Braking system for a motor vehicle, associated operating procedure and motor vehicle

Abstract

Braking system (2) for a motor vehicle, in particular a scooter or a motorcycle, with at least one front wheel (122), one rear wheel (123), with at least one front wheel brake (10) and one rear wheel brake (18), a control unit for controlling the brake pressures at the respective front wheel brake (10) and the rear wheel brake (18), and a primary actuation device which actuates both the respective front wheel brake (10) and the rear wheel brake (18) via the control unit, wherein an electric motor (84) driving the motor vehicle is provided, the drive shaft of which is connected to the rear axle (88) of the motor vehicle, wherein the control unit is configured such that, when the primary actuation device is actuated, it operates the electric motor (84) as a generator to generate recuperative braking torque on the rear axle (88), wherein a secondary actuation device is provided via which the rear wheel brake (18) is actuated.

Description

[0001] The invention relates to a braking system for a motor vehicle, in particular a scooter or a motorcycle, having at least one front wheel, one rear wheel, having at least one front wheel brake and one rear wheel brake, a control unit for controlling the braking pressures at the respective front wheel brake and the rear wheel brake, and a primary actuating device which controls both the respective front wheel brake and the rear wheel brake via the control unit.

[0002] Individual transport plays an important role in road traffic. The use of a motor vehicle offers its driver maximum mobility, flexibility, and independence. Motor vehicles include cars, but also single-track motorcycles. These include, for example, motorcycles and scooters. There are also motorized tricycles. In a so-called trike, a front wheel is used for steering, while the rear axle is equipped with two wheels mounted at a relatively wide distance from each other. In an alternative variant, a motorized tricycle has one rear wheel and two front wheels, which are used for steering. Depending on the distance between the two front wheels, such a tricycle is classified as a single- or two-track vehicle or scooter.

[0003] Modern developments in the automotive sector include new and alternative drive technologies. For environmental reasons and due to the limited availability of fossil fuels and raw materials, hybrid systems, which combine a combustion engine with an electric motor, are increasingly being used instead of pure combustion engines. However, electric motors can also be used as such to power motor vehicles. In addition to their good environmental compatibility and high efficiency, the electric motor has the particular advantage over combustion engines that they deliver maximum torque even at low speeds.

[0004] For safety reasons, the law requires two independent brake circuits for motor vehicles. This ensures that if one of the two brake circuits fails, for example due to a leak in a brake line, the other brake circuit is still available for braking. This legal requirement is usually implemented in modern cars with the help of a tandem master cylinder. The tandem master cylinder contains two pistons arranged one behind the other, which are coupled to one another in terms of movement; each piston exerts braking pressure on the front and rear wheel brakes. If one of the brake circuits fails, for example due to a leak, sufficient brake pressure can still be built up in the other brake circuit to at least provide reduced braking. The anti-lock braking system (ABS) stabilizes the vehicle during braking by protecting the individual wheels from locking.ABS systems are common in both cars and motorcycles.

[0005] Motorcycles are usually equipped with two separate brake circuits, associated brakes, and associated control devices. Typically, the front brake is operated by a handbrake lever, while the rear brake is operated by a foot pedal. In the simplest case, these control devices act exclusively on each brake, so it is the rider's responsibility to distribute the required braking force as optimally as possible between the two brakes during a braking maneuver.

[0006] An integral brake provides the driver with significantly greater safety and comfort. With an integral brake, at least one of the actuating devices controls both brakes simultaneously. If this applies to both actuating devices, it is referred to as a fully integral brake; if only one of the two actuating devices activates both brakes, it is referred to as a partially integral brake.

[0007] Integral brakes can be implemented in different ways. In the simplest case of a hydraulic brake system, the brake fluid is distributed between the two brakes in a fixed ratio when the brake is applied. Alternatively, one brake can be actuated hydraulically, while the other brake is actively controlled, i.e., "by wire" or electrohydraulically. Such an integral brake is known, for example, from DE 10 2007 025 273 A1.

