HYDRAULIC CLUTCH PRESSURE CONTROL APPARATUS

Abstract: The present invention provides an apparatus for controlling a hydraulic pressure usable for a clutch wherein the appratus is employed for a transmission mounted on a construction machine or the like in such a manner that it is provided separately for a plurality of clutches 1 and it is controlled individually. The apparatus includes a first valve 3 for allowing a large amount of hydraulic oil to flow in the clutch and a second valve 4 for electronically controlling a clutch pressure so that the termination of filling and the clutch pressure are detected by a simple structural arrangement on the basis of a displacement of a spool 21 for the first valve 3 and a separately disposed piston. In addition, appearing of an overshoot pressure on the termination of filling is prevented by providing a difference in pressue receiving areas on the spool 21 for the first valve.

Description: The present invention relates to an apparatus for controlling a hydraulic pressure usable for a clutch and more particularly to an apparatus of the foregoing type which assures that detection of filling and detection of a clutch pressure are carried out by a simple electronic control type valve arrangement to prevent an occurrence of double engagement with clutches and speed changing is smoothly achieved. Fig. 7 illustrates a hitherto widely employed control for speed changing with a transmission. In the illustrated case, speed changing from a first speed to a second speed is taken into account. This conventional control for speed changing is such that a clutch for the first speed is turned off when a command for speed changing is outputted and at the same time a hydraulic oil starts to flow in a clutch for the second speed. Consequently, a hydraulic pressure in the clutch for the first speed is lowered from a predetermined pressure to a level of zero when the command for speed changing is outputted, while a hydraulic pressure in the clutch for the second speed starts to increase gradually after a period of filling time t f elapses. This filling time t f designates a period of time required for filling the interior of a clutch pack of the clutch for the second speed with a hydraulic oil. In this manner, with the conventional apparatus, the time t f that elapses until the clutch pack is filled with a hydraulic oil is reserved and no torque is transmitted during the period of time t f . This causes a so-called breathing phenomenon to appear during a period of speed changing with the conventional apparatus and the breathing phenomenon gives rise to a problem concerning running performances such as riding comfortability, acceleration characteristic or the like. Particularly, with respect to a large-sized construction machine, a period of filling time is prolonged due to a large capacity of respective clutches, which has a substantial effect on running performances. In view of the foregoing problems, in the recent years attention has been paid to a crossover control as disclosed in an official gazette of Japanese Laid-Open Patent NO. 13758/1963 and the crossover control has been lately carried out using electronic type pressure control valves. Specifically, according to the prior invention as proposed by the inventors under Japanese Patent Application NO. 271055/1985, a crossover control as shown in Fig. 8 is carried out using an electronic modulation system for all clutches to prevent an occurrence of breathing during a period of speed changing due to the presence of filling time. The proposal as shown in Fig. 8 is such that when a command for speed changing is outputted, a hydraulic oil starts to flow in a clutch for the second speed to be next brought in an engaged state, thereafter when the termination of filling is detected, a clutch for the first speed which has been previously brought in an engaged state is turned off and a build-up control is initiated for the clutch for the second speed. According to this proposal, an occurrence of breathing phenomenon due to the presence of filling time t f is not only prevented reliably but also speed changing can be smoothly achieved, resulting in improved running performances being assured. However, to properly carry out such speed changing, it is required that the filling time t f is exactly detected and an occurrence of double engagement is prevented without fail. Hitherto, detection of the filling has been performed by properly controlling a pattern with which a hydraulic pressure is gradually increased as time elapses after a command for speed changing is outputted. Specifically, hitherto, a time required for filling the clutch pack with a hydraulic oil is suitably set on the basis of prior experiments, the termination of filling is identified when the set time elapses after a command for speed changing is outputted, and thereafter a hydraulic pressure is increased gradually. However, it has been found that detecting of the filling having such time control employed there for can not absorb fluctuation in filling time. For instance, when the clutch pack is filled with a hydraulic oil before the set time elapses, this allows an useless waiting time to be produced, which brings a factor of causing time lag. In addition, since there is a shortage in reliability of detection, a problem is that the aforementioned time control can not be applied to the conventional crossover control for speed changing. Additionally, according to this crossover control for