motor vehicle with a hybrid drive

Abstract

Motor vehicle with a hybrid drive comprising at least one wheel (4, 6, 8, 10) that can be driven by an electric machine, wherein a recuperation device is provided which enables energy recuperation during a braking process in a recuperation phase, wherein a braking system (12) is provided with a pedal (14), at least one master brake cylinder (18, 20, 26) and at least one wheel brake (22, 24, 28, 30) which fluidly actuates the wheel brake (22, 24, 28, 30) by means of a brake pressure due to movement of the pedal (14), wherein a pressure reducing valve device (36) is provided which reduces the brake pressure in the recuperation phase and wherein a compensator (18) is provided to compensate for a hydraulic effect of the pressure reducing valve device (36), wherein two master brake cylinders are located in the operating range of the pressure reducing valve device (36). (18,18'; 20) are provided, whose pistons (19, 21;58, 21) are rigidly coupled to each other via a connecting element (55), characterized in that the pressure reducing valve device (36) has a hydraulic actuator (42) and a balance cylinder (44) comprising a balance piston (46) which is slidably arranged to accommodate a hydraulic volume and provide two hydraulic chambers (48, 50), wherein the first hydraulic chamber (48) is fluidically connected to the first master brake cylinder (18; 18') and the second hydraulic chamber (50) is fluidically connected to the second master brake cylinder (20), wherein the hydraulic actuator (42) is fluidically connected to a separate hydraulic unit (38) via a 4 / 3 servo valve (40).

Description

[0001] The invention relates to a motor vehicle with a hybrid drive comprising at least one wheel that can be driven by an electric machine, wherein a recuperation device is provided which enables energy recuperation during a braking process in a recuperation phase, wherein a braking system is provided comprising a pedal, at least one master brake cylinder and at least one wheel brake which fluidly actuates the wheel brake by means of a brake pressure due to a movement of the pedal, wherein a pressure reducing valve device is provided which reduces the brake pressure in the recuperation phase and wherein a compensator is provided to compensate for a hydraulic effect of the pressure reducing valve device.

[0002] Such a motor vehicle is known from DE 10 2010 008 018 A1. In this vehicle, a front axle is driven by an electric motor and the rear axle by an internal combustion engine. The present invention also assumes such a design of the motor vehicle, but it is not limited to such a drive system. In the event of braking, the electric motor acting on the front axle can also be used as a generator, thereby converting braking energy into electrical energy and relieving the hydraulic brake system. It is known to provide a pressure-reducing valve device to regulate the hydraulic brake system during the recuperation phase. A disadvantage of this design is that the driver finds this regulation process disruptive due to brake pedal feedback.To avoid this disadvantage, it is known from DE 10 2010 008 018 A1 to use a so-called compensator, which counteracts the hydraulic effect of the pressure reducing valve device. However, this known solution has the disadvantage that it is only applicable to a brake system with a balance beam system, and that, due to the purely hydraulic mode of operation, there is still a delay, albeit minimal, in the effect of the pressure reducing valve device.

[0003] The object of the invention is therefore to provide a motor vehicle with a hybrid drive that avoids the aforementioned disadvantages in a cost-effective and simple manner.

[0004] This task is accomplished by providing two master brake cylinders within the operating range of the pressure reducing valve device, whose pistons are rigidly coupled to each other via a connecting element. In this way, it is ensured in a very simple and direct manner that the pistons of the master brake cylinders, in this case for the front axles, remain in the controlled position even during the recuperation phase.

[0005] In a first embodiment, a balance beam is provided which is operatively connected to the pedal and to which a master brake cylinder is connected. This embodiment is particularly suitable for racing cars. In a second embodiment, which is particularly advantageous for road-legal passenger cars, a tandem master cylinder is provided as the first master brake cylinder.

[0006] Advantageously, the first master brake cylinder is designed as a compensator and is fluidically connected to a compensating chamber. The compensating chamber can include a spring element, the design of which ensures that the volumetric stiffness of the brake hydraulics is identical to that of the compensating chamber.

