Brake booster system

Abstract

Even in hybrid vehicles, it efficiently assists braking without reducing the durability of the brake booster. [Solution] A brake booster system 30 is installed in a hybrid vehicle 1 having a supercharger 14, comprising a brake booster 32 that boosts the brake pedal force, and a positive pressure tank 33 that secures positive pressure to drive the brake booster 32, wherein the positive pressure tank 33 is supplied with positive pressure via a first passage 36 that branches off from upstream of the intake throttle 17 of the internal combustion engine 11.

Description

Technical Field

[0005] , ,

[0001] The present invention relates to a brake booster system.

Background Art

[0002] A brake booster that assists a driver's brake pedal operation during vehicle braking is known. For example, Patent Document 1 discloses a brake booster that secures negative pressure from the downstream side of a throttle valve provided in an intake passage of an engine and uses the negative pressure to boost the driver's braking force.

[0003] By the way, in a hybrid vehicle equipped with an engine and a motor as a driving source for traveling, since the engine basically stops during deceleration, negative pressure supplied to the brake booster may not be secured. Therefore, in such a vehicle, a negative pressure storage tank for securing negative pressure in advance is mounted, and the throttle valve is closed and controlled to perform engine motoring by a generator, or the engine is restarted to generate negative pressure and secure it in the negative pressure storage tank.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, with the conventional technologies described above, the engine is motored or driven solely for the purpose of securing negative pressure, which increases the number of engine starts and engine running time during driving, thus reducing the advantages of hybrid vehicles. Furthermore, engine motoring consumes battery power, which may lead to a decrease in fuel efficiency. In addition, if the engine is equipped with a supercharger, negative pressure cannot be secured even if the engine is running when supercharged. Moreover, a positive pressure booster configuration that utilizes exhaust gas discharged from the engine as positive pressure is also conceivable, as described in Patent Document 2, but this would supply high-temperature, unpurified exhaust gas to the brake booster, which may lead to a decrease in the durability of the brake booster.

[0006] This invention has been made in view of these problems, and its objective is to provide a brake booster system that can efficiently assist braking operations without reducing the durability of the brake booster, even in hybrid vehicles. [Means for solving the problem]

[0007] To achieve the above objective, the brake booster system of the present invention is a brake booster system mounted on a hybrid vehicle having a supercharger, comprising: a brake booster device that amplifies the brake pedal force; and a positive pressure tank that secures positive pressure for driving the brake booster device, wherein the positive pressure is supplied to the positive pressure tank via a first passage branching from upstream of the intake throttle of an internal combustion engine. [Effects of the Invention]

[0008] Hybrid vehicles are often driven at their discretionary fuel consumption point (high load) while the engine is running, so positive pressure can be unconditionally secured during that period. The brake booster system according to the present invention is equipped with a positive pressure tank that secures positive pressure used for brake boost control during braking in a hybrid vehicle with a supercharger, and positive pressure is supplied to the positive pressure tank via a first passage that branches off from upstream of the intake throttle of the internal combustion engine. For this reason, the brake booster system according to the present invention can easily secure positive pressure even in a hybrid vehicle where the engine may stop while driving, and can obtain brake boost with positive pressure without supplying exhaust gas to the brake booster as in the conventional technology. Accordingly, the brake booster system according to the present invention can efficiently assist braking operations even in a hybrid vehicle without reducing the durability of the brake booster. [Brief explanation of the drawing]

[0009] [Figure 1] This is a block diagram of the drivetrain and brake booster system of the hybrid vehicle related to this disclosure. [Figure 2] This is a conceptual diagram illustrating the multiple drive modes of a brake booster system. [Figure 3] This is a flowchart illustrating the control of the brake booster system. [Figure 4] This is a flowchart representing the subroutine for ensuring negative pressure. [Figure 5] This is a flowchart representing the subroutine for ensuring positive pressure. [Modes for carrying out the invention]

[0010] The embodiments will be described in detail below with reference to the drawings. However, this disclosure is not limited to the content described below, and can be modified and implemented as such without altering its essence. Furthermore, the drawings used in describing the embodiments are schematic representations of the components, and may have been partially emphasized, enlarged, reduced, or omitted to enhance understanding, and may not accurately represent the scale or shape of the components.