speed changing, there is a danger that clutches are brought in double engagement, if releasing and engagement timing of clutches located at the preceding stage as well as at the following stages ore deviated from correct ones. Accordingly, this becomes a serious problem from the viewpoint of measures to be taken for safety. However, any particular measure for assuring safety is not taken with the conventional apparatus and this leads to a fear of causing troubles such as damage or injury of components or instruments. From DE-A-30 10 865 is known an apparatus for controlling a hydraulic pressure for a cross-over control in a hydraulic clutch. The end of filling of the clutch is detected by measuring the voltage induced at the windings of an electrohydraulic current controlled pressure regulator when a pressure peak occurs. The occurence of the peak is strictly necessary for that solution, whereby the peak has to be detected independently from all other influences in the electronic circuit. To prevent an occurrence of double engagement, it suffices that an engaged state of the respective clutches can be determined. To this end, there is a need of watching which clutch is filled with a hydraulic oil having a certain intensity of pressure. To provide structural arrangement for the purpose of watching in that way, there has been made a proposal for arrangement of a strain gauge type pressure sensor or a semiconductor type pressure sensor which is available on the commercial basis. However, the proposal has a problem that the commercial pressure sensor is expensive and it has a difficulty in durability. Further, to prevent an occurrence of double engagement, it suffices that whether or not the clutch is filled with a hydraulic oil having a certain intensity of pressure is known. According, a quantitatively detected value derived by a pressure sensor is not required. The present invention has been made with the foregoing background in mind and its object resides in providing an apparatus for controlling a hydraulic pressure usable for a clutch which assures that detection of filling and detection of presence or absence of a hydraulic pressure for clutches can be exactly attained by a simple and inexpensive structural arrangement. Other object of the present invention is to provide an apparatus for controlling a hydraulic pressure usable for a clutch which assures that an overshoot pressure generated on the termination of filling is reduced substantially. Another object of the present invention is to provide an apparatus for controlling a hydraulic pressure usable for a clutch which assures that a shock appearing during a period of speed changing is reduced by smooth speed changing and an occurrence of double engagement with clutches can be prevented without fail. There is provided in accordance with the present invention an apparatus for controlling a hydraulic pressure usable for a clutch comprising a first valve including a spool with an orifice formed at an output port leading to the clutch, the first valve being opened under the effect of a differential pressure appearing across the orifice and closed under the effect of a restorable force of a first spring disposed on one end of the spool, a second valve in the form of a pressure control valve adapted to be activated in response to an electrical signal, the second valve functioning to open the first valve by feeding to the latter a hydraulic oil delivered from a pump during a period of speed changing and gradually increase a hydraulic pressure for the clutch after the termination of filling, a second spring disposed on the other end side of the spool for the first valve, and detecting means for detecting the termination of filling and a clutch pressure on the basis of a displacement of the spool for the first valve against a resilient force of the second spring. With such construction, a hydraulic oil delivered from the pump is fed to the first valve by actuating the second valve. Then, the first valve is opened due to the orifice formed in the first valve so that a hydraulic oil flows in the clutch through the first valve. Thereafter, when the clutch is filled with a hydraulic oil, the differential pressure across the orifice disappears, resulting in the first valve being closed under the effect of a restorable force of the spring. After the spool is returned to the neutral position in the course of a return movement, it is displaced further by a hydraulic pressure for the clutch against a resilient force of the spring disposed on the other end side thereof. The detecting means determines the termination of filling and presence or absence of a clutch pressure by detecting a displacement of the spool. This permits the termination of filling to be detected simply and exactly. Accordingly, crossover control for speed changing can be carried out exactly and safely and thereby speed changing can be smoothly achieved without an occurrence of breathing, resulting in improved running performances being assured. Further, with this construction, if a difference in pressure receiving area is given to the spool for the first valve, the spool is returned under the effect of a restorable force of the spring with a force generated by the difference in pressure receiving area added thereto so that a return speed of the spool can be increased. Consequently, an overshoot pressure appearing on the termination of filling can be reduced. With such construction, since a spring active in the