US3434283A

US3434283A - Hydraulic antishock device

Info

Publication number: US3434283A
Application number: US679712A
Authority: US
Inventors: Jean Piret
Original assignee: Simca Automobiles SA
Current assignee: Simca Automobiles SA
Priority date: 1966-11-03
Filing date: 1967-11-01
Publication date: 1969-03-25
Anticipated expiration: 1986-03-25
Also published as: ES347163A1; DE1650546A1; BE706029A; GB1171217A; SE337747B; DE1650546B2; DE1650546C3

Description

March 25, 1969 J. PIRET HYDRAULIC ANTISHOCK DEVICE Sheet Original Filed Feb.

9$ 0 o NVK RQ\ 5 v i Q\ \Q\ J. PIRET HYDRAULIC ANTISHOCK DEVICE Original Filed Feb. 5, 1965 March 25, 1969 Sheet .KT 5 mm u a, W. W H R E o J n 9 Wvi United States Patent Int. C1. 1 13/44 U.S. CI. 60-52 5 Claims ABSTRACT OF THE DISCLOSURE A hydraulic antishock device for use with a hydraulic jack provided with a piston having two faces which are capable of being alternately connected, by means of a main distributor, with the delivery circuit of a pump, the return circuit of the pump to a tank or simultaneously, in the non-working position of the jack, with the two circuits. Two electromagnets for selectively operating the distributor, a pressure regulator interposed between the circuits. A master distributor is connected to the tank return circuit and is controlled by an electromagnet so as to cut off or to establish communication with the tank return circuit.

An electric circuit controlling the pump motor and the electromagnets includes two first double switches having sets of contacts, One set of which is interposed in the electric control circuit of an electromagnet so as to prevent excitation of the latter when another electromagnet is excited and a second set of contacts is interposed in the electric control circuit of the electromagnet of the master distributor so as to be closed when the master distributor occupies an extreme position and a second double switch connected with the first double switches and two end of travel switches so as to control the operation of the two electromagnets of the main distributor.

This application is a continuation of application Ser. No. 430,156 filed Feb. 3, 1965, now Patent No. 3,225,541, dated Dec. 28, 1965.

Prior known devices provide very good results as regard the elimination of hydraulic shock waves when the piston of a jack changes its direction of displacement, but had the disadvantage that they necessitate using a large number of electrical elements such as contactors, relays, etc., to control the various distributors provided in the hydraulic circuit of the device.

The present invention has for an object to minimize or eliminate this disadvantage and to enable a hydraulic antishock device of very simple conception to be made which is adapted to use all the elements of the hydraulic circuit of the existing devices and some of the electrical elements whilst providing the same technical advantages of operation as those obtained with the device of the parent patent.

According to the present invention, the hydraulic antishock device associated with a hydraulic jack having a piston, the two faces of which are adapted to be connected, by means of a main distributor controlled alternately by two electromagnets either alternately, during the working of the jack, with the delivery circuit of a pump and the tank return circuit of the pump, or simultaneously in the non-workin g position of the jack, with the two said circuits, and comprising: a pressure regulator disposed in the delivery circuit downstream of the main distributor and provided with a valve interposed between the delivery circuit and the tank return circuit and rigidly secured to a piston defining two chambers of which the lower chamber communicates directly with the delivery circuit and the upper chamber, provided with a return spring urging the valve into its closing position communicates by means of a calibrated channel with the delivery circuit; a master distributor connected to the upper chamber of the valve piston and to the tank return circuit and adapted to be controlled by an electromagnet so as to cut off or establish communication between the upper chamber of the valve piston and the tank return circuit; and an electric circuit provided with switches and relays for starting and stopping the pump motor and for controlling the various electromagnets.

This device is characterized according to the present invention by two first double switches the sets of contacts of each of which open and close alternately, each adapted to be controlled through a uni-directional mechanical transmission by one of the two electromagnets of the main distributor and each having a first set of contacts interposed in the electric circuit of the other electromagnet so as to prevent excitation of the latter when the first electromagnet is excited, and a second set of contacts interposed in the electric circuit of the electromagnet of the master distributor so as to be closed when the master distributor occupies the corresponding extreme position; by a second double switch, the sets of contacts of which close simultaneously, adapted to be controlled through a uni-directional mechanical transmission by the master distributor and in which one set of contacts is mounted in series with the first set of contacts of the two first double switches; by two double end of travel switches the set of contacts of each of which close alternately, disposed one at either side of a jack, and adapted to be actuated by a rod rigidly connected to the jack piston, one of the two sets of contacts of each of the two end of travel switches being mounted in the electrical circuit of the electromagnet of the master distributor, while the other set of contacts is mounted in parallel with one of the sets of contacts of the first double switch in one or the other of the electrical circuits of the two electromagnets of the main distributor.

