DE102012005594A1 - Traction drive for internal combustion engine of commercial vehicle, has control unit for controlling drive memory valve during braking process when pressure medium connection between hydraulic machine and hydraulic accumulator is closed - Google Patents

Abstract

The traction drive (1) has a pressure limiting valve (40), which is attached to the pressure medium flow path of a hydraulic machine (8) to a drive memory valve (38). The drive memory valve is controlled by a control unit (84) during complete opening for supercharging a hydraulic accumulator (16). The control unit is designed to control the drive memory valve during the braking process when the pressure medium connection between a hydraulic machine (8) and the hydraulic accumulator is closed.

Description

The invention relates to a traction drive according to the preamble of patent claim 1.

Such a drive preferably has a conventional drive train with an internal combustion engine, for example a diesel engine, which is in operative connection with a hydraulic machine. When braking the then acting as a pump hydraulic machine is driven due to the inertia of the vehicle during the deceleration process and charged a hydraulic accumulator, in which case a corresponding braking torque is transmitted to the drive train via the hydraulic machine.

Such a drive is in the DE 10 2006 041 823 A1 described. In this case, a pressure medium flow path is arranged between the over a zero position (short: above zero), in which the stroke volume is zero, pivotable hydraulic machine and the hydraulic accumulator, a driving accumulator valve, which during charging of the hydraulic accumulator during regenerative braking and during acceleration of the vehicle with the support Hydromachine is switched to an open position. The maximum pressure at the pressure connection of the hydraulic machine acting as a pump and the pressure in the hydraulic accumulator are limited by a pressure relief valve. In addition, the hydraulic accumulator is still protected by a storage pressure relief valve. The swivel angle of the hydraulic machine is controlled in dependence on the desired braking or acceleration torque and the accumulator pressure.

A disadvantage of previously known traction drives that the accumulator pressure at the end of a braking process drops below a previously reached maximum value again. The hydraulic accumulator is thus partially discharged, with this pressure loss can be in the two-digit range.

When accelerating the vehicle, the drive train can be supported by adding the hydraulic machine, wherein the hydraulic energy is then provided from the hydraulic accumulator. However, due to the above-described drop in the hydraulic accumulator pressure, less hydraulic energy is available to support the acceleration process.

In contrast, the invention has for its object to provide a travel drive, in which the support of a conventional drive train is improved by a hydraulic drive.

This object is achieved by a traction drive with the features of claim 1.

According to the invention, the traction drive with a hydraulic machine which is adjustable in its stroke volume, which can be coupled to a drive shaft of a conventional drive and over which a hydraulic accumulator via a driving accumulator valve in a braking operation is chargeable. At the pressure fluid flow path from the hydraulic machine to the driving accumulator valve, a pressure relief valve is connected. The driving accumulator valve can be controlled to charge the hydraulic accumulator via a control unit in the sense of a complete opening. In addition, the control unit is designed to control the drive accumulator valve during a braking operation in the sense of closing the pressure medium connection between the hydraulic machine and the hydraulic accumulator.

By this measure, a partial discharge of the hydraulic accumulator is avoided at the end of a braking process, so that it can support the conventional drive train longer in a subsequent acceleration process, and over the conventional solution, a significant energy savings can be achieved. In a renewed braking process without intervening acceleration process, the driving accumulator valve can be opened again first

Advantageous embodiments of a traction drive according to the invention can be found in the dependent claims.

In a variant of the traction drive according to the invention, the drive accumulator valve is closed when the pressure relief valve has responded. This avoids that the lower closing pressures, which has the pressure relief valve due to a largely unavoidable hysteresis, lead to a pressure drop in the hydraulic accumulator.

It is favorable, with a sensor, the function of the pressure relief valve is detected and the control unit controls the driving accumulator valve in response to the sensor signal. The sensor may be a displacement transducer on the pressure relief valve. In this way it can be ensured that the driving accumulator valve is closed only when the pressure limiting valve has reached the maximum opening degree for the current operating state and the pressure is maximal because of the rising characteristic of the pressure limiting valve.

It can also be the pressure in the hydraulic accumulator detected by a pressure sensor and the driving accumulator valve are closed when the pressure in the hydraulic accumulator during a Braking process stops at a level or begins to fall off.