opposite direction to such a direction that a clutch pressure is exerted on the spool is disposed so as to allow the termination of filling and a clutch engaged state to be detected by a simple structural arrangement comprising this spring and a contact, detection can be reliably attained at an inexpensive cost. In addition, since detecting of the filling is exactly carried out, the aforementioned crossover control can be favorably achieved and moreover running performances can be improved. Additionally, by monitoring the detecting signal to determine which clutch is brought in an engaged state, an occurrence of double engagement can be detected without fail, and if a proper measure is taken, damage or injury of pertinent components or instruments can be prevented. Fig. 1 is a block diagram illustrating a structural arrangement to be monitored by a pressure detecting switch, Fig. 2 is a time chart illustrating a clutch pressure during a period of speed changing in which an overshoot pressure is generated, Fig. 3 is a hydraulic circuit illustrating a preferred embodiment of the present invention, Fig. 4 is a sectional view illustrating by way of example the inner structure of a hydraulic pressure control valve for a clutch in accordance with the preferred embodiment, Fig. 5 is time charts illustrating by way of example operation of the hydraulic pressure control valve in accordance with the preferred embodiment respectively, Fig. 6 is a hydraulic circuit illustrating clutches for each of which an electronic type hydraulic pressure control valve is provided, Fig. 7 is time charts illustrating a conventional control for speed changing respectively, and Fig. 8 is time charts illustrating a control for speed changing in accordance with the conventional crossover control system. Figs. 3 and 4 illustrate a preferred embodiment of the present invention. This embodiment is such that both a filling detecting function and a clutch pressure detecting function are attained by a single sensor construction. Specifically, referring to Figs. 3 and 4, a hydraulic pressure control valve 60 comprises a pressure control valve 61 for controlling a hydraulic pressure usable for a clutch, a flow rate detecting valve 62 and a sensor section 63 for detecting a filling and a clutch pressure. The pressure control valve 61 is controlled by a controller 5, and a detection signal S from the sensor section 63 is inputted in the controller 5. A hydraulic oil delivered from a pump which is shown in Fig. 6 is introduced into the hydraulic pressure control valve 60 via an input port 70 and it is then fed to the clutch 1 via an output port 71. At this moment, a port 72 is kept closed and ports 73 and 74 represent a drain port respectively. The electronic type pressure control valve 61 includes a spool 75 of which right end comes in contact with a plunger 77 of a proportional solenoid 76, and a coil spring 78 is disposed at the left end of the spool 75. Additionally, a hydraulic pressure in a hydraulic passage 82 is introduced via a hydraulic passage 81 into a hydraulic chamber 80 defined by the spool 75 and the piston 79. Indeed, with respect to hydraulic pressure control valve, it has been found that when the spool for the flow rate detecting valve is closed after the filling time t f elapses, an overshoot pressure as shown in Fig. 2 is generated and this gives rise to a factor that a shock occurs during a period of speed changing or an abnormal sound is generated. Unless this overshoot pressure is reduced, any effort becomes useless which is intended to reduce a shock due to speed changing by carrying out torque compensation using the electronic type hydraulic pressure control valve. Accordingly, reduction of the overshoot pressure becomes a serious problem. To absorb the overshoot pressure, there has been proposed a method of providing an accumulator. However, problems arise that this method is practiced at an expensive cost and moreover structure in the proximity of the valve is enlarged and complicated. For the reason, the conventional method fails to be put in practical use. As results derived from a variety of research works conducted by the inventors with the foregoing problems in mind, it has been found that the overshoot pressure is generated when a return speed of the spool in the flow rate detecting valve is slow during a period in which the spool returns (moves in the rightward direction) after the termination of filling. The flow rate detecting valve 62 includes a spool 85 which defines hydraulic chambers 86, 87 and 88. An orifice 90 is formed between both the hydraulic chambers 87 and 88. The spool 85 is so constructed that it has three different pressure receiving areas S₁, S₂ and S₃ which have a relationship among them as represented by S₁ + S₃ > S₂ and S₂ > S₃. A coil spring 91 is disposed at the left end of the spool 85 and another coil spring 92 is disposed at the right-hand end of the same. When no hydraulic pressure is introduced into the hydraulic chambers 87 and 88, the spool 85 is maintained at a neutral position shown in Fig. 3 where both the springs 91 and 92 have their free length. Accordingly, when the spool 85 is held at a neutral state, a hydraulic oil which flows in the flow rate detecting valve 62 from a hydraulic passage 84 via the input port 70 is caused to stay in the hydraulic chamber 86. Here, when it is assumed that spring constants of the springs 91 and 92 are represented by k₁ and k₂, hydraulic pressures in the