brake control unit

Abstract

The brake control unit according to one embodiment serves to control, for example, a hydraulic brake capable of generating a hydraulic braking force on both the front and rear wheels of a four-wheel drive vehicle, and an electric parking brake capable of generating a parking braking force, different from the hydraulic braking force, on the front wheels or on the rear wheels, wherein the brake control unit is provided with: a detection unit for detecting an actuation of the parking brake in order to cause the electric parking brake to generate a parking braking force;and a control unit for reducing the hydraulic braking force generated on the front wheels and on the rear wheels, and adjusting the hydraulic braking force generated on the other from the front wheels or the rear wheels to a level that allows a steady state of the vehicle to be maintained before a parking brake force is generated by the electric parking brake when an actuation of the parking brake is detected, while a steady state is maintained solely by the hydraulic braking force generated on both the front and rear wheels.

Description

Technical field

[0001] The present invention relates to a brake control unit. State of the art

[0002] In the prior art, there is a proposed technology to reduce a hydraulic braking force during an actuation of an electric parking brake in order to reduce a load due to the overlapping generation of the hydraulic braking force by a hydraulic brake and a parking braking force by the electric parking brake on predetermined vehicle wheels. Citation list patent document Patent document 1: US 8,494,745 B2 Patent document 2: DE 10 2014 216 986 A1

[0003] Patent document 2 is considered to be the closest prior art. Summary of the invention: Technical problem

[0004] However, if, in the prior art technology described above, the time at which the hydraulic braking force is reduced and the time at which the parking braking force is generated are not appropriately set, the hydraulic braking force and the parking braking force will not be optimally distributed to the predetermined vehicle wheels. Additionally, due to insufficient braking force, it may not be possible to maintain a steady state of the vehicle, or in some cases, excessive braking force may result in unnecessary hardware stress.

[0005] In this respect, it is an object of the invention to provide a brake control unit that is able to reduce a load on a predetermined vehicle wheel due to an overlapping generation of a hydraulic braking force and a parking brake force, while reliably maintaining a steady state. Solution to the problem

[0006] A brake control unit according to the invention serves to control, for example, a hydraulic brake capable of generating a hydraulic braking force on both the front and rear wheels of a four-wheel drive vehicle, and an electric parking brake capable of generating a parking braking force on the front wheels or the rear wheels that differs from the hydraulic braking force, wherein the brake control unit has: a sensing unit for detecting an actuation of the parking brake to cause the electric parking brake to generate a parking braking force; and a control unit for reducing the hydraulic braking force generated on the front wheels or the rear wheels and adjusting the hydraulic braking force generated on the other wheels from the front wheels or the rear wheels to a level that allows a steady state of the vehicle to be maintained.Before the electric parking brake generates the parking brake force, when the parking brake is activated, a steady state is maintained solely by the hydraulic braking force applied to both the front and rear wheels. In this configuration, even if, for example, the hydraulic braking force on the front or rear wheels is zero, the steady state can be maintained solely by the hydraulic braking force from the other wheels. Thus, it is possible to reduce the load due to overlapping generation of the hydraulic braking force and the parking brake force on the predetermined vehicle wheels (the front or rear wheels) while maintaining a more reliable steady state.

[0007] In the brake control unit, the control unit causes the electric parking brake to generate the parking braking force after the hydraulic braking force applied to the front or rear wheels has been reduced to zero. In this configuration, it is possible to reliably prevent the overlapping generation of hydraulic braking force and parking braking force on the front or rear wheels.

[0008] Additionally, in the brake control unit, for example, the control unit terminates the control to reduce the hydraulic braking force generated on the front or rear wheels, and the control to adjust the hydraulic braking force generated on the other wheels from the front or rear wheels, when the parking brake force reaches a level that allows the steady state to be maintained solely by the parking brake force. In this configuration, the control to reduce the hydraulic braking force of the front or rear wheels is deactivated, thereby reducing unnecessary control load. Furthermore, the control to adjust the hydraulic braking force of the other wheels from the front or rear wheels is deactivated, thereby limiting the application of unnecessary load to any of the brake mechanisms from the other wheels from the front or rear wheels.

