Vehicle with one front axle and at least two sprung rear axles

Abstract

The invention relates to a vehicle with a front axle (1) and at least two sprung rear axles (2, 3), the level of which relative to the roadway can be adjusted by controlling pressurized spring elements (7, 8) arranged on the rear axles (2, 3), wherein the rear axles (2, 3) are each electrically driven by an electric motor (10) controlled by at least one control unit (11), wherein each rear axle (2, 3) is assigned a separate gearbox (13) with a positively acting shifting element, wherein the rear axles (2, 3) are assigned at least one control device (15) which is designed to detect the presence of a shifting operation on one of the rear axles (2, 3) and, depending on the presence of the shifting operation, to reduce the pressure of the pressurized spring elements (7, 8) of the shifting rear axle (2, 3) and to increase the pressure of the pressurized spring elements (7, 8) of the other rear axle (2, 3).

Description

The invention relates to a vehicle, in particular a commercial vehicle, having a front axle and at least two sprung rear axles according to the preamble of claim 1.DE 10 2017 213 199 A1 discloses a vehicle having a front axle and at least two sprung rear axles, the level of which with respect to the roadway can be adjusted by actuating pressurized spring elements arranged on the rear axles, wherein the rear axles are each electrically driven by an actuated electric motor. The level with respect to the roadway is adjusted by means of an adjustment device when a recuperation mode is detected, in order to optimize the recuperation by adjusting the axle load.DE 10 2015 000 215 A1 relates to a method for controlling a vehicle having a front axle and at least two sprung rear axles, each of which is electrically driven by an actuated electric motor. The vehicle has an air suspension system which is configured for distributing the axle load to the sprung, driven rear axles. The method is intended to achieve consumption-optimized operation of the vehicle by distributing a predefined total torque, as a function of detected axle load values, to setpoint torques which are transmitted to the driven rear axles.Each driven rear axle can be assigned a separate shift transmission with a shift element acting in a positive-locking manner. During a shifting process at one of the driven rear axles, a traction force interruption occurs by means of the shift element acting in a positive-locking manner. In order to compensate for this traction force interruption, the other driven rear axle is subjected to an increased torque, which can lead to slip occurring depending on the operating and driving situation. This has the consequence that the tractive force collapses more during the shifting process than in the case of the tractive force collapse which is attributable to the interruption of the tractive force at the other rear axle.Proceeding from the prior art described above, it is now the object of the present invention to develop a vehicle which avoids disadvantages of the prior art.This object is achieved from a technical point of view of the device starting from the preamble of claim 1 in conjunction with its characterizing features. From the process engineering point of view, the object is achieved proceeding from the preamble of the subordinate claim 15 in conjunction with its characterizing features. The dependent claims represent advantageous further developments of the invention.According to the invention, a vehicle, in particular a commercial vehicle, is proposed, having a front axle and at least two sprung rear axles, the level of which with respect to the roadway can be adjusted by actuating pressurized spring elements arranged on the rear axles, wherein the rear axles are each electrically driven by an electric motor actuated by a control unit, wherein each rear axle is assigned a separate shift transmission with a shift element acting in a positive-locking manner. According to the invention, it is provided that at least one control device is assigned to the rear axles, which control device is configured to detect the presence of a shifting process at one of the rear axles and, depending on the presence of the shifting process, to reduce the pressure of the pressurized spring elements of the shifting rear axle and to increase the pressure of the pressurized spring elements of the other rear axle.The increase in the axle load of the driven rear axle, which is subjected to a higher torque in order to compensate for the interruption of the tractive force at the shifting rear axle, by the increase in pressure of the spring elements subjected to pressure, leads to a reduction and / or delay in the occurrence of slip at the wheels of this rear axle. At the shifting rear axle, the pressure of the pressurized spring elements is lowered and the pressure of the pressurized spring elements at the other rear axle, which takes over the drive until the target rotational speed for the new gear of the shifting rear axle is reached, is increased. Losses of comfort due to tensile force collapse can thereby be at least minimized.Preferably, the vehicle has a 6x4 axle configuration. In a 6x4 axle configuration, two wheels are located