[0011] Figure 1 is a block diagram of the drivetrain and brake booster system of the hybrid vehicle 1 according to this disclosure. The hybrid vehicle 1 is a hybrid-type electric vehicle (HEV) that drives the drive wheels W by at least one of the internal combustion engine and motor described later, and can switch between series driving, parallel driving, and EV driving depending on the driving conditions. The hybrid vehicle 1 may also be a plug-in hybrid vehicle (PHEV) that can be charged from an external source and can supply power to an external source.

[0012] Hybrid vehicle 1 includes, in general terms, an intake and exhaust system 10, a drive system 20, a brake booster system 30, and an ECU 40, as part of the brake booster configuration described later. In addition to the configuration shown, hybrid vehicle 1 is also equipped with various components that are commonly found in hybrid vehicles.

[0013] <Intake and Exhaust System> The intake and exhaust system 10 includes an internal combustion engine 11, an intake passage 12, and an exhaust passage 13. A supercharger 14 is also provided so as to span the intake passage 12 and the exhaust passage 13. Furthermore, an air cleaner 15, an intercooler 16, an intake throttle 17, an intake port 18, and an intake manifold pressure sensor 19 are provided along the flow path of the intake passage 12.

[0014] The internal combustion engine 11 is, for example, a direct injection gasoline engine that injects gasoline as fuel into the combustion chamber, and functions as a driving power source for the hybrid vehicle 1 together with the motor. In addition, in series driving, it drives the generator 23 to generate power for power generation. Further, as will be described later in detail, the internal combustion engine 11 generates the positive pressure and negative pressure necessary for driving the brake booster system 30.

[0015] In the intake passage 12, the intake air taken in from the atmosphere is filtered by the air cleaner 15, compressed by a compressor (not shown) of the supercharger 14, cooled by the intercooler 16, and supplied to the intake port 18 of the internal combustion engine 11 through the intake throttle 17. At this time, the intake air amount taken into the internal combustion engine 11 is controlled according to the valve opening degree of the intake throttle 17. Further, the intake manifold pressure sensor 19 monitors the intake air amount for controlling the internal combustion engine 11 in a so-called D-jetronic system by measuring the pressure of the intake air in the intake port.

[0016] In the exhaust passage 13, the exhaust gas discharged from the internal combustion engine 11 is discharged to the atmosphere through the supercharger 14 and a purification device (not shown). At this time, the exhaust gas rotates a turbine (not shown) in the supercharger 14 to drive the compressor of the supercharger 14 interlocked with the turbine and supercharge the intake air.

[0017] <Drive system> The drive system 20 includes a motor 21, a clutch 22, a generator 23, an inverter 24, and a battery 25.

[0018] The motor 21 is a traction motor that can drive the drive wheels W via the axle when power is supplied, and is also a motor generator (electric generator) that can regenerate electricity during deceleration of the hybrid vehicle 1.

[0019] The clutch 22 is a power transmission device that transmits or cuts off the power from the internal combustion engine 11 to the drive wheels W, and controls whether to use the driving force of the internal combustion engine 11 for the running of the hybrid vehicle 1.

[0020] The generator 23 is a generator that can generate electricity by the power output from the internal combustion engine 11, and controls the power generation amount within the output range of the internal combustion engine 11 by controlling the power generation load. Further, the generator 23 is configured as an electric generator capable of engine motoring that rotationally drives the internal combustion engine 11 by the power of the battery 25.

[0021] The inverter 24 is a power conversion device that converts DC power and AC power, and can drive the motor 21 by supplying the power output from at least one of the generator 23 and the battery 25 to the motor 21, and can charge the battery 25 by supplying the power output from at least one of the motor 21 and the generator 23 to the battery 25.

[0022] The battery 25 is a secondary battery composed of a lithium ion battery or a nickel hydrogen battery, and outputs the power necessary for driving the motor 21, and also supplies power to various electrical equipment (not shown) mounted on the hybrid vehicle 1.