[0009] Additionally, in the brake control unit, for example, the control unit omits an adjustment of the hydraulic braking force generated on the front or rear wheels. It reduces the hydraulic braking force generated on the front or rear wheels when the magnitude of the hydraulic braking force generated on the front or rear wheels is equal to or greater than the magnitude required to maintain steady state. This occurs when the parking brake is activated, and steady state is maintained solely by the hydraulic braking force. In this configuration, the hydraulic braking force of the front and rear wheels is not adjusted if sufficient hydraulic braking force is already ensured to maintain steady state.This makes it possible to reduce the unnecessary tax burden. Brief description of the drawings The Fig. Figure 1 is an exemplary configuration drawing that represents a schematic configuration of a brake device which is a control target of a brake control unit according to one embodiment. The Fig. Figure 2 is an exemplary block diagram that represents a functional configuration of the brake control unit according to the embodiment. The Fig. Figure 3 is an exemplary time diagram that represents an example of a change in a load applied to the front wheels and to the rear wheels, as implemented in the embodiment. The Fig. Figure 4 is an exemplary flowchart that represents a series of processes performed by the brake control unit according to the embodiment. Method for carrying out the invention

[0010] An embodiment of the invention is described below with reference to the drawings. A configuration of the embodiment, which will be described below, and an operation and a result (effect) to be obtained through the configuration are merely examples and are not limited to the content of the following description.

[0011] The Fig. Figure 1 is an exemplary configuration drawing that represents a schematic configuration of a brake device that controls a brake control unit 100 (not included in the Fig. 1 shown, but on Fig. 2 (which will be described below) according to one embodiment. This braking device is provided, for example, in a four-wheel drive vehicle for general use.

[0012] As in the Fig. As shown in Figure 1, the braking device according to the embodiment has a hydraulic brake 1, which is configured to apply a braking force (frictional braking torque) to both vehicle wheels 2FL and 2FR as front wheels and vehicle wheels 2RL and 2RR as rear wheels, and an electric parking brake 2, which is configured to apply a braking force only to the vehicle wheels 2RL and 2RR as rear wheels. Where it is necessary in the following to distinguish the braking force generated by the hydraulic brake 1 from the braking force generated by the electric parking brake 2, the former is referred to as a hydraulic braking force, and the latter is referred to as a parking brake force.

[0013] The hydraulic brake has a pressure generating unit 32, wheel cylinders 38FL, 38FR, 38RL and 38RR, pressure adjusting units 34FL, 34FR, 34RL and 34RR, and a recirculation mechanism 37. The pressure generating unit 32 is configured to generate pressure (hydraulic pressure) in response to the application of a brake pedal 31 by the vehicle's driver. The wheel cylinders 38FL, 38FR, 38RL and 38RR are mechanisms that pressurize corresponding friction brake elements, thereby applying braking forces to the vehicle wheels 2FL, 2FR, 2RL and 2RR, respectively. The pressure adjustment units 34FL, 34FR, 34RL and 34RR are mechanisms that adjust a hydraulic pressure applied to the wheel cylinders 38FL, 38FR, 38RL and 38RR. The recirculation mechanism 37 is a mechanism that causes a fluid (hydraulic fluid), as a medium that generates hydraulic pressure, to return to an upstream side.

[0014] More precisely, the pressure generating unit 32 has a master cylinder 32a and a storage tank 32b. The master cylinder 32a is pushed by the actuation (pressing) of the brake lever 31, thereby delivering fluid supplied by the storage tank 32b to two discharge ports. The two discharge ports are connected to the pressure adjusting unit 34FR on one side and the pressure adjusting unit 34RL on the other, and to the pressure adjusting unit 34FL on the front and the pressure adjusting unit 34RR on the rear, via solenoid valves 33, which can be electrically switched between an open and a closed state. Incidentally, the solenoid valve 33 is controlled by the brake control unit 100 (see the Fig. 2) opened and closed, which will be described below.