on a steering axle and four drive wheels on the driven rear axles behind the steering axle.The shift element of the transmission acting in a positive-locking manner can be, in particular, a claw shift.The increase in the pressure of the pressurized spring elements of the other rear axle can be carried out linearly or non-linearly.In particular, the at least one control device can be configured to analyze a currently present driving situation and to vary a pressure ratio between the spring elements of the rear axles depending on the determined driving situation. This allows flexible adaptation to different driving situations in order to optimize driving stability.The analyzed driving situation can be a road drive during which the at least one control device applies a higher axle load to one of the rear axles by controlling the pressurization of the spring elements assigned to this rear axle compared to the further rear axle. In particular, the last driven rear axle, viewed in the longitudinal direction of the vehicle, starting from the front axle, can be subjected to a higher axle load compared to the at least one further rear axle arranged in front. This contributes to an increase in driving stability.Furthermore, the analyzed driving situation can be a maneuvering process in which the at least one control device releases one of the rear axles by controlling the pressurization of the spring elements assigned to this rear axle. In particular, even in the maneuvering process driving situation, the last driven rear axle, as viewed in the longitudinal direction of the vehicle, can be relieved by controlling the pressurization of the spring elements assigned to this rear axle. Relieving the load on the last driven rear axle reduces the erasering during the maneuvering process. This can occur particularly in dual wheel axle assemblies at each end of the rear axles which are used to increase the load carrying capabilities of heavy duty vehicles. Typically, the pairs of wheels may be secured together at each end of the rear axles so that they rotate together about an axle. Heavy steering maneuvers during the maneuvering process lead to increased tire wear due to the erasering or drag.According to a further development, the at least one control device can apply a maximum permissible axle load to one of the rear axles by actuating the spring elements assigned to this rear axle, and the at least one further rear axle can apply a maximum permissible axle load by actuating the pressurization of the spring elements assigned to the at least one further rear axle in accordance with the remaining axle load to be distributed. This is based on the fact that one of the rear axles as the main drive axle is always subjected to maximum axle load and the remaining axle load is distributed to the at least one further rear axle, as a result of which it is possible to achieve optimization of the traction during regular driving operation. In this case, it can be provided that, in order to make the wear more uniform, a cyclic change is made between the driven rear axles, which is in each case subjected to maximum axle load as the main drive axle during driving operation.The analyzed driving situation can preferably be a starting process on a smooth surface, during which the at least one control device applies a maximum permissible axle load to one of the rear axles by controlling the pressurization of the spring elements assigned to this rear axle, wherein a control unit applies a greater torque to this rear axle than the at least one further rear axle by controlling the electric motor of this rear axle. On a smooth surface, for example due to snow smoothness or due to the nature of the surface, the traction required during the starting, the transmission of a tensile force to the surface, can be low or even not at all. Wheels on the driven rear axles then under certain circumstances rotate during driving, and starting of the vehicle is made more difficult or even prevented. This can be counteracted by controlling the application of pressure for applying a maximum permissible axle load to the spring elements assigned to this rear axle, wherein the control unit applies a greater torque to this rear axle than the at least one further rear axle by controlling the electric motor of this rear axle. By the load distribution to a rear axle and the driving of this rear axle with the greater torque according to this starting assistance mode, an optimum traction can be achieved during starting on a smooth ground.In particular, the analyzed driving situation can be a starting process on loose and / or uneven ground, during which the at least one control device applies a uniformly distributed axle load to the rear axles by controlling the application of pressure to the spring elements assigned to them, wherein the control unit applies a uniformly distributed torque to the rear axles by controlling the electric motors of the rear axles. In this way, an equal distribution of axle load and traction to all driven rear axles can be achieved in order to support the starting on loose and / or uneven ground according to this starting support mode.Furthermore, when slip on wheels of the driven rear axles occurs repeatedly during the