[0023] With the above configuration, the drive system 20 can selectively switch a plurality of driving control modes according to the running state of the hybrid vehicle 1 by cooperative control with the internal combustion engine 11. For example, at the start of the hybrid vehicle 1, in a state where the driving of the internal combustion engine 11 and the generator 23 is stopped, by driving and controlling the motor 21 with the power of the battery 25, it is possible to perform high energy efficiency EV driving in a low speed range.

[0024] Also, when performing running with a relatively low acceleration requirement, the clutch 22 disconnects the axle and the internal combustion engine 11, and assigns the power generated by the generator 23 with the power of the internal combustion engine 11 to charge the battery 25 via the inverter 24, and can switch to series running in which the motor 21 is driven and controlled with the power of the battery 25.

[0025] Furthermore, when driving with relatively high acceleration requirements or at high speeds, the clutch 22 connects the axle to the internal combustion engine 11, allowing the vehicle to be driven by the power of the internal combustion engine 11. Additionally, the vehicle can switch to parallel driving mode, where the motor 21 is driven by the power of the battery 25 to assist in driving, as needed.

[0026] <Brake booster system> The brake booster system 30 includes a brake pedal 31, a brake booster 32, a positive pressure tank 33, a negative pressure tank 34, a first valve V1, a second valve V2, an atmospheric outlet pipe 35, a first passage 36, a second passage 37, and a third valve V3.

[0027] The brake pedal 31 is located inside the passenger compartment of the hybrid vehicle 1 and is pressed by the driver when braking the vehicle. The brake booster 32 is a mechanism that amplifies the driver's braking force applied to the brake pedal 31. More specifically, the brake booster 32 includes an operating rod OR, a master cylinder MS, an amplification chamber BC, a control chamber CC, a valve plunger VP, and a power piston PIS.

[0028] The operating rod OR is connected at one end to the brake pedal 31 and at the other end to the master cylinder MS, thereby transmitting the pressing force of the brake operation to the master cylinder MS. The master cylinder MS is connected to the brake caliper on the drive wheel W via hydraulic pipes (neither of which are shown), thereby applying braking force to the drive wheel W.

[0029] An amplification chamber BC and a control chamber CC are provided between the master cylinder MS and the brake pedal 31. The amplification chamber BC is divided into a front chamber B1 and a rear chamber B2 by a power piston PIS connected to an operating rod OR. The power piston PIS amplifies the braking force applied to the brake pedal 31 via the operating rod OR when the pressure in the rear chamber B2 is relatively higher than that in the front chamber B1. A return spring (not shown) is provided in the front chamber B1 to press against the power piston PIS, so that when there is no brake operation, the brake pedal 31 is pushed back to its original position via the operating rod OR.

[0030] The control room CC is provided with a flow path for supplying positive pressure or atmospheric pressure to the rear chamber B2, and the pressure in the rear chamber B2 is controlled in conjunction with the operation of the brake pedal 31 by opening or closing the flow path via a valve plunger VP connected to the operating rod OR.

[0031] The positive pressure tank 33 is a tank that secures positive pressure in advance so that positive pressure can be supplied to the rear chamber B2 via the control room CC. The positive pressure tank 33 is equipped with a positive pressure sensor 33s that measures the internal pressure, and monitors whether or not it is in a state where positive pressure can be supplied to the amplification chamber BC.

[0032] The negative pressure tank 34 is a tank that secures negative pressure in advance so that negative pressure can be supplied to the front chamber B1. The negative pressure tank 34 is equipped with a negative pressure sensor 34s that measures the internal pressure and monitors whether or not it is in a state where negative pressure can be supplied to the amplification chamber BC.

[0033] The first valve V1 is a three-way valve located in the flow path from the positive pressure tank 33 to the brake booster 32. The second valve V2 is also a three-way valve located in the flow path from the negative pressure tank 34 to the brake booster 32. The atmospheric vent pipe 35 is a T-shaped pipe, with both ends connected to the first valve V1 and the second valve V2, respectively, and has an opening in the middle that is vented to the atmosphere.

