Method for operating a trailer with an electric drive and friction brakes, as well as trailer brake control unit and trailer for carrying out the method

Description

[0001] The invention relates to the field of commercial vehicles, and in particular to trailers designed as commercial vehicles. A trailer designed as a commercial vehicle is pulled by a towing vehicle, which is also designed as a commercial vehicle, for example. Such trailers referred to here include, in particular, semi-trailers and drawbar trailers.

[0002] According to the state of the art, commercial vehicles designed as towing vehicles are primarily equipped with an internal combustion engine to power the towing vehicle and, if necessary, to pull a trailer. These commercial vehicles are increasingly being equipped with an electric drive according to the state of the art. Accordingly, an electric drive can be provided in addition to the internal combustion engine in the towing vehicle, so that the towing vehicle is designed as a hybrid vehicle. It is also known for an electric drive to be arranged in the trailer vehicle to form a hybrid combination of towing vehicle and trailer.

[0003] Regardless of whether an electric drive is installed in the towing vehicle, the trailer vehicle, or both vehicles of a combination, the electric drive primarily serves to support the combustion engine, namely to operate the towing vehicle's combustion engine in an energy-efficient speed range or to provide additional thrust, for example, when starting off or driving uphill. Furthermore, the electric drive can recover the kinetic and potential energy of the combination, for example, during braking, and store it as electrical energy in one or more energy storage units. This energy can be made available again for propulsion when needed.

[0004] An electric drive also serves to support or fully implement a required negative acceleration, namely braking. This is particularly advantageous in protecting the friction brakes of both the towing vehicle and the trailer.

[0005] However, compared to trailers without an electric drive, electric drives in trailers not only lead to changes in behavior that are directly attributable to the electric drive, but also to an overall change in the behavior of the trailer, particularly when braking. An electric drive, which in trailers usually only acts on one axle, results in additional weight due to the electric drive, which is essentially located in the area of the electrically driven axle. Despite a trailer vehicle usually being evenly loaded, this results in an imbalance of the masses acting on the wheels. Depending on the type of braking - namely whether braking is done with an electric drive or with friction brakes or a combination - either the wheels on the driven axle or the wheels on the non-driven axle are more likely to lock than the other wheels.

[0006] For example, the electric drive is usually used preferentially for braking, with friction brakes only being used when greater braking requirements are required. Since the electrically driven axle also has friction brakes, and all friction brakes are usually controlled with identical brake pressure, the wheels of the driven axle lock before the non-driven wheels due to the summation of the braking effect of the electric drive and the friction brakes. For this reason, it is known to completely switch off the torque of the electric drive when the friction brakes are activated when the friction brakes are activated, and to control deceleration solely using the friction brakes. If the friction brakes exert the same braking force on all wheels, the wheels with a lower mass will lock earlier than those with a comparatively higher mass.This behavior is particularly problematic because speed sensors that can detect wheel locking are often not located on every wheel or axle for cost reasons and to reduce complexity. Thus, a wheel locking, which must be responded to in order to maintain vehicle stability, is only detected if the wheel has a sensor. If the weight distribution in the trailer is even, this is not a problem because all wheels behave the same or very similarly anyway. However, if the weight is unevenly distributed due to the mass of the electric drive, a locking drive wheel would only be detected very late if sensors were only located on the non-driven axle, which could lead to stability problems.

[0007] DE 10 2019 119 786 A1 discloses a method for assisting a towing vehicle in the event of a loss of traction by a trailer vehicle. A trailer brake control unit determines the vehicle state of the trailer vehicle, and a control signal for an electric drive of the trailer vehicle to assist the towing vehicle is generated depending on an acceleration request and the vehicle state of the trailer vehicle. To determine the vehicle state, an axle load of the trailer vehicle's axles and / or a mass distribution in the trailer vehicle is determined. This allows different drive torques to be generated depending on the mass distribution or the overall load state, particularly in the case of electric drives with independent wheel drive, i.e., with multiple electric motors, each of which is assigned to drive a single wheel.In this case, these different drive torques would be specified in the control signal for the electric drive.

