with: a front-wheel drive unit having a front-side MG (electric generator) as a front-side drive source and a front-side transmission mechanism; and a rear-wheel drive unit having a rear-side MG as a rear-side drive source and a rear-side transmission mechanism. The output of the front-side transmission mechanism is distributed to the left and right front wheels by a front-side differential, and the output of the rear-side transmission mechanism is distributed to the left and right rear wheels by a rear-side differential.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2023-102684 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] When a vehicle decelerates, the load on the front wheels increases and the load on the rear wheels decreases due to the vehicle's inertia. Consequently, the suspension springs on the front wheels are compressed and the suspension on the rear wheels are stretched, resulting in a phenomenon known as front-end sag, where the vehicle tilts forward. This front-end sag can cause discomfort to passengers or may cause cargo to collapse.

[0008] This nose-diving phenomenon can be mitigated by reducing the braking force on the front wheels and increasing the braking force on the rear wheels. However, during vehicle deceleration, the reduced load on the rear wheels decreases the friction between the rear tires and the road surface. When the braking force on the rear wheels approaches the friction limit, the vehicle's behavior becomes unstable. Especially when increasing the braking force on the rear wheels during cornering, in addition to the braking force, the rear wheels also generate a lateral force resisting centrifugal force. Therefore, the braking force of the left and right rear wheels, especially the inner wheel during cornering, is prone to approach the rear wheel friction limit, which may lead to oversteer and make it difficult to control the vehicle's attitude.

[0009] Therefore, the purpose of this invention is to provide a vehicle that can suppress both front-end drop and vehicle behavior instability.

[0010] Methods for solving problems

[0011] To achieve the above objectives, the present invention provides a vehicle comprising: a front wheel-side device corresponding to a pair of left and right front wheels; a rear wheel-side device corresponding to a pair of left and right rear wheels; and a control device that controls the front wheel-side device and the rear wheel-side device to brake the pair of left and right front wheels via the front wheel-side device and the pair of left and right rear wheels via the rear wheel-side device when the vehicle decelerates. The front wheel-side device brakes the pair of left and right front wheels via at least one of a frictional braking force generated by a friction brake and a rotational resistance of a front wheel-side drive source driving the pair of left and right front wheels when the vehicle decelerates. The wheel-side device includes a rear-wheel-side drive source for driving the left and right pairs of rear wheels and a differential device for distributing the driving force of the rear-wheel-side drive source to the left and right pairs of rear wheels. When the vehicle decelerates, the differential device can apply a braking force to the left and right pairs of rear wheels through the rotational resistance of the rear-wheel-side drive source. When the vehicle decelerates, the control device controls the front wheel-side device and the rear wheel-side device in a manner that makes the braking force applied to the left and right pairs of rear wheels greater than the braking force applied to the left and right pairs of front wheels. The differential device has a differential limiting mechanism that generates a differential limiting force for limiting the differential rotation of the left and right pairs of rear wheels.

[0012] Invention Effects

[0013] The vehicle according to the present invention can suppress the phenomenon of front-end drop while suppressing the instability of vehicle behavior. Attached Figure Description

[0014] Figure 1 This is a schematic diagram illustrating a structural example of a vehicle equipped with a drive device according to an embodiment of the present invention.

[0015] Figure 2A It is a schematic diagram showing the suspension springs, suspension arms, front wheel load, and rear wheel load on the front and rear wheel sides when the vehicle is traveling at a constant speed.

[0016] Figure 2B This is a schematic diagram showing the suspension springs, suspension arms, front wheel load, and rear wheel load on the front and rear wheel sides when the vehicle is decelerated by front wheel bias braking.

[0017] Figure 2C This is a schematic diagram showing the suspension springs, suspension arms, front wheel load, and rear wheel load on the front and rear wheel sides when the vehicle is decelerated by rear-wheel bias braking.

[0018] Figure 3A This is an explanatory diagram showing the friction circle of the left rear wheel when a vehicle is traveling at a constant speed.

[0019] Figure 3BThis is an explanatory diagram showing the friction circle of the left rear wheel when a vehicle decelerates by braking with the front wheels heavier than the rear wheels.

[0020] Figure 3C This is an explanatory diagram showing the friction circle of the left rear wheel when a vehicle decelerates by braking with the rear wheels heavier than the other.

[0021] Figure 4 It is a cross-sectional view showing the differential device and its surrounding parts.

[0022] Figure 5 It is a perspective view showing the differential mechanism housed in the differential housing, with a portion of the main body of the housing cut away.

[0023] Figure 6 It is along Figure 4 A cross-sectional view of the AA-line shell body and differential mechanism.

[0024] Figure 7A This is a graph showing the extension and contraction of the suspension springs of the left and right front wheels when the vehicle decelerates through regenerative braking with rear-wheel bias braking versus when the vehicle decelerates through regenerative braking with front-wheel bias braking.

[0025] Figure 7B This is a graph showing the extension and contraction of the suspension springs of the left and right rear wheels when the vehicle is decelerated by regenerative braking through rear-wheel bias braking and when the vehicle is decelerated by regenerative braking through front-wheel bias braking.

[0026] Figure 8 It is a graph showing the change in yaw rate when regenerative braking of each wheel is applied with the throttle off during cornering. Detailed Implementation

[0027] [Implementation Method]

[0028] Reference Figures 1 to 8 Embodiments of the present invention will be described below. Furthermore, the embodiments described below are shown as preferred specific examples for carrying out the present invention. Although some details specifically illustrate various technically preferred aspects, the technical scope of the present invention is not limited to these specific solutions.

