Method for position detection in a claw switching element

Abstract

Method for position detection in a hydraulically actuated claw switching element that can be closed by spring force, wherein an actuating pressure (p_B) is applied to open the claw switching element, characterized in that after closing the claw switching element a test pressure (p_P) is applied and the actuating pressure profile and the test pressure profile are recorded and evaluated.

Description

The present invention relates to a method for position detection in a hydraulically actuated claw shifting element that can be closed by spring force. The invention further relates to a hydraulic control device of a hydraulically actuated claw shifting element that can be closed by spring force.In this case, DE 10 2008 001 197 A1 discloses a hydraulically or pneumatically actuatable positive-locking shifting element in the form of a claw clutch.It is known from automotive engineering that a transmission controller requires confirmation, for example, when executing a shift operation, whether a dog shift element installed in the transmission is opened or closed. When the dog shift element is closed, the shift may be completed and the powertrain may be torqued. However, if the dog shift element remains open despite actuation, measures must be taken to close the dog shift element. For example, the shift element can be actuated again or the rotational speed or the torque between the two shafts to be connected can be changed for synchronization. Consequently, claw position detection is urgent.For example, additional components are provided on the shift pawl for this purpose, with which the respective position of the pawl shift element can be detected. However, the disadvantage here is that additional installation space is required in the region of the switching claw. This additional installation space is not available in some applications. In addition, manufacturing costs are increased as a result, and the structural design of the claw shifting element is more complex and the weight is increased.Accordingly, the present invention is based on the object of proposing a method for position detection in a claw shifting element and a hydraulic control device for carrying out the method, which enable reliable position detection without additional components on the shifting claw of the claw shifting element.This object is achieved according to the invention by the features of patent claims 1 and 6. Advantageous and claimed developments are evident from the dependent claims and the description and the drawings.Thus, a method for position detection is proposed in a hydraulically actuated normally closed claw shift element (when no pressure is generated in the hydraulic system, such as when the transmission is at a standstill, thus the pump), wherein an actuation pressure is applied for opening the claw shift element. In order to realize a particularly simple position detection, it is provided that a test pressure is applied after the closing of the claw shifting element and the actuating pressure profile and the test pressure profile are recorded and evaluated.The proposed method for position detection is implemented by a pressure curve detection and a corresponding evaluation in the hydraulically actuated claw shifting element. Because position detection is realized by pressurization and measurement, no additional components are advantageously required on the switching claw, whereby no additional installation space is required in this area. Thus, the mobility of the switching claw as well as the signal transmission is not impaired. In order to carry out the proposed method, only a pressure sensor or the like and evaluation software are required, so that the costs for the position detection are minimized.The object on which the invention is based is also achieved by a hydraulic control unit of a hydraulically actuated claw shifting element which can be closed by means of a restoring spring, wherein at least one pressure sensor and an evaluation device are provided for detecting and evaluating an actuation pressure profile and a test pressure profile. This results in the advantages described above and further advantages. The proposed method can preferably be executed with the hydraulic control unit.The present invention is explained in more detail below with reference to the drawings. It shows: FIG. 1 is a schematic view of a dog shift element with operating pressure applied to open the dog shift element; FIG. 2 shows a diagram with a corresponding actuating pressure profile according to FIG. 1 ; FIG. 3 is a schematic view of the pawl shift element with test pressurization for closing the pawl shift element; FIG. 4 shows a diagram with a corresponding actuating pressure profile and with a corresponding test pressure profile when the pawl shift element is detected in the closed state; FIG. 5 is a schematic view of the pawl shift element with test pressurization for detecting the closed state of the pawl shift element; and FIG. 6 shows a diagram with a corresponding actuating pressure profile and the corresponding test pressure profile when the clutch shift element is detected in the non-closed state.FIGS. 1, 3 and 5 show, by way of example, a claw switching element which can be actuated hydraulically and can be closed by spring force. With reference to this dog shift element, a method for position detection in the dog shift element proposed according to the present invention will be described by way of example.The pawl switching element comprises an axial switching pawl 2 which can be actuated by an actuating piston 1, the switching pawl 2 being mounted on a first shaft W 1 so as to be axially movable and being connected to a second shaft W 2 in a rotationally fixed manner. In the closed state of the claw shifting element, the shifting claw 2 is displaced axially via the actuating piston 1 in such a way that the shifting claw 2 is connected to the first shaft W 1 in a rotationally fixed manner by means of a driving toothing 4. Consequently, in the closed state of the pawl shifting element, a rotationally fixed connection is realized between the first shaft W 1 and the second shaft W 2 via the shifting pawl 2, so that a torque transmission between the first shaft W 1 and the second shaft W 2 is made possible. The switching claw 2 is actuated axially displaceably via the actuating piston 1 against the spring force of a restoring spring or of a spring pack 3. The pawl switching element is configured as a so-called normally closed switching element, i.e., the return spring 3 moves the switching pawl 2 into the closed state when no actuation pressure is applied to the actuation piston 1.In FIG. 1, the switching claw 2 of the claw switching element is acted upon by an actuating pressure p_B via the actuating piston 1, so that the switching claw 2 is moved axially into its open position by the actuating piston 1 and the claw switching element is open. The hydraulic actuation, represented by the arrow, thus takes place via the actuation pressure p_B. The associated diagram is shown in FIG. 2, in which an actuation pressure profile over time t is shown. It can be seen from this that a constant increase of the actuating pressure curve takes place until it approaches the predetermined value of the actuating pressure p_B for opening the switching claw 2.In FIG. 3, for closing the claw switching element, the actuating pressure p_B on the actuating piston 1 is lowered to zero, so that the spring-loaded switching claw 2 is closed. As a result, the switching claw 2 and the actuating piston 1 are in their right end position in the plane of the drawing, since the switching claw 2 is pressed to the right without application of actuating pressure. After closing the claw shifting element, a test pressure p_P is applied to the actuating piston 1, so that the actuating piston 1 is brought into contact with the shifting claw 2 by the test pressure p_P. The test pressure p_P is only so high that the actuating piston 1 comes into contact with the switching claw 2 without compressing the restoring spring 3. It can be seen from the associated diagram in FIG. 4 that after the actuation pressure p_B has been lowered to zero, the test pressure p_P immediately rises to its predetermined value and then falls again. The time required for this purpose until the test pressure is reached is denoted p_P by the defined time period t 1 and serves to define a correct detection of the closed state.In FIG. 5, the switching claw 2 is not closed despite the lowering of the actuating pressure p_B. This means that, for example, due to a tooth on tooth position or the like, the shift pawl 2 cannot be closed and thus no torque transmission is possible between the two shafts W 1 and W 2. In order to detect this faulty state in the pawl shifting element, the test pressure curve is evaluated in the method for position detection of the non-closed faulty state of the shifting pawl 2. The corresponding diagram in FIG. 6 shows that the test pressure profile is changed with respect to the test pressure profile according to FIG. 4. To achieve the predetermined test pressure p_P, a significantly longer time period t 2 is required. This time difference Δt results from the test pressure p_P being reached only slowly, because the air space between the actuating piston 1 and the switching claw 2 must first be filled until the test pressure p_P can be reached. Accordingly, with the method according to the present invention, this defective state of the dog shift element can be easily detected.Thus, in the proposed method, when a predetermined time difference Δt is detected between the detected time period t 2 and the fixed time period t 1, the state of the shift dog 2 of the dog shift element is not reached. The method recognizes the achievement of the closed state of the shifting pawl 2 of the pawl shifting element when the detected time period t 2 approximately matches the fixed time period t 1.Furthermore, a hydraulic control unit of a hydraulically actuated claw shifting element that can be closed via a restoring spring 3 is proposed, having at least one pressure sensor and an evaluation device for detecting and evaluating an actuation pressure profile and a test pressure profile, in particular for carrying out the method according to the invention. By means of the hydraulic control device, the pawl switching element, which is preferably designed as normally closed, is acted upon with actuating pressure p_B for opening the switching pawl, wherein, for closing the switching pawl 2, the actuating pressure acting on the actuating piston 1 is lowered to zero, so that the switching pawl 2 is moved into its closed position by means of the restoring spring 3. For position detection, an applied test pressure p_P is measured via the pressure sensor. With the aid of the pressure sensor and the evaluation device, the actuating pressure profile and the test pressure profile can be correspondingly detected and evaluated in order to realize position detection in the case of the claw shifting element.Reference numerals denote reference numerals1 Actuating piston 2 Switching claw 3 Restoring spring 4 Driving toothing p Pressure p_B Actuating pressure p_P Test pressure t Time t 1 Defined or predefined time period t 2 Detected time period Δt Time difference or time delay W 1 First shaft W 2 Second shaft