In this way, the hydraulic antishock device is constructed in an extremely simple manner, can be adapted to existing hydraulic circuits, no longer necessitates use of electrical control relays and enables hydraulic shock waves to be suppressed in an efficient and certain manner.

In order that the invention may be more fully understood, an embodiment in accordance therewith will now be described by way of example with reference to the accompanying drawings in which:

FIG. 1 shows a hydraulic circuit of a jack, for example of a machine tool, which jack is provided with one embodiment of the hydraulic antishock device of the invention.

FIG. 2 is a schematic representation of one form of electrical control circuit of the pump motor and of the electromagnets of the hydraulic antishocl; device.

As can be seen from FIG. 1, the jack 101, for example of a machine tool, has a double acting piston 102 whose two sides are rigidly connected respectively to rods 103a, 103b one of which is associated for example with a tool (not shown) through a connecting mechanism which is also not shown.

The piston 102 defines, in the jack cylinder 101, two

chambers

104 and 105, each of which is adapted to communicate through a

conduit

106 and 107 respectively with one of the end chambers 108 and 109 of a main distributor 111, which chambers are situated one at either side of a central chamber 110.

This main distributor 111 comprises a double piston slide enabling each of the end chambers 108 and 109 to be brought into communication with the central chamber 110 and through this chamber with the delivery circuit 112 of a pump P driven by a motor M, these three chambers 108, 109 and 110 being also adapted to be connected to a return circuit 113 leading to a feed tank 114 for the pump P. The term return-circuit will be understood in the following description to mean all conduits leading to the tank 114.

When the slide of the main distributor 111 is in its intermediate position in which it is maintained by means of two

springs

115 and 116 each having one end applied against a fixed abutment, the other ends being applied respectively against abutments rigidly fixed to

rods

117 and 118, themselves fixed to either side of the slide of the main distributor 111, the delivery conduit 112 of the pump P is connected directly to the return circuit 113. When the slide of the main distributor 111 occupies its extreme right or left hand position, the delivery conduit 112 communicates with the

chamber

105 or 104 of the jack 101 and the return circuit 113 communicates with the

chamber

104 or 105.

In the delivery circuit 112 there is located a main pressure regulator 119 of known design which is identical to the main pressure regulator described in Ser. No. 3,225,541 and which interrupts communication between the delivery circuit 112 and the return circuit 113 when the pressure in the delivery circuit 112 is less than a maximum reference pressure and when its escape valve (not shown) is closed by the action of a master distributor 120 connected to the pressure regulator 119 through a master conduit 121.

This master distributor 120 is also of known design and has a slide adaptable to establish or interrupt, according to its position (122, 123), communication between the master conduit 121 and the return circuit 113 so that when this communication is interrupted, the communication between the delivery circuit 112 and the return circuit 113 is also interrupted by means of the pressure regulator 119 which thus determines the maximum reference pressure in the delivery circuit 112. The master distributor 120 is subjected at one side to the action of a spring 124 urging the slide of this master distributor into the position shown in FIGURE 1, i.e., a position in which the conduit 121 communicates with the return circuit 113.

At the opposite end, the slide of this master distributor 120 is provided with a transmission rod 125 adapted to cooperate with a pushrod 126 associated with the control electromagnet EP of the master distributor.

At each side of the main distributor 111, is provided a control electromagnet. For ease of reference, the control electromagnet situated on the left will be referred to as advance electromagnet EA and that situated at the right as return electromagnet ER. The

movable armature

127, 128 of each control electromagnet EA and ER cooperates by means of a

transmission rod

129, 130 with the

rod

118, 117 respectively, rigidly connected to the slide of the main distributor 111, which armatures also cooperate each with an end of a lever having arms 131, 132. The other end of each lever cooperates respectively with a first double switch 133, 134, the two sets of contacts of each of which close alternately, each of said switches being urged by a

return spring

135, 136 into a position such that the other end of each lever 131, 132 is in contact, or at least has the tendency to come into contact with the corresponding

movable armature

127, 128. The delay in the movement of these levers with respect to the displacement of the

movable armatures

127, 128 in a direction towards the main distributor 111 can be adjusted by carefully choosing the location of the mass referred to above. Each first double switch has two sets of contacts 133a, 133b, and 13411, 13411 of which the sets of

contacts

133a, 134a are normally closed under the action of the

return springs

135, 136. The operation of these double switches 133, 134 will be explained hereinafter.