[0029] Figure 1 This is a schematic diagram illustrating a structural example of vehicle 1 according to an embodiment of the present invention. Vehicle 1 is a four-wheel drive vehicle capable of driving a pair of front wheels, namely the left front wheel 11 and the right front wheel 12, and a pair of rear wheels, namely the left rear wheel 13 and the right rear wheel 14.

[0030] The vehicle 1, as a main component, includes: a body 10; a front wheel side device 2 corresponding to the left front wheel 11 and the right front wheel 12; a rear wheel side device 3 corresponding to the left rear wheel 13 and the right rear wheel 14; a steering control device 4 for steering control of the left front wheel 11 and the right front wheel 12; a brake hydraulic pressure generating device 5 for generating brake hydraulic pressure; a control device 6 for controlling the front wheel side device 2 and the rear wheel side device 3; and a rechargeable secondary battery, i.e., a high-voltage storage battery 15. Brake discs 110, 120, 130, and 140 are respectively provided on the left front wheel 11 and the right front wheel 12, as well as on the left rear wheel 13 and the right rear wheel 14.

[0031] The front wheel side device 2 includes: an electric motor 21 that serves as the front wheel side drive source for driving the left front wheel 11 and the right front wheel 12; a transmission 22 that changes the rotation of the output shaft 210 of the electric motor 21; a differential device 23 that distributes the driving force of the electric motor 21 transmitted from the transmission 22 to the left front wheel 11 and the right front wheel 12; drive shafts 24 and 25 that connect the left front wheel 11 and the right front wheel 12 to the left and right sides of the differential device 23, respectively; a friction brake 26 that brakes the left front wheel 11; a friction brake 27 that brakes the right front wheel 12; a front wheel side hydraulic circuit 28; and a front wheel side inverter 29.

[0032] The differential 23 of the front wheel side device 2 is an open differential without a structure for limiting the differential rotation of the left front wheel 11 and the right front wheel 12. The differential 23 includes: a gear ring 230 driven and connected to the output shaft 210 of the transmission 22 and the electric motor 21; a differential housing 231 that rotates integrally with the gear ring 230; a pinion shaft 232 fixed to the differential housing 231; a pair of pinions 233 supported on the pinion shaft 232; and a first half-shaft gear 234 and a second half-shaft gear 235 meshing with the pair of pinions 233. The pair of pinions 233, the first half-shaft gear 234, and the second half-shaft gear 235 are bevel gears. The left drive shaft 24 is connected to the first half-shaft gear 234 in a non-rotatable manner. The right drive shaft 25 is connected to the second half-shaft gear 235 in a non-rotatable manner.

[0033] The rear wheel side device 3 includes: an electric motor 31 that serves as the rear wheel side drive source for driving the left rear wheel 13 and the right rear wheel 14; a transmission 32 that changes the speed of the output shaft 310 of the electric motor 31; a differential device 33 that distributes the driving force of the electric motor 31 transmitted from the transmission 32 to the left rear wheel 13 and the right rear wheel 14; drive shafts 34 and 35 that connect the left rear wheel 13 and the right rear wheel 14 to the left and right sides of the differential device 33, respectively; a friction brake 36 that brakes the left rear wheel 13; a friction brake 37 that brakes the right rear wheel 14; a rear wheel side hydraulic circuit 38; and a rear wheel side inverter 39.

[0034] In this embodiment, the gearboxes 22 and 32 of the front wheel side device 2 and the rear wheel side device 3 are reducers that reduce the rotation of the output shafts 210 and 310 of the motors 21 and 31 by a fixed reduction ratio. However, the gearboxes 22 and 32 may also be gearboxes that can change the gear ratio in a multi-stage or continuously variable manner.

[0035] The steering control device 4 includes: a steering shaft 41 connected to a steering wheel 40 operated by the driver of the vehicle 1; a pinion 42 fixed to the steering shaft 41; a rack shaft 43 meshing with the pinion 42; and left and right tie rods 44 and 45 pivotally connected between the rack shaft 43 and the left front wheel 11 and the right front wheel 12. When the steering wheel 40 is operated, the pinion 42 rotates according to the steering control angle, and the rack shaft 43 moves left and right, thereby turning the left front wheel 11 and the right front wheel 12.

[0036] The brake hydraulic fluid generating device 5 includes: an input rod 51 that receives the force from the brake pedal 50 as a thrust; an electrically operated brake booster 52 that increases the thrust received from the input rod 51; a master cylinder 53 that pressurizes the brake fluid based on the output of the brake booster 52; and a reservoir 54 for storing brake fluid. The brake fluid output from the master cylinder 53 is input into the front wheel-side hydraulic circuit 28 and the rear wheel-side hydraulic circuit 38.

[0037] The friction brakes 26 and 27 on the front wheels are operated by brake fluid supplied from the front wheel hydraulic circuit 28 via brake hoses 281 and 282, pressing the brake pads against the brake discs 110 and 120 to generate friction, thereby braking the left front wheel 11 and the right front wheel 12. The friction brakes 36 and 37 on the rear wheels are operated by brake fluid supplied from the rear wheel hydraulic circuit 38 via brake hoses 381 and 382, ​​pressing the brake pads against the brake discs 130 and 140 to generate friction, thereby braking the left rear wheel 13 and the right rear wheel 14.

[0038] The high-voltage battery 15 supplies DC voltage to the front wheel-side inverter 29 and the rear wheel-side inverter 39. During vehicle deceleration, regenerative braking is applied to the left front wheel 11, right front wheel 12, left rear wheel 13, and right rear wheel 14 via the front wheel-side device 2 and the rear wheel-side device 3. The electricity generated by this regenerative braking is used to charge the high-voltage battery 15. This extends the driving range of vehicle 1.