[0008] Conventional integral braking systems typically use standard components. Drum or disc brakes are typically used, converting kinetic energy into thermal energy through friction during deceleration of the vehicle. The thermal energy generated during braking by conventional integral braking systems is dissipated into the environment and cannot be further utilized.

[0009] The document DE 10 2008 017 478 A1 discloses a method for operating a vehicle braking system for motor vehicles with hybrid drive or electric drive.

[0010] The document DE 10 2007 051 559 A1 discloses a bicycle with electric auxiliary drive.

[0011] The document US 2005 / 0143878 A1 discloses an apparatus and method for controlling regenerative braking of an electric vehicle.

[0012] The document DE 10 2006 055 766 A1 discloses a method for operating a combined vehicle braking system.

[0013] The document DE 41 24 496 A1 discloses a braking system for motor vehicles with electric drive.

[0014] The invention is therefore based on the object of specifying a braking system for a motor vehicle implemented as an integral system, which is characterized by high environmental compatibility, economic efficiency and conservation of energy resources and at the same time meets modern safety standards.

[0015] With regard to the braking system, this object is achieved according to the invention in that an electric motor driving the motor vehicle is provided, the drive shaft of which is connected to the rear axle of the motor vehicle, wherein the control unit is configured such that, upon actuation of the primary actuation device, it operates the electric motor as a generator for generating recuperative braking torque on the rear axle.

[0016] Advantageous embodiments of the invention are the subject of the subclaims.

[0017] The invention is based on the idea that in motor vehicles with an integral braking system, energy can be recovered to a particularly advantageous extent through the braking process, with an electric motor operating as a generator during the braking process being used to generate the energy. Vehicle braking systems for passenger cars in which braking torque is generated recuperatively by an electric motor, thereby recovering energy, are known. One such vehicle braking system is described, for example, in DE 10 2008 017 480. However, due to the tandem master cylinder commonly installed in passenger cars, braking torque is generated hydraulically by both brakes during a braking process. In this case, the electric motor operating as a generator can only be used to generate additional, recuperative braking torque, and overbraking on the rear axle must be avoided.

[0018] Since the two brake circuits in an integral braking system are not linked by a tandem master cylinder but rather function independently of each other, it has now been recognized that such a braking system offers the possibility of generating braking torque on the rear axle primarily through recuperation. If the braking torque generated in this recuperative manner is insufficient, the rear wheel brake can be actively controlled to generate additional braking torque.

[0019] Such an integral braking system also offers the option of performing the initial braking entirely with regenerative braking when the driver requests deceleration. In this case, the greatest possible energy recovery is possible. Only when more intense deceleration is desired or when recuperation is not desired for other reasons do the brakes need to be activated or applied.

[0020] The braking system according to the invention can be used particularly advantageously in motor vehicles that are primarily powered by an electric motor. Two- or three-wheeled scooters and motorcycles are particularly suitable for this purpose due to the available range of common electric motor and energy storage systems.

[0021] Maximum braking energy recovery in the respective driving situation can be achieved if the control unit is configured in such a way that the available regenerative braking torque is fully utilized, provided that the resulting braking torque does not exceed a deceleration target value for the rear wheel determined by the control unit. Only if the regenerative deceleration is insufficient will the control unit activate the rear-wheel brake to provide the additional deceleration torque required.

[0022] Advantageously, the electric motor is connected to the vehicle's electrical system to supply energy during recuperation. The recovered energy can then be stored directly in the vehicle, for example, in rechargeable batteries or accumulators. The energy thus recovered is then immediately available again for the electric motor to power the vehicle.

[0023] The control unit that controls the two brakes, or the entire braking system, can be implemented in different ways. For example, it can be designed as a brake-by-wire system. The brakes can also be controlled electrohydraulically or electromechanically. In an advantageous embodiment, the control unit comprises a combined hydraulic-electronic control unit assigned to the brakes, which, when the primary actuation device is actuated, hydraulically controls the respective front-wheel brake in an assigned hydraulic primary brake circuit and electrohydraulically controls the rear-wheel brake, as well as an electronic control unit assigned to the electric motor. This electronic control unit should be connected to the hydraulic-electronic control unit on the signal input and output sides.When the driver requests deceleration, the hydraulic-electronic control unit sends the command to the electronic control unit assigned to the electric motor to build up braking torque through recuperation.