[0015] Additionally, each of the pressure adjustment units 34FL, 34FR, 34RL, and 34RR has solenoid valves 35 and 36 that can be switched between the open and closed states. Solenoid valves 35 and 36 are provided between solenoid valve 33 and a reservoir 41. Solenoid valve 35 is connected to solenoid valve 33, and solenoid valve 36 is connected to reservoir 41.

[0016] The solenoid valves 35 and 36 are controlled by the combustion control unit 100 (see the Fig. 2) opened and closed, thereby increasing, maintaining, or decreasing the pressure generated by the wheel cylinders 38FL, 38FR, 38RL, and 38RR. Wheel cylinder 38FL is connected between solenoid valves 35 and 36 of the pressure adjustment unit 34FL, and wheel cylinder 38FR is connected between solenoid valves 35 and 36 of the pressure adjustment unit 34FR. Additionally, wheel cylinder 38RL is connected between solenoid valves 35 and 36 of the pressure adjustment unit 34RL, and wheel cylinder 38RR is connected between solenoid valves 35 and 36 of the pressure adjustment unit 34RR.

[0017] The recirculation mechanism 37 has reservoirs 41, pumps 39, and a pump motor 40 that drives the pumps 39 on the front and rear sides and transfers the fluid to the downstream side. The reservoirs 41 and the pumps 39 are provided according to a combination of pressure adjustment units 34FR and 34RL or a combination of pressure adjustment units 34FL and 34RR.

[0018] Incidentally, the hydraulic brake 1 has a stroke sensor 51, which is capable of detecting the actuation range (stroke) of the brake pedal 31, and a pressure sensor (not in the Fig. 1 shown), which is capable of detecting a pressure generated by the main cylinder 32a, or similar.

[0019] In this embodiment, an electric parking brake (EPB) motor 60 is operated under the control of the brake control unit 100 (see the Fig. 2) is driven, and is connected to each of the wheel cylinders 38RL and 38RR at the rear. Consequently, in this embodiment, the frictional brake elements of the wheel cylinders 38RL and 38RR at the rear are pressurized depending on the drive of the EPB motor 60, thereby applying the braking force to the vehicle wheels 2RL and 2RR as the rear wheels. Thus, in this embodiment, the wheel cylinders 38RL and 38RR at the rear and the two EPB motors 60, which are connected to the two wheel cylinders 38RL and 38RR, function as the electric parking brake 2, which is capable of generating the parking braking force differently from the hydraulic braking force by the hydraulic brake 1.

[0020] However, in a vehicle equipped with hydraulic brake 1 and electric parking brake 2, a driver can appropriately use one actuation to generate the hydraulic braking force through hydraulic brake 1 (hydraulic braking operation) and another actuation to generate the parking braking force through electric parking brake 2 (parking braking operation), thereby generating a suitable braking force on the vehicle depending on the state. For example, in a state where only the hydraulic braking operation causes the vehicle to reach a steady state, and then sufficient parking braking force is obtained through the parking braking operation, the steady state remains unchanged, even if the hydraulic braking operation is terminated in such a way that the hydraulic braking force is zero.

[0021] The prior art proposes a technology to reduce the hydraulic braking force generated on the rear wheels during application of the electric parking brake 2, in order to reduce the load on predetermined vehicle wheels (in this embodiment, the rear wheels) resulting from the overlapping generation of the hydraulic braking force and the parking brake force. However, if, as described above, the time at which the hydraulic braking force is reduced and the time at which the parking brake force is generated are not appropriately set in the prior art technology, the hydraulic braking force and the parking brake force are not optimally distributed to the rear wheels. Additionally, it is not possible to maintain a steady state of the vehicle due to insufficient braking force, or an unnecessary hardware load remains due to excessive braking force in some cases.

[0022] In this respect, the brake control unit 100, according to the embodiment, avoids bringing about a state in which the braking force is insufficient in the steady state, starting from a configuration that will be described below, and thereby reduces a load that is applied to a braking mechanism due to the overlapping generation of the hydraulic braking force and the parking brake force on the predetermined vehicle wheels (in the embodiment the rear wheels), while maintaining the steady state of the vehicle more reliably.