[0039] The control device 6 controls the front wheel side device 2 and the rear wheel side device 3 based on vehicle information. The vehicle information includes: the detected value of the steering control angle of the steering wheel 40, the detected value of the brake pedal sensor that detects the amount of brake pedal 50 being depressed, the detected value of the accelerator pedal sensor that detects the amount of accelerator pedal 16 being depressed, the detected values ​​of the wheel speed sensors that detect the rotational speeds of the left front wheel 11, the right front wheel 12, the left rear wheel 13, and the right rear wheel 14, and the detected values ​​of various sensors such as the yaw rate sensor.

[0040] Control device 6 controls front wheel-side device 2 by sending electrical signals to front wheel-side hydraulic circuit 28 and front wheel-side inverter 29, and controls rear wheel-side device 3 by sending electrical signals to rear wheel-side hydraulic circuit 38 and rear wheel-side inverter 39. The electrical signals sent by control device 6 to front wheel-side hydraulic circuit 28 and rear wheel-side hydraulic circuit 38 are excitation currents used to adjust the opening of control valves, which are used to increase or decrease the friction braking force generated between friction brakes 26, 27, 36, 37 and brake discs 110, 120, 130, 140.

[0041] The electrical signals sent by the control device 6 to the front wheel-side inverter 29 and the rear wheel-side inverter 39 are, for example, PWM (Pulse Width Modulation) signals used to turn multiple switching elements on and off. Alternatively, if the front wheel-side inverter 29 and the rear wheel-side inverter 39 themselves have the function of generating PWM signals, electrical signals representing the current to be supplied to the front wheel-side motor 21 and the rear wheel-side motor 31 can also be sent from the control device 6 to the front wheel-side inverter 29 and the rear wheel-side inverter 39, for example, via CAN (Controller Area Network). Motors 21 and 31 are three-phase AC motors, and the front wheel-side inverter 29 and the rear wheel-side inverter 39 each have multiple switching elements connected in a three-phase bridge configuration.

[0042] When vehicle 1 accelerates, the motor 21 of the front wheel-side device 2 and the motor 31 of the rear wheel-side device 3 generate positive torque corresponding to the current supplied from the front wheel-side inverter 29 and the rear wheel-side inverter 39, respectively. Conversely, when vehicle 1 decelerates, the motor 21 of the front wheel-side device 2 and the motor 31 of the rear wheel-side device 3 function as generators, generating negative torque as rotational resistance. The positive torque is the driving force used to increase the rotational speed of the left front wheel 11, right front wheel 12, left rear wheel 13, and right rear wheel 14, while the negative torque is the regenerative braking force used to decrease the rotational speed of the left front wheel 11, right front wheel 12, left rear wheel 13, and right rear wheel 14.

[0043] The motor 21 of the front wheel-side device 2 generates regenerative power through the rotational force of the left front wheel 11 and the right front wheel 12 during deceleration, thereby generating rotational resistance. The motor 31 of the rear wheel-side device 3 generates regenerative power through the rotational force of the left rear wheel 13 and the right rear wheel 14 during deceleration, thereby generating rotational resistance.

[0044] Vehicle 1, controlled by control device 6, brakes the left front wheel 11, right front wheel 12, left rear wheel 13, and right rear wheel 14 during deceleration via front wheel-side device 2 and rear wheel-side device 3. Front wheel-side device 2 brakes the left front wheel 11 and right front wheel 12 using at least one of the frictional braking force generated by friction brakes 26 and 27 during deceleration and the rotational resistance of electric motor 21. At low vehicle speeds, control device 6 primarily brakes the left front wheel 11 and right front wheel 12 using the frictional braking force generated by friction brakes 26 and 27. At medium and high vehicle speeds, it primarily brakes the left front wheel 11 and right front wheel 12 using the regenerative braking force of electric motor 21 as rotational resistance. This is because at low vehicle speeds, the regenerative control of electric motor 21 alone cannot apply sufficient braking force to the left front wheel 11 and right front wheel 12.

[0045] Furthermore, for example, in situations requiring rapid deceleration or sudden stopping of vehicle 1 at high speeds, the front wheel-side device 2 simultaneously uses the friction braking force generated by friction brakes 26 and 27 and the rotational resistance of the electric motor 21 to brake the left front wheel 11 and the right front wheel 12. Thus, the control device 6 controls the front wheel-side device 2 to ensure that the sum of the friction braking force generated by the friction brakes 26 and 27 and the regenerative braking force of the electric motor 21—that is, the braking force of the left front wheel 11 and the right front wheel 12—is an appropriate magnitude corresponding to the vehicle information.

[0046] Similarly, for the rear wheel side device 3, at low vehicle speeds, the left rear wheel 13 and right rear wheel 14 are mainly braked by the friction braking force generated by the friction brakes 36 and 37. At medium and high vehicle speeds, the left rear wheel 13 and right rear wheel 14 are mainly braked by the regenerative braking force of the electric motor 31 as rotational resistance.

[0047] When the vehicle decelerates, the control device 6 controls the front wheel-side device 2 and the rear wheel-side device 3 in a manner that makes the braking force acting on the left rear wheel 13 and the right rear wheel 14 greater than the braking force acting on the left front wheel 11 and the right front wheel 12. Furthermore, when using the regenerative braking force of the electric motors 21 and 31 as rotational resistance to brake the left front wheel 11, the right front wheel 12, the left rear wheel 13, and the right rear wheel 14, the control device 6 controls the front wheel-side device 2 and the rear wheel-side device 3 in a manner that makes the braking force based on the rotational resistance generated by the electric motor 31 of the rear wheel-side device 3 greater than the braking force based on the rotational resistance generated by the electric motor 21 of the front wheel-side device 2. This alleviates the phenomenon of the front of the vehicle being lower than the rear, improving the ride comfort for the driver and other passengers.