[0024] Advantageously, the control unit is connected on the signal input side to a primary pressure sensor that measures the pressure in the hydraulic primary brake circuit. It is configured to determine a deceleration target value for the rear wheel based on the pressure measured by the primary pressure sensor. The driver's deceleration request is essentially expressed by actuating the primary actuation device, which builds up pressure in the hydraulic primary circuit. The corresponding and optimized deceleration target value for the rear wheel is calculated accordingly by the control unit. By actuating the primary actuation device alone, the driver can thus control both brakes with optimized brake force distribution.

[0025] If the integral brake system is designed according to the brake-by-wire concept, in which the primary actuation device is decoupled from the hydraulic brake circuits, a travel length sensor, for example, can be used instead of a primary pressure sensor, which electronically transmits how strongly the primary actuation device has been actuated or how far it has been moved.

[0026] In an advantageous embodiment of the braking system, a pressure accumulator with an associated accumulator valve is provided in the primary brake circuit associated with the respective front wheel brake, which accumulator is designed such that upon initial actuation of the primary actuation device with the accumulator valve closed, it absorbs brake fluid while pressure builds up in the primary brake circuit, wherein upon further actuation with the accumulator valve opened, the respective front wheel brake is pressurized.

[0027] Such a braking system design enables braking to be performed exclusively using recuperative means or to utilize the recuperative braking torque to the greatest possible extent. Although the driver operates the primary actuation device, this deceleration request is not transmitted directly, for example hydraulically, to the front brake. A reservoir valve, which is closed in this case, prevents the brake fluid from being passed on to the front brake. Instead, the brake fluid is absorbed by a pressure accumulator. This builds up pressure in the primary brake circuit, presenting the driver with the familiar re-coupling behavior of a brake lever or brake pedal. Only upon further actuation of the primary actuation device are the front brakes pressurized by opening the reservoir valve.

[0028] This brake system configuration can also include additional valves and a pump controlled by the control unit. If necessary, the rear wheel brake can also be actively controlled to provide additional braking torque on the rear axle.

[0029] Advantageously, a secondary actuation device is provided to control the rear wheel brake. If necessary, the rear wheel brake can be actuated exclusively via this secondary actuation device or, when the primary actuation device is actuated, in combination with the electrohydraulic actuation.

[0030] The braking system preferably comprises two separate brake circuits, with the front wheel brake circuit being controlled directly (e.g., hydraulically) by the primary actuation device and the rear wheel brake circuit by the secondary actuation device. Pressure can also be actively built up in the rear wheel brake circuit by the control unit (e.g., electrohydraulically).

[0031] Depending on the type of vehicle, the primary and secondary actuation devices can be designed differently. In a three-wheeled, two-track vehicle, for example, the primary actuation device can be implemented as a foot pedal and the secondary actuation device as a handbrake lever. A foot pedal provides the driver with a familiar primary brake operation from a car. Alternatively, in a motorcycle, for example, the primary actuation device can be implemented as a handbrake lever and the secondary actuation device as a foot brake. It is also conceivable for both actuation devices to be implemented as handbrake levers.

[0032] Preferably, the control unit's signal input is connected to the wheel speed sensors assigned to the respective front and rear wheels. This provides the control unit with the current wheel speed and, by calculating the difference between the wheel speeds at different times, the wheel decelerations. These variables, which are measured at both the front and rear wheels, can then be used to determine the optimal brake force distribution to the respective wheels.