[0023] The Fig. Figure 2 is an exemplary block diagram illustrating a functional configuration of the brake control unit 100 according to the embodiment. For example, the brake control unit 100 configures a part of an electronic brake control unit (ECU) with hardware similar to a normal computer, such as a processor or memory. The brake control unit 100 can be integrated with the other part of the brake ECU or configured separately.

[0024] As from the Fig. As can be seen in Figure 2, the brake control unit 100 is configured to control the hydraulic brake 1 and the electric parking brake 2. More precisely, the brake control unit 100 has, as a functional configuration, a sensing unit 101 and a control unit 102, which are provided with a hydraulic brake control unit 103 and a parking brake control unit 104. The hydraulic brake control unit 103 is configured to control the hydraulic braking force generated on the hydraulic brake 1. Additionally, the parking brake control unit 104 is configured to control the parking braking force generated by the electric parking brake 2. For example, a processor of the brake control unit 100 executes various programs stored in memory. As a result, the functional configurations are implemented.Incidentally, in this embodiment, a part of the entirety of the functional configurations can be implemented by a dedicated circuit or similar.

[0025] The detection unit 101 detects a driver's application of the brakes, such as actuation (hydraulic brake actuation) to cause the hydraulic brake 1 to generate hydraulic braking force, or actuation (actuation of the parking brake) to establish a state in which it is possible to generate parking braking force. For example, actuation of the hydraulic brake means actuation of the brake pedal 31 by the driver. For example, actuation of the parking brake means actuation of an EPB switch, a lever, or similar (not in the Fig. (1 shown), which is located near a driver's seat. The detection unit 101 detects the actuation of the hydraulic brake based on a detection result from a lift sensor 51 or similar device, and detects the actuation of the parking brake based on an electrical signal or similar signal output depending on the actuation of the EPB switch, lever, or similar device.

[0026] The control unit 102 reduces the hydraulic braking force generated on the rear wheels and adjusts the hydraulic braking force generated on the front wheels to a level that allows the vehicle to remain stationary before the electric parking brake 2 applies the parking brake when the parking brake is activated. During this adjustment, the vehicle remains stationary solely due to the hydraulic braking force generated on both the front and rear wheels. In other words, the control unit 102 increases the hydraulic braking force on the front wheels to compensate for a reduction in braking force when the braking force becomes so insufficient that maintaining the vehicle's stationary state is no longer possible due to the reduction in hydraulic braking force on the rear wheels.Consequently, even if the hydraulic braking force of the rear wheels is zero, it is possible, for example, to maintain a steady state solely through the hydraulic braking force. This makes it possible to reduce the load applied to the rear wheel braking mechanism, where the hydraulic braking force and the parking brake force are generated in an overlapping manner, while more reliably maintaining the vehicle's steady state.

[0027] Thus, the control unit 102 causes the electric parking brake 2 to generate the parking braking force after the hydraulic braking force applied to the rear wheels has been reduced to zero. Consequently, it is possible to more reliably avoid the overlapping generation of the hydraulic braking force and the parking braking force on the rear wheels. Furthermore, the control unit 102 can control the timing at which the EPB motor 60 of the electric parking brake 2 is driven such that the time when the hydraulic braking force applied to the rear wheels is zero coincides with the time when the generation of the parking braking force begins. As described above, this timing control allows for a sudden transition from a steady state powered solely by the hydraulic braking force to a steady state powered solely by the parking braking force.

[0028] Furthermore, control unit 102 terminates the control of reducing the hydraulic braking force applied to the rear wheels and the control of adjusting the hydraulic braking force applied to the front wheels when the magnitude of the parking brake force reaches a level that allows the vehicle to remain stationary solely due to the parking brake force. Consequently, the control of reducing the hydraulic braking force of the rear wheels is terminated, thereby reducing unnecessary control load. Additionally, the control of adjusting the hydraulic braking force of the front wheels is terminated, thereby limiting the application of unnecessary load to the front wheel braking mechanism.Incidentally, generally speaking, once the parking brake force has been increased to the level necessary to maintain a steady state, and this level is maintained, the mechanisms of the hydraulic brake 1 and the electric parking brake 2 do not allow the hydraulic braking force, applied in response to the hydraulic brake actuation, to be added to the parking brake force and thus create a load on the rear wheels, even if the driver applies the hydraulic brake. Therefore, in a state where it is possible to maintain a steady state solely through the parking brake force, the load applied to the rear wheel braking mechanism does not increase, even after the control system for reducing the hydraulic braking force applied to the rear wheels is released.

