Apparatus and method for braking a system to a standstill

Abstract

The invention relates to a system, an apparatus and a method for determining a velocity trajectory for braking a system to a standstill. The method comprises using a polynomial having a plurality of parameters to define the velocity trajectory for braking the system to a standstill, wherein the zeroth and the first time derivatives of the polynomial are zero at the time at which the system reaches a standstill; and determining the plurality of parameters for defining a velocity trajectory, wherein determining the plurality of parameters for defining a velocity trajectory comprises: using a boundary condition to ensure that the velocity trajectory is continuous at the time at which braking of the system to a standstill begins; and using a boundary condition to ensure that the feedforward torque corresponding to the velocity trajectory is continuous at the time at which braking of the system to a standstill begins. The method may be used to determine a plurality of velocity trajectories in order to generate a weighted velocity trajectory that can be used to brake the system to a standstill.

Description

[0001] R. 417372

[0002] - 1 -

[0003] Description

[0004] title

[0005] Device and method for braking a system to a standstill

[0006] The present invention relates to a device and a method for electrically braking a system to a standstill, hereinafter also referred to as "e-braking to zero".

[0007] State of the art

[0008] In "e-braking to zero," one or more electric motors and / or one or more hydraulic systems can be used to bring a vehicle to a complete stop. Without limitation of generality, electric braking is described in particular below. However, the disclosure is valid analogously for hydraulic braking systems or a combination of several braking systems. The method can involve converting the vehicle's kinetic energy into electrical energy, which is then released as heat or stored. Such electric braking can be used, for example, in electric and hybrid vehicles to reduce wear on conventional braking systems and / or to increase energy efficiency, for example, by recovering energy generated during braking.

[0009] Braking to a standstill is distinct from regenerative braking. Regenerative braking aims to optimally capture kinetic energy that would otherwise be lost as heat and dust during braking and convert it into electrical energy. The energy recovered in this way can then be stored in an energy storage system for later use or directly supplied to a consumer to directly or indirectly increase the vehicle's range. R. 417372

[0010] - 2 -

[0011] Braking, on the other hand, is aimed at controlling the torque of, for example, a vehicle's electric motor or hydraulic system from a certain point until the vehicle comes to a complete stop, and at keeping the vehicle stationary. Braking can provide a continuous transition to a standstill, thus offering a comfortable driving experience, both on level ground and uphill or downhill.

[0012] Conventional methods for braking a system to a standstill calculate a velocity trajectory and a pre-control torque. The vehicle's motion is then controlled by a controller to follow the calculated velocity trajectory, assuming a linear decrease in speed to allow for a continuous transition to standstill.

[0013] However, such braking is often perceived as unnatural by vehicle users because the braking is at least partially jerky and / or at least partially too fast or too slow, compared to, for example, the braking behavior of an average vehicle user in a traffic situation.

[0014] Disclosure of the invention

[0015] The invention provides a device and a method for braking a system to a standstill with the features of the independent patent claims.

[0016] Preferred embodiments are the subject of the respective dependent claims.

[0017] The present invention solves the aforementioned problems. Using a polynomial approach, a velocity trajectory that is at least once differentiable over time, preferably twice differentiable, and a corresponding pre-control torque that is at least continuous over time, preferably once differentiable, are calculated to enable a smooth braking process down to a standstill.

[0018] The temporal change in the velocity trajectory and the temporal change in the pre-control torque exhibit no discontinuities over the time until standstill, thus enabling braking to a standstill. Jerky braking is R. 417372

[0019] - 3 -

[0020] This is possible if a vehicle is brought to a standstill purely electrically without friction brakes. The speed, the change in speed, and the change in acceleration all transition to zero continuously, without any discontinuities, until a desired stopping time is reached. The stopping time can fall within an interval limited by a minimum and a maximum stopping time.

[0021] According to a first aspect, the invention relates to a method for determining a velocity trajectory for braking a system to a standstill, wherein the method comprises: using a polynomial with a plurality of parameters to define the velocity trajectory for braking the system to a standstill, wherein the zeroth and the first time derivatives of the polynomial have a zero at the time of standstill; and determining the plurality of parameters for defining a velocity trajectory, wherein determining the plurality of parameters for defining a velocity trajectory comprises: using a boundary condition to ensure the continuity of the velocity trajectory at the time of commencement of braking the system to a standstill;and using a boundary condition to ensure the continuity of the feedforward torque from the time the system begins to brake until it comes to a standstill, which corresponds to the velocity trajectory.