starting process is detected, the at least one control device can activate the spring elements assigned to the rear axles and the at least one control unit in order to switch between activation during the starting process on loose and / or uneven ground and during the starting process on smooth ground. For this purpose, wheel speed sensors can be assigned to the wheel or to the pair of wheels of the respective rear axle. Using the speed signals generated by the wheel speed sensors, which indicate a wheel speed, wheel spin or wheel pairs can be quickly and easily detected. The wheel speed sensors can be known wheel speed sensors of an anti-lock brake system (ABS), for example. By changing between the start assist modes according to claims 7 and 8 between the driven rear axles, it can be achieved that the vehicle can be accelerated better even in adverse starting conditions.In particular, the at least one control device can be configured to evaluate signals from pressure sensors of the spring elements in order to determine existing axle loads at the driven rear axles. In particular, the at least one control device can actuate the axle load distribution as a function of the determined axle loads. This can preferably be used for the different driving situations according to claims 4 to 6 and for the start-up assistance modes according to claims 7 and 8.According to a preferred development, a transmission control unit of the respective electric motor can actuate the respective transmission of the rear axles and transmit a control signal for the respective transmission to the control device for evaluation. This makes it possible to achieve predictive control of the pressurized spring elements arranged on the rear axles. Thus, a change in an existing driving situation, such as the shift for a gear change, can be preliminarily reacted. The control device can actuate the pressurization of the spring elements in a predictive manner, i.e. in a temporally preceding manner.Preferably, each rear axle can have at least two spring elements subjected to pressure. More preferably, each rear axle can have four spring elements.In particular, the spring elements can be designed as pneumatic or hydraulic spring elements. Pneumatic spring elements can be, in particular, air spring bellows. Hydraulic spring elements can be designed as hydraulic cylinders with springs.According to a preferred development, each driven rear axle can have a control unit which is configured to actuate the respective electric motor, wherein the function of the control device is integrated into the respective control unit. In this way, the number of hardware required can be reduced.The object set at the beginning is furthermore achieved by a method having the features of independent claim 15.According to claim 15, a method for operating a vehicle having a front axle and at least two sprung rear axles, the level of which with respect to the roadway is adjusted by actuating pressurized spring elements arranged on the rear axles, is proposed, wherein the rear axles are each electrically driven by an electric motor actuated by at least one control unit, wherein each rear axle is assigned a separate shift transmission with a shift element acting in a form-fitting manner, wherein the rear axles are assigned at least one control device by means of which the presence of a shift operation on one of the rear axles is detected and, depending on the presence of the shift operation, pressure of pressurized spring elements of the shifting rear axle is lowered and pressure of pressurized spring elements of the other rear axle is increased. Reference may be made to the advantages of the vehicle according to the invention.The invention is not limited to the combination of features of the subordinate claims or of the claims dependent thereon. There are also possibilities for combining individual features, even if they emerge from the claims, the following description of preferred embodiments of the invention or directly from the drawings. Reference to the claims on the drawings using reference numerals is not intended to limit the scope of the claims.An advantageous embodiment of the invention, which is explained below, is illustrated in the drawing. It shows: FIG. 1 schematically and exemplarily shows a representation of a 6x4 axle configuration of a vehicle.FIG. 1 shows schematically and by way of example a representation of a 6x4 axle configuration of an electrically drivable vehicle, preferably a commercial vehicle, which is not shown in more detail.The vehicle has a front axle 1 and at least two sprung rear axles 2, 3. The only schematically illustrated front axle 1 is designed as a steering axle. The two rear axles 2, 3 are arranged one behind the other as viewed in the longitudinal direction LR of the vehicle.In the 6x4 axle configuration, two wheels 4 are arranged on the front axle 1 designed as a steering axle and four drive wheels 5 are arranged on the driven rear axles 2, 3 behind the front axle 1. The rear axles 2, 3 are arranged on a vehicle frame 6.The level with respect to the roadway can be adjusted by actuating pressurized spring elements 7 arranged on the rear axles 2, 3. For this purpose, each rear axle 2, 3 has at least two spring