It can also be the pressure at the pressure output of the hydraulic machine detectable by a pressure sensor and the driving accumulator valve are closed when the pressure at the pressure output of the hydraulic machine during a braking process remains at a level or begins to fall off.

In another variant, the drive accumulator valve is closed when the flow rate from the hydraulic machine to the hydraulic accumulator falls below a limit. In particular, the product of the displacement and the speed of the hydraulic machine is determined to do so. The accumulator valve is closed when the product falls below a certain limit. This criterion can be used in particular even if the pressure relief valve has responded. It is then even a fairly accurate criterion because the internal leaks of the hydraulic machine are pressure-dependent and the pressure is at least approximately known when the pressure relief valve response.

In particular, if the pressure relief valve has not responded, the pump pressure / storage pressure can be taken into account when determining the limit value of the product.

Advantageously, the driving accumulator valve is a logic valve whose spring chamber can be acted upon by a pilot valve in a switching position with tank / low pressure and in another switching position with accumulator pressure / high pressure, wherein in the opening direction of the pump pressure and / or the accumulator pressure are effective.

The structure of the hydraulic machine is particularly simple if one, for example, electroproportionally controlled, axial piston unit is used.

A preferred embodiment of the invention will be explained in more detail below with reference to drawings.

Show it:

1 a hydraulic circuit diagram of the traction drive according to the invention,

2 a detailed representation of the circuit diagram 1 and

3 a diagram illustrating the function of the traction drive during a braking operation.

The following is an example of a traction drive 1 of a commercial vehicle explained. This has a conventional powertrain, which in the illustration according to 1 merely as a circle with a reference numeral 2 is indicated and its propeller shaft via a hydraulically operated clutch 4 with a drive shaft 6 a hydraulic machine is connected. This is in the illustrated embodiment as a zero position (in short: above zero) pivotable axial piston machine 8th whose swing angle is controlled by a pump regulator 10 is adjustable, which is designed in this embodiment with an electro-proportional control behavior (EP control). Such pump regulators are known from the prior art, so that further explanations are unnecessary. Pivoting about a zero position means that reverses the direction of the pressure medium flow through a hydraulic unit in a pump or motor mode while maintaining the direction of rotation of a drive shaft and change from high pressure and low pressure connection or that, as in the present case, while maintaining high pressure and Low pressure connection and while maintaining the direction of rotation of a drive shaft, a change between pump operation and engine operation takes place.

During pump operation, the axial piston machine sucks 8th Pressure medium from a tank T and promotes this toward a dot-dash line indicated HRB valve block 14 , at its high-pressure port HD via a storage line 15 a hydraulic accumulator 16 connected. Instead of a single hydraulic accumulator 16 Also, multiple hydraulic accumulators can be grouped together to form a hydraulic accumulator battery, as in 1 indicated by dashed lines. HRB is an abbreviation for Hydraulic Regenerative Braking.

The actuation of the clutch 4 via a coupling valve block 18 in the illustrated embodiment via a supply pump 20 can be supplied with pressure medium. The supply pump 20 is via a control oil valve block 22 with a clutch control line 26 connected from an output A of the control valve block 22 to the coupling valve block 18 leads and via the hydraulic control of the clutch 4 is possible. As in 1 indicated, are via the supply pump 20 other hydraulic consumers supplied with pressure medium. The pump pressure is via the control oil valve block 22 on the for the control of the clutch 4 reduced suitable control pressure. For this purpose, the control oil valve block 22 a pressure reducing valve 24 , which reduces the pump pressure to the control pressure, which then via the clutch control line 26 to Kupplunsventilblock 18 is guided. To a port S of the control oil valve block connected internally directly to the output A. 22 is a control oil storage 28 connected. in the Control oil manifold 22 is also a control oil pressure relief valve 30 provided that opens a pressure medium connection to the tank T when a maximum control oil pressure is exceeded. The inlet port of the pressure reducing valve 24 is at the output port of a shuttle valve 32 connected, at one input of which the pump pressure of the supply pump 20 is present and the other input with a pressure line 34 which in turn is in fluid communication with the pump line 12 stands. This connection is made to a port P1 of the HRB valve block.

