The invention relates to a method for performing a cold start in a vehicle, which has a power-split transmission having a hydrostatic element comprising hydrostatic units.
The basic structure of a vehicle having a power-split transmission, which has a hydrostatic element comprising hydrostatic units, is known to persons skilled in the art. For instance, DE 10 2007 047 194 A1 discloses the structure of a drive train of such a motor vehicle. The drive unit or an engine is coupled to an input shaft of the power-split transmission. The power-split transmission has a hydrostatic branch and a mechanical branch, which are combined using a summation gear designed as a planetary gear. The power-split transmission provides at least two driving ranges in a forward direction of travel and at least two driving ranges in a reverse direction of travel. To this end, the power-split transmission comprises a clutch for forward drive and a clutch for reverse drive, wherein the clutch for the forward drive and the clutch for the reverse drive are also referred to as reversing clutches. The driving ranges in the forward and reverse directions are provided via speed clutches, also referred to as range clutches. The hydrostatic branch of the power-split transmission comprises a hydrostatic element. Such a hydrostatic element is provided by a first hydrostatic unit and a second hydrostatic unit, wherein one of the hydrostatic units functions as a pump and the other hydrostatic unit functions as a motor.
From DE 10 2009 045 510 further details of a hydrostatic element are known, wherein this hydrostatic element also comprises two hydrostatic units. The hydrostatic units of the hydrostatic element interact with a position control valve. The position control valve can be used to apply a hydraulic pressure to the hydrostatic units of the hydrostatic to actuate the latter.
In DE 2009 045 510 A1, a high-pressure control valve furthermore interacts with the position control valve. However, a hydrostatic element, which does not require such a high-pressure control valve but just has a position control valve, is also known.
From practice, it is also known to install pressure sensors in the area of the hydrostatic element. Typically, two pressure sensors are installed in a hydrostatic system, wherein, amongst others, the hydrostatic units of the hydrostatic element are pressurized and regulated as a function of the measured values of these pressure sensors.
Hydrostatic power-split transmissions have the disadvantage that, unlike converter transmissions, insufficient heat energy is generated in the transmission to sufficiently heat the hydraulic fluid in the power-split transmission.
From DE 10 2015 200 682 A1, a method for performing a cold start in a vehicle having a power-split transmission comprising a hydrostatic element is known. There, several cold-start steps are completed, wherein the order and the length of the cold-start steps depend on the start temperature of the hydraulic fluid at the beginning of the cold start and are altered. Even though the method known from DE 10 2015 200 682 A1 provides an effective method for a cold start of a vehicle having a power-split transmission, which comprises a hydrostatic element, the cold start of such a vehicle needs to be improved further.
From DE 10 2010 007 987 A1 a method for a cold start of a motor vehicle comprising an automatic transmission is known.
On this basis, the invention addresses the problem of providing a novel method for performing a cold start in a vehicle having a power-split transmission having a hydrostatic element.
This object is achieved by a method according to the independent claim(s).
In accordance with the invention, during the execution of at least one cold-start step, one state of the power-split transmission deviating from the temperature of the power-split transmission is monitored, wherein a transition is made from that cold-start step to a subsequent cold-start step depending on respective states, thus adapting the length of time of the respective cold-start steps.
In the method according to the invention for performing a cold start of a vehicle having a power-split transmission, which has a hydrostatic element, when performing at least one cold-start step, one state of the power-split transmission, which differs from the temperature of the latter, is monitored preferably by means of an in-transmission sensor. Depending on that state, i.e. depending on whether [certain] conditions are met in a cold-start step, there is a change from the current cold-start step to a subsequent cold-start step, thereby adapting the length of time of the individual cold-start step, by monitoring the state deviating from the temperature of the power-split transmission state. As a result, the cold start of a vehicle having a power-split transmission can be performed within a shorter period of time.