[0029] Incidentally, control unit 102 eliminates the need to adjust the hydraulic braking force applied to the front wheels and reduces the hydraulic braking force applied to the rear wheels when the magnitude of the hydraulic braking force applied to the front wheels is equal to or greater than the magnitude required to maintain steady state. This occurs when the parking brake is engaged, and steady state is maintained solely by the hydraulic braking force. Consequently, the hydraulic braking force of the front wheels is not adjusted if sufficient hydraulic braking force is already ensured to maintain steady state. This reduces unnecessary control load.

[0030] In the configuration described above, the control unit 102, according to the embodiment, controls the hydraulic brake 1 and the electric parking brake 2 such that, as an example, the loads applied to the front wheels and the rear wheels change according to a time diagram to be described below.

[0031] The Fig. Figure 3 is an exemplary time diagram illustrating an example of a change in the load applied to the front wheels and rear wheels, as implemented in the embodiment. Incidentally, in the Fig. 3 (a) represents a change in load over time on the front wheels, and (b) represents a change in load over time on the rear wheels. Additionally, in the Fig. 3 (c) represents a change in time of the presence and absence (ON / OFF) of the hydraulic brake actuation, and (d) represents a change in time of the presence and absence (ON / OFF) of the parking brake actuation. Additionally, in the Fig. 3 (e) represents a time change of a current that is output to the EPB motor 60 depending on the application of the parking brake. Additionally, in the Fig. 3 (f) represents a time change of a displayed pressure of the solenoid valve 33, which functions as a pressure-regulating valve; (g) represents a time change of a displayed pressure of the solenoid valves 35 (namely the solenoid valves 35 of the pressure-adjusting units 34RL and 34RR), which function as holding valves on the rear side; and (h) represents a time change of a displayed pressure of the solenoid valves 36 (namely the solenoid valves 36 of the pressure-adjusting units 34RL and 34RR), which function as pressure-reducing valves on the rear side. Additionally, in the Fig. 3 (i) represents a time change of a drive state (ON / OFF) of the pump motor 40.

[0032] In one example of the Fig. 3. The hydraulic brake is applied at time t1, and the load on the front wheels and the load on the rear wheels begin to increase (see L1, L2, and L3). The load on the front wheels increases to a load f1 in response to the hydraulic brake application. Similarly, the load on the rear wheels increases to a load f2 in response to the hydraulic brake application. Loads f1 and f2 are essentially maintained as long as the hydraulic brake application continues. Subsequently, the load f1 on the front wheels, maintained in response to the hydraulic brake application, is smaller than the minimum load F1 required to maintain a steady state using only the front wheels.

[0033] In one example of the Fig. 3. The parking brake is applied at time t2 after the load on the front wheels and the load on the rear wheels have ceased (see L4). Here, as described above, at time t2 the load f1 on the front wheels, held in response to the hydraulic brake application, is less than the minimum required load (hereafter described as the required load F1) to maintain steady state using only the front wheels. Thus, at time t2, the control unit 102 begins to drive the solenoid valves 33 as the pressure-actuating valves, the solenoid valves 35 (namely the solenoid valves 35 of the pressure-adjusting units 34RL and 34RR) as the holding valves on the back, the solenoid valves 36 (namely the solenoid valves 36 of the pressure-adjusting units 34RL and 34RR) as pressure-reducing valves on the back, and the pump motor 40.In this way, the control unit begins to control the reduction of the hydraulic braking force to the rear wheels and the increase of the hydraulic braking force to the front wheels.