The pump line 12 leads to a port P and a tank line 36 is connected to a tank connection T of the HRB valve block. As will be explained in more detail below, the HRB valve block has 14 a drive storage valve 38 , a pump pressure relief valve 40 , a reservoir pressure relief valve 42 , a prefill valve 44 and a drain valve 46 ,

Details of the HRB valve block are described below 2 explained.

The driving accumulator valve 38 is designed as a pilot-operated logic valve, wherein an end face of the stepped valve body 47 is acted upon by the pressure at a front-side port and an annular end face with the pressure at a radial port. The end connection is via a pump channel 50 connected to port P to which the pump line 12 connected. The radial connection opens into a memory channel 52 leading to a pressure port HD to which the storage line 15 connected. A spring room 54 of the logic valve 38 is via a pilot valve 48 in its spring-biased basic position via a control channel 56 , a nozzle 58 and a pilot channel 60 and another nozzle 62 with the memory channel 52 connected. The pilot valve 48 can be electrically switched to a switching position in which the spring chamber 54 over the nozzle 62 , the pilot channel 60 and a control line 64 and another nozzle with a leading to the tank T control oil relief line 66 connected is. The valve body 47 is about a spring 68 biased in its illustrated closed position. The pressure equivalent of the spring 68 is about 4 bar. This means that the logic valve in the basic position of the pilot valve at a pressure difference of 4 bar between the pressure in the pump channel 50 and the pressure in the memory channel 52 would open. As explained later, however, is also when filling the hydraulic accumulator 16 the spring chamber 54 relieved of pressure, so that between the frontal connection and the radial connection of the driving accumulator valve 38 only a very small pressure drop occurs.

The pump pressure relief valve 40 is designed as a 2-way valve, whose valve body 68 in the closing direction of the force of a spring (4 bar) and in the opening direction of the pressure in the pump channel 50 is charged. An output port of the pump pressure relief valve is connected to a tank channel 70 connected to the tank connection T and thus to the tank line 36 connected. A spring room 72 the pump pressure limiting valve 40 is via a DB control line 74 to the outlet of a shuttle valve 76 connected, whose one input to the pump channel 50 and its other input via another nozzle 78 to the memory channel 52 connected. That is, via the shuttle valve 76 becomes the higher of the pressures in the pump channel 50 and the memory channel 52 tapped and in the spring chamber 72 reported. The maximum pressure in the spring chamber 72 is via a maximum pressure limiting valve 80 limited to a pressure of, for example, 300 bar. When this pressure is exceeded, the maximum pressure limiting valve opens 80 a pressure medium connection to the control oil relief line 66 , About the shuttle valve 76 is thus the higher of the pressures in the hydraulic accumulator 16 or at the pressure connection of the axial piston machine 6 limited.

The accumulator pressure relief valve 42 , Also called memory safety valve is also designed with a pilot control, the accumulator pressure is adjustable according to the respective safety requirements. Usually, the maximum accumulator pressure is limited to a pressure value which is slightly above the maximum pump pressure at the maximum pressure relief valve 80 is set. In the described embodiment, the maximum storage pressure is about 325 bar. This storage safety valve is provided solely for safety reasons. It has no function for normal operation.

The pre-fill valve 44 is designed as a seat valve and biased by a spring into a closed position in which a bypass line 82 is shut off, resulting in bypassing the driving accumulator valve 38 between the memory channel 52 and the pump channel 50 extends. The pre-fill valve 44 can be brought via a solenoid in a passage position, so that the pump channel 50 and the pump line 12 when the driving accumulator valve is closed 38 can be pre-filled from the hydraulic accumulator at the beginning of an acceleration process without a pressure shock.

The emptying valve 46 is with its inlet connection via a drainage nozzle 84 and a drain line 86 with the memory channel 52 connected. In its spring-biased basic position, the emptying valve connects 46 the drainage pipe 86 with the control oil relief line 66 so that the hydraulic accumulator 16 can be unloaded. In normal operating condition is the emptying valve 46 switched to a blocking position. Also the emptying valve 46 is designed as a seat valve, so that a leak-free barrier is guaranteed.

The control of the above-described valves and their pilot controls via a control unit 84 Among other things, the signal processing also depends on measuring signals from pressure transducers 88 (Reservoir pressure), 90 (Pump pressure) and a swivel angle sensor 92 he follows.