[0008] EP 2 172 378 A1 discloses a hybrid-powered vehicle with an internal combustion engine for driving a front axle of the vehicle and an electric motor for driving a rear axle of the vehicle and for regenerative braking on the rear axle. Both the front axle and the rear axle each have a right and a left wheel brake in the form of a friction brake. Braking force is gradually shifted from the driven rear axle to the driven front axle, with this shift depending on the degree of vehicle instability.

[0009] EP 3 381 774 A1 discloses a continuous braking device for a vehicle having an electric machine designed for regenerative braking, wherein a continuous braking control device is designed to determine a continuous braking braking request depending on a set vehicle deceleration request.

[0010] The object of the present invention is therefore to address the problems of the prior art. In particular, the stability of trailer vehicles of the aforementioned type, particularly in the event of one of the wheels locking, is to be improved and / or tire wear reduced with as little additional effort as possible. In any event, the object of the present invention is to find an alternative to the prior art.

[0011] To this end, the invention relates to a method according to claim 1.

[0012] The method is used to operate a trailer vehicle that has an electric drive and friction brakes. The method first comprises determining a differential mass between a first mass of the driven axle of the trailer vehicle and a second mass of the non-driven axle of the trailer vehicle. The first mass and the second mass each refer to the masses of the corresponding axle itself, without including a mass acting on the axle, for example due to a chassis or a load. A deceleration torque is then determined as a function of the differential mass, and at least, in particular exactly, the determined deceleration torque is generated on the driven axle using the electric drive when the friction brakes of the trailer vehicle are activated. Activating the friction brakes here includes building up, but also maintaining, a braking pressure at the friction brakes.In contrast, the term deactivation of the friction brakes is also used below, which includes releasing brake pressure on the friction brakes or retracting electronic actuators of the friction brakes.

[0013] By determining the differential mass and the resulting deceleration torque, which is then applied to the driven axle by the electric drive, a type of compensating torque is provided by the electric drive. This compensating torque ensures that the driven and non-driven axles behave almost identically in the event of a friction brake activation and a resulting change in slip.

[0014] The method is based on the realization that during heavy braking, when an anti-lock braking system intervenes, an electric drive typically immediately reduces its torque to zero to allow the anti-lock braking system to control the braking process by activating all friction brakes without the influence of the electric drive. This typically ignores the mass of the electric drive acting on the driven wheels, resulting in non-ideal control of the friction brakes by the anti-lock braking system. The determined differential mass, which corresponds to an additional mass of the driven axle generated by the electric drive compared to a non-driven axle, is then taken into account during braking.

[0015] With the present invention, the identical behavior of all wheels in the event of a slip change due to the use of friction brakes also allows the use of a few speed sensors on the wheels. A change in the speed of one wheel essentially represents a change in the speed of all wheels. This also eliminates the need for individual control of each friction brake on each wheel, allowing for improved performance during heavy braking despite the two separate controls for the left and right sides of the trailer.

[0016] According to a first embodiment, the determined deceleration torque is generated during a braking and / or pressure holding phase generated by an anti-lock braking system.

[0017] An anti-lock braking system, referred to as ABS for short, typically engages when a trailer wheel locks. This locking of the wheel is detected by a wheel speed sensor. Locking is assumed either when the wheel speed drops completely to zero or when a speed gradient changes abruptly.

[0018] If a locked wheel is detected, the ABS significantly reduces the brake pressure in order to release the locked wheel. After the pressure has been reduced and the wheel has been released, the brake pressure is increased again; this increase in brake pressure can be referred to as the ABS braking phase. In contrast, a reduction in brake pressure can be referred to as the ABS venting phase. When the brake pressure is increased, it is usually increased gradually and held constant for short periods of time in order to detect any further locking of the wheels. This maintenance of pressure can also be referred to as the pressure holding phase, although the pressure holding phase can occur within the braking phase.The determined deceleration torque is therefore generated at least when an ABS activates the wheel brakes during the braking and / or pressure holding phases in order to enable the wheels to behave in the same way despite the different weight of the axles, especially when the friction brakes are activated.