elements 7. Optionally, two further spring elements 8 can be arranged on each rear axle 2, 3, as illustrated in FIG. 1 by the dashed-line illustration of the spring elements 8.The spring elements 7, 8 can be designed as pneumatic or hydraulic spring elements 7, 8. In the exemplary embodiment shown, the spring elements 7, 8 are designed as air spring bellows 9. In an embodiment as hydraulic spring elements 7, 8, these can each be designed as hydraulic cylinders with a spring. At least one pneumatic pressure source is provided for the pressure supply of the pneumatic spring elements 7, 8 designed as air spring bellows 9. For controlling or regulating the pressure, valve arrangements are assigned to the air spring bellows 9, which are designed for pressurizing with an air pressure provided by the at least one pressure source and for venting the air spring bellows 9.Each of the at least two driven rear axles 2, 3 is electrically driven by exactly one electric motor 10 controlled by at least one control unit 11. Furthermore, each electric motor 10 has power electronics 12. The task of the power electronics 12 is, among other things, to convert the direct current from at least one battery of the vehicle into alternating current for use in the electric motor 10.Each of the at least two driven rear axles 2, 3 is assigned a separate shift transmission 13 with a shift element acting in a form-fitting manner. The shift element of the transmission 13 acting in a positive-locking manner can be, in particular, a claw shift. In commercial vehicles, because of the high tractive force requirements, three-speed shift transmissions are generally used which have two forward gears and one reverse gear. A transmission control unit of the respective electric motor 10 controls the respective transmission 13 of the rear axles 2, 3. The transmission control unit may be integrated into the control unit 11.Furthermore, an auxiliary output 14 can be provided on a drive shaft of the respective electric motor 10, for example for a hydraulic pump.To actuate the pressurised spring elements 7, 8 arranged on the rear axles 2, 3 for setting the level to the roadway, at least one control device 15 is assigned to the rear axles 2, 3. Preferably, each rear axle 2, 3 is assigned a separate control device 15.Wheel speed sensors 16 can be assigned to at least one wheel 5 or to a pair of wheels of the respective rear axle 2, 3. Using the rotational speed signals generated by the wheel speed sensors 16, which indicate a wheel speed, the spinning of wheels 5 or pairs of wheels can be detected quickly and easily. The wheel speed sensors 16 may be, for example, known wheel speed sensors of an anti-lock brake system (ABS). The signals of the wheel speed sensors 16 are transmitted to the respective control device 15 and / or the respective control unit 11 of the rear axles 2, 3 for evaluation.The at least one control device 15 is configured to evaluate signals from pressure sensors 17 of the spring elements 7, 8 in order to determine existing axle loads on the driven rear axles 2, 3. Furthermore, the control device 15 is configured to actuate the valve arrangements assigned to the air spring bellows 9 in order to undertake an adaptation of the axle loads absorbed by the driven rear axles 2, 3 by a change in the air pressure.During a gear change which is carried out at one of the driven rear axles 2, 3, the torque of the other driven rear axle 2, 3 is significantly increased in order to compensate for the traction force interruption during the gear change. In order to prevent slip occurring during boost operation of this driven rear axle 2, 3, which slip is attributable to a low coefficient of friction and / or an excessively low axle load, which would reinforce the traction force dip, it is provided that the control device 15 is configured to detect the presence of a shifting process at the one rear axles 2, 3 and to reduce the pressure of the pressurized spring elements 7, 8 of the shifting rear axle 2, 3 and to increase the pressure of the pressurized spring elements 7, 8 of the other rear axle 2, 3 as a function of the presence of the shifting process.In order to determine the presence of a shifting process for one of the driven rear axles 2, 3, the transmission control unit of the respective electric motor 10 can transmit a control signal for controlling the respective transmission 13 in parallel, in particular in advance, to the control device 15 for evaluation. This allows a predictive or leading control of the pressurized spring elements 7, 8 arranged on the rear axles 2, 3 to be achieved. Thus, a change in an existing driving situation, such as the shift for a gear change, can be preliminarily reacted. For this purpose, the actuation of the pressurized spring elements 7, 8 can be initiated by the control device 15 in order to reduce the pressure of the pressurized spring elements 7, 8 of the shifting rear axle 2, 3 and to increase the pressure of the pressurized spring elements 7, 8 of the other rear axle 2, 3.The at least one control device 15 can furthermore be configured to analyze a currently present driving situation and to vary a pressure ratio between the spring elements 7, 8 of the driven rear axles 2, 3 depending on the