[0034] More precisely, the control unit 102 begins to drive the pump motor 40 and gradually increases the indicated pressure of the solenoid valve 33, acting as the pressure-inducing valve, thereby gradually increasing the hydraulic braking force on the front wheels to a level corresponding to the required load F1 (see L1, L6, and L9). Simultaneously, the control unit 102 suddenly increases the indicated pressure of the solenoid valves 35, acting as the holding valves, preventing the hydraulic braking force on the rear wheels from rising to a value greater than the current value. The control unit then opens the solenoid valves 36, acting as the pressure-reducing valves, reducing the hydraulic braking force on the rear wheels to zero (see L2, L7, and L8). As a result, the load on the front wheels rises to the required load F1 at time t3, and the load on the rear wheels decreases to zero at time t4.Incidentally, the solenoid valves 36 are closed as pressure reducing valves at time t4.

[0035] Incidentally, if the load on the front wheels increases to the required load F1, the load on the front wheels is maintained as such until the control of the solenoid valves 33 and the pump motor 40 is released by the control unit 102 (see L1). Similarly, if the load on the rear wheels decreases to zero, the load on the rear wheels is maintained as such until the control of the solenoid valves 35 and the pump motor 40 is released by the control unit 102 (see L2). In this embodiment, the time t3 at which the load on the front wheels reaches the required load F1 is set to be earlier than the time t4 at which the load on the rear wheels reaches zero. Consequently, the hydraulic braking force of the rear wheels becomes zero before the hydraulic braking force of the front wheels increases to a required level, thus preventing the vehicle from moving.

[0036] If, in the example of the Fig. At time t4, when the load on the rear wheels is reduced to zero, a current begins to flow to the EPB motor 60 (see L5). The current of the EPB motor 60 initially rises sharply as an inrush current, then decreases again to approximately zero, and begins to gradually increase from time t5 after a predetermined delay time, which is unavoidable in the mechanism of the electric parking brake 2. Consequently, the electric parking brake 2 begins to generate the parking braking force on the rear wheels at time t5, and at this time the load on the rear wheels begins to increase (see L2). The load on the rear wheels rises to a minimum required load F2 (hereafter described as the required load F2) to maintain steady state using only the rear wheels. Then, at time t6, when the load on the rear wheels reaches the required load F2, the drive to the EPB motor 60 is stopped.Consequently, the parking brake force of the rear wheels remains on the order of magnitude corresponding to the required load F2, and thus it is possible to maintain the steady state solely by means of the parking brake force of the rear wheels.

[0037] As described above, if it is possible to maintain the steady state solely through the parking brake force of the rear wheels, the adjustment of the hydraulic braking force, which began at time t2—namely, controlling the increase of the hydraulic braking force of the front wheels while reducing the hydraulic braking force of the rear wheels—is terminated. This is particularly relevant in the example of... Fig. 3. When, at time t6, the load on the rear wheels increases to the required load F2, the indicated pressure of solenoid valve 33, acting as the pressurizing valve, is gradually reduced, and the indicated pressure of solenoid valves 35, acting as the holding valves at the rear, is also gradually reduced (see L2, L6, and L7). Then, when, at time t7, the indicated pressures of solenoid valves 33 and 35 have been reduced to zero, the driving of the pump motor 40 is stopped.

[0038] Incidentally, in the example of the Fig. 3. At time t6, when the control of increasing the hydraulic braking force of the front wheels while decreasing the hydraulic braking force of the rear wheels begins to end, the hydraulic brake actuation is still being carried out (see L3). If the load is taken into account as usual, the load in response to the hydraulic brake actuation, which is different from the load in response to the parking brake force, is thus generated on the rear wheels after time t6 (see a dot-dash line L20).However, as described above, generally, once the parking brake force has been fully applied and held, the mechanisms of the hydraulic brake 1 and the electric parking brake 2 do not allow the hydraulic braking force to be added to the parking brake force in response to the application of the hydraulic brake, and thus prevent the load from being applied to the rear wheels, even if the driver applies the hydraulic brake. Therefore, in the example, the... Fig. 3. The load on the rear wheels does not reach the required load F2 or more after time t6 (see L2). Then, in the example, the Fig. 3 the steady state is realized solely by the parking brake force of the rear wheels at a time t8, at which the actuation of the hydraulic brake is completely finished.

[0039] Next, the actuation of the brake control unit 100 according to the embodiment will be described in detail.