[0022] According to further training, the second time derivative of the polynomial P(t) at time t also shows f The standstill has a zero point.

[0023] According to further training, determining the multitude of parameters for defining the velocity trajectory includes using a boundary condition to ensure the continuity of the first temporal derivative of the feedforward torque at the time of the start of braking the system until it comes to a standstill.

[0024] According to further training, determining the multitude of parameters for defining the velocity trajectory includes selecting a stopping time from the time the system begins braking until it comes to a standstill, up to the point of...

[0025] Standstill.R. 417372

[0026] - 4 -

[0027] According to further training, the stopping time lies within a time interval that is limited by a minimum stopping time and / or a maximum stopping time.

[0028] According to a second aspect, the invention relates to a method for braking a system to a standstill, wherein the method comprises: determining a first velocity trajectory for braking the system to a standstill according to the method described above, wherein determining the plurality of parameters for defining the velocity trajectory includes using a boundary condition to ensure the continuity of the first temporal derivative of the feedforward torque at the time of the commencement of braking the system to a standstill;

[0029] Determine a second velocity trajectory for braking the system to a standstill according to the procedure described above, where determining the multitude of parameters for defining the velocity trajectory includes selecting a stopping time from the time braking begins until the system comes to a standstill; weighting the first velocity trajectory over the stopping time; weighting the second velocity trajectory over the stopping time; adding the weighted first velocity trajectory and the weighted second velocity trajectory; and braking the system to a standstill based on the added velocity trajectory. Braking the system can be achieved by calculating a target braking torque based on the velocity trajectory. The target braking torque can be transmitted, for example, to an electric motor and / or a mechanical braking system.Mixed braking systems such as electric, hydraulic and / or mechanical braking are also possible.

[0030] According to a further development, the procedure for braking a system to a standstill also includes numerically determining an added pre-control torque, which corresponds to the added velocity trajectory.

[0031] According to further training, the procedure for braking a system to a standstill also includes transforming the system into a planar and frictionless system in order to separate incline moments from the braking of the system.

[0032] According to further training, in the procedures described above, the polynomial in the interval from the time of the start of braking of the system to the time of R. 417372

[0033] - 5 -

[0034] Standstill of the system is defined until P(t) = (a ■ t + b) ■ (t — t f ) 3, where a, b, and tf are the multitude of parameters for defining the velocity trajectory.

[0035] According to a third aspect, the invention relates to a system comprising: at least one braking device with an electric motor configured to brake the system to a standstill; at least one device for controlling the system, the device comprising a computer with a storage medium containing instructions stored thereon which, when executed by the computer, cause the computer to perform a method as described above for braking the system to a standstill.

[0036] According to a third aspect, the invention relates to a computer-readable storage medium which has instructions stored thereon which, when executed by a computer, cause the computer to carry out a method as described above.

[0037] a

[0038] Brief description of the drawings

[0039] It shows:

[0040] Figure 1 shows a schematic representation of a velocity trajectory and a corresponding pre-control torque as a function of time according to an exemplary embodiment of a method for braking a system to standstill;

[0041] Figure 2 shows a schematic representation of an exemplary embodiment of a method for determining a velocity trajectory for braking a system to a standstill;

[0042] Figure 3 shows a schematic representation of an exemplary embodiment of a method for weighting the velocity trajectories of Figure 2; and

[0043] Figure 4 shows a schematic representation of a vehicle with an exemplary device for braking the vehicle to a standstill. R. 417372

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[0045] In all figures, identical or functionally equivalent elements and devices are designated with the same reference numerals. The numbering of process steps serves for clarity and generally does not imply a specific chronological order. In particular, several process steps can be performed simultaneously.

[0046] Description of the exemplary implementations

[0047] Figure 1 shows a schematic representation of a velocity trajectory v(t) and a corresponding pre-control torque q(t) as a function of time t according to an exemplary embodiment of a method for braking a system to standstill at t = t f .

[0048] According to the exemplary embodiment, the velocity trajectory v(t) is used to brake a system between time t = t, = 0 until it comes to a standstill at time t = t fdescribed by a polynomial P(t) in time. For example, without loss of generality, let

[0049] v(t) = P(t) = (a · t + b) · (t — tf) 3 (1)

[0050] where a and b are parameters determined such that the boundary conditions shown in Figure 1 are met at time t = t, = 0 and at time t = t f The conditions are met. The velocity trajectory v(t) is continuous at time t = t, = 0. In other words, it shows that

[0051]

[0052] = 0 no jump discontinuities such that v(tj = 0) = v0.