[0034] Therefore, the first valve V1 can switch between a state in which positive pressure is supplied from the positive pressure tank 33 to the rear chamber B2 via the control chamber CC, and a state in which the rear chamber B2 is connected to the atmospheric vent pipe 35 to bring the inside of the rear chamber B2 to atmospheric pressure. Similarly, the second valve V2 can switch between a state in which negative pressure is supplied from the negative pressure tank 34 to the front chamber B1, and a state in which the front chamber B1 is connected to the atmospheric vent pipe 35 to bring the inside of the front chamber B1 to atmospheric pressure.

[0035] The first passage 36 is provided upstream of the intake passage 12 between the supercharger 14 and the intake throttle 17, and in this embodiment, it branches off from between the supercharger 14 and the intake throttle 17 of the intake passage 12. It is a pipe that can supply the positive pressure generated between the supercharger 14 and the intake throttle 17 to the positive pressure tank 33 when the internal combustion engine 11 is driven together with the supercharger 14.

[0036] The second passage 37 is provided so as to branch off from the intake throttle 17 of the intake passage 12, and is a pipe capable of supplying the negative pressure generated between the intake throttle 17 and the internal combustion engine 11 to the negative pressure tank 34 when the internal combustion engine 11 is not being supercharged.

[0037] The first passage 36 and the second passage 37 are connected to the positive pressure tank 33 and the negative pressure tank 34, respectively, via a third valve V3 which acts as a four-way valve. As a result, when positive pressure is generated in the first passage 36, the third valve V3 connects the first passage 36 to the positive pressure tank 33, thereby ensuring positive pressure in the positive pressure tank 33. Similarly, when negative pressure is generated in the second passage 37, the third valve V3 connects the second passage 37 to the negative pressure tank 34, thereby ensuring negative pressure in the negative pressure tank 34. The third valve V3 also blocks communication between the passages during periods when positive and negative pressure are not being maintained.

[0038] The ECU40 is an electronic control unit that performs overall control of the hybrid vehicle 1, and is composed of input / output devices, memory devices (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), etc. The ECU40 controls the hybrid vehicle 1 in multiple driving control modes as described above by acquiring and controlling the status of each component of the intake / exhaust system 10 and the drive system 20.

[0039] Furthermore, the ECU 40 in this embodiment controls the third valve V3 according to the state of the intake and exhaust system 10 and the drive system 20, and the pressure of the intake manifold pressure sensor 19, thereby ensuring positive pressure in the positive pressure tank 33 and negative pressure in the negative pressure tank 34 before the driver operates the foot brake. Then, when the brakes are applied, the ECU 40 controls the first valve V1 and the second valve V2 to boost the brake pedal force in the brake booster system 30.

[0040] Furthermore, the ECU40 may be composed of multiple electronic control units, each responsible for a specific function. For example, the brake boosting function may be managed by the brake ECU in conjunction with other brake control functions.

[0041] Next, the drive modes of the brake booster system 30 will be described. Figure 2 is a conceptual diagram showing the multiple drive modes of the brake booster system 30. The brake booster system 30 operates in either positive pressure booster mode, negative pressure booster mode, or positive / negative pressure booster mode, depending on the circumstances under which the brakes are applied.

[0042] The positive pressure boosting mode is a mode in which, when there is sufficient positive pressure in the positive pressure tank 33, positive pressure is supplied from the positive pressure tank 33 to the rear chamber B2 via the first valve V1, and the front chamber B1 is connected to the atmospheric vent pipe 35 via the second valve V2. As a result, in the amplification chamber BC, the pressure in the rear chamber B2, which is under positive pressure, is higher than that in the front chamber B1, which is under atmospheric pressure, making boosting possible. The negative pressure boosting mode is a mode in which, when there is sufficient negative pressure in the negative pressure tank 34, negative pressure is supplied from the negative pressure tank 34 to the front chamber B1 via the second valve V2, and the rear chamber B2 is connected to the atmospheric pressure vent pipe 35 via the first valve V1. As a result, in the amplification chamber BC, the pressure in the rear chamber B2, which is at atmospheric pressure, is higher than that in the negative pressure front chamber B1, making boosting possible.