[0048] Next, refer to Figure 2A , Figure 2B , Figure 2C This explains the relationship between the magnitude of the braking force of the left front wheel 11 and right front wheel 12, and the left rear wheel 13 and right rear wheel 14 and the phenomenon of the front of the vehicle sinking.

[0049] Figure 2A , Figure 2B , Figure 2C This is a schematic diagram representing the front wheel side suspension spring 171 and suspension arm 172, the rear wheel side suspension spring 181 and suspension arm 182, and the front wheel load NF and the rear wheel load NR. Figure 2A This indicates the state of vehicle 1 when it is traveling at a constant speed on a level road surface 90. Figure 2B This indicates a state in which the vehicle 1 is decelerated by front-wheel bias braking, where the front-wheel bias braking exerts a greater braking force on the left front wheel 11 and right front wheel 12 than on the left rear wheel 13 and right rear wheel 14. Figure 2C This indicates a state where vehicle 1 is decelerated through rear-wheel bias braking, where the left rear wheel 13 and right rear wheel 14 are subjected to a greater braking force than the left front wheel 11 and right front wheel 12. Figure 2B , Figure 2C In the diagram, the length of the dashed arrow indicates the magnitude of the braking force BF acting on the left front wheel 11 and the right front wheel 12, and the braking force BR acting on the left rear wheel 13 and the right rear wheel 14. Additionally, in... Figure 2A , Figure 2B , Figure 2C In the diagram, the length of the arrow indicates the magnitude of the front wheel load NF and the rear wheel load NR.

[0050] Figure 2A An exemplary illustration shows the case where the front wheel load NF and the rear wheel load NR are equal when vehicle 1 is traveling at a constant speed. When vehicle 1 decelerates, the center of gravity 91 of vehicle 1 is located above the contact surfaces 9F and 9R of the tires of the left front wheel 11, right front wheel 12, left rear wheel 13, and right rear wheel 14, resulting in a pitching motion. This causes the front portion of the vehicle body 10 to sink and the rear portion to rise. Consequently, on the left front wheel 11 and right front wheel 12 sides, the suspension spring 171 contracts and the front wheel load NF increases; on the left rear wheel 13 and right rear wheel 14 sides, the suspension spring 181 extends and the rear wheel load NR decreases. Here, pitch refers to the rotation of the vehicle body 10 about the center of its left and right axes passing through the center of gravity 91 of vehicle 1.

[0051] The braking force BR of the left rear wheel 13 and the right rear wheel 14 suppresses the extension of the rear wheel side suspension spring 181. Therefore, by braking the vehicle 1 with a heavier weight on the rear wheels, the vehicle 1 is decelerated. This reduces the pitch of the vehicle body 10 compared to braking the vehicle 1 with a heavier weight on the front wheels. As a result, the nose-down phenomenon is alleviated, reducing the discomfort and anxiety caused to the driver or passengers of the vehicle 1.

[0052] However, when vehicle 1 is decelerated by rear-wheel bias braking, the friction between the tires of the left rear wheel 13 and the right rear wheel 14 and the road surface 90 is used to decelerate vehicle 1, making it difficult to ensure the lateral force required for vehicle 1 to turn. Therefore, during deceleration and turning while simultaneously decelerating, the left rear wheel 13 and the right rear wheel 14 are prone to sideslip. Regarding this point, please refer to the following... Figure 3A , Figure 3B , Figure 3C To provide a more specific explanation.

[0053] Figure 3A This is an explanatory diagram showing the friction circle FC of the left rear wheel 13 when vehicle 1 is traveling at a constant speed on road surface 90. Figure 3B This is an explanatory diagram showing the friction circle FC of the left rear wheel 13 when vehicle 1 is turning left and decelerating while braking with the front wheels biased. Figure 3C This is an explanatory diagram showing the friction circle FC of the left rear wheel 13 when vehicle 1 is braking with uneven weight distribution while turning left and decelerating. Figure 3A , Figure 3B , Figure 3C In the diagram, the size of the friction circle FC represents the frictional force between the left rear wheel 13 tire and the road surface 90°. Additionally, in... Figure 3A , Figure 3B , Figure 3C In the figure, let the X-axis direction represent the front-to-back force of the tire, the Y-axis direction represent the lateral force of the tire, and the arrow represents the maximum lateral force FY of the tire that can be ensured within the friction circle FC.

[0054] like Figure 3A , Figure 3B , Figure 3C As shown, the size of the friction circle FC decreases as the rear wheel load NR decreases. When the vehicle 1 is decelerated by rear-wheel bias braking, compared with the case of deceleration by front-wheel bias braking, the front-rear force FX of the tire in the deceleration direction borne by the left rear wheel 13 increases, and the tire lateral force FY that can be ensured within the friction circle FC decreases. When the vehicle 1 decelerates while turning left, due to centrifugal force, the proportion of the rear wheel load NR on the left rear wheel 13, which is the inner wheel of the turn, decreases. Therefore, the maximum braking force that can be applied to the left rear wheel 13 decreases, and the left rear wheel 13 is prone to slippage.

[0055] Here, assuming that the differential device 33 of the rear wheel side device 3 is the same open differential as the differential device 23 of the front wheel side device 2, when decelerating and turning to the left, the front-to-back force of the right rear wheel 14, which is the outer wheel of the turn, will be equal to that of the left rear wheel 13, which has a reduced front-to-back force due to the reduced load. Therefore, not only can the vehicle 1 not be sufficiently decelerated by the braking force of the left rear wheel 13 and the right rear wheel 14, but oversteer is also likely to occur.

