Drive degradation system for vehicles with multiple power sources

Abstract

Drive degradation system for a vehicle with at least one electronically controlled electric motor (6) that drives the vehicle by generating electric motor power (PEM), with at least two power sources for generating the electric motor power (PEM), wherein a first power source is in the form of a high-voltage battery (9; HVS) and a second power source is in the form of a fuel cell (8; FCS), which can be used alternatively or together for generating the electric motor power (PEM), with a degradation module (12), characterized in that the degradation module (12) is dependent on a currently maximum possible power (PFCS_max) of the fuel cell (8;FCS) calculates a maximum fuel cell power-related vehicle speed (v_max) for steady-state operation, and with a torque coordinator (4) that limits an electric motor setpoint power (PEM_setpoint) such that the maximum fuel cell power-related vehicle speed (v_max) is not exceeded in steady-state operation, wherein the high-voltage battery (9; HVS) as a power source is not used for driving the vehicle in steady-state operation at least until a dynamic requirement is met.;

Description

State of the art:

[0001] In fuel cell vehicles, hydrogen is used as an energy carrier for propulsion. The energy bound in the hydrogen is converted into electrical energy via a fuel cell and serves as an energy source for one or more so-called electric motors to power the vehicle's electric drive.

[0002] Furthermore, fuel cell vehicles contain electrical energy storage devices, such as lithium-ion batteries – also known as high-voltage batteries or high-voltage storage systems (HVS). These are needed to absorb and store kinetic energy during deceleration or braking (recuperation), to support the fuel cell during acceleration (boosting), and to cover dynamic power differences (over- and under-supply) between the fuel cell as the energy source and the electric motors and auxiliary consumers as energy sinks.

[0003] Depending on the driver's acceleration and deceleration requests, the electric motors and fuel cell are controlled via software. Due to the typically significantly lower energy content of the electrical energy storage compared to the hydrogen storage, the power required for vehicle movement is covered (at least in the long term) by the fuel cell.

[0004] Both the fuel cell and the electrical energy storage system are more or less (statically) limited in terms of their power output, depending on the design, layout and operating point.

[0005] During operation, certain driving profiles, environmental influences and / or fault conditions may necessitate additional degradation of the fuel cell with regard to power output.

[0006] In the prior art, limiting the fuel cell output leads to a greater discharge of the high-voltage battery and, furthermore, to a limitation of the available drive power (electric motor output) that can be accessed by the driver via the accelerator pedal. The object of the invention is to solve this problem.

[0007] This problem is solved by the features of claim 1. Advantageous embodiments of the invention are contained in the dependent claims.

[0008] The invention describes a drive degradation system for a vehicle with at least one electric motor that drives the vehicle by generating electric motor power, with at least two power sources for generating the electric motor power, wherein a first power source is in the form of a high-voltage battery and a second power source is in the form of a fuel cell, which can be used alternatively or together to generate the electric motor power, with a degradation module that calculates a maximum fuel cell power-related vehicle speed for steady-state operation depending on the current maximum possible power of the fuel cell, and with a torque coordinator that limits the target electric motor power in such a way that the maximum fuel cell power-related vehicle speed is not exceeded in steady-state operation.where the high-voltage battery is not used as a power source for driving the vehicle, at least until a dynamic requirement arises.

[0009] In summary, the invention represents a drive degradation concept for vehicles with multiple power sources without loss of dynamics.

[0010] The invention is based on the following findings: The unique feature of a fuel cell vehicle is that, in current designs, the fuel cell contributes only a small share of the total drive power compared to a hybrid vehicle with an internal combustion engine (see state of the art). At the same time, the energy content of the high-voltage battery is not designed to provide the main drive power over the long term; it is intended solely to provide the vehicle's dynamic performance.

[0011] Due to this distribution of drive power, operating the vehicle above the fuel cell power leads to a strong discharge of the HV battery and consequently quickly to the loss of the HV storage as an energy source. This operating condition occurs more frequently with degraded fuel cell performance, especially after a prolonged uphill drive and / or after driving at high speed. The driver perceives this as a very strong limitation of the available drive power / acceleration dynamics.

[0012] The present invention is intended to prevent this: The design of the energy capacities of the H2 tank and the high-voltage battery, as well as the performance data of these energy sources, mean that dynamic driving phases are primarily covered by the high-voltage battery. In contrast, the steady-state drive power requirements (steady-state driving resistance, power requirements for uphill driving and higher speeds) must be covered by the fuel cell.

[0013] To counteract the increased discharge of the HV battery when the fuel cell's performance is degraded, the vehicle should not be operated in areas with higher stationary drive power requirements.

[0014] If the stationary drive power demand (stationary driving resistances) exceeds the maximum available fuel cell power, the high-voltage battery will discharge. The invention is intended to prevent this.

[0015] The stationary driving resistances result from influencing factors such as rolling resistance, air resistance, and gradient resistance. These influencing factors, in turn, result from constant, unchanging parameters such as vehicle mass, drag coefficient, and road gradient, as well as the variable vehicle speed.