The movable armature 137 of the electromagnet EP cooperates by means of the rod 126 with the rod 125 of the slide of the master distributor 120 and also with one of the ends of a two arm lever .138 of which the other end cooperates with a double switch 139 of which the two sets of contacts close simultaneously. The two sets of contacts 139a and 139b of this double switch are urged into the closed position by means of a return spring 140 which is weaker than the return spring 124 of the master distributor so that these two sets of contacts 139a, 13% are held open when the electromagnet EP is not excited. The role of this double switch will be explained hereinafter.

Each of the rods 103a and 10311 of the piston 102 is adapted to cooperate by means respectively of cams 103a and 1030. when the piston 102 occupies one of its extreme positions, with one of two double end of

travel switches

141, 142. One of each set of

contacts

141a, 141b and 142a, 1421) of each of the

switches

141, 142 is normally closed under the action of a return spring 143, 144 and is held open when this switch is actuated by the corresponding cam 1030, 103d of the piston rods 103a; 103b. The role of these end of travel switches will be explained hereinafter.

It will be seen that the control of the double switches 133, 134 and the switch 139 is effected by a uni-directional transmission mechanism. In the case of the double switches 133, 134, this uni-directional transmission mechanism is constituted, for example, as far as the switch 133 is concerned, by the movable armature 128 of the electromagnet ER, the rod the rod 117, the slide of the main distributor 111, the rod 118, the rod 129, the movable armature 117 of the electromagnet EA and the lever 131. As far as the switch 134 is concerned, the transmission elements are practically the same with the excep tion of the lever 131 which is in this case replaced by the lever 132.

In the case of the switch 139, the uni-directional transmission is constituted by the spring 124, the slide of the master distributor 120, the

rods

125 and 126, the movable armature 137 of the electromagnet EP and the lever 138.

The electrical control circuit of the hydraulic antishock device is shown in FIGURE 2. A three phase system 145 feeds the motor M, and also the hydraulic control circuit through the transformer 146. At the secondary side of this transformer 146 are mounted, downstream of a principal feed switch 147, several units U U U and U, of electrical elements, these units being fed in parallel from the secondary winding of the transformer 146.

Generally speaking, the different contacts and switches shown in FIGURE 2 are of two different types. All the contacts and switches outside a line looking in the direction of the arrows F, are closed when they are not actuated by their corresponding control elements. The contacts and switches inside this line are open when they are not actuated by their corresponding control elements.

The first unit of electrical elements U comprises a relay D, which is a control relay for the motor M. Upstream of this relay D, a holding contact D is connected in parallel with a manual control switch Mm generally open and enabling the motor to be started. A three contact switch D is connected in the feed lines of the motor M, the three contacts of which are closed when the relay D is excited.

The second unit of electrical elements U essentially includes a group of several switches connected in parallel to which reference will be made hereinafter, connected in series with the excitation winding of the advance electromagnet EA of the main distributor 111. This group of parallel contacts includes, in one of its branches, a manual switch DC, while the other branch includes the set of contacts 133a of the double switch 133 adapted to be controlled by the return electromagnet ER. This set of contacts 133a is connected in series with a group connected in parallel comprising the set of contacts 13% of the double switch 139 associated with the electromagnet EP of the master distributor 120 and also the set of contacts 142!) of the end of travel switch 142 connected in series with a manual switch Im which holds the position into which it is placed.

The third unit of electrical elements U comprises the set of contacts 134a of the double switch 134 adapted to be actuated by the advance electromagnet EA, followed by a group connected in parallel comprising the sets of contacts 139a, 141b which group is itself connected in series with the excitation winding of the return electromagnet ER. The set of contacts 139a is held in its open position by the master distributor 120 by means of

rods

125, 126, the movable armature 137 of the electromagnet EP and the lever 138, while the set of contacts 141b is held in its closed position by means of the cam 103c rigid with the rod 103a when the piston 102 occupies its extreme right hand position (end of travel position).