[0056] In this embodiment, the differential device 33, which serves as the rear wheel-side device 3, employs a device with a differential limiting function. This ensures vehicle stability during deceleration and cornering, even when the vehicle 1 is decelerated by rear-wheel bias braking. The differential limiting function utilizes a differential limiting force corresponding to the driving force and rotational resistance generated by the electric motor 31, which is the rear wheel-side drive source, to limit the differential rotation of the left rear wheel 13 and the right rear wheel 14. In other words, in this embodiment, by using the differential device 33 with the differential limiting function, for example, during a deceleration and cornering motion to the left, even if the tire of the left rear wheel 13 reaches its grip limit, a greater front-to-back force than that of the left rear wheel 13 can be distributed to the right rear wheel 14. This allows for a greater regenerative braking force from the electric motor 31 than before, enabling smooth deceleration of the vehicle 1. Simultaneously, the front-to-back force of the right rear wheel 14, which is the outer wheel of the cornering wheel, in the deceleration direction helps to suppress oversteer.

[0057] Next, refer to Figures 4 to 6 The structure of the differential device 33 of the rear wheel side device 3 is explained in detail.

[0058] Figure 4 This is a cross-sectional view showing the differential 33 and its surrounding parts. The differential 33 is a mechanical differential without electronic control elements, and includes: via a transmission 32 (see reference 32). Figure 1 The gear ring 330 is driven and connected to the output shaft 310 of the motor 31, the differential housing 7 rotates integrally with the gear ring 330, and the differential mechanism 8 is housed in the differential housing 7.

[0059] The differential housing 7 is housed within a differential housing 30 mounted on the body of the vehicle 1, and is supported on the differential housing 30 by bearings 331 and 332 in a manner that allows it to rotate about the rotation axis O. The differential housing 7 has a bottomed cylindrical housing body 71 and a housing cover 72 configured to block the opening of the housing body 71. The housing body 71 and the housing cover 72 are fastened together by a plurality of bolts 73. The gear ring 330 is fastened to the differential housing 7 by a plurality of bolts 74. Hereinafter, the direction parallel to the rotation axis O of the differential housing 7 will be referred to as the axial direction.

[0060] The differential housing 30 is sealed with lubricating oil (differential oil) for lubricating the differential mechanism 8. In addition, the differential housing 30 is provided with insertion holes 301 and 302 for inserting the left and right drive shafts 34 and 35, and sealing members 303 and 304 for preventing lubricating oil leakage are arranged inside the insertion holes 301 and 302.

[0061] Figure 5 This is a perspective view showing the differential mechanism 8 housed in the differential housing 7, with a portion of the housing body 71 cut away. Figure 6 It is along Figure 4 A cross-sectional view of the shell body 71 and the differential mechanism 8 of the AA line.

[0062] The differential mechanism 8 includes: a first half-shaft gear 81 and a second half-shaft gear 82 arranged side-by-side along the axial direction, a plurality of pinion gear sets 83, a central washer 84 disposed between the first half-shaft gear 81 and the second half-shaft gear 82, a first side washer 85 disposed between the first half-shaft gear 81 and the housing body 71, and a second side washer 86 disposed between the second half-shaft gear 82 and the housing cover 72. The first half-shaft gear 81 and the second half-shaft gear 82 are helical gears with helical tooth lines. The first half-shaft gear 81 outputs driving force to the left rear wheel 13, and the second half-shaft gear 82 outputs driving force to the right rear wheel 14.

[0063] A splined fitting hole 810 is formed at the center of the first half-shaft gear 81, allowing the end of the drive shaft 34 to be connected in a non-rotatable manner. A splined fitting hole 820 is formed at the center of the second half-shaft gear 82, allowing the end of the drive shaft 35 to be connected in a non-rotatable manner. A pinion set 83 is disposed on the outer periphery of the first half-shaft gear 81 and the second half-shaft gear 82. In this embodiment, the differential mechanism 8 includes three pinion sets 83.

[0064] Each pinion set 83 is composed of multiple meshing pinions. In this embodiment, a pinion set 83 is formed by meshing one first pinion 831 with two second pinions 832. The first pinion 831 and the second pinions 832 are supported on the differential housing 7 in a manner that allows them to rotate about a rotation axis parallel to the rotation axis O.

[0065] The first pinion 831 and the second pinion 832 are helical gears with spiral tooth lines. The axial length of the first pinion 831 is equivalent to the sum of the axial lengths of the first half-shaft gear 81 and the second half-shaft gear 82. The axial length of the second pinion 832 is equivalent to the axial length of the second half-shaft gear 82.

[0066] The first pinion 831 meshes with the first half-shaft gear 81. Two second pinions 832 are located on either side of the first pinion 831 in the circumferential direction of the differential housing 7 and mesh with the second half-shaft gears 82. The first pinion 831 and the two second pinions 832 mesh at the outer periphery of the second half-shaft gear 82. The diameter of the portion of the first pinion 831 that meshes with the first half-shaft gear 81 is larger than the diameter of the portion that meshes with the two second pinions 832.

[0067] When the driving force of the motor 31 is transmitted from the differential housing 7 to the drive shafts 34 and 35 through the differential mechanism 8, an axial thrust corresponding to the torsional angle of the tooth lines is generated on the first half-shaft gear 81, the second half-shaft gear 82, the first pinion 831, and the second pinion 832. Additionally, when the motor 31 generates regenerative braking force, a thrust in the opposite direction to the driving force generated by the motor 31 is generated on the first half-shaft gear 81, the second half-shaft gear 82, the first pinion 831, and the second pinion 832.