The function of the traction drive according to the invention is now with the inclusion of 3 explained. This shows the behavior of a conventional system.

It is first assumed that the hydraulic accumulator 16 is partially discharged due to a preceding acceleration process. The coupling 4 is disengaged, so the drive shaft 6 is decoupled and the pump speed is zero or very low. The propeller shaft speed is comparatively high according to the engine speed of the conventional powertrain. The swivel angle of the axial piston machine 8th is set to approximately zero (no delivery volume or intake volume).

When braking the vehicle decreases as shown in 3 in the phase 1 the propeller shaft speed. At the beginning of the deceleration process is via the coupling valve block 18 the coupling 4 engaged so that the drive shaft 6 comes into operative connection with the propeller shaft, wherein a transmission may be provided for speed adjustment. The swivel angle of the axial piston machine 8th is via the EP pump regulator 10 increased to a value with which the desired braking torque is obtained at the present accumulator pressure. The unit 8th promotes as a pump pressure medium in the pump line 12 and via the open driving accumulator valve in the hydraulic accumulator 16 , This is the Vorfüllventil 44 in its closed position. The pilot valve 48 is about the control unit 88 switched to the switching position in which the spring chamber 54 is relieved to the tank T out, so that the valve body 47 lifted by its acting on its faces in the opening direction pressure from its valve seat and the pressure medium connection between the pump channel 50 and the memory channel 52 unthrottled opened. Because of the pressure relief of the spring chamber 54 Thus, the accumulator pressure corresponds almost to the pump pressure.

According to the diagram 3 a case is considered in which the hydraulic accumulator 16 soon after the start of the braking maneuver fully on the pressure relief valve 40 set pressure is loaded. As soon as the pressure in the pump channel 50 at the pump pressure relief valve 40 set maximum value, for example, exceeds 300 bar, opens the maximum pressure relief valve 80 so that the spring chamber 72 the pump pressure limiting valve 40 is relieved to the tank T out and the valve body 68 lifts from its valve seat, so that the pressure in the pump channel 50 and in the hydraulic accumulator 16 does not exceed the preset maximum value. During further deceleration, the entire flows from the unit 8th delivered quantity of pressure medium via the pressure relief valve 40 back to the tank.

Due to the deceleration of the vehicle, the propeller shaft speed and thus the pump speed decrease accordingly. In one phase 2 At the end of the braking process is the speed of the unit 8th low. In addition, the unit is swung back in the direction of zero position. It has now been found that in the conventional solutions at this stage 2 the accumulator pressure decreases, whereby this pressure loss can be in the range of 15 bar. In the conventional solutions this means that in a subsequent acceleration process less hydraulic energy is available to support the conventional powertrain than in a case where the pressure in the hydraulic accumulator would be maintained at the highest level ever achieved.

The described effect of the pressure loss in the hydraulic accumulator at the end of the braking process is due to two reasons in the case under consideration. As the speed decreases and the swing angle decreases, the unit decreases 8th subsidized pressure medium quantity. The pressure relief valve begins to close gradually with decreasing amount of pressure medium, but this closing operation is associated with a hysteresis compared to the opening operation and runs according to a lying below the opening characteristic curve. During the closing process so flows through the pressure relief valve 40 not just those of the unit 8th Promoted pressure medium quantity but also amount from the hydraulic accumulator 16 from. Furthermore, by the unit 12 due to internal leakage even at a noticeably larger swing angle than zero no pressure medium more in the pump line 12 promoted. The pressure medium flow can even reverse, so that leakage amount of the pump is removed from the hydraulic accumulator.

The pressure drop in the hydraulic accumulator at the end of the braking process is inventively avoided in that the driving accumulator valve already during a braking operation in the sense of shutting off the pressure medium connection between the Hydro unit 8th and the hydraulic accumulator 16 is controlled.