The fourth unit of electrical elements U comprises a group connected in parallel, which group contains two branches, one containing two sets of contacts 133]) and 142a connected in series and the other containing two sets of contacts 134!) and 141a also connected in series, this group being followed by a manual switch AC which will be referred to as the cycle stop switch, which is itself connected in series with the excitation winding of the control electromagnet EP of the master distributor 12 0.

The operation of this device is as follows: it will be assumed first of all that the current is interrupted and that there is therefore no excitation of any of the three electromagnets EA, ER, EP. The different elements of the device, which include the sets of switch contacts, occupy the positions in which they are shown in FIGURES 1 and 2.

In order to start up the motor M, and consequently the pump P, the manual switch Mm is closed and this causes the relay D to be excited. The holding contact D closes and in this position ensures that the relay D is continuously fed; the three contact switch D is also closed under the action of the relay D so that the motor M is supplied with current and the pump P delivers fluid (for example oil) into the delivery circuit 112. This fluid returns to the feed tank 114 through the main distributor 111 which is in its neutral position, as well as through the pressure regulator 119.

To control the pressurisation, that is to say the feed of the chamber 105 of the jack 101, and in order thus to displace the piston 102 from left to right, which displacement will be referred to hereinafter as the advance of the piston 102 the manual switch DC is closed and this enables the excitation coil of the advance electromagnet EA to be supplied with current, the movable armature 127 of this magnet being thus displaced towards the right and this moves the slide of the main distributor 111 by means of the

rods

129 and 118 so that the chamber 105 of the jack 101 is connected to the delivery circuit 112 and the chamber 104 is connected to the return circuit 113. The pressure in the delivery circuit 112 remains low, however, because this circuit 112 is still connected to the feed tank 114 through the pressure regulator 119. This displacement towards the right of the movable armature 127 is also transmitted through the slide of the main distributor 111,

rods

117, 130, and the movable armature 128 of the return electromagnet ER, the winding of which is not excited, to the lever 132. As soon as the armature 127 starts to move the lever 132 opens the set of contacts 134 against the action of the spring 136, and at the end of the movement of this movable armature 127, that is to say, when the slide of the main distributor 111 occupies the position in which the latter connects the circuit 112 to the conduit 107 and the circuit 113 to the conduit 106, the lever 132 closes the set of contacts 13417 of the double switch 134.

In this way, it is thus impossible to excite the winding of the return electromagnet ER as soon as the electromagnet EA is supplied, and it is certain that the electromagnet EP of the master distributor 120 can only be excited by closure of the set of contacts 134!) when the main distributor 111 has established the aforesaid connection.

As soon as the set of contacts 134k is closed, the movable armature 137 of the electromagnet EP moves from right to left and thereby causes corresponding movement of the slide of the master distributor 120 which, in its other extreme position, interrupts the connection between the conduit 121 and the return circuit 113, the effect of this being progressively to close the adjustable valve of the pressure regulator so that the connection between the delivery circuit 112 and the return circuit 113 is progressively blocked by the pressure regulator 119 and the pressure increases progressively in the delivery circuit and consequently in the chamber of the jack 101. The piston 102 then moves towards the right.

When the movable armature 137 of the electromagnet EB, moves towards the left, the lever 13 8 in contact with this armature enables the two sets of contacts 139a and 13917 of the double switch 139 to be closed under the action of the spring 140. As soon as the set of contacts 13% closes, the winding ofthe electromagnet EA is supplied through the closed sets of contacts 133a and 13% so that it is no longer necessary to hold the manual switch DC closed. The set of contacts 139a is also closed and prepared a feed path for the excitation winding of the electromagnet ER which cannot however be supplied since the set of contacts 134a has been previously opened.

When the piston 102 arrives at the end of its travel, that is to say occupies its extreme right-hand position, the cam 1030 of the rod 103a actuates the end of travel switch 141 and first opens the set of contacts 141a and then closes the set of contacts 141k against the resistance of the spring 143.

Opening the set of contacts 141a interrupts the supply to the electromagnet EP so that the master distributor reestablishes, by its movement towards the right, the connection between the conduit 121 and the return circuit 113 and by this means, the connection between the delivery circuit and the circuit 113 through the pressure regulator 119 so that the pressure in the delivery circuit is progressively decreased until it reaches a very low reference pressure. The movement towards: the right of the master distributor also causes the sets of contacts 139a and 13917 to open by operating the

rods

125, 126 the movable armature 137 and the lever 138.