[0043] The positive pressure / negative pressure boosting mode is a mode used when stronger braking force than that required in the positive pressure boosting mode and the negative pressure boosting mode is needed. In this mode, positive pressure is supplied from the positive pressure tank 33 to the rear chamber B2 via the first valve V1, and negative pressure is supplied from the negative pressure tank 34 to the front chamber B1 via the second valve V2. As a result, in the amplification chamber BC, the high pressure difference between the negative pressure front chamber B1 and the positive pressure rear chamber B2 enables stronger boosting than in the positive pressure boosting mode and the negative pressure boosting mode.

[0044] Next, the operating procedure of the brake booster system 30 will be explained. Figure 3 is a flowchart showing the control of the brake booster system 30. The ECU 40 constantly repeats this procedure while the ignition of the hybrid vehicle 1 is ON, thereby performing the preparation for boosting before braking and the brake boosting control during braking.

[0045] When the operation procedure of the brake booster system 30 is initiated, the ECU 40 determines whether there is an emergency stop signal for the hybrid vehicle 1, such as an airbag deployment flag (step S1). If it is determined that the airbag deployment flag is ON (Yes in step S1), the ECU 40 obtains the pressure Pp of the positive pressure tank 33 via the positive pressure sensor 33s and the pressure Pn of the negative pressure tank 34 via the negative pressure sensor 34s. The ECU 40 also determines whether the positive pressure Pp is greater than or equal to a predetermined first threshold Th1 and the negative pressure Pn is less than or equal to a predetermined second threshold Th2 (step S2).

[0046] Here, the first threshold Th1 is a pressure threshold set in advance to determine whether the positive pressure Pp is high enough to drive the brake booster system 30 in positive pressure booster mode. The second threshold Th2 is a pressure threshold set in advance to determine whether the negative pressure Pn is low enough to drive the brake booster system 30 in negative pressure booster mode.

[0047] If the ECU 40 determines that the positive pressure Pp is greater than or equal to the first threshold Th1 and the negative pressure Pn is less than or equal to the second threshold Th2 (Yes in step S2), it drives the brake booster system 30 in positive / negative pressure booster mode during brake operation (step S3). This allows for sufficiently strong braking force to be applied to the drive wheels W even with a small amount of brake pedal pressure, thereby mitigating damage in emergencies such as vehicle collisions.

[0048] If the airbag deployment flag is OFF (No in step S1), or if at least one of the positive pressure Pp and the negative pressure Pn is insufficient for power assist control (No in step S2), the ECU 40 determines whether the internal combustion engine 11 is running (step S4).

[0049] If the internal combustion engine 11 is in operation (Yes in step S4), the ECU 40 obtains pressure Pi from the intake manifold pressure sensor 19 and determines whether the pressure Pi is less than or equal to a predetermined fourth threshold Th4 (step S5). Here, the fourth threshold Th4 is a pressure that is not sufficient to supply positive pressure to the rear chamber B2.

[0050] Then, if the pressure Pi is not below the fourth threshold Th4 (No in step S5), the ECU 40 assumes that it is in a state where it can supply positive pressure to the brake booster system 30 from upstream of the intake throttle 17, and drives the brake booster system 30 in positive pressure booster mode during brake operation, regardless of the pressure Pp in the positive pressure tank 33.

[0051] On the other hand, if the internal combustion engine 11 is stopped (No in step S4), or if the internal combustion engine 11 is running but the pressure Pi is below the fourth threshold Th4 (Yes in step S5), the ECU 40 determines whether the pressure Pp of the positive pressure tank 33 is below a predetermined third threshold Th3 (step S7). Here, the third threshold Th3 is set in advance as a value slightly higher than the first threshold Th1, and is a pressure threshold for detecting that the positive pressure Pp has decreased even though the positive pressure boosting mode can be selected.

[0052] The ECU 40 determines that if the pressure Pp of the positive pressure tank 33 is higher than the third threshold Th3 (No in step S7), it is possible to drive the brake booster system 30 with the pressure Pp of the positive pressure tank 33, and drives the brake booster system 30 in positive pressure booster mode during brake operation, regardless of the operating state of the internal combustion engine 11 and the pressure Pi of the intake manifold pressure sensor 19.