The method according to the invention has further advantages in addition to the short period of time, in which the cold start according to the invention can be performed. For instance, the method according to the invention for performing a cold start is robust with respect to the existing boundary conditions, such that in particular no adaptation of the method with respect to different degrees of coldness of the power-split transmission, with respect to different viscosities of the hydraulic oil, and with respect to structural changes in the transmission has to be made. Thus, regardless of the period of time during which the power-split transmission has cooled down, regardless of whether the power-split transmission uses a winter oil or a summer oil, and regardless of the specific design of the transmission, the method can be used to perform a cold start within a short period of time and thus with little loss of comfort.
According to an advantageous development of the invention, the following cold-start steps are performed successively for a cold start: First, a pressurization step to pressurize the power-split transmission and to heat the latter by operating a transmission pump. Subsequently, a pressure-gauge step to assess the pressurization of the transmission. Then, a first heating step to engage at least one reversing clutch in the power-split transmission and to heat the former using the power losses incurred in the power-split transmission. Subsequently, a pulsation step to engage and disengage the range clutches of the power-split transmission in a pulsed manner therein. Subsequently, a second heating step to heat at least one position control valve of the hydrostatic element in the power-split transmission. Subsequently, a drive-off preparation step to check a behavior of the reversing clutches and the hydrostatic element of the power-split transmission and to prepare the power-split transmission for the vehicle driving off. Due to the sequential cycling of these cold-start steps, the cold start can be performed very effectively within a short period of time. The function of the power-split transmission is continuously monitored during at least some of the above cold-start steps. Based on this assessment, the duration of the respective cold-start steps is determined at least for some cold-start steps of the cold-start process.
Preferably, during the pressurization step, a first partial pressurization step, in which a drive unit is operated at a relatively low drive unit speed, leads to a second partial pressurization step, in which the drive unit operates at a relatively high engine speed, wherein the transition from the first partial pressurization step to the second partial pressurization step depends on at least two pressures in the hydrostatic element.
Preferably, the shift from pressurization step to pressure-gauge step depends on a minimum period of the pressurization step, This makes for a particularly advantageous transition from the pressurization step to the pressure-gauge step.
The shift from the pressure-gauge step to the first heating step preferably depends on at least two pressures in the hydrostatic element. This makes for a particularly advantageous transition from the pressure-gauge step to the first heating step.
The shift from the first heating step to the pulsation step preferably depends on a comparison of an actual behavior of the hydrostatic element with a defined actuation of the latter and a corresponding target behavior of the hydrostatic element. This makes for a particularly advantageous transition from the first heating step to the pulsation step.
Preferably, the transition from the pulsation step to the second heating step depends on a definite number of pulsations, which is selected at the beginning of the cold start depending on the temperature representing the start temperature of the power-split transmission. This makes for a particularly advantageous transition from the pulsation step to the second heating step.
Preferably, the transition from the second heating step to the drive preparation step depends on a defined time period, which is independent of the temperature representing the start temperature of the power-split transmission. This makes for an advantageous transition from the second heating step to the drive preparation step.
Preferably, the drive preparation step and thus the cold start are terminated as a function of a reduction of the differential rotational speed, which develops during an engagement process of the reversing clutches, and as a function of a reaction time resulting from the actuation of the hydrostatic element. This makes for a particularly advantageous termination of the drive preparation step and thus the actual cold start.
Preferred developments are presented in the subclaims and the description below. Exemplary embodiments of the invention will be described with reference to the drawings, without being limited thereto. In the figures:
The invention relates to a method for performing a cold start in a vehicle, which has a power-split transmission comprising a hydrostatic element.
For such a vehicle, a drive unit is coupled to an input shaft of the power-split transmission.
The power-split transmission comprises a mechanical branch in addition to a hydrostatic branch into which the hydrostatic element is integrated. The mechanical branch and the hydrostatic branch are combined and split, respectively. The power-split transmission can provide at least two driving ranges and thus speeds each for both one forward and one reverse direction, wherein the power-split transmission has reversing clutches and range clutches for that purpose. The hydrostatic element, which is also referred to as hydrostatic element, can be controlled using a position control valve of the former, Pressure sensors can be used to monitor the pressure in the hydrostatic element, which comprises two hydrostatic units acting as pump and motor.