[0040] The Fig. Figure 4 is an exemplary flowchart that represents a series of processes performed by the brake control unit 100 according to the embodiment.

[0041] In a processing flow of Fig. 4. First, in S1, the detection unit 101 determines whether the parking brake has been applied or not, specifically whether the electrical signal has been detected in response to an actuation of the EPB switch or lever as described above. This processing of S1 is repeated until the detection unit determines that the parking brake has been applied. Once the detection unit determines that the parking brake has been applied in S1, the processing proceeds to S2.

[0042] In S2, the detection unit 101 determines whether the hydraulic brake is being applied, specifically whether the brake pedal is being pressed or not. If the detection unit in S2 determines that the hydraulic brake is being applied, processing proceeds to S3.

[0043] In S3, the control unit 102 determines whether the load generated on the front wheels in response to the application of the hydraulic brake is less than the minimum required load (required load F1 in the Fig. 3) to maintain the stationary state only by controlling the hydraulic braking force of the front wheels or not.

[0044] If, in S3, the control unit determines that the load applied to the front wheels is less than the required load, the process proceeds to S4. Then, in S4, control unit 102 increases the hydraulic braking force of the front wheels until the load applied to the front wheels reaches the required load. Then, in S5, control unit 102 decreases the hydraulic braking force of the rear wheels until the load applied to the rear wheels becomes zero.

[0045] Incidentally, if in S3 the control unit determines that the load generated on the front wheels is equal to or greater than the required load, the S4 process is not executed, and the process proceeds to S5. In other words, if the control unit determines that the load generated on the front wheels is equal to or greater than the required load in S3, control unit 102 does not perform the process to increase the hydraulic braking force of the front wheels, but instead performs the process to decrease the hydraulic braking force of the rear wheels.

[0046] In S6, control unit 102 determines whether the hydraulic brake force adjustment is complete, as described above, following the processes in S4 and S5 (or just S5). In other words, in S6, control unit 102 determines whether the load on the front wheels increases to the required level and the load on the rear wheels decreases to zero. This S6 process is repeated until the control unit determines that the hydraulic brake force adjustment is complete. Once the control unit determines that the hydraulic brake force adjustment in S6 is complete, the process proceeds to S7.

[0047] In S7, the control unit 102 begins to drive the EPB motor 60. Consequently, the electric parking brake 2 actually begins to generate the parking braking force over the course of the predetermined deceleration time, which inevitably occurs in this mechanism.

[0048] In S8, the control unit 102 determines whether the parking brake force required to maintain the steady state is ensured or not. In other words, in S8, the control unit 102 determines whether the load generated on the rear wheels is at the minimum required load (required load F2 in the Fig.3) increases to maintain the steady state solely through the parking brake force of the rear wheels, or not. This processing of S8 is repeated until the control unit determines that the required parking brake force is ensured. If the control unit then determines in S8 that the required parking brake force is ensured, processing proceeds to S9.

[0049] In S9, the control unit 102 terminates the control of the hydraulic braking forces of the front and rear wheels, which was started in S4 and S5 (or the control of the hydraulic braking force of only the rear wheels, which was started in S5 if S4 was omitted).

[0050] Consequently, it is possible to complete the transition from the stationary state by means of the hydraulic braking forces of the front and rear wheels to the stationary state solely by means of the parking brake force of the rear wheels. The process then ends.

[0051] Incidentally, S2 includes a case where the detection unit determines that the hydraulic brakes will not be applied. In this case, no hydraulic braking force is generated on the front and rear wheels, and therefore it is necessary to quickly generate the parking brake force. If the detection unit determines that the hydraulic brakes will not be applied in S2, processes S10 and S11 are executed similarly to S7 and S8. As a result of executing processes S10 and S11, it is then possible to maintain the steady state solely through the parking brake force of the rear wheels, and thus the processing is terminated.