[0019] According to a further embodiment, the deceleration torque is reduced during an ABS venting phase, and if a new braking and / or pressure-holding phase is generated by the ABS, the determined deceleration torque is reapplied. This enables all wheels to roll quickly after locking, in particular also the wheels of the driven axle to roll after locking.

[0020] According to a further embodiment, the deceleration torque is determined as a function of the differential mass, the acceleration due to gravity, and a dynamic tire radius. The dynamic tire radius preferably corresponds to the standing height of a loaded wheel between the contact patch and the wheel center. This is determined, for example, based on the trailer's load before the start of the journey.

[0021] The determined deceleration torque per wheel (M rad ) can be determined using the following formula: M rad = m Achse 2 ⋅ g ⋅ r dyn

[0022] M rad denotes the torque of the motor at a wheel of the driven axle in Nm, and m axle denotes the additional mass of the electric drive on the driven axle in kg, i.e., the differential mass. Furthermore, g corresponds to the acceleration due to gravity in m / s 2<, and r dyn corresponds to the dynamic tire radius in m.

[0023] According to a further embodiment, the deceleration torque is determined as a function of the differential mass, the acceleration due to gravity, a dynamic tire radius and an inclination of the trailer vehicle, in particular a rotation of the trailer vehicle about a longitudinal axis and / or a transverse axis of the trailer vehicle with respect to a horizontal alignment of the trailer vehicle.

[0024] The determined deceleration torque per wheel (M rad ) can be determined using the following formula: M rad = m Achse 2 ⋅ g ⋅ cos φ ⋅ r dyn

[0025] M rad, m axle, g, and r dyn are used as above. The quantity φ denotes an angle and corresponds to the inclination of the trailer vehicle due to the inclination of the road on which the trailer vehicle is positioned. The inclination or road inclination can preferably be determined using an inclination sensor on the trailer vehicle or a sensor whose sensor signal can be used to derive an inclination of the trailer vehicle.

[0026] By taking into account not only the differential mass, but also, optionally, the trailer's inclination, and the dynamic tire radius, the deceleration torque calculation can be determined even more precisely. This allows the trailer's behavior during heavy braking to be influenced even more precisely, further reducing tire wear and improving trailer stability.

[0027] According to the aforementioned formula, a distinction must be made as to whether the determined deceleration torque is determined for both wheels of an axle or for one wheel of an axle. In the case of the formulas listed, the deceleration torque is therefore determined for one of the wheels of the driven axle. This is advantageous when the electric drive comprises several electric motors, each of which drives a wheel. If, on the other hand, a central axle motor is provided that drives two or more wheels, and the deceleration torque is determined for the central axle motor, i.e., for two or more wheels, the deceleration torque is preferably determined using one of the aforementioned formulas, whereby division by two is omitted.

[0028] According to a further embodiment, after a locked wheel is detected, a feed torque is generated by the electric drive, in particular at the start of the venting phase or even before, namely immediately after the locking is detected. The feed torque is generated until the wheel is no longer locked or the friction brakes are reactivated. This improves the dynamics of the trailer vehicle because the restart of the driven wheels is accelerated, for example during a venting phase. A sluggish reaction of the friction brake, which, for example, requires a certain amount of time after deactivation until enough air has been released to release the locked wheel, is counteracted by generating a force with the electric drive to restart the wheel. Despite the braking torque still being present from the friction brakes, a rapid restart is thus possible.