driving situation determined.For this purpose, the at least one control device 15 is configured to evaluate sensor signals provided by sensor devices of the vehicle, the wheel rotational speed sensors 16 and the pressure sensors 17, in order to analyze the currently present driving situation. Furthermore, the control signal provided by the transmission control unit can be used to analyze the currently present driving situation.If the analyzed driving situation is a road drive, during the road drive the at least one control device 15 can apply a higher axle load to one of the rear axles 2, 3 by controlling the pressurization of the spring elements 7, 8 assigned to this rear axle 2, 3 compared to the further rear axle 2, 3. In particular, the last driven rear axle 3, viewed from the front axle 1 in the vehicle longitudinal direction LR, can be subjected to a higher axle load than the further rear axle 2 arranged in front. This contributes to an increase in driving stability.If the analyzed driving situation is a maneuvering process, it is advantageous if, during maneuvering, the at least one control device 15 relieves one of the rear axles 2, 3 by controlling the pressurization of the spring elements 7, 8 assigned to this rear axle 2, 3. The presence of a maneuvering process can be deduced in particular by the control signal provided by the transmission control unit, since the maneuvering is often associated with gear changes for forward travel and reverse travel at low travel speed.Furthermore, the at least one control device 15 can apply a maximum permissible axle load to one of the rear axles 2, 3, preferably the front rear axle 2, as seen in the vehicle longitudinal direction LR, by actuating the spring elements 7, 8 assigned to this rear axle 2, and the at least one further rear axle 3 can apply a maximum permissible axle load by actuating the pressurization of the spring elements 7, 8 assigned to the at least one further rear axle 3 in accordance with the remaining load of the vehicle to be distributed.A driving situation analyzed by the control device 15 is a starting process on a smooth surface. On a smooth surface, for example due to snow smoothness or due to the nature of the surface, the traction required during the starting, the transmission of a tensile force to the surface, can be low or even not at all. In a start assist mode, it is provided that the at least one control device 15 applies a maximum permissible axle load to one of the rear axles 2, 3 by controlling the pressurization of the spring elements 7, 8 assigned to this rear axle 2, 3, wherein in this start assist mode the at least one control unit 11 applies a greater torque to this rear axle 2 by controlling the electric motor 10 of this rear axle 3 than the at least one further rear axle 2, 3.A further driving situation analyzed by the control device 15 can be a starting process on loose and / or uneven ground. For a starting support, the at least one control device 15 can apply a uniformly distributed axle load to the rear axles 2, 3 by controlling the pressurization of the spring elements 7, 8 assigned to them. The at least one control unit 11 can, in parallel with this, by controlling the electric motors 10 of the rear axles 2, 3, subject the latter to a torque distributed uniformly over both rear axles 2, 3.Furthermore, when slip at the drive wheels 5 of the driven rear axles 2, 3 occurs repeatedly during the starting process is detected, the at least one control device can actuate the spring elements 7, 8 assigned to the rear axles 2, 3 and the at least one control unit 11 in order to switch between the actuation during the starting process on loose and / or uneven ground and during the starting process on smooth ground.Reference numerals denote reference numerals1 Front axle 2 Rear axle 3 Rear axle 4 Wheel 5 Drive wheel 6 Vehicle frame 7 Spring element 8 Spring element 9 Air spring bellows 10 Electric motor 11 Control unit 12 Power electronics 13 Transmission 14 Auxiliary power take-off 15 Control device 16 Wheel rotational speed sensor 17 Pressure sensor LR Vehicle longitudinal directionReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2017 213 199 A1

[0002] DE 10 2015 000 215 A1

[0003]

Claims

Vehicle having a front axle (1) and at least two sprung rear axles (2, 3), the level of which with respect to the road surface can be adjusted by actuating pressurised spring elements (7, 8) arranged on the rear axles (2, 3), wherein the rear axles (2, 3) are each electrically driven by an electric motor (10) actuated by at least one control unit (11), wherein each rear axle (2, 3) is assigned a separate gearbox (13) having a shift element acting in a positively locking manner, characterized in that the rear axles (2, 3) are assigned at least one control device (15) which is designed to detect the presence of a shift operation on one of the rear axles (2, 3) and, as a function of the presence of the shift operation, to reduce the pressure of the pressurised spring elements (7, 8) of the shifting rear axle (2, 3) and to reduce the pressure of the pressurised spring elements (7, 8) of the other rear axle (2, 3), 3).Vehicle according to Claim 1, characterized in that the at least one control device (15) is designed