[0007] According to the invention, the pressure reducing valve device comprises a hydraulic actuator and a balancing cylinder, which includes a balancing piston that is slidably arranged to accommodate a hydraulic volume and provide two hydraulic chambers, wherein the first hydraulic chamber is fluidically connected to the first master brake cylinder and the second hydraulic chamber is fluidically connected to the second master brake cylinder. Advantageously, the hydraulic actuator is fluidically connected to a separate hydraulic unit via a 4 / 3 servo valve. Alternatively, it is also possible for the hydraulic actuator to be controlled via a central hydraulic unit.

[0008] The invention is explained in more detail with reference to a drawing, which shows: Fig. 1 a hydraulic circuit diagram of a motor vehicle with a first embodiment of a brake system, and Fig. 2 a hydraulic circuit diagram of a motor vehicle with a second embodiment of a braking system.

[0009] Fig. Figure 1 shows a motor vehicle 2 in the form of a hydraulic circuit diagram. Two front wheels 4, 6 are provided on a front axle (not shown). Correspondingly, rear wheels 8, 10 are arranged on a rear axle (not shown). The motor vehicle 2 can also be described as a hybrid vehicle and has an electric motor (not shown) operatively connected to the front axle and an internal combustion engine (not shown) operatively connected to the rear axle. It should be clear that there are a multitude of so-called hybrid drives, all of which fall within the scope of protection of the invention.

[0010] The electric machine functions as an electric motor when it drives wheels 4 and 6 of the front axle. Furthermore, during a recuperation phase, in which it acts as a generator, the electric machine can convert braking energy generated by the vehicle into electrical energy. This energy recovery during braking is also known as recuperation. The energy recovered during braking can be stored in batteries or capacitors.

[0011] In addition to recuperation as a braking function, the motor vehicle 2 includes a hydraulic braking system 12. This system incorporates a pedal 14 that acts on a balance beam 16. This balance beam 16 serves to adjust the brake pressure distribution between the front axle, and thus between the front wheels 4 and 6, and the rear axle, or rather the rear wheels 8 and 10. Regarding the brake pressure distribution to the front wheels 4 and 6, a first and a second master brake cylinder 18 and 20, each with pistons 19 and 21, are connected to the balance beam 16. The second master brake cylinder 20 is fluidly connected to the wheel brakes 22 and 24 located on the front wheels 4 and 6. A third master brake cylinder 26 is connected to the opposite side of the balance beam 16 and is fluidly connected to the wheel brakes 28 and 30 of the rear wheels 8 and 10 in a known manner.Both the brake pressure acting on the front wheels 4, 6 and the brake pressure acting on the rear wheels 8, 10 are monitored in a known manner by sensors 32, 34.

[0012] As previously described, the electric motor is operatively connected to the front axle of the vehicle 2 and acts as a generator during recuperation, converting the braking energy generated during deceleration into electrical energy. To reduce the brake pressure of the brake system 12 during recuperation, a pressure-reducing valve 36 is provided, which reduces the brake pressure applied to the wheel brakes 22, 24 of the front wheels 4, 6 accordingly. In the present embodiment, the pressure-reducing valve 36 consists of a separate hydraulic unit 38, which provides the pressure supply. The hydraulic unit 38 is connected to a hydraulic actuator 42 via a 4 / 3 servo valve 40. The brake pressure can be increased or decreased via this hydraulic actuator 42, so that the brake pressure can be adjusted during recuperation within the operating range of the pressure-reducing valve 36, in this case the front axle.For this purpose, the actuator 42 acts on a balancing cylinder 44, which includes a balancing piston 46 that is slidably arranged such that a hydraulic volume can be provided in two hydraulic chambers 48, 50. The first hydraulic chamber 48 is fluidically connected to the first master brake cylinder 18, and the second hydraulic chamber 50 is fluidly connected to the second master brake cylinder 20. The first master brake cylinder 18 is also fluidically connected to a compensating chamber 52, which has a spring element 54 to ensure that the volumetric stiffness of the brake hydraulics in the area of ​​the front axle is identical to that of the compensating chamber 52. In this way, the first master brake cylinder 18 acts as a compensator, preventing any movement of the brake pedal 14 that would be perceived as disruptive when the pressure reducing valve 36 is used.For this purpose, the piston 19 of the first master brake cylinder 18 is directly connected to the piston 21 of the second master brake cylinder 20 via a rigid connecting rod 55.