Claims

Method for position detection in a hydraulically actuated claw shifting element which can be closed by spring force, wherein an actuation pressure (p_B) is applied for opening the claw shifting element, characterized in that after the closing of the claw shifting element a test pressure (p_P) is applied and the actuation pressure profile and the test pressure profile are detected and evaluated.Method according to Claim 1, characterized in that, for opening the claw switching element, a predetermined actuating pressure (p_B) is applied to an actuating piston (1) in order to move a spring-loaded switching claw (2) of the claw switching element into an open state, in that the actuating pressure (p_B) for closing the claw switching element is lowered to zero in order to move the switching claw (2) of the claw switching element into a closed state, in that a predetermined test pressure (p_P) is applied to the actuating piston (1) in order to bring the actuating piston (1) into contact with the switching claw (2), and in that a time period (t2) for reaching the predetermined test pressure on the actuating piston (1) is detected and evaluated.Method according to Claim 2, characterized in that the detected time period (t2) until the predetermined test pressure (p_P) is reached is compared with a fixed time period (t1).Method according to Claim 3, characterized in that the closed state of the switching claw (2) of the claw switching element is detected from not being reached if a predetermined time difference (Δt) is detected between the detected time period (t2) and the fixed time period (t1).Method according to one of Claims 2 to 4, characterized in that the attainment of the closed state of the switching claw (2) of the claw switching element is detected if the detected time period (t2) corresponds approximately to the fixed time period (t1).Hydraulic control device of a hydraulically actuated claw switching element which can be closed by means of a restoring spring, having at least one pressure sensor and an evaluation device for detecting and evaluating an actuating pressure profile and a test pressure profile, in particular for carrying out the method according to one of the preceding claims.

Images