[0052] As described above, according to the embodiment, the control unit 102 reduces the hydraulic braking force generated on the rear wheels and adjusts the hydraulic braking force generated on the front wheels to a level that allows the vehicle to remain stationary before the parking brake force is generated by the electric parking brake 2 when the parking brake is activated, while the stationary state is maintained solely by the hydraulic braking force generated on both the front and rear wheels. Even if the hydraulic braking force of the rear wheels is zero, it is possible, for example, to maintain the stationary state solely by the hydraulic braking force of the front wheels.Thus, it is possible to reduce the load on the rear wheels due to the overlapping generation of the hydraulic braking force and the parking brake force, while maintaining a more reliable steady state.

[0053] As described above, the control unit 102, according to the embodiment, also causes the electric parking brake 2 to generate the parking brake force after the hydraulic braking force generated on the rear wheels has been reduced to zero. Consequently, it is possible to more reliably avoid the overlapping generation of the hydraulic braking force and the parking brake force on the rear wheels.

[0054] As described above, according to the embodiment, the control unit 102 also terminates the control of reducing the hydraulic braking force of the rear wheels and the control of adjusting the hydraulic braking force of the front wheels when the magnitude of the parking brake force of the rear wheels reaches a level that allows the steady state to be maintained solely by the parking brake force. Consequently, the control of reducing the hydraulic braking force of the rear wheels is terminated, thereby reducing unnecessary control load. Additionally, the control of adjusting the hydraulic braking force of the front wheels is terminated, thereby limiting the application of unnecessary load to the braking mechanism of the front wheels.

[0055] As described above, according to the embodiment, the control unit 102 also omits the adjustment of the hydraulic braking force of the front wheels and reduces the hydraulic braking force of the rear wheels when the magnitude of the hydraulic braking force of the front wheels is equal to or greater than the magnitude required to maintain the steady state, in a case where the parking brake is activated, while the steady state is maintained solely by the hydraulic braking force. Consequently, the hydraulic braking force of the front wheels is not adjusted if sufficient hydraulic braking force is already ensured to maintain the steady state. This makes it possible to reduce unnecessary control load.

[0056] As described above, the control unit 102, according to the embodiment, can control the time at which the EPB motor 60 is driven such that the time at which the hydraulic braking force generated on the rear wheels is reduced to zero coincides with the time at which the parking brake force is generated. As described above, the timing controls enable a rapid transition from the steady state of hydraulic braking force alone to the steady state of parking brake force alone.

Claims

[1] A brake control device that controls a hydraulic brake (1) capable of generating a hydraulic braking force on both the front and rear wheels of a four-wheel drive vehicle, and an electric parking brake (2) capable of generating a parking braking force, different from the hydraulic braking force, on the front wheels or on the rear wheels, the brake control device comprising: a detection unit (101) for detecting an operation of the parking brake to cause the electric parking brake to generate a parking braking force; and a control unit (102) for reducing the hydraulic braking force generated on the front wheels or the rear wheels, characterized by , that the control unit (102) is configured to adjust the hydraulic braking force generated on the other of the front wheels or the rear wheels to a magnitude that enables a stationary state of the vehicle to be maintained before the parking braking force is generated by the electric parking brake (2) when the operation of the parking brake (2) is detected, while the stationary state is maintained only by the hydraulic braking force generated on both the front and rear wheels. [2] A brake control apparatus according to claim 1, wherein the control unit (102) causes the electric parking brake (2) to generate the parking braking force after the hydraulic braking force generated on the front wheels or on the rear wheels has been reduced to zero. [3] A brake control apparatus according to claim 2, wherein the control unit (102) stops the control of reducing the hydraulic braking force generated to the front wheels or the rear wheels and stops the control of adjusting the hydraulic braking force generated to the other of the front wheels or the rear wheels when a magnitude of the parking braking force reaches a magnitude that enables the stationary state to be maintained only by the parking braking force. [4] A brake control apparatus according to any one of claims 1 to 3, wherein the control unit (102) omits adjustment of the hydraulic braking force generated to the other of the front wheels or the rear wheels and reduces the hydraulic braking force generated to the front wheels or the rear wheels when the magnitude of the hydraulic braking force generated to the other of the front wheels or the rear wheels is equal to or greater than the magnitude enabling the steady state to be maintained in a case where the operation of the parking brake (2) is detected while the steady state is maintained only by the hydraulic braking force.

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