[0033] With regard to the motor vehicle, the object stated at the outset is achieved according to the invention in that the motor vehicle is equipped with exactly two front wheels, exactly one rear wheel, and a braking system of the type described above. Depending on the distance between the two front wheels, this is a single- or two-track vehicle. Alternatively, the motor vehicle can be designed as a motorcycle with exactly one front wheel, exactly one rear wheel, and a braking system of the type described above. This can in particular be a motorcycle or a (single-track) scooter. The motor vehicle is driven by the electric motor, which is part of the braking system. The electric motor can be the sole drive unit of the motor vehicle; alternatively, it can also be part of a hybrid drive that includes the electric motor and an internal combustion engine.In this case, too, the electric motor can be used to recover braking energy and, if necessary, to drive the vehicle.

[0034] With regard to the method, the above-mentioned object is achieved according to the invention in that, when the driver expresses a deceleration request by actuating the primary actuation device, the respective front wheel brake is subjected to brake pressure and, depending on the deceleration request, a deceleration target value of the rear wheel is determined by the control unit and wherein a portion of the deceleration target value is transmitted as recuperative braking torque from the electric motor to the rear axle and the other portion is transmitted by active brake pressure buildup from the control unit to the rear wheel brake.

[0035] The amount of deceleration that can be generated by the electric motor during braking depends on various factors. Depending on the situation of the on-board electrical system and its charge level, more or less energy can be fed into the electrical system. On the other hand, the maximum amount of energy that can be recovered depends on the vehicle speed, as the electric motor, which operates as a generator, can recover varying amounts of energy through recuperation depending on the vehicle's speed. If the deceleration generated through recuperation is insufficient, the control unit actively brakes the rear wheel using the rear brake.

[0036] In a preferred variant of the braking system with a pressure accumulator, when the driver expresses a deceleration request by actuating the primary actuation device in the primary brake circuit assigned to the respective front wheel brake with the accumulator valve closed, brake fluid is to be fed into the pressure accumulator and pressure is thus built up and a deceleration target value of the rear wheel is to be determined by the control unit depending on the deceleration request.

[0037] One portion of the deceleration target value is therefore to be transferred as recuperative braking torque from the electric motor to the rear axle, and the other portion is to be transferred from the control unit to the respective rear wheel brake through active brake pressure build-up. Upon further actuation of the primary actuation device, the respective front wheel brake is to be hydraulically subjected to braking pressure by opening the accumulator valve. In this case, when the primary actuation device is initially actuated, braking is initially carried out exclusively on the rear axle or rear wheel. By filling the pressure accumulator with brake fluid, it is simultaneously ensured that pressure is built up in the primary brake circuit and that the driver receives noticeable feedback from the primary actuation device. With greater force on the primary actuation device, the front wheel brake can also be used to decelerate the vehicle by opening the accumulator valve.

[0038] Advantageously, the available regenerative braking torque is fully utilized, provided the resulting braking torque does not exceed the deceleration target value. This ensures that the maximum amount of energy available at any given time is made available to the vehicle, for example, for charging batteries.

[0039] Advantageously, when the driver requests deceleration, the control unit selects an optimized brake force distribution between the front and rear axles based on the current driving situation. The calculation or determination of the optimized deceleration target value for the rear wheel can depend on several variables related to the vehicle's driving dynamics or current driving situation. These variables include, for example, the driver's desired deceleration, the brake pressure at the respective front wheel brake, the vehicle speed measured by the speed sensors on the wheels, the vehicle's deceleration or its negative acceleration and / or positive acceleration, as well as the wheel speeds. The driver's desired deceleration can be determined, for example, by measuring the pressure at one or more points in the primary pressure circuit.

[0040] Depending on the vehicle's electrical system's charge level, more or less energy can be absorbed by the system. Therefore, it is advantageous to select the size of the recuperatively generated portion of the deceleration setpoint based on the vehicle's electrical system's charge level.

[0041] The advantages of the invention lie in particular in the fact that an electric motor operated as a generator in an integral braking system can recover energy during the braking process, which is available to the motor vehicle and can, for example, be fed into the on-board electrical system and used at a later time to drive the motor vehicle.

[0042] The use of regenerative braking torque protects the brakes and reduces wear. Furthermore, safety systems such as ABS can be seamlessly integrated into the braking system according to the invention.