This basic setup is familiar to the person skilled in the art and is known in particular from DE 10 2007 047 194 A1 and from DE 10 2009 045 510 A1.
To perform a cold start on such a motor vehicle, several cold-start steps are performed in succession. The length of at least one of the cold-start steps depends on a temperature representing the start temperature of the power-split transmission, such as the start temperature of the hydraulic oil of the power-split transmission.
The start temperature is preferably a temperature measured at the time of engine start or ignition, for instance, the pertinent temperature of the hydraulic oil in the power-split transmission.
According to the invention, during the execution of at least one cold-start step, one state of the power-split transmission deviating from the temperature of the power-split transmission, in particular the temperature of the hydraulic oil, is monitored. Depending on this state, a transition from the individual cold-start step, in which the state deviating from the temperature of the power-split transmission is monitored, is then made to the subsequent cold-start step, wherein the length of time of the relevant cold-start step, in which the state deviating from the temperature of the power-split transmission is monitored, will be adapted.
The method according to the invention for performing a cold start is described in detail below with reference to
In the cold start according to the invention, first a pressurization step 1 is performed to pressurize the power-split transmission in a defined manner, and to heat the power-split transmission using the operation of a transmission pump thereof. In the pressurization step 1, the power-split transmission is heated solely by the gear pump of the former.
According to
Accordingly, in the first partial pressurization step 2, the rotational speed of the drive unit and thus of the gear pump is lower than that in the second partial pressurization step 3.
In block 4 of the signal flow diagram of
There, provision is made in particular for a minimum dwell time or minimum period of the first partial pressurization step 2, such that the transition from the first partial pressurization step 2 to the second partial pressurization step 3 is only made when the minimum period of the first partial pressurization step 2 has been reached and both pressure sensors also provide measured values that are above a defined threshold or limit.
During the pressurization step 1, an assessment is made as to whether a minimum dwell time or minimum period has been achieved for the second partial pressurization step 3 as well. In that case and if the corresponding transition condition 5 is fulfilled, starting from the pressurization step 1, that is, from the second partial pressurization step 3, transition is made to a pressure-gauge step 6.
It should be noted at this point that the minimum dwell times or minimum periods of the first partial pressurization step 2 and of the second partial pressurization step 3 can depend on the start temperature of the power-split transmission or on the start temperature of the hydraulic oil.
The lower the start temperature, the longer the corresponding minimum dwell times to be selected.
In
The viscosity of the hydraulic oil, in particular whether there is high-viscosity or low-viscosity hydraulic oil, can be inferred from the time offset Δt.
The time profiles of
Accordingly, the pressure sensor providing the measuring signal 23 is again an undamped pressure sensor without a hydraulic aperture and the pressure sensor providing the measuring signal 24 is a damped pressure sensor having a hydraulic aperture.
In
At the time t3, the measured values 23 and 24 of both pressure sensors reach a threshold value S, such that a transition from the first partial pressurization step 2 to the second partial pressurization step 3 and an increase of the drive unit speed can generally occur starting at the time t3, wherein in
Thus the first partial pressurization phase 2 of the pressurization phase 1 extends from the time t1 to the time t4 in
In the pressure-gauge step 6, the measured value provided by the two pressure sensors of the hydrostatic element is assessed. In particular, an assessment is made as to whether the measured value of both pressure sensors is above a defined threshold value or limit value. In that case, i.e. if the relevant transition condition 7 of the block 7 of
Details of the pressure-gauge step 6 are shown in the time diagram of
In the first heating step 8, a reversing clutch of the power-split transmission is engaged for the first time, namely either the clutch for the reverse drive or the clutch for the forward drive. As a result of this engagement of the relevant reversing clutch, a force flow to the planetary gear or to the superposition gear and thus to the hydrostatic element is established, generating power dissipation for heating the power-split transmission in the first heating step using the generated power dissipation. While the relevant reversing clutch is engaged during the first heating phase 8, the position control valve is used to apply an initially small and later larger current amplitude to the hydrostatic element, This actuation moves the hydrostatic element between a certain angle and a specific ratio.