According to the in 3 shown example in which the pressure relief valve 40 has addressed, the closing of the driving accumulator valve is advantageously then when the pressure relief valve 40 has addressed and thus the hydraulic accumulator 16 is charged to its maximum pressure value, so even before the beginning of the phase 2 , The drive accumulator valve can already directly after the response of the pump pressure relief valve 40 getting closed. However, this could mean waiving a smaller further increase in pressure in the hydraulic accumulator 16 go along because the pressure relief valve 40 opens according to a rising characteristic and the highest storage pressure is reached only at maximum open pressure relief valve. Maximum open means that a valve body of the pressure limiting valve is located at a stop or one of the pressure medium quantity to be discharged corresponding intermediate position is located, which then corresponds to the maximum opening.

The response of the pump pressure limiting valve 40 or the maximum pressure limiting valve 80 For example, it can be detected by a displacement sensor which detects the opening stroke of the valve body 68 captured and sent to the control unit 84 reports. in a similar way, the signal of the pressure transducer 84 can be used over which is detectable when the hydraulic accumulator 16 is charged to its maximum value and thus the driving accumulator valve 38 no longer needs to be kept open. By a pressure sensor can be found in general, when the pressure in the hydraulic accumulator has reached a maximum value, which does not necessarily have to correspond to a fully charged hydraulic accumulator, and then close the driving accumulator valve. For example, the accumulator valve may be closed when the accumulator pressure has remained at a certain level for a period of time, or immediately when accumulator pressure begins to decrease.

The closing of the driving accumulator valve takes place in the concrete embodiment in that the pilot valve is de-energized, so in the spring chamber 54 the pressure in the hydraulic accumulator 60 is effective. The same pressure acts approximately in the opening direction on the valve body 47 of the driving accumulator valve 38 so that it is pressurized on both sides with the same pressure and by the force of the spring 68 is brought into its closed position - the pressure medium connection of the hydraulic accumulator 16 to the tank T is thus shut off and unloading can be reliably prevented.

As a result, the pressure in the hydraulic accumulator can 16 be kept at its maximum value of about 300 bar (see dot-dash line in 3 in the phase area 2 ), so that on the one hand the braking process is hydraulically assisted in an optimized manner and on the other hand provided in a subsequent acceleration significantly more hydraulic energy than is the case in the prior art.

The same strategy can also be used when filling the hydraulic accumulator 16 be used when no full charge of the hydraulic accumulator takes place. Then speaks the pressure relief valve 40 not on. But with the pressure sensor 84 can be a maximum of the pressure determine.

• 1.) Das Produkt aus dem von dem Schwenkwinkelsensor erfassten oder durch die EP-Regelung vorgegebenen Schwenkwinkel und der Drehzahl der Welle 6 der Hydramaschine 8 unterschreitet einen Grenzwert. Dieser Grenzwert liegt in einem Bereich, in dem aufgrund der inneren Leckage die Förderung von Druckmittel in die Pumpenleitung 12 endet. Dieses Kriterium kann vor allem auch dann herangezogen werden, wenn das Druckbegrenzungsventil nicht anspricht, weil der Hydrospeicher nicht voll geladen wird. Das Kriterium kann jedoch auch dann herangezogen werden, wenn das Druckbegrenzungsventil angesprochen hat. Es ist dann sogar ein ziemlich genaues Kriterium, weil die inneren Leckagen der Hydromaschine druckabhängig sind und beim Ansprechen des Druckbegrenzungsventils der Druck wenigstens annähernd bekannt ist. Hat das Druckbegrenzungsventil nicht angesprochen, so könnte der von einem Drucksensor erfasste Speicherdruck oder Pumpendruck mit bei der jeweiligen Festlegung des Produkts herangezogen werden.
• 2.) Die Druckmittelströmung in der Pumpenleitung 12 wird null oder kehrt sich um. Dies könnte unmittelbar durch einen Stromzähler erfasst werden.
• 3.) Die Druckmittelströmung am Eingang des Hydrospeicher 16 wird null oder kehrt sich um. Dies könnte unmittelbar durch einen Stromzähler erfasst werden.
• 4.) Das Druckbegrenzungsventil 40 hat angesprochen und der Förderstrom beziehungsweise das Produkt aus dem Schwenkwinkel und der Drehzahl der Hydromaschine 8 nimmt ab.