[0043] If the control unit is configured in such a way that the maximum available recuperative braking torque compatible with the deceleration setpoint is used, the greatest possible amount of energy can be recovered at that time.

[0044] An embodiment of the invention is explained in more detail with reference to a drawing, which shows, in a highly schematic representation: Fig. 1 a block diagram of a braking system for an electrically powered scooter, Fig. 2 a three-wheeled electrically powered scooter with a braking system, and Fig. 3 a flowchart of a method for operating a braking system in a preferred embodiment.

[0045] Identical parts are provided with the same reference numerals in all figures.

[0046] The Fig. The braking system 2 shown in Figure 1 is designed as an integral braking system. It comprises a front-wheel brake circuit 6 with two associated front-wheel brakes 10 and a rear-wheel brake circuit 14 with an associated rear-wheel brake 18. The front-wheel brakes 10 are directly hydraulically controlled by the driver via a foot pedal 22. The rear-wheel brake 18 is actuated by the driver using a handbrake lever 26. Both actuating devices, i.e., the foot pedal 22 and the handbrake lever 26, are each connected to a master brake cylinder 30, to each of which a brake fluid reservoir 34 is connected. The pressure in the respective brake circuit 6, 14 is measured at several points by pressure sensors 38.

[0047] In the present example, both front wheel brakes 10 are controlled by a front wheel brake circuit 6. Alternatively, in a motor vehicle with two front wheels, each wheel can be assigned a separate brake with a separate brake circuit. This makes it possible to ensure the stability of the vehicle by specifically and separately controlling the two brakes, even when the two wheels are traveling on different surfaces.

[0048] The braking system 2 includes an anti-lock braking system (ABS). For this purpose, inlet valves 42 and outlet valves 46 are arranged in each of the two brake circuits 6 and 14. A separating valve 48 and a switching valve 52 are also arranged in the rear wheel brake circuit 14.

[0049] In the basic position, when the foot pedal 22 or the handbrake lever 26 is not actuated, the outlet valves 46 are each closed. The outlet valves are each inserted into a return line 56. This return line connects the respective front wheel brake 10 or rear wheel brake 18 to a low-pressure accumulator 60 and a suction path 64 of a pump 68. Both pumps are driven by an electric pump motor 72. The two hydraulic brake circuits 6, 14 are separate from each other and can be activated by the foot pedal 22 or the handbrake lever 26, respectively.

[0050] The braking system 2 is designed as a partially integrated braking system. When the handbrake lever 26 is actuated, only the rear wheel brake 18 is actuated. When the foot pedal 22 is actuated, in addition to the direct brake pressure buildup in the front wheel brake circuit 6 and thus the application of brake pressure to the front wheel brake 10, the rear wheel brake 18 can also be actively controlled, in this case electrohydraulically. For this purpose, the pump electric motor 72 activates the pump 68 corresponding to the rear wheel brake circuit 14. In doing so, it draws pressure from the master brake cylinder 30 and delivers it to the rear wheel brake 18. The isolating valve 48 separates the pump pressure side from the master brake cylinder 30. In this way, braking torque can be generated by both brakes by actuating just one actuating device, in this case the foot pedal 22. The distribution of braking torque to the front wheel brakes orThe rear wheel brake is selected in an optimized manner to ensure the stability of the vehicle during braking.

[0051] Pumps 68 and valves 42, 46, 48, and 52 implement brake slip control in braking system 2, which functions as an ABS system. Additionally, routines are implemented in braking system 2 to prevent the rear wheel from lifting off during heavy braking (Rear Wheel Lift-off Protection, RLP). The rotational speeds of the individual wheels (not shown) are measured by speed sensors 80.

[0052] Braking system 2 is designed to generate and utilize regenerative braking torque to generate electrical energy, which can be fed, for example, into the vehicle's electrical system. For this purpose, an electric motor 84 is provided, the drive shaft of which (not shown) is connected to the vehicle's rear axle 88. A motor control unit 92 is assigned to the electric motor 84, the assignment being indicated by a first double arrow 94.