It will thus be seen that for the moment the set of contacts 139a plays no role in the advance of the piston 102 but its role will become evident in the following description.

Opening the set of contacts 13912 causes the supply to the advance electromagnet EA to be cut so that the slide of the main distributor regains its central position under the action of the

springs

115 and 116. It will also be seen that even before the main distributor reaches its central position, the pressure in the delivery circuit has been decreased, thus avoiding the production of hydraulic shock waves.

The return to its central position of the main distributor 111 causes first the set of contacts 134b to open and then the set of contacts 134a to close under the action of the spring 136. Opening the set of contacts 134b has no effect for the moment because in the extreme right hand posi tion of the piston 102, the set of contacts 141 is already open.

By contrast, closing the set of contacts 134a, which only happens when the slide of the main distributor 111 actually occupies its central position, controls the excitation of the winding of the return electromagnet ER, the set of contacts 141!) located in the feed line of this winding having previously closed. From this moment onwards, the movable armature 128 of the electromagnet ER moves from right to left and causes the movement, through the agency of the rods and 115, of the slide of the main distributor which then establishes a hydraulic connection on the one hand between the delivery circuit 112 and the chamber 104 and on the other hand between the return circuit 113 and the chamber 105, the pressure in the delivery circuit 112 remaining at its low reference pressure because it is still connected to the return circuit 113 through the pressure regulator 119. Movement of the main distributor 111 towards the left is transmitted through a

rod

118 and 129 to the movable armature 127 of the advance electromagnet EA which is not now excited to the lever 131 which actuates the double switch 133 against the force of the return spring 135 so that as soon as the movement of the slide of the main distributor 111 from its central position towards the left commences, it opens the set of contacts 133a and, at the end of this movement, that is to say, when the main distributor 111 has established the aforesaid connection, it closes the set of contacts 13312. The closure of the set of contacts 133b connected in the supply line of the electromagnet EP in series with the set of contacts 142a which is still closed for the moment, causes this electromagnet to be excited and the movable armature 137 thereof will be displaced again towards the left. There is thus produced the same effect as previously described for the pressurising of the delivery circuit for the advancing movement of the piston 102. Thus, the pressure progressively increases in the delivery circuit 112 and in the chamber 104 of the jack and this causes the piston 102 to be moved in a continuous movement towards the left. As soon as the cam 103c of the rod 103a leaves the end of travel switch 141, the set of contacts 141b is opened, and then the set of contacts 141a is closed again but the excitation of the electromagnet ER is maintained through the sets of contacts 134a, 139a which were previously closed when the piston 102 arrived at the end of its travel at the extreme left of the cylinder 101, the cam 103d of the rod 10312 actuates the end of travel Switch 142 and first opens the set of contacts 142a and then closes the set of contacts 142]) against the force of the spring 144. Opening the set of contacts 142a interrupts the feed to the electromagnet EP so that the master distributor 120 occupies once more the position in which it permits communication between the conduit 121 and the return circuit 113 and also the progressive decompression of the delivery circuit 112 through the pressure regulator 119. When the electromagnet EP is de-excited, the sets of contacts 139a, 13% also open according to the cycle previously described. When the set of contacts 139a is open, the return electromagnet ER is also de-excited so that the slide of the main distributor 111 can regain its central position under the action of

springs

116 and 117. At this moment, the set of contacts 133 is again closed and the set of contacts 142 is still closed.

If the switch Im has been previosuly closed, a further cycle of movement of the piston 102 begins and this continues as long as the switch Im remains closed. If the switch Im is open, the piston 102 can only perform a single cycle.

Supposing that this switch Im has been previously closed, the electromagnet EA is then excited once more through the closed sets of contacts 133a, 14% and switch Im. The main distributor 111 is then pushed once more towards the right therefore occur the same operations which have already been described, and the electromagnet EA remains excited despite the opening of the set of contacts 142b after the departure of the piston 142 towards the right because the set of contacts 139]: remains closed in the meantime.

If, at a given moment, during the displacement of the piston 102, it is desired to stop the movement of the latter, it is possible simply to open the manual cycle stop switch AC which interrupts the supply to the electromagnet EP, the effect of this being to decompress the delivery circuit 112 which causes the piston 102 to stop.