Further criteria for closing the driving accumulator valve 38 during a braking process can be:

• 1.) The product of the swivel angle detected by the swivel angle sensor or specified by the EP control and the speed of the shaft 6 the hydramaser 8th falls below a limit. This limit is in a range in which due to the internal leakage of the promotion of pressure medium in the pump line 12 ends. This criterion can be used especially if the pressure relief valve does not respond because the hydraulic accumulator is not fully charged. However, the criterion can also be used when the pressure relief valve has responded. It is then even a fairly accurate criterion because the internal leaks of the hydraulic machine are pressure-dependent and the pressure is at least approximately known when the pressure relief valve response. If the pressure relief valve has not been addressed, the accumulator pressure or pump pressure detected by a pressure sensor could be used in the respective definition of the product.
• 2.) The pressure medium flow in the pump line 12 becomes zero or turns around. This could be detected directly by an electricity meter.
• 3.) The pressure fluid flow at the inlet of the hydraulic accumulator 16 becomes zero or turns around. This could be detected directly by an electricity meter.
• 4.) The pressure relief valve 40 has addressed and the flow or the product of the swing angle and the speed of the hydraulic machine 8th decreases.

Although the above is a swivel angle or a swivel angle sensor, while this has always been an appeal to an axial piston machine, but is intended without limitation to axial piston machines in general Stroke volume or a displacement sensor of an adjustable hydraulic displacement unit include.

Disclosed is a traction drive with a conventional drive, which interacts with a HRB system. This has a hydraulic machine, which is connected via a driving accumulator valve with a hydraulic accumulator. According to the invention, the driving accumulator valve can be activated during a braking operation in the sense of closing the pressure medium connection between the hydraulic machine and the hydraulic accumulator.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102006041823 A1 [0003]

Claims (10)

Travel drive with a hydraulic machine ( 8th ), which is adjustable in its stroke volume, which can be coupled to a drive shaft of a conventional drive and via which during a braking operation via a driving accumulator valve ( 38 ) a hydraulic accumulator ( 16 ) is chargeable, wherein to the pressure medium flow path of the hydraulic machine ( 8th ) to the accumulator valve ( 38 ) a pressure relief valve ( 40 ) and wherein for charging the hydraulic accumulator ( 16 ) the driving accumulator valve ( 38 ) via a control unit ( 84 ) is controllable in the sense of a complete opening, characterized in that the control unit ( 84 ) is adapted to the driving accumulator valve ( 38 ) during a braking operation in the sense of closing the pressure medium connection between the hydraulic machine ( 8th ) and the hydraulic accumulator ( 16 ) head for. Travel drive according to claim 1, wherein the driving accumulator valve ( 38 ) is closed when the pressure relief valve ( 40 ) has addressed. Travel drive according to claim 2 and with a sensor for detecting the function of the pressure relief valve ( 40 ), wherein the control unit is the driving accumulator valve ( 38 ) in response to the sensor signal. Travel drive according to claim 3, wherein the sensor is a displacement transducer on the pressure relief valve ( 40 ). Travel drive according to any preceding claim, wherein the pressure in the hydraulic accumulator ( 16 ) by a pressure sensor ( 88 . 90 ) is detectable and the driving accumulator valve ( 38 ) is closed when the pressure in the hydraulic accumulator ( 16 ) stops at a level during a braking operation or begins to fall off. Travel drive according to any preceding claim, wherein the pressure at the pressure outlet of the hydraulic machine ( 8th ) by a pressure sensor ( 90 ) is detectable and the driving accumulator valve ( 38 ) is closed when the pressure at the pressure outlet of the hydraulic machine ( 8th ) stops at a level during a braking operation or begins to fall off. Travel drive according to any preceding claim, wherein the driving accumulator valve ( 38 ) is closed when the flow from the hydraulic machine ( 8th ) to the hydraulic accumulator ( 16 ) falls below a threshold. Travel drive according to any preceding claim, that the driving accumulator valve ( 38 ) is closed when the product of the stroke volume and the speed of the hydraulic machine falls below a certain limit. Travel drive according to claim 8, wherein in determining the limit value of the pump pressure / storage pressure is taken into account. Travel drive according to any preceding claim, wherein the driving accumulator valve ( 38 ) is a logic valve whose spring chamber ( 54 ) via a pilot valve ( 48 ) can be acted upon in a switching position with tank / low pressure and in another switching position with accumulator pressure / high pressure, wherein in the opening direction of the pump pressure and / or the accumulator pressure is effective.

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