[0053] Depending on the driver's desired deceleration and the vehicle's dynamic driving situation, more or less braking torque should be generated recuperatively. The braking system 2 therefore includes a hydraulic-electric control unit (HECU) 96, which is responsible for the electrohydraulic control of the brakes. The HECU 96, in turn, communicates on both sides with an electronic control unit (ECU) 100 assigned to the electric motor 84. The bidirectional communication is indicated by the second double arrow 104. When the foot pedal 22 is actuated, the HECU 96 hydraulically builds up braking pressure in the front wheel brakes 10. The ABS and RLP routines can be superimposed on the processes required for recuperative braking torque generation. The HECU 96 then commands the ECU 100 to generate recuperative braking torque.The ECU 100, in turn, communicates with the electronic engine control unit 92, through which it receives information about the possible recuperative energy recovery in the current driving situation. The engine control unit 92 can be designed and configured as an additional ECU.

[0054] The ECU 100 controls the electric motor 84 via the engine control unit 92 in such a way that the greatest possible available recuperation torque is utilized, provided it is compatible with the overall deceleration target value of the rear wheel. If there is no energy requirement, for example, if the vehicle electrical system and / or batteries are fully charged, regenerative braking torque generation can be dispensed with entirely. In any case, the difference between the deceleration torque of the rear wheel generated by recuperation and the optimal deceleration torque determined by the HECU 96 is actively applied electrohydraulically by building up pressure on the rear wheel brake 18. The pressures in the brake circuits 6, 14 or at the brakes 10, 18 are subject to a control process. For this purpose, the HECU 96 can use the pressures measured by the pressure sensors 38 and the wheel rotation speeds measured by the speed sensors 80.

[0055] In general, the total braking force of the motor vehicle is the sum of the hydraulically operated and the electro-hydraulically controlled brakes as well as the braking force of the electric motor acting as a generator.

[0056] The Fig. The electric scooter 120 shown in Figure 2 with two front wheels 122 and one rear wheel 123 is in a first variant, not shown here again in all details, with the braking system according to Fig. 1. In a second embodiment, the braking system is modified as described below. It is also conceivable to equip a four-wheeled motor vehicle with the braking system, in which case two rear wheel brakes 18 correspond to the two rear wheels 123.

[0057] The electric scooter 120 is powered solely by the electric motor 84. This electric motor 84 can be used to recover energy during braking in generator mode. In this case, the front wheel brakes 10 are actuated by the foot pedal 22, while the rear wheel brake 18 is actuated by the handbrake lever 26. As already described above, the braking system of the electric scooter 120 is designed as a partially integrated braking system, so that when the foot pedal 22 is actuated, in addition to the front wheel brakes 10, the rear wheel brake 18 and the electric motor 84, which acts as a generator in recuperation mode, are also actuated.

[0058] In a version compared to the basic version according to Fig. 1 modified embodiment, a pressure accumulator 124 with an associated accumulator valve 128 is inserted into the front wheel brake circuit 6. The accumulator valve 128 is arranged in the brake line section between the pressure accumulator 124 and the front wheel brakes 10. In Fig. 1 these additional components are shown in dashed lines.

[0059] When the foot pedal 22 is actuated, brake fluid is fed into the low-pressure accumulator 124, building up pressure in the front-wheel brake circuit 6. At this point, the front-wheel brake(s) 10 are not subjected to braking pressure because the accumulator valve 128 is closed. The HECU 96 now communicates with the ECU 100 and attempts to achieve purely recuperative deceleration of the vehicle. Only upon further actuation of the foot pedal 22 is the accumulator valve 128 switched, so that the front-wheel brakes 10 are now subjected to braking pressure. In this case, too, if necessary, the HECU 96 can electrohydraulically build up pressure on the rear-wheel brake 18 in addition to the regenerative braking torque.

[0060] The operative relationship between the HECU 96 and the front wheel brakes 10 is illustrated by a first dashed arrow 170, and the operative relationship between the HECU 96 and the rear wheel brake 18 is illustrated by a second dashed arrow 174. The communication between the ECU 100 and the electric motor 84 (including the engine control unit 92) is indicated by a fourth double arrow 178.