[0016] This consideration leads to the conclusion that the only (meaningfully) controllable variable for reducing the stationary drive power requirement is the vehicle speed.

[0017] Therefore, a maximum fuel cell-power-related vehicle speed is calculated from the available fuel cell output using a model, and the drive system is limited accordingly. This approach prevents the high-voltage battery from discharging, typically with only a slightly reduced maximum vehicle speed. As a result, full acceleration dynamics are maintained, and drivability is significantly improved.

[0018] Simply limiting the vehicle speed to a maximum fuel cell-power-related value cannot completely prevent high-voltage battery discharge in all driving situations. For example, repeated acceleration maneuvers can still lead to battery discharge. Errors or inaccuracies in the calculation model can also result in gradual battery discharge.

[0019] To also take these cases into account, the following additional functionalities are preferably provided: - Provision of a minimum charging power within the framework of determining the maximum fuel cell power-related vehicle speed for charging the HV battery depending on the battery state of charge (SOC). - Limitation to a maximum total drive power depending on the ratio of fuel cell power to total drive power. - Determination of the maximum total drive power depending on the battery state of charge (SOC). Certain temporary driving resistances can be detected via predictive data acquisition (e.g., navigation data) and specifically taken into account or ignored in the calculation of the maximum fuel cell-power-related vehicle speed (e.g., predictive data ignores a "small hill" by manipulating the incline angle. Similarly, a downhill slope leads to an increase in the maximum fuel cell-power-related vehicle speed). - The function may include the ability to "override" the speed limit to the maximum fuel cell power-related vehicle speed via the accelerator pedal (e.g., kickdown). - The limitation to a maximum vehicle speed related to fuel cell power can always be active or activatable, regardless of degradation of the fuel cell system (application example: driving uphill or manual selection of this function by the driver via a corresponding control element). Transitions from the non-degraded system to the various degradation levels should not result in sudden jumps in vehicle speed, but rather be implemented smoothly. The same applies to limiting the drive power. This leads to improved drivability.

[0020] The drawing shows an embodiment of the invention. Fig. 1 a schematic overview of a functional structure according to the invention with corresponding signal flows and Fig. 2 a driving profile example using the functional structure according to the invention.

[0021] The following is an overview of the power distribution in a concept with an electric motor, an on-board network with auxiliary consumers, a fuel cell, and a high-voltage storage system: P EM + P BNNV = P FCS + P HVS P EM Electric motor power (driver request; not influenced by operating strategy) P BNNV Power consumption of on-board electrical system and auxiliary consumers (storage heating or cooling, interior heating or cooling, 12 V consumers; partially influenced by operating strategy) P FCS Fuel cell output (can be varied, must be P in the medium term) EM + P BNNV cover; influenced by operational strategy) P HVS Power output of HV storage (= "Resultant", arises from the power balance; influenced by operating strategy)

[0022] P FCS => P HVSby increasing or decreasing FCS power: → P FCS ≠ PEM + P BNNV → Charging / Discharging HV Storage → Increase in high-voltage storage temperature

[0023] An advantageous functional structure according to the invention is described below using the following examples: Fig. 1 explained in more detail. Fig. 1 is from a brake pedal 1 a brake pedal pressure p_B (or a brake pedal force or a brake pedal travel) to an electronically controlled brake control system 2 guided. The brake control system 2 The system splits the deceleration request requested by the brake pedal pressure p_B into a wheel brake pressure p_R and a brake recuperation request REKU_soll. The brake recuperation request REKU_soll is the input signal of a torque coordinator. 4 Similarly, the accelerator pedal angle FW of an accelerator pedal actuated by the driver is input signal 5 of the torque coordinator. 4and reflects the driver's request. The moment coordinator 4 From these two input signals, a target torque or target drive power P is determined. EM_soll , which are assigned to a performance coordinator 7 is issued. The performance coordinator 7 preferably depending on the maximum power P HVS_max the high-voltage battery 9 , which is determined in particular by the battery's state of charge (SOC) and other storage limits, depending on the requested power P BNNV the secondary consumer 10 and possibly depending on the current power output P FCS_ist the fuel cell 8 a target power P FCS_soll to the fuel cell 8 out of.

[0024] The essential aspect of the invention is that the currently maximum possible power P FCS_max the fuel cell 8 determined and assigned to a degradation module 12The output calculates a maximum fuel cell power-related vehicle speed v_max for steady-state operation. Steady-state operation is defined as driving at a substantially constant vehicle speed v, i.e., without any dynamic demands, in particular without any positive acceleration demand via the accelerator pedal 5 or the accelerator pedal angle FW.

[0025] The vehicle is operated in stationary mode with at least one electronically controlled electric motor. 6 driven, with the electromotive power P EM to do this using the moment coordinator 4 preferably exclusively by the fuel cell 8 is generated as a power source. The maximum fuel cell-related vehicle speed v_max for steady-state operation is the input signal of the torque coordinator. 4 , which is limited by a v_max limiting module 11the electromechanical target power P EM limited in such a way that the maximum fuel cell power-related vehicle speed v_max is not exceeded in steady-state operation. The high-voltage battery is used in this process. 9 as a power source, at least until a dynamic requirement arises, it is not used for propelling the vehicle.