[0029] According to a further embodiment of the method, the trailer vehicle comprises an air suspension system, in particular an electronic one, in which each of the wheels is suspended via an air bellows. By controlling the air suspension system, the pressure in the air bellows can be regulated depending on the trailer vehicle's load. At the same time, sensors can measure the air pressure in the air bellows, which in turn can be used to determine the mass of the trailer vehicle. Accordingly, to determine the partial masses acting on the axles, the air pressure in the corresponding air bellows is measured, and the partial masses acting on the axles are added together to form the total mass of the trailer vehicle. In In this way, the mass of the trailer vehicle can be determined easily at any time.

[0030] According to a further embodiment, the trailer vehicle comprises a trailer brake control unit. The trailer brake control unit preferably receives the partial masses from the air suspension system in order to determine the total mass of the trailer vehicle. Alternatively, the trailer brake control unit receives the total mass of the trailer vehicle already determined by the air suspension system from the partial masses. The trailer brake control unit serves to control the friction brakes and the electric drive. Accordingly, at least the differential mass is retrieved with the trailer brake control unit or determined from data provided to the trailer brake control unit. In particular, the trailer brake control unit also comprises an anti-lock braking system.This allows the friction brakes to be controlled and the electric drive to be actuated centrally in a single control unit, so that coordination, particularly when an anti-lock braking system intervenes, is quickly enabled by central data processing without the need for delayed data communication between individual control units.

[0031] Furthermore, the invention relates to a trailer brake control device which is configured to carry out the method according to one of the aforementioned embodiments.

[0032] According to one embodiment, the trailer brake control unit comprises an anti-lock braking system and serves to control the friction brakes of the trailer vehicle and the electric drive of the trailer vehicle.

[0033] Furthermore, the invention relates to a trailer vehicle with an embodiment of the aforementioned trailer brake control unit.

[0034] According to one embodiment, the trailer vehicle comprises an electric drive and friction brakes.

[0035] According to a further embodiment, the trailer vehicle comprises an air suspension system, in particular an electronic one.

[0036] Furthermore, the invention relates to a combination comprising an embodiment of the aforementioned trailer vehicle and a towing vehicle.

[0037] Further embodiments are shown in the figures, which show Figure 1 shows a team and Figure 2 shows the steps of the method according to an embodiment.

[0038] Figure 1shows a vehicle combination 10 on a roadway 11. The vehicle combination 10 comprises a towing vehicle 12 and a trailer vehicle 14 with a braking system 15. A brake pedal 16 is arranged in the towing vehicle 12, with which a braking request 20 can be generated by a driver. The braking request 20 is sent to a brake control unit (EBS) 18 of the towing vehicle 12. The braking request 20 is then forwarded from the brake control unit 18 to a trailer brake control unit (TEBS) 22, unchanged or adjusted. The trailer brake control unit 22 has an anti-lock braking system 23 in order to reduce the period during which the wheels 30 are locked in the event of heavy braking in which the wheels 30 of the trailer vehicle 14 lock.

[0039] The braking request 20 is thus converted by the brake control unit 18 of the towing vehicle 12 into a braking pressure 34 for actuating friction brakes (not shown) of the towing vehicle 12. Depending on the type of braking request 20, the braking request 20 itself or a braking request 20 generated by the brake control unit 18 of the towing vehicle 12 for the trailer brake control unit 22 is transmitted to the trailer brake control unit 22 of the trailer vehicle 14. The trailer brake control unit 22 controls an electric drive 24 depending on the braking request 20 by also forwarding the braking request 20 to a control unit 26 of the electric drive 24. In a further exemplary embodiment not shown here, but which is also encompassed by the invention, the control unit 26 of the electric drive 24 is a component of the trailer brake control unit 22.Depending on the braking request 20, friction brakes 28 are also activated, which are arranged on each wheel 30 of the axles 32 of the trailer vehicle 14. This is achieved by transmitting a brake pressure 34 to activate the friction brakes 28.