[0061] In Fig.Figure 3 illustrates a preferred embodiment of the method for operating the braking system in a flowchart. The method begins at the start time START 140, when the driver expresses a deceleration request by actuating the primary actuation device. In block 144, the HECU 96 hydraulically builds up pressure in the front wheel brake circuit 6. In block 148, the HECU 96 determines a deceleration target value for the rear wheel 123 as a function of the pressure measured in the front brake circuit 6 and the wheel rotational speeds measured with the aid of the speed sensors. The processes assigned to blocks 144 and 148 can also run essentially simultaneously. As soon as this deceleration target value has been determined, the HECU 96 sends the command to the ECU 100 in block 152 to generate regenerative braking torque. The ECU 100 queries the engine control unit 92 as to the extent to which regenerative braking torque can be generated.This may depend on the charge state of the vehicle's electrical system or the vehicle's speed. In block 156, the ECU 100 transmits the amount of available regenerative braking torque to the HECU 96.

[0062] At branch 158, a check is now made to determine whether the available regenerative braking torque is sufficient to meet the deceleration setpoint. To prevent overbraking, the regenerative braking torque is only used to the extent that the deceleration setpoint is not exceeded. If the regenerative braking torque is sufficient to meet the deceleration setpoint, braking is performed purely regeneratively at the rear, and the branch follows the "Yes" decision 160 to the "STOP" step 162 of the process.

[0063] If, on the other hand, the regenerative braking torque is insufficient, the process proceeds from the "No" decision 164 to block 166. In block 166, the HECU 96 actively applies brake pressure, in this case electrohydraulically, to the rear wheel brake 18. Just enough brake pressure is generated so that the sum of the electrohydraulically and regeneratively generated braking torque results in the desired deceleration of the rear wheel. Alternatively or additionally, the front wheel brake 10 is applied with brake pressure. The process is thus terminated and continues to STOP 162.

[0064] The individual parts or steps of the method can be performed multiple times during a braking process, possibly even in different sequences. In particular, the required brake pressure is essentially controlled by the HECU 96 throughout the entire braking process. The HECU 96 communicates with the ECU 100 and monitors the vehicle's dynamic driving state via the pressure sensors 38 and the speed sensors 80. List of reference symbols 2 braking system 6 Front wheel brake circuit 10 Front brake 14 Rear brake circuit 18 Rear brake 22 Foot pedal 26 Handbrake lever 30 master brake cylinders 34 storage containers 38 pressure sensor 42 Inlet valve 46 Exhaust valve 48 Isolating valve 52 changeover valve 56 Return line 60 low-pressure accumulators 64 suction path 68 Pump 72 Pump electric motor 76 brake line 80 speed sensor 84 electric motor 88 rear axle 92 Engine control unit 94 first double arrow 96 HECU 100 ECU 104 second double arrow 108 third double arrow 120 electric scooters 122 front wheel 123 rear wheel 124 pressure accumulators 128 storage valve 140 START 144, 148 Block 152, 156 Block 158 Branching 160 Yes decision 162 STOP 164 No decision 166 Block 170 first dashed arrow 174 second dashed arrow 178 fourth double arrow