[0026] The moment coordinator 4 with the v_max limit module 11 , the performance coordinator 7 and the degradation module 12 These are functional modules that can be contained in at least one electronic control unit.

[0027] The maximum fuel cell power-related vehicle speed v_max can also be determined by other vehicle parameters, such as the current driving resistance. S1 , the angle of inclination S2 the roadway, navigation data S3 and / or the provision of a minimum charging capacityS4 of the high-voltage storage system 9 .

[0028] Preferably, a limitation to the maximum fuel cell power-related vehicle speed v_max is only applied up to a predetermined comparatively low speed reduction below the driver-requested target power P. EM_soll This was done to ensure that the driver does not perceive too strong a power limitation.

[0029] A further limitation of the vehicle speed v is achieved, for example, by switching on the high-voltage battery. 9 avoided.

[0030] The maximum fuel cell-related vehicle speed v_max can also depend on the maximum possible power P. HVS_max or the state of charge HVS_SOC of the high-voltage battery 9 be determined.

[0031] The limitation to the maximum fuel cell power-related vehicle speed v_max can only be activated if the maximum possible power P FCS_max the fuel cell 8 a defined degradation threshold P FCS_deg has fallen below this limit. However, this limit can also be manually activated and deactivated by the driver using a control element.

[0032] Finally, the invention is further described using 5 phases. P1 until P5 a driving profile example according to Fig. 2 explained in more detail: - The upper curve describes the vehicle speed v over time t. - The middle curve describes the state of charge of the high-voltage battery HVS_SOC over time t. - The lower curve describes the driver's request or the accelerator pedal angle FW over time t. phase without invention with invention P1 Acceleration to a (slightly) higher speed than with the invention. Acceleration until the vehicle speed is regulated by the speed controller to the speed limit v_max calculated according to the invention. P2 The high-voltage storage (battery) is discharged because the stationary power demand for the driving task is not covered by the The high-voltage storage (battery) is being recharged because there is still a power reserve from the fuel cell available for recharging. The fuel cell can be covered. If the high-voltage storage is completely discharged, the vehicle speed drops. The vehicle speed can be maintained continuously. P3 During vehicle deceleration, the HV storage is recharged at a relatively low level through recuperation and the fuel cell. During vehicle deceleration, the HV storage is recharged to a relatively high level through recuperation and the fuel cell. P4 The energy content of the high-voltage battery is insufficient to maintain the vehicle acceleration (dynamic demand) desired by the driver throughout the entire acceleration process. The vehicle acceleration drops significantly below the driver's desired level. The energy content of the high-voltage (HV) battery is sufficient to maintain the vehicle acceleration desired by the driver throughout the entire acceleration process. The HV battery is recharged immediately after reaching a constant speed phase or a lower acceleration demand. P5 The HV storage can only be recharged after the significantly slower / longer acceleration process has finished. The HV storage unit reaches a high state of charge early on in order to be able to cover further intermediate accelerations with high dynamics.

Claims

[1] Drive degradation system for a vehicle with at least one electronically controlled electric motor (6) which generates an electric motor power (P EM ) the vehicle, with at least two power sources for generating the electromotive power (P EM ), wherein a first power source in the form of a high-voltage battery (9; HVS) and a second power source in the form of a fuel cell (8; FCS) are provided, which can be used alternatively or together to generate the electromotive power (P EM ) can be used with a degradation module (12) which depends on the current maximum possible power (P FCS_max ) of the fuel cell (8; FCS) calculates a maximum fuel cell power-related vehicle speed (v_max) for steady-state operation, and with a torque coordinator (4) that calculates the electromotive target power (P EM) such that the maximum fuel cell power-related vehicle speed (v_max) is not exceeded in stationary operation, whereby the high-voltage battery (9; HVS) is not used as a power source for driving the vehicle in stationary operation at least until a dynamic requirement arises. [2] Drive degradation system according to claim 1, characterized by , that a limitation to the maximum fuel cell power-related vehicle speed (v_max) only applies up to a predetermined speed reduction extent depending on the driver-requested target power (P) EM_soll ) is carried out. [3] Drive degradation system according to one of the preceding claims, characterized by , that a limitation to the maximum fuel cell power-related vehicle speed (v_max) only applies up to a predetermined speed reduction extent depending on the driver-requested target power (P)EM_soll ) is carried out and that a further limitation of the vehicle speed (v) by switching on the high-voltage battery (9; HVS) is avoided. [4] Drive degradation system according to one of the preceding claims, characterized by , that the maximum fuel cell power-related vehicle speed (v_max) depends on the maximum possible power (P) HVS_max ) and / or the state of charge (HVS_SOC) of the high-voltage battery (9; HVS). [5] Drive degradation system according to one of the preceding claims, characterized by , that the limitation to the maximum fuel cell power-related vehicle speed (v_max) is only activated when the maximum possible power (P) FCS_max ) of the fuel cell (8; FCS) a defined degradation threshold (P FCS_deg has fallen below the threshold.