[0053] If the pressure Pp in the positive pressure tank 33 is less than or equal to the third threshold Th3 (Yes in step S7), the ECU 40 determines whether the pressure Pn in the negative pressure tank 34 is greater than or equal to the second threshold Th2 (step S8). If it is determined that the pressure Pn in the negative pressure tank 34 is less than the second threshold Th2 (No in step S8), the ECU 40 determines that it is possible to drive the brake booster system 30 with the pressure Pn in the negative pressure tank 34, and drives the brake booster system 30 in negative pressure booster mode when the brakes are applied (step S9).

[0054] If the pressure Pn of the negative pressure tank 34 is equal to or greater than the second threshold Th2, the ECU 40 checks the remaining state of charge (SOC) of the battery 25 and determines whether the SOC is equal to or greater than a predetermined SOC threshold Tsoc (step S10). Here, the SOC threshold Tsoc is a threshold of SOC that is arbitrarily set in advance to check whether the battery 25 can be sufficiently charged with power. If the remaining SOC is equal to or greater than the SOC threshold Tsoc (Yes in step S10), the ECU 40 controls the negative pressure securing by engine motoring, which will be described next (step S11), and then drives the brake booster system 30 in negative pressure booster mode when the brake is applied (step S9).

[0055] Figure 4 is a flowchart representing the subroutine for ensuring negative pressure. When the subroutine for ensuring negative pressure is started, the ECU 40 checks the pressure Pp of the positive pressure tank 33 and determines whether the pressure Pp is less than or equal to the first threshold Th1 (step S20).

[0056] If the pressure Pp is less than or equal to the first threshold Th1 (Yes in step S20), the brake booster system 30 cannot be driven by either positive or negative pressure during brake operation. Therefore, the ECU 40 determines that there is an urgent need to secure negative pressure and generates negative pressure upstream of the intake throttle 17 by engine motoring and supplies negative pressure to the negative pressure tank 34 (step S21).

[0057] However, since engine motoring consumes power from the battery 25, it leads to a decrease in the fuel efficiency of the hybrid vehicle 1. Therefore, if the pressure Pp of the positive pressure tank 33 is higher than the first threshold Th1 (No in step S20), the ECU 40 controls the system to drive the brake booster system 30 in a way that consumes as little power as possible by following the procedure below.

[0058] The ECU 40 determines whether the hybrid vehicle 1 is in parallel driving mode (step S22), and if it is in parallel driving mode (Yes in step S22), it determines whether or not the brakes have been applied (step S23). If the brakes have been applied while the vehicle is in parallel driving mode (Yes in step S23), the ECU 40 performs braking control in positive pressure booster mode and cuts off the engine fuel to the internal combustion engine 11 while the supercharger 14 is stopped. At this time, since the internal combustion engine 11 is connected to the axle via the clutch 22, it can generate negative pressure upstream of the internal combustion engine 11 by continuing to rotate even when the fuel is cut off (step S24).

[0059] On the other hand, during periods when no brake operation is performed (No in step S23), braking control can be performed in positive pressure boost mode, so the system waits until an opportunity arises to efficiently secure positive or negative pressure.

[0060] Furthermore, if the vehicles are not in parallel driving mode (No in step S22), the ECU 40 determines whether or not hybrid vehicle 1 is in series driving mode (step S25), and if it is in series driving mode (Yes in step S25), it determines whether or not the brakes have been applied (step S26).

[0061] If braking is performed during series driving (Yes in step S26), regenerative braking by motor 21 generates electricity, and while braking control is performed in positive pressure booster mode, the combustion of the internal combustion engine 11 and the supercharger 14 are stopped, and the internal combustion engine 11 is motored with regenerative power, thereby generating a negative pressure upstream of the intake throttle 17 (step S27). This makes it possible to secure a negative pressure by motoring while suppressing the power consumption of the battery 25.

[0062] Furthermore, during periods when no brake operation is performed during series driving (No in step S26), braking control can be performed in positive pressure boost mode, so the system waits until an opportunity arises to efficiently secure positive or negative pressure.

[0063] Furthermore, if hybrid vehicle 1 is not in series driving mode (No in step S25), the ECU 40 determines that hybrid vehicle 1 is in EV mode. If it is in EV mode, positive pressure is maintained by starting the internal combustion engine 11 while driving the turbocharger 14 in a stopped state.