to analyze a currently present driving situation and to vary a pressure ratio between the spring elements (7, 8) of the rear axles (2, 3) as a function of the driving situation determined.Vehicle according to Claim 2, characterized in that the at least one control device (15) is set up for evaluating sensor signals provided by sensor devices (16, 17) of the vehicle in order to analyze the currently present driving situation.Vehicle according to Claim 2 or 3, characterized in that the driving situation analyzed is road travel, during which the at least one control device applies a higher axle load to one of the rear axles (2, 3) by actuating the pressurization of the spring elements (7, 8) assigned to this rear axle (2, 3) in comparison with the further rear axle (2, 3).Vehicle according to one of Claims 2 to 4, characterized in that the driving situation analyzed is a maneuvering process in which the at least one control device (15) relieves one of the rear axles (2, 3) by actuating the pressurization of the spring elements (7, 8) assigned to this rear axle (2, 3).Vehicle according to one of the preceding claims, characterized in that the at least one control device acts on one of the rear axles (2, 3) with a maximum permissible axle load by actuating the spring elements (7, 8) assigned to this rear axle (2, 3), and the at least one further rear axle (2, 3) acts on the other one of the spring elements (7, 8) assigned to the at least one further rear axle (2, 3) by actuating the application of pressure in accordance with the remaining load of the vehicle to be distributed.Vehicle according to one of Claims 2 to 6, characterized in that the driving situation analyzed is a starting process on a smooth surface, during which the at least one control device (15) applies a maximum permissible axle load to one of the rear axles (2, 3) by actuating the pressurization of the spring elements (7, 8) assigned to this rear axle (2, 3), wherein the at least one control unit (11) applies a greater torque to this rear axle (2, 3) by actuating the electric motor (10) of this rear axle (2, 3) than the at least one further rear axle (2, 3).Vehicle according to one of Claims 2 to 7, characterized in that the driving situation analyzed is a starting process on loose and / or uneven ground, during which the at least one control device (15) acts on the rear axles (2, 3) with a uniformly distributed axle load by controlling the application of pressure to the spring elements (7, 8) assigned to them, wherein the at least one control unit (11) acts on the electric motors (10) of the rear axles (2, 3) with a torque distributed uniformly to them by controlling them.Vehicle according to claim 7 or 8, characterised in that the at least one control device (15), when detecting slip on wheels (5) of the driven rear axles (2, 3) which occurs repeatedly during the starting process, actuates the spring elements (7, 8) assigned to the rear axles (2, 3) and at least one control unit (11) in order to change between the actuation during the starting process on loose and / or uneven ground and during the starting process on smooth ground.Vehicle according to one of Claims 2 to 9, characterized in that the at least one control device (15) is designed to evaluate signals from pressure sensors of the spring elements (7, 8) in order to determine existing axle loads on the driven rear axles (2, 3).Vehicle according to one of the preceding claims, characterized in that a transmission control unit of the respective electric motor (10) actuates the respective transmission (13) of the rear axles (2, 3) and transmits a control signal to the control device (15) for evaluation.Vehicle according to one of the preceding claims, characterized in that each rear axle (2, 3) has at least two spring elements (7, 8) subjected to pressure.Vehicle according to one of the preceding claims, characterized in that the spring elements (7, 8) are designed as pneumatic or hydraulic spring elements.Vehicle according to one of the preceding claims, characterized in that each driven rear axle (2, 3) has a control unit which is configured to actuate the respective electric motor (10), wherein the function of the control device (15) is integrated into the respective control unit (11).Method for operating a vehicle having a front axle and at least two sprung rear axles (2, 3), the level of which with respect to the road surface is adjusted by actuating pressurised spring elements (7, 8) arranged on the rear axles (2, 3), wherein the rear axles (2, 3) are each electrically driven by an electric motor (10) actuated by at least one control unit (11), wherein each rear axle (2, 3) is assigned a separate shift transmission (13) having a shift element acting in a positive-locking manner, characterized in that the rear axles (2, 3) are assigned at least one control device (15), by means of which the presence of a shift operation on one of the rear axles (2, 3) is detected and, as a function of the presence of the shift operation, pressure of pressurised spring elements (7, 8) of the shifting rear axle (2, 3) is lowered and pressure of pressurised spring elements (7, 8) of the other rear axle (2, 3) is assigned, 3).

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