[0053]

[0054] = 0) = v0(2)

[0055] The zeroth, first, and second time derivatives of the polynomial P(t) show at time t f The standstill has a zero point. Generally, the system is at time t. fAt rest, without acceleration, and experiencing no change in acceleration. In other words, the boundary conditions apply.

[0056] v(t = t) = 0 (3)R. 417372

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[0058] dv(t = t f ) = o dt dv 2 (t = t f )

[0059]

[0060] The feedforward torque q(t) corresponding to the velocity trajectory v(t) can be determined by the relationship

[0061] q(t) = r w ■ M ■ ( 6 )

[0062]

[0063] at

[0064] be linked to the polynomial P(t), i.e., the velocity trajectory v(t), where M is the torque of the electric motor used for braking and r wThe lever arm acting on the shaft of the electric motor is denoted by . Analogous to the velocity trajectory v(t) described above at time t = t, = 0, the feedforward torque q(t) is also continuous at time t = t, = 0. In particular, its change at time t = t, = 0 is also continuous, which implies that the velocity trajectory v(t) is also continuous at time t = t, = 0. In other words, the following boundary conditions apply to the feedforward torque q(t).

[0065] q(t = tj) = q0(7) dq(t — tj) - ^7 - = dq

[0066]

[0067] at0

[0068] For the parameters a and b, the following conditions result from the boundary conditions (2) and (7):

[0069] a = — - Qo (9) tf r w - M ■ tf v0b = ~A (10)

[0070]

[0071] tf

[0072] For a selected time until standstill at t = tf The parameters a and b can thus be determined. Under the additional boundary condition (8), the additional condition R results for the parameters a and b. 417372

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[0074] 6 ■ a ■ tf 2 — 6 ■ b ■ t f = — (11)

[0075]

[0076] r w ■ M

[0077] Substituting conditions (9) and (10) into condition (11) yields a second-order polynomial in standstill t. f

[0078] dq0■ t 2 + 6 ■ q0■ t f + 12 ■ v0■ r w ■ M = 0 (12)

[0079] A zero of the polynomial is the desired time until standstill at t = t. It can be calculated in the conventional way using the quadratic formula.

[0080] As shown in the example above, the time until the vehicle comes to a standstill can also be chosen so that it lies within a stopping time interval. This interval can be limited by a minimum and a maximum stopping time. A maximum stopping time may be desirable at low speeds v0. A minimum stopping time may be desirable at high speeds v0. Alternatively or additionally, the interval can also be restricted by the requirement that the velocity trajectory v(t) does not overshoot, thus preventing the vehicle from moving.

[0081] If the time until standstill according to the solution of the polynomial (12) with the first velocity trajectory Vi(t) is not within a desired time interval, a second velocity trajectory v2(t) can be determined, which leads to a shorter or a longer time until standstill.

[0082] The two velocity trajectories Vi(t) and v2(t) can be weighted to enable, for example, smooth braking from the start of braking to a standstill, possibly using a predetermined stopping time.

[0083] Figure 2 shows a schematic representation of an exemplary embodiment of a method for determining a velocity trajectory for braking a system to a standstill.

[0084] The method includes an optional transformation (2210) into a planar and frictionless system to, for example, separate slope moments and external friction from the electric motor torque for braking the system to standstill. R. 417372

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[0086] The procedure includes calculating the derivative of the electric motor's torque and filtering (2220) to determine the boundary conditions as described above with reference to Figure 1.

[0087] The procedure comprises calculating a first velocity trajectory Vi(t) and / or a second velocity trajectory v2(t) as described above with reference to Figure 1. The calculations can be performed in a single step. The first velocity trajectory Vi(t) can be a velocity trajectory with a stopping time within an interval bounded by a minimum stopping time and a maximum stopping time.

[0088] The procedure can involve weighting the first velocity trajectory Vi(t) and the second velocity trajectory v2(t). The weighting can be equivalent to multiplying the velocity trajectory Vi(t) and the second velocity trajectory v2(t) by a respective weighting function over the stopping time. The weighting function can be increasing for one velocity trajectory, while decreasing for another. The resulting velocity trajectory can, for example, be defined by

[0089] W

[0090]

[0091] i(t) ■ ViCt) + (1 - w^t)) ■ v2(t) (13)

[0092] The desired weighted velocity trajectory is obtained using the boundary conditions (2), (3), (4), (5), (7), and (8). To reduce the effort required for the analytical determination of the solutions using the weighting function, the feedforward torque q(t) can also be determined numerically. The analytical solutions are obtained using the conventional rules of differentiation.