From the foregoing it will be seen that the device of the present invention ensures in a simple fashion the suppression of all the hydraulic shocks during the pressurisetion of the jack or during the reversal of the movement of the piston. This device lends itself also very easily to modifications of existing hydraulic installations and imparts to the latter all the safety and efficiency of operation of the device itself according to the invention.

Due to the use of the transmission levers 131, 132, 138, which are adapted to be provided at well-defined positions thereon, with a supplementary mass of a certain weight, lagging or time delay eifects can also be produced in the control of the various sets of contacts by virtue of the inertias of these supplementary masses cooperating with springs of weak force and stiffness.

It is also very advantageous to place the control electromagnets, the lever and the double switch with which it is associated, in a box which is then easily mountable on existing installations. In FIGURE 1, there are shown schematically casings (148, 149, 150) indicated by broken lines surrounding, for example, respectively the electromagnets EA, ER, EP, the

levers

131, 132, 138, and the

double switches

133, 134, 139.

It will be evident that the embodiment described herein is only given by way of example and can be modified in various ways without departing from the scope of the present invention.

Thus, the invention can also be applied to hydraulic motors. The control of the

double switches

133, 134 and 139 can be effected from a slide in a hydrovalve used in place of a distributor control directly by electromagnets.

What is claimed is:

1. A hydraulic antishock device for use with a hydraulic jack provided with a piston having two faces; a main distributor; two electromagnets alternately controlling said distributor to selectively connect the two faces of the piston with a delivery circuit of a pump or a return circuit of the pump to a tank, or simultaneously, in the non-working position of the jack, with the two said circuits, and comprising: in the delivery circuit downstream of the main distributor, a pressure regulator interposed between the delivery circuit and the return circuit to the tank; a master distributor connected to the tank return circuit, and adapted to be controlled by an electromagnet so as to cut off or to establish communication with the tank circuit; and an electric circuit provided with switches and relays for starting and stopping the pump motor and for controlling all of the electromagnets; two first double switches the sets of contacts of each of which open and close alternately, each double switch adapted to be controlled through a unidirectional mechanical transmission by one of the two electromagnets of the main distributor and each having a first set of contacts interposed in the electric control circuit of an electromagnet so as to prevent excitation of the latter when another electromagnet is excited, and a second set of contacts interposed in the electric control circuit of the electromagnet of the master distributor so as to be closed when the master distributor occupies an extreme position; a second double switch having sets of contacts which close simultaneously and which are adapted to be controlled through a uni-directional mechanical transmission by the master distributor, one set of contacts of said second double switch being mounted in series with the first set of contacts of the two first double switches; two double end of travel switches having sets of contacts which close alternately, disposed one at either side of the jack, and adapted to be actuated by a rod rigidly connected to the jack piston, one of the two sets of contacts of each of the two end of travel switches being mounted in the electrical circuit of the electromagnet of the master distributor, while the other set of contacts of each travel switch is mounted inparallel with one of the sets of contacts of the first double switch in one or the other of the electrical circuits of the two electromagnets of the main distributor.

2. A device according to claim 1 wherein the unidirectional transmission of each first double switch comprises a first rod rigidly connected to a movable armature of the corresponding control electromagnet; a slide valve mounted in the main distributor cooperating with said first rod; a'second rod rigidly connected to a movable armatureof the other electromagnet and also cooperating with the said slide, and a pivoted two-armed lever, one end of which cooperates with a movable armature of the electromagnet controlling the other switch, the other end of the lever cooperating with the said double switch.

3. A device according to claim 2, wherein the unidirectional mechanical transmission for the second double switch comprises a rod rigid with the movable armature of the electroniagnet of the master distributor and cooperating with the slide valve of the master distributor and a two-armed lever cooperating with said second switch and with the armature of the electromagnet of the master distributor.

4. A device according to claim 2 wherein the twoarmed lever is provided with supplementary masses the positions of which are adjustable on one of the two arms.

5. A device according to claim 2 wherein the twoarmed lever and its associated double switch are housed in a common casing.

References Cited UNITED STATES PATENTS 2,602,294 8/ 1952 Sedgwick. 2,677,285 5/1954 Volk. 3,225,541 12/1965 Piret 60-52 3,363,514 1/1968 Rarncke.

EDGAR W. GEOGHEGAN, Primary Examiner.

U.S. Cl. XJR.