hydraulic chambers 87 and 88 are represented by P₁ and P₂ and a displacement of the spool 85 from the neutral position is represented by x, a force F₁ represented by the following formula (1) is exerted on the spool 85 in the rightward direction when the spool 85 is located leftward of the neutral position shown in Fig. 13. F₁ = k₁ x + S₁ P₂ + P₁ (S₃ - S₂) (1) On the contrary, when the spool 85 is located rightward of the neutral position, a force F₂ represented by the following formula (2) is exerted on the spool 85 in the leftward direction. F₂ = k₂ x - S₁ P₂ - P₁ (S₃ - S₂) (2) Incidentally, in this case, k₂ > k₁ is assumed. Specifically, in this case, the spring 91 functions as a return spring for the spool 85 and the spring 92 functions as a pressure setting spring for the purpose of detecting a hydraulic pressure for the clutch. A detecting pin 94 made of metallic material is disposed on the upper right side of the valve body 93 in order to detect that the spool 85 is displaced further rightward of the neutral position shown in Fig. 4 against a resilient force of the spring 92. The detecting pin 94 is attached to the valve body 93 by means of a cover 95 in the presence of an electrical insulating sheet 96 and a lead wire 97 is extended from the detecting pin 94. The lead wire 97 is connected to a point c between resistances R₁ and R₂ which in turn are connected to one another in series. A predetermined magnitude of DC voltage V (for instance, 12 V) is applied to the resistances R₁ and R₂ therebetween and the valve body 93 is earthed. Namely, the sensor 63 for detecting a filling and a hydraulic pressure for the pertinent clutch comprises the spring 92, the detecting pin 94 serving as a contact on the spool 85 and the resistances R₁ and R₂. The hydraulic pressure control valve 60 having the sensor section 63 used therefor is disposed individually for clutches for respective speed change stages. Next, operation of the apparatus constructed as illustrated in Figs. 3 and 4 will be described below with reference to time charts as shown In Fig. 5. It should be noted that Fig. 5(a) shows a command electrical current I from the controller 5, Fig. 5(b) does a pump pressure P p , Fig. 5(c) does a hydraulic pressure P₁ in the hydraulic chamber 87 before the orifice 90, Fig. 5(d) does a hydraulic pressure (clutch pressure) P₂ in the hydraulic chamber 88 behind the orifice 90 and Fig. 5(e) does an output S from the sensor 63. When it is required that a clutch allocated to a certain speed change stage is brought in an engaged state, the controller 5 is so activated that a trigger command electrical current I₁ is inputted in the solenoid 76 of the pertinent valve 60 (time t₁), a command electrical current I is later lowered to an initial pressure command electrical current I o corresponding to an initial pressure Pa for the hydraulic pressure for the pertinent clutch (Fig. 5(d)) and it is then held in a waiting state till the termination of filling while the foregoing operative state is maintained. As the trigger command electrical current I₁ is inputted in that way, the spool 75 in the pressure control valve 61 is displaced in the leftward direction and a hydraulic oil delivered from the pump flows in the hydraulic chamber 87 of the flow rate detecting valve 62 via the input port 70 and the hydraulic passage 82. Hydraulic oil introduced into the hydraulic chamber 87 flows in the hydraulic chamber 88 via the orifice 90 and it flows further in the clutch 1 via the hydraulic passage 83 and the output port 71. At this moment, a differential pressure (P₁ - P₂) is generated between both the hydraulic chambers 87 and 88 due to the provision of the orifice 90. Here, since the pressure P₂ is approximately equal to zero, the spool 85 is displaced in the leftward direction under the effect of a force represented by (S₂ - S₃) P₁ - k₁ x (where S₂ is larger than S₃) which is derived by inserting a condition of P₂ = 0 in the formula (1). As a result, the flow rate detecting valve 62 is opened so that hydraulic oil introduced into the hydraulic passage 84 flows in the hydraulic chamber 87 via the hydraulic chamber 86 and thereafter it flows further in the clutch 1 via the orifice 90, the hydraulic chamber 88, the hydraulic passage 83 and the output port 71. The flowing of hydraulic oil continues until the clutch pack is completely filled with hydraulic oil. Here, when the spool 85 is held at the neutral position shown in Fig. 4 as well as during a period of filling time t f in which the spool 85 is displaced leftward of the neutral position, the spool 85 is parted away from the detecting pin 94. As long as the foregoing operative state is maintained, a potential appearing at the point c assumes a value of voltage which is derived by dividing the voltage V by the resistances R₁ and R₂, as shown in Fig. 5(e). When the clutch pack is filled with oil, the filling is terminated and no hydraulic oil flows any more. Thus, the differential pressure across the orifice 90 disappears. Namely, pressure P₁ becomes equal to pressure P₂. Consequently, the spool 85 is displaced in the rightward direction under the effect of a force derived from inserting a condition of P₁ = P₂ in the formula (1), that is, a force represented by the following formula, until it is returned to the neutral position. F₁ = K₁ x + P₂ (S₁ + S₃ - S₂) Here, since the respective pressure receiving areas S₁, S₂ and S₃ on the spool 85 are set in accordance with a relationship represented by S₁ + S₃ > S₂, a force P₂ (S₁ + S₃ - S₂) generated due to a difference in pressure receiving area is exerted on the spool 85 in the same direction as that of a restorable force of the spring 91 whereby the spool 85 is displaced in the rightward direction under the effect of a force which is derived by the restorable force of the spring 91 with the force due to the difference in pressure receiving area on the spool 85 added thereto. While the spool 85 is returned in that way, a hydraulic pressure from the pump is transmitted to a hydraulic pressure for the pertinent clutch via the hydraulic passage 84, the hydraulic chamber 87, the orifice 90 and the hydraulic chamber 88, resulting in a shoot pressure as shown in Fig. 5(d) being generated. The spring constant k₂ of the spring 92 is set to a pressure value Th larger than the initial pressure Pa but smaller than the aforesaid shoot pressure (see Fig. 5(d)). Thus, during a period of return movement of the spool 85, the latter is displaced in the rightward direction to the neutral position as shown in Fig. 4 and thereafter it is displaced further in the rightward direction in the presence of the shoot pressure against the energizing force k₂ x of the spring 92 whereby the right end surface of the spool 85 comes in contact with the detecting pin 94. Namely, in this case, the spool 85 is displaced in the rightward direction under the effect of a force derived by putting a condition of P₁ = P₂ in the formula (2). Consequently, since the detecting pin 94 is electrically conducted to the earthed valve body 93 via the spool 85, the potential at the point c is lowered to a level of zero as shown in Fig. 5(e) and thereby no voltage appears at the point c (time t₂). The potential at the point c is inputted in the controller 5 as a detecting signal S so that the controller 5 determines the termination of filling by an initial rising of the potential at the point c . When the termination of filling is determined, the controller 5 gradually increases the initial command electrical current I for the pertinent clutch from the initial pressure electrical current I o without delay (see Fig. 5(a)). Incidentally, when the controller 5 determines the termination of filling, it lowers a command electrical current for the clutch located at the previous stage to a level of zero as shown by an one-dotted line in Fig. 5(a). As a result, a clutch pressure for the pertinent clutch is lowered from the aforesaid value of shoot pressure to the initial pressure Pa and thereafter it is gradually increased, as shown in Fig. 5(d). Accordingly, the spool 85 is once displaced in the leftward direction toward the neutral position from the operative state in which it contacts the pin 94. Thereafter, since the clutch pressure P₂ is gradually increased, it exceeds the set pressure Th of the spring 92 at a certain time point t₃. Consequently, the spool 85 is displaced in the rightward direction again against the energizing force k₂ x of the spring 92 until its right end surface comes in contact with the detecting pin 94. Thus, a potential at the point c is lowered to a level of zero again at the time t₃ and thereafter this zero level is maintained. Specifically, since the potential at the point c is such that it becomes zero when the clutch is activated with a pressure higher than the set pressure Th and it assumes a predetermined value of voltage when the clutch pressure is lower than the preset pressure Th, presence or absence of the clutch pressure, that is, an engaged state of the clutch can be known by monitoring the potential at the point c . Additionally, in this case, since the potential at the point c is once lowered to a level of zero due to the shoot pressure on the termination of the feeling, the termination of the latter can be detected by detecting the first lowering. According to this embodiment, the electronic type hydraulic pressure control valve 60 having the aforementioned sensor section 63 attached thereto is provided for the respective clutches so that outputs from the plural sensor sections 63 are inputted in the controller 5, as shown in Fig. 1. The controller 5 monitors outputs from the plural sensor sections 63 to determine the termination of filling and presence or absence of double engagement on the basis of results derived from the monitoring. Namely, the controller 5 outputs a trigger command I o to a clutch to be brought in an engaged state and thereafter determines the time when the filling is terminated, by detecting the first lowering of a detection signal S to be inputted therein from the sensor section 63 of the clutch. In addition, the controller 5 determines which clutch is held in an engaged state, by monitoring outputs from the plural sensor sections 63, and in a case where clutch pressure detecting signals are simultaneously outputted from two sensor sections 63, it determines that this is identified as double engagement. When the double engagement is determined by the controller 5, the latter immediately outputs a command for lowering a hydraulic pressure for one of the clutches or takes a countermeasure such that all the clutches are turned off immediately, in order to prevent associated components or instruments from being damaged or injured due to the double engagement. In this manner, according to this embodiment, since a spring 92 is disposed on the opposite side to the return spring 91 and a displacement of the spool 85 from the neutral position toward the spring 92 side