[0064] Returning to Figure 3, if the remaining SOC is less than the SOC threshold Tsoc (No in step S10), the ECU 40 performs the control to ensure positive pressure by engine supercharging operation, which will be described next (step S12), and then drives the brake booster system 30 in positive pressure booster mode when the brakes are applied (step S6).

[0065] Figure 5 is a flowchart representing the positive pressure maintenance subroutine. When the positive pressure maintenance subroutine is started, the ECU 40 determines whether or not the internal combustion engine 11 is running (step S30). If the internal combustion engine 11 is running (Yes in step S30), the ECU 40 determines whether or not the pressure Pi of the intake manifold pressure sensor 19 is greater than or equal to the fourth threshold Th4 (step S31).

[0066] If the pressure Pi is greater than or equal to the fourth threshold Th4 (Yes in step S31), the ECU 40 assumes that positive pressure is being generated upstream of the intake throttle 17 and ensures positive pressure by connecting the first passage 36 to the positive pressure tank 33 (step S32).

[0067] If the internal combustion engine 11 is stopped (No in step S30), the ECU 40 drives the internal combustion engine 11 (step S33) and then controls the engine to raise its operating state to the supercharged range (step S34). As a result, positive pressure is generated upstream of the intake throttle 17, allowing the ECU 40 to maintain positive pressure in the positive pressure tank 33.

[0068] Furthermore, if the pressure Pi is less than the fourth threshold Th4 despite the internal combustion engine 11 being in operation (No in step S31), the ECU 40 determines that the operating state of the internal combustion engine 11 is insufficient to ensure positive pressure and performs control to raise the operating state of the internal combustion engine 11 to the supercharged region to ensure positive pressure (step S34).

[0069] Furthermore, if the operating state of the internal combustion engine 11 is increased to the supercharged range in step S34, and the output of the internal combustion engine 11 becomes greater than the vehicle's required output, the excess output of the internal combustion engine 11 that exceeds the vehicle's required output can be consumed by increasing the power generation load of the generator 23. The positive pressure maintenance subroutine is executed when the remaining SOC is less than the SOC threshold Tsoc, so the power generated by increasing the power generation load of the generator 23 can be used to charge the battery 25.

[0070] The ECU 40 repeatedly executes a series of control operations shown in Figures 3 to 5 while the ignition of the hybrid vehicle 1 is ON, thereby ensuring at least one of positive and negative pressure before braking, and maintaining a state in which brake boost control can be performed.

[0071] As described above, the brake booster system 30 according to this disclosure is equipped with a positive pressure tank 33 that secures positive pressure for use in brake booster control during braking in a hybrid vehicle 1 having a supercharger 14, and positive pressure is supplied to the positive pressure tank 33 via a first passage 36 that branches off from upstream of the intake throttle 17 of the internal combustion engine 11. Since the hybrid vehicle 1 is often operated at approximately the best fuel efficiency point (high load) while the engine is running, positive pressure can be secured unconditionally during that period. For this reason, the brake booster system 30 according to this disclosure can easily secure positive pressure even in a hybrid vehicle 1 in which the internal combustion engine 11 basically stops during deceleration. Furthermore, brake boosting can be obtained with positive pressure without supplying exhaust gas to the brake booster 32 as in the prior art. Accordingly, the brake booster system 30 according to this disclosure can efficiently assist braking operations even in a hybrid vehicle 1 without reducing the durability of the brake booster 32.

[0072] Furthermore, the brake booster system 30 includes a negative pressure tank 34 that secures negative pressure for use in booster control during braking. Negative pressure is supplied to the negative pressure tank 34 via a second passage 37 that branches off from downstream of the intake throttle 17 when the internal combustion engine 11 is started and stopped. For example, even if a situation arises where positive pressure cannot be secured in the positive pressure tank 33, such as when the internal combustion engine 11 is started or stopped, negative pressure can be secured from downstream of the intake throttle 17. Therefore, by configuring the booster control by the positive pressure tank 33 and the booster control by the negative pressure tank 34 to complement each other, the brake booster system 30 can minimize situations in which booster control cannot be performed.