[0068] The first pinion 831 and the second pinion 832 are held in the pinion holding portion 710 formed in the housing body 71. In this embodiment, since the differential mechanism 8 has three sets of pinion sets 83, three pinion holding portions 710 are formed on the housing body 71. Each pinion holding portion 710 has a first holding hole 711 for holding the first pinion 831 and two second holding holes 712 for holding the two second pinions 832 respectively. When the rotational speeds of the left rear wheel 13 and the right rear wheel 14 differ, and the first half-shaft gear 81 and the second half-shaft gear 82 rotate differentially, the first pinion 831 rotates in the first holding hole 711, and the second pinion 832 rotates in the second holding holes 712.

[0069] When the first pinion 831 and the second pinion 832 rotate within the first retaining hole 711 and the second retaining hole 712, the tooth tip surface 831a of the first pinion 831 slides on the inner surface 711a of the first retaining hole 711, and the tooth tip surface 832a of the second pinion 832 slides on the inner surface 712a of the second retaining hole 712. The frictional force generated by these slidings becomes a differential limiting force that inhibits the differential rotation of the first half-shaft gear 81 and the second half-shaft gear 82. That is, the differential housing 7 and the plurality of pinion sets 83 constitute a differential limiting mechanism 70 that generates a differential limiting force for limiting the differential rotation of the left rear wheel 13 and the right rear wheel 14.

[0070] Furthermore, the frictional force generated by the axial end faces 831b and 831c of the first pinion 831 and the axial end faces 832b and 832c of the second pinion 832 rotating and sliding on the housing body 71 or the housing cover 72 also becomes a differential limiting force that suppresses the differential rotation of the first half-shaft gear 81 and the second half-shaft gear 82. Moreover, the frictional forces between the first half-shaft gear 81 and the second half-shaft gear 82 and the central washer 84, the frictional forces between the first half-shaft gear 81 and the housing body 71 and the first side washer 85, and the frictional forces between the second half-shaft gear 82 and the housing cover 72 and the second side washer 86 also become differential limiting forces that suppress the differential rotation of the first half-shaft gear 81 and the second half-shaft gear 82.

[0071] The differential limiting force of the differential device 33 restricts the differential rotation of the left rear wheel 13 and the right rear wheel 14, so that even if the friction (traction) between one of the left rear wheel 13 and the right rear wheel 14 and the road surface decreases significantly, as long as the friction between the other wheel and the road surface is ensured, the driving force or braking force can be transmitted to the other wheel.

[0072] The force pressing the tooth tip surfaces 831a and 832a of the first pinion 831 and the second pinion 832 against the inner surfaces 711a and 712a of the first retaining hole 711 and the second retaining hole 712 increases with the torque generated by the motor 31. Furthermore, the axial pressing force on the first pinion 831, the second pinion 832, the first half-shaft gear 81, and the second half-shaft gear 82 also increases with the torque generated by the motor 31. That is, the differential device 33 is an LSD (Limited Slip Differential) with torque proportional differential limiting function, which uses a differential limiting force corresponding to the torque (driving force and regenerative braking force) generated by the motor 31 to limit the differential rotation of the left rear wheel 13 and the right rear wheel 14.

[0073] In this embodiment, the torque bias ratio (TBR) of the differential device 33 is 1.4 or higher and 2.8 or lower. Here, the torque bias ratio refers to the torque distribution ratio expressed as the ratio of the torque transmitted to the wheel with lower torque (e.g., the left rear wheel 13) as the denominator and the torque transmitted to the wheel with higher torque (e.g., the right rear wheel 14) as the numerator when a torque difference is generated between the left rear wheel 13 and the right rear wheel 14.

[0074] The torque offset ratio increases with the increase of the differential limiting force. The magnitude of the torque offset ratio can be adjusted by, for example, the torsion angle, pressure angle, tip circle diameter, axial length, and surface roughness of the tip surfaces 831a and 832a of each of the first half-shaft gear 81, second half-shaft gear 82, first pinion 831, and second pinion 832. In typical open differentials, the torque offset ratio is less than 1.3, for example, approximately 1.1 to 1.2.

[0075] If the torque offset ratio is too large, the torque difference between the left and right sides will be too large, which can easily cause slippage on the outer wheel during cornering. Therefore, the torque offset ratio of the differential device 33 is preferably 2.8 or less. In addition, in order to ensure the driving stability of the vehicle under various road conditions, the torque offset ratio is preferably set to 2.5 or less.

[0076] (Verification results of vehicle behavior)

[0077] Figure 7A and Figure 7B This is a graph illustrating an example of the changes in the extension and contraction of the suspension springs corresponding to each wheel before and after braking begins, with the left side of the vehicle being weighted and traveling in a straight line at a constant speed, taking a stationary state with no occupants as the baseline. The graph shows the effects of regenerative braking on the rear wheels and regenerative braking on the front wheels before and after braking begins. Here, the extension and contraction of the suspension springs refers to the change in spring length relative to the baseline state. The braking force ratio (front wheel side: rear wheel side) is 7:3 during front wheel weighted braking and 4:6 during rear wheel weighted braking.

[0078] Figure 7A This indicates the extension and retraction of the suspension springs on the left front wheel 11 and the right front wheel 12. Figure 7B This indicates the extension / retraction amount of the suspension springs for the left rear wheel 13 and the right rear wheel 14. Figure 7A and Figure 7B In the graph, solid lines represent rear-wheel bias braking, and dashed lines represent front-wheel bias braking. The vertical axis of the graph shows the suspension spring compression, with compression set to negative (-) and extension set to positive (+). The horizontal axis of the graph is the time axis, with time T1 representing the start of regenerative braking. Additionally, in... Figure 7A and Figure 7B In the diagram, a straight line with a single dot parallel to the time axis represents the extension or contraction of the suspension spring before regenerative braking begins.