[0040] In order to generate a suitable braking force in the form of the brake pressure 34 by the trailer brake control unit 22 depending on the braking request 20, a control unit 37 of an air suspension system, shown here as an electronic air suspension system (ECAS) 38, supplies the trailer brake control unit 22 with data corresponding to partial masses 42a, 42b, 42c acting on the individual axles 32 or the individual wheels 28 of the trailer vehicle 14. According to an alternative embodiment of the invention not shown in the figures, all features of the Figure 1 includes, whereby, in deviation from Figure 1The air suspension system 38 is integrated into the trailer brake control unit 22. Thus, alternatively, the bellows pressure 34 is also measured directly in the trailer brake control unit 22, and the partial masses 42a, 42b, 42c are determined accordingly in the trailer brake control unit 22 without a separate control unit 37 of the air suspension system 38.

[0041] In the trailer brake control unit 22, a total mass of the trailer vehicle 14 can be determined from these partial masses 42a, 42b, 42c. The partial masses 42a, 42b, 42c are determined in the control unit 37 of the electronic air suspension system 38 by measuring pressure values of air bellows 40 arranged on each of the wheels 30 and deriving the partial masses 42a, 42b, 42c of the trailer vehicle 14 therefrom. According to an alternative embodiment not shown in the figures, essentially all features of the Fig. 1 contain, whereby only deviating from the Fig. 1only one sensor in one of the air bellows is provided to measure a total mass.

[0042] In addition to the control unit 26 for the electric drive 24, the electric drive 24 has an inverter 44 which, depending on the control with the control unit 26, supplies an electric motor 46, which in this case is a central axle motor, with energy from a battery 48 in order to drive the wheels 30 of the axle 32, which are connected to the electric motor 46. For braking, the inverter 44 is controlled such that electrical energy flows into the battery 48 during generator operation of the electric motor 46. According to this exemplary embodiment, the control unit 26 of the electric drive receives control signals from the trailer brake control unit 22 in order to operate the electric drive 24. To regulate the inverter 44, information 49 from the brake control unit 22 is supplied to the control unit 26 of the electric drive 24.The control unit 26 of the electric drive 24 or the trailer brake control unit 22 also determines a wheel speed of the wheels 30 of the electrically driven axle 32 as a function of the speed of the electric motor 46 or as a function of wheel speed sensors 50, which are shown here only on the non-driven wheels 30. From this, slippage can be determined using the control unit 26 or the trailer brake control unit 22, so that locking wheels can be detected. Furthermore, a deceleration torque 54 can be determined using the trailer brake control unit 22 in order to operate the electric drive 24 during the braking and / or pressure-maintaining phases in generator mode, also called recuperation mode, during braking performed by the anti-lock braking system 23.

[0043] Figure 2shows steps of an embodiment of the method 68. In a step 70, a first mass 69 of a driven axle 32 and a second mass 71 of a non-driven axle 32 of the trailer vehicle 14 are determined by the trailer brake control unit 22, for example, retrieved from a memory. Based on the first mass 69 and the second mass 71, a difference mass 72 is determined in step 74. The difference mass 72 corresponds to the mass that is more applied to the wheels 30 of the middle axle in Figure 1 shown axle 32 than on the wheels 30 of the other axles 32 due to the weight of the electric drive 24, in particular the electric motor 46. In step 75, further values, such as the acceleration due to gravity 76 and the dynamic tire radius 78, as well as an inclination 80 exhibited by the trailer vehicle, are retrieved in order to also determine the deceleration torque 54 in this step 75.