[0073] Furthermore, the brake booster system 30 performs boost control in the positive pressure booster mode described above when the hybrid vehicle 1 is braking and the positive pressure is above a predetermined first threshold Th1 and the negative pressure is below a predetermined second threshold Th2. As a result, the brake booster system 30 can prioritize applying the positive pressure booster mode, which uses the positive pressure that is easier to secure while the hybrid vehicle 1 is running, during braking, even if sufficient negative pressure can be secured in the negative pressure tank 34, as long as sufficient positive pressure can be secured in the positive pressure tank 33.

[0074] Furthermore, the brake booster system 30 ensures negative pressure in the negative pressure tank 34 by engine motoring (step S21) if the positive pressure in the positive pressure tank 33 is less than or equal to a predetermined first threshold Th1 (Yes in step S20) and the negative pressure in the negative pressure tank 34 is greater than or equal to a predetermined second threshold Th2 (No in step S8). This allows the brake booster system 30 to ensure negative pressure by engine motoring as an emergency measure, even if it is not possible to ensure positive pressure and negative pressure in the positive pressure tank 33 and the negative pressure tank 34, respectively.

[0075] Furthermore, when the hybrid vehicle 1 is braking, if the positive pressure in the positive pressure tank 33 is below a predetermined third threshold (Yes in step S7) and above a predetermined first threshold Th1 (No in step S20), and the negative pressure in the negative pressure tank 34 is above a predetermined second threshold Th2 (Yes in step S8), the brake booster system 30 drives the brake booster 32 in positive pressure boost mode and drives the internal combustion engine 11 with the supercharger 14 stopped to secure negative pressure (step S24 or step S27). This allows the brake booster system 30 to suppress the consumption of fuel from the internal combustion engine 11 and power from the battery 25 even when it is necessary to generate negative pressure.

[0076] Furthermore, when a collision is detected by the hybrid vehicle 1, the brake booster system 30 is driven in a positive pressure / negative pressure booster mode that uses both positive and negative pressure (step S3), thereby applying a sufficiently strong braking force to the drive wheels W even with a small amount of brake pedal pressure, thereby mitigating collision damage. [Explanation of Symbols]

[0077] 1. Hybrid vehicle 11 Internal Combustion Engine 14 Supercharger 17 Intake throttle 19. Intake manifold pressure sensor 21 Motor 24 Inverters 25 batteries 30 Brake Booster System 32 Brake booster 33 Positive pressure tank 33s positive pressure sensor 34. Vacuum Tank 34s negative pressure sensor 35. Open-air pipe 36 1st aisle 37 2nd aisle 40 ECU B1 Anterior chamber B2 rear room W drive wheels

Claims

1. A brake booster system installed in a hybrid vehicle equipped with a supercharger, A brake booster that doubles the braking force, The system includes a positive pressure tank that secures positive pressure for driving the brake booster, The positive pressure tank is supplied with the positive pressure through a first passage branching off from upstream of the intake throttle of an internal combustion engine, and is part of a brake booster system.

2. The system includes a negative pressure tank that secures negative pressure for driving the brake booster, The brake booster system according to claim 1, wherein the negative pressure tank is supplied with negative pressure via a second passage branching from downstream of the intake throttle when the internal combustion engine is started and stopped.

3. The brake booster system according to claim 2, wherein, during braking of the hybrid vehicle, the positive pressure drives the brake booster when the positive pressure is above a predetermined first threshold and the negative pressure is below a predetermined second threshold.

4. The brake booster system according to claim 2, wherein when the positive pressure is below a predetermined first threshold and the negative pressure is above a predetermined second threshold, the negative pressure is maintained in the negative pressure tank by engine motoring.

5. The brake booster system according to claim 2, wherein, during braking of the hybrid vehicle, when the positive pressure is below a predetermined third threshold and above a predetermined first threshold, and the negative pressure is above a predetermined second threshold, the brake booster is driven with the positive pressure, and the internal combustion engine is driven with the supercharger stopped to secure the negative pressure.

6. The brake booster according to claim 2, wherein the brake booster is driven by both positive and negative pressure when a collision is detected in the hybrid vehicle.

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