In the first heating step 8, therefore, the hydrostatic element is actuated in a defined manner and in doing so, an actual behavior of the hydrostatic element is determined. The defined actuation denotes the application of an alternating current amplitude to the latter, and the reaction or in the actual behavior denotes the ratio, which can be determined using speed sensors mounted at the hydrostatic element,
When the actual behavior corresponds to a predetermined target behavior or deviates from the target behavior by no more than a defined limit value, the transition condition 9 is fulfilled and then the transition from a pulsation step 10 to the first heating step 8 is made. During the first heating step 8, the drive unit speed can be changed, preferably increased.
At the time t1, the energization of the position control valve of the hydrostatic element reaches a minimum. Subsequently, at the time t2, the ratio of the hydrostatic element reaches a corresponding minimum. The time offset Δt1, which is determined by these two times t1 and t2, corresponds to a first parameter of the actual behavior of the hydrostatic element as a result of the defined actuation of the position control valve.
At the time t3 in
When it is determined that the actual time offsets correspond to respective target time offsets, or do not deviate from them by more than a threshold value of these time offsets Δt1 and Δt2, the transition condition 9 is fulfilled and the transition from the first heating step 8 to the pulsation step 10 is made.
In the pulsation step 10, range clutches of the power-split transmission are alternately engaged and disengaged, i.e. pulsed. The pulsing of the range clutch of the power-split transmission is conducted based on a fixed number. When the fixed number of pulses for engaging and disengaging the range clutches of the power-split transmission is reached, the transition condition 11 is fulfilled, and the transition from the pulsation step 10 to a second heating step 12 is made.
In the second heating, step 12 of the cold start, the position control valve of the hydrostatic element is warmed up and overshot, in accordance with a fixed time scheme. The length of time of the second heating step is identical for all temperature ranges, i.e. independent of the start temperature of the power-split transmission or of the temperature representing or corresponding to the start temperature of the latter.
The second heating step 12 is used to overstretch the position control valve of the hydrostatic element in its two end positions using a suitable magnet and thus to flush any existing, highly viscous oil out of the position control valve. The second heating step 12 ensures that the adjustment system of the hydrostatic element, which consists of adjustment cylinder, adjustment valve, adjustment magnet and feedback system was fully actuated and thus no undesirable behavior is to be expected in the end positions of the former.
The transition from the second heating step 12 to a drive-off preparation step 14 is made when a transition condition 13 is fulfilled, depending on a defined period of time, which is independent of the start temperature of the power-split transmission or the temperature representing the start temperature of the power-split transmission.
The transition condition 13 for the transition from the second heating step 12 to the drive preparation step 14 is therefore the temperature-independent, defined time period of the second heating step, and the transition from the second heating step 12 to the drive preparation step 14 is made once the time period of the second heating step has elapsed.
A behavior of the reversing clutches and the hydrostatic element of the power-split transmission is assessed in the drive preparation step 14, and the power-split transmission is prepared for a subsequent drive-off operation of the vehicle.
When a defined differential speed reduction develops during the engagement of the reversing clutches, and when depending on an actuation of the hydrostatic element, a defined reaction time has developed at the former, the drive preparation step, and thus the actual cold start, is terminated if the pertinent transition condition 15 is fulfilled, to thus make the transition from the drive preparation step 14 to a wait state or a standby state for a drive-off request, wherein this standby state is visualized by the block 16 in
Details of the drive preparation step 14 will be described below with reference to
The primary and the secondary rotational speed of the reversing clutch, i.e. the difference between the primary and the secondary rotational speed, are important for the evaluation of a reversing clutch.