[0013] The following description of the brake system 12 is limited to explaining the operating range of the pressure-reducing valve device, i.e., the front axle. As long as no recuperation of the electric motor takes place, the brake system 12 functions like a conventional brake system, whereby the braking process is initiated via the pedal 14 and the brake pressure is transmitted via the balance beam 16 and the first master brake cylinder 18 to the second brake cylinder 20, which is fluidly connected to the wheel brakes 22, 24 in a known manner. The wheel brakes 28, 30 are fluidly connected to the third master brake cylinder 26.

[0014] When a recuperation phase is initiated, this inevitably leads to a reduction in brake pressure in the area of ​​the front axle. The balancing piston 46 is moved to the right by the hydraulic actuator 42, resulting in a pressure drop in the first hydraulic chamber 50 and consequently also at the wheel brakes 22, 24. Conversely, a pressure increase occurs in the first hydraulic chamber 48, which is transferred to the compensating chamber 52 and absorbed by the spring element 54. This ensures that the volumetric stiffness and thus the positions of the pistons 19, 21 of the master brake cylinders 18, 20 remain constant. This prevents the disruptive feedback effect.

[0015] Fig. Figure 2 shows the hydraulic circuit diagram of a second embodiment of a brake system 12, as is commonly used in road-legal passenger cars. Instead of a balance beam 16 (see here) Fig. 1) A simple lever arrangement 17 is used here, which is operatively connected to a first master brake cylinder 18'. The first master brake cylinder 18' is designed as a tandem master cylinder, which has two pistons 56, 58 that form two hydraulic chambers 60, 62. Here, hydraulic chamber 60 is fluidically assigned to the wheel brakes 28, 30 of the rear axle. Hydraulic chamber 62 is comparable to the hydraulic chamber of the first master brake cylinder 18 in Fig. 1 and, together with the second master brake cylinder 21, is responsible for the brake pressure acting on the wheel brakes 22, 24. Consequently, the hydraulic chamber 62 of the first master brake cylinder 18' can also be considered as a compensator. The second piston 58 is rigidly coupled to the piston 21 of the second master brake cylinder via the connecting element 55.

[0016] The brake pressure reduction during a recuperation phase works as follows: Fig.1 described from.

Claims

[1] Motor vehicle with a hybrid drive comprising at least one wheel (4, 6, 8, 10) that can be driven by an electric machine, wherein a recuperation device is provided which enables energy recuperation during a braking process in a recuperation phase, wherein a braking system (12) is provided with a pedal (14), at least one master brake cylinder (18, 20, 26) and at least one wheel brake (22, 24, 28, 30) which fluidly actuates the wheel brake (22, 24, 28, 30) by means of a brake pressure due to movement of the pedal (14), wherein a pressure reducing valve device (36) is provided which reduces the brake pressure in the recuperation phase and wherein a compensator (18) is provided to compensate for a hydraulic effect of the pressure reducing valve device (36), wherein in the effective range of the pressure reducing valve device (36) two Master brake cylinders (18,18'; 20) are provided, whose pistons (19, 21;58, 21) are rigidly coupled to each other via a connecting element (55), ; characterized by , that the pressure reducing valve device (36) comprises a hydraulic actuator (42) and a balance cylinder (44) comprising a balance piston (46) which is slidably arranged to accommodate a hydraulic volume and provide two hydraulic chambers (48, 50), wherein the first hydraulic chamber (48) is fluidically connected to the first master brake cylinder (18; 18') and the second hydraulic chamber (50) is fluidically connected to the second master brake cylinder (20), wherein the hydraulic actuator (42) is fluidically connected to a separate hydraulic unit (38) via a 4 / 3 servo valve (40). [2] Motor vehicle according to claim 1, characterized by , that a balance beam (16) is provided which is in operative connection with the pedal (14) and to which a master brake cylinder (18, 26) is connected. [3] Motor vehicle according to claim 1, characterized by, that a tandem master cylinder is provided as the first master brake cylinder (18'). [4] Motor vehicle according to one of claims 1-3, characterized by , that the first master brake cylinder (18; 18') is designed as a compensator and is fluidically connected to a compensating chamber (52). [5] Motor vehicle according to claim 4, characterized by , that the compensation chamber (52) has a spring element (54). [6] Motor vehicle according to any one of the preceding claims, characterized by , that the hydraulic actuator (42) can be controlled via a central hydraulic unit.

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