[0079] like Figure 7A and Figure 7BAs shown in the chart, the compression of the suspension springs of the left front wheel 11 and the right front wheel 12 is not significantly different under front-wheel-weighted braking and rear-wheel-weighted braking conditions. However, the elongation of the suspension springs of the left rear wheel 13 and the right rear wheel 14 is less under rear-wheel-weighted braking than under front-wheel-weighted braking. That is, by applying a greater braking force to the left rear wheel 13 and the right rear wheel 14 than to the left front wheel 11 and the right front wheel 12, the lift of the rear part of the vehicle body 10 is reduced, and the front-end sinking phenomenon is suppressed.

[0080] Figure 8 This is a graph illustrating the change in yaw rate when the accelerator pedal is depressed to zero (throttle off) and regenerative braking is applied to all wheels during cornering. The horizontal axis of the graph is the time axis, with time T... 21 Indicates the time point at which the turn begins, time T. 22 This indicates the time point at which the throttle is set to the off state. Figure 8 The solid line in the chart represents the change in yaw rate when the vehicle 1 of this embodiment, equipped with a differential device 33 with differential limiting function, performs rear-wheel bias braking with a front-wheel bias braking force ratio of 4:6. Figure 8 The dashed line in the diagram represents the change in yaw rate when the rear-wheel differential 33 of vehicle 1 is replaced with an open differential that has the same structure as the front-wheel differential 23, and the braking force ratio between the front and rear wheels is 4:6 with rear-wheel bias braking. Additionally, Figure 8 The single-dotted line in the chart represents the change in yaw rate when the differential 33 on the rear wheel side of vehicle 1 is replaced with an open differential and the braking force ratio on the front wheel side and the rear wheel side is 7:3 with front wheel bias braking.

[0081] like Figure 8 As shown by the dotted line in the diagram, when the rear-wheel differential 33 uses an open differential and rear-wheel bias braking is applied, the inner wheel slips during cornering, causing the braking force to be unable to be applied to the outer wheel. When the throttle is closed, the wheel enters a spin state, and the yaw rate increases sharply. Additionally, as... Figure 8 As shown by the dashed line in the chart, when the differential device 33 on the rear wheel side adopts an open differential and front wheel bias braking is applied, the load on the front wheel side in the longitudinal direction of the vehicle increases, and the lateral force of the tire cannot be fully generated, resulting in an understeer state with insufficient yaw rate.

[0082] In contrast, such as Figure 8 As shown by the solid line in the chart, in vehicle 1 equipped with LSD (differential device 33) with torque proportional differential limiting function, understeer and oversteer are suppressed when the rear wheels are braked with a bias, and the vehicle behavior is relatively stable.

[0083] (Effects of the implementation method)

[0084] According to the embodiments of the present invention described above, rear-wheel bias braking can suppress front-end dive, and by using the differential device 33 with differential limiting function, instability in vehicle behavior can be suppressed even when decelerating during cornering. In particular, in this embodiment, since the differential device 33 is mechanical, there is no action delay time as with electronic control components such as electromagnetic clutches, and appropriate differential limiting force can be generated immediately according to the vehicle's driving state.

[0085] (Postscript)

[0086] The present invention has been described above based on embodiments, but these embodiments do not limit the invention as defined in the claims. Furthermore, it should be noted that not all combinations of features described in the embodiments are necessary for solving the problems of the invention. Additionally, the present invention may be implemented with appropriate modifications, such as omitting parts of the structure or adding or replacing structures, without departing from its spirit. Moreover, it may be implemented in modifications, for example, as follows.

[0087] In the above embodiment, the case where the front wheel-side differential 23 is an open differential is described, but it is not limited to this. The front wheel-side differential 23 may also be configured as an LSD with differential limiting function, similar to the rear wheel-side differential 33. Furthermore, as the drive source for the front wheel side, an engine utilizing fuel such as gasoline may be used instead of the electric motor 21. Moreover, the present invention can also be applied to vehicles where the front wheel-side device 2 does not have a drive source such as an electric motor 21 and only drives the rear wheels.

[0088] Furthermore, in the above embodiment, a set of pinions 83 was described by meshing two second pinions 832 with a first pinion 831 to form a set of pinions 83. However, this is not a limitation; a set of pinions can also be formed by meshing one pinion meshing with the first half-shaft gear 81 and another pinion meshing with the second half-shaft gear 82. In this case, the pinion meshing with the first half-shaft gear 81 and the other pinion meshing with the second half-shaft gear 82 are meshed at a position where they are not radially parallel to the first half-shaft gear 81 and the second half-shaft gear 82.

[0089] Furthermore, while the above embodiments describe a driver controlling the steering wheel 40, the invention is not limited to this. It can also be applied to fully automated vehicles without a steering wheel, or to vehicles equipped with a steer-by-wire system that does not connect the steering wheel to the rack and pinion shaft via a steering axis, but instead uses a motor to steer the front wheels according to the steering wheel angle. Additionally, the friction brake is not limited to hydraulic types; for example, it can also be an electric brake that uses the rotation of a motor to press brake pads onto the brake disc.

[0090] Furthermore, in the above embodiments, the differential device 33 is described as a mechanical LSD with torque proportional differential limiting function, but it is not limited to this. It may also be a differential limiting device that uses an elastic body such as a spring to generate friction between the half-shaft gear and the differential housing, or between a pair of half-shaft gears, under a specified load. Alternatively, it may be a differential limiting device that uses a multi-plate clutch arranged between the differential housing and the half-shaft gear and uses an electric motor or hydraulic piston to adjust the pressing pressure of the multi-plate clutch to change the differential limiting force.