is detected by the contact switch arrangement comprising a detecting pin 94 and resistances R₁ and R₂, this makes it possible to detect the termination of filling and determine a clutch engaged state by the single sensor arrangement including a single spool. Further, since a relationship as represented by S₁ + S₃ > S₂ and S₂ > S₃ is provided for the respective pressure receiving areas S₁, S₂ and S₃ on the spool 85, a force generated by a difference in pressure receiving area with a restorable force of the return spring 91 added thereto is exerted on the spool 85 when the latter is displaced in the rightward direction after the termination of filling whereby the spool 85 can be returned to the neutral position at a high speed. Incidentally, when returning of the spool 85 is achieved only by a resilient force of the spring 91, the spool 85 has a reduced return speed with the result that an overshoot pressure as represented by a dotted line in Fig. 5(d) is generated on the termination of filling and this gives rise to a factor of causing a shock due to speed changing. In this case, the overshoot pressure can be reduced by increasing the return speed of the spool by the aforementioned difference in pressure receiving area. It should of course be understood that the present invention should not be limited only to this embodiment but various changes or modifications may be made in a suitable manner. For instance, structural arrangememt for detecting a filling time may be arbitralily made in any other fashion, provided that the termination of filling can be detected by a movement of the spool 75. The present invention is advantageously applicable to a transmission for a construction machine such as truck, wheel loader or the like as well as a passenger car.

Claims: An apparatus for controlling a hydraulic pressure usable for a clutch (1) comprising a first valve (62) including a spool (85) with an orifice (90) formed at an output port (71) leading to said clutch (1), said first valve (62) being opened under the effect of a differential pressure appearing across said orifice (90) and closed under the effect of a restorable force of a first spring (91) disposed on one end of said spool (85), a second valve (61) in the form of a pressure control valve adapted to be activated in response to an electric signal, said second valve (61) functioning to open said first valve (62) by feeding to the latter a hydraulic oil delivered from a pump (6) during a period of speed changing and gradually increase a hydraulic pressure for the clutch (1) after the termination of filling, a second spring (92) disposed on the other end side of said spool (85) for said first valve (62), and, filling and clutch pressure detecting means for detecting the termination of filling and a clutch pressure on the basis of the displacement of said spool (85) for said first valve (62) against a resilient force of said second spring (92). The apparatus of claim 1, wherein a spring constant of said second spring (92) is determined larger than that of said first spring (91). The apparatus of claim 1 or 2, wherein a spring constant of said second spring means (92) is set larger than an initial pressure for the clutch (1) on the termination of filling and smaller than a shoot pressure generated when the spool (85) for the valve (62) is closed in response to the termination of filling. The apparatus of one of claims 1-3, wherein said filling and clutch pressure detecting means is adapted to detect the termination of filling during a period of first displacement of the spool (85) against a resilient force of said second spring (92) for the spool (85) after a speed changing command is produced. The apparatus of one of claims 1-4, wherein said filling and clutch detecting means comprises a member disposed on the housing of the apparatus and contact and non-contact detecting means (63) for detecting contacting of the spool (85) for the first valve (62) with said member and parting of the former away from the latter. The apparatus of claim 5, wherein said member comprises an electrically conductive detective pin (94) disposed on the housing of the apparatus with an electrical insulating material (96) used therefore and said contact and non-contact detecting means (63) is such that contacting of the spool (85) for the first valve (62) with said detecting pin (94) and parting of the formed away from the latter are represented in the form of an electrical ON or OFF signal. The apparatus of claim 6, wherein said contact and non-contact detecting means (63) comprises voltage applying means for applying a predetermined magnitude of voltage to said detecting pin (94) and voltage detecting means for detecting a voltage appearing on said detecting pin (94) when the spool (85) for the first valve (62) comes in contact with the detecting pin (94) and the former is parted away from the latter. The apparatus of one of claims 1-7, wherein the spool (85) for the first valve (62) is such that a pressure receiving area (S₁,S₃) of the spool (85) located on the side where the first valve (62) functions in the direction of closing is determined larger than that (S₂) of the spool (85) located on the side where the first valve (62) functions in the direction of the opening.

Inventors: ASAYAMA, YOSHIO, OKURA, YASUNORI, SATO, TAKAYUKI, TSUBOTA, MAKIO
Applicants: KABUSHIKI KAISHA KOMATSU SEISAKUSHO
Application year: 1987
Main classification: F16D25
IPC codes: F16H61, F16D48, F16H43, F15B11, F16H59