[0093] The procedure includes an optional inverse transformation (2250) into the original system before the optional transformation (2210) into the planar and frictionless system.

[0094] Figure 3 shows a schematic representation of an exemplary embodiment of a method for weighting 3240 the velocity trajectories of Figure 2. R. 417372

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[0096] The procedure includes calculating the derivative and filtering the weighting function.

[0097] Figure 4 shows a schematic representation of a vehicle 4000 with exemplary braking device 4100, which is controlled by exemplary embodiments of the device 4200 for controlling the system 4000.

[0098] The vehicle 4000, for example, comprises four brake devices 4100. One, several, or each brake device 4100 may include an electric motor and / or hydraulics and be coupled to one or more devices 4200 for controlling the system 4000. The system 4000 may be steered by a steering system 4300. The steering system 4300 may be coupled directly or indirectly to one or more devices 4200 for controlling the system 4000.

Claims

1. R. 417372 - 11 - Claims 1. Method for determining a velocity trajectory v(t) for braking a system to standstill, wherein the method comprises: Using a polynomial P(t) with a multitude of parameters to define the velocity trajectory v(t) for braking the system to a standstill, where the zeroth and first time derivatives of the polynomial P(t) at time t f exhibits a zero point of standstill; and determining the multitude of parameters for defining a velocity trajectory v(t), wherein determining the multitude of parameters for defining a velocity trajectory includes: Using a boundary condition to ensure the continuity of the velocity trajectory v(t) at time t, the start of braking the system until it comes to a standstill; and using a boundary condition to ensure the continuity of the feedforward torque q(t) at time t, the start of braking the system until it comes to a standstill, which corresponds to the velocity trajectory v(t).

2. Method for determining a velocity trajectory v(t) for braking a system to a standstill according to claim 1, wherein also the second time derivative of the polynomial P(t) at time t f The standstill has a zero point.

3. Method for determining a velocity trajectory v(t) for braking a system to a standstill according to claim 1 or 2, wherein determining the plurality of parameters for defining the velocity trajectory further comprises: Using a boundary condition to ensure the continuity of the first time derivative of the feedforward torque q(t) at time t, the start of braking the system until standstill. R. 417372 - 12 - 4. Method for determining a velocity trajectory v(t) for braking a system to a standstill according to claim 1 or 1, wherein determining the plurality of parameters for defining the velocity trajectory comprises: Select a holding time from time t, the start of braking of the system, until standstill at time t. f of standstill.

5. Method for determining a velocity trajectory v(t) for braking a system to a standstill according to claim 4, wherein the stopping time lies within a time interval limited by a minimum stopping time and / or a maximum stopping time.

6. Method for braking a system to a standstill, the method comprising: Determining a first velocity trajectory V1(t) for braking the system to a standstill according to the method of claim 3; Determining a second velocity trajectory v2(t) for braking the system to a standstill according to the method according to any one of claims 4 and 5; Weights of the first velocity trajectory V1(t) over the stopping time; Weights of the second velocity trajectory v2(t) over the stopping time; Adding the weighted first velocity trajectory V1(t) and the weighted second velocity trajectory v2(t); and Braking the system to a standstill based on the added velocity trajectory.

7. Method for braking a system to a standstill according to claim 6, wherein the method further comprises: Numerical determination of an added pre-control torque corresponding to the added velocity trajectory. R. 417372 - 13 - 8. Method for braking a system to a standstill according to claim 6 or 7, wherein the method further comprises: Transforming the system into a planar and frictionless system to separate slope moments from the braking of the system.

9. Method according to any one of claims 1 to 8, wherein the polynomial P(t) in the interval from time t, the start of braking of the system, to time t f the standstill of the system is defined until P(t) = (a ■ t + b) ■ (t — t f ) 3 , where a and b and t f the multitude of parameters for defining the velocity trajectory v(t).

10. System (4000), wherein the system (4000) comprises: at least one braking device (4100) with an electric motor configured to brake the system (4000) to a standstill; at least one device (4200) for controlling the system (4000), wherein the device (4200) comprises a computer with a storage medium having instructions stored thereon which, when executed by the computer, cause the computer to perform the method according to any one of claims 1 to 9 for braking the system (4000) to a standstill.

11. A computer-readable storage medium comprising instructions stored thereon which, when executed by a computer, cause the computer to perform the method according to any one of claims 1 to 9.

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