[0044] If locking of one of the wheels 30 is detected in step 84 during a braking request 20, ABS braking is triggered in step 86. For this purpose, the pressures 34 at the friction brakes 28 are reduced in step 88. This begins a venting phase 89. In step 90, as soon as the wheels 30 start moving again, braking with the deceleration torque 54 is generated by the electric drive 24. At the same time, the friction brakes 28 are activated in step 92. This begins a braking and / or pressure holding phase 93. As soon as a new locking of the wheels 30 is detected in step 94, a feed torque 97 is generated with the electric drive 24 in step 96 and, at the same time, the friction brakes 28 are released again in step 98. Then step 90 follows again and the following steps are repeated until the braking request 20 has been withdrawn by the driver or the vehicle combination 10 has come to a standstill. List of reference symbols [part of the description]

[0045] 10Trailer combination 11Roadway 12Towing vehicle 14Trailer vehicle 15Braking system 16Brake pedal 18Brake control unit (EBS) 20Braking request 22Trailer brake control unit (TEBS) 23Anti-lock braking system 24Electric drive 26Control unit 28Friction brakes 30Wheels 32Axles 34Brake pressure 37Control unit 38Electronic air suspension system (ECAS) 40Air bellows 42aPartial mass 42bPartial mass 42cPartial mass 44Inverter 46Electric motor 48Battery 49Information 50Wheel speed sensor 54Deceleration torque 68Procedure 69First mass 70Receiving partial masses 71Second mass 72Differential mass 74Determining differential mass 75Retrieving further values and determining deceleration torque 76Gravity 78Dynamic tire radius 80Trailer tilt 84Detection of wheel locking 86ABS braking activation 88Reduction of friction brake pressure 89Venting phase 90Generation of braking 92Activation of friction brakes 93Braking and / or pressure holding phase 94Further detection of wheel locking 96GenerationFeed torque 97Feed torque 98Solution Friction brakes

Claims

1. Method (68) for operating a trailer vehicle (14) having an electric drive (24) and friction brakes (28), wherein the method (68) comprises: - determining (74) a differential mass (72) between a first mass (69) of a driven axle (32) of the trailer vehicle (14) and a second mass (71) of a non-driven axle (32) of the trailer vehicle (14), wherein the first mass (69) and the second mass (71) each denote the masses of the corresponding axle itself, without including a mass acting on the axle; - determining a deceleration torque (54) on the basis of the differential mass (72), - generating at least or exactly the determined deceleration torque (54) with the electric drive (24) when the friction brakes (28) are activated (92).

2. Method (68) according to claim 1, wherein the generation of the determined deceleration torque (54) takes place during a braking and / or pressure holding phase (93) generated by an anti-lock braking system (23).

3. Method (68) according to claim 1 or 2, wherein, during a venting phase (89), the deceleration torque (54) is reduced, and the deceleration torque (54) is generated again if a new braking and / or pressure holding phase (93) is generated by the or an anti-lock braking system (23).

4. Method (68) according to any of the preceding claims, wherein the deceleration torque (54) is determined on the basis of the differential mass (72), the acceleration due to gravity (76), a dynamic tire radius (78), and optionally an inclination (80) of the trailer vehicle (14).

5. Method (68) according to any of the preceding claims, wherein, upon detection of a locking wheel (30) driven by the electric drive (24), a propulsion torque (97) is generated until the wheel (30) is no longer locked or the friction brakes (28) are reactivated.

6. Method (68) according to any of the preceding claims, wherein the generation of the deceleration torque (54) with the electric drive (24) is carried out by means of an actuation of the electric drive (24) by a trailer brake control unit (22).

7. Trailer brake control unit (22) which is configured to carry out the method according to any of claims 1 to 6.

8. Trailer brake control unit (22) according to claim 7, wherein the trailer brake control unit (22) is configured to actuate an electric drive (24) of the trailer vehicle (14).

9. Trailer vehicle (14) comprising a trailer brake control unit (22) according to claim 7 or 8.

10. Trailer vehicle (14) comprising a trailer brake control unit (22) according to claim 9 and an electric drive (24) and friction brakes (28).

11. Trailer vehicle (14) according to claim 10, further comprising an in particular electronic air suspension system (38).

12. Combination (10) comprising a towing vehicle (12) and a trailer vehicle (14) according to any of claims 9 to 11.