As stated above, in the drive preparation step 14, not only the behavior of the reversing clutches is assessed, but also the behavior of the hydrostatic element, to be exact, as soon as the relevant reversing clutch is engaged and there is a complete flow of power to the hydrostatic dement. As soon as the respective reversing clutch is engaged, the hydrostatic element is actuated by energizing the position control valve of the latter in a defined manner. For that purpose, the energization is increased from an idle current, which is slightly higher than a so-called diagnostic current, to a current slightly higher than a so-called zero-angle current, the zero-angle current being derived from a calibration of the hydrostatic element. In doing so, the length of a time offset or a time lag between the activation of the hydrostatic element and the reaction thereof is evaluated. The evaluation is performed similar to a step response.
This process is repeated or performed several times using a reversible clutch. If the time offset between the activation and the response of the hydrostatic dement is within a defined range of values, the hydrostatic element is evaluated and recognized as functioning properly.
When both the reversing clutches and the hydrostatic element are detected to be properly operating in the drive preparation step 14, the transient condition 15 is fulfilled, and the transition is made from the drive preparation step 14 to the wait state 16 or to the drive-off standby state 16.
During the wait state 16, i.e. after completion of the cold start, the system waits for a drive-off request by the driver. In doing so, an engine control unit specifies the drive unit speed instead of a transmission control unit controlling the cold-start process. During the wait state 16, the fulfillment of a transition condition 17 is therefore assessed, which transition condition is a request for a drive-off process, wherein if that transition condition is fulfilled, transition is made to the drive-off state 18 of
If, during the waiting state 16, the driver does not request a drive-off process for a defined period of time, at least one reversing clutch can be engaged in a defined manner during the waiting state to generate power dissipation in the power-split transmission and thus avoid re-cooling of the power-split transmission.
The event-based cold start method according to the invention can be used to perform a cold start of a vehicle having a power-split transmission comprising a hydrostatic element within a short time and extremely robustly. The reversible clutches and the hydrostatic element can be checked for their proper functionalities.
The method for performing a cold start according to the invention in a vehicle provides a kind of field diagnosis for the transmission which can be used to monitor the proper operation of the transmission in the field. All the steps or phases of the process are run through, warranting the safe operation of the transmission. Upon completion of the process, a vehicle having a transmission with increased or full dynamics and with reduced or no loss of comfort is available. The method is robust and therefore not prone to failure in case of an unsuccessful start of the drive unit at low temperatures, a cold restart of the drive unit and viscosity of the gear oil used.
1 pressurization step
2 partial pressurization step
3 partial pressurization step
4 transition condition
5 transition condition
6 pressure-gauge step
7 transition condition
8 first heating step
9 transition condition
10 pulsation step
11 transition condition
12 second heating step
13 transition condition
14 preparatory drive step
15 transition condition
16 wait state
17 transition condition
18 drive-off state
19 time profile
20 time profile
21 time profile
22 time profile
23 time profile
24 time profile
25 time profile
26 time profile
27 time profile
28 time profile
29 time profile
30 time profile
31 time profile
32 time profile
33 time profile
34 time profile
35 time profile
36 time profile
37 time profile
38 time profile
39 time profile
40 time profile
41 time profile
42 time profile
43 time profile
44 Power-Take-Out
45 drive unit
46 reversing gear
47 power-split transmission
48 hydrostatic element
49 planetary gear set
50 summation gear
51 driving range gear
52 output
Number | Date | Country | Kind |
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10 2016 221 126.9 | Oct 2016 | DE | national |
This application is a National Stage completion of PCT/EP2017/073655 filed Sep. 19, 2017, which claims priority from German patent application serial no. 10 2016 221 126.9 filed Oct. 26, 2016.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2017/073655 | 9/19/2017 | WO | 00 |