[0091] Label Explanation

[0092] 1…vehicles

[0093] 11…Left front wheel

[0094] 12…Right front wheel

[0095] 13…Left rear wheel

[0096] 14…Right rear wheel

[0097] 2…Front wheel side assembly

[0098] 21… Electric motor (front wheel drive source)

[0099] 26, 27… Friction brakes

[0100] 3… Rear wheel side assembly

[0101] 31… Electric motor (rear wheel drive source)

[0102] 33… Differential device

[0103] 36, 37… Friction brakes

[0104] 6…Control device

[0105] 70…Differential limiting mechanism Claims (as amended under Article 19 of the Treaty) 1. A vehicle comprising: a front wheel side device disposed corresponding to a pair of left and right front wheels; a rear wheel side device disposed corresponding to a pair of left and right rear wheels; and a control device for controlling the front wheel side device and the rear wheel side device. When the vehicle decelerates, the front wheel-side device brakes the pair of left and right front wheels, and the rear wheel-side device brakes the pair of left and right rear wheels. The front wheel-side device brakes the left and right front wheels during vehicle deceleration using at least one of the friction braking force generated by the friction brake and the rotational resistance of the front wheel-side drive source driving the left and right front wheels. The rear wheel-side device includes a rear wheel-side drive source for driving the left and right pair of rear wheels and a differential device for distributing the driving force of the rear wheel-side drive source to the left and right pair of rear wheels. When the vehicle decelerates, the differential device can apply braking force to the left and right pair of rear wheels through the rotational resistance of the rear wheel-side drive source. The control device controls the front wheel side device and the rear wheel side device in a manner that makes the braking force acting on the left and right rear wheels greater than the braking force acting on the left and right front wheels when the vehicle decelerates. The differential device is a mechanical differential device without electronic control components. It has a differential limiting mechanism and uses a differential limiting force corresponding to the driving force and rotational resistance generated by the rear wheel side drive source to limit the differential rotation of the left and right pair of rear wheels. The differential limiting mechanism generates a differential limiting force to limit the differential rotation of the left and right pair of rear wheels. 2. The vehicle according to claim 1, wherein, The torque bias ratio of the differential device is 1.4 or higher. 3. The vehicle according to claim 2, wherein, The torque bias ratio of the differential device is 2.8 or less. 4. The vehicle according to any one of claims 1 to 3, wherein, The rear wheel drive source is an electric motor that generates regenerative electricity by utilizing the rotational force of the left and right rear wheels when the vehicle decelerates, thereby generating rotational resistance. 5. The vehicle according to claim 4, wherein, The front wheel-side device has an electric motor as the drive source for the front wheels. When the vehicle decelerates, the electric motor generates regenerative electricity through the rotational force of the left and right front wheels, thereby generating rotational resistance. The control device controls the front wheel-side drive source and the rear wheel-side drive source in such a way that the braking force based on the rotational resistance generated by the rear wheel-side drive source is greater than the braking force based on the rotational resistance generated by the front wheel-side drive source when the vehicle decelerates.

Claims

1. A vehicle comprising: a front wheel side device disposed corresponding to a pair of left and right front wheels; a rear wheel side device disposed corresponding to a pair of left and right rear wheels; and a control device for controlling the front wheel side device and the rear wheel side device. When the vehicle decelerates, the front wheel-side device brakes the pair of left and right front wheels, and the rear wheel-side device brakes the pair of left and right rear wheels. The front wheel-side device brakes the left and right front wheels during vehicle deceleration using at least one of the friction braking force generated by the friction brake and the rotational resistance of the front wheel-side drive source driving the left and right front wheels. The rear wheel-side device includes a rear wheel-side drive source for driving the left and right pair of rear wheels and a differential device for distributing the driving force of the rear wheel-side drive source to the left and right pair of rear wheels. When the vehicle decelerates, the differential device can apply braking force to the left and right pair of rear wheels through the rotational resistance of the rear wheel-side drive source. The control device controls the front wheel side device and the rear wheel side device in a manner that makes the braking force acting on the left and right rear wheels greater than the braking force acting on the left and right front wheels when the vehicle decelerates. The differential device has a differential limiting mechanism that generates a differential limiting force to limit the differential rotation of the left and right pair of rear wheels.

2. The vehicle according to claim 1, wherein, The differential device of the rear wheel side device is a mechanical differential device without electronic control components. It uses a differential limiting force corresponding to the driving force and rotational resistance generated by the rear wheel side drive source to limit the differential rotation of the left and right pair of rear wheels.

3. The vehicle according to claim 2, wherein, The torque bias ratio of the differential device is 1.4 or higher.

4. The vehicle according to claim 3, wherein, The torque bias ratio of the differential device is 2.8 or less.

5. The vehicle according to any one of claims 1 to 4, wherein, The rear wheel drive source is an electric motor that generates regenerative electricity by utilizing the rotational force of the left and right rear wheels when the vehicle decelerates, thereby generating rotational resistance.

6. The vehicle according to claim 5, wherein, The front wheel-side device has an electric motor as the drive source for the front wheels. When the vehicle decelerates, the electric motor generates regenerative electricity through the rotational force of the left and right front wheels, thereby generating rotational resistance. The control device controls the front wheel-side drive source and the rear wheel-side drive source in such a way that the braking force based on the rotational resistance generated by the rear wheel-side drive source is greater than the braking force based on the rotational resistance generated by the front wheel-side drive source when the vehicle decelerates.

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