Claims

[1] Braking system (2) for a motor vehicle, in particular a scooter or a motorcycle, with at least one front wheel (122), one rear wheel (123), with at least one front wheel brake (10) and one rear wheel brake (18), a control unit for controlling the brake pressures on the respective front wheel brake (10) and the rear wheel brake (18), and a primary actuating device which controls both the respective front wheel brake (10) and the rear wheel brake (18) via the control unit, wherein an electric motor (84) driving the motor vehicle is provided, the drive shaft of which is connected to the rear axle (88) of the motor vehicle, wherein the control unit is configured such that, upon actuation of the primary actuating device, it operates the electric motor (84) as a generator for generating recuperative braking torque on the rear axle (88), wherein a secondary actuating device is provided via which the rear wheel brake (18) is controlled. [2] Braking system (2) according to claim 1, wherein the control unit is configured such that the available recuperative braking torque is fully utilized, provided that the braking torque caused thereby does not lead to exceeding a deceleration target value of the rear wheel (123) determined by the control unit. [3] Braking system (2) according to claim 1 or 2, wherein the electric motor (84) is connected to the on-board electrical system of the motor vehicle for supplying energy in recuperation mode. [4] Braking system (2) according to one of claims 1 to 3, wherein the control unit comprises a combined hydraulic-electronic control unit associated with the brakes (10, 18), which, upon actuation of the primary actuating device, hydraulically controls the respective front wheel brake (10) in an associated hydraulic primary brake circuit and electrohydraulically controls the rear wheel brake (18), as well as an electronic control unit associated with the electric motor (84). [5] Brake system (2) according to claim 4, wherein the control unit is connected on the signal input side to a primary pressure sensor which measures the pressure in the hydraulic primary brake circuit and is configured such that it determines a deceleration target value of the rear wheel (123) as a function of the pressure measured by the primary pressure sensor. [6] Brake system (2) according to claim 4 or 5, wherein in the primary brake circuit associated with the respective front wheel brake (10) a pressure accumulator with an associated accumulator valve is provided, which is designed such that upon initial actuation of the primary actuation device with the accumulator valve (128) closed, it absorbs brake fluid with pressure build-up in the primary brake circuit, wherein upon further actuation with opening of the accumulator valve (128) the respective front wheel brake (10) is pressurised. [7] Braking system (2) according to one of claims 1 to 6, wherein the control unit is connected on the signal input side to wheel speed sensors (80) assigned to the respective front and rear wheels (122, 123). [8] Motor vehicle (2) with exactly two front wheels (122), exactly one rear wheel (123) and a braking system (2) according to one of claims 1 to 7. [9] Motor vehicle, in particular motorcycle, with exactly one front wheel (122), exactly one rear wheel (123) and a braking system (2) according to one of claims 1 to 7. [10] Motor vehicle according to claim 8 or 9, wherein the electric motor (84) is part of a hybrid drive system comprising the electric motor (84) and an internal combustion engine. [11] Method for operating a braking system (2) according to one of claims 1 to 7, wherein when the driver expresses a deceleration request by actuating the primary actuating device, the respective front wheel brake (10) is subjected to braking pressure and, depending on the deceleration request, a deceleration setpoint value of the rear wheel (123) is determined by the control unit, and wherein a portion of the deceleration setpoint value is transmitted as recuperative braking torque from the electric motor (84) to the rear axle (88) and the other portion is transmitted by active brake pressure buildup from the control unit to the rear wheel brake (18). [12] Method for operating a braking system (2) according to claim 6, wherein, upon expression of a deceleration request by the driver by actuating the primary actuating device in the primary brake circuit assigned to the respective front wheel brake (10) with the accumulator valve (128) closed, brake fluid is fed into the pressure accumulator and pressure is thus built up, and a deceleration target value of the rear wheel (123) is determined by the control unit as a function of the deceleration request, and wherein a portion of the deceleration target value is transmitted as recuperative braking torque from the electric motor (84) to the rear axle (88) and the other portion is transmitted by active brake pressure buildup from the control unit to the respective rear wheel brake (18), wherein upon further actuation of the primary actuating device, the respective front wheel brake (10) is hydraulically subjected to braking pressure by opening the accumulator valve (128). [13] Method according to claim 11 or 12, wherein the available recuperative braking torque is fully utilized, provided that the braking torque caused thereby does not lead to an exceeding of the deceleration target value. [14] Method according to one of claims 11 to 13, wherein the deceleration target value of the rear wheel is calculated as a function of one or more of the following variables or is determined on the basis of data stored in the control unit: deceleration request of the driver, brake pressure at the respective front wheel brake (10), speed of the vehicle, deceleration of the vehicle, wheel speeds. [15] Method according to one of claims 11 to 14, wherein the size of the recuperatively generated portion of the deceleration setpoint is selected as a function